Selective pressure leaching of Fe (II)-rich limonitic laterite ores from Indonesia using nitric acid

The selective extraction of nickel and cobalt over iron from an Indonesian limonitic laterite was investigated using nitric acid pressure leaching (NAPL). The mineralogical analysis showed that the major minerals were goethite and magnetite, and the content of the divalent iron was as high as 7.06%. Nickel and cobalt were mainly distributed in these two minerals; however, the distribution was non-uniform. A series experiments were conducted to examine the basic parameters and propose the optimal conditions for the extraction. When the ore was treated via HPAL under the optimal condition, the extracted nickel and cobalt were less than 75%, and the iron concentration in the leach liquor was over 12.5 g/L. By contrast, over 85% of nickel and cobalt were extracted and about 1.8 g/L iron was achieved using NAPL. The loss of nickel and cobalt can be mainly attributed to the undissolved magnetite and manganese minerals. The leaching process of NAPL is a dissolution–oxidation–precipitation mechanism, and in this process nitric acid acts as both a lixiviant and an oxidant. The formation of hematite results in a low iron concentration in the leach liquor without oxygen injected. Meanwhile, the oxidation and the precipitation of dissolved divalent iron results in a calculated savings in acid consumption of about 120 kg nitric acid per ton of ore can be obtained, which is equal to over 93 kg of sulfuric acid per ton of ore. Moreover, lower residual acid (20 g/L nitric acid) is a significant advantage of NAPL. The iron residues had a high iron content (>56 wt%) with no sulfur, making it suitable as raw materials for ironmaking.     

Leaching of limonitic laterite ore by acidic thiosulfate solution

Cobalt is usually recovered as a by-product of copper and nickel processing, and only a small amount of cobalt is derived from laterites although a vast majority of cobalt resources in them. The exploitation of limonitic laterite containing high content of cobalt is becoming increasingly important. The mineralogy of a limonitic laterite ore was characterized by environmental scanning electron microscope (ESEM) and X-ray diffraction (XRD) in this paper. The results show that nickel occurs in goethite mainly, while cobalt is predominantly associated with manganiferous minerals. Thiosulfate is found to be able to selectively leach cobalt from limonitic laterite in the presence of sulfuric acid, and 91% Co, 22% Ni, 10% Fe are leached from an ore containing 0.13% Co, 1.03% Ni within the first 5 min at 90 °C under the conditions of 10 g/L sodium thiosulfate, 8% (w/w) sulfuric acid and 10:1 L/S ratio. The leaching kinetics of Mn and Co by acidic sodium thiosulfate solution can be characterized by the Avrami equation. In acidic solution, thiosulfate readily decomposes into sulfur and sulfur dioxide as intermediary reagents to reduce pyrolusite (MnO₂) and goethite (FeOOH); therefore, nickel and cobalt associated with goethite and pyrolusite respectively are extracted due to reduction dissolution. Furthermore, cobalt is selectively leached over iron and nickel because pyrolusite is preferentially reduced by acidic thiosulfate rather than goethite. The novel process may give an alternative method to selectively recover cobalt as the primary product from limonitic laterites at atmospheric pressure.     

Acid leaching and rheological behaviour of a siliceous goethitic nickel laterite ore: Influence of particle size and temperature

This study investigates the isothermal, batch, H₂SO₄ acid leaching behaviour of siliceous goethitic (SG) nickel (Ni) laterite ore and its links to pulp rheology. Specifically, the effect of feed ore particle size (−0.2 vs −2.0 mm), leaching temperature (70 vs 95 °C) and pulp rheology on Ni and pay metal, cobalt (Co) extraction kinetics and yield was studied for 4 h on 40 wt.% solid dispersions at pH 1. The leaching behaviour was distinctly incongruent, reflecting the disproportionate proliferation of major gangue mineral’s constituent elements (e.g., Fe, Al, Mg, Na, Si) alongside Ni and Co in the pregnant leach solution. At 70 °C, Ni/Co extraction rates were notably lower (<20%) in contrast with 95 °C where a significant increase in Ni/Co extraction to 78/77% and 74/77%, respectively, for the −0.2 and −2.0 mm feeds occurred. The slurries displayed a non-Newtonian, shear thinning Bingham plastic rheological behaviour of which the viscosity and shear yield stress increased markedly in the course of 4 h leaching. The pulp viscosity and shear yield stress were greater at lower temperature than at higher temperature and they were also greater in slurries with finer than coarser feed particles. The dynamic pulp rheology, however, had no marked effect on the overall Ni/Co extraction rates. Whilst the feed ore particle size had no remarkable impact on overall Ni/Co extraction, it led to noticeably higher acid consumption and enhanced slurry rheology in the finer sized ore. The mechanism of leaching the SG ore followed a two-stage, first order chemical reaction-controlled shrinking core model, the kinetics of which gave higher rate constants and lower activation energies for the release of Ni, Co, Fe and Mg in the first stage. A faster leaching process involving more reactive minerals during the first 30 min is envisaged to be followed by leaching of the more refractory minerals.     

