Effect of microwave pre-treatment on ultramafic nickel ore slurry rheology

Low-grade ultramafic nickel ores, while representing a large potential nickel resource, are difficult to process due to their high serpentine content. Serpentine is anisotropic and the mineral particles tend to be non-spherical, resulting in challenging slurry rheology. In general, suspensions of serpentine minerals have high viscosity and yield stress, which can be detrimental in comminution and flotation operations. It is proposed that ultramafic nickel ores be treated with microwave radiation prior to grinding in order to reduce slurry viscosity and yield stress. The rheology of two different ultramafic nickel ores, before and after microwave pre-treatment, was characterized in this work. Serpentine minerals were found to dominate the rheology of the untreated ultramafic nickel ores, with the ore containing minor chrysotile exhibiting higher viscosity and yield stress than the ore containing strictly lizardite serpentine. Microwave pre-treatment was found to greatly reduce the shear viscosity (average 80% reduction at 200 s⁻¹) and direct yield stress (peak yield stress reduced by 92–93%) of ultramafic nickel ore slurries. The reduction in slurry viscosity and yield stress of the ore slurries as a result of microwave pre-treatment was attributed to the conversion of serpentine to olivine.     

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.     

Effect of saline stress on fungi metabolism and biological leaching of weathered saprolite ores

Biological leaching of nickel laterite ores is based on the use of heterotrophic microorganisms and their metabolic products to dissolve nickel and cobalt from oxide minerals. High salinity of water supplies and soils in the vicinity of nickel laterite ore bodies can be a major challenge in the application of bio-leaching process in situ. Salt stress can imbalance the osmotic potential in fungi cells generating a water deficit and the influx of sodium may lead to metabolic toxicity. The purpose of this study is to examine salt tolerance development of Aspergillus foetidus using gradual acclimatization technique to salt concentrations up to 2% and to assess the use halotolerant microorganisms in leaching weathered saprolite ores under saline conditions. It has been observed that salinity stress affects the growth but not the energy metabolism of the organism. Kinetic of metal leaching, nature of secondary reactions and metal dissolutions were also influenced by salt stress.     

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.     

Reductive dissolution of ferric iron minerals: A new approach for bio-processing nickel laterites

Nickel laterites represent the major ore reserves of this base metal present in the lithosphere. However, processing these ores by conventional technologies involves considerable energy or reagent expenditure and consequently is less cost-effective than extracting nickel from sulfide ores. Biological options, using metal-complexing organic acids and mineral acids generated by fungi and bacteria, have been investigated but generally found to be ineffective in terms of extraction dynamics or yields. We have examined the possibility of using bacteria that can bring about the reductive dissolution of ferric iron minerals and thereby facilitate the extraction of nickel from a lateritic ore at relatively low (<30-45 °C) temperatures.Four species of iron-reducing acidophilic bacteria were screened for their abilities to solubilise nickel from a limonitic laterite ore in which the major iron mineral present was goethite. One of these (Acidithiobacillus ferrooxidans) was selected for further study only the basis of it being able to use a cost-effective energy source (elemental sulfur) to mediate the dissolution of goethite at mildly acidic conditions (pH < 2). Cultures were set up in 2 L bioreactors, maintained at pH 1.8 (±0.1) and 30 °C, and initially aerated (to promote growth of the bacteria on sulfur) and then switched to anaerobic conditions when nickel laterite ore (crushed to <6 mm, with a nickel grade of 0.5%) was added. Over 70% of the nickel present in the ore was solubilised within 14 days, and solubilised metals remained in solution due to the low pH of the leachate. In contrast, only 10% of the nickel was solubilised (by non-reductive acid dissolution) when the cultures were continuously aerated. The results suggest that biological processing of limonitic nickel laterites is technically feasible and, more generically, that reductive dissolution can be used to bioprocess ferric oxide mineral ores.     

