Abstract: A hydrometallurgical process is described for recovery of precious metals from ores refractory to treatment by lixiviating agents by crushing the ore to no finer than a nominal 1/4 inch size, treating the ore with about 100% to about 300% of the stoichiometric amount of nitric acid required to react with the ore, maintaining the reaction mixture until the reaction is substantially complete, placing the treated ore in a permeable ore bed, washing the permeable ore bed to remove nitric acid, placing the washed ore in a heap permeable ore bed and passing a lixiviate solution for precious metals through the bed and recovering the dissolved precious metal from the lixiviate solution. All NOx gases generated during the reaction of nitric acid with the ore are recovered for conversion into nitric acid which is recycled for treating ore.

Abstract: A hydrometallurgical process is described for recovery of a precious metals from ores refractory to treatment by lixiviating agents by crushing the ore to no finer than a nominal 1/4 inch size, acidifying the ore with a mineral acid, treating the ore to a preliminary oxidation with nitric acid, optionally adding a binder to the oxidized ore, heap treating the ore with nitric acid to complete oxidation of the ore, water washing the heaped ore, optionally increasing the alkalinity of the heaped ore, heap treating the ore with a lixiviating solution and recovering precious metals from the lixiviating solution. The process recovers NO.sub.x gases generated during the preliminary oxidation and binder addition stage for conversion into nitric acid which is recycled for treating ore. Chemical treatments in the process can be carried out at ambient temperatures and atmospheric pressures.