Hydrometallurgical process for extracting metal values from complex ores containing arsenic and sulfur

Claim 2

In a method for extracting and recovering cobalt, nickel or silver from feedstock derived from complex ore concentrates containing other mineralization including arsenic and sulphur and having a finely particulate character, the step of subjecting such feedstock to a first stage oxidative caustic leach at elevated temperatures and pressures and wherein the caustic introduced is calculated to produce in the converted reactants a pH of the order of 13 or greater followed by the steps of separating and recovering the liquor and solids phases therefrom respectively, followed by the further step of subjecting such recovered solids phase to a second stage oxidative caustic leach at elevated temperatures and pressures and wherein the caustic introduced is calculated to produce in the converted reactants a pH of the order of 13 or greater followed by the still further steps of separating and recovering the liquor and solids phases therefrom respectively.

Claim 3

The method according to claim 1 wherein the recovered solids phase derived from the second stage caustic leach is subjected to a first stage sulphuric acid leach proceeding in the presence of low residual free sulphuric acid followed by the steps of separating and recovering the liquor and solids phases therefrom respectively followed by the further step of subjecting such recovered solids phases to a second stage sulphuric acid leach proceeding in the presence of high residual free sulphuric acid followed by the steps of separating and recovering the liquor and solids phases therefrom respectively.

Claim 4

The method according to claim 2 wherein the residual free sulphuric acid in the first stage acid leach is of the order of 5 g/l.

Claim 5

The method according to claim 3 wherein the free residual sulphuric acid in the second stage acid leach is of the order of 400-500 g/l.

Claim 7

The method according to claim 2 wherein the liquor recovered from the first stage acid leach is purified by subjecting same to the step of introducing lime slurring thereinto at an elevated temperature calculated to produce in the converted reactants a pH of the order of 3.5 or thereabouts followed by the further step of recovering the liquor phase and separating the solids phase therefrom.

Claim 8

The method according to claim 6 wherein the further recovered liquor phase is further purified by the step of introducing lime slurry thereinto calculated to produce in the converted reactants a pH of the order of 6.8 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 9

The method according to claim 7 wherein the further recovered liquor phase is further treated by the step of introducing lime slurry thereinto calculated to produce in the converted reactants a pH of the order of 11.0 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 10

The method according to claim 8 wherein the further recovered solids phase is further purified by the step of subjecting same to the addition of further sufficient sulphuric acid calculated to redissolve same followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 11

The method according to claim 9 wherein the further recovered liquor phase is subjected to the steps of introducing chlorine gas and caustic thereto calculated to produce in the converted reactants a pH of the order of 5.5 or thereabouts followed by the further steps of separating and recovering the liquor and solid phases therefrom.

Claim 12

The method according to claim 10 wherein the further recovered liquor phase is subjected to the step of introducing caustic thereinto calculated to produce in the converted reactants a pH of the order of 1.10 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 13

The method according to claim 1 wherein the recovered solids phase is subjected to the step of introducing sodium hydroxide and sodium cyanide calculated to produce in the converted reactants a pH of the order of 11.5 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 14

The method according to claim 12 wherein the further recovered liquor phase is subjected to the step of introducing sodium sulphide calculated to precipitate substantially all of the silver as silver sulphide followed by the further steps of separating and recovering the liquor and solid phases therefrom.

Claim 15

The method according to claim 1 wherein the temperature of each recovered liquor phase is so controlled that between 50-80% of the dissolved sodium arsenate is crystallized as Na 3 AsO 4 .12H 2 O followed by the further steps of separating and recovering of the liquor and solids phases therefrom.

Claim 16

The method according to claim 14 wherein the further liquor phase recovered from the separation of the NA 3 AsO 4 .12H 2 O is recycled for use in said oxidative caustic leaching steps.

Claim 17

The method according to claim 15 wherein said further recovered liquor phase recycled for use is directed to the first stage caustic leaching step and additional caustic is added in an amount sufficient to produce in the converted reactants a pH of the order of 13 or greater.

Claim 18

The method according to claim 15 wherein said further recovered liquor phase recycled for use is directed to the second stage caustic leaching step and and additional caustic is added in an amount sufficient to produce in the converted reactants a pH of the order of 13 or greater.

