Every pickling line, anodizing plant, plating shop and etching bay buys acid, works it until the bath goes off, and then pays somebody to destroy it. The acid arrives as a raw material and leaves as a hazardous waste — and in between, most of it was never actually consumed. That last point is the entire basis of acid recycling. Why Spent Acid Is Not Really Spent A pickling or etching bath does not fail because the acid runs out. It fails because dissolved metal builds up. Spe