I think that the safest way to stop the cyanidation is to filter the slurry as quickly as possible.  Once you have the pregnant solution separated from the residue, rinse the residue to remove any residual pregnant solution prior to drying the solids. If you don't wash/rinse the solids, you will get a higher residue value from the residual pregnant solution retained in the moisture of the solids.

You could add hydrogen peroxide to the slurry which would destroy the free cyanide complex, but you might still get adsorption on the solids and you still need to filter the slurry as quickly as possible.

Filter the solution off immediately.  Then re-pulp the solids in water and filter again.  Repeat 2 more times.

Hello. The best way is to form a WAD cyanide in your solution. This can be done by adding copper sulphate solution that is a bit higher with concentration of your average cyanide concentration in that particular circuit (e.g Molarity). Cu2+ reacts quickly with cyanide ion to form Cu2+ + CN- = CuCN, CuCN + CN- = Cu(CN)2-, Cu(CN)2- + CN- = Cu(CN)3-. The last specie (Cu(CN)3-) is very stable and it will help stop the cyanidation process. So what you can simply do after taking the sample is to add immediately the copper sulphate solution and agitate on your slurry sample for 1 min or 2 min just to ensure that your reaction is enhanced. All the best with your new good results 🙂

The direct balanced equation will be Cu2+ + 3CN- = Cu(CN)3-
And remember your sulphate ion (SO4 2-) will just be a spectator ion.

Thank you very much for the advices!

I believe the best way is to figure out how to filter the slurry quickly and feasible to introduce in the procedure on operational routine. The WAD cyanide formation and also neutralization with H2O2 was really helpfull but as I'll use the solution instead the solids, and I'll use it to quantify gold, pH and free cyanide on the tanks, using chemicals will not be the solution.

But thanks you all!

Regards!

Samuel, how do you take the sample. If the sampling can be done to a standard small volume (say 500 ml) every time, you may wish to try a lab centrifuge to rapidly settle out the solids and decant the required volume of the clear solution for analysis. Centrifuging should be faster than filtration. If necessary,  a few drops of a suitable flocullant may be added before centrifuging to improve solution clarity.