Claim 19

The method according to claim 15 wherein said further recovered liquor phase to be recycled for use having a concentration of the order of 100 g/l or greater of sodium sulphate is directed to a caustic leaching stage including fresh ore concentrate so as to consume residual caustic therein until a pH of the order of 7.5 to 8.0 is reached followed by the further step of separating and recovering the liquor and solids phases therefrom respectively.

Claim 20

The method according to claim 18 wherein said further recovered liquor phase from the converted reactants having a pH of the order of 7.5 to 8, is reacted at pH 3.5 or thereabouts and at elevated temperatures with copper sulphate solution so as to precipitate any crystalline copper arsenate followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 21

The method according to claim 19 wherein said further recovered liquor phase following separation of same from said recovered copper arsenate is treated with ferric sulphate and lime slurry to pH 7 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 22

The method according to claim 20 wherein said further recovered liquid phase is subjected to the further steps of double evaporation/crystallization to yield sodium sulphate and to separate and recover the liquid phase therefrom.

Claim 23

The method according to claim 14 wherein the recovered sodium arsenate is redissolved and reacted at pH 3.5 or thereabouts and at elevated temperatures with one of copper sulphate and zinc sulphate solution to precipitate crystalline products of one of copper arsenate and zinc arsenate followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 24

The method according to claim 1 wherein the selected finely particulate character of the feedstock is of the order of -400 mesh or thereabouts.

Claim 25

The method according to claim 1 wherein the selected elevated temperatures are of the order of between 120°-140° C. and the selected elevated pressures are of the order of between 120-140 psig, and wherein the slurry of the first of said twostage oxidative caustic leach is subjected to preheating of the order of between 85°-100° C.

Claim 26

The method according to claim 1 wherein the initial reactants to the said first stage are calculated on the basis of from 13-14% dry solids and of between 150-180 g/l free caustic whereby the converted reactants have a pH of the order of 13 or greater and a residual caustic concentration of the order of between 60-80 g/l.

Claim 27

The method according to claim 23, 24 or 25 wherein the second stage reactants are calculated on the basis of from 14 to 15% dry solids and of between 120-140 g/l free caustic whereby the converted reactants produce a pH of the order of 13 or greater and a residual free caustic concentration of the order of between 60-80 g/l.

Claim 28

In a method for extracting and recovering cobalt, nickel and silver from feedstock derived from complex ore concentrates containing other mineralization including arsenic and sulphur and having a finely particulate character of the order of -400 mesh or thereabouts, the step of subjecting such feedstock to a two-stage oxidative caustic leach, commenced by heating the slurried intial reactants of feedstock and caustic to an elevated temperature of the order of between 85°-100° C., followed by the introduction of finely dispersed oxygen at a pressure of the order of between 120-140 psig and at a temperature of the order of between 120°-150° C. until the reactions are substantially complete followed by the steps of separating and recovering the liquor and solid phases therefrom, and reslurrying said recovered solids with caustic and repeating the introduction of finely dispersed oxygen at said range of pressures and at said range of temperatures until the reactions are substantially complete followed by the steps of separating and recovering the liquor and solids phases therefrom said caustic introduced in each of the aforementioned stages being an amount sufficient to produce in the converted reactants respectively a pH of the order of 13 or greater.

Claim 29

In a method for extracting and recovering cobalt, nickel and silver from feedstock derived from complex ore concentrates containing other mineralization including arsenic and sulphur and having a finely particulate character of the order of -400 mesh or thereabouts, the step of subjecting such feedstock to a two-stage oxidative caustic leach, commenced by heating the slurried intial reactants of feedstock and caustic to an elevated temperature of the order of between 85°-100° C., followed by the introduction of finely dispersed oxygen at a pressure of the order of between 120-140 psig and at a temperature of the order of between 120°-150° C. until the reactions are substantially complete followed by the steps of separating and recovering the liquor and solid phases therefrom, and reslurrying said recovered solids with caustic and repeating the introduction of finely dispersed oxygen at said range of pressures and at said range of temperatures until the reactions are substantially complete followed by the steps of separating and recovering the liquor and solids phases therefrom said caustic introduced in each of the aforementioned stages being an amount sufficient to produce in the converted reactants respectively a pH of the order of 13 or greater.

