Anhydrous Aluminium chloride is used as a catalyst in Friedal Crafts reaction in pharmaceutical industries. It is used for a wide variety of purposes in chemical industry for carrying out reactions like dehydrogenation, decarboxylation, oxidation, alkylation, acylation, desulphonation, amylation, and polymerisation. Aluminium Chloride is used particularly in industries that manufacture drugs like Ibuprofen, Ciprofloxcin and R.floxcin etc in large quantities per day. After its use in Friedal Crafts reaction Aluminium salts are let out into streams along with other organic compounds. The high concentrations of Aluminium salts acts as retardant as they cause imbalance in osmolytic pressure and inhibit the degradation of organic compounds.

If the wastewater contains high concentration of inorganic compounds than certain permissible limits then a phenomenon called plasmolysis occurs in which cell shrinks and dies. Usually the designers of wastewater treatment systems go by BOD and COD values of the effluents and design aerobic and anaerobic biological treatment units, but such designed units do not function if cations and anions like metal ions, chlorides, sulphates etc. are in osmotically high concentration. Due to these high concentrations most of the biological waste treatment systems designed and installed in many bulk drug-manufacturing wastes today are failing in the actual treatment.

Dissolved inorganic chemicals in wastewater are considered to pollute the water to a less extent than suspended solids and organic compounds, and hence less attention was given to these values.

The general methods employed for removing inorganic matter from wastewater are

Evaporation

Dialysis and electro dialysis

Ion exchange

Reverse osmosis

Almost all of these are expensive and require close monitoring, special

equipment and additional input of energy. There are two aspects one has to consider in treatment of wastewaters containing soluble salts

• is there a possibility of recovering the useful and important salts in an economic way?
• --Can there be a method to reduce their concentration in the waste effluents to counter the osmolytic effect so that the biologically oxidisable matter can be treated by waste treatment units.

The aim of the is directed towards separating aluminium salts from waters or wastewaters and recovering them as quantitatively as economically as possible so that osmolytic effect can be reduced as much as possible. Use of chemical methods is contra indicated since more and more soluble chemicals may be introduced. Therefore attention is paid to physical dissolved solid methods, known and used in industries.

Since purity of recovered chemicals is also an important criteria, ion exchange and adsorption were selected for this short term experimentation.

II CHAPTER

If the complexing agent can simultaneously satisfy all the coordinate sites of the metal ion and produce a complex with zero over all charge the chelate compound is said to be coordinately saturated. If however the charge on the central atom is neutralized but some coordination sites remain unsatisfied, the complex is said to be coordinately unsaturated. For Al3+ acetyl acetone is used as complexing agent, the stability constant of the complex is 22.3 log B and pH= 3.3. The larger the stability constant of the complex the more acidic the solutions from which extraction can be made and the higher the distribution constant.

Acetyl acetone can be used as both chelate forming and as extraction solvent for separation of aluminium at different pH values brown (brown W.B. 1968) have isolated Al, Co, Cr, cu, mn, mo, ni, pb and vanadium at low concentration levels.

The use of aliphatic monocarboxylic acids, in acidic pH for the isolation of Al has also been extensively studied (stary J.1963).

This reagent trifloroacetylacetone reacts with solvents such as benzene and chloroform in the separation of aluminium using gas chromatography has been extensively studied (Ramanujam 1978).

The Al can also be extracted using thenolytrifloroacetone in hexane (Eshelman 1959) 100% extraction is obtained by the above method.

The extraction of Al using 1phenyl 3methyl 4 benzyl 5 pyrazolone reagent in various organic solvents with varying degree of extraction percentage has been studied (Shoekotybula et al 1977).

The extraction of Al has been studied with dibenzoyl methane (Steinbach J.F 1954) yielding nearly 80% of aluminium.

8hydroxyquinoline in various solvents (Unland F.Z, 1961) (Riley J.P 1959) at various pH ranges yields Al in varying degrees of percentage and purity.

Chakroborty (1963), (Stary 1963) has studied the effect of cupferron on the removal of Al (III) at various pH ranges both acidic and alkaline.

The removal of Al using kerosene and di (2-ethyl hexyl) phosphoric acid as the reagent at neutral pH has been studied. (Laurall 1961).

The studies of separation and removal of Al using benzoyl phenyl hydroxylamine in chloroform and tributyl phosphate have been done. They have suggested the method for the removal of Al from wastewaters.

Al also forms a variety of complexes with thiocyanate in various solvents like diethylether, isoamylalchohol isobutylacetate (Rozycki 1970), (Bock R.Z 1951).

Ion exchange has been extensively used for the separation of metals e.g. transition metals with selective ligands and extractants containing nitrogen and oxygen e.g hydroxoamines. There is a considerable economic incentive to develop solid phase ion exchange processes for the recovery of precious alternative toxic metals, such as mercury from low-grade dilute solutions (Vernon 1975)

Many manufacturing processes resulting in effluents containing salts of heavy metals, but because of the complex composition of wastewater’s a general treatment cannot be specified. The recovery seems to be attractive but at times the water recovery may not be economical where only detoxification is required, for which ion exchange would be the appropriate.

The use of magnetic resins in fluidized beds may be beneficial, as preclarification of the wastewater is not necessary and quite high levels of suspended can be tolerated. For e.g. Zn containing effluent has been treated with a magnetic weak acid resin by a continuos method. The same resin will remove temporary hardness from unfiltered lime-treated sewage.

The adsorption of Al (III) cations by cellulose in aqueous solution has been studied by Jorge Renato (1971).

It has been investigated that the effects of aqueous acetone medium on the separation of the metal ions like Al³⁺ on chelex 100 ion exchanger (Bragter K. 1981)

Mg (OH)₂ and chelating resin where brought in contact with acidic wastewater to neutralize the waste water and to remove heavy metals. The acidic waste water was thus detoxified and 10% Mg (OH)₂ for wastewater of 3.1 can reduce Al from a concentration of 20ppm to 0ppm when passed through polystyrene.

The biggest environmental problem associated with the metal finishing industry the presence of Nickel ions along with aluminium and tin in the effluent. A chelating resin has been applied to recover Nickel along with Al when the pH is adjusted to 5-11 the nickel ions adsorb on the resin together with some of the aluminium ions. The bed is then treated with a nickel salt that displaces the aluminium into the effluent.

Pollution of the environment by metals is normally associated with human activity. Rapid development and increase in industrial activities have gradually redistributed many of the toxic metals from the earth’s crust to environment and thus increasing the exposure of man to these metals in excess through inhalation, ingestion or skin contact.

These metals find there way into oceans, onto land, into fresh water bodies probing danger to biological life. Thus water pollution by harmful metal of industrial wastewater is a serious threat to the world.

The separations of inorganic pollutants from aqueous solutions have been accomplished with a variety of techniques for many elements. Methods such as coprecipitation, freeze concentration (Beig E.W. 1963), gas chromatography (Musheir R.W. 1965), adsorptive bubble separation and membrane technique (Ciacco L.L. 1971) have been applied to their extraction from aqueous solution with limited success. Generally these methods often have limited applicability because of non-selectivity necessary extensive pretreatment and fouling.

Aluminium can be precipitated as AlCl₃ 6H₂O by adding saturated solution of HCl (Chwastosaka et al 1968). The aluminium can also be precipitated from silicate samples using ammonium thioglycollate (Sandell E.B.1949).

A sample of carbonates and chlorides of alkali metals, alkaline earth’s and Mg reagents, aluminum can be coprecipitated by adding H₂S and Na diethyldithiocarbonate which is used as a precipitant.

In steel samples aluminium can be coprecipitated along with Co, Sb, T, V, W by using aqueous NH₃ as a precipitant.

The treatment method for waste chemicals (Man E.R. 1962) suggests Al can be coprecipitated and disjoined.

Use of the flocculent VPK-402 in coagulation of water; a cationic polymer containing a tertiary amine group as a coagulating aid, significantly increases the removal of suspended solids and Fe and Al compounds, while decreasing the dose of coagulant.

Electro precipitation treatment of acidic wastewater was done by the electro couple involved in the active process including a consumable metal anode and an inert cathode. Heavy metal removal is either by precipitation of hydroxides or by adsorption. Reduction is 100% for aluminium.

