Research On The Solid-State Reduction Roasting Of Nickeliferous Laterite Ore Intensified By Sulfur-bearing Additives

Nickel is mainly consumed in stainless steel, accounting for about66%of the worldwide nickel production. As stainless steel industry has been developing rapidly, the supply of nickel product fell short of demand in the world in recent years. It is necessary to utilize nickel laterite ore since the nickel sulphide ore would be exhausted.The influence of sulfur bearing additives on reduction roasting of laterite ore is studied. The thermodynamic behaviours and conditions of laterite ore in the process of reduction roasting with sulfur bearing additives are analysed. Beneficiation of nickeliferous laterite by reduction roasting in the presence of sodium sulfate are studied by using pure materials, based on the studies of the microstructure and phase transformation of roasted pellets, strengthening mechanism of additives on the ferronickel-gangue separation is also illuminated.S, CaSO₄-2H₂O, NaS2, FeS and Na₂SO₄can intensify reduction roasting and magnetic separating of laterite ore, and Na₂SO₄was the most effective additive.The optimal conditions of the process of reduction followed by magnetic separation with addition of Na₂SO₄addictive were:reduction temperature1100℃, reduction time60min, grinding fineness90%passing0.043mm, magnetic field intensity1kGs. A ferronickel with nickel grade of9.48%, iron grade of79.30%, and nickel and iron recovery of83.02%and56.36%respectively can be achieved. The ultrasonication had a significant effect on the nickel、 iron grade and recovery of the ferronickel products.Thermodynamic analysis showed that Na₂SO₄and CaSO₄were reduced to Na2S and CaS by CO, at the same time Na2S and CaS reacts with FeO to form FeS respectively in the presence of SiO₂. However, there is no FeS formed in the absence of SiO₂.XRD analysis and microstructure of reduced products showed that FeS was formed when the temperature exceed500℃. Research on the phase transformation of components in the reduction roasting process in the pure materials system indicate that the reason for FeS formation was Na2S and SiO2react with FeO. Experimental evidence showed that troilite （FeS） serves as an activating agent to accelerate melt phase formation via a low melting point （985℃） Fe-FeS eutectic. This markedly facilitated the aggregation of ferronickel particles during reduction. Nickel sulfide was formed during the process that will reduce the recovery of nickel. Meanwhile, FeS was nonmagnetic, along with the selective enrichment of Ni by suppressing the complete metallization of Fe resulted from the formation of FeS.