Ferric Chloride Leaching Research Articles

Laccase-mediator system for enzymatic degradation of carbonaceous matter in the sequential pretreatment of double refractory gold ore from Syama mine, Mali

The sequential bio-treatment of refractory carbonaceous gold ore is a promising solution to recover gold effectively by environmentally friendly technology, which includes bio-oxidation of sulfide and biodegradation of carbonaceous matter by lignin-degrading enzymes. There are several drawbacks in enzyme treatment using cell-free spent medium (CFSM), including lignin peroxidase and manganese peroxidase from Phanerochaete chrysosporium, in particular the poor stability of enzyme activities. In the present work, laccase-mediator system (LMS) was applied for the degradation of carbonaceous matter in real gold ore to improve the efficiency of gold extraction as well as handling. The LMS was intended to be a great alternative process of CFSM with utilizing purified laccase in the presence of 1-hydroxybenzotriazole as a mediator. The application of LMS provided several advantages including not only greater stability, greater efficiency to degrade carbonaceous matter, better handling, much saving the treatment time, but also wider availability in laccase. In addition, replacing bio-oxidation with ferric chloride leaching as the dissolution path of sulfides facilitated avoiding the formation of jarosite and saving the required time. The gold recovery by cyanidation was improved from 41.5 ± 0.3% for the starting material to 81.3 ± 3.9% (n = 2) for the solid residues after the modified sequential pretreatment. This is correspondent to 86.3% of gold recovery for the extractable maximum gold excluding the enclosed gold in acid-insoluble silicates. The improved process involving LMS can be proposed with valuable advantages to fit a sustainable metallurgical technology of gold ores.

Copper Recovery from Printed Circuit Boards Using Acidic Ferric Chloride Leaching and Electrodeposition

In this work, 0.5 mol L−1 HCl and 0.13 mol L−1 FeCl3 have been used as leaching solution of industrially wasted copper at room temperature. Copper recovery from the leaching solution has been studied by batch electrodeposition at room temperature and either by using different constant current densities or by pulsing the current. The deposits obtained at 20 mA cm−2 show low efficiencies and are mainly composed of Cu0 with CuCl being a minor component. When the deposits are obtained at 50 mA cm−2, the efficiency is higher, but the adherence is poor and the porosity is high. By using pulsed electrodeposition, it is possible to improve the adherence of the deposits. However, the deposits are contaminated with copper and iron oxides, as well as with chloride compounds. Tin was not detected in any of the deposits obtained using all the electrodeposition conditions tested in this work.

Effect of redox potential and OCP in ferric and cupric chloride leaching of gold

The research presented contributes to the global goal of responsible production by providing robust tools for the optimization of gold dissolution in cyanide-free gold leaching solutions, which represent emerging non-toxic gold technologies. In the current study, gold dissolution was investigated in ferric and cupric chloride solutions. The effect of the redox potential on the open circuit potential (OCP) and dissolution rate of gold was investigated experimentally in the parameter range of T = 25–95 °C, [Fe3+/Cu2+] = 0.02–1.0 M, [Cl−] = 1–5 M, pH = 0.0–2.0, and ωcyc = 2500 RPM. A high rotational speed was chosen to minimize the effects of limited mass transfer rate. The aim was to provide tools for estimating the gold dissolution rate in ferric and cupric chloride solutions, using the solution properties. The results showed that redox potentials, OCPs, and dissolution rates were constantly higher in ferric chloride solutions compared to corresponding cupric chloride solutions. The multilinear regression models for redox potential showed that a rise in temperature and oxidant concentration increased the redox potential in both ferric and cupric chloride solutions. However, an increase in the chloride concentration decreased the redox potential in ferric chloride solutions, whereas the effect was the opposite in cupric solutions. A rise in the pH value increased the redox potential in ferric solutions, but this was found to be an insignificant variable in cupric chloride leaching within the investigated parameter range. The redox potential had a positive correlation with OCP and the logarithm of the gold dissolution rate in both investigated systems. The results suggest that, in the chloride leaching systems examined, the solution properties can be used to determine the redox potential, and furthermore, the redox potential can be used to estimate the gold dissolution rate. This study provides an experimentally verified tool for the robust estimation of the gold dissolution rate in chloride systems.

