Process for the recovery of gold from refractory ores by pressure oxidation

Claim 2

A process for recovering gold from a refractory ore slurry, said process comprising the steps of: introducing the slurry to at least one agitated autoclave maintained at an autoclave temperature in excess of about 150° C. and an autoclave oxygen partial pressure in excess of about 10 psia; agitating the slurry to allow oxygen to oxidize at least part of the substances which cause the ore to be refractory to form an oxidized slurry; passing the oxidized slurry to a plurality of stages in which the oxidized slurry is contacted with a cyanide and activated charcoal, the charcoal flowing in countercurrent fashion with said oxidized slurry whereby precious metals are transferred to the activated charcoal; and separating the activated charcoal from the oxidized slurry.

Claim 3

The process as recited in claim 1 wherein the autoclave temperature is maintained between about 180° C. to about 225° C.

Claim 4

The process is recited in claims 1 or 2 wherein the autoclave oxygen partial pressure is maintained at a minimum between about 10 psia and about 25 psia.

Claim 5

A process as recited in claim 1 wherein a basic compound, is added to the ore slurry to form an insoluble species with free sulfate ions.

Claim 6

A process as recited in claim 4 wherein the basic compound comprises sodium carbonate.

Claim 7

A process as recited in claim 1, comprising the further step of: cooling the oxidized slurry before the oxidized slurry is contacted with the cyanide.

Claim 8

A process as recited in claim 1, comprising the further step of: raising the pH of the oxidized slurry before the oxidized slurry is contacted with the cyanide.

Claim 9

A process as recited in claim 1, comprising the further step of: diluting the oxidized slurry before the oxidized slurry is contacted with the cyanide.

Claim 10

A process as recited in claim 1 wherein the ore slurry is maintained within the autoclave step from approximately 30-90 minutes.

Claim 11

A process for recovering gold, said process comprising the steps of: forming an ore slurry from a refractory gold bearing ore; introducing the slurry to to at least one autoclave which is maintained at an autoclave temperature in excess of about 150° C. and an autoclave oxygen partial pressure maintained in excess of about 10 psia; agitating the slurry sufficiently to oxidize at least part of the substances which cause the ore to be refractory to form an oxidized slurry; passing the oxidized slurry to a plurality of stages in which the oxidized slurry is contacted with a cyanide and activated charcoal at a cyanidation temperature less than about 50° C., said charcoal flowing in countercurrent fashion with said oxidized slurry whereby gold is transferred to the activated charcoal; and separating the activated charcoal from the oxidized slurry.

Claim 12

A process for recovering gold, said process comprising the steps of: forming an ore slurry from a refractory gold bearing ore; introducing the slurry to to at least one autoclave which is maintained at an autoclave temperature in excess of about 150° C. and an autoclave oxygen partial pressure maintained in excess of about 10 psia; agitating the slurry sufficiently to oxidize at least part of the substances which cause the ore to be refractory to form an oxidized slurry; passing the oxidized slurry to a plurality of stages in which the oxidized slurry is contacted with a cyanide and activated charcoal at a cyanidation temperature less than about 50° C., said charcoal flowing in countercurrent fashion with said oxidized slurry whereby gold is transferred to the activated charcoal; and separating the activated charcoal from the oxidized slurry.

Claim 13

The process as recited in claim 10 wherein the autoclave temperature is maintained between about 180° C. to about 225° C.

Claim 14

The process as recited in claims 10 or 11 wherein the autoclave oxygen partial pressure is maintained at about 15 psia.

Claim 15

A process as recited in claim 10 wherein a basic compound is added to the ore slurry to form an insoluble species with free sulfate ions.

Claim 16

A process as recited in claim 13 wherein the basic compound is selected from the group consisting of sodium carbonate, sodium bicarbonate and sodium hydroxide.

Claim 17

A process as recited in claim 10 wherein the gold in the ore exists in a finely disseminated form with an average size of less than 10 microns.

Claim 18

A process as recited in claim 10 wherein the refractory ore contains a sulfur bearing compound which is at least partially oxidized in at least one autoclave.

Claim 19

A process as recited in claim 10 wherein the ore is less than 60% amenable to standard cyanidation techniques.

Claim 20

A process as recited in claim 17 wherein more than 85% of the gold existing in the ore slurry is transferred to the activated charcoal.

Claim 21

A process as recited in claim 10 wherein the ore slurry is maintained within at least autoclave for from about ten minutes to about thirty minutes.

Claim 22

A process as recited in claim 10 wherein the activated charcoal is separated from the oxidized slurry from about 4 hours to about 8 hours after said activated charcoal is contacted with the oxidized slurry.

Claim 23

A process for recovering gold, said process comprising the steps of: forming an ore slurry by grinding a refractory gold bearing ore to form a slurry which is mixed with a diluent stream; introducing the slurry to at least one autoclave which is maintained at an autoclave temperature in excess of about 150° C. and an autoclave oxygen partial pressure maintained in excess of about 10 psia; agitating the slurry to oxidize substances which cause the ore to be refractory to form an oxidized slurry; cooling the oxidized slurry to a temperature less than about 150° C.; passing the oxidized slurry to a plurality of stages in which the oxidized slurry is contacted with a cyanide and activated charcoal, the activated charcoal flowing in countercurrent fashion with the oxidized slurry whereby gold is transferred to the activated charcoal; separating the activated charcoal from the oxidized slurry; collecting a tailings stream from the oxidized slurry; treating a water portion of the tailings stream to destroy any free cyanide and form a treated reclaimed water stream; and recycling the treated reclaimed water stream to a step of the process upstream from the step of passing the oxidized slurry to a plurality of stages.

Claim 24

A process as recited in claim 21 wherein the treated reclaimed water stream is combined with a feed stream to form the diluent stream.

Claim 25

A process as recited in claim 21 wherein the oxidized slurry is cooled by a heat exchanger which is utilized to preheat the slurry.

Claim 26

A process as recited in claim 21, comprising the further step of: diluting the oxidized slurry to dethicken said oxidized slurry before the oxidized slurry is contacted with the cyanide.

Claim 27

A process as recited in claim 24 wherein the reclaimed water stream is used to dilute the oxidized slurry.

Claim 28

A process as recited in claim 21 wherein the ore slurry is maintained within at least one autoclave from about 10 minutes to less than about 60 minutes and the carbon-in-leach residence time is from about 4 hours to about 8 hours.

Claim 29

A process as recited in claim 26 wherein the ore slurry is less than 60% amenable to standard cyanidation techniques and more than 85% of the gold in said ore slurry is transferred to the activated charcoal.