Calcium Polysulfide (CP) is supplied in a 29% aqueos solution with a pH of approx 11.5, and is widely used for remediation of waste water and other excavation sites. Molecular wt is 199.8, and gravity is 1.27, with a deep orange-red color. Best results are obtained in a pH range of 7.0-10.0 for metals precipation, and all applications should be bench tested.
When mixed with water, CP dissociates into bisulfide, aqueous hydrogen sulfide and other sulfur anions, which react to the heavy metals to form less soluble, and non-toxic metal sulfides. Hexavalent chromium Crvi is reduced to trivalent chromium CrIII, which then precipitates as chromium hydroxide.
CP is routinely used to precipitate metals in contaminated aquifers and wastewater treatment systems. When injected into the ground it causes precipitation of cations as sulfides (FeS, ZnS, PbS, CdS, and CuS) and chromium, unlike the other metals listed, precipitates as hydroxide