A study of atmospheric acid leaching of a South African nickel laterite

Nickel and cobalt acid leaching from a low-grade South African saprolitic laterite using sulphuric acid was studied. Ore characterisation was performed by XRD and XRF. Batch agitation leaching tests were conducted at atmospheric pressure investigating main parameters: particle size and percent solids at 25 °C and 90 °C. Ore characterisation showed that the ore is a saprolitic laterite with nickel present in lizardite. Leaching tests showed that nickel and cobalt could be leached from the ore at atmospheric pressure. Nickel was found to be more leachable from the coarser −106 + 75 μm fraction, with 98% Ni being extracted at 90 °C after 480 min. Cobalt was not favoured by variation in particle size and increased percent solids. Increasing ore percent solids improved nickel extraction at 25 °C however at 90 °C extraction decreased due to a diffusion layer build-up as a result of amorphous colloidal silica. The co-dissolution of magnesium and iron was elucidated. Nickel leaching data at increased temperature and percent solids fit the shrinking core model equation, k_dt = 1−2/3x − (1 − x)^2/3 showing that nickel leaching reaction was diffusion controlled under the set conditions.     

Hydrometallurgical processing of nontronite type lateritic nickel ores by MHP process

The research work presented in this paper determined the optimum conditions at which nickel and cobalt could be obtained at maximum efficiency from the column leach liquor of the lateritic nickel ore existing in Gördes region of Manisa in Turkey by performing effective hydrometallurgical methods. This column leach solution was initially neutralized and purified from its basic impurities by a two-stage iron removal process, nickel and cobalt were precipitated in the form of mixed hydroxide precipitate from the purified leach solution by a two-stage precipitation method called “MHP” and a manganese removal process was performed at the optimum conditions determined experimentally. By decreasing manganese concentration with this process to an acceptable level yielding at most 10% Mn in hydroxide precipitate, it was possible to produce a qualified MHP product suitable to the current marketing and standard conditions. The experiments conducted showed that by maintaining recycle leaching with sulfuric acid at which 95% of Ni-Co could be recovered from the precipitates, about 81% of Ni and 63% of Co in the lateritic nickel ore (9.72 kg Ni/ton of ore and 0.28 kg Co/ton of ore) could be extracted as mixed hydroxide precipitate by MHP process.     

Sulphuric-Acid Leaching of Ural Oxidized Nickel Ore with Sodium Sulfite and Fluoride Additives

The process of leaching oxidized nickel ore in sulphuric acid with the additives of sodium sulfite and fluoride is investigated. Tochilnogorsky deposit ore (Sverdlovsk Region) is used to prove theoretically and experimentally efficient application of fluoride in dissociation of nickel minerals (nontronite and garnierite) in oxidized nickel ore. It is shown that at NaF consumption of 10 kg/t, it is possible to enhance maximum extraction of nickel to solution from 82.3–86.9 to 96.0–98.7% at the residual sulphuric acid concentration of 10–20 g/l in the working bath. It is found that the sodium fluoride additives lower the process activation energy from 22.8 to 12.9 kJ/mole. This means that the reaction of sulphuric-acid leaching proceeds in diffusion–kinetic mode and that sodium fluoride is applicable as the leaching accelerator.     

