Wastewater Control and Treatment

Increasing regulations governing discharge water have led to improved techniques for reducing the quantities of wastes that must be treated. These techniques have not only reduced the quantity of wastewater to be treated, but have also reduced the quantity of chemicals used and have lowered water consumption. These methods can be applied to any plating operation. Many references are available, including Ref 11, that cover waste treatment technologies.

The use of counterflow rinses has reduced water consumption and wastewaters while maintaining adequate rinsing between plating operations. Reduced dragout of plating electrolytes can be accomplished by allowing processed parts leaving the plating solution to drain into the plating solution. Drip pans also reduce the amount of electrolyte dragout.

Closed-loop systems have dramatically reduced wastewater, lowered water consumption, and diminished chemical usage. Closed-loop systems allow recovery of rinse waters and chemicals by evaporative, reverse osmosis, or ion exchange recovery methods. Care must be exercised when using closed-loop systems, especially with copper plating, to keep impurities and contaminants from preplate operations out of the copper plating bath where they will be trapped by the closed-loop operation.

In any plating operation, wastewaters must be treated to reduce the hazardous materials to meet regulations. The general procedures for treating copper plating electrolytes and rinse waters resulting from copper plating systems are:

• Cyanide-bearing solutions require oxidation of the cyanide with an oxidizing agent such as chlorine or hypochlorite, followed by precipitation of the heavy metals.

• Noncyanide alkaline solutions are pH-adjusted and have calcium chloride added to precipitate the copper.

• Pyrophosphate wastes require low pH hydrolysis to orthophosphate, followed by precipitation of the heavy metals.

• Acid sulfate and fluoborate wastes are pH-adjusted to precipitate the copper.

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