Waste and treatment recycling in electroplating industries

Abstract

Electroplating is the process by which metallic coatings are produced on metals, alloys and plastics. These electrochemically produced coatings applied in various thickness not only enhance the decorative appearance of consumer goods but also frequently increase the resistance to corrosion and wear as well as the hardness of components and equipment subjected to particularly arduous duties. Of the multitude of metals and alloys that can be electroplated, the most commonly used in Malta re copper, nickel, chromium, zinc, cadmium, tin, silver and gold. In a plating shop, several of these metals are usually being plated each requiring its own plating solution and tanks. Sometimes there may be a series of coatings to be deposited over one another; for example for chromium plating zinc die-castings, they are first plated with copper, then with nickel and finally with chromium. Besides electroplating, other related processes such as alkaline cleaning, phosphating, vapour degreasing, anodising, pickling and stripping are usually also carried out in a plating department. After each of these treatments the parts have to be rinsed clean of drag out from treatment solutions (and thorough rinsing is also required after each cleaning step), before the next operation to avoid contamination of process solutions. The large quantities of contaminated swill waters from these rinses constitute the bulk of the effluent from an electroplating shop. Although the process solutions themselves need never be dumped if correct periodic maintenance is carried out, other solutions like cleaners, pickles and stripping solutions have to be parodically discarded. These was wastes, often low in relative volume, but high in toxic chemical contaminants, are generally of a highly acidic or alkaline character and frequently contain a high proportion of toxic metals, both in solution and in suspension, as well as highly dangerous toxic substances such as cyanides or chromates. Thus wastes from electroplating processes generally fall into two categories; a continuous discharge of dilute rinsing waters, and batch discharges of smaller quantities of highly concentrated spent liquors. There are two main aspects to the problem of treating wastes. There is the recovery of potential values from waste solutions, but there is also the need to ensure that the effluents do not contain deleterious contents which will impair the biological operations of sewage treatment plants, damage the sewer fabric or interfere with fish life in the sea into which the effluent may eventually be discharged. In the first part of this project, a description of planting ship process has been given and a review of the literature dealing with electroplating waste treatment and recycling has been carried out and the most commonly used systems describe. In the latter part, an investigation of local electroplating, shops and a study of the processes and waste treatments employed has been attempted. However due to the non-compliance of most of the firms the study was restricted to two firms employing electroplating as one of their production processes. At the end, some areas offering further scope of investigation have been pointed out.