Ferric chloride leaching of antimony from stibnite

A circulatory hydrometallurgical process: ferric trichloride (FeCl3) leaching of antimony sulfide (Sb2S3) (production of Sb by replacing it with iron) followed by membrane electrowinning of ferrous chloride (FeCl2), was developed to cleanly extract Sb from stibnite. First, Sb was leached (leaching efficiency >98%), using FeCl3 as leaching reagent, under the following optimum conditions: temperature of 50 °C, liquid-to-solid ratio of 8:1, α(FeCl3) of 1.2 (where α represents the excess coefficient), and time of 1 h. Then, an Fe plate was used to replace Sb from the leaching solution using a two-step process. Approximately 96.86% of the Sb in the leaching solution was extracted, and pure FeCl2 was obtained. Finally, the FeCl2 solution was subjected to membrane electrowinning to regenerate the FeCl3 solution used as leaching solution at the anode and the Fe plate used as cathode. The optimal membrane electrowinning conditions were as follows: current density of 300 A/m2, temperature of 40 °C, and pH = 2.0. Both the anode and cathode current efficiencies were higher than 99%. The FeCl3 solution and Fe plate were reused for the leaching process and Sb replacement, respectively, while superfluous metallic Fe was open circuited. This novel process presents several advantages, including recirculating all solutions, high current efficiency, and low reagent consumption.

Kinetics and mechanisms of gold dissolution by ferric chloride leaching

Gold dissolution was investigated in ferric chloride solution, being one alternative cyanide-free leaching media of increasing interest. The effect of process variables ([Fe3+]=0.02–1.0M, [Cl−]=2–5M, pH=0–1.0, T=25–95°C) on reaction mechanism and kinetics were studied electrochemically using rotating disk electrode with ωcyc=100–2500 RPM and Tafel method. The highest gold dissolution rate (7.3·10−4molm−2s−1) was achieved at 95°C with [Fe3+]=0.5M, [Cl−]=4M, pH =1.0 and ωcyc=2500 RPM. Increase in gold dissolution rate was observed with increase in temperature, ferric ion concentration and chloride concentration, but gold dissolution rate did not have a clear dependency on pH. Redox potential was found to vary between 636 and 741mV vs. SCE during experiments. According to the calculated equilibrium and measured open circuit potentials, gold was suggested to dissolve as aurous ion Au+ and form AuCl2−, rather than auric ion Au3+ and form AuCl4−. Further, it is suggested that AuCl2− does not oxidize to AuCl4− under the investigated conditions. Levich plot and the calculated activation energies suggested that gold dissolution was limited by mass and electron transfer. According to a mechanistic kinetic model developed in the current work, intrinsic surface reaction mainly controls gold dissolution, especially at higher rotational speeds (>1000 RPM). Uncertainties in the model parameters of the mechanistic kinetic model were studied with Markov chain Monte Carlo methods.

Comparative evaluation of microbial and chemical leaching processes for heavy metal removal from dewatered metal plating sludge

