Novel Process And Mechanisms Of Preparing Ferronickel Materials From Nickeliferous Laterite Ores

Nickel, which is an important strategic metal material with properties of antioxidation, corrosion resistance, high temperature resistance, high strength and ductility, has been widely used in modern industry. Nickel is mainly consumed in stainless steel, accounting for about 66% of the worldwide nickel production. The stainless steel apparent consumption was 82.2 million tons, and the production of crude stainless steel output reached to 88 million tons in China 2009, which ranked first in the world. The apparent production consumption increased by 14.77%, while the production of crude stainless steel output increased by 10.55% ranging from 2007 to 2009. The rapid development of stainless steel industry is resulting in the increasing demand for nickel.Nickeliferous laterite accounts for 72% of the world land-based nickel resources, however, only accounts for 42% of the world nickel production. Thus, in the long run, nickeliferous laterite will be the main resources for nickel prodution. It's an effective route to prepare low-cost ferronickel as materials for the rapid developing stainless steel industry from nickeliferous laterite, as the cost of nickel occupies 70% of the cost of austenitic stainless steel, to greatly reduce the cost of stainless steel.In this paper, physicochemical properties of nickeliferous laterite, direct reduction-magnetic separation process and strengthening mechanism of additives were investigated using X-ray diffraction, X-ray fluorescence spectrum, optical microscope and scanning electron microscope (SEM) analysis etc. A novel process of preparing ferronickel as raw materials for stainless steel from nickeliferous laterite was developed and several conclusions were obtained as follows:(1) Thermodynamic analysis showed that NiO was more easy to be reduced than Fe3O4 and FeO, and accelerated the reduction of iron oxides to form NiFe2O4 with Fe2O3. T-4 reacted with MgSiO3 and Mg2SiO4 prior to T-2, while the product of them were in the same order of Na2Si205> Na2SiO3> Na2Mg2Si2O7> Na4Mg2Si3O10> Na2MgSiO4> Na4SiO4> Na2Mg2Si6O15.(2) The optimal conditions of the process of direct reduction followed by magnetic separation with addition of composite addictives were: reduction temperature 1,100℃, reduction time 60min, grinding fineness 92.6% passing 0.043 mm, magnetic field intensity 1kGs. A ferronickel with nickel grade of 7.49%, iron grade of 80.47%, and nickel and iron recovery of 82.7% and 62.8% respectively can be achieved. Ferronickel chemical analysis indicated that the content of P was very low, but S content was high, which were 0.004% and 0.49% respectively. However, the high content of S would not hinder the use of this ferronickel to produce stainless steel.(3) XRD analysis of reduction product showed that the Fe-Ni peak was intensified by the increase of reduction time and reduction temperature, however, not by the addition of T-4, T-2 or T-3. The formation of FeS by the reduction of T-2 weaken Fe-Ni peak, which was in favor of the separation of nickel and iron, while the formation of S lowered the surface tension and melting point and then promoted the aggregation and growth of ferronickel grain. T-4 rather than T-2 and T-3 would react with Mg2Si04 to free nickel and iron in which they were associated at 1100℃. Surface scaning of element showed that nickel and iron almost presented in the same area, so did magnesium,silicon and sodium with the addition of composite addictives (20% T-2,3% T-3, 7.5% T-4). Nickel is concentrated by the means of iron grain, however, there is sulfur in the area of iron due to embedding of adsorbing sulfur on the surface of iron.(4) The higher ratio of Fe/Ni of the laterite raw material, the higher recovery of nickel by magnetic separation. By the addition of high ferrous materials to the used laterite, nickel recovery was inproved. Paigeite used as additive not only improved overall iron content to benefit the recovery of nickel, but also replaced the addition of borax to weaken reduction swelling and improved the comprehensive utilization of paigeite resources.(5) The process of preparaing ferronickel as raw materials for stainless steel from nickeliferous laterite innovate the short process for production of ferronickel, without the process of pre-beneficiation, blast furnace, submerged arc furnace or arc furnace reduction and melting. The new technique can efficiently utilize the large amount of laterite resources to produce low cost ferronickel for stainless steel with high economic and application value.