Nickeliferous Limonitic Laterite Ore Research Articles

Mechanism of carbothermic reduction of a sulfur-containing nickeliferous limonitic laterite ore

ABSTRACT An increasing amount of nickel is currently being extracted from the nickeliferous laterite ores, rather than from the sulfide deposits. Consequently, new processes are being developed to extract the nickel from these ores and selective reduction is one possibility. In these processes, it has been shown that the addition of sulfur can improve the grade and/or the recovery. In the current work, the mechanism of the carbothermic reduction of a sulfur-containing nickeliferous limonitic laterite ore was investigated by utilising TGA/DTA and both thermodynamic and kinetic analyses. It was found that, in addition to dehydroxylation and reduction, the reaction sequence also consisted of the following major stages: (1) conversion of pyrite to pyrrohtite and (2) subsequent desulfurisation. Analyses of the reacted samples showed that both the particle size and the amount of ferronickel increased with both particle growth temperature and retention time at temperature. The thermodynamic predictions were in general agreement with the experimental findings and were consistent with the postulated formation of an iron-sulfur-oxygen solution.

Thermodynamic Analysis of the Selective Reduction of a Nickeliferous Limonitic Laterite Ore by Hydrogen

AbstractNickeliferous limonitic laterite ores are becoming increasingly attractive as a source of metallic nickel as the costs associated with recovering nickel from the sulphide ores increase. Unlike the sulphide ores, however, the laterite ores are not amenable to concentration by conventional mineral processing techniques such as froth flotation. One potential concentrating method would be the pyrometallurgical solid state reduction of the nickeliferous limonitic ores at relatively low temperatures, followed by beneficiation via magnetic separation. A number of reductants can be utilized in the reduction step, and in this research, a thermodynamic model has been developed to investigate the reduction of a nickeliferous limonitic laterite by hydrogen. The nickel recovery to the ferronickel phase was predicted to be greater than 95 % at temperatures of 673–873 K. Reductant additions above the stoichiometric requirement resulted in high recoveries over a wider temperature range, but the nickel grade of the ferronickel decreased.

Factors Affecting the Upgrading of a Nickeliferous Limonitic Laterite Ore by Reduction Roasting, Thermal Growth and Magnetic Separation

There is considerable interest in the development of new processes to extract the nickel from the oxidic nickeliferous laterite deposits, as the global nickel sulphide resources are rapidly becoming more difficult to access. In comparison to sulphide ores, where the nickel-containing mineral can be readily concentrated by flotation, nickel laterites are not amenable to significant upgrading, due to their complex mineralogy. In this paper, firstly, a brief overview of the conventional techniques used to process the nickeliferous limonitic laterites is given, as well as a review of current research in the area. Secondly, a thermodynamic model is developed to simulate the roasting process and to aid in the selection of process parameters to maximize the nickel recovery and grade and also to minimize the magnetite content of the concentrate. Thirdly, a two-stage process involving reduction roasting and thermal growth in either a tube furnace or a rotary kiln furnace, followed by magnetic separation, was investigated. Thermogravimetric, differential thermal and mineral liberation analyses techniques were utilized to further understand the process. Finally, the nickel grades and recovery results were compared to those available in the literature.

Extraction of nickel and cobalt from nickeliferous limonitic laterite ore using borax containing slags

The diminishing availability of nickel sulfide ores and the increasing demand for nickel and its compounds have led to a growing interest in laterite deposits as an alternative source for producing nickel. However, extracting nickel from laterite ores differs from sulfides because nickel contained minerals are generally disseminated throughout the ore. Laterites cannot be concentrated using classic mineral processing techniques such as flotation.The present study proposes a new smelting process for limonitic nickeliferous laterite ore in order to separate nickel and cobalt from the ore and produce a nickel matte at lower smelting temperature compared with the current industrial techniques. The nickel and cobalt recoveries were evaluated at various flux additions. The highest recovery condition for Ni (98% Ni recovery with Ni content of 10wt%) was achieved with the addition of 27g of flux (50%Na2CO3+35%Na2B4O7·10H2O+15%SiO2), 0.8g coke and 5g elemental sulfur to 25g of the roasted ore. The above conditions led to achieving 95% Co recovery with 0.06% Co.

