Oxidative Leaching Research Articles

First-principle study on the oxidative leaching mechanism of sphalerite in Ammoniacal solution

The oxidative leaching mechanism of sphalerite in ammoniacal solution was investigated by the combination of experimental method and first-principle calculations based on density functional theory. The interaction machanism of NH3, O2, and Na2S2O8 with the ZnS (110) surface was investigated by first-principle calculations. The NH3 molecule preferred to interact with the ZnS (110) surface at TZn with an interaction energy of −366.17 kJ/mol. The active site changed to BZn site on the ZnS (110) surface with the addition of oxidant (O2 or Na2S2O8). The ZnS bond on the ZnS (110) surface was dissociated, where S2− was oxidized into S22−. Zn extraction was enhanced by the addition of the oxidants. In water, S2O82− is more active than the O2 molecule to interact with the ZnS (110) surface with an interactional energy of −588.77 kJ/mol. The effects of the kinds and amount of the oxidant on the Zn extraction were determined under optimum leaching condition ([NH3]: [NH4+] = 5:3, liquid to solid ratio = 25, temperature = 383 K and leaching time = 4 h). Experiment results showed that Zn extraction was significantly enhanced from 4.32% to 70.30% within 4 h at O2 partial pressure of 0.50 MPa or to 28.40% with the addition of persulfate.

Implementación de Dos Sistemas de Biorremediación como Estrategia para la Prevención y Mitigación de los Efectos del Drenaje Ácido de Roca en la Cordillera Blanca, Perú

En los Andes tropicales, los efectos del cambio climático son excepcionalmente intensos. Sus consecuencias son una amenaza para la conservación de los ecosistemas altoandinos, la biodiversidad y los diversos servicios ecosistémicos brindados a las poblaciones. Durante estos últimos 40 años, los glaciares peruanos han mostrado una reducción de 43% de su superficie, lo que tiene profundas implicancias en el abastecimiento de agua, en términos de cantidad y calidad. El retroceso glaciar deja expuestas a la intemperie rocas mineralizadas y ricas en sulfuro, alterando la calidad del agua, generando drenaje ácido de roca (DAR). Aunque se requiere de mayor investigación, uno de los supuestos es que el drenaje ácido natural de roca se produce por reacciones de oxidación y lixiviación de los minerales. Los metales son movilizados hacia los cuerpos aguas abajo, ocasionando cuadros de toxicidad en los ecosistemas acuáticos y en los usuarios de este recurso. En este artículo, proponemos la biorremediación como una estrategia eficaz y de bajo costo para mitigar los efectos de DAR y presentamos dos metodologías participativas aplicadas en campo. Entre 2013 y 2017, la Comunidad Campesina Cordillera Blanca, Recuay, Ancash, realizó una Investigación Acción Participativa, articulando conocimiento local y científico, para remediar las aguas del canal Chonta, alteradas por el fenómeno de DAR. La comunidad diseñó e implementó un sistema de biorremediación, recuperando la calidad del agua para su uso agrícola. En 2016, la misma experiencia fue replicada y perfeccionada por el Comité de Usuarios de Agua Shallap-Huapish-Toclla, Huaraz, Ancash, implementando un piloto. Estas dos experiencias se desarrollaron con el apoyo del Instituto de Montaña y de la Universidad Nacional Santiago Antúnez de Mayolo en Huaraz.

Novel Approach for Enhanced Scandium and Titanium Leaching Efficiency from Bauxite Residue with Suppressed Silica Gel Formation

The need of light weight alloys for future transportation industry puts Sc and Ti under a sudden demand. While these metals can bring unique and desired properties to alloys, lack of reliable sources brought forth a supply problem which can be solved by valorization of the secondary resources. Bauxite residue (red mud), with considerable Ti and Sc content, is a promising resource for secure supply of these metals. Due to drawbacks of the direct leaching route from bauxite residue, such as silica gel formation and low selectivity towards these valuable metals, a novel leaching process based on oxidative leaching conditions, aiming more efficient and selective leaching but also considering environmental aspects via lower acid consumption, was investigated in this study. Combination of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) was utilized as the leaching solution, where various acid concentrations, solid-to-liquid ratios, leaching temperatures and times were examined in a comparative manner. Leaching with 2.5 M H2O2: 2.5 M H2SO4 mixture at 90 °C for 30 min was observed to be the best leaching conditions with suppressed silica gel formation and the highest reported leaching efficiency with high S/L ratio for Sc and Ti; 68% and 91%; respectively.

