Chromium, zinc, copper, lead, cadmium, mercury and arsenic are among the most common metal contaminants found at remediation sites. Remotox, a Calcium Polysulfide Solution, precipitates these highly soluble metals as less soluble, less toxic metal sulfides. In the case of chromium, the metal precipitates as chromium hydroxide. See Elements and their Potential In-Situ Precipitates.
Calcium Polysulfide is fairly safe to handle out in the field. It is a non-toxic reagent that oxidizes under aerobic conditions to form calcium, elemental sulfur and sulfate.
Over the past 30 years, numerous Calcium Polysulfide applications have been successfully conducted at various remediation sites around the world. Calcium Polysulfide is also widely used in agricultural applications on fruit trees and berries, and as a soil amendment for treating saline and saline-sodic soils.
When introduced into the environment, Calcium Polysulfide dissociates to form bisulfide, aqueous hydrogen sulfide and other sulfur compounds. Heavy metal ions are precipitated as less soluble, less toxic metal sulfides by these breakdown products. Metal hydroxides change solubility with changes in pH. Metal sulfides remain insoluble within a wide pH range. See Solubility of Metal Hydroxides and Sulfides as a Function of pH. While effective treatment can be achieved over a wide pH range, best results are typically obtained within pH 7-10. Adjustments to pH of the treatment system can enhance the metal precipitation process. See Treatment of Soluble Metal Streams.
The US EPA has identified calcium polysulfide as a reagent suitable for use in in-situ chemical reduction (ISCR), stabilization and solidification of multiple contaminants. Several abstracts and studies are available through CLU-IN, the Hazardous Waste Clean-Up Information website, sponsored by the US EPA. Also see Summary of Studies on Cr(VI) Reduction by Calcium Polysulfide.
Bench scale evaluation and case studies on Calcium Polysulfide for the remediation of hexavalent chromium can also be found in the Chromium (VI) Handbook. Purchasing information available at CRC Press Online or at Amazon.com.