Thermodynamic analysis of selective reduction of nickeliferous limonitic laterite ore by carbon monoxide

The nickel sulphide ore deposits are becoming more expensive to mine, and increasing attention is being paid to the recovery of the nickel from the nickeliferous laterite ore deposits. In contrast to the sulphide ores, these oxide ores cannot be beneficiated by flotation or other conventional mineral processing techniques. One potential concentrating method would be the solid state pyrometallurgical reduction of the ore followed by upgrading using magnetic separation. In this research, a thermodynamic model has been developed in order to investigate the solid state reduction of a nickeliferous limonitic laterite ore by carbon monoxide. The objective was to recover all of the nickel as a high grade ferronickel and convert the goethite (FeO·OH) to wüstite (FeO), so that the ferronickel could be recovered by subsequent magnetic separation. For the calcined ore, at the stoichiometric carbon monoxide/ore ratio of 0.558 kmol/100 kg, nickel recoveries of ∼98% and nickel grades of ∼65% were possible at an optimum reduction temperature of 660°C. The results showed that the nickel recovery and the grade of the ferronickel depended on the reduction temperature and the reductant/ore ratio. For the uncalcined ore, the recoveries were slightly lower and the grades slightly higher due to the increased oxidation potential.

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.

Reducibility of nickeliferous limonitic laterite ore from Central Anatolia

Limonitic nickel laterite from Sivrihisar reserve in Turkey was reduced at 700–1100°C by the addition of 5·74, 8·61 and 11·48 wt-% coal under an argon atmosphere. The run-of-mine ore and the reduced samples were studied using X-ray diffraction. The metallisation of Fe was found to be limited up to 900°C, but increased rapidly at higher temperatures. The metallisation of Ni and Co increased when the temperature was increased from 700 to 800°C, almost levelled off up to 900°C and then increased up to 1100°C. The results also showed that increased coal additions did not affect Fe metallisation up to 900°C. At 1000°C the metallisation of Fe became slightly better, but its effect was more pronounced at 1100°C. The increased coal addition affected the nickel reduction equally at all temperatures, while it had no effect on the metallisation of Co.La réserve de nickel limnétique en Turquie a été réduit à 700-1100 ° C par l'addition de 5.74, 8.61 and 11.48 wt-% de charbon sous atmosphère d'argon. Le minerai et les échantillons réduits ont été étudiés par DRX. La métallisation de Fe a été jugée limitée à 900 ° C, mais elle a augmenté rapidement à des températures plus élevées. La métallisation de Ni et Co a augmenté lorsque la température a été augmentée de 700 à 800 ° C, presque stabilisé jusqu'à 900 ° C puis 1100 ° C. Les résultats ont également montré que l'augmentation des ajouts de charbon n'a pas affecté Fe métallisation jusqu'à 900° C. A 1000 ° C, la métallisation de Fe s'est un peu ameliorée, mais son effet était plus prononcé à 1100 ° C. L'augmentation du taux de charbon a affecté une constante réduction de nickel à toutes les températures, alors qu'il n'a eu aucun effet sur la métallisation de Co.

Thermodynamic analysis of the Fe–Ni–Co–Mg–Si–O–H–S–C–Cl system for selective sulphidation of a nickeliferous limonitic laterite ore

An increasing percentage of nickel is being extracted from the laterite ores for which there exists considerable potential for new process development. In the current research, a thermodynamic analysis of the Fe–Ni–Co–Mg–Si–O–H–S–C–Cl system has been performed in order to establish the possible sulphidation conditions for the upgrading of a limonitic laterite ore. The study was performed using the equilibrium module of HSC Chemistry® 6.1, and the data available in the literature were utilised to determine the activity coefficients of the various species employed in the calculations. The effects of variables such as temperature, amount of sulphur and carbon and chlorine additions on both the nickel grade and recovery in the monosulphide solid solution (mss) were determined. Alternative sulphidizing agents were also considered. Nickel recoveries of about 85% could be achieved at a grade of 10% nickel in the mss. Limiting factors in the sulphidation process were the formation of iron sulphide (FeS) and the relatively high stability of nickel oxide in the nickel ferrite (NiFe2O4), in comparison to the other phases, which resulted in excessive sulphur requirements of over 100kg of S/tonne of ore. Methods to overcome these restrictions were discussed and the thermodynamic results were compared to the published experimental values.