Reasonableness of usage of hyperduplex stainless steel as autoclave equipment material for high-temperature oxidation leaching of gold-bearing sulphide concentrates

Reasonableness of usage of hyperduplex stainless steel as autoclave equipment material for high-temperature oxidation leaching of gold-bearing sulphide concentrates

Arsenic behavior in the autoclave-hydrometallurgical processing of refractory sulfide gold-platinum-bearing products

Among various types of gold-bearing ores a special place belongs to the ores, which contain gold finely-dispersed in sulphide minerals, mostly in arseno-pyrite and pyrite. Autoclave-hydrometallurgical processing technologies for such raw materials seem to be of a particular interest for study. However, autoclave oxidation of sulfide-arsenic material results in significant amounts of technological solutions with high concentrations of arsenic, iron and sulfuric acid.This article represents the studies of how arsenic behaves in autoclave oxidative leaching of a refractory sulphide gold-platinum-bearing concentrate. We studied how the composition of arsenic-bearing solutions in autoclave leaching (acidity, concentration of iron and arsenic) influences the depth of arsenic precipitation when neutralized with calcium-containing reagents, which allows converting the maximum amount of arsenic together with iron in the form of iron arsenate into a stable long-term storable precipitation.

Reclamation and Harmless Treatment of Waste Cathode Ray Tube Phosphors: Novel and Sustainable Design

In this paper, we propose a novel and sustainable process for recycling rare earths (REs) and zinc (Zn) simultaneously from waste cathode ray tube (CRT) phosphors. First, 95% of the impurities such as glass cullets and aluminum foils are removed by simple screening. Then, a self-propagating, high-temperature synthesis reaction following a water-leaching process is performed to recycle Zn selectively. The REs are recycled by a combined process of oxidative leaching and ionic-liquid-based extraction. They are then regenerated to form a new Y2O3:Eu3+ phosphor. By following this green recycling design, the recovery efficiencies of REs and Zn reach 99.5% and 99%, respectively. The negative bivalent sulfur in ZnS and Y2O3:Eu3+ is converted completely to SO42–, which efficiently avoids the secondary pollution. It should also be pointed out that the main recovery processes are all carried out at room temperature, and the “three wastes” emissions are minimized throughout the process. This work is expected to open ...

The leaching behavior of minerals from a pyrrhotite-rich pentlandite ore during heap leaching

Due to decreasing ore grades and increasingly complex ore bodies, the heap leaching of sulfide ores is of increasing interest. In this research, the heap leaching phenomena of a pyrrhotite-rich pentlandite ore was investigated for the first 150 days of operation in order to understand the phenomena taking place in the early phase of leaching in an industrial scale heap. The ore investigated originates from Terrafame (Finland) and contains approximately 20 wt% metal sulfides, the majority of which are pyrrhotite and pyrite. The nickel and zinc minerals of interest, pentlandite and sphalerite, are minor constituents of the ore. The oxidative leaching behavior of sulfidic minerals was shown to follow for the most part the order of nobility of sulfides. In the heap leaching investigated, pyrrhotite especially was shown to be far more reactive than pentlandite and sphalerite and thus the recovery of valuable metals can occur only after pyrrhotite dissolution. It was found that the nickel, zinc, and copper present in the irrigation solution can partially precipitate into the heap where more reductive metal sulfides, such as pyrrhotite and alabandite, are present, a metathesis phenomenon postulated elsewhere for copper and now confirmed in industrial scale operation. Pyrrhotite was also shown to create the majority of the reagent (acid and oxygen) demand and the majority of the reagent demand variation during the early days of heap leaching. In addition, the height of the heap was shown have an important role in determining the leaching time, due to physical, chemical, and practical limitations on acid feed. The acid demand for pyrrhotite leaching in low-oxygen consuming reactions was found to be higher (approx. 62 kg/tonne of ore) than the possibility to feed acid on a tall heap (23 kg/tonne of ore at maximum). This was shown to result in heavy precipitation of iron compounds, such as goethite. The results give more clarity for the initial stages of leaching at Terrafame and thereby enable clearer strategies to be formulated for solution circulation management according to heap age.