The purpose of the study described in this paper was to evaluate the application of bioleaching technique involving Acidithiobacillus ferrooxidans to recover heavy metals (Zn, Cu, Ni, Pb, Cd and Cr) in dewatered metal plating sludge (with no sulfide or sulfate compounds). The effect of some conditional parameters ( i.e. pH, oxidation–reduction potential (ORP), sulfate production) and operational parameters ( i.e. pulp density of the sludge and agitation time) were investigated in a 3 l completely mixed batch (CMB) reactor. The metal recovery yields in bioleaching were also compared with chemical leaching of the sludge waste using commercial inorganic acids (sulfuric acids and ferric chloride). The leaching of heavy metals increased with decreasing of pH and increasing of ORP and sulfate production during the bioleaching experiment. Optimum pulp density for bioleaching was observed at 2% (w/v), and leaching efficiency decreased with increasing pulp density in bioleaching experiments. Maximum metal solubilization (97% of Zn, 96% of Cu, 93% of Ni, 84% of Pb, 67% of Cd and 34% of Cr) was achieved at pH 2, solids contents of 2% (w/v), and a reaction temperature of 25 ± 2 °C during the bioleaching process. The maximum removal efficiencies of 72% and 79% Zn, 70% and 75% Cu, 69% and 73% Ni, 57% and 70% Pb, 55% and 65% Cd, and 11% and 22% Cr were also attained with the chemical leaching using sulfuric acids and ferric chloride, respectively, at pH 2, solids contents of 2% (w/v), and a reaction temperature of 25 ± 2 °C during the acid leaching processes. The rates of metal leaching for bioleaching and chemical leaching are well described by a kinetic equation related to time. Although bioleaching generally requires a longer period of operation compared to chemical leaching, it achieves higher removal efficiency for heavy metals. The efficiency of leaching processes can be arranged in descending order as follows: bioleaching > ferric chloride leaching > sulfuric acid leaching. These results suggest that bioleaching may be an alternative or adjunct to conventional physicochemical treatment of dewatered metal plating sludge for the removal hazardous heavy metals.

Ferric chloride leaching of chalcopyrite: Synergetic effect of CuCl 2

This work presents a study of the leaching of chalcopyrite in acidic ferric chloride. Two chalcopyrite samples (natural chalcopyrite crystal and chalcopyrite concentrate) were leached under different conditions. The effects of stirring speed and temperature were investigated. It was found that agitation had a negative effect on copper recovery from chalcopyrite during the leaching process. This is explained by the fact that cupric chloride complexes are formed during the leaching process where cupric ion is considered as a stronger oxidant than ferric ion. Agitation sweeps away the cupric chloride complexes formed, whereas, under stagnant conditions cupric chloride complexes accumulate at the reaction interface causing enhanced dissolution of copper. The overall leaching reaction was found to be sensitive to temperature. The shrinking core model was fitted to the data and it was found that the leaching process was controlled by chemical reaction with activation energy of 69 kJ/mole.

A study on the acidified ferric chloride leaching of a complex (Cu–Ni–Co–Fe) matte

The acidified ferric chloride leaching of an artificial matte was carried out to investigate the extraction behaviour of copper, nickel, and cobalt. The composition of the synthetically prepared Cu–Ni–Co–Fe matte was: 24.95% Cu, 35.05% Ni, 4.05% Co, 11.45% Fe, and 24.5% S. The major mineral phases of the matte were: CuFeS 2, CuS 2, (FeNi) 9S 8, (FeNi)S 2, Ni 9S 8, Ni 3S 2, (CoFeNi) 9S 8 and Co metal. The effects of time (0–7 h), temperature (30–90 °C), FeCl 3 (0.5–2.0 M) and HCl (0.1–0.5 M) concentrations were studied with and without the presence of an organic solvent (CCl 4). The Cu extraction was fast compared to Ni and Co and reached equilibrium within 3 h in FeCl 3 medium. The extraction of all the three metals increased with increase of temperature. The effect was found to be the maximum for Co, followed by Ni and Cu. Under optimum conditions (1.5 M FeCl 3, 0.3 M HCl, 90 °C and 7 h), 99.5% Cu, 93.2% Ni and 85.2% Co was extracted to the solution. When carbon tetrachloride was added to the reaction medium, the extraction of metals increased due to the solubilisation of elemental sulphur coated around the sulphide mineral particles. From the XRD study the undissolved Ni phase was found to be (FeNi) 9S 8 and undissolved Co phase was cobalt metal.

Dissolution kinetics of sphalerite in acidic ferric chloride leaching

Abstract This paper presents a study for leaching kinetics of sphalerite concentrate in FeCl3–HCl solution. The shrinking core model was applied to the results of experiments investigating the effects of stirrer speed of 200–600 rpm, ferric ion concentration in range of 0–1 M, solid/liquid ratio in range of 1/100–1/5, leaching temperature range of 40–80 °C and particle size on zinc dissolution rate. The activation energy for the leaching process was found to be 45.30 kJ/mol and the Arrhenius constant was calculated to be 5.454 s−1. The order of reaction for ferric ion concentration, solid/liquid ratio and particle size were also obtained. The rate of the reaction based on reaction-controlled process can be expressed as, [ 1 − ( 1 − α ) 1 / 3 ] = k 0 ( F e 3 + ) 0.36 ( ρ S / L ) − 0.33 r 0 − 0.97 exp ( − 45300 / R T ) t . The dissolution of sphalerite with acidic ferric chloride solution was found to be controlled by reaction-controlled process.