The recovery of nickel from high-pressure acid leach solutions using mixed hydroxide product – LIX®84-INS technology

This route for the recovery of nickel from HPAL laterite solutions was successfully demonstrated by the Centaur Mining Cawse Nickel Operation and has been selected by BHPBilliton for their Ravensthorpe Nickel–Yabulu Refinery circuit. The mixed hydroxide route is also well suited to treatment of solutions by other leach processes such as Activox^®.The technology can use an acid strip coupled to nickel electrowinning or an ammonia strip and basic nickel carbonate production. The solvent extraction technology involved in these two circuits is reviewed and compared. The ancillary operations of pregnant leach solution clarification, reagent remediation, reductive stripping of cobalt, zinc and copper transfers are discussed. The treatment of ammoniacal leach solutions containing higher copper concentrations than those normally seen in laterite processing is also addressed.Possible routes for recovery of cobalt and nickel from the solvent extraction circuit are also discussed.     

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.     

Kinetics of selective chlorination of pre-reduced limonitic nickel laterite using hydrogen chloride

The selective chlorination process of pre-reduced limonitic nickel laterite using hydrogen chloride was investigated in this work. In HCl-O₂-H₂O-N₂ atmosphere, the effects of variations in temperature, the partial pressures of hydrogen chloride, oxygen and water vapor, and total gas flow rate were all studied. It was found that the chlorination of nickel and cobalt could be described by two stages; and it was controlled by gas diffusion through product layer. Four apparent activation energies, including 20.43 kJ/mol and 12.89 kJ/mol for the first and second stage of nickel chlorination, 14.95 kJ/mol and 13.02 kJ/mol for the first and second stage of cobalt chlorination respectively, were obtained in the temperature range of 420-460 °C. And the apparent reaction order of hydrogen chloride was also obtained. During the selective chlorination, the oxidation of pre-reduced ore could take place with the selected conditions; chlorinated iron was mostly rejected as hematite and thus nickel and cobalt were selectively chlorinated by hydrogen chloride.     

Some aspects of nickel extraction from chromitiferous overburden by sulphatization roasting

Nickel bearing chromitiferous overburden of Sukinda region, Orissa, India, was pugged with sulphuric acid and subjected to roasting in two stages. Various operating parameters, such as roasting temperature, time, acid concentration and role of additives were studied. Addition of moisture, during pugging, helped in the formation of insoluble ferric hydroxy sulphate that maintains the equilibrium of SO₂/SO₃ partial pressure. The double stage roasting improved the nickel extraction over the single stage isothermal roasting of the material at 700°C. An extraction of 85% nickel with 2–3% iron could be achieved at a temperature of 700°C when roasted for 15 mins, 25 wt% sulphuric acid and 20 wt% moisture in two stages. The nickel extraction was improved a further 8–10% by the addition of alkali and alkaline earth metal salts. The role of additives during roasting was also investigated.     

Hydro–pyro integration in the processing of nickel laterites

Hydrometallurgical process routes are seen to be the future of treatment of the lower grade nickel laterites ores. Hydrometallurgical projects of recent years have focused on HPAL and have been largely unsuccessful economically so far, with huge capital cost overruns.The simplest and least capital intensive of the possible alternatives to HPAL is atmospheric heap leaching. Development work is also underway by several companies into atmospheric tank leaching which is also a potentially viable alternative.The natural product for a leaching process is a high grade nickel intermediate either from a direct precipitation process (containing approx. 36% Ni) or via ion exchange (>50% Ni).There are many existing pyrometallurgical facilities which could easily be adapted to take this nickel intermediate giving them significant potential benefits especially as nickel laterite ore grades diminish. The nickel production from these plants could also be increased and for new plants large capital and operating cost savings achieved by using suitable intermediates.There are also potential environmental benefits with much less energy consumed and lower greenhouse gases emitted per tonne of nickel produced.In the future an integrated hydrometallurgical plant with attached existing smelter or a more advanced pyrometallurgical smelting process (e.g. a DC arc furnace) could well be the way forward for new projects.     

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.     

