ABSTRACT
Chemical precipitation uses the addition of chemicals to convert a soluble component in a liquid feed into an insoluble solid material. The precipitate can then be removed from the solution by filtration, flotation, or settling. The process is widely used for the removal of dissolved toxic metals as insoluble metal salts. It is effective for both waste automotive lubricating oils and for aqueous wastes from the metalworking, metal finishing, and electronics industries. Chemical precipitation is also used as a pretreating technique for aqueous wastes destined for biological treatment. Such treatment can be done in either an on-site plant or a publicly owned treatment works (POTW). It can remove heavy metals and toxic materials which are above the limits allowed for feed to the biological treating plant. The commonest forms of anions used to form the insoluble metal salts are hydroxides from the addition of lime or caustic and sulfides from the addition of ferrous sulfide.
