Microwave carbothermic reduction roasting of a low grade nickeliferous silicate laterite ore

The known resources of nickel sulphide ores are quickly diminishing and in order to satisfy future nickel demands, nickel laterite deposits are being investigated as an alternative. Currently, expensive leaching and smelting processes are used to process the nickel laterite ores. The objective of the present research was to produce a high grade nickel concentrate via microwave carbothermic reduction roasting followed by magnetic separation. A thermodynamic model was developed for the roasting process in order to determine the optimum experimental conditions. The experimental variables investigated were: microwave energy and argon shrouding for the reduction tests and the magnetic field strength for the concentration stage. The behaviours of nickel and cobalt were studied in the reduction and magnetic separation processes. By optimizing the reducing and magnetic separation conditions, a high grade concentrate containing 9.2% nickel with a nickel recovery of 88.8% was achieved.     

Use of oxidation roasting to control NiO reduction in Ni-bearing limonitic laterite

Use of limonitic laterite as an iron source in conventional ironmaking is restricted due to its gangue composition and small particle size. Even direct reduction cannot effectively produce direct reduced iron (DRI) because NiO would be reduced together with iron oxide to form Fe–Ni. A small amount of Ni (about 2 wt.%) in DRI degrades the physical properties of final steel products. The current study investigated how oxidation roasting of limonitic laterite ores affected NiO reduction, with the goal of producing Ni-free DRI and Ni-bearing slag. Ni-bearing slag can be a good secondary Ni resource. Oxidation roasting made NiO inert under H₂ reduction at 900 °C by forming Ni-olivine. Optimum roasting temperature was proposed by examining phase transformation of limonitic laterite ores during heating and by FactSage calculation of the equilibrium Ni fraction in Ni-bearing phases. Furthermore, the effect of Mg–silicate forming additives on the control of NiO reducibility was clarified to maximize the suppression of NiO reduction. Among various additives such as MgSiO₃, Mg₂SiO₄ and Fe–Ni smelting slag, Ni-free olivine-typed flux was found to be the most effective form of Ni-olivine because Ni–Mg ion exchange between Ni-bearing phase and Ni-free olivine occurs more readily than other Ni-olivine formation schemes. Finally, the mechanism of Ni-olivine formation during roasting was studied using a diffusion couple test. Calculated diffusivity values of Ni in Mg₂SiO₄ indicated that the two major routes of Ni-olivine formation while roasting limonitic laterite ore are (1) Ni partitioning within Mg–Ni silicate before crystallization and (2) Ni diffusion from spinel to Ni free olivine after crystallization.     

硫化钠对硅镁型红土镍矿气基还原焙烧的影响

镍是一种重要的战略金属,随着优质硫化镍矿日益匮乏,资源丰富的红土镍矿成为重要的提镍原料。本文以红土镍矿为研究对象,甲烷为还原剂,硫化钠为添加剂,考察了还原温度、甲烷浓度、还原时间及添加剂用量对镍、铁金属化率的影响,并通过扫描电子显微镜与能量色散光谱(SEM-EDS)分析对还原产物中镍铁的聚集情况进行了研究。结果表明：在还原温度900℃、还原时间60min、甲烷浓度20％、硫化钠添加量10％的条件下,还原产物中的镍、铁金属化率可分别达到89.05％、5.10％。硫化钠的加入促进了镍铁颗粒的聚集长大,有利于镍铁颗粒与杂质的分离,同时生成的FeS抑制了铁的深度还原,实现了镍的选择性还原。     

褐铁矿型红土镍矿硫酸高压浸出的研究

研究了褐铁矿型红土镍矿硫酸高压浸出过程中浸出温度和时间、硫酸用量对镍、钴、锰、铁、铝、镁、硅、铬浸出的影响。在浸出温度为250℃,浸出压力3.9 MPa,浸出时间为40 min,硫酸用量240kg/t干矿的优化条件下,镍,钴,锰的浸出率分别为96.8%,96.6%,98.7%,铁、铝、镁、硅的浸出率分别降低到2.6%,16.9%,61.8%,1.9%,铬的浸出率降低到0.7%,浸出液中的铬以Cr~(3+)的形式存在,浸出液中没有Cr~(6+)。静置分离试验表明,在此浸出条件下的浸出矿浆固液分离效率较高。扫描电镜分别对30、40、60 min浸出渣相微观形貌的分析表明,浸出30 min时针铁矿中Fe~(3+)绝大部分溶出并经过水解重新沉淀,延长浸出时间只是使铁相的等粒-圆粒状颗粒分布趋于均化。浸出渣相的主要成分为Fe_2O_3,(H_3O)Al_3(OH)_6(SO_4)_2,KAl_3(SO_4)_2(OH)_6及Si O_2。     

