Electrowinning

Electrowinning differs from most other water treatment schemes in that elemental metal is recovered during the process. Essentially electrowinning could be considered "mining" of a waste stream to produce raw metals. Its primary application is in recovering metals from concentrated sources such as ion exchange regenerant acid solution, highly concentrated rinsewaters or spent plating solution prior to disposal. It can also be used to recover metals directly from plating rinses having relatively low metal concentration.

Process Overview

process flow In its simplest form electrowinning is conducted in a chamber containing a metal bearing electrolyte solution. This chamber is outfitted with anodes and cathodes. When direct current is applied to the apparatus by means of a rectifier the metals are reduced onto the cathodes where they can then be recovered. In general the factors that govern the degree of metal recovery are the concentration of metal in the electrolyte, the size of the cathode area, the amount of current applied and the species of metal being recovered.

Practical Applications

With the widespread use of Ion Exchange for capturing metals from aqueous solutions, acid regenerants from cation resins are ideal for an electrowinning application. These regenerants are very high in metal concentration and acid making them an ideal electrolyte. This type of application can lessen the overall burden on an end of pipe waste treatment system and has the added financial benefit of returning metal that can be salvaged. Another excellent candidate for electrowinning is spent plating baths and spent micro-etch. These can be processed very rapidly and yield large quantities of metals that would otherwise need to be disposed of.

With the advent of high surface area cathodes for electrowinning another area to be considered for processing is drag-out rinses. A small electrowinning apparatus connected in a loop directly to a drag-out tank can dramatically lengthen the life of the rinse and recover significant metals. This is especially effective for copper sulfate plating systems as any build up of sulfuric acid in the electrowinning apparatus enhances its efficiency.

There are many situations in todays metal finishing industry where electrowinning is practical both financially and environmentally. Contact KB Technologies Inc. for further information on using electrowinning as a part of an overall treatment scheme or as a point source recovery unit.