Potassium permanganate will immediately kill any cyanide.

It is therefore used (in some plants) as an addative to the sample bucket so that the gold ratio between solid and solution remains as it was at the time of sampling.

Without the permanganate the cyanide solution continues to dissolve gold from the solid fraction. The total gold assay is unchanged but the ratio of gold in solution does change.

It is better if the sample is immediately filtered and prepared as soon as taken, but in a plant with only a few sample people some plants combine all the samples at one location in the same bucket so the first "sample" may sit in the bucket for 10 hrs before being prepared.

Hope I've explained it.. if not ask again

Nice and clear! After 20 years in chemistry I finally found out about the application of this redox reaction.

Perfectly explained, potassium permanganate  is suitable for destroying cyanide and complexes in samples, Maya I hope you weren't considering it for cyanide destruction for the whole plant.

I perfeclty understood, thanks. I wanted to kwow why the most of process plants doesn't use this reagent and prefer to use hydroxide peroxide or chlorine to destroy cyanide.

Peroxide is cost effective for small samples but if you want to destroy the cyanide in 100% of tailings effluent one needs cheaper systems. Of these some combination of CO2-Air is the cheapest.

Potassium permanganate will destroy cyanide, however to get the cyanide levels to dischargeable effluent levels a lot more of it is required. This will however increase your cost and subsequent introduction of potassium and manganese levels which might also be a problem. You can consider aeration prior to the use of the potassium permanganate to reduce cost.

You can destroy cyanide with potassium permanganate from both clean water and slurry pulp. You need large qualities to get total destruction. What are you thinking off?

Permanganate Oxidation with NaCN: Potassium permanganate can also be used to oxidize cyanide, although it is not widely practiced. The method is advantageous because hydroxide ion is a product of the reaction, keeping the medium alkaline throughout the reaction

and the permanganate oxidizes the cyanide only to cyanate.

Hello,

Permanganate is not very good at this.  You need to use a stronger oxidant if you want low WAD or Total -CN.

For all of the oxidants tested, sufficient removal of heavy metals was achieved. Depending on the lime dose used, fluoride removal was sufficient as measured by ISE, and with effective oxidation of hypophosphite, appropriate removal was also observed with IC analysis (elimination of analytical interference). All of the treated samples that were analyzed for P4 indicated less than the method detection limit of 0.020 ug/L. With the exception of permanganate, all of the oxidants shown in Table 3 produced treated samples with total and WAD cyanide concentrations less than the treatment objectives in Table 1.

An article called Developments of an alternative technology to remove cyanide from mining wastewater may tell you more.  A method was tested using Potassium Permanganate as oxidant, for the treatment of cyanide-contaminated mine process water. The technology was tested for its ability to detoxify cyanide and immobilize metals in wastewater from cyanide leaching. A pilot-scale demonstration is described in which a testing was carried out to demonstrate the possibilities of the technology on Río Narcea mine wastewater in Belmonte (Asturias).

Based on the redox reaction: 3CN- + 2MnO4- + H2O = 2MnO2 + 3CNO- + 2OH- or

* + 2KMnO4 + H2O = 2MnO2 + 3CNO- + 2KOH

a 4:1 mass ratio of KMnO4 to free CN is generally sufficient to oxidize free CN to the single digits; I don't believe an excess of KMnO4 will affect your clarified solutions except for a change in color to violet-pink...although Mn wavelengths & slit widths are not within close proximity to Au/Ag, you may want to check w/your lab if hi-Mn in solution interferes w/precious metal AAS readings.