Wastewater Treatment

Many industries, including metal finishing, printed circuit board manufacturing, pulp and paper, food processing, and mining produce wastewater streams containing significant amounts of metals. 

REMOTOX® is commonly used for efficient and practical removal of heavy metal ions and other organic compounds from various wastewater sources.

Application Advantages

• High reactivity with heavy metal ions and extremely low solubility of resulting metal sulfides over a wide pH range. See Solubility of Metal Hydroxides and Sulfides as a Function of pH. 
• Can break and precipitate chelated and/or complexed heavy metals, typically without pretreatment.
• Removes chromates and dichromates without preliminary reduction of the chromium to its trivalent state. See Overall Effectiveness of Water Treatment Process for Hexavalent Chromium (CrVI) and Trivalent Chromium (CrIII).
• Converts waste cyanides into less toxic thiocyanates and precipitates metals to levels generally
  within sewer use ordinances. See study on Cyanide Treatment with Polysulfides.
• Selective metal precipitation allowing for recovery of valuable metals.
• 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 excerpt from Source Reduction Technology Report in Circuit Board Manufacture. 
  
• REMOTOX® can be adapted to enhance any existing treatment system.

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. See Calcium Polysulfide Chemical Reactions. 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. 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 bisulfite, metabisulfite, sulfur dioxide or sulfuric acid.

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 at 623-328-5175 or by email at  info@grauschemicals.com.