Treatment of high arsenic content lead copper matte by a pressure oxidative leaching combined with cyclone and vertical electro-deposition method

Abstract In this work, pyrite was first used to precipitate arsenic in lead copper matte as the form of FeAsO4 during pressure oxidative leaching process. Initial content of arsenic in lead copper matte is of 7.92 wt%, and concentration of arsenic in leaching liquid can be less than 0.25 g·L−1 when the dosage of pyrite reaches 10 g. Leaching time, liquid-to-solid ratio, oxygen partial pressure, temperature, sulfuric acid concentration, agitation speed, and sodium lignosulfonate content were systematically studied and optimized during pressure oxidative leaching process, and the optimized conditions for pressure oxidative leaching are: leaching time 2 h, liquid-to-solid ratio 5:1, oxygen partial pressure 1.2 MPa, temperature 150 °C, sulfuric acid 200 g·L−1, agitation speed 500 r·min−1, sodium lignosulfonate 4 g. A cyclone and vertical electro-deposition method is introduced to treat the above optimized leaching solution. This method is first applied for leaching solution which is obtained from lead copper matte. After having the cyclone and vertical electro-deposition step finished, cathode copper can be greater than 99.00%.

添加 NaCl 提高黄铜矿的铜提取率

The addition of NaCl in the ammonium persulfate-APS (as an oxidant) leaching was investigated. APS has some advantages compared with conventional oxidants and its standard redox potential (E°) is 2.0 V. Effect of six parameters such as NaCl concentration, APS concentration, temperature, time, liquid–solid ration (L/S), and stirring speed on the leaching behavior was studied. Results showed that metals extraction increased with increasing of NaCl concentration, APS concentration, leaching temperature (up to 333 K), and L/S ratio. During oxidative leaching of sulfide minerals, the occurrence of elemental sulfur layer on particle surface is known as primary problem that causes low metal extraction. According to the results, the passivation effect of sulfur layer and low dissolution problems can be eliminated in the presence of chloride ions. Copper and iron extraction yields were obtained as 75% and 80%, respectively under leaching conditions as follows: APS concentration 250 g/L; NaCl concentration 150 g/L; time 180 min; temperature 333 K; stirring speed 400 r/min; and L/S 250 mL/g.

Recovery of Precious and Base Metals from Waste Printed Circuit Boards Using a Sequential Leaching Procedure

This paper considers the issue of recycling of waste printed circuit boards (WPCBs) containing precious and base metals in appreciable amounts. High-pressure oxidative leaching (HPOL) with dilute sulfuric acid resulted in removal of a significant amount of base metals from a WPCB ash sample obtained by incineration at 800°C. The parameters investigated in the precious metal leaching from WPCB residue after HPOL included the sulfuric acid concentration, thiourea concentration, oxidant concentration, leaching temperature, and leaching time. Recovery of gold, silver, and palladium of 100%, 81%, and 13% from the WPCB residue sample was achieved by thiourea leaching under optimized conditions. The results show that the efficiency of precious metal dissolution from the WPCB sample using thiourea solution depended strongly on the concentration of both thiourea and oxidant.

