Atmospheric Leaching Research Articles

Leaching of a copper flotation concentrate with ammonium persulfate in an autoclave system

The leaching behavior of a copper flotation concentrate was investigated using ammonium persulfate (APS) in an autoclave system. The decomposition products of APS, active oxygen, and acidic medium were used to extract metals from the concentrate. Leaching experiments were performed to compare the availability of APS as an oxidizing agent for leaching of the concentrate under atmospheric conditions and in an autoclave system. Leaching temperature and APS concentration were found to be important parameters in both leaching systems. Atmospheric leaching studies showed that the metal extractions increased with the increase in APS concentration and temperature (up to 333 K). A similar tendency was determined in the autoclave studies up to 423 K. It was also determined that the metal extractions decreased at temperatures above 423 K due to the passivation of the particle surface by molten elemental sulfur. The results showed that higher copper extractions could be achieved using an autoclave system.

Acid resistance of goethite in nickel laterite ore from Western Australia. Part II. Effect of liberating cementations on acid leaching performance

The acid resistance of some West Australian laterite ores has been reported to be associated with its cementation structure at submicron level. Although closely related, iron and silicon are found not to be intimately mixed in the goethite-silica/silicate cementations from the current Energy Filtered Transmission Electron Microscopy examination. The round or diamond tips of the liberated goethite crystals suggest slow crystal growth in high silicate conditions. The effect of pre-treating the cementation structure by potassium hydroxide liquor digestion upon the atmospheric pressure acid leaching performance is also studied in this paper. Both particle size analysis using laser diffraction and direct imaging using Transmission Electron Microscopy confirm the effective disintegration of the cementations and the liberation of goethite crystals. As a result, the leaching rates of these nickel laterite ores increase by more than 6 times; nickel recoveries of these laterite ores are also increased from under 50% to near 90% after 16h acid leaching. The accelerating effect of the potassium hydroxide pre-treatment upon acid leaching rates verified that an envelope of silica and/or silicates hindered the contact between acid and goethite crystals during atmospheric leaching of these nickel laterite ores.

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.

Leaching of Ni–Cu–Fe–S converter matte at varying iron endpoints; mineralogical changes and behaviour of Ir, Rh and Ru

The Bushveld Igneous Complex in South Africa is a rich source of platinum group elements (PGEs), as well as base metal sulphides. Typical beneficiation routes entail milling and flotation, smelting, matte converting and hydrometallurgical processing of converter matte to selectively recover metal values. The primary focus is on PGE recovery, with the secondary objective of base metals recovery. At the Western Platinum Pty. Ltd. Base Metals Refinery, converter matte typically contains 48% Ni, 29% Cu, 21% S and 0.6–5% Fe by weight, and the major mineral phases have compositions approaching heazlewoodite (Ni3S2), chalcocite (Cu2S) and a Ni–Cu alloy. It has been observed that the iron content of converter matte can have a significant impact on performance of the first stage atmospheric leach, in which the primary goal is to precipitate copper and PGEs from spent electrolyte (via metathesis and cementation reactions) and the secondary goal is the dissolution of nickel. In this work, laboratory scale batch leach tests were carried out with samples of converter matte with varying Fe-endpoints (0.53%, 0.83% and 5.72%), under oxygenated and non-oxygenated conditions, to improve understanding of the effect of the Fe-endpoint. X-ray diffraction and scanning electron microscopy techniques were employed to understand mineralogical changes that take place during leaching. Matte with a higher iron content was characterised by a lower Ni–Cu alloy content than matte with a lower iron content, and the presence of relatively inert pentlandite (NiFe)9S8. Under oxygenated conditions, nickel was leached more readily from low iron matte and copper and PGEs were precipitated more readily onto low iron matte than high iron matte. Under non-oxygenated conditions, copper was precipitated more readily onto the low iron matte and more nickel was leached from a low-iron matte than high iron matte, this can probably be attributed to the presence of the alloy phase in the low iron matte, which galvanically inhibits the metathesis reaction.

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.

