CALMET® | Calcium Polysulfide Solution

Calmet is a non-hazardous liquid used in various waste treatment applications as a metal precipitant.

Calmet (Calcium Polysulfide Solution) is a lime-sulfur based liquid solution designed to be used in various treatment systems as a metal precipitating agent. When used as part of a waste treatment program, Calmet effectively stabilizes and reduces soluble metals.

Soluble toxic metals, such as chromium, lead, arsenic, cadmium and copper, as well as other heavy metals could present a health risk. Geochemical fixation using a chemical reductant such as Calmet converts the soluble toxic metals into an insoluble nontoxic compound. The extent of metals precipitation is a function of the pH environment. Metal hydroxides change solubility with changes in pH. Metal sulfides remain insoluble within a pH range of about 5 to 9. Calmet with a pH range of 10.7 to 11.7 typically forms sulfides with most metals and hydroxides in the case of chromium. 

Calmet is a 27%-29% aqueous solution of calcium polysulfide. It forms a filterable sludge and operates well in areas where the pH of the system is higher than 7.0. The excess
calcium precipitates as calcium carbonate or gypsum (calcium sulfate). Liquid Calmet is easy to apply and handle in comparison to solid materials that must be dissolved prior to application.

Plant Water Management

Why Calmet?

  • Converts hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] to precipitate Cr(III) as chromium hydroxide in a one step reaction
  • Provides soluble sulfide precipitation of heavy metals for easy, low cost treatment
  • Precipitates metals from chelation, avoiding a separate process
  • Reduces mercury in waste streams to low parts per billion
  • Produces its own flocculant, reducing treatment costs
  • Is versatile and can be adapted to enhance existing treatment systems
  • Meets ANSI NSF 60 Standard for drinking water

Calmet is easy to apply and handle in comparison to solid materials. Calmet does not need to be dissolved prior to use. When used as part of a wastewater treatment program, Calmet effectively stabilizes and reduces soluble metals. Calmet typically forms filterable sulfide sludges on treatment; an exception is treatment of chromium, which forms hydroxides. Any excess calcium usually precipitates as calcium carbonate or gypsum (calcium sulfate); the extent of effectiveness in treatment is generally a function of the pH of the system.

Calmet® | Calcium Polysulfide Solution

Calmet is NSF certified.


Technical Bulletin

Safety Data Sheet