Leaching behavior of metals from limonitic laterite ore by high pressure acid leaching

The leaching behavior of metals from a nickeliferous limonitic laterite ore was investigated by high pressure acid leaching process for the extraction of nickel and cobalt. The effects of sulfuric acid added, leaching temperature, leaching time and liquid/solid (L/S) ratio on metals extraction were examined. More than 97% Ni, 96% Co, 93% Mn, 95% Mg and less than 1% Fe are extracted under optimum conditions. Analysis of the high pressure acid leaching residue by chemical and XRD analysis indicates that the residual iron and sulfur are mainly present in phases of hematite and alunite, respectively. The high pressure leaching process provides a simple and efficient way for the high recovery of nickel and cobalt from laterite ore, leaving residue as a suitable iron resource.

MICROWAVE DRYING OF NICKELIFEROUS LIMONITIC LATERITE ORES

Nickeliferous laterite ores contain large amounts of both free and combined water which are removed during processing for metal extraction. In this study, the application of microwaves for the drying of a briquetted nickeliferous limonitic laterite ore, was investigated. Microwave drying tests were performed at a frequency of 2460 MHz and the sample mass was continuously monitored in order to determine the drying rate. The variables investigated were sample mass, microwave power, briquette aspect ratio, specific surface area and compaction pressure. For comparison purposes, conventional drying tests were performed in the temperature range of 44 to 228°C. It was found that the microwave drying rates were two to three times higher than the conventional drying rates. This was attributed to the inverse temperature gradient with microwave heating which promoted enhanced mass transfer of the water.Les minerais nickélifères de latérite contiennent de grandes quantités d’eau tant à l’état libre que combinées qui sont enlevées lors du traitement d’extraction du métal. Dans cette étude, on a investigué l’utilisation des micro-ondes pour le séchage d’un minerai nickélifère briqueté de latérite limonitique. On a effectué des essais de séchage par micro-ondes à une fréquence de 2460 MHz alors que la masse de l’échantillon était continuellement surveillée afin de déterminer le taux de séchage. Les variables étudiées incluaient la masse de l’échantillon, la puissance du micro-onde, le rapport longueur/diamètre de la briquette, la surface spécifique et la pression de compaction. Pour le but de comparaison, on a effectué des essais de séchage conventionnel dans la gamme de température de 44 à 228°C. On a trouvé que les taux de séchage par micro-ondes étaient deux ou trois fois plus élevés que les taux de séchage conventionnel. Ceci était attribué au gradient inverse de température du chauffage par micro-ondes qui favorisait un transfert amélioré de la masse d’eau.

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-Fe2−x/3O3−xOHx)) 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.

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) · nH 2O) 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 (tan δ= 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 (tan δ) 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/3 O 3− x OH 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.

Drying kinetics of nickeliferous limonitic laterite ores

The drying kinetics of a nickeliferous limonitic laterite ore were investigated in the temperature range of 44–228 °C, using a thermogravimetric technique, and the results were characteristic of a non-hygroscopic porous solid. For drying temperatures below 100 °C, the drying rate curves exhibited three stages: a relatively short incubation or set-up period, a constant rate drying period and a decelerating rate drying period. At temperatures above the boiling point of water, there was no constant rate drying period and only the incubation and the decelerating rate stages were observed. The graphical critical moisture fraction, X Cr , which is the moisture content at which the transition from the constant rate period to the decelerating rate period occurs, was found to be 0.064 and was independent of the drying temperature and thus the drying rate. Using the concepts of the relative drying rate ( f) and the characteristic moisture content ( Φ), a characteristic drying curve was determined for the ore. The drying kinetics, when the sample had attained the equilibrium temperature, exhibited non-Arrhenian behavior and the drying process was approximated using two linear relationships. The activation energies over the two temperature ranges were determined to be as follows: 25.5 kJ/ mole 44 ° C⩽T⩽100 ° C 12.9 kJ/ mole 100 ° C⩽T⩽228 ° C The activation energies were both relatively low and this indicates that the process was diffusion controlled in both temperature regimes. It is postulated that at temperatures below 100 °C, the rate-determining step was attributed to boundary layer control while at higher temperatures the rate-determining step was internal diffusion control. Effective diffusion coefficients ( D e) were calculated from the drying rate data and they varied with both concentration and temperature. At low moisture contents, a maximum was observed in the effective diffusion coefficient and this was explained in terms of a maximum in the vapour phase diffusivity at low moisture contents. At temperatures below the boiling point of water, the plateau at the maximum was extended and the diffusion coefficient was relatively constant over the concentration range X=0.02 –0.055. The maximum in the diffusion coefficient was found to vary with temperature as T n , where n=1.8.