Solvent extraction of copper(ii) from concentrated leach liquors

Hydrometallurgical treatment of complex copper sulfidic ores, by-products and concentrates requires aggressive, oxidative leaching methods and application of Fe(III) ions and oxygen or bacteria assisted environment. Leach liquors generated in the process are usually copper and iron-rich solutions of high acidity. Such conditions require the application of suitably strong and selective reagent to extract copper in SX operations. This paper discusses the copper extraction behavior of commercial copper rea- gents: LIX 984N, LIX 612N-LV and Acorga M5640. Aqueous feed solutions used in SX studies were PLS' generated in atmospheric leaching of commercial flotation concentrate, produced at Lubin Concen- trator (KGHM). McCabe-Thiele diagrams were generated and copper net transfer values were compared and discussed. It was shown that stronger modified aldoxime reagents (Acorga, LIX 612) are superior over non-modified salicylaldoxime/ketoxime mixture (LIX 984N). Particularly, the ester modified Acor- ga M5640 showed advantages in recovery and copper net transfer values.

Acid leaching of uranium from a low-grade Indian uranium ore deposit

This paper discusses the leaching behavior of uranium from a low-grade unconformity-related uranium ore occurring in the northwestern part of the Kadapa basin in southern India. This is the major unconformity-related deposit located in India. The U3O8 assay of the ore is about 0.06%. The chief uranium-bearing phase is uraninite, and the ore also has a minor quantity of coffinite. The carbonaceous matter, as well as the porous titanium phases occurring in the ore, is also radioactive. The major gangue mineral is quartz, followed by minor quantities of sericite, chert, chlorite and feldspar. Detailed parametric variation studies were carried out on the ore to optimize conditions for sulfuric acid leaching of uranium values. Based on the laboratory results, preliminary design criteria were developed for process engineering. About 82% of uranium values were leached under conventional atmospheric leaching conditions. Uranium values present in the carbonaceous matter and the other refractory phases were solubilized only after roasting the leach residue. This process improved the overall leach recovery to about 89%.

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.

Leaching behaviour of low and high Fe-substituted chlorite clay minerals at low pH

The behaviour of low-Fe and high-Fe substituted chlorite mineral dispersions was investigated under industrially-relevant, atmospheric leaching conditions typical of low grade, uranium-bearing lateritic ore processing. The main focus was on the influential role played by the clay mineral chemistry. Preferential leaching of Al(III), Fe(II/III) and Mg(II) metal ions over tetrahedral Si species was indicated at pH 1 and 70°C by supernatant speciation, the kinetics of which was faster at high-Fe than at low-Fe substitution. For the low-Fe chlorite, the incongruent leaching behaviour of Al(III), Fe(II/III) and Mg(II) species was substantially similar. In the case of the high-Fe chlorite however, despite its lower Mg(II) content, Al(III) and Fe(II/III) species leaching rates were relatively lower than that of Mg(II). Crystallo-chemical (XRD, XRF and EM) and spectroscopic (FTIR and XPS) analyses indicated that the incongruent leaching led to significant bulk particle and interfacial layer structures' modification, impacting dramatically upon pulp chemistry, mineralogy and particle interactions. Mineral chemistry-mediated formation of polycondensed, sub-crystalline aluminosilicate gel structures and secondary mineral phases prevailed in the course of leaching. A greater increase in high-Fe pulp particle interactions, in contrast with the low-Fe pulp, was observed during leaching, reflecting remarkably high, time-dependent shear yield stresses, reminiscent of highly viscous gels. The development of viscous gel structures whose strength is strongly dependent upon chlorite mineral chemistry has important implications for the efficacy of aqueous processing of clay-rich lateritic ores.

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 mechanism of chalcopyrite leaching in the presence of silver-enhanced pyrite in the Galvanox™ process

A dramatic improvement in the leaching kinetics of chalcopyrite in ferric sulfate media was observed upon the addition of silver-enhanced pyrite. In this process, pyrite samples are pretreated with a miniscule amount of silver and used as a catalyst in atmospheric leaching of chalcopyrite. The aim of this study was to understand the mechanism of this process and to reveal the role of silver and pyrite in accelerating the rate of chalcopyrite leaching. It is shown that this process, known as Galvanox™, is the galvanically assisted leaching of chalcopyrite, where pyrite provides an alternative surface for ferric reduction. As the leaching reaction proceeds, in the absence of silver-enhanced pyrite, a non-conductive sulfur layer forms on the surface of chalcopyrite. This layer prevents electrical contact between pyrite and chalcopyrite particles in the slurry. However, it is observed that, in the presence of silver-enhanced pyrite, a small proportion of the added silver to the pyrite dissolves and reacts with the elemental sulfur around chalcopyrite particles to form silver sulfide. In spite of the very low silver level in this layer, its conductivity increases significantly and allows the transfer of electrons from chalcopyrite to pyrite. In this study, it is shown that pyrite and silver have critical roles in enhancing the kinetics of chalcopyrite leaching. Pyrite provides an alternative surface area for ferric reduction. Silver increases the catalytic properties of pyrite and therefore, the rate of ferric reduction on the surface of silver-enhanced pyrite is faster than this rate on the surface of natural pyrite. Another role of silver is to decrease the resistivity of the sulfur product layer and to facilitate the electrical contact between pyrite and chalcopyrite.