Surface reactivity of amphibole asbestos: a comparison between crocidolite and tremolite

Among asbestos minerals, fibrous riebeckite (crocidolite) and tremolite share the amphibole structure but largely differ in terms of their iron content and oxidation state. In asbestos toxicology, iron-generated free radicals are largely held as one of the causes of asbestos malignant effect. With the aim of clarifying i) the relationship between Fe occurrence and asbestos surface reactivity, and ii) how free-radical generation is modulated by surface modifications of the minerals, UICC crocidolite and fibrous tremolite from Maryland were leached from 1 day to 1 month in an oxidative medium buffered at pH 7.4 to induce redox alterations and surface rearrangements that may occur in body fluids. Structural and chemical modifications and free radical generation were monitored by HR-TEM/EDS and spin trapping/EPR spectroscopy, respectively. Free radical yield resulted to be dependent on few specific Fe2+ and Fe3+ surface sites rather than total Fe content. The evolution of reactivity with time highlighted that low-coordinated Fe ions primarily contribute to the overall reactivity of the fibre. Current findings contribute to explain the causes of the severe asbestos-induced oxidative stress at molecular level also for iron-poor amphiboles, and demonstrate that asbestos have a sustained surface radical activity even when highly altered by oxidative leaching.

Oxidative acid leaching of mechanically activated sphalerite

ABSTRACTThe pressure leaching kinetics of mechanically activated sphalerite was investigated in this work. X-ray diffraction and scanning electron microscopy were used to characterise the influences of crystalline structure and morphology, respectively. A laser particle size analyser and specific surface area tester were used to determine the particle size and specific surface area, respectively. Compared to the non-activated sample, the activated samples demonstrated distinct physicochemical properties with higher reaction efficiencies and increased Zn recovery ratios. The activation energy of sphalerite decreased from 69.96 to 45.91, 45.11, and 44.44 kJ mol−1 as the activation time increased from 0 to 30, 60, and 120 min, respectively. The reaction orders for the H2SO4 solutions of the sphalerite samples activated for 0, 30, 60, and 120 min were 1.832, 1.247, 1.214, and 1.085, respectively, which indicated that the dependency of the sphalerite leaching process on H2SO4 could be reduced by means of mechanical activation.

Redox potential measurement during pressure oxidation (POX) of a refractory gold ore

ABSTRACTPressure oxidation (POX) leaching has been commercially applied to refractory gold ores since the 1980s. In the process, sulphide material is oxidised and dissolved in order to release the gold encapsulated in the sulphide matrix, making the gold available for further recovery. Redox potential is a significant parameter during POX; however, it is measured ex situ only at atmospheric conditions. In situ redox potential measurement would provide instant information that allows adjusting the process parameters accordingly. In the present study, redox potential measurements were performed during POX of sulphide material at high temperatures and high pressures. The working electrode was an Ir electrode combined with a flow-through reference electrode in a novel and robust configuration. Experiments were performed in a 2 L titanium autoclave, at 200–220°C, 345–760 kPa oxygen overpressure, and 10–30% solids mass fraction. Temperature and oxygen pressure conditions were selected in order to reflect POX of refractory gold ores. Results show that the Ir electrode is consistent with theory and is able to perform well under these conditions, showing promise as a new in situ sensor.

Research Advances in Applications of Oxidants in Oxidation Leaching of Chalcopyrite

Research Advances in Applications of Oxidants in Oxidation Leaching of Chalcopyrite

