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Cyanide destruction with calcium polysulfide (3 replies)

Jean Rasczak
8 months ago
Jean Rasczak 8 months ago

I can discuss their experiences in using calcium polysulfide instead of sodium metabisulfite. What would be the advantages of using calcium polysulfide?

Tests Plan and laboratory! I wish to change the sodium metabisulfite and use the calcium polysulfide, where I beneficiary.

Raje Singh
8 months ago
Raje Singh 8 months ago

Ca polysulfide works for treating heavy metals including Hg from soils & water it forms thiocyanates in the presence of free cyanide.

SMBS: Na2S2O5 + H2O = 2NaOH + 2SO2
SO2 + O2 + H2O + CN- = OCN- + SO42- + 2H+ (presence of Cu+2 provides catalytic activity)
Polysulfide: CaSx + xCN- = xSCN- + Ca+2

The toxic effects of thiocyanate are significantly greater than cyanate (you should access publications on the web or your local library for edification) if thiocyanate laden tailings decant is recycled to your grind/leach circuit.

Sandeep Bisht
8 months ago
Sandeep Bisht 8 months ago

Using CPS (calcium polysulfide) to oxidize cyanide is not a good idea. The use of CPS is to remove metal ions after freed from the cyanide complexes. You can use CPS after all cyanide is reacted with peroxide or other oxidizers.

The replacement of metabisulfite (Na2S2O5) can be H2O2, NaOCl, or ClO2, or UV/H2O2. You can use CPS after any one of these added, check for free and WAD cyanide make sure it is below 0.5 ppm. You can add CPS after confirming there is cyanide left. CPS is a metal precipitant and reducing agent, not very good with cyanide removal. If you have questions on cyanide detoxification and metal precipitation!

8 months ago
Gruppen 8 months ago

As discussed polysulphide is suitable for polishing metals after the cyanide has been destroyed. Commercially for high tonnage mine slurries the main options for cyanide destruction are the INCO process i.e. sodium metabisulphite, and Caro's Acid. Which is better really depends on your particular situation. Peroxide is very effective for solutions.

Can I ask why you want to move away from the metabisulphite process? This process is usually very cost effective but must be operated in a relatively narrow operating range. If you get the reagent and mixing regime out of balance it will have unreliable performance and high operating costs. Optimizing the operation can often give large improvements for a small effort.

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