Recovery of Valuable Metals from Zinc Plant Residues by Two-Stage Selective Atmospheric Leaching Process

A hydrometallurgical process was used for selectively extraction of valuable metals from zinc plant residues. The process includes the following two steps. (1) The zinc plant residue is treated by sulfuric acid atmospheric leaching process with KMnO4 as oxidatant to selectively dissolve zinc while leaving most (above 98 pct) of indium and germandium in the iron residues. (2) The iron residues are treated by acidic atmospheric leaching process with NaClO3 as oxidant to dissolve indium and germanium. The valuable metals of indium and germanium in the second leaching solution can be reclaimed by further treatment. The optimum operating parameters of the first stage and the second stage were established by conditional tests. The experimental data indicated that under the conditions employed the zinc extraction in the first stage was above 95%, and the leaching percentage of indium and germanium in the second stage reached 91.6% and 90.7%, respectively.

An experimental evaluation of the leaching kinetics of PGM-containing Ni–Cu–Fe–S Peirce Smith converter matte, under atmospheric leach conditions

In a first stage atmospheric leach in a typical Sherritt Ni–Cu matte leach process, a Ni–Cu–Fe–S Peirce Smith converter matte is contacted with recycled copper spent electrolyte (an aqueous copper sulphate/sulphuric acid solution) at 85 °C with the purpose of dissolving nickel, while simultaneously removing copper from solution. In the PGM industry, copper removal is also important because it serves as a leading indicator in the removal of Ir, Rh, and Ru from the spent electrolyte. The matte mainly consists of heazlewoodite, chalcocite/djurleite, a Ni–Cu alloy phase and inert spinel minerals (magnetite and trevorite). Nickel is leached from the matte by two mechanisms: (i) leaching by sulphuric acid and oxygen; and (ii) an anaerobic metal exchange reaction (cementation and metathesis) between cupric ions in solution and nickel in the matte, which is also responsible for the removal of copper from solution. This study investigates the oxidative and non-oxidative leaching of converter matte in a laboratory batch reactor, with attention specifically being given to the effects of initial copper and acid concentrations and their effects on leaching kinetics. Experimental conditions were varied based on a 2 N experimental design. The availability of oxygen for acid-leaching reactions was found to be the most important factor influencing copper removal and nickel extraction. A 63% nickel extraction could be achieved during oxidative tests vs. 22% in a non-oxidative test. This also indicates that cementation did not take place to a significant degree and that nickel leaching mostly took place via leaching by acid and oxygen. It is suspected that the low degree of copper removal can be attributed to the solids/reactants ratio was employed in tests. The initial copper and acid concentrations did not have a significant effect on the rate of nickel extraction or the total amount of nickel extracted. The rate of copper removal was not significantly influenced by the initial copper concentration, but copper removal was affected by the initial acid concentration. In oxidative tests with high initial acid concentrations, the rate at which copper was leached from the matte was faster than the rate of cementation. The results suggest that operating under high initial acid conditions could interfere with copper removal with no significant benefit in terms of nickel extraction. The results allow the regression of rate expressions.

Enhancing the kinetics of chalcopyrite leaching in the Galvanox™ process

Pyrite is an effective catalyst for the atmospheric leaching of chalcopyrite in iron sulfate media via the Galvanox™ process. However, not all pyrite samples have the same catalytic effect on the process. Techniques to enhance the catalytic properties of pyrite were investigated. Specifically, the effects of pyrite treated with silver (enhanced pyrite) on the kinetics of chalcopyrite leaching were examined with the aim of improving the Galvanox™ process. It has been shown that by pretreating natural pyrite samples with miniscule amounts of silver ions, the rate of chalcopyrite leaching increases dramatically. As little as 50 ppm silver on pyrite, or about 50 g silver (about 1.5 troy ounces) per tonne of pyrite, is sufficient to ensure rapid chalcopyrite leaching kinetics in the Galvanox™ process, regardless of the source of the pyrite. With this new process, the catalytic properties of pyrite are improved such that all pyrite samples accelerate the rate of copper extraction from chalcopyrite significantly.