Claim 30

The method according to claim 27 wherein the initial reactants are calculated on the basis from 13-14% dry solids and of between 150-180 g/l free caustic whereby the converted reactants have a pH of the order of 13 or greater and a residual caustic concentration of the order of between 60-80 g/l.

Claim 31

A method according to claim 27 or 28 wherein the second stage reactants are calculated on the basis from 14-15% dry solids and of between 120-140 g/l free caustic whereby the converted reactants have a pH of the order of 13 or greater and a residual free caustic concentration of the order of between 60-80 g/l.

Claim 32

The method according to claim 27, wherein the recovered solids phase is subjected to a two-stage sulphuric acid leach, the first acid leach proceeding in the presence of low residual free sulphuric acid of the order of 5 g/l and the second stage acid leach preceding in the presence of high residual free sulphuric acid of the order of 400-500 g/l.

Claim 33

The method according to claim 30 wherein the recovered second stage acid leach liquor phase is diluted and recycled for use in the first stage acid leach.

Claim 34

The method according to claim 31 wherein the liquor recovered from the first stage acid leach is purified by subjecting same to the step of introducing lime slurry thereinto at an elevated temperature calculated to produce in the converted reactants a pH of the order of 3.5 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 35

The method according to claim 32 wherein the further recovered liquor phase is further purified by the step of introducing lime slurry thereinto calculated to produce in the converted reactants a pH of the order of 6.8 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 36

The method according to claim 33 wherein the further recovered liquor phase is further treated by the step of introducing lime slurry thereinto calculated to produce in the converted reactants a pH of the order of 11.0 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 37

The method according to claim 34 wherein the further recovered solids phase is further purified by the step of subjecting same to the addition of further sufficient sulphuric acid calculated to redissolve same followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 38

The method according to claim 35 wherein the further recovered liquor phase is subjected to the step of introducing chlorine gas and caustic thereto calculated to produce in the converted reactants a pH of the order of 5.5 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 39

The method according to claim 30 wherein the recovered solids phase is subjected to the step of introducing caustic and sodium cyanide calculated to produce in the converted reactants a pH of the order of 11.5 or thereabouts followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 40

The method of claim 37 wherein the further recovered liquor phase is subjected to the step of introducing sodium sulphide calculated to precipitate all of the silver sulphide followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 41

The method according to claim 27, wherein the temperature of the recovered liquor phase is so controlled that between 50-80% of the dissolved sodium arsenate is crystallized as Na 3 AsO 4 .12H 2 O followed by the further steps of separating and recovery of the liquor and solids phases therefrom.

Claim 42

The method according to claim 39 wherein the further liquor phase recovered from the separation of the NA 3 AsO 4 .12H 2 O is recycled for use in said two-stage oxidative leaching step.

Claim 43

The method according to claim 40 wherein said further recovered liquor phase recycled for use is directed to one of the first or second of said two-stage leaching step and additional caustic is added in an amount sufficient to produce in the converted reactants a pH of the order of 13 or greater.

Claim 44

The method according to claim 40 wherein said further recovered liquor phase recycled for use is directed to a first leaching stage of said two-stage leaching step and wherein the caustic concentration is maintained to produce in the converted reactants a pH of the order of 7.5 to 8 followed by the further steps of separating and recovering the liquid and solids phases therefrom.

Claim 45

The method according to claim 42 wherein said further recovered liquor phase from the converted reactants having a pH of the order of 7.5 to 8, is subjected to elevated temperatures so as to precipitate crystalline copper arsenate followed by the further steps of separating and recovering the liquor and solids phases therefrom.

Claim 46

The method according to claim 43 wherein said further recovered liquor phase following separation of same from said recovered copper arsenate is treated with ferric sulphate and lime slurry to pH 7 or thereabouts followed by the further steps of separating and recovering the liquor and solid phases therefrom.

Claim 47

The method according to claim 44 wherein said further recovered liquor phase is subjected to the further steps of double evaporation/crystallization to yield sodium sulphate and to separate and recover the liquor phase therefrom.

Claim 48

The method according to claim 39 wherein the recovered sodium arsenate is redissolved and reacted at pH 3.5 or thereabouts and at elevated temperatures with one of copper sulphate and zinc sulphate solution to precipitate crystalline products of one of copper arsenate and zinc arsenate followed by the further steps of separating and recovering the liquor and solids phases therefrom.