Special Treatment for Complexed Metals

Sodium polysulfide and sodium hydrosulfide are other agents that are used. They do not produce excess sludge, but can generate highly toxic hydrogen sulfide gas. Good ventilation and pH control are needed in any system employing these chemicals. 

Insoluble starch xanthate (ISX) releases magnesium and takes up heavy metals. There are also a number of proprietary chemicals developed by various companies (e.g. Environmental Technology of Sanford, Florida) for removal of complexed copper, silver (from photographic process wastes), arsenic, nickel, lead, mercury, zinc, cadmium, barium, and other heavy metals. 

Gluconates and glucoheptonates are essential components of many alkaline rust removers and cleaners, paint strippers, and etchants. They frequently cause complexation of dissolved heavy metals such as copper, nickel, and zinc. Conventional sodium hydroxide treatment does not result in sufficient precipitation of these complexed metals to meet EPA standards. In tests performed by Srinivasan (1983), the use of lime or calcium hydroxide proved far better. In particular, lime treatment resulted in more metal removal, better flocculation and faster sludge settling, and could also be used in conjunction with sodium hydroxide treatment. 

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