Research On Direct Reduction Process Of Low-grade Laterite Nickel Ore Pellets

With the increase of demand for nickel and nickel sulfide ore resources is less, development and utilization of laterite nickel ore is particularly important. A company in Pan Zhi Hua use Indonesia Philippines laterite nickel ore as raw material, choose rotary kiln direct reduction-electric furnace deep reduction, melting points and process production of nickel and iron, the production line run smoothly, and obtained a lot of experience, rough nickel ferroalloy product quality is stable. Nonetheless, there are still some problems to be solved in production:(1) The law of laterite nickel ore direct reduction to be in-depth study, in order to give a more reasonable direct reduction technology parameters, in a relatively short time, low energy consumption under the access to meet the demand of metalized pellets.(2) Secondary pulverization of pellets reduction process likely to cause ring kiln body, the higher pulverization rate cause the harmful influence on the subsequent deep reduction operation, so studying the cause of the secondary pulverization of pellets reduction, increased the strength of pellets, reduced pulverization method is necessary.According to the above problems, carried out a series of research work:(1) Determination of pellet heat softening point, determination of pellets inflation, the measurement of the compressive strength and falling strength for wet and dry bulb. The experiment concluded:The high temperature softening point of pellets is1150℃; Pellets shrinkage rate reached the maximum at1100℃, its value is8%; The suitable addition amount of bentonite is6%, wet and dry ball drop strength were6.3times/ball and8.5times/ball, compressive strength were21.56N/ball and174.44N/ball; Suitable addition amount of moisture is8%, the drop strength and compressive strength of wet ball were6.8times/ball and24.5N/ball.(2) Using DTA-TG study the dehydration and reduction process thermodynamics of raw material, determining the various stages of the reaction and the reaction mechanism. The reduction of thermodynamic analysis shows:NiO is began to restore metal Ni when the temperature reaches452℃. By X-ray diffraction (XRD) analysis of mineral composition, serpentine(Mg,Fe,Ni)3Si2O5(OH)4as main consisting of laterite nickel ore minerals, the thermal decomposition products for serpentine were forsterite and enstatite by calcination. At the same time, the nickel and magnesium turn into forsterite and enstatite phase. Therefore, it is difficult to separate nickel by physical method.(3) Come to the conclusion through nickel and iron to grow up and gathered, the situation of nickel and iron grade and recovery:Carbon content is4%, content of CaO is20%, the reduction temperature is1300℃for60min, the grinding fineness of roasting mineral was passing0.074mm, the intensity of magnetic field was1000Gs. The grade of nickel and iron can reach to7.29%and69.19%and the recovery rate reach to95.05%and91.7%under these conditions.(4) In order to get better reduction effect, the tests try to join FeS, Na2B4O7.10H2O as composite additives. The results are shown as follow:When the content of CaO is10%, the content of FeS is6%, with2%Na2B4O7.10H2O, the grade of nickel and iron can reach to8.47%and88.65%; When the content of CaO is14%, content of FeS is5%, with2%, the recovery rate of nickel and iron can reach to83.53%and98.96%;...