Atmospheric Acid Leaching Research Articles

Reductive atmospheric acid leaching of lateritic smectite/nontronite ores in H2SO4/Cu(II)/SO2 solutions

Despite the success of reductive atmospheric acid leaching (RAAL) of limonitic nickel laterite ores in recent studies limited attempt has been made to apply this method to smectite/nontronite ores of different mineralogies. A comparative study of four smectite/nontronite ores in this study showed that the use of 700kgH2SO4/ton dry ore leaches only 74–86% Ni, 37–76% Co, 47–58% Fe and 24–66% Mn at 90°C from slurries of 20–35% (w/w) pulp density even after 10h, depending upon the mineralogy. These values increased to 90–97% Ni, 94–97% Co, 92–98% Mn and 72–85% Fe in the presence of Cu(II)/SO2. The first order dependence of initial fraction of iron, aluminium and nickel leached from a typical smectite ore in the first 0.5h on the initial acid concentration provides evidence for the involvement of hydrogen ions in the surface reaction. Low activation energy of 10kJ/mol based on the fraction of nickel leached in the first 0.5h indicates a diffusion controlled reaction. This is supported by the applicability of a shrinking core kinetic model for metal dissolution over the first 2h, with different apparent rate constants (kap) depending upon the iron oxide content, mineralogy and porosity. A log–log plot of kap for ores with high iron content as a function of acid concentration agrees reasonably well with the correlation already established for the leaching of nickel from limonitic laterite and manganese nodules. Thus, initial fast leaching can be related to the higher porosity and a rate controlling step which involves the diffusion of H+ through a thickening solid layer. The slow leaching at latter stages is a result of low remnant acid, thickening solid layer and changes in mineral composition.

A novel hydrometallurgical approach to recover valuable metals from laterite ore

A novel hydrometallurgical process was developed to produce metal co-doped magnesium ferrites from saprolite and limonite laterite blends by using an atmospheric acid leaching–coprecipitation method. The effects of initial acid concentration, liquid to solid ratio and leaching time on the metal leaching efficiencies were investigated systematically. It is shown that extraction efficiencies of Fe, Ni, Mn, Co and Mg can reach 94.6%, 96.9%, 86.0%, 84.8% and 72.6%, respectively, after leaching for 60min at 100°C with the liquid (2.75mol·L−1 HCl acid) to solid (saprolite and limonite laterite blends) ratio of 10:1mL·g−1, and saprolite to limonite mass ratio (Msaprolite/limonite) of 5:5. Under the optimum leaching conditions, the influence of Msaprolite/limonite on the synthesis of metal co-doped magnesium ferrites from leaching solutions was also discussed. X-ray Diffraction (XRD) results showed that pure metal co-doped magnesium ferrites could be obtained when the Msaprolite/limonite was controlled at 7:3, with the initial acid concentration of 2.75 and 3.0mol·L−1, respectively.

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 −200μm feed solid loading (30 vs. 45wt.%) and temperature (70 vs. 90°C) on leach kinetics, acid consumption capacity and Ni and cobalt (Co) extraction was studied under isothermal, batch (4h) 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 45wt.% solid loading, Ni/Co extraction after 4h was the lowest (∼14/16%) whilst the highest extraction (∼67/56%) was observed at 90°C and 30wt.% 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 30min 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.

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+75μm fraction, with 98% Ni being extracted at 90°C after 480min. 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, kdt=1−2/3x−(1−x)2/3 showing that nickel leaching reaction was diffusion controlled under the set conditions.

Kinetics of Atmospheric Acid Leaching of a Limonitic Laterite

A limonitic nickel laterite was leached by sulfuric acid at atmospheric pressure. Kinetics of leaching within the temperature range of 75-100°C was studied. The leaching kinetics followed the shrinking core model. The diffusion through the liquid film could be negligible under the agitation speed of 600rpm or above. Surface chemical reaction was the rate-controlling step. The semi-empirical kinetic equation was determined and the activation energy was 52.843kJ/mol.

Mineralogical characterisation of Indonesian laterites prior to and post atmospheric leaching

Nickel laterite is of increasing importance as an economically viable source of Ni. However, practical strategies for low cost atmospheric leaching of laterites have been hampered in part by poor recovery and the formation of potentially environmentally harmful residues, for instance jarosite. It is important therefore to define the mineralogical forms of nickel present, using readily accessible laboratory-based approaches, in the ores and residues, and the form of secondary precipitates in the residues, as a means for future optimisation of leach parameters. To this end a detailed mineralogical study of an Indonesian laterite and residues resulting from atmospheric acid leaching has been undertaken. The leach process involved the sequential reactions of first, limonite (3h) and then saprolite (11h) in sulphuric acid leach liquor. The acid, dry limonite and saprolite ores were added in the weight ratio of 1.4:1:1. At 100°C, over 80% of the total Ni was extracted into solution during the whole leach process.The limonite ore was found to contain Ni (1.2wt.%) predominantly within Fe oxy/hydroxides, serpentine and phyllomanganate whilst in the residue Ni (0.4wt.%) is present in highly crystalline leach resistant minerals, such as spinels. The majority of the Ni (1.6wt.%) in the saprolite ore was present in serpentine with a small fraction also present in phyllomanganate. This association is further confirmed by the similar saprolite leach extraction curves of Ni and Mg. Goethite and jarosite are both found to be concentrated in the saprolite residue, as is consistent with the decrease in Fe extraction during the saprolite leach. For the final 11h residue of the saprolite leach, the Ni (0.3wt.%) is mainly present in undissolved lizardite and leach resistant pyroxene and spinel minerals.