Use of pressure flotation removed Al (OH)₃ from wastewater’s neutralized to pH 7 with lime. C_7-9 synthetic fatty acid required was 50% of normal pneumatic flotation. Effluent was left with traces of aluminium.

Metal distribution in activated sludge system controlled pilot plant studies revealed accurately, removal of metals by the activated sludge process.

Wastewater treatment by lime coagulation and subsequent settling followed by activated carbon adsorption, with ultrafiltration process resulted in the removal of 99% of heavy metals (Barnes 1985).

In the method of dephosphorisation of water containing phosphate and aluminium, these are removed with crystallization seed containing Ca₃(PO₄)₂ at pH >6. The removal is 99%.

Removal of aluminium from aqueous effluents by settling of Al (OH)₃ is improved by addition of alkaline earth oxide, hydroxides or carbonates at elevated temperatures. The removal is 99%.

Carbonization of alkaline wastewater containing aluminium by passing 10% CO₂ gas in the presence of crystallization seed gibbisite powder has resulted in 99% removal. Aluminium was precipitated by bayerite.

The recovery of Cr from tannery sludge Al was precipitated by cupferron at a pH of 2.4 - 4.0.

Filter made from semiconductor material, silicon, is used for removing impurities from liquid. The filter is particularly useful for recovering aluminium from spent solution.

Low pressure non-cellulosic ultrafiltration membranes were used in a bench scale unit to treat heavy metal wastewaters and membrane processes were evaluated rejection of complex metals.

The other methods used for the separation of aluminium from various complex matters include liquid – liquid extraction methods.

In this way the complexes of aluminium are prepared and thus extracted with various organic solvents. Complexes may coordinately unsaturated (Morrison 1964), (Leonard M.A 1960) and also saturated. If the complexing agent can simultaneously satisfy all the coordination sites remain unsatisfied, the complex is said to be coordinately unsaturated. For Al³⁺ acetyl acetone is used as complexing agent the stability constant of the complex is 22.3 log B and pH = 3.3. The larger the stability constant of the complex, the more acidic the solutions from which extraction can be made, and higher the distribution constant.

There are around 28 major pharmaceutical industries in and around Hyderabad and they use nearly 2500 tones of AlCl₃/ month and produce 2400-3000 kiloliters of AlCl₃ /day. Some of the industries have effluent treatment plants and some do not, if this is let into watercourse without treatment this would pose a high scale hazard, as the permissible limit of Al for aquatic life is less than 100ppm.

At present separation and removal of Al from industrial effluents has achieved by methods of precipitation and solvent extraction. In precipitate with lime the AlCl₃ precipitates along with calcium as hydroxide and it will be very difficult to get commercially pure AlCl₃. In solvent extraction procedures AlCl₃ is complexed with the solvent making the recovery of pure AlCl₃ difficult and time consuming and involves wastage of large quantities of inflammable solvents.

There is a necessity for the search for cost effective methods for the removal and recovery of aluminium chloride as this help in removing AlCl₃ which will help in not only facilitating the proper biological waste treatment but also in conserving time useful research.

In view of this, the author has taken up detailed and systematic investigations for developing low cost technologies for the removal and recovery of AlCl₃ from pharmaceutical effluents using ion exchange process and these results are presented in this thesis.

REAGENTS AND CHEMICALS:

Reagent solution was prepared from analytical reagent grade chemicals and stored in glass containers.

100ppm of AlCl₃, 0.02N ZnSo₄, 0.02N of EDTA solutions were prepared and standardized as per standard procedures (Vogel 1995).

Aluminium is supposed to produce many hazardous effects on various living organisms and environment.

HAZARDS TO AQUATIC LIFE:

It is thought that the principal deleterious effects of acid waters upon the fish arises from the solubilization of aluminium from soil and its subsequent existence as a free ion in the acidic water. The Al (OH) ₃ precipitates as a gel when it comes into contact with the less acidic gills of the fish, and the gel prevents the normal intake of O₂ from water thus suffocating the fish.

Acidification of surface waters has serious implications for biota and species diversity (Kirkwood R.C langley A.J, 1995). In particular it has a major effect on fish population.

Elevated concentrations of aluminium in surface water is associated with pH and various hydroxy- aluminium complexes are formed depending on the level of acidity.

In lab tests survival of frontally has been shown to reduce in a concentration of 250 mg/l especially if the associated calcium concentration is low. Salmons are particularly effected and it is thought that mortality rate substantially increased during episodic acid events.

HAZARDS TO SOIL:

Aluminium mobilisation is one of the stresses that acid rain places on trees, and that results in death of forest.

Soils that contain limestone are usually considered to be buffered against such change in pH due to the ability of carbonate and bicarbonate ion to neutralise H⁺, but over a period of decades surface soil may gradually loose its carbonate content due to continuous bombardment by acid rain. The soils receiving acid rain eventually become acidified. When the pH of the soil drops below 4.2, Al leaching from the soil and rocks becomes particularly appreciable.

HAZARDS TO HUMAN HEALTH:

Aluminium chloride in the presence of moisture forms hydrochloric acid, which will cause thermal and acid burns (Charles R. Foden and jack L.weddell 1995).

The salt causes irritation in the eyes, when exposed to the skin it causes irritation and after few minutes of contact causes second degree burns. It also causes suffocation and burns of first and second degree to all the exposed parts.

High aluminium levels have been found in some regions of the brain of patients who died of Alzheimer’s disease. This started the investigation of the possible role of aluminium in the ageing process and in Alzheimer’s disease (Orrulg E. 1987).

Aluminium in water causes dementia, convulsions and death among kidney patients using dialysis machine.

It does much damage when Ca⁺ and Mg⁺ are absent, it then binds with proteins across wall and disrupt biological processes.

MECHANISM OF ALUMINIUM TOXICITY:

(Mohammed Athar and Sashi B. Vohra 1995)

Disturbances on calcium and Ferritin concentration in the brain.

Dephosphorylation of proteins.

E.g.: complex formation with inositol phosphate.

Activation of the protein.

An overall of 65 tons of aluminium chloride per day is utilized by pharmaceutical industry in and around Hyderabad. So a total of 24,500 tons per year is utilized, only 10% of this aluminium chloride is recovered and remarketed by some small-scale enterprises. About 15% of aluminium is present in the effluent generated from Friedal crafts reaction, while 3-5 % will be present in combined effluent of pharmaceutical industry.

ALUMINIUM IN NATURAL WATERS:

The concentration of aluminium ions in natural waters is normally quite low usually 10⁶ (Colin Baird, 1995).

This low value is the consequence of the fact that the pH in the natural waters is usually 6-9, the solubility of aluminium contained in rocks and soils to which the water is exposed is small. The fact that aluminium is not very soluble in water is controlled by the insolubility of Al (OH) _3. The solubility product of the hydroxide is about 10^-33 at usual water temperature.

Al (OH) ₃ Al⁺³ + 3OH^-

It follows [Al⁺³] [OH^-]³ = 10^-33

Aluminium is much more soluble in highly acidified rivers and lakes than those whose pH values do not fall between 6-7. Al⁺³ is the principal cation in waters whose pH is less than 5, exceeding the concentration of Ca⁺² and Mg⁺² which are the dominant cations at pH value greater than 5.

APPLICATIONS OF ALUMINIUM SALTS IN VARIOUS PROCESSES:

Aluminium compounds have been of service to man for over 4000 years. Aluminium Hydroxide and the oxides derived from it have several uses range from fire retardants to refractories, cement to ceramics, paint to paper, abrasives to catalysts and water treatment, feed stocks to toothpaste.

Al(OH)₃:

Al(OH)₃ can be employed as a fire retardant/ smoke suppresant( Brown S.C and Harbert M.J. 1992) at minimum cost. In toothpaste (Unilever 1968), it is used as an abrasive agent, to bestow a therapeutic or polyphylacetic property. The abrasive filter used should be suufficiently abrasive so that material adhering to the teeth is removed without causing damage to the tooth enamel or any exposed dentine.

The use of Al(OH)₃ in paper industry is to impart high brightness, high capacity, high gloss and good ink receptivity.

In paints Al(OH)₃ is used to make a vinyl latex coating formulation without loss of capacity but at lower cost, as acrylic and alkyl paint systems but the scale is currently small. Small quantities are also used in fire retardant paint, mastics, intermescent coatings, and abrasive coating for its fire and smoke inhibiting characteristics.