印尼某低品位红土镍矿的热解性能

为提高红土镍矿火法冶炼工艺技术指标,对印尼某低品位红土镍矿进行了热解性能分析。结果表明：该红土镍矿属于典型的低品位过渡层红土镍矿,主要组成矿物为利蛇纹石、针铁矿、石英、铁蛇纹石、叶蛇纹石和高岭石,镍主要赋存于蛇纹石、橄榄石等硅酸盐类矿物中,部分以氧化镍形式赋存于针铁矿中。红土镍矿热解分析结果表明：在86 ℃时有1次失重过程,形成1个吸热峰,有H2O溢出,对应自由水的脱除;在268 ℃时有1次失重过程,形成1个吸热峰,有H₂O溢出,对应针铁矿的脱羟基过程;在589 ℃时发生失重,形成1个吸热峰,有H₂O溢出,对应高岭石、利蛇纹石的脱羟基反应;在816 ℃时有1个放热峰,而红土镍矿质量没有变化,对应利蛇纹石热解产生无定型的硅酸盐重结晶后产生镁橄榄石（Mg₂SiO₄）及顽火辉石（MgSiO₃）的过程;在1 126 ℃时有1次失重过程,有CO₂溢出,由白云石分解产生。试验结果对红土镍矿火法工艺的改进有指导作用。     

红土镍矿资源现状及工艺综述

综合论述了世界红土镍矿的资源概况和利用现状,分析了我国对镍的需求情况,对红土镍矿的处理方法和目前有前景的加工工艺进行了较为详细的阐述和分析。     

Calcination of low-grade laterite for concentration of Ni by magnetic separation

With the continuous depletion of high-grade nickel ores such as millerite and niccolite, nickeliferous laterites have become the major source for the production of nickel metal. However, only 42% of the world’s production of nickel comes from laterites, since the concentration of Ni is relatively low (ca. 2 wt.%). In addition, other metals, such as magnesium, iron and silicon can be found in laterite, which make the concentration of nickel even more difficult.In this study, a low-grade nickeliferous laterite ore was first calcinated and then processed by using a wet magnetic separator in order to recover nickel. Since, the ore contains both Ni and Fe, the calcination of laterite is effective in altering the crystalline structure of Fe species and therefore its magnetic properties, which in turn enable the selective concentration of nickel by magnetic separation that is an easy and environmentally-friendly technique. The experimental results have indicated the importance of carefully controlling: (1) the calcination temperature; (2) the pulp density and (3) applied magnetic field strength. The main finding of this work was that magnetic separation is effective in recovering 48% of nickel from laterite, increasing the Ni grade in the recovered product from 1.5% to 2.9%, when prior to the separation the ore was calcinated at 500 °C for 1 h.     

红土镍矿资源现状及其冶炼工艺的研究进展

随着硫化镍矿资源的逐渐减少,高效低成本地开发红土镍矿资源以满足逐渐增加的镍需求有着重要意义。介绍了世界红土镍矿资源现状和特点,并阐述了目前红土镍矿处理的火法工艺、湿法工艺以及其它工艺技术的研究现状及进展,同时分析了这些处理方法的优势与不足,指出了未来的发展方向,以期为低品位红土镍矿的开发提供参考。     

Microwave heating behaviour of nickeliferous limonitic laterite ores

The nickeliferous laterite ores, in which the nickel occurs in oxide form, represent a significant potential resource of metallic nickel. However, in comparison to the nickel-containing sulfide ores, the extraction costs are relatively high and thus it will be necessary to develop new processing techniques, which are both technically and economically viable. In the present research, the potential application of microwaves for the heating of a nickeliferous limonitic laterite ore ((Fe,Ni)O(OH) · nH₂O) was investigated. Firstly, since the nickeliferous limonitic laterite ore contains considerable moisture, both free and combined, then thermogravimetric analysis (TGA) was performed in order to characterize the changes, which result from the dehydration processes. Derivative thermogravimetric analysis (DTGA) curves were calculated from the TGA data. Secondly, the real (ε^′) and imaginary (ε^″) permittivities of the ore were measured at frequencies of 912 and 2460 MHz at temperatures up to about 1000 °C using the cavity perturbation technique and these results were related to the DTGA curves. Also, the loss tangent (tanδ=ε^″/ε^′) was calculated from the permittivity data. Finally, the microwave heating behaviour of the nickeliferous limonitic laterite ore was determined at 2460 MHz.The results show that the both the real (ε^′) and imaginary permittivities (ε^″) and the loss tangent (tanδ) increase with temperature and change as both the free and the combined moisture are removed. The permittivities (ε^′ and ε^″) increased with increasing slope of the TGA curve and vice versa during the goethite to hematite dehydroxylation reaction, where there was a maximum in the permittivities (ε^′ and ε^″). It is proposed that these changes, which occur during the dehydroxylation reaction, are a result of the liberation of hydroxyl units from the goethite structure. Furthermore, some hydroxyl units were retained in the hematite structure (i.e. hydrohematite (α-Fe_2−x/3O_3−xOH_x)) even after the goethite to hematite transition and thus the permittivities of the dehydroxylated ore were higher than that of normal hematite. With regards, to their microwave heating behaviour, it is shown that despite the relatively low permittivities (ε^′ and ε^″) of these materials at low temperatures, they can be heated using microwaves. The microwave heating process can be improved by conventional preheating of the sample or by the addition of charcoal as a susceptor or by selecting a crucible material, which acts as a susceptor. There is a rapid increase in the permittivities over the temperature range of about 600–800 °C and this combined with the low thermal conductivities of these oxides, can result in rapid internal heating of the sample and thermal runaway.     