Spectroscopic and electrochemical characterization of the surface layers of chalcopyrite (CuFeS 2) reacted in acidic solutions

XPS, Fe Lα,β and Cu Lα,β X-ray emission and Fe L-, Cu L-, S L-edge and O K-edge absorption spectroscopies, Mössbauer spectroscopy and cyclic voltammetry were applied to study reacted surface layers of natural chalcopyrite, CuFeS 2. The surfaces became metal-depleted after the anodic oxidation in 1 M HCl and the leaching in 1 M H 2SO 4+0.2 M Fe 2(SO 4) 3 or 1 M HCl+0.4 M FeCl 3 solutions, with the sulfur excess and iron/copper ratio been higher in the last instance, and were enriched in copper after the electrochemical reduction. The electronic structures of the metal-deficient layers up to several tenths of micrometer thick were similar to that of chalcopyrite, except that the density of the highest occupied states depended on sulfur anions formed (predominant S 3-anions after the ferric sulfate treatment, S 4-anions after the ferric chloride leaching or the potential sweep to 0.9 V, etc.). The layers created by the preliminary oxidation had only a small effect on the chalcopyrite voltammetry. We suggest a new reaction mechanism considering a role of the surface changes, including disordering and Anderson localization of the electronic states.

Pressure sulpuric acid leaching of a sulphide concentrate to recover copper, nickel and cobalt

Ore from the Jaduguda mines, India, includes significant contents of important metals,1 such as Cu (0.1%), Ni (0.1%), Co (0.006%) and Mo (0.02%), together with appreciable amounts of other valuable materials, such as apatite (3–4%), rare earths (0.1% including Y) and magnetite (5.5%). The purpose of the by-product recovery plant of the uranium mill is to recover as much of these minerals as possible to augment India’s supply. It currently produces a complex sulphide concentrate at the rate of about 1200 t/year, which yields a high-grade copper concentrate and a low-grade silicate tailing containing Cu and Ni, together with a salable molybdenum concentrate. The copper concentrate was formerly sold to the Indian Copper Complex (ICC) at Ghatsila, but of late the ICC has discontinued processing of the concentrate because of its high nickel content. As a result, the copper concentrate has remained stockpiled for want of a suitable process. This product, which was previously designated a copper concentrate, but is now referred to as a sulphide concentrate, comprises 15% copper, 10.85% nickel and 0.37% cobalt (Table 1). Several processing options present themselves and some have been tried at various institutes in India. Mukherjee et al.2 peformed tests at kilogram scale in which roasting in the presence of NaCl in the temperature range 400–500°C was followed by water leaching and solution purification. The three metals, copper, nickel and cobalt, were separated from the leach liquor of salt-roasted material as their sulphate salts by solvent extraction3 with D2EHPA for subsequent recovery in the desired form. The salt roast–leach–solvent extraction– electrowin route was also followed at NML4 for recovery of the metals as electrolytic-grade cathodes. Because of excessive corrosion during roasting, however, the process was considered unfavourable. Other important process routes for the extraction of metals from sulphide concentrates are ferric chloride leaching5 and cupric chloride–O2 leaching6 in acid conditions. Although high recoveries of the metals are often achieved, ferric chloride leaching is also known to present corrosion problems and, therefore, has not been considered by Indian investigators for this concentrate. Preliminary experiments with pressure leaching in acidic conditions are reported to have yielded metal recoveries of 70–75% Ni and 10–20% Cu.7,8 Despite these developments, it has long been considered that smelting is likely to remain the principal processing route for sulphide concentrates. This view is being challenged through pressure-leaching developments by Dynatec and Cominco Engineering Services, Ltd. (CESL), in Canada, the installation at Mt. Gordon in Queensland, Australia, and the very recent announcement by Phelps Dodge.9 The CESL process10 for copper concentrate, which uses an oxidative pressure leach with a mixed sulphate–chloride solution, is reported to have been piloted successfully. Chloride ions play a catalytic role and are required to prevent excessive sulphur oxidation that would otherwise make the process uneconomic. Pressure leaching is followed by solvent extraction and electrowinning. The Dynatec process11 for chalcopyrite concentrate treatment also uses chloride additions to the leach liquor to minimize sulphide oxidation to sulphur. In addition, fine coal is used as a dispersant for the molten sulphur formed under the leaching conditions in the autoclave. This is much cheaper than the sodium or calcium lignosulphonate or quebracho used as additives in the zinc concentrate pressureleach process. Solvent extraction is the process of choice for copper recovery from the leach liquor. The Activox process11 is claimed to offer the potential to treat sulphide concentrate directly without the need for intermediate pyrometallurgical treatment. The process involves fine grinding and low-pressure oxidative leaching. The autoclave leaching conditions are typically 100°C at an oxygen pressure of 100 kPa with a residence time of 4 h for chalcopyrite oxidation. The solution generated by leaching is finally treated by solvent extraction and electrowinning. Recently,12 a two-stage acid pressure leach at 140°C and pO2 of 600 kPa was applied to a low-grade copper–nickel concentrate containing 2% Ni, 0.43% Cu and 6.2% Mg, when it was recognized that a preleach step was required to recover more than 90% of metals.12 Acid pressure leaching was deemed to merit consideration as a potential means of extracting the valuable metals from the Jaduguda sulphide concentrate.