Al₂O₃:

Al₂O₃ is used as additive in technical ceramics ( Newkirk M.S et al 1987) as they have outstanding resistance to heat, water and chemicals. Laboratory ware crucibles and thermo coupleheaths are manufactured with the minimum glassy component and with an alumina content of 99%. The plug insulator contain 88-95% alumina. Electronic /electrical applications include thin and thick film substrates for integrated circuits, electronic packages, vaccum tube envelopes r.f windows rectifier housings,sodium vapour lamps, tubes and huge voltage insulators.

In bioceramics the use of alumina is in bone substitutes in joints and in dental implants. Alumina is used in ceramics containing 99.9% Al₂O₃ is employed in order to achieve chemical inertness. It is also used armour materials, and other components like wire drawing pulleys, for steel and copper fabrication, bearing for pumps, joint seals,tap washer seals, lining for coal or mineral handling equipment, cyclone liners, grinding media ball mill linings, lines and seed drill in agriculture equipment and cutting tools (Schwartz B. 1990).

AlCl₃:

ANHYDROUS AlCl_3:

Anhydrous AlCl₃ is used as catalyst in freidal crafts reactions and employed in wide variety of reactions in the industry. Reactions include dehydrogenation, decarboxylation, oxidation, alkylation, acylation, desulphorization, amination and polymerisation of many types (Grams C.W 1991).

AlCl₃ is utilized as a nucleating agent in the manufacture of titanium oxide. Other uses include the removal of dissolved gases and Mg from Al alloys, during secondary melting, as a components of the flux used in arc welding titanium alloys, as awater repellant agent for the impregnation of cotton textiles, as binding agent for the fire resistant ceramic products and as a hardening agent for photgraphic fixing chemicals.

Hydrated AlCl₃

Hydrated AlCl₃ has a large number of application in industry, being used in textile finishing to impart grease resistance and non yellowing properties to cotton fabrics, antistatic properties to polyster, polyamide and acrylic fibres and improved flammability resistance and non- yellowing properties to cotton fabrics,antistatic properties to polyster, polyamide and acrylic fibres and improved flammability of nylon.

PAC:

PAC(poly aluminium chloride) is widely used as a water coagulant sodium aluminate is being used in the water treatment and paper industries. In water treatment it is used as a coagulating agent. In the paper industry, it improves sizing and filter retention.

Al(NO₃)₃ 9H₂O:

It is used as a salting agent in the extraction of actinides is also used as a source of alumina used in the preparation of insulating paper in transformer core laminates and in cathode ray tube heating elements.

AlPO₄:

It is used high temperature binding agents. The Al poly - orthophosphates and metaphosphates are employed in glasses, ceramics and catalyst. They are incorporated into special glasses when particularly high chemical resistance is required.

Al₂(CO)₃:

Aluminium carbonates used as finishing agents for the water proofing of the cloth, as mordents in dyeing textiles, pharmaceutical preparations because of their antiseptic, astringent and basic prorperties and in the manufacture of cosmetics due to the gelling properties of some of the higher molecular aluminium carboxylates.

Aluminium stearates:

Aluminium stearates (Wadek and Banister A.J; 1973) are soluble in water, alcohol and ethers and are used for a broad range of thickening applications because of their capacity to gel with vegetable oils and hydrocarbons. Monostearates find several uses in the pharmaceutical industry as a gellant. A number of drugs are converted to their aluminium salts to reduce acidity and make them more palatable. Typical examples include aluminium acetysalcylate, used as analgesic and antipyretic.

Al₂ (SO₄) _3:

Aluminium sulfate is mainly used in the treatment of potable water where its excellent coagulating characteristics are used to remove suspended solids and reduce color. It is also effective in reducing the presence of microorganisms in water and trihalomethanes. Other uses include water proofing, textiles, dyeing, tanning, photography for the production of colloidal Al (OH) ₃ for gastric disorders, as a fire retardant in cellulosic fiber loft insulation slug killing products and in fire extinguishers.

Organo aluminium products:

These are important commercially and used in thousands of tones/annum scale as catalyst or starting materials for the production of plastics, elastomers, detergents and organometallics containing tin, zinc or phosphorous are odf particular importance in the polymerization of olefins by Ziegler Natta catalysts. These are heterogeneous catalysts prepared by mixing organoaluminium compounds with transition metal halides.

Al₂ (NO) _3:

This is used in ceramics armor, law enforcement vehicles, helicopter, aircraft and military vehicle protection.

Pharmaceutical uses of aluminium compounds:

Al (OH) ₃ is used in significant amount as gel in antacid preparation and medicines for the control of phosphate levels. A high degree of purity is required and the product is designed to have high reactivity in order to readily react with excess stomach acids.

Aluminium carboxylates (McLenna A.L.1991) generally used in pharmaceutical preparation because of their antiseptic, astringent and basic properties. In volume terms the largest uses are for the production of ethyl benzene (for styrene production), cumene, aluminium alkyls, ibuprofen, phenyl ethyl alcohol and polymerization of isoprene, isobutylene and ketines used in pharmaceutical industry.

It is also used as an antiperspirant, a number of drugs are converted to their aluminium salts form to reduce acidity and make them more palatable.

III chapter

Procedures of analysis as described in standard methods of analysis for the examination of water and wastewater published by APHA, AWWA and WPCF, 12^th edition are followed. A brief methodology for the analysis of each parameter is given below.

HYDROGEN –ION –CONCENTRATION (pH):

pH is the measure of intensity of acidity or alkalinity and measures the concentration of hydrogen ions in water. Digion pH meter was used for the study. Standard buffer solutions having pH values of 4.0, 7.0 and 9.2 were prepared by dissolving the pH – powder of 4, 7 and 9.2 values respectively in 100ml of distilled water and were used for calibration of the pH meter.

PROCEDURE:

The glass electrode of pH meter was dipped in a beaker containing standard buffer solution of pH 4 and the "CAL"(calibration) switch was adjusted to bring the value to 4. And now on replacing the other two buffer i.e., 7 and 9.2 the instrument showed the exact values respectively. The electrode was taken out and washed with distilled water. Then the cleaned electrode was dipped in a beaker of effluent and pH of the sample was noted.

TOTAL SOLIDS (TS):

PRINCIPLE:

Total solids are determined as the residue left after evaporation of the unfiltered sample.

PROCEDURE:

10 ml. Of the unfiltered sample was taken in a pre-weighed clean and dry beaker and evaporated on a hot plate with temperature 98⁰C. The residue was dried at 103-105 ⁰ C in an oven for one hour. Then the final weight was taken after cooling in a dessicator.

CALCULATIONS:

Total solids, mg/l = (A-B)*1000/V

Where,

A = final weight of the beaker in grams

B = initial weight of the beaker in grams

V = volume of the sample taken in ml.

TOTAL DISSOLVED SOLIDS (TDS):

PRINCIPLE:

Total dissolved solids are determined as the residue left after evaporation of a filtered sample.

PROCEDURE:

10 ml of the filtered sample was taken in a clean evaporated and pre-weighed beaker and evaporated on a hot plate with temperature of 98 ⁰ C. The residue was dried at 103-105 ⁰ C in an oven for an hour. Then the final weight was taken after cooling in a dessicater.

CALCULATION:

TDS, mg/l ==(A-B) *1000 / V

Where, A = final weight of the beaker in grams

B =initial weight of the beaker in grams

And V = volume of the sample taken in ml

TOTAL SUSPENDED SOLIDS (TSS):

The difference between the total solids and total dissolved solids indicates the total suspended solids.

CALCULATIONS:

Total suspended solids =Total solids-total dissolved solids

i.e., TSS = TS - TDS

TOTAL HARDNESS: (CALCIUM and MAGNESIUM)

Hardness of water is a measure of its capacity to form precipitates with soap and scales with certain anions present in the water sample. Hardness of sample was determined by direct titration with EDTA.

PRINCIPLE:

Ca and Mg ions form a weak complex with the blue dye, Eriochrome black-T and a more stable complex with EDTA. When the dye is added to hard water a wine red complex is formed and when EDTA is added the wine red complex is disrupted with the release of the dye. The end point is wine red to blue colour.

