Recycling

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Liquids

(Current Recycling Technology and Processes)

Acid Recycling Process  (Page 1)

The acid recycling process is mostly used in the metal finishing industry were many industrial acids and acids mixtures are used.  The current technology for this process is called diffusion dialysis, a membrane separation process that recovers certain acids.  Some of the recoverable liquids include nitric, hydrochloric, hydroflouric, fluoboric, or sulfuric acids from depleted process baths.  With this technology, the manufacturer can reduce the amount of harmful chemicals they are dumping into our environment and at the same time save money on these costly chemicals since they can now be reused.  The process of acid recycling can be summarized into three generalized steps.  For a complete list of today's recyclable acids, please visit our section Current Recyclable Materials - Liquids. Step 1: First, water and acid are delivered into the acid recycling system.  The streams of these two liquids will then flow into the membrane stack thanks to the force of gravity.  Step 2: Once inside the membrane, many things are removed before the acid can go into the diffusion dialysis.  Spent nitric acid solutions is one of the first material to be removed and disposed off as a hazardous waste.  Spent hydrochloric acid solutions is used for waste treatment.  According to Donald Offinger, "an anion exchange membrane acts as a diaphragm.  Acid molecules diffuse into water containing lower concentrations of that acid.  By causing the acid to flow across the membranein the opposite direction of the water flow, a high percentage of the acid diffuses into the water.  This results in a metaldepleted acid solution and an aciddepleted, metal-bearing solution." Step 3: The recovered acid is sent to the operating bath and it will eventually be dumped again into the membrane stack for reprocessing.  The metal-rich, aciddepleted acid is then sent for treatment or to a recovery reduction system.

Figure: Diffusion dialysis diagram. [Courtesy of: WMRC Technology Update.]

Figure: Acid recycling process. [Courtesy of: Donald Offinger.]

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