Cost Savings And Quality Improvements Through Chemical Recovery Of Caustic Etch And Anodizing Baths

With the increased focus on environmental concerns in all facets of business, anodizers can look at a number of opportunities in their plants that will reduce process chemical costs, reduce waste treatment chemical and labor costs, and, in many cases, enhance product quality. Recycling is an environmentally pro-active step that demonstrates a responsible corporate image to customers, employees, and to the local authorities.

Aluminum is anodized using water-based chemicals that can be treated in a fairly straightforward manner. However, many plants now use recycling equipment to extend chemical life and reduce waste treatment costs. This is due, in part, to the large amount of solid waste that etching and anodizing generates. As most methods of recycling involve some degree of purification, anodizers often find that quality improvements go hand in hand with chemical savings.

It is well known that etching and anodizing generates large volumes of aluminum hydroxide sludge. Recycling reduces this waste, lowers chemical costs, and, frequently, improves product quality. For example, processing 1,000 ft² of anodized surface area, weighing about 400 lb, down a typical architectural anodizing line can result in 420 lb of aluminum hydroxide sludge eventually being produced in waste treatment. 1 lb of aluminum processed can result in 1 lb of aluminum sludge being produced. Implementing recovery techniques can potentially result in an 85% reduction of waste sludge being generated.

Three recovery techniques will be reviewed that are commonly used to regenerate the caustic soda etching bath, recover phosphoric acid bright dip solution from rinse water, and purify the sulfuric acid anodizing bath.

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