Ferric chloride leaching of a mechanically activated pentlandite–chalcopyrite concentrate

Mechanical activation accelerates the leaching of non-ferrous metals from sulfide ores by increasing the surface area and reactivity of the concentrate, and through lattice distortions resulting from deformation due to milling. In this study we examine the feasibility of applying the process to a complex ore concentrate containing both pentlandite and chalcopyrite through the use of a horizontal ball mill for the mechanical activation of chalcopyrite, using a concentrated (∼5 M Cl −) ferric chloride solution for the leaching. The kinetics of dissolution are correlated with specific area and with line broadening as determined by X-ray diffraction. Mechanical activation improves the kinetics both of copper extraction from the chalcopyrite, and of nickel extraction from the pentlandite. As both leached readily using the ferric chloride solution, selective leaching using this lixiviant does not seem feasible.

Simultaneous autogenous milling and ferric chloride leaching of chalcopyrite

Mechanical activation by autogenous milling has previously been shown to improve leaching kinetics. In this study autogenous milling was conducted simultaneously with ferric chloride leaching. A sequence of products was observed, with chalcopyrite being replaced by synthetic nantokite (CuCl) and the nantokite being more gradually replaced by synthetic eriochalcite (CuCl 2·2H 2O).

Model for the ferric chloride leaching of galena

A shrinking core model for the FeCl3 leaching of galena (PbS), which accounts for the microstructure previously observed during this process, is presented. The microstructure is characterized by two distinct product layers—PbCl2 in direct contact with the PbS core and So above the PbCl2 layer. Rate equations for the evolution of the three solid phases and the PbS leaching conversion are derived for the case of flat plate geometry appropriate for the reaction of massive galena fragments. In the case of rate control by diffusion of the lead chloride reaction products through the So layer, the system is shown to exhibit parabolic behavior as long as the So layer is built up primarily at the PbCl2-So interface. For the mechanism considered in this study, negative deviation from parabolic behavior is observed to increase as the amount of So forming at the external So-solution interface rises. When the system is controlled by surface reaction kinetics, the model predicts linear rates under all circumstances.

