Investigation On Manufacturius Low Ferronickel From Nickel Laterite Ore By Prereducing-Smelting Process

As Chinese 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, because the nickel sulphide ore would be exhausted. As the raw material of stainless steel production, ferronickel was mainly imported abroad by Chinese stainless steel mills. Few studies on smelting ferronickel from nickel laterite ore due to the shortage of laterite nickel resource. This study was carried out on smelting low ferronickel using 2 types nickel laterite ore (assaying 1.42% Ni and 49.09% Fe in JCH-2 nickel laterite ore, assaying 1.83% Ni and 26.08% Fe in JCH-4 nickel laterite ore) imported from overseas. The ferronickel manufactured by the new process could be used as the raw material of stainless steel, alloy-steel, alloy-ingot, and the Band 200 stainless steel.The new process developed consists of prereducing, wet magnetic separation, and reducing smelting. The contents of this investigation include: optimizing the processing parameters of pre-enrichment and reducing smelting, effect of reducing smelting processing parameter and slag composition on desulphurizing, analyzing on the mineralogy of prereduced agglomerate, analyzing characteristics of Ni-Fe concentrate, mensurating the melting temperature of slag and so on.By analyzing the mineralogy of raw ore and prereduced agglomerate, it is found that it's difficult to separate Ni and Fe, because Ni and Fe are isomorphism in mineral and eutectic in prereduced agglomerate. The optimal conditions for prereduction and wet magnetic concentration were determined as follows: 2% coal in raw, prereducing at 1100^C for 80min, grinding ore to 91.8% passing 0.043mm, the magnetic intensity was 0.8KG andl.7KGs for JCH-2 and JCH-4 respectively. And recovery of 96.11% and 94.28% were achieved for JCH-2 and JCH-4 respectively. The processing of pre-enrichment not only transferred Ni and Fe to metal phases, but also rejected of about 20% impurity, reducing smelting load and fuel rate of electrical furnace. The XRD results indicated that the components of two prereduced concentrates are similar, and the compositions of mineral include metallic iron, metallic nickel and forsterite. And the most valuable constituent Ni and Fe occur in metal state, which will help improve reducing smelting.Experimental investigation indicated that the processing parameters of smelting impart significant influence over the separation of metals from slag. When reducing smelting JCH-2 at 1510℃for 10 min, and reducing smelting JCH-4 at 1550℃for 10 min, high quality ferronickel was produced. The basicity (CaO/SiO₂) of slag highly affects, because the viscosity gradient would be minished in basic range by damaging the structure of Si_xO_y^z-. However, the viscosity gradient increases with an augment in the content of CaO, resulting in an increase in melting temperature. The optimal basicity (CaO/SiO2) of slags was 1.1 and 1.0 for JCH-2 and JCH-4 respectively. The optimal slag component is recommended at melilite (2CaO·MgO·2SiO₂) after analyzing the phase diagram. The content of MgO in slag is the most important influencing factor, the optimal content of 10% and 18% MgO for JCH-2 and JCH-4 are suggested. Experimental investigation indicated that when the content of Al₂O₃ was in the range of 7%～15%, the viscosity gradient of slag is low. Slag will be stable and not affected by changes in compositions of other elemets in the slag. The lower the melting temperature of slag, the better is for separating ferronickel and slag. Full flow sheet experiment indicated that the overall recoveries of Ni are 94.98% and 93.38%; of Fe are 82.57% and 89.57% for JCH-2 and JCH-4 respectively. The overall recoveries of two ores were all higher than normal sintering-blast furance process for smelting ferronickel at 90%. Experimental investigation also indicated that by reducing smelting the mixture of two concentrate, ferronickel can be made from the two types of laterite ores.It's shown that raising slag temperature will enhance reaction speed as well as it's shown reduce the partition coefficient of S in ferronickel. The partition coefficient of S in ferronickel is elevated by augmenting reductant content, but desulphurizing reaction speed can be achieved at higher temperanture due to more reductant. The optimal content of coke ranges between 7.5% and 10.0%. The desulphurizing is improved with an increase in basicity within the stated range. But too high basicity leads to higher viscosity gradient, worsing desulphufizing conditions. The optimal desulphuritation occurs in 1.0～1.1 basicity. The effect of MgO on desulphurizing was investigated; the proper content of MgO can accelerate desulphurizing. The optimal content of MgO is recommended at 10% and 18% range for JCH-2 and JCH-4 respctively. And higher content of A1203 was harmful for desulphurizing due to higher viscosity of salg.