5.7.5 Water quality
control
As discussed earlier water in mining complexes is polluted
due to various activities and to meet the water requirement for various purposes
it is necessary to supply the desired quality of water. Hence, water quality
control in the mining complexes is important.
In the mining complexes water is available from various sources including the
water being pumped out of the mines. In order to plan and undertake the water
quality control measures it is necessary to know the quality of water that is
being pumped out of the mines and the charcterisistics of the effluents.
Depending upon the characteristics of the pumped water, waste waters and the
effluents and the quality requirement, the water pollution control and management
strategies are planned. The various methodologies that can be used in water
and effluent treatment are as listed hereunder (Ghosh, et al.,2002).
1. Control of suspended solids
· Mechanical separation
· Centrifuges
· Cyclones
· Screening
· Filtering
· Thickening
· Inclined plate settlers
· Flocculation
· Floatation
· Floto-flocculation
· Settling ponds
2. Control of dissolved solids
· Neutralisation
· Adsorption
· Ion-exchange
· Reverse-osmosis
· Freezing
3. Control of bacteria, etc.
· Disinfection
The various issues that are to be addressed in water management in mining complexes
are as discussed hereunder.
Augmentation of pumped out mine water
The mining industry has to discharge millions of litres of water every day to
the adjacent water courses and thereby may cause water pollution problems in
and around the mining areas. This water otherwise a valuable water resource
because of nearly-acceptable quality, becomes contaminated with various domestic
and industrial trade effluents and subsequently is just wasted while putting
on an energy cost burden on the underground mines. Further costs are incurred
on abstraction of water from adjoining surface waterbodies containing this water
and also additional costs are required for treatment to meet the water quality
objective criteria. It is emphasised here to augment and protect this precious
ground water availability of nearly acceptable quality to meet various water
demands (as detailed in Fig.5.6) particularly of drinking water of already affected
mining population.
Coagulants such as lime and alum, sodium aluminate or polyelectrolytes are introduced
into the inlet of a small mixing tank prior to entering the pyramidal floculating
settling tanks. Sludge produced in the settlement tank is drawn off frequently.
After settlement the effluent is passed through enclosed pressure filters. Following
pressure filtration, chlorine is added to the water in a small tank and finally
potable water results for distribution to consumers.
Effluent from Workshops and Vehicle Wash Plants
Depending on the number of HEMM and other vehicles in a mine, a number of vehicles
are washed per day and generally a larger number of vehicles are washed on the
designated day of maintenance. The waste water contains oil and grease as well
as mud carried by the vehicles' tyres and under body. In the effluent from the
workshop one may have other chemicals which are used for metal processing and
grease and oil. Generally the quantity of waste water involved is small and
with suitable control measures such as oil and grease traps, the problem can
be solved.