Characterization and atmospheric hydrochloric acid leaching of a limonitic laterite from Indonesia

The characterization and atmospheric hydrochloric acid leaching of a limonitic laterite from Indonesia were investigated in the current paper. The mineral and chemical compositions of the laterite were studied by X-ray diffraction (XRD) analysis, optical microscopy, scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/EDS), carbon/sulfur (C–S) analysis, and Fe(II) content titration. The laterite mainly contained goethite, siderite (~16.6wt.%), chrysotile, and magnetite (~14.6wt.%); Ni was incorporated in all major minerals. Complete leaching of the host minerals in hydrochloric acid was investigated, given that economical regeneration of the acid by hydrolysis was possible. Atmospheric leaching experiments were carried out to investigate the effect of acid–ore ratio (a/o), liquid–solid ratio (l/s), leaching temperature and time on the leach recovery of Ni (95.1%), Co (99.0%), and Fe (94.6%). Siderite and chrysotile in the ore were highly leachable; goethite dissolved in a wide range of a/o; magnetite and maghemite were moderately active.

Physicochemical laws of the atmospheric sulfuric acid leaching of the copper—nickel concentrates from the beneficiation of disseminated ores

A physicochemical substantiation is performed for the organization of a combined flotation hydrometallurgical technology for the processing of the copper—nickel concentrates from the beneficiation of disseminated ores. This technology is used instead of the traditional pyrometallurgical technology providing the production of a sulfide concentrate with a total nickel, copper, and cobalt content of 14.64% for the through extraction of (wt %) 92.2 Ni, 74.0 Cu, 95.3 Co, 91.9 Pt, 95.9 Pd, and 96 Rh to the concentrate.

Effect of the trivalent iron content in a pyrrhotine concentrate on the reaction mechanism of its sulfuric acid leaching

The laws of atmospheric sulfuric acid leaching of pyrrhotine concentrate are analyzed as a function of the redox potential of a reaction system, which is determined by the Fe(III) content in a solution.

The effect of iron precipitation upon nickel losses from synthetic atmospheric nickel laterite leach solutions: Statistical analysis and modelling

Atmospheric acid leaching (AL) of low-grade nickel laterite ores can produce a pregnant leach solution (PLS) containing large amounts of soluble iron. Purification of the leach solution by iron precipitation with an alkaline reagent often causes an associated loss of valuable nickel. In this study, the effects of the factors governing the iron precipitation process upon nickel loss were investigated in synthetic nickel laterite AL liquors containing just nickel and iron by statistical analysis and modelling. The factors examined in this study were pH, temperature, neutralizing agent, initial Fe/Ni ratio in the PLS and stirring speed. The significance of each factor and their interactive effects were evaluated using statistically-designed experiments, where iron removal efficiency (%) and nickel loss (%) were the measured responses. A one quarter fractional factorial design was performed to screen for factors that have more important effects on the responses, and then the principal factors were further optimized in a Box–Behnken Design (BBD) experiment. The BBD which is an effective response surface methodology was applied to fit quadratic models to describe the relationships between the responses and factors. Quadratic response functions were derived for iron removal efficiency (%) and nickel loss (%) by applying a least squares method. The three-dimensional response surface and corresponding contour plots clearly showed the relationships between the responses and interactive factors.

Dissolution behaviour of a Turkish lateritic nickel ore

The atmospheric pressure sulphuric acid leaching characteristics of Adatepe (Eskişehir, 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.

Reductive atmospheric acid leaching of West Australian smectitic nickel laterite in the presence of sulphur dioxide and copper(II)

Atmospheric acid leaching of West Australian nickeliferous smectite ore was found to be much more effective in the presence of SO 2 as a reductant. The rate of leaching was further catalysed by the presence of Cu(II) in solution. The effects of SO 2, acid concentration, temperature, particle size and pulp density were examined to optimise the leaching parameters. In the presence of SO 2, it was possible to achieve 97% nickel extraction within 10 h leaching with less than 0.1% nickel in the leach residue using 600 kg H 2SO 4/t of ore with 35% w/w pulp density at 90 °C. The calculated acid consumption was 540 kg/t of dry ore for obtaining > 90% nickel extraction in the presence of Cu(II) catalyst. Cobalt and manganese extractions were very rapid, with most of their extractions within half an hour in SO 2–H 2SO 4 solution. The increase of initial acid concentration, temperature and pulp density increased the metal extraction from the ore, whereas particle size had no effect on the leaching.

Microwave assisted atmospheric acid leaching of nickel from laterite ore

The recovery of nickel from laterite ore with sulphuric acid under the effect of microwave irradiation was studied. The experimental results indicated that the extraction rate of nickel was influenced by reaction time, sulphuric acid concentration, and temperature, especially by microwave power. The results obtained from the experiments of orthogonal arrays showed that the optimum conditions of sulphuric acid concentration, reaction time, microwave power, and temperature were 25 vol.%, 1.5 h, 600 W, and 90°C, respectively. Under the optimal conditions, the nickel recovery could reach approximately 90.8%, which was higher than that obtained by conventional water bath heating. Kinetic experiments showed that the leaching of nickel in a sulphuric acid medium was controlled by chemical reaction occurring on the surface of laterite ore. The apparent activation energy was 38.9 kJ/mol. Microwave heating technology is efficient, clean, and easy to control and facilitate continuous processing of materials.

Atmospheric acid leaching of nickel laterites review: Part I. Sulphuric acid technologies

This review examines the atmospheric leaching (AL) of nickel laterite ores with sulphuric acid, specifically the limonite, smectite (clay) and saprolite fractions. The kinetics and mechanism of leaching of the key minerals are reviewed together with methods for enhancing nickel recovery. Existing and developing AL processes for extracting nickel and cobalt from these ores are then considered with comparison to high pressure acid leaching (HPAL) technology. This review also provides an overview of the emerging hybrid HPAL/AL and heap leaching technologies.