The effect of sodium sulphate on the hydrogen reduction process of nickel laterite ore

A series of nickel laterite ores with different calculated amounts of anhydrous sodium sulphate were prepared by physical blending or sodium sulphate solution impregnation. The reduction of the prepared nickel laterite ore by H₂ was carried out in a fluidised-bed reactor with provisions for temperature and agitation control, and the magnetic separation of the reduced ore was performed using a Davis tube magnetic separator. The mineralogical properties of the raw laterite ore, reduced ore and magnetic concentrate were characterised using ICP, TG–DSC, N₂ adsorption, X-ray diffraction and optical microscopy. The catalytic activity of sodium sulphate was also studied by using Hydrogen temperature-programed reduction. The experimental results indicate that Na₂SO₄ could overcome the kinetic problems faced by the laterite ore and that it exhibited noticeable catalytic activity only if the temperature reached at least 750 °C. This high temperature accelerated the crystal phase transition of the silicate minerals and increased the utilisation of H₂. In comparing the results from the two different methods for adding Na₂SO₄, the nickel content and recovery of the magnetic concentrate were increased by using the impregnation method rather than the physical blending method and the increasing amount of sodium sulphate assisted in the further beneficiation of nickel. The partial pressure of H₂ and the reducing time also affected the reduction process of the iron oxides. The results of the microscopic study indicated that the formation of a Fe–S solid solution, which was derived from the SO₂ sulphide reduction of FeO, was conducive to mass transfer and accelerated the coalescence of metallic ferronickel particles. For the nickel laterite ore, under the synergistic effect of sodium sulphate and hydrogen, a nickel content and nickel recovery of 6.38% and 91.07% were obtained, respectively, with high product selectivity.     

Chemical and mineral transformation of a low grade goethite ore by dehydroxylation,reduction roasting and magnetic separation

The utilization of abundant low grade goethite (α − FeOOH) ores is potentially important to many countries in the world, especially Australia. These ores contain many detrimental impurities and are difficult to upgrade to make suitable concentrates for the blast furnace. In this paper, chemical and mineral transformations of a goethite ore were studied by dehydroxylation, reduction roasting in CO and CO₂ gas mixtures, and magnetic separation. The goethite sample was taken from a reject stream at an iron ore mine from the Pilbara region, Western Australia. The roasting temperature range investigated was 400–700 °C. Chemical and mineralogical analysis was conducted using XRF, XRD, optical microscope, EPMA, and SEM. Magnetic separation was conducted using a Davis tube tester and a high intensity magnetic separator.The results show that reduction roasting can remove moisture and impurities but does not significantly change the Fe content in the feed. However, reduction roasting transforms goethite to hematite and eventually maghemite which can be recovered by magnetic separation, allowing upgrading. Further studies are needed to optimize the reduction roasting and correlate it with the magnetic separation to maximize the efficiency of iron upgrading.     

The reduction of nickel from low-grade nickel laterite ore using a solid-state deoxidisation method

The reduction of nickel from low-grade nickel laterite ore using a solid-state deoxidisation method was studied. The effects of temperature, time, reductant type and CaO content on the conversion percentage of the total nickel to metallic nickel (α_Ni) in the nickel laterite ore reduction process were investigated. The results showed that α_Ni was strongly influenced by the reaction temperature in both gas–solid and solid–solid reduction processes, and a higher temperature was more favourable for nickel reduction. Because the reduction mechanism of nickel laterite ore (NiO + CO → CO₂ + Ni) is indirect, a higher α_Ni (>80%) can be obtained by increasing the CO and anthracite content. In the gas–solid reduction process, a longer reaction time favoured nickel reduction, and the conversion percentage decreased when a gaseous reductant was used at 850 °C because of phase transformation. In the solid–solid reduction process, the conversion percentage of the total nickel to metallic nickel first increased and then decreased with increasing reduction time and CaO content. In both reduction processes, taenite was found by XRD in the reduced ore because of iron oxide reduction and metallic nickel formation. SEM revealed that the nickel laterite ore was transformed from large granular and sandwich structures to small granular and flocculent structures during the reduction process.