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Equipment: Selective Ion-Exchange

Ion- exchange using specially selected resins can be used to remove or reduce specific heavy metals contaminants from water to lower concentrations. It is unaffected by other dissolved solids in the feed stream and is used for:
  • Purification of a process stream, by removal of trace contaminants.
  • Removal of a specific, regulated, wastewater contaminant.
  • Selective recovery of a valuble material for reuse.

Selective ion exchange resins are available for a wide range of applications for metals such as chromium, copper, zinc, nickel and cadmium.


Copper Removal from Electroplating Solution Effluent

Electroplating and metal working processes cause pollution with heavy metals through discharge in rinse waters and through disposal of spent plating solution tanks. Most plating process water is used to cleanse the surface of the parts after each process bath. In order to maintain quality standards, the level of dissolved solids in the rinse water must be regulated and fresh water is added to the rinse tank to accomplish this. The overflow water is treated to remove pollutants and then discharged.

This is an area where ion-exchange resins can be employed. The use of special chelating resins will selectively remove the heavy metal such as copper and effectively concentrates the effluent. When the ion exchange resin is regenerated the regeneration effluent can typically contain 2-4% of copper which can then be precipitated in a conventional effluent treatment plant .


Purification of Trivalent Chromium Electroplating Solutions by Removal of Copper, Nickel and Zinc Contaminants

Trivalent chromium plating has become more and more important in recent years. Many electroplaters have come to realize that the operational advantages of trivalent chromium plating combined with substantially lower wastewater treatment costs make trivalent chromium an economic winner when compared to traditional hexavalent chromium plating baths.

In the past, however, one major limitation to the success of trivalent chromium plating has been the bath's sensitivity to relatively low levels of ionic, metal contaminants. The contaminants that have caused the most concern are copper, zinc and nickel. Copper and zinc have been reported to cause discoloration and poor coverage when present at levels of 20 ppm or more, while nickel causes problems at concentrations above 50 ppm. When contaminant metal concentrations reach unacceptable levels, the plating bath must be treated to restore proper bath performance.

 

The ion exchange resin has chelating functional groups that have a high selectivity for metal ions such as copper, nickel and zinc.The resin will absorb these ions until the resin has exceeded its' capacity at which time the resin will require regeneration. The frequency between regenerations will depend upon the rate of contaminants entering the bath and therefore the level of contaminations should be analysed regularly to establish this frequency. A properly sized treatment unit requires regeneration about every week to two weeks

The regeneration sequence is fully automatic and typically takes about two hours and can be scheduled during a time that is most convenient for the operator. Regeneration can also be performed while the bath is in operation.

Efficient and cost-effective treatment of trivalent chromium plating baths for the removal of contaminant metal ions is readily accomplished using ion exchange technology. The benefits gained include the following:

  • Copper, zinc and nickel ions are all removed from the bath simultaneously.
  • Treatment can be done during bath operation (no shutdown time required).
  • Treatment can be done continuously or intermittently depending on need.
  • The treatment units are small and usually can be located right at the plating tank.
  • Treatment is simple, consisting of pumping solution from the tank, through the treatment unit and back to the tank.



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