Dissolution behaviour of a Turkish lateritic nickel ore

The atmospheric pressure sulphuric acid leaching characteristics of Adatepe (Eski?ehir, Turkey) laterite ore that has recently been put into operation was investigated. The effects of sulphuric acid concentration (5-95%), temperature (20-95 °C) and time (30-240 min) on leaching were determined by nickel, iron and arsenic analyses. The amounts of Ni, Fe and As in solution were observed to increase with increase of temperature from 20 °C to 70 °C for sulphuric acid concentrations between 5% and 95%. Further increase of temperature to 95 °C showed that the dissolution of Ni, Fe and As were increased until 60% sulphuric acid concentration and over 60% a decrease in the dissolution percentages was observed due to the probable formation of nickel and silicon containing ferric sulphate type compounds that cause nickel loss from the leach solution. Experimental results showed that maximum nickel dissolution of 99.2% at 95 °C could be reached in 120 min of leaching time for a sulphuric acid concentration of 60%. The congruency of Ni dissolution with respect to Fe was found to be congruent over about 25% Ni and 15% Fe dissolution values. XRD analyses on the residues obtained after leaching showed that it was not required to dissolve all goethite phase to reach maximum dissolution of nickel contained in the sample. An activation energy of 30.36 kJ/mole was determined for Ni dissolution showing that leaching is controlled by external diffusion and chemical reactions.     

Atmospheric acid leaching of siliceous goethitic Ni laterite ore: Effect of solid loading and temperature

In this study, atmospheric acid leaching behaviour of siliceous goethitic nickel (Ni) laterite ore is investigated. Specifically, the effect of −200 μm feed solid loading (30 vs. 45 wt.%) and temperature (70 vs. 90 °C) on leach kinetics, acid consumption capacity and Ni and cobalt (Co) extraction was studied under isothermal, batch (4 h) leaching conditions at pH 1. Incongruent leaching was observed for constituent elements reflecting slow but steady release of value (Ni and Co) and some of gangue metals such as Fe, Mg and Al accompanied by faster and sharp release of Na and Si. Higher temperature and lower pulp solid loading, both led to a 40–50% increase in overall Ni and/or Co extraction and higher acid consumption. At 70 °C and 45 wt.% solid loading, Ni/Co extraction after 4 h was the lowest (∼14/16%) whilst the highest extraction (∼67/56%) was observed at 90 °C and 30 wt.% solid loading. Temperature appeared to have dramatic influence on Ni/Co and other impurity metals’ extractions revealing the chemical reaction controlled nature of the leaching. Higher solid loading and longer leaching time also both slowed down the leach kinetics. A two-stage chemical reactions-controlled leaching mechanism involving a faster initial leaching kinetics followed by a slower leaching at lower rate constants and higher activation energies was established for release of Ni, Co, Fe and Mg. The mechanism reflects the fast leaching of reactive host mineral phases (e.g., clays and Mg–silicates) during first 30 min followed by slow leaching of more refractory mineral phases (e.g., goethite and quartz) during the rest of leaching period. The findings provide a greater understanding for enhanced atmospheric acid leaching process of siliceous goethitic laterite ores.     

Leaching of manganese ores using sawdust as a reductant

In this study sawdust was used as reductant for sulphuric acid leaching of manganese ore. Effects of pulp density, amount of acid, temperature, particle size of ore and amount of sawdust were studied. Manganese extraction of ∼98% was achieved under the conditions: leaching time 8 h, 5% H₂SO₄ (v/v), 10% pulp density, 90 °C and 5% sawdust (w/w), i.e. 0.5 g/g ore. Other Mn containing materials like low grade manganese ore, manganese nodule and Mn-nodule leach residues were tested and all these materials responded well giving more than 98% Mn extraction.     

Leaching of pyrolusite using molasses alcohol wastewater as a reductant

Extraction of manganese from a pyrolusite ore was investigated using molasses alcohol wastewater as a reducing agent in dilute sulfuric acid medium. The effects of molasses alcohol wastewater dosage, concentration of sulfuric acid, leaching temperature and reaction time were studied. High manganese recovery, coupled with relatively low Fe and Al extraction yields, was obtained with this leaching process. The optimal leaching conditions were obtained using 1.9 mol/L H₂SO₄ and 2.0 mL/g ratio of molasses alcohol wastewater to pyrolusite for 120 min at 90 °C. These conditions resulted in leaching yields of 93% for Mn, with relatively low recoveries of 37% for Fe and 25% for Al.These results demonstrate that molasses alcohol wastewater is a low cost resource, containing renewable and non-hazardous reducing agents (when compared to other available reagents) that can be used for manganese leaching under mild acidic conditions. In short, the method provides a good extraction yield while making an economically productive use of molasses alcohol wastewater.     

