Method For Metal Recovery and Leaching Agent Recycle in Agitation Leach Plants

Abstract

This invention is directed to an improved process for metal recovery from ore using agitation leaching comprising dividing leaching of the crushed and mined ore into at least two sequential leaching-solids-liquid separation-solvent extraction sub-circuits, with no significant dilution during solids-liquid separation in these units, and the raffinate from solvent extraction being recycled back to the leaching, with the underflow pulp from the second liquid-solids separator being sent to a final solid-liquid separator, with water washing, from which the washed solids are sent to disposal and the clarified aqueous wash solution is sent to a final solvent extraction, with some or all of the metal-depleted aqueous raffinate from this final solvent extraction being optionally neutralized, and/or being circulated back to the third solid-liquid separation as wash solution and/or to recovery of other metals and/or to disposal to maximize metal recovery and maintain water balance.

1 . A process for recovering desired metal values from crushed and milled ore solids comprising the steps of:
 (a) mixing a first aqueous leach solution with the crushed and milled ore solids in a first agitated tank leach unit, whereby at least a portion of the desired metal values in the ore solids is dissolved into the first aqueous leach solution to obtain a first aqueous leach pulp comprising a mixture of leached solids and first aqueous leach solution;   (b) subjecting the first aqueous leach pulp to a first solids-liquid separation, without significant water dilution, to provide a first clarified aqueous leach solution and a second aqueous leach pulp, wherein the second aqueous leach pulp comprises leached solids at a percent solids level that is greater than that in the first aqueous leach pulp;   (c) subjecting the first clarified aqueous leach solution to a first solvent extraction, whereby at least a portion of the desired metal values are extracted into a first organic phase comprising one or more extraction reagents specific for the desired metal, and a first aqueous raffinate, depleted of desired metal values, is obtained;   (d) mixing a second aqueous leach solution with the second aqueous leach pulp in a final agitated tank leach unit, whereby at least a portion of the desired metal values formerly in the second aqueous leach pulp is dissolved into the second aqueous leach solution to obtain a third aqueous leach pulp, wherein the third aqueous leach pulp comprises a mixture of twice-leached solids and a second aqueous leach solution, rich in desired metal values;   (e) subjecting the third aqueous leach pulp to a second solids-liquid separation, without significant water dilution, to provide a second clarified aqueous leach solution and a fourth aqueous leach pulp, wherein the fourth aqueous leach pulp comprises leached solids at a percent solids level that is greater than that in the third aqueous leach pulp;   (f) subjecting the second clarified aqueous leach solution to a second solvent extraction, whereby at least a portion of the desired metal values are extracted into a second organic phase comprising one or more extraction reagent(s) specific for the desired metal, and a second aqueous raffinate, depleted of desired metal values, is obtained;   (g) subjecting the fourth aqueous leach pulp to a third solids-liquid separation, with significant dilution via an aqueous stream, to provide a third clarified aqueous leach solution and a fifth aqueous pulp, wherein the concentration of desired metal values in the third clarified aqueous leach solution is less than the concentration of desired metal values in the second clarified aqueous leach solution, and the fifth aqueous pulp comprises a mixture of leached solids and aqueous leach solution; and   (h) subjecting the third clarified aqueous leach solution to a third solvent extraction whereby at least a portion of the desired metal values are extracted into a third organic phase comprising one or more extraction reagents(s) specific for the desired metal, and a third aqueous raffinate, depleted of desired metal values, is obtained.   
     
     
         2 . The process according to  claim 1 , wherein the providing of a second aqueous leach pulp in step (b) further comprises an intermediate leaching step, wherein a first intermediate aqueous leach pulp obtained from the first solid-liquid separation is mixed with an intermediate aqueous leach solution in an intermediate agitated tank leach unit to obtain a second intermediate aqueous leach pulp, subjecting the second intermediate aqueous leach pulp to an intermediate solid-liquid separation to obtain the second aqueous leach pulp and an intermediate clarified aqueous leach solution, wherein the intermediate clarified aqueous leach solution is subjected to an intermediate solvent extraction to obtain an intermediate aqueous raffinate. 
     
     
         3 . The process according to  claim 1 , wherein the desired metal is selected from the group consisting of copper, zinc, nickel and cobalt. 
     
     
         4 . The process according to  claim 1 , wherein the first aqueous leach solution and the second aqueous leach solution comprise sulphuric acid. 
     
     
         5 . The process according to  claim 1 , wherein the first aqueous leach solution and the second aqueous leach solution comprise ammonia. 
     
     
         6 - 9 . (canceled) 
     
     
         10 . The process according to  claim 1 , wherein the third solid-liquid separation comprises counter-current decantation. 
     
     
         11 . The process according to  claim 1 , wherein the concentration of the desired metal in the first clarified aqueous leach solution is at least 30% greater than the concentration of the desired metal in the second clarified aqueous leach solution. 
     
     
         12 . The process according to  claim 1 , wherein the concentration of the desired metal in the first clarified aqueous leach solution is at least 50% greater than the concentration of the desired metal in the second clarified aqueous leach solution. 
     
     
         13 . The process according to  claim 1 , wherein the concentration of the desired metal in the first clarified aqueous leach solution is at least 70% greater than the concentration of the desired metal in the second clarified aqueous leach solution. 
     
     
         14 . The process according to  claim 1 , wherein the concentration of the metal in the first clarified aqueous leach solution is at least 100% greater than the concentration of the desired metal in the second clarified aqueous leach solution. 
     
     
         15 . The process according to  claim 1 , wherein the first aqueous leach solution comprises at least a portion of the first aqueous raffinate. 
     
     
         16 . The process according to  claim 15 , wherein the first aqueous leach solution further comprises fresh leaching agent. 
     
     
         17 . The process according to  claim 16 , wherein the second aqueous leach solution comprises at least a portion of the second aqueous raffinate. 
     
     
         18 . The process according to  claim 17 , wherein the second aqueous leach solution further comprises fresh leaching agent. 
     
     
         19 . The process according to  claim 18 , wherein the first aqueous leach solution, second aqueous leach solution, and fresh leaching agent comprise sulphuric acid. 
     
     
         20 . The process according to  claim 18 , wherein the first aqueous leach solution and second aqueous leach solution comprise ammonia, and the fresh leaching agent comprises gaseous ammonia and/or ammonium hydroxide. 
     
     
         21 . The process according to  claim 1 , wherein the third aqueous raffinate is neutralized and further processed according to a step selected from the group consisting of being circulated back to the third solids-liquid separation, being sent to disposal, being treated to recover one or more other metal values, and combinations of two or more of these.