Recovering nickel

Abstract

A process for recovering valuable metals from laterite ores and concentrates that are contaminated with iron is disclosed. The process includes reducing ferric ions to ferrous ions in a leach liquor containing a valuable metal and iron in solution using a reductant, neutralising the liquor to reduce the free acid concentration in solution to levels suitable for nickel precipitation; and precipitating the valuable metal using the reductant and seed particles under process conditions, including one or more of seed particle size, seed composition, and temperature, that are selected to maximise nickel precipitation and to minimise iron precipitation.

1 . A process for recovering valuable metals from laterite ores and concentrates that are contaminated with iron, which process includes the steps of: 
 (a) reducing ferric ions to ferrous ions in a leach liquor containing a valuable metal and iron in solution using a suitable reductant, the leach liquor being obtained by processing laterite ores or concentrates of the ores that contain the valuable metal and are contaminated with iron;    (b) neutralising the liquor to reduce the free acid concentration in solution to levels suitable for nickel precipitation; and    (c) precipitating the valuable metal using the reductant and seed particles under process conditions, including one or more of seed particle size, seed composition, and temperature, that are selected to maximise nickel precipitation and to minimise iron precipitation.    
   
   
       2 . The process defined in  claim 1  wherein the reduction step (a) includes reducing ferric ions to ferrous ions using the reductant in the presence of 40-90 g/l free acid.  
   
   
       3 . The process defined in  claim 1  wherein the reductant is a gaseous reductant.  
   
   
       4 . The process defined in  claim 3  wherein the gaseous reductant is H 2 S.  
   
   
       5 . The process defined in  claim 1  wherein the neutralisation step (b) increases the pH of the solution to 2.  
   
   
       6 . The process defined in  claim 1  wherein the neutralisation step (b) maintains iron in the ferrous state.  
   
   
       7 . The process defined in  claim 1  wherein the valuable metal is nickel.  
   
   
       8 . The process defined in  claim 1  wherein the valuable metals are nickel and cobalt.  
   
   
       9 . The process defined in  claim 1  wherein the laterite ores are ores that contain nickel in a chlorite mineral phase.  
   
   
       10 . The process defined in  claim 1  wherein the process conditions for the precipitation step (c) include operating at a partial pressure of the gaseous reductant of less than 60 psi.  
   
   
       11 . The process defined in  claim 10  wherein the gas partial pressure is less than 40 psi.  
   
   
       12 . The process defined in  claim 11  wherein the gas partial pressure is less than 30 psi.  
   
   
       13 . The process defined in  claim 12  wherein the gas partial pressure be less than 25 psi.  
   
   
       14 . The process defined in  claim 1  wherein the process conditions for the precipitation step (c) include operating at a liquor temperature of at least 50° C.  
   
   
       15 . The process defined in  claim 14  wherein the liquor temperature is at least 60° C.  
   
   
       16 . The process defined in  claim 1  wherein the seed particles for the precipitation step (c) have a particle size of P 50  less than 100 micron.  
   
   
       17 . The process defined in  claim 16  wherein the particle size of the seed particles is P 50  less than 80 micron.  
   
   
       18 . The process defined in  claim 17  wherein the particle size of the seed particles be P 50  less than 60 micron.  
   
   
       19 . The process defined in  claim 16  wherein the seed particle concentration for the precipitation step (c) is greater than 30 g/l.  
   
   
       20 . The process defined in  claim 17  wherein the seed particle concentration is greater than 40 g/l.  
   
   
       21 . The process defined in  claim 1  wherein the ratio of iron and the valuable metal in the leach liquor supplied to step (a) is greater than 2:1.  
   
   
       22 . The process defined in  claim 21  wherein the ratio is greater than 3:1.  
   
   
       23 . The process defined in  claim 22  wherein the ratio is greater than 5:1.