REAGENTS REQUIRED:

Ammonia buffer solution

Eriochrome Black ‘ T ‘ indicator (EBT)

Standard EDTA solution (0.01)

Murexide indicator

Sodium hydroxide

PROCEDURE FOR TOTAL HARDNESS:

10ml of 100 times diluted sample was taken in a conical flask, pH of this solution was made 12 by adding 1-2ml of ammonia buffer then a pinch of EBT indicator was added and titrated against EDTA till the wine red colour changed to blue. The volume of the EDTA consumed was noted by reading the burette and calculated.

CALCULATIONS:

Total hardness = Volume of EDTA *1000/ Volume of sample taken

PROCEDURE FOR CALCIUM HARDNESS:

10ml of 100 times diluted sample was taken in a conical flask, pH of the solution was made 14 by adding 1-2ml NaoH. Then a pinch of murexide indicator was added and titrated against EDTA till the pink colour changed to purple. The volume of the EDTA consumed was noted by reading the burette and calculated.

CALCULATIONS:

Calcium hardness ==Volume of EDTA*1000 /Volume of sample taken

MAGNESIUM HARDNESS:

Magnesium hardness = Total hardness –Calcium hardness

IRON:

Estimation of iron was done by colorimetric method.

PRINCIPLE:

In the phenanthroline method, the ferric form of iron is reduced to ferrous form by boiling with hydrochloric acid and Hydroxylamine. The reduced iron chelates with 10 – phenanthroline at pH of 3.2 –3.3 to form a complex of orange red colour. The intensity of colour is proportional to the concentration of iron.

REAGENTS REQUIRED:

50ml of 100 times diluted sample was taken in a conical flask. To it 1ml of concentrated HCl followed by 0.5ml-hydroxylamine hydrochloride solution was added. This was boiled for 5 minutes, cooled, and then 5ml of ammonium acetate buffer followed by 1-10 phenanthroline solution was added and changes in colour were observed. The absorbance was measured in spectrophotometer at 510nm.

Standard graph was prepared between concentrations and absorbance from 1ppm –5ppm. The concentration of iron was known from standard graph.

CHEMICAL OXYGEN DEMAND:

Chemical oxygen demand test determines the oxygen required for chemical oxidation of organic matter with the help of strong chemical oxidant under acidic conditions.

PRINCIPLE:

The organic matter gets oxidised completely by K₂Cr₂O₇ in the presence of conc. H₂SO₄ to produce CO₂ + H₂O. The excess K₂Cr₂O₇ remaining after the reaction is titrated with Fe (NH₄)₂SO₄ using ferroin as indicator. The dichromate consumed gives the oxygen required for oxidation of the organic matter.

The organic matter in the sample is related to the oxygen required (COD) in accordance with the equation.

C_XH_YO_Z +[X+(Y/4) (Z/2)] XCO₂ +Y/2 H₂

REAGENTS REQUIRED:

Standard potassium dichromate solution (0.25N).

Ferrous ammonium sulphate (FAS)(0.1N).

Ferroin indicator solution.

Sulphuric acid.

Mercuric sulphate.

PROCEDURE:

A pinch of mercuric sulphate was taken in a conical flask. To it, 20ml of 100 times diluted sample was added. Then 10ml K₂Cr₂O₇ followed by 30ml of conc. H₂SO₄ was added. The mouth of the conical flask was closed with a watch glass and then it was placed on a hot plate for 2 hours at 150 –200⁰C.

After 2 hours, the solution was allowed to cool. The sides and the watch glass were washed with distilled water to wash the vapours into the solution. To this solution ferroin indicator was added and titrated against Ferrous ammonium sulphate till the colour changed blue green to wine red. Burette readings were noted and calculated.

CALCULATIONS:

COD in mg/l = Volume of FAS *Normality of FAS * 8 *1000 /Volume of sample taken

ALUMINIUM:

PROCEDURE FOR THE ESTIMATION OF AL:

To the elluent solution 20ml of 0.05 EDTA solution was added. Few drops of NH₃ are added and the pH was raised between 7-8. This solution was boiled to effect complete complexation of Al with EDTA. The solution was cooled and checked for pH and EBT indicator was added and titrated against standardized ZnSO₄ solution. The end point was indicated by a color change from blue to wine red.

EQUIPMENT:

A tempo shaking water bath with temperature control in the range of 30-80⁰ c was used for experiments.

An elico pH meter was used for measuring initial and equilibrium pH of the system.

The equipment used in ion exchange process is relatively simple. The column was an ordinary glass burette with a glass wool or quartz wool plug at the bottom to support the resin bed. The resin was held in place by a glass wool plug or a fused in sintered-glass disc. In order to pack a column with water swollen ion exchanger, the column was filled with water to certain level and the ion exchanger suspended in H₂O was introduced and allowed to settle freely to form the bed.

Eriochrome black T (EBT) indicator was prepared by mixing 0.5 g of EBT with 100 mg of NaCl and finely grinded in a motor.

0.01N of HCl, 0.01 NaOH and ammonia solutions, ammonium chloride, ammonia buffer solutions were prepared from analytical samples.

In order to concentrate industrial waste waters so that particular chemicals can be removed recovered and reused, there is a great need for the development of suitable separation techniques. Along with other processes, ion exchange is an appropriate technique for such purposes.

Like every unit processes ion exchange has its limitations. Theoretically, ion exchange allows one to separate aqueous solutions of ions into water and a concentrated solution of salts. The main problem with the application of ion exchange to the recycling of wastewater constituents is not how to achieve a suitable level of separation which is rather easily attained, but how to obtain the desired results at a reasonable cost. Hence, optimization of the selected technique is a vital issue.

Cation ion exchanger amberlite-400 and powdered activated carbon for the removal of AlCl₃ after optimizing the conditions, the removal was maximum for cation ion exchanger resin.

BATCH STUDIES:

The batch adsorption is a simple stage process where a known quantity of resin is mixed continuously for desired time with a specific volume of the solution. The resin is then removed and regenerated for use with another volume of solution.

In batch treatment, the concentration of solute in contact with a specific quantity of resin constantly decreases as absorption proceeds, there by decreasing the efficiency of the adsorbent for removing the solute.

PROCEDURE:

The first step in both the batch studies and column studies is to optimize the conditions in a systematic procedure.

pH:

The effluent, which comes out of any treatment plant, should have a pH between 7-8.5. Therefore, the different pH taken for optimizing were in the range of 4 –10, 4 was the original pH of the Al salt (AlCl₃) with concentration of 100ppm.

All the solutions were taken in glass reagent bottles at room temperature with different pH ranging between 4 –10 and stirred for 1hr. 1hr-mixing time was opted, as within an hour the process of ion exchange is complete in any solution. The pH was adjusted using 0.1n NaOH, 0.1N HCl, and 0.1N NH₄Cl.

CONTACT TIME:

After optimizing, the pH contact time was optimized. 100ml of 100ppm solution at room temperature was taken in different bottles with optimized pH and 1g of resin and stirred for different contact time starting with a contact time of 15min. To a contact time of 2hrs.

DOSAGE:

After optimizing pH, contact time dosage was optimized. 100ml of 100ppm solution was taken in different glass reagent bottles at room temperature with optimized pH and contact time. Different doses of resin starting from 0.5g to 2g were added and stirred.

All these solutions were removed and filtered through wattman-42 filter paper and estimated for aluminium which is obtained by titrating the elluent by adding excess of EDTA (0.02N) and back titrating with ZnSO₄.

COLUMN STUDIES:

PRINCIPLES OF COLUMN OPERATION:

An ion exchange bed is usually operated in a cylindrical form located in a vertical column. During the service of exhaustion cycle three zones are formed (Bolto P.A. 1988).

They are

zone containing exhausted resin

working zone

Zone containing regenerated resin.

The exhausted resin is fully loaded with the ions removed from the feed water, while regenerated resin is completely unloaded. The ion exchange reactions occur in the working zone, which moves down the resin bed as the ion exchange reaction advances, until the working zone reaches the bottom of the bed. When this happens the ions to be removed start breaking through and their concentration in the product water gradually increases until it is the same as that of the feed water. When the concentration of ions which break through into the product water reaches the permitted level the service cycle is terminated.