Optimization of gold recovery from copper anode slime by acidic ionic liquid

Hydrometallurgical gold recovery from primary or secondary sources is mainly based on a cyanide process, which is very dangerous for the environment due to the high toxicity levels. In view of the environmental effect, the present study proposes a new green solvent called 1-ethyl-3-methyl-imidazolium hydrogen sulfate (EmimHSO4) ionic liquid (IL) to recover gold from copper anode slime (CAS). The optimum leaching conditions for maximizing gold recovery were determined by orthogonal array (OA) of Taguchi’s experimental design method. OA L16 (44) including four parameters with four levels each, was used to examine the effects of IL concentration (20%, 40%, 60%, 80% v/v), temperature (25, 50, 75, 95 °C), time (½, 1, 2, 4 h) and solid/liquid ratio (1/10, 1/15, 1/20, 1/25 g/mL) on leaching efficiency of the gold recovery. Statistical analysis of variance (ANOVA) was used to determine the relevance between experimental conditions and gold recovery. The selective leaching tests results showed that gold recovery up to 89.07% was attained on laboratory scale under the optimum leach conditions: 80% IL concentration, 75 °C, 4 h and 1/25 g/mL solid/liquid ratio. According to these results, EmimHSO4 IL provides a very good ambiance for the oxidative leaching of gold and can be offered as an alternative leaching agent instead of harmful cyanide-based solvents.

Hydrometallurgical Treatment of Copper Smelting Dust by Oxidation Leaching and Fractional Precipitation Technology

In this study, we report the recovery of metals from copper smelting dust by oxidation leaching and fractional precipitation technology. Under the optimum conditions, the leaching efficiencies achieved for Cu, As, Fe, Cd, and Zn are 93.4%, 94.2%, 39.7%, 98.1%, and 90.7%, respectively. Fractional precipitation technology is then employed for the recovery of Cu, As, Zn, and Cd from the leaching solution. The precipitates generated in the sequential steps contain 54.2% Cu, 25.8% As, 65.3% Cd, and 59.5% Zn. The precipitation of Cu, Cd, and Zn as their sulfides can be modulated by controlling the redox potential, and the optimal values are +312 mV, +126 mV, and +30 mV, respectively.

Electron microscope investigations of activated chalcopyrite particles via the FLSmidth® ROL process

Because of its unique semiconductor properties, the world’s most abundant copper mineral, chalcopyrite (CuFeS2), is refractory with respect to atmospheric leaching using traditional acidic ferric sulfate lixiviants. FLSmidth® has developed a novel approach manipulating lattice properties of semi-conducting minerals with the benefit of increasing chemical reactivity and dissolution kinetics. In the FLSmidth® Rapid Oxidative Leach (ROL) process, leach kinetics are still further enhanced by combining chemical and mechanical processes with the assistance of a Stirred Media Reactor. Due to the reduction in surface passivation problems associated with atmospheric leaching, this process is typically able to achieve copper recoveries exceeding 95% in 6 h. An important factor contributing to this extraordinary process performance is a mineral preconditioning step (the focus of this study), which uses between 0.1 and 5 mol percent of copper (II) to dope the lattice and thereby “activate” chalcopyrite. Since lattice restructuring can have such a dramatic influence on semiconductor reactivity, the associated physico-chemical phenomena are worth studying. In this regard, we investigate the relationship between chemical activation and deformation of the chalcopyrite crystal lattice through the use of electron microscopy. Although the activation process took only an hour and the extent of conversion was on the order of a few mol%, the lattice was found to be strained throughout the particle. This paper draws some insights into the impact of applying chemical activation as a pretreatment for mechanochemical processes.

Recovery of tin from metal powders of waste printed circuit boards

To avoid the adverse effects of tin on the smelting process used to recover copper from metal powders of waste printed circuit boards, an effective process is proposed that selectively extracts tin and its associated metals. That impacts of alkaline pressure oxidation leaching parameters on metal conversion were systematically investigated. The results showed that Sn, Pb, Al and small amounts of Zn in the metal powders were leached out, leaving copper residue. By optimizing the conditions, leaching recovery of 98.2%, 77.6%, 78.3 and 6.8% for Sn, Pb, Al and Zn, respectively, were achieved. Subsequently, more than 99.9% of Pb and Zn in the leaching solution were removed as a mixture of PbS-ZnS in the purification process, which can be used as a raw material in Pb smelting. Approximately 86.2% of Sn in the purified solution was recovered by electrowinning, and the purity of the cathode tin was over 99.8%.

