Experimental Investigation On The Smelting Process Of Ferronickel From Mixed Two Types Of Laterite Ores

Nickel is one of the important alloying components in the production of stainless steels.In recent years,the demand for nickel has increased tremendously due to the wide utilization of stainless steel in industry and daily life.Nickel is mainly extracted from nickel sulfide and laterite?nickel oxide?ores.As sulfide ores and high-grade nickel resources are exhausted gradually,much attention has been paid recently to recovery of nickel from low-grade nickel laterite ore.Up to now,preparation of ferronickel alloy via direct reduction in rotary kiln?RK?followed by physical separation?magnetic or gravity separation?has been studied to produce ferronickel from nickel laterite ore.However,the specified process still has some problems with respect to the current studies,including low enrichment efficiency of nickel from laterite at low temperature??1250??.Elevating reducing temperature is beneficial to the reduction and aggregation of nickel,but lots of problems,such as high energy consumption,equipment corrosion and slag bonding phenomenon with refractory material still exist at high temperature??1400??.In order to solve the above problems,the additives?S,alkali salt and CaO et al.?are always used during reductive roasting for improving the growth of ferronickel granules,which would cause heavy environment pollution and equipment corrosion.As a result,based on the previous research,study on the smelting process of ferronickel from mixed two types of laterite ores was proposed to increase the enrichment efficiency as well as avoid the formation of ring in rotary kiln and slag bonding with refractory material.The study is financially supported by a key research project of National Natural Science Foundation of China?No.51234010?.In this study,the reduction mechanism of laterite ore was initially revealed.Then the feasibility and effectiveness of smelting mixed two different types of laterite ores was further investigated.Several conclusions were drawn as follows:?1?The thermodynamic analysis indicated that the liquid phase region of slag moves towards lower temperatures after adding limonitic laterite ore to garnierite laterite ore.The melting temperature of slag is reduced which is beneficial to the aggregation of ferronickel particles.The content of Ni in the ferronickel can be adjusted by controlling the proportion of reducing agent.When the mass fraction of carbon is 5.6%?C/O=0.80?,the content of Ni in the alloy is able to reach 10.05%.?2?The kinetics analysis indicated that the reduction of garnierite laterite ore with graphite can be divided into three stages.In the first stage??=0.1⁰.45?,the activation energy is small and gradually increases since the iron oxides are gradually reduced by solid carbon.The kinetic model fitted the two-dimensional diffusion function(g?7???8??28?^?_??1-?1-??^12??_?²).In the second stage??=0.45⁰.65?,the activation energy gradually decreases as the reaction of Boudouard occours intensely.The oxides were reduced by CO which was derived from the Boudouard reaction.The kinetic model fitted the three-dimensional diffusion function(g?7???8??28??_???1-??^-13-1^??_?²)at this stage.In the third stage??=0.65-1?,the activation energy is gradually increased.The FeO and complex compound orthopyroxene were reduced by CO in this stage.The equation(g?7???8??28??1-??^-1-1)which corresponds to chemical reaction mechanism gives the best fit.The phase analysis during reduction showed that the order of reducing iron oxides in laterite is Fe₂O₃?Fe₃O₄?FeO/?Mg_xFe_y?Si₂O₆?Fe.?3?The experimental investigation on the smelting process of ferronickel from mixed limonitic laterite ore and garnierite laterite ore showed that the reduction of laterite and the aggregation of ferronickel can be improved with elevating reducing temperature.And the contents of Ni,Fe in concentrate and their recovery ratios were increased with the increasing of reduction temperature.However,it is difficult to separate the samples from crucible due to the melting phenomenon of slag at the higher temperature.Therefore,the best temperature is at 1380?in this study.The melting temperature of slag after smelting can be decreased and the aggregation of ferronickel can be enhanced by adding limonitic laterite ore.However,too much limonitic laterite ore will result in the reduction of Ni content in the concentrate.The results also indicated that the content of Ni and Fe in the concentrate first increased and then decreased with the decreasing carbon content.In this study,a ferronickel product with8.08%Ni and 80.09%Fe was prepared via reductive roasting at 1380?C for 30 min with B/?A+B?proportion of 5%and the mass fraction of carbon is 6.0%?C/O=0.91?and then followed by wet magnetic separation.The corresponding recovery ratio of Ni reached up to 89.26%,and the briquette remained its original shape which is beneficial to discharge the pellet from crucible after reduction.The study on the preparation of ferronickel by smelting mixed two types of laterite ores is of great significant on deepening the understanding of reducing iron,nickel oxides under different conditions and its effect on the subsequent separation.Moreover,this study plays an important role in evaluating the novel process of smelting mixed two types of laterite ores,optimizing the current processes as well as developing a new route for utilizing nickel laterite ore via direct reduction followed by gravity or magnetic separation.