During regeneration (down flow) the sequence of the zone is reversed. The bottom zone contains the resin in the exhausted form, and the top zone contains the regenerated resin.

COLUMN PREPARATION:

The cation exchange resin was weighed, washed in distilled water and with 0.1M HCl, and then filled in the column. The height of the column was measured. It was ensured that no air bubbles or spaces are trapped in the column. This column was again washed with distilled water before passing the test solution. To the upper end of the column, a burette was attached so that the test solution was allowed to to fall into the column in a uniform manner.

The column so prepared is now ready for column studies and treatment studies. The amount of Al present in the solution was estimated by titrimetry. The exchange capacity of the resin was studied by observing the amount of aluminium retained by column, which is obtained by titrating the elluent solution by adding excess EDTA and back tirating with ZnSO₄ solution.

PROCEDURE FOR THE ESTIMATION OF ALUMINIUM IN THE ELLUENT

To the elluent solution 20ml of 0.05 EDTA solution was added. Few drops of NH₃ are added and the pH was raised between 7-8. This solution was boiled to effect complete complexation of Al with EDTA. The solution was cooled and checked for pH and EBT indicator was added and titrated against standardized ZnSO₄ solution. The end point was indicated by a color change from blue to wine red.

GENERAL PRINCIPLES AND APPLICATION OF SEPERATION TECHNIQUES FOR THE REMOVAL OF INORGANIC POLLUTANTS FROM INORGANIC EFFLUENTS:

GENERAL ASPECTS OF TREATMENT OF INDUSTRIAL EFFLUENTS:

As industrial effluent posses dissolved solids, suspended particles, heavy particles, acidic and basic nature, metals, metallic oxides metalloids non-metallic ions/particles or radical etc., their treatment basically falls into three methods.

J primary treatment

J secondary treatment

J tertiary treatment

Primary treatment is used for removing suspended solids, odors, colour and neutralize the high or low pH.

Secondary treatment involves biological processes and bacteria that are utilized for the oxidation. The organic substances present in the effluent serve as food for the bacteria and within a short time they make the effluent free from organic matter by consuming it.

Tertiary treatment is needed for the effluent for the removal of bacteria and dissolved inorganic matter (metals, metal oxides, metal carbonates, metal sulfates etc.)

Separation processes based on mechanical and chemical methods are widely adopted processes for the removal and recovery chemicals from industrial effluents either before the secondary treatment or in the tertiary treatment.

Normally the removal of inorganic substance the methods employed are reverse osmosis, chemical precipitation, evaporation, dialysis, removal of algae, ion exchange, absorption on polyurethane foams, activated carbon and exchange resins.

SEPARATION PROCESSES:

The technique of separation of chemicals from the effluents can be classified as:

Distillation

Solvent extraction

Adsorption

Chemical coagulation

Ion exchange

The size of the sample available, the simplicity and selectivity of the method, the degree of resolution required and the general applicability of the procedure usually governs the choice of separation tools. Yield, separation capacity and efficiency can evaluate the separation method or process.

The general principles of various separation processes are briefly discussed in the following pages.

DISTILLATION:

The simplest case involving the volatilization of a liquid by application of heat and subsequent condensation of the vapor back to the liquid state. (Jaganathan P.B. 1979)

SOLVENT EXTRACTION:

Solvent extraction as applied to solids is selective dissolution of the solute portion of a solid with an appropriate solvent. (Carr et al 1941) liquid extraction is a physical partitioning process dependant on the favorable distribution of the given solute between two immiscible solvents. The distribution of the components between the two immiscible phase follows the distribution law when the system is at equilibrium

C₁/C₂ = K

C₁ and C₂ represent the concentration of the solute in the respective phases and K is the distribution constant or partition coefficient.

ADSORPTION:

Adsorption first observed by Weber for gases and later for solutions is recognized, as a significant phenomenon is most natural physical, biological and chemical process.

Sorption on solids, particularly active carbon, has become a widely used operation for purification of water and wastewater’s. Adsorption involves the interface accumulation or concentration of substances at a subface or interface. The material being concentrated or adsorbed is the adsorbate and the adsorbing phase is termed the adsorbent.

The process can occur at an interface between any two phases

liquid-liquid

gas-liquid

gas-solid

Adsorption is primarily of two types

Physical adsorption

Chemical adsorption

Physical adsorption occurs in cases in which the adsorbed molecules is not affixed to a specific site at the surface but is rather free to undergo translational movement within the interface. Adsorption of this is some times referred to an ideal adsorption. If the adsorbate undergoes chemical interaction with the adsorbent, the phenomenon is referred to as a chemical adsorption, activated adsorption or chemisorption.

Chemically sorbed molecules or are considered not to be free to move on the surface or within the interface.

Conditions for physical adsorption

Predominant at low temperatures

Characterized by low energy of adsorption.

Conditions for chemical adsorption

Higher temperatures

High energy of adsorption because the adsorbate forms strong localized bonds at active centers on the adsorbent.

Adsorption phenomena are combinations of different physical and chemical adsorption processes.

LANGMUIR ADSORPTION ISOTHERM:

The Langmuir isotherm results from assuming that adsorption is reversible and occurs only for monolayer on the sorbent surface and that an equilibrium exists between condensation and evaporation of adsorbed molecules.

Considering a monolayer adsorption layer

X/M = abC_e / (1+aC_e)

This can be expressed in linear form as

1/(X/M) = 1/b + 1/abC_e

Where

a = constant which increases with increasing molecular size

b = amount of adsorbent to form a complete monolayer on the surface

and

C_e = the equilibrium concentration

Constants of this equation can be evaluated by plotting 1/ (X/M) V_s 1/C_e

Linearity if the plot suggests the applicability of Langmuir model.

FREUNLICH ADSORPTION ISOTHERM:

This model is stated as follows

X/M = k. Ce ^1/n

Where X, M = empirical constants

C_e = equilibrium concentrations of adsorbate in solution after adsorption.

The constants of this equation can be evaluated by plotting log (X/M) V_s log C_e.

COAGULATION:

The aggregation of the colloidal particles can be considered as involving two separate and distinct steps:

Particle transport to effect interparticle contact.

Particle destabilization to permit attachment when contact occurs.

According to Lamer (1981), coagulation refers to destabilization produced by compression of the electric double layers surrounding all colloidal particles. Coagulation is applied to the overall process of particle aggregation, including both particle destabilization and particle transport.

ION EXCHANGE:

The term ion exchange is generally understood to mean the exchange of ions of like sign between a solution and a solid highly insoluble body in contact with it.

MATERIALS:

Many substances both natural (e.g. Certain clay materials) and artificial/ have ion exchanging properties, but for analytical work synthetic organic ion exchangers are of interest, although some inorganic materials e.g. zirconyl phosphate and ammonium 12-molybdophosphate also posses useful ion exchange and have specialized applications.

PROPERTIES OF ION-EXCHANGE PROCESS:

All ion exchangers of value in analysis have several properties in common, they are insoluble in water and inorganic solvents and they contain active or counter-ions that will exchange reversibly with other ions in a surrounding solution without any appreciable physical change occurring in the material.

PHYSICAL PROPERTIES:

Ion exchanger consists of a polymeric skeleton, held together by linking crossing from one polymer chain to the next; the ion exchange groups are carried on their skeleton. The physical properties are mainly determined by cross-linking in the polymer.

CHEMICAL PROPERTIES:

(As the author has taken up systematic studies on the removal and recovery of AlCl₃ using ion exchange process, The chemistry of ion exchange resins are presented briefly in the following paragraphs.)

All ion exchangers are of value in analysis and have several properties in common. They are insoluble in water and in organic solvents, and they contain active or counter ions that will exchange reversibility with other ions in a surrounding solution with out any appreciable physical change occurring in the material.

The cation exchanger consists of a polymeric anion and active cation while an anion exchanger is a polymeric cation with active anions. The synthetic ion-exchanger resin consists of a net work of hydrocarbons molecules to which are attached soluble ionic functional groups.

The hydrocarbon molecules are cross-linked in a three-dimensional matrix imparting overall insolubility and toughness to the resin. The extent or degree of cross-linking determine the internal pore structure of the resin and must not be so good as to restrict free movement of exchanging ions.

By proper selection of the degree of cross-linking the larger ions may be excluded from reaction as the ions diffuse into and the resin for the exchange to occur. The nature of the ionic group attached to the framework of the resin determines to a large extent the behavior of the resin.