红土镍矿酸浸沉镍后液中镁资源化的研究进展

红土镍矿的加压酸浸、常压酸浸、堆浸工艺分别适用于褐铁矿型红土镍矿、过渡层和硅镁镍矿型红土镍矿,两种或两种以上的湿法联合处理工艺对矿石适用范围更广。在红土镍矿酸浸过程中,Mg和Ni、Co等同时被不同程度的浸出进入溶液,浸出液沉淀富集Ni、Co后产生大量的含镁废水。若不对其进行有价回收,不仅造成了资源的浪费,还会污染环境。本文综述了红土镍矿酸浸沉镍后液中Mg资源化工艺的研究进展及工业化情况,其中包括沉镍后液中Mn(II)的净化,并对今后的研究发展方向进行了展望,以期为红土镍矿中Mg的综合回收提供技术参考。     

Recovery of copper,nickel and cobalt from acidic pressure leaching solutions of low-grade sulfide flotation concentrates

Recovery of copper, nickel and cobalt from the acidic pressure leaching solutions of Jinbaoshan (YN Province, PRC) low-grade sulfide flotation concentrates was investigated. The proposed technique includes four major steps: (1) the acidity adjustment of the acidic pressure leaching solutions; (2) solvent extraction (SX) separation of copper by organic reagent XD5640, and then stripped from the loaded organic phase by H₂SO₄ solution for copper recovery; then (3) iron in raffinates after copper extracting is selectively removed by high-temperature hydrolysis precipitation in an autoclave; and lastly (4) nickel and cobalt are selectively precipitated by Na₂S from the final solutions after removing iron. The experimental results for treating 1 L acidic leaching solutions per batch by this new technique were reported, and some evaluation and further comparisons with previous investigations were also carried out. It was reported that the total percent recovery of Cu could reach 95% or more, and that of Ni and Co were all more than 99%. In the processing, the percent removal of impurities, such as Fe, Mg and Ca, were all also near to 99%.     

从某高镁铁贫红土镍矿中酸浸富集镍试验

某难选贫氧化镍矿中铁和氧化镁含量较高,镍品位仅为0.71%,物理方法难以选别。研究采用碎磨—酸浸—净化—硫化沉镍—碳化沉镁的工艺,考察了矿石粒度、浸出时间、浸出剂用量、浸出温度以及液固比等因素对镍浸出率的影响。结果表明:在矿石粒度为-0.35 mm占60%,浸出时间为2 h,硫酸+盐酸的用量为50+200 g/L,浸出温度为70℃,液固比为4:1的最佳条件下,镍的浸出率达到87.29%。研究结果对该类矿石中镍的回收有一定的参考意义。     

Agglomeration and column leaching behaviour of goethitic and saprolitic nickel laterite ores

Processability of complex, low-grade nickel (Ni) laterite ores via heap leaching is very limited due to some intractable geotechnical and hydrological challenges such as poor heap porosity/permeability and structural stability. This work presents some investigations on laboratory batch drum agglomeration and continuous column leaching behaviour of saprolitic (SAP) and goethitic (G) Ni laterite ores as part of the quest for an effective ore pre-treatment process for enhanced heap leaching. As a focus, the effect of ore mineralogy/chemistry on the agglomeration and column leaching behaviour of −2 mm (crushed from −15 mm run-of-mine) G and SAP Ni laterite ores was examined. To produce ∼5–40 mm agglomerates in <15 min, the SAP ore required a higher H₂SO₄ (30 wt.%) binder dosage compared with the G ore, although both ores displayed substantially similar, coalescence-controlled agglomeration mechanism. The resulting G agglomerates were more robust than the SAP ones based upon their compressive strength and acidic solution soak test measurements. However, over 100 days of continuous column leaching, the structural stability of the SAP agglomerate bed was slightly greater than that of G agglomerates, reflecting a lesser slump of the former. The pregnant leach solution analysis revealed greater Ni/Co extraction rates from the SAP than the G agglomerates. Whilst the total mass of acid consumed per ton dry ore processed was greater for the SAP ore, the total kg acid per kg Ni extracted was markedly lower. Incongruent leaching of gangue minerals’ constituent elements (e.g., Fe, Mn, Mg, Al and Si) occurred and contributed significantly to the overall acid consumption. The findings show the relevance of agglomeration and column leaching tests for providing useful information for plant designing and optimization of Ni laterite heap leaching operations.