REMOTOX® is one of the most effective and routinely used reagent for in-situ geochemical fixation of Hexavalent Chromium (VI).
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 Technologies, the Hazardous Waste Clean-Up Information website, sponsored by the US EPA.
Bench scale evaluation, case studies and dosage guidelines on Calcium Polysulfide for the remediation of hexavalent chromium can also be found in the Chromium (VI) Handbook, available for purchase at Amazon.com or at Routledge.com.
REMOTOX®, a 29% Calcium Polysulfide Solution, precipitates highly soluble metals as less soluble, less toxic metal sulfides. In the case of chromium, the metal precipitates as chromium hydroxide.
Calcium Polysulfide is fairly safe to handle out in the field. It is a non-toxic remedial amendment that oxidizes under aerobic conditions to form calcium, elemental sulfur and sulfate. When introduced into the environment, Calcium Polysulfide breaks down 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, whereas metal sulfides remain insoluble within a wide pH range. See Solubility of Metal Hydroxides and Sulfides as a Function of pH. While effective treatment by Calcium Polysulfide can be achieved over a wide pH range, best results are typically obtained within pH 7-10. Adjustments to the pH of the treatment system can enhance the metal precipitation process. See pH Guidelines for Treatment of Soluble Metal Streams.