Recovery of precious metal values from refractory ores

A hydrometallurgical process for recovery of precious metals form an ore which is refractory to treatment by lixiviating agents comprising:

• a. crushing the ore to a nominal size of from about 1/4 inch to about 1 inch,
• b. treating the crushed ore with sulfuric acid to a pH of about 2 or below,
• c. treating the acidified ore with from about 5% to about 200% of the stoichiometric amount of nitric acid required to react with the ore wherein the nitric acid has a concentration of from about 20 weight percent to about 70 weight percent HNO.sub.3, and recovering andy NO.sub.x gas evolved from the ore,
• d. placing the thus-treated ore in a heap permeable ore bed on top of an impermeable collector,
• e. heap treating the permeable ore bed by dispersing continuously or intermittently and aqueous nitric acid solution through the bed having a concentration of about 6 weight percent to about 20 weight HNO.sub.3,
• f. separating residual acid liquor from the heap permeable ore bed,
• g. water washing the heap permeable ore bed to remove nitric acid solution therefrom, and separating the washings from the ore bed,
• h. separating nitric acid values from said residual acid liquor of step f. and recycling the nitric acid for use in treating said ore,
• i. introducing any NO.sub.x gases recovered from steps . into a nitric acid generator for conversion of the NO.sub.x into nitric acid and recycling said nitric acid of use in treating said ore,
• j. treating the heap permeable ore bed with sufficient calcium, sodium or magnesium ions under alkaline conditions to increase the pH of the liquor removed from the bed to about 10 or above,
• k. treating the heap permeable ore bed by dispersing continually or intermittently a sodium cyanide lixiviating solution for precious metals through the bed,
• l. separating the lixiviating solution containing dissolved precious metals from the heap permeable ore bed and recovering said precious metals from the lixiviating solution.

A hydrometallurgical process for recovery of precious metals from an ore which is refractory to treatment by lixiviating agents comprising:

• a. crushing the ore to no finer than about a nominal 1/4 inch size,
• b. treating the crushed ore with a mineral acid in amounts to bring the resulting mixture to a pH of about 2 or below,
• c. treating the acidified ore with from about 5% to about 200% of the stoichiometric amount of nitric acid required to react with the ore, and recovering any NO.sub.x gas evolved from the ore,
• d. adding an acid resistant binder to the nitric acid-treated ore to form ore agglomerates capable of maintaining a porous bed of ore, maintaining the binder and ore in contact with one another for a sufficient curing time to permit the ore agglomerates to maintain their particulate form, and recovering any NO.sub.x evolved from the ore,
• e. placing the thus-treated ore in a heap permeable ore bed on top of an impermeable collector,
• f. heap treating the permeable ore bed by dispersing continuously or intermittently and aqueous nitric acid solution through the bed,
• g. separating residual acid liquor from the heap permeable ore bed,
• h. water washing the heap permeable ore bed to remove nitric acid solution therefrom, and separating the washings from the ore bed,
• i. introducing any NO.sub.x gases recovered from any of steps c. and d. into a nitric acid generator for conversion of the NO.sub.x into nitric acid recycling said nitric acid for use in treating said ore,
• j. treating the heap permeable ore bed with sufficient calcium, sodium or magnesium ions under alkaline conditions to increase the pH of the liquor removed from the bed to about 10 or above,
• k. treating the heap permeable ore bed by dispersing continuously or intermittently a lixiviate for precious metals through the bed,
• l. separating the lixiviate solution containing dissolved precious metals from the heap permeable ore bed and recovering said precious metals from the lixiviate.