In a recent blog, we discussed the importance of maintaining pure water during the plating process. Of equal, if not critical importance, is the cleanliness and reduction of the waste that is generated. The reality is that electroplating involves chemicals and other bi-products. Many are potentially hazardous to humans and the environment. In order to minimize impact, several things must happen. Heavy metals must be removed, cyanide destroyed, and chromic acid reduced. These tasks are achieved by using several multi-step processes as follows:
Removing Heavy Metals
Metal bearing rinse water streams have their metals removed by hydroxide precipitation. Rinse water streams from throughout the facility and collects in a main neutralization tank. The pH is adjusted to 9.0 and a coagulant is added to aid in the precipitation of metals. An insoluble metal hydroxide solid is formed. The metal hydroxide solid is separated from the water stream by adding a polymer and passing the solution through a lamella clarifier. The clarifier separates the metal hydroxide solid from the water. The metal hydroxide solid settles to the bottom of the clarifier, where it is removed. The solid is then dewatered and sent out for 100% recycling of the metals. The remaining water, now with low metal concentration, is then filtered through a sand to remove any residual solids.
Destroying Cyanide
Cyanide rinse waters must be pretreated before entering the main neutralization tank. All cyanide is destroyed using a two-stage process. First, the pH is adjusted to 10.9-11.5, then bleach is added. That’s it. As a result, and the carbon-nitrogen cyanide bond breaks, converting it to carbon dioxide and nitrogen gas.
Reducing Chromic Acid
Similarly, chromic acid rinse waters are pretreated by lowering the pH to 2.0 and adding sodium metabisulfite. This reduces the hexavalent chromium present in the chromium rinse stream to trivalent chromium. The trivalent chromium is now ready for further treatment. Next stop? The main neutralization tank.
Wastewater treatment systems are essential components to the electroplating process. They come with an organization’s important responsibility to help protect, conserve, and sustain the environment; while serving its customers with high quality plated components.
At AEP, we take great pride in maintaining the highest quality when it comes to environmental controls, safety and responsibility. AEP is in full compliance with all applicable city, state, and federal environmental regulations. Our community and our customers can be assured of our full commitment to environmental protection and care.