Atmospheric Tank Leaching of Nickel Laterite Ore
ENK is in the process of developing and commercialising a proprietary, low cost tank leaching process for extracting nickel from nickel laterite ore.
ENK recently completed extensive laboratory and continuous pilot plant testing of atmospheric tank leaching applied to Acoje ore. These tests have allowed ENK to develop a three–stage leach process that allows efficient use of acid, minimises other neutralising agent requirements (such as limestone) and maximises Ni and Co extraction.
Test work indicates that Ni extraction of 92% can be obtained using the ENK atmospheric tank leach process. This can be compared to 72% extraction for the heap leach process. It should also be noted that the tank leach process consumes less acid per ton of Ni produced than the heap leach process, thereby meaning that for a constrained amount of acid available, more Ni containing product can be produced using the atmospheric tank leach process.
Ore is crushed and scrubbed and screened into three distinct ore grades that will feed three independent milling circuits. The milled slurry from each independent milling circuit then becomes the fresh ore feed to each of the three sequential leaching stages. Acid is introduced into the primary leaching stage. Residue pulp from primary leaching is combined with fresh secondary ore and undergoes secondary leaching. Tertiary ore is combined with secondary residue slurry in the tertiary leaching stage.
Ni and Co bearing PLS is then recovered in a in a counter-current decantation circuit. The washed residue is neutralised, filtered and disposed as solid residue, suitable for backfilling into mined out areas.
Ni is then recovered from the PLS selectively using ion exchange. The Ni rich eluate is precipitated to produce a Nickel Hydoxide Product (NHP) of approximately 53% Ni content, making the NHP a highly versatile intermediate Ni product that required little further refining due to high Ni purity in respect of metals content.
Co is then recovered from the Ni depleted solution, also by using ion exchange. The Co rich eluate is precipitated as Cobalt Carbonate. Once again, high Co purity makes this product sought after due to its versatility.