Method for recovering nickel from high magnesium-containing Ni-Fe-Mg lateritic ore

A method for recovering nickel from particulate high magnesium lateritic ore containing Ni, Fe and Mg by counter-current leaching which comprises:

• providing a first leaching stage and a second leaching stage wherein primary leaching and neutralization are carried out in the second leaching stage;
• leaching said ore with a mineral acid in said second leaching stage to form a solution containing nickel iron, magnesium and recyclable solids;
• subjecting said leached ore to solid/liquid separation and thereby recover said recyclable solids for further leaching in said first leaching stage;
• recycling said solids to said first leaching stage to which recycle mineral acid is added;
• passing a first leachate from said first leaching stage to said second leaching stage to which fresh ore is added for primary leaching;
• leaching said ore in said second stage;
• passing said second leached ore to solid/liquid separation to separate solids from leachate formed during leaching;
• recycling the solids from said second leaching stage to said first leaching together with recycle mineral acid;
• subjecting said leachate to further neutralization with recycle MgO;
• said neutralization being sufficient to precipitate a basic iron compound in a solution containing dissolved nickel and magnesium;
• subjecting said Ni/Mg containing solution to solid/liquid separation to remove the precipitate and provide a Ni/Mg containing solution;
• adjusting the pH of the solution with recycle MgO to selective precipitate Ni(OH).sub.2 and provide a solution containing dissolved magnesium;
• pyro-hydrolyzing the magnesium-containing solution to form a precipitate of MgO;
• and
• recycling said precipitate of MgO to the leachate resulting from the first and second leaching stage to neutralize the leachate to a desired pH to precipitate said basic iron compound and provide a solution containing said Ni and said Mg from which Mg is separated as a solution for pyro-hydrolysis.

A method of heap leaching magnesium Ni-Fe-Mg containing laterite ore in the particulate state containing at least about 5% Mg, at least about 10% Fe and at least about 0.5% nickel by weight which comprises:

• agglomerating said particulate ore of particle size less than about one inch with hydrochloric acid of concentration ranging up to 10M,
• forming a heap of said agglomerated ore,
• said heap of the ore being characterized by interstices throughout said heap for passing hydrochloric acid therethrough,
• allowing hydrochloric acid of concentration of at least about 0.25M to percolate througout said heap of ore at a rate sufficient to effect dissolution of the nickel as nickel chloride together with some iron and magnesium as chlorides and form a pregnant solution in thereof;
• passing said pregnant solution through a bed of resin selective to the absorption of nickel in preference to iron and magnesium chlorides which chlorides are removed as a raffinate;
• subjecting said raffinate to neutralization at a pH selective to the precipitation of iron as FeOH.sub.3 while maintaining magnesium chloride in said solution;
• passing a stripping solution of HCl of about 2 to 6 molar through said bed of resin after washing said resin with wash water to extract the nickel therefrom as nickel choride;
• subjecting said magnesium chloride solution to pyrohydrolysis to form MgO suitable for recycling to neutralization;
• hydrolizing said nickel chloride solution in a separate pyro-hydrolysis step to produce NiO and HCl for recycling to heap leaching and to produce water for recycling as wash water within the leaching system,
• and recovering nickel from said NiO.

A method for leaching in a leaching system comprising a first leaching stage and a second leaching stage, a high magnesium containing Ni-Fe-Mg lateritic ore containing at least about 0.5% Ni, at least about 5% magnesium and at least about 10%iron, which comprises:

• feeding a charge of particulate ore of mesh size less than about one inch to said second leaching stage,
• adding to said charge hydrochloric acid of concentration at least about 0.25 molar at a temperature of at least sufficient to dissolve substantial amounts of nickel from said ore and form a pregnant nickel chloride solution containing iron chloride, magnesium chloride and undissolved solids,
• recycling said undissolved solids to said first leach stage,
• subjecting said pregnant nickel chloride solution to neutralization sufficient to precipitate iron hydroxide and provide a solution of nickel chloride and magnesium chloride,
• separating said iron hydroxide from said pregnant nickel chloride solution,
• neutralizing said pregnant nickel solution sufficient to form nickel hydroxide and leave a solution of magnesium chloride,
• subjecting said magnesium chloride solution to pyro-hydrolysis to form recycle hydrochloric acid and recycle MgO for neutralization,
• and recycling said hydrochloric acid to said first leaching stage for leaching said solids recycled from said second leaching stage.