Determination of the relative leaching kinetics of Cu, Rh, Ru and Ir during the sulphuric acid pressure leaching of leach residue derived from Ni–Cu converter matte enriched in platinum group metals

Hydrometallurgical process routes are typically used for separation of platinum group metals (PGMs) from base metals in Ni–Cu converter matte. Nickel dissolution is primarily achieved in the first stage leach (high pressure or atmospheric leaching, or a combination of the two), which is followed by second stage high pressure sulphuric acid/oxygen leaching to dissolve copper and the remaining nickel. PGMs are recovered from the leaching residue, and their dissolution must hence be limited. The leaching of base metals in the first stage has been characterised, but there is a limited understanding of the behaviour of metals, and more specifically PGMs, in the second stage pressure leach. This research presents the results of laboratory work performed to investigate the kinetics of leaching in the second stage pressure leach. The influence of key operating parameters such as the temperature, pressure, and initial acid concentration on PGM dissolution was investigated.

Recovery of copper from zinc leaching liquor using ACORGA M5640

The present paper describes the solvent extraction and separation of Cu(II) from a leaching liquor obtained by the direct atmospheric leaching of a zinc concentrate with an oxidative mixture of Fe 2(SO 4) 3 (0.4 M) and H 2SO 4 (0.5 M) in the presence of O 2 at 353 K. The obtained solution, containing 1.35 g L −1 Cu(II), 5 mg L −1 In(III), 41 g L −1 Fe {20% Fe(III), 80% Fe(II)}, and 34 g L −1 Zn(II), was extracted with 25% (v/v) solution of ACORGA M5640 (modified with 12.5% (v/v) isodecanol). Quantitative (>98%) and selective transfer of Cu(II) in to the organic phase was achieved in pH range of 1.3–1.5 (A/O = 1). The presence of isodecanol in the extractant solution helped in obtaining complete stripping of copper. Three stages of extraction at an A/O ratio of 5 concentrated the initial metal content {Cu(II) initial-aqueous = 1.35 g L −1} in the organic phase {Cu(II) after extraction, in LO = 6.6 g L −1}. This extraction was selective over Zn(II), Fe(II), Fe(III), and In(III). The loaded organic phase was scrubbed with 20 g L −1 H 2SO 4 followed by the stripping of Cu(II) with 25 g L −1 of Cu 2+ in 180 g L −1 of H 2SO 4 (A/O = 1, two stages).

A new route of ferric ions rejection in a synthetic nickel leach solution

A new route of impurity rejection to remove ferric iron from a synthetic nickel leach solution was introduced, which simulated the chemical composition of a typical acid leach solution of nickel laterites under atmospheric pressure. The synthetic solution underwent a stepwise neutralization process, with each step adopting different pH value-temperature combinations. In a conventional nickel atmospheric leach (AL) process, the nickel loss could be as high as 10wt%, which was a longstanding issue and prevented this process from commercialization. The new impurity rejection route is the first step towards resolving this issue. The results show that, the best neutralization performance is achieved at the nickel loss of 3.4wt% in the neutralization scheme that employs ethylenediaminetetraacetic acid as a nickel stabilizer (pH: 1.3–3.5; temperature: 95–70°C)

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.

Leaching of nickel laterite ore assisted by microwave technique

The application of microwave technique in the hydrometallurgy of nickel laterite ores was described. The mixture of nickel laterite ores and sulfuric acid was pre-treated by microwave irradiation. The dissolving of nickel was conducted in hot water at the atmospheric pressure. The effects of factors, such as microwave power, microwave irradiation time, and sulfuric acid dosage, were investigated. In microwave field, the migration of ionic species and/or rotation of dipolar species promote the liquid–solid reaction process due to the increased contact area of reactants and leaching reaction rate constant. Thanks to the strengthening action of microwave, the microwave-assisted leaching process has its advantages, such as higher extracting rate than conventional atmospheric leaching, and no need for high-pressure operation as high pressure acid leaching (HPAL). The ferric iron in leaching solution could be effectively removed by sodium jarosite process with a little loss of nickel in the jarosite precipitate.