Electroplating wastewater comes from surface plating operations where the metal is dipped in an electroplating solution of various types of metals and then rinsed.
Typical plating includes brass, nickel, cadmium, zinc, silver, copper, and gold. Electroplating wastewater is typically from washing, rinsing and batch dumps and is at a low pH of ~3-5 and contains soluble forms of the various metals. In order to remove soluble metals from the wastewater it must first be made insoluble. The insoluble metal is then coagulated, flocculated and clarified by sedimentation.
The typical method to reduce and remove soluble electroplating metals from wastewater is as follows:
Stage 1– Precipitation and Coagulation:
pH is raised from ~3 to 8.5 with the pH controller using caustic while adding a coagulant such as ferric chloride. Testing of the wastewater may confirm that a coagulant is not needed. A “pin floc” is developed indicating the metal is insoluble. Some applications have plating enhancing chemicals present, emulsifiers and such that may require more sophisticated high performance coagulants to break the bonds and allow the metal to precipitate.
Stage 2 - Flash Mix:
The wastewater with it’s precipitated pin floc is introduced to the flash mix zone where a polymer flocculent is added. This stage maximizes flocculent dispersion throughout the coagulated wastewater.
Stage 3 - Flocculation:
The wastewater is now introduced to the slow mix zone to agglomerate the pin floc into larger rapid settling particles.
Clarifier, Inclined Plate:
The flocculated wastewater is introduced into the clarifier where the settling particles land on the inclined plates and are directed downward and into the sludge chamber. The clarified treated water then exits the top of the clarifier and flows downstream to sewer or further treatment if necessary.
Clarifier Sludge Handling:
The resulting clarifier waste sludge is periodically removed from the clarifier at a slow rate and sent to the sludge holding tank where it further thickens and accumulates a batch for disposal or processing in a filter press.
The thickened clarifier sludge is allowed to accumulate sufficiently to provide a full batch for the Filter Press. The filter press is pumped full of the sludge until it is full. The filter press is then emptied of the “cake” which is a semi solid of approximately 20-35 % solids. Sludge cake is high in phosphate and should be disposed of according to environmental regulations.
Electroplating shops are found in typically two categories, captive and independent shops. Some industries operate their own captive, in house electroplating operation while others outsource to an independent operation.
Typical industries include:
Electroplating shops, captive or independent
Automotive suppliers, trucks, motorcycles etc – Metal to rubber suspension and body parts
Machine tool mfg.
Metal forming such as stamped metal parts that require plating of various types.
Building materials, cadmium plated nuts, bolts etc. .
Wire forming - nails, screws etc
Electronics – gold and silver plating of electrical connectors etc.