The total number of groups per unit weight of resin determines the exchange capacity and the group type affects both the ion-exchange equilibrium and the ion selectivity. Cationic resins have functional group as sulfonic R-So₃H, phenolic R-OH, carboxylic R-COOH and phosphoric R-PO₃ H₂. The R represents the organic network of the resin.

Strong acidic cationic resins are derived from strong acids e.g.: H₂SO₄ and weakly acidic cations from e.g.: H₂CO₃ weak acids. Anions exchange resins contain functional groups as the primary amine R-NH₂, secondary amine R R" NH, tertiary amines R-R’3N⁺ OH^-. The R⁺ represents organic radical such as methyl group, CH₃ that in a given resin may or may not be the same throughout the resin.

Strongly basic resins (anion exchange) are derived from quaternary ammonium compounds. Weakly basic anion exchange resins are derived from weak base amines.

NATURE OF EXCHANGING IONS:

a) At low aqueous concentration and at ordinary temperature the extent of exchange increases with increasing charge of the exchanging ion i.e.

Na⁺ < Ca²⁺ < Al³⁺ < Th⁴⁺

b) Under similar conditions and constant charge, for singly charged ions the extent of exchange increases with decrease in size of the hydrated cation i.e.

Li⁺ < H⁺ < Na⁺ < NH4⁺ < K⁺ < Rb⁺ < Cs+

While for doubly charged ions the ionic size is an important factor but the incomplete dissociation of salts of such cations also plays a important role.

Cd²⁺ < Be²⁺ < Mn²⁺ <Mg²⁺ = Zn²⁺ < Cu²⁺ = Ni²⁺ < Co²⁺ < Ca²⁺ < Sr²⁺ < Pb²⁺ <Ba²⁺

c) With strongly basic anion exchange resins, the extent of exchange for singly charged anions varies with size of the hydrated ion in a similar manner to that indicated for cations. In dilute solutions multicharged anions are generally absorbed preferentially.

d) When a cation in a solution is being exchanged for an ion of different charge the relative affinity of the ion of higher charge increases in direct proportion to dilution. Thus to exchange an ion of higher charge on the exchanger for one of lower charge in solution, exchange will be favored by increasing the concentration, while if the ion of lower charge is in the exchanger and the ion of higher charge is in solution, exchange will be favored by dilutions.

NATURE OF THE ION EXCHANGE RESIN:

The absorption of ions will depend upon the nature of the functional group in the resin. It will also depend upon the degree of cross-linking: as the degree of cross-linking is increases, resins become more selective towards ions of different sizes (the volume of the ion is assumed to include the water of hydration) the ion with the smaller hydrated volume will usually be absorbed preferentially.

METHODS OF PREPARATION:

A widely used cation exchange is obtained by copolymerization of styrene and a small portion divinyl benzene, followed by sulphonation.

CHANGING THE IONIC FORM:

It is necessary to convert a resin completely from one form to another. This should be done after regeneration. An excess of a suitable salt solution should be run through a column of resin. Ready conversion will occur if the ion to be introduced into the resin has a higher or only a slightly lower affinity than that actually on the resin.

When replacing an ion of lower charge number on the exchanger by one of the higher charge number, the conversion is assisted by using a dilute solution of replacing salt (preferably as low as 0.01M), while to substitute a more highly charged ion in the exchanger by one of lower charge number of comparatively concentrated solution be used (1M). The resins are available in standard grade and in some cases, in a pure ‘chromatographic’ grade and in some cases in more highly purified ‘analytical grade’. Standard grade material should be subjected to primary cleaning by regeneration procedure.

The standard grade resin as received from the manufacture may contain unwanted ionic impurities and sometimes traces of water soluble intermediates or incompletely polymerized material, these must be wasted out before use. The standard grade resin must be soaked in a beaker of in about twice volume of 2M HCl for about 30-60 minutes with occasional stirring, the fine particles are removed by decantation or by back washing a column with distilled or deionised water until a supernatant liquid is clear.

For all resins the final treatment must be with a solution leading to the resin in the desired ionic form.

APPROPRIATE REGENERANTS ARE GIVEN FOR THE EXCHANGERS LISTED BELOW.

J strongly acidic cation exchangers.

Hydrogen form, regenerate with HCl or H₂SO₄

2R-SO₃H + Ca²⁺ ----- (R-SO₃)₂Ca + 2H⁺

sodium form regenerate with NaCl

2R-SO₃ Na + Ca²⁺ ------------- (R-SO₃)₂Ca + 2Na⁺

J weakly acidic cation exchangers

hydrogen form regenerate with HCl or H₂SO₄

2R –COOH + Ca²⁺ ---------- (R-COO)₂Ca + 2H⁺

sodium form regenerate with NaOH

2R-COOH + Ca²⁺ ------------- (R-COO)₂Ca + 2Na⁺

J Strongly basic anions exchanger

hydroxide form regenerate with NaOH

2R-R’₃NOH + SO₄^-2 --------------------- (R-R’₃N)₂SO₄ + 2OH^-

chloride form, regenerate with NaCl or HCl

2R-R’₃NCl + SO₄^-2 -------------- (R-R’N)₂So₄ + 2Cl^-

weakly basic anion exchanger

free base or hydroxide form, regenerate with NaOH, NH₄OH or Na₂CO₃

2R-NH₃OH + SO₄^-2 -------------- (R-NH₃)₂SO₄ + 2OH^-

chlride form regenerate with HCl

2R-NH₃Cl + SO₄^-2 -------------------- (R-NH₃)₂SO₄ +2Cl^-

MECHANICAL AND CHEMICAL STABILITY:

The mechanical stability (resistance to abrasion etc) of ion exchangers is generally satisfactory for analytical purposes and becomes an important factor only in industrial process applications. Determination of the mechanical stability is usually done by comparative sieve testing before and after the ion exchanger has been used for a specified number of exchanger cycles, or before and after it has been in a ball mill in standard conditions.

The chemical stability depends on the chemical nature and structure of the particular ion exchanger. Synthetic organic ion-exchangers are prone to organic thermal degradation at elevated temperatures and chemical degradation by oxidants, concentrated alkali’s etc other exchangers e.g.: zirconium phosphate and heteropolyacid salts are stable in acid media but hydrolyze in alkaline media.

Inorganic exchangers, zeolites and hydrous oxides are stable only with in a narrow pH range at about 7. Polymer matrix ion-exchangers are more resistant to chemical agents that are the condensation types and cation- exchangers are on the whole more stable than anion exchangers.

THERMAL STABILITY:

Elevated temperatures often aid ion-exchangers processes. Therefore ion-exchangers which are stable at high temperature are particularly available. Polymer matrix carboxylic cation-exchangers can withstand a temperature of 160⁰c and of the organic cation-exchangers containing sulfonated groups those with styrene divinyl benzene matrix are stable.

SWELLING:

When brought into contact with water, ion-exchangers especially organic ones expand or ‘swell’. The effect is associated with the tendency of with the tendency of the ions in the ion-exchanger phase to surround themselves with appropriate salvation shells. The elastic forces of the matrix lattice oppose the stretching forces and thus prevent swelling beyond a certain limit.

Swelling is directly related to a resin’s exchange capacity and to the dissociation of functional groups and inversely related to the number of cross-links.

SELECTIVITY:

The selectivity of an ion- exchanger is defined as the capability of the ion-exchanger to select certain counter ions in preference to others. Utilization of selectivity properties forms the basis for every type of separation. To understand the source of selectivity properties on the nature of the physico-chemical factors involved is of paramount importance for prediction of the course of ion-exchange reactions and their practical use.

COLUMN PROCESS:

Simple exchange of one ion for another is one of the simplest applications of ion exchange. Ion exchange chromatography permits resolution of complex mixtures of constituents with closely related properties. As in other types of chromatography three fundamental techniques may be distinguished, involving

Frontal analysis

Elution development

Displacement development

FRONTAL ANALYSIS:

Involves feeding continuously a mixture of electrolytes e.g.: AQ, BQ and CQ into a column of ion-exchanger in Z form. The counter-ion, Z should be less strongly sorbed by the resin than A, B, and C (selectivity sequence; Z<A<B<C). The frontal analysis technique allows only one component (A) to be isolated in pure form and in rather limited amount. In its classical version, the technique is therefore of minor importance as a procedure for resolution. However, when the ions B and C are trace constituents with high affinity for the ion-exchanger, frontal analysis may be very useful for preconcentration and separation of the traces from the major components which under experimental conditions are sorbed by the ion-exchanger to a much lesser extent. Preconcentration of elements by frontal analysis may be combined with subsequent selective elution of the individual components retained in the column.