Ferric chloride leaching of mechanically activated chalcopyrite

Mechanical activation is a means of accelerating the leaching process. Contributing to the success of this technique are (1) increased surface area; (2) increased surface reactivity; and (3) the microstructural modifications stemming from the deformation. Previous studies have focused on gaining a fundamental understanding of these factors. This study represents a divergence from this approach, as we set out to determine the effectiveness of the technique when applied on a scale more reflective of how the process might actually be practised. To this end, chalcopyrite was autogenously milled in a horizontal mill, and leaching was conducted using a 5 M chloride leach solution. Leaching of as-received concentrate resulted in copper extractions of 75% in 5 h of leaching, whereas leaching mechanically activated concentrates resulted in copper extractions over 95% after 3 h of leaching. This study investigated the critical parameters affecting the efficiency of mechanical activation as a means of accelerating the oxidative leaching of sulfide minerals. The processes of attrition and fragmentation enhance reaction rates by increasing both the surface area and the density of defects. A small laboratory shaker mill and a small tumbling mill were used to mechanically process chalcopyrite; the former using steel grinding media, the latter using sized ore. The increase in surface area was determined using BET; and X-ray diffraction analysis was utilized to determine the full width at half maximum (FWHM) for chalcopyrite, which is subsequently used as a marker of the relative deformation. Leaching experiments were conducted with as-received concentrate and with processed concentrate. The contributions of the increased surface area and the deformed structure were correlated with the leaching kinetics.

Influence of solid state properties on ferric chloride leaching of mechanically activated galena

The reaction of mechanically activated galena with ferric chloride solution was investigated in the concentration range [Fe 3+] =0.01–0.6 M at temperatures between 303 and 338 K. The mechanical activation lasting 5–30 min was carried out in a planetary mill. It has been found that this reaction is sensitive to the microstrains produced in the structure of galena during grinding as well as to the concentration of Fe 3+ in the solution. The influence of Fe 3+ concentration is in operation practically only in the region [Fe 3+] < 0.2 M.

An investigation of the electrochemical nature of the ferric chloride leaching of sphalerite

Although considerable research has been reported on the hydrometallurgical behavior of zinc sulfide in chloride media, the electrochemical nature of the dissolution reaction involving a ferric/ferrous couple and the accelerating effects of the chloride ion and of cupric chloride have not been fully elucidated. It is shown that the decrease in dissolution rate of sphalerite in the presence of ferrous ions is due to a decreased cathodic half cell potential and therefore a less favorable mixed potential. The addition of chloride ion to the anodic half cell significantly increases the cell current, indicating that chloride ion plays a direct role in the anodic dissolution of ZnS and has relatively little effect on the cathodic half cell. It is also shown that Ag + has no effect on the dissolution of ZnS in a ferric chloride electrolyte. In addition the data suggests that cupric ion may accelerate the dissolution of sphalerite through a mechanism other than simply providing an additional oxidizing reagent to complement ferric ion. This investigation has demonstrated the utility of a relatively simple, dual cell technique for the study of electrochemical leaching reactions by separating the two half reactions. Although this technique would not replace standard leaching experiments, it does provide a useful complementary approach, and in some cases can provide data that would be particularly difficult or impossible to obtain through typical, standard leaching experiments.

The leaching of sulphide minerals in chloride media

Recent studies on the ferric chloride and cupric chloride leaching of chalcopyrite, galena and sphalerite are reviewed. Although the chloride leaching of chalcopyrite concentrates has been proven at the demonstration plant scale, the leaching reaction is difficult. In contrast, galena dissolves rapidly in FeCl 3 media, and both the leaching rate and lead solubility increase significantly with increasing chloride concentration. The hydrometallurgical treatment of lead concentrates seems to be technically feasible. The sphalerite leaching rate is strongly affected by its solid solution iron content, and leaching processes for iron-rich zinc concentrates could probably be developed. The importance of intermediate sulphide phases and insoluble reaction products on the leaching of sulphides is discussed. In addition, it is postulated that at least part of the elemental sulphur reaction product is formed via the oxidation of dissolved H 2S. The ability of chloride leaching processes to generate elemental sulphur while leaving pyrite largely unaffected makes them especially useful for the treatment of pyritic complex sulphides. Thus, recent chloride leaching technologies for complex sulphides are also reviewed.

