Heavy metals, such as copper, zinc, mercury, cadmium, nickel, lead, chromium, cyanide 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 calcium polysulfide liquid consisting of multiple sulfur anions that strongly bond to heavy metals in water.  The metal sulfides formed have a very low solubility and persist as stable solids, which allows for a more environmentally sound disposal as the metals will not leach out.

Application Advantages:

• High reactivity with heavy metal ions and extremely low solubility of resulting metal sulfides over a wide pH range.
  
• Ability to remove metals from chelated metal compounds by ligand exchange process.
• Removes chromates and dichromates without preliminary reduction of the chromium to its trivalent state.
• Selective metal precipitation allowing for recovery of valuable metals.
• Converts cyanide wastes into less toxic thiocyanate ions. See study on cyanide treatment with polysulfides. 
• Dissolved calcium ions form a coagulant aid (Ca(OH)2).
• Better settling and dewatering aspects of the metal sulfides, resulting in a more compact solid sludge. See abstract on Source Reduction Technology Report in Circuit Board Manufacture.
• REMOTOX can be adapted to enhance any existing treatment system. 
  
  

Product Features:

• A strong yet relatively inexpensive metal precipitant.
• Its residues are inert and non-toxic.
• Unlike carbamate and carbonate salts, it does not contain or release carbon disulfide.
  
• Not regulated by the Department of Transportation (DOT).
• Compared to other sulfides, it provides more stability in acidic medium.
  
• REMOTOX has been tested to maintain its effectiveness for a minimum of one year.
• No need to dissolve prior to use as compared to solid material.
  
• It has a low crystallization temperature.

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. 

For additional information, heavy-metal removal studies, samples or assistance, please contact us.