Thermodynamic analysis of the carbothermic reduction roasting of a nickeliferous limonitic laterite ore

As the sulfide ore deposits become less economically viable as a source of nickel, increasing attention is being paid to the nickeliferous laterite ores. However, in contrast to the sulfide ores, these oxide ores cannot be as easily concentrated by current technologies. Consequently, considerable research effort is being directed at developing new techniques for beneficiating the nickeliferous laterites. The pyrometallurgical production of a high-grade ferronickel alloy using a low cost carbonaceous reductant at relatively low temperatures is particularly attractive. In the current research, a thermodynamic model has been developed to aid in the understanding of the carbothermic reduction roasting process as a potential upgrading method for the nickeliferous limonitic laterite ores. The effects of process parameters such as temperature and reductant to ore ratio on the grade of the ferronickel alloy produced and the nickel recovery in the alloy have been studied. The thermodynamic predictions are shown to be in general agreement with the experimental results currently available in the literature.     

Rheological behaviour of lateritic smectite ore slurries

The characterisation and rheology of several nickel laterite smectite ores and pure minerals are compared to assess the effect of mineralogy and particle size on the viscosity of high pulp density slurries. A vane viscometer was used to determine the “optimum pulp density” (OPD) that gave a yield stress of 100 Pa which is considered to be optimal for pumping slurries into autoclaves in the HPAL process. In general, slurries containing finer particles were more viscous and smectite slurries exhibited poor rheological behaviour as compared to slurries of goethite < kaolin < talc < hematite < maghemite < magnesite. Blending the smectite ores with a fraction of the pure minerals improved the rheological behaviour of the pulp and can increase the optimum pulp density of the smectite blend by over 5% w/w.When the physical properties of the smectite ore and slurry were examined, a very good linear correlation was obtained between the optimum pulp density and the settling density which provides a simple measure of predicting rheological behaviour of slurries. The variation in the viscosity of the nickel laterite ores depends largely on their mineralogy and particle size distribution. The mean particle size and P₈₀ values of various smectite ores containing the same mineral phases were also found to have a reasonably good linear correlation with OPD in saline water, but the correlation of ore surface area with OPD was a poorer fit.     

基于BP神经网络技术的红土镍矿还原焙烧-磁选工艺条件的优化

还原焙烧—磁选工艺可有效提取红土镍矿中的镍和铁等有价金属,由于影响红土镍矿还原焙烧—磁选效果的因素较多,导致工业生产中的选矿指标不稳定。为进一步提高还原焙烧—磁选工艺处理红土镍矿的效果,本研究以青海某镍矿为原料,采用正交试验与BP神经网络相结合的方法,对还原焙烧—磁选工艺的还原剂用量、焙烧温度、料层厚度、焙烧时间及磁场强度等因素进行了优化。结果表明:通过BP神经网络模型优化后的试验条件为还原剂用量9.5%、焙烧温度1 070℃、料层厚度10.0 mm、焙烧时间65 min及磁场强度2.5 kA·m-1,在此条件下可获得产率为30.29%的镍粗精矿,比采用正交试验最优因素组合条件所得的镍粗精矿产率提高了2.83%。      

镍矿的处理工艺现状及进展

镍矿是国民经济中一种重要的金属矿产资源,随着经济的发展,人们对镍矿资源的消耗呈逐年上升趋势。目前所查明的镍矿资源中,有近70%的镍矿资源都是硫化镍矿,近30%的镍矿资源属于红土镍矿。随着镍矿资源查明储量的下降,其镍矿资源的综合利用受到越来越多国家的重视。在查阅大量文献的基础上,简要的论述了镍矿资源的总体情况,概述了硫化镍矿常规的处理方法,以及近年来浮选法的一些实际应用及发展。最后,介绍了当前状况下红土镍矿的火法和湿法处理工艺现状及进展,以及一些其他处理镍矿石的方法。为以后镍矿石资源的综合利用和处理工艺的研究提供了一定的参考价值。     

