Heap Neutralization Rinse Down Tests
Once leaching is terminated in either a laboratory column leach test or in a commercial heap leach environment, it is time to neutralize the cyanide. This can be done either on a small laboratory scale column or on samples obtained from a commercially operating leach dump.
On a laboratory leach test this testing can be done on column leach residues during the project development phase. Rinse-down tests are completed to neutralize the CN as part of the testing to determine the general leach parameters.
Determining the neutralization parameters of a commercial heap leach is significantly more difficult, but just as effective. Representative samples of each 20ft leach interval is obtained by trenching and auger drilling the entire height of the leach dump. The testing is then performed on each interval, rinsing with site or barren solution to determine WAD cyanide neutralization, rate of decrease in rinse effluent pH, stabilization of any dissolved minerals and the dissolved gold recovery during recirculation rinsing.
Once complete, the drain down procedure is conducted sequentially through the columns and the solutions are analyzed for all US EPA primary and secondary drinking water constituents.