Gold and silver recovery processes by electrolytic generation of active bromine

A continuous flow, non-batch, process for recovering gold or silver from material containing gold or silver, the process not requiring use of cyanide, the process comprising:

• feeding the material to a series of elevationally cascading leaching tanks, the leaching tanks including means for agitating their contents;
• simultaneously feeding a stream of 5% to 50% NaBr solution to the series of elevationally cascading leaching tanks to produce a mixture of material and NaBr solution in the leaching tanks;
• passing a quantity of electric current through the mixture in one or more of the leaching tanks to electrochemically generate from the 5% to 50% NaBr solution a quantity of HOBr dissolved in solution within the mixture for leaching gold or silver from the material, a significant number of the leaching tanks being single chambered vessels as opposed to multi-chambered vessels having separate anolyte and catholyte compartments, and thereby;
• oxidizing with HOBr a substantial portion of base metal sulfides present in the material into acid soluble base metal compounds, and;
• oxidizing with HOBr available gold to AuBr.sub.3 or available silver to AgBr, the AuBr.sub.3 or AgBr present being substantially complexed into a soluble form with the NaBr in solution and thereby;
• creating a stream of pregnant NaBr solution flowing from the series of elevationally cascading tanks, the pregnant NaBr solution containing both dissolved base metal compounds and dissolved AuBr.sub.3 or AgBr;
• introducing lime to at least one of the series of elevationally cascading leaching tanks to precipitate the base metal compounds from the pregnant NaBr solution;
• filtering solids from the pregnant NaBr solution flowing from the series of elevationally cascading leaching tanks, and collecting the filtered solution;
• separating gold from the complexed AuBr.sub.3 in the filtered solution or silver from the complexed AgBr in the filtered solution while simultaneously generating Br.sup.- ions in solution from the complexed AuBr.sub.3 or complexed AgBr;
• and
• collecting that Br.sup.- ion containing solution and introducing it back into the series of elevationally cascading leaching tanks to make Br.sup.- ions in such solution available for electrochemical regeneration into HOBr within the mixture of material and NaBr solution whereby only a minimal amount, if any, of bromine is depleted in the process.

A process for recovering gold or silver from a material containing substantially no or a negligible amount of base metal sulfides, the process not requiring use of cyanide, the process comprising the following steps:

• combining the material with a volume of 5% to 50% NaBr solution to produce a mixture of material and NaBr solution;
• passing a quantity of electric current through the mixture of material and NaBr solution to electrochemically generate a quantity of HOBr dissolved in solution within the mixture, the quantity of electric current being applied through the mixture of material and NaBr solution in a single chambered vessel as opposed to a multi-chambered vessel having separate anolyte and catholyte compartments;
• maintaining the pH of said mixture of material and NaBr solution at from 4.0 to 8.0 by the addition of acid to keep a substantial quantity of an active bromine in HOBr form and thereby;
• oxidizing with the active bromine available gold to AuBr.sub.3 or available silver to AgBr, the AuBr.sub.3 or AgBr present being substantially complexed into a soluble form with the NaBr in solution and thereby;
• creating a pregnant NaBr solution containing dissolved AuBr.sub.3 or AgBr;
• separating gold from the complexed AuBr.sub.3 in the pregnant solution or silver from the complexed AgBr in the pregnant solution while simultaneously generating Br.sup.- ions in solution from the complexed AuBr.sub.3 or complexed AgBr;
• and
• combining the Br.sup.- ion containing solution with the mixture containing the volume of 5% to 50% NaBr solution and material to make the Br.sup.- ions in such solution available for electrochemical regeneration into active bromine whereby only a minimal amount, if any, of bromine is depleted in the process.

A process for recovering gold or silver from carbonaceous ore, the process not requiring use of cyanide, the process comprising the following steps:

• combining the material with a volume of 5% to 50% NaBr solution to produce a mixture of material and NaBr solution;
• passing a quantity of electric current through the mixture of material and NaBr solution to electrochemically generate a quantity of active bromine dissolved in solution within the mixture, the quantity of electric current being applied through the mixture of material and NaBr solution in a single chambered vessel as opposed to a multi-chambered vessel having separate anolyte and catholyte compartments;
• maintaining the pH of said mixture of material and NaBr solution at from 4.0 to 8.0 by addition of acid to keep a substantial quantity of the active bromine in HOBr form and thereby;
• oxidizing with the active bromine available gold to AuBr.sub.3 or available silver to AgBr, the AuBr.sub.3 or AgBr present being substantially complexed into a soluble form with the NaBr in solution and thereby;
• creating a pregnant NaBr solution containing dissolved AuBr.sub.3 or AgBr;
• separating gold from the complexed AuBr.sub.3 in the pregnant solution or silver from the complexed AgBr in the pregnant solution while simultaneously generating Br.sup.- ions in solution from the complexed AuBr.sub.3 or complexed AgBr;
• and
• combining the Br.sup.- ion containing solution with the mixture containing the volume of 5% to 50% NaBr solution and material to make Br.sup.- ions in such solution available for electrochemical regeneration into active bromine whereby only a minimal amount, if any, of bromine is depleted in the process.