Recovery of nickel from lateritic nickel ore using Aspergillus niger and optimization of parameters

The present study deals with the extraction of nickel from lateritic nickel ore of Sukinda mines, Orissa, through microbial leaching using Aspergillus niger. The presence of significant metals in oxidic nickel ores, are potential sources of nickel for the future. Thus, experiments were carried out with ore to optimize the conditions for maximum nickel recovery. Experiments designed as per central composite design technique, were carried out for fitting an empirical reduced second order model. The factors studied were sucrose concentration, pulp density, temperature and duration. In addition to main effects of four factors, sucrose concentration, pulp density and duration had quadratic effect on the percentage extraction and there were interactions between different factors also. There was also significant interaction between temperature and duration as well as sucrose and pulp density. The F-value for the model shows that model is significant at less than a 0.01% level (i.e. at 99.99% confidence level). The predicted maximum nickel extraction was 31.34% with a pulp density of 8.75%, sucrose concentration of 10.04 g/l, temperature 33.8 °C and duration of 37.5 days.     

Effect of sulfur on the mineral phases of laterite ores at high temperature reduction

Recovery of nickel and cobalt from nickel laterites processed according to the Caron process is hampered by reduction of iron in limonite ores and formation of fosterite in saprolite ores. The Caron process involves the reduction of the ores at temperatures between 700 and 800 °C followed by ammoniacal leaching. The presence of sulfur has been found to markedly improve the Ni and Co recoveries from laterite ores. In this study, limonite and saprolite laterite ores were reduced in the presence of an activator, in the form of elemental sulfur. The mineral phases resulting from the reduction, both in the presence and absence of sulfur were related to recoveries and selectivity obtained from laboratory reduction and leaching tests. The mineral phases were examined using X-ray diffraction with a synchrotron radiation source. The role of sulfur and the history of reduction in effecting the increase in recovery and selectivity of nickel and cobalt was investigated in this study.     

红土镍矿酸浸渣综合利用进展

近年来随着不锈钢及新能源用镍需求的增长,红土镍矿湿法提镍工艺得到更多应用,相应的红土镍矿酸浸渣堆存量也迅速增加,对此类固废进行科学消纳和资源综合利用迫在眉睫。针对红土镍矿酸浸渣有害元素硫、有价金属铁含量高的特点进行综合利用新技术、新装备研究对红土镍矿湿法冶金工业的持续发展具有重要的理论和现实意义。本文主要介绍红土镍矿酸浸渣的湿法冶金形成过程及其成分组成和物理化学性质,较为系统地梳理了红土镍矿酸浸渣在尾矿坝堆积、地下压滤回填和深海填埋等直接处理方法,提取利用铁、铬、铝、稀土等有价金属资源,消纳制备硅藻土、陶粒、矿物纤维等建筑材料、制备锂电池电极、沸石等高附加值材料综合利用技术上的研究进展,展望了红土镍矿酸浸渣流态化降硫提铁技术及装备的发展前景。     

赣南某红土镍矿工艺矿物学研究及选矿方案论证

为了查清矿石性质,制定合理的选矿方案,本研究采用荷兰PHILIPS XL300型扫描电镜(SEM)、电子探针、电子显微镜等先进测试仪器对赣南某红土镍矿进行了详细的工艺矿物学研究,研究表明,该矿石矿物组成复杂,矿物种类繁多,其中镍矿物多呈分散状态分布于钴镍蛇纹石、含钴镍磁铁矿、含镍铬铁矿中,独立镍矿物仅有红砷镍矿、斜方砷镍矿,含量甚微,且粒度很细,不能用机械选矿方法予以富集,只能采用化学选矿或冶炼富集方法来提取镍,综合分析提出采用酸浸工艺进行提镍.     

红土镍矿处理工艺研究现状

随着世界上硫化镍矿资源日趋枯竭以及未来镍需求量不断增长,红土镍矿将成为未来镍的主要来源,因此红土镍矿的有效处理以及高效利用对我国的经济建设有着极大的意义。红土镍矿由于其具有储量丰富、易开采、便于运输等特点,已成为研究开发的热点。本文主要从不同矿层的红土镍矿角度,介绍了当前不同红土镍矿冶炼方法和技术,概述了不同矿层的红土镍矿及其适用的冶炼工艺,分析了不同红土镍矿处理工艺的优势与不足,实现不同类型红土镍矿的综合利用。