ELUTION DEVELOPMENT:

Involves introducing a mixture of ions e.g.: A, B and C at the top of the column of ion- exchanger in Z form, as a narrow band, the counter-ions, z having less affinity for the resin than the ions of mixtures to be resolved (selectivity sequence Z<A<B<C). Next, an electrolyte ZQ is fed into the column i.e. the ions A, B and c are eluted with counter ion Z. In this process the ions travel down the column at different rates, separating progressively until, in the course they are completely resolved, provided a suitable column length. In the effluent, the ion appears as individual peak (elution curves). Since the fluent, counter ions Z have a less affinity for the ion-exchanger than the ions being separated, Z ions are continuously are continuously overtaking A, B and C ion band on their way downstream during the elution. The boundaries of these bonds become progressively more diffuse and so slower the migration rate of the band. As a result, the maximum concentration of resolved ions in the ellute (peak heights) are usually much lower than the concentration of Z ions in the elluent.

DISPLACEMENT DEVELOPMENT:

Involves displacing the ions retained in the column by a counter-ion, which has more affinity for the ion-exchanger than any ion of the mixture to be resolved. When the ions A, B, C retained on a column of ion-exchanger in the Z-form, are displaced by an electrolyte DQ (selectivity sequence Z<A<B<C), they separate into individual bands along the column in the order of increasing efficiency for the ion-exchanger. Between these bands arise relatively sharp (self-sharpening) boundaries which do not become very diffused when moving down the column. Once a certain length of the column has been traversed a steady-state condition is established and further increase in column does not improve the resolution. In displacement development, the band, migrate down the column at equal rates, determined by the flow rate of the displacing agent (DQ). The concentration in gram equivalent of individual elements in the effluent are also identical and equal to that of the displacing ion provide that there is enough of the component to produce a pure band under experimental conditions. Displacement development is of minor analytical importance, especially with regards to the resolution of traces, but it has been widely applied for preparative of rare earth’s alkali metals (Cornet 1958).

THEORY OF BREAK-THROUGH CURVES:

If a mixture of two ions- one a trace constituent of high affinity and the other a major constituent of low affinity for the ion-exchangers are continuously passed through an ion-exchanger column. Then the major constituent –weakly held by the ion-exchanger will be according to the frontal analysis mechanism, appear rapidly in the effluent at a concentration equal to that in the influent, whereas the trace constituents owing to its high affinity and low concentration- will not appear in the effluent until a long period of time has elapsed. This procedure may therefore be used as a convenient method for preconcentration of trace ions from large solution volumes. In practice, the form in which an ion exchanger is used is often that of the ion, which constitutes the major component of the solution (e.g. to remove multiple charged metal ions from dilute acid solutions the H⁺ form of the strong acid cation exchanger is used). Formally, the process of retention of trace ions bears much resemblance to the single exchange of one ion for another. However, in the present case the exhausted zone does not correspond, for obvious reason, to an ion exchanger completely converted into the trace ion form but rather to one in which the trace to major ion ratio reflects the prevailing equilibrium condition (at the experimental composition of the solution). The resulting break-through curve is similar to the classical break-through curve except that the c/c₀ ratios plotted as ordinates refer to the concentration of trace ions rather than overall ion concentrations in the solution. The curve makes it possible to calculate the weight distribution coefficient of the trace ions.

 _B = u - u₀ – v/m_j

Where u is the effluent volume (cm³) at C = C₀/2, u₀ is the dead volume (cm³) in the column (the volume of the liquid between the lower end of the resin bed and the column outlet, V is the void (inter- particle) resin bed volume (cm³) which amounts to Ca. 0.4 of the resin bed volume and m_j is the dry resin weight (g).

Ion exchange preconcentration of traces is usually done under conditions chosen so as to prevent the break-through of the ions. The length of the time required for identical ions in solutions of identical compositions to break-through in columns of equal length may be different and depend upon column efficiency. The more efficient the column, the steeper the break-through curve. A quantitative measure of column efficiency is the number of theoretical plates, N, which can be calculated from the following equation

N = (u - u₀) (u’ - u₀) / (u - u’)²

where u’ is the effluent volume at C = 0.159 C₀

Batch studies for the removal of AlCl₃:

To evaluate the performance of the adsorbents systematic and detailed experiments were carried out using synthetic AlCl₃ solutions under various experimental conditions by batch studies.

Effect of Different Adsorbents:

The magnitude of AlCl₃ removal by the three adsorbents as a function of contact time and concentration was systematically investigated. The extent of uptake of AlCl₃ by resin increases with time and attains equilibrium just in 30min and the results are tabulated and graphically presented in fig.1

In general, the adsorption curves are characterized by a sharp rise in initial stages flattening near equilibrium. The findings that the low and high concentration ranges are both fit for maximum removal of the salt can be exploited for treating industrial wastes containing AlCl₃.

EFFECT OF pH:

The experiments with solution pH as a variable were conducted to determine the optimum pH range for maximum absorption by the three adsorbents and the results are presented in table x and graphically presented in fig. From the results it is clear that the aluminium is absorbed / extracted more in pH range of4-6.

The aqueous chemistry of Al⁺³ ion is complicated. The ions themselves do not exist in solution as uncomplexed species in the absence of other ions and molecules, they are surrounded by a number of H₂O molecules, each of which is attracted by metals positive charge. The presence of the metal ions makes the water more acidic than usual, in other words the loss of H⁺ occurs more readily. Al³⁺ exists as Al(OH)₂³⁺₆ only in a highly acidic condition. At pH values near 5, such ions in solutions loose the H⁺ from one water molecule, yielding the ion Al(H₂O)³⁺₅(OH)^- which often is written for simplicity as Al(OH)²⁺. Near a pH of 6 a second water molecule looses a proton yielding Al(H₂O)₄³⁺ (OH^-)₂ or Al(OH)₂⁺. The loss of a proton from a third molecule yields the neutral species Al(H₂O)₃ (OH^-)₃³⁺ or Al(OH)₃ which occurs to a tiny extent as dissolved material but in greater amounts as the gelatinous semi-solid. Under neutral and alkaline conditions, most dissolved Al exists as the anionic species with still another proton lost from a water molecule namely Al(H₂O)₂³⁺(OH^-)₄ or Al(OH)^-₄. Indeed the ready formation of this ion takes place in alkaline waters than in those, which are neutral. Some of the Al precipitates from water if its pH lies in the range of pH 5-8 it dissolves to yield the anion as indicated by fig. Due to the formation of cation species Al(H₂O)₆ ³⁺ in 2 – 6 pH range where quantitative exchange with protons of the, Cationic exchange resin occurs maximum recovery is obtained in the ion exchange process in this pH range.

EFFECT OF DOSAGE:

Different dosages were taken from 0.5g-2g and the results are shown in the figs 7, 8 &9 and tabulated in the table 7.

COLUMN STUDIES FOR THE REMOVAL AND RECOVERY OF AlCl₃ USING CATION EXCHANGE RESIN.

In order to evaluate the total capacity of the resin and its ability to change the protons for Al ions in the column process the effluent of various experimental parameters like flow rate, pH, various Al concentrations, bed height and column in series. The break through capacity and total capacity were also monitored for different conditions.

Al, which was adsorbed on the resin, recovered by eluting the column with 2M hydrochloric acid. The recovery of Al was almost complete.

The reusability of the resin was also studied by conducting a number of recycles on the same resin to show the effect of sorption capacity on the resin.

In all these experiments pure Aluminium chloride solution was used in the column studies.

The recovery of absorbed/ extracted Al with HCl and the reuse of the resin for a number of recycles with out effecting its sorption capacity were examined critically. Recrystallisation studies were also conducted using various solvents.

pH:

The pH 4 was taken as the optimum pH from the batch studies at different flow rates of 0.5ml/min, 1ml/min and 2ml/min.

