Heavy metals, such as copper, zinc, mercury, cadmium, nickel, lead, chromium and arsenic, can be found in many wastewater sources including, printed circuit board manufacturing, electroplating & surface finishing, copper polishing, paint manufacturing, wood preservatives and stormwater runoff.
Remotox is a water-soluble calcium polysulfide liquid that consists of multiple sulfur compounds, which strongly bond to these highly soluble metals. The metal sulfides formed have a very low solubility and persist as stable solids, which allows for a more environmentally sound disposal.
When mixed with water, Remotox decomposes to form bisulfide, aqueous hydrogen sulfide and other sulfur compounds. Most heavy metal ions are precipitated as metal sulfides by these breakdown products. Metal sulfides are much less soluble than metal hydroxides. 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.
In the case of chromium, Remotox reduces hexavalent chromium to trivalent state which then precipitates as chromium hydroxide in a one-step reaction; therefore, no need for sodium bisulfite, metabisulfite, sulfur dioxide or sulfuric acid. See Overall Effectiveness of Water Treatment Process for Cr(III) and Cr(VI).
While effective treatment can be achieved over a wide pH range, best results are typically obtained within water system pH 7-10. See pH Guidelines for Treatment of Soluble Metal Streams. Ensuring adequate contact time and thorough mixing is critical to successful treatment. Dewatering the resulting precipitate can be expedited by employing an anionic flocculant.