Challenges with elemental sulfur removal during the leaching of copper and zinc sulfides, and from the residues; a review

The hydrometallurgical recovery of metal values from sulfide concentrates, such as chalcopyrite, enargite, and sphalerite, typically generates elemental sulfur in the oxidative leaching processes. The main disadvantage of the generation of sulfur is that it retards or hampers the efficiency of the leaching process. The oxidative leaching of sulfide mineral concentrates at temperatures above 180°C and at high pressures, known as total pressure oxidation (TPOX), completely converts the sulfide minerals to sulfate ions and sulfuric acid. However, the TPOX process has several negative aspects that increase costs, including the capital cost of the TPOX operations, the high oxygen demand to convert sulfide to sulfate, and the lime that is required to neutralize the excess acid in the autoclave discharge. Alternative processes that can reduce the capital and operating costs associated with the treatment of sulfidic concentrates include the medium temperature pressure oxidation (MT-POX) processes that operate at or below 150°C, such as the Cominco Engineering Services Ltd. (CESL) process, and atmospheric leaching (ATL) processes, such as the Albion and Galvanox™ processes. In the MT-POX and ATL processes, a proportion of the sulfides from the sulfide concentrates are oxidized to elemental sulfur, reducing the generation of acid and the oxygen demand of the oxidative leaching processes. Despite the lower operating and capital costs of the MT-POX and ATL processes, elemental sulfur may cause environmental problems such as acid mine drainage, or downstream process operation problems such as low solid/liquid separation efficiency or leaching efficiency. Thus, it is important to remove the elemental sulfur effectively during the leach process or from the residues after the leach process. In this paper, we present a summary of the research that has been conducted to decrease the passivating effect of molten or solid sulfur during the leaching of copper sulfide and zinc sulfide, and the approaches to remove the elemental sulfur from the leach residues. Also, the paper reviews the most important approaches that have been developed to address the elemental sulfur issue, including the application of polytetrafluoroethylene (C2F4)n, carbon tetrachloride (CCl4), ozone, nanosilica, sulfur-oxidizing bacteria, thermophilic iron-oxidizing archaea, sulfur-reducing bacteria (SRB), calcium lignosulfonate, quebracho, tetrachloroethylene (C2Cl4), Na2S leaching–CO2 precipitating, and vacuum and atmospheric distillation.

Simultaneous enhancement of sludge dewaterability and removal of sludge-borne heavy metals through a novel oxidative leaching induced by nano-CaO2.

The production of sewage sludge with the presence of various contaminants has been a serious issue for the operation of wastewater treatment plants on both the economical and environmental sides. To minimize the sludge volume to be handled and limit the potential environmental risk, this study developed a novel oxidative leaching process for enhanced sewage sludge dewatering and simultaneous removal of heavy metals based on nano-CaO2. Response surface methodology determined the following optimal conditioning parameters in terms of capillary suction time reduction: 0.0906g/g dry solid (DS) nano-CaO2, 0.9969mmol/g DS Fe2+, and pH of 5.59. The speciation partitioning analysis of the heavy metals pre and post nano-CaO2 peroxidation indicated that the content of organically bound metals decreased and the percentage of soluble fraction increased substantially, which was beneficial for the removal of heavy metals through the dewatering unit. Nano-CaO2 peroxidation could also induce the transformation of extracellular polymeric substances (EPS) from the tightly bound layers to the loosely bound layers of sewage sludge flocs. Through the decline of the Ryan-Weber constant of fluorescence titration and the pseudo-first-order kinetic constant of complexation, it was verified that the binding capacity of EPS with metal ions could be damaged by nano-CaO2 peroxidation, which was the primary mechanism behind the substantial reduction of organically bound metals. This study is believed to provide novel insights into the application of nanotechnology in terms of the simultaneous volume and toxicity reduction of sewage sludge. Graphical abstract.