The column studies indicated that 4 pH was effective for the recovery of Al from different initial concentrations of the influent supporting the results of batch studies.

EFFECT OF FLOW RATE:

At various flow rates ranging from 0.5ml/min to 2ml/min the column studies were conducted. The capacity of the resin was studied at various bed heights and flow rates.

These studies indicate that flow rate of 0.5ml/min gives maximum recovery of Al ions. In the event of dealing with large volume of solutions, 2ml/min-flow rate is also recommended to speed up the process operating without sacrificing much on the adsorption efficiency.

EFFECT OF BED HEIGHT:

Studies were carried out with different bed heights taken in ratio with diameter of the column (2). Different ratios of 1:1, 1:2, 1:4, 1:6 were taken and studied and from the results it can be inferred from that as the bed height increases the absorption/extraction increases. All these results are represented in fig. 4-10

BREAKTHROUGH CAPACITY:

The practical usefulness and the overall efficiency of a separation medium can be adjudged by measuring its break through volumes and breakthrough capacity apart from other physical characteristics of the material, like porosity, particle size, density, surface area, mechanical stability etc.

The breakthrough capacity is defined as the amount of the constituent or solute that can be retained on the solvent when the solution under test containing the solutes is passed through it at optimized conditions of 0.5ml/min flow rate and room temperature of 30+ 1⁰C until the constituent or solute is first detected in the effluent solution. This volume is termed as breakthrough volume and the corresponding breakthrough capacity is determined by multiplying it with the concentration and dividing with weight of sorbent and is represented as mg/g.

RECYCLES:

The resin filled in the column was used under optimized conditions. After passing the influent AlCl₃ through the resin until saturation is attained the column is desorbed and again used for the next experiment after regeneration with 0.1M HCl, 0.1M NaOH, 0.1M HNO₃. The same column is used for absorption/ desorption studies for upto 8 times. No changes in the capacity of the resin were observed.

The results indicate clearly that there is no change in the absorption capacity of the resin media even after the repeated use of the column a number of times. The major advantage of this process is the desorption/ recovery of the adsorbed Al with the different solvents, which also includes regeneration step. The stability of the material is quite good and there is no sign of any sort of deterioration in the physical nature of the material even after several recoveries.

DESORPTION STUDIES:

Recovery of AlCl₃ is one of the important aim of the present work. The desorption of Al ions from the ion exchange resin was studied systematically by using different regenerants 0.1M HCl, 0.1M HNO₃, 0.1M NaOH. It was observed that the maximum desorption occurred using low volumes of 1M HCl. The results are represented in the table.

APPLICATION OF THE OPTIMISED CONDITIONS TO THE EFFLUENT:

After optimizing the conditions (which are shown in the table.11) and examining the results they were applied to the effluent. But as the pH of the sample was 0.43 the pH was not raised to 4, as it would consume huge volumes of NaOH. The rest of the conditions were kept as per the results obtained during the systematic study of optimizing the conditions.

Procedure:

For batch process:

Al was estimated in the effluent using back titration method and it was around 28,890mg/l. The effluent was taken and under optimized conditions and stirred for the optimized time (1hr) and the removal was around 52%.

For column process:

First the Al was estimated in the effluent using back titration method and it was around 28,890 mg/l. Then this was sent through the column with bed height of 1:6(optimum bed height). The effluent, which came after passing through the column, was estimated for Al, the removal was found to be 53% coinciding with the batch study results.

The resin column, which was saturated, was regenerated (which is also a process of elution) using 1N of HCl. 1N of HCl was used as the concentration of the effluent was more. During regeneration simultaneous elution occurred and Al came out as AlCl₃. This elluent was estimated and about 90% of the Al absorbed came out.

After regeneration this was again used as a fresh column. The effluent, which was passed through the column for once, was again passed through the regenerated column. The effluent was free of Al and the whole of the Al was removed after passing through the column for second time. There was no effect on the removal efficiency of the resin even after regeneration.

DISCUSSION:

Tried three substances for separation of soluble aluminium on solid surface, cation exchanger, powdered activated carbon and amberlite IR - 120 ion exchange resin. The removal of aluminium is dependent on the pH of the solution. Under different pH conditions the removal of the metal and amount remaining are given in the table - 5 and showed as a graph in fig -1, 2 & 3.based on the figures as percentages the cation exchanger gave best removal at pH 4. Infact comparison of the three materials gave best at the same pH 4.

Due to the formation of cation species Al(H₂O)₆ ³⁺ in 2 – 6 pH range where quantitative exchange with protons of the, Cationic exchange resin occurs maximum recovery is obtained in the ion exchange process in this pH range.

Further experiments were carried out the same pH. Ion exchange increases with increase in time and attains stability with in 30min and hence different contact times were tried using all the three substances. The maximum removal was obtained for a contact time of 1hr for the cation exchanger, but as the contact time increased removal decreased, the reason may be due to desorption. The results for the other substances also reveal the same result. From the table 6 it is evident that the best contact time is 1hr and is graphically represented in fig 4, 5 & 6.

The rest of the experiment was conducted with pH 4 and with 1hr contact time. The optimum dosage was evaluated by conducting further experiments with different dosages starting from 0.5 - 2 g the results show that as the dosage was increased the removal was also increased which are shown in the table 7 and in the figs 7, 8& 9. The removal increased with increase for all the three substances, but the best results were for the cation exchange resin as shown in the results.

As the results of the batch studies were in accordance with the cation exchange resin as the removal substances pH 4, column studies were conducted with the same resin. Column studies were carried out at different bed heights and with different flow rates.

The ratio of the resin height to that of the diameter of the column was taken as the bed height. Different bed heights 1:1, 1:2, 1:4 &1:6 were taken with different flow rates 0.5ml/min, 1ml/min, 2ml/min. the breakthrough curves for these different bed heights and flow rates are given in the tables 8, 9 & 10 and in the figures 10, 11 &12.

The results show that the maximum removal was obtained at bed height 1:6 with flow rate of 0.5ml/min as increase in bed height and decrease in flow rate causes the solution to be in maximum contact with the resin or any removing substance and hence there is maximum removal.

The optimum conditions for column studies are 1:6(the ratio of the diameter of the column to that of the bed height of resin) of bed height, 0.5ml/min of flow rate.

The pH for both the processes was 4 but as the pH of the effluent was 0.43, raising the pH of this sample to 4 would consume large amounts of alkali so the original pH was used to carry on the experiments.

The concentration of the cations other than Al were more than Al i.e. approximately 96000mg/l and the concentration of Al was only 28,890 mg/l. The hardness mainly consisted of Mg²⁺ but this did not interfere the removal of Al as this is one of the properties of ion exchange that, in a effluent if there are many cations it would select that ion which has more charge and whose ionic size is more. And hence it selected the ion with higher charge and ionic size i.e. Al.

Al was eluted back using different elluents shown in the table 12, from the results it is clear that the best elluent is HCl. Al was removed without any interference and eluted back using 1N HCl. HCl of high normality was used as the concentration of the effluent was high. And after regeneration the resin was again used and there was no change in the efficiency. The removal of Al when these optimum conditions using both the processes was around 53%. In the column process the effluent with a concentration of 13,000 mg/l i.e. after sending for one time through the column was send through the regenerated column and the rest of the Al was removed.

The elluent which was obtained in the form of AlCl₃ can be reused after checking for purity or it can be precipitated as Al (OH)₃ using 1N NaOH as this does not carry any impurities, the precipitate can be centrifuged and dried. The precipitate Al (OH)₃ dries at room temperature.

REMOVAL OF ALUMINIUM USING DIFFERENT ADSORBANTS AT DIFFERENT pH (TABLE.3- FIG1,2&3)

INITIAL CONCENTRATION –9mg OF AlCl₃

		POWDERED ACTIVATED CARBON		AMBERLITE IR-120		CATION EXCHANGER
S.No	pH	% OF Al REMOVED	% OF Al REMAINED	% OF Al REMOVED	% OF Al REMAINED	% OF Al REMOVED	% OF Al REMAINED
1	4	82	18	89	11	99	1
2	6	70	30	87	13	98	2
3	7	79	21	75	25	95	5
4	8	76	24	80	20	92.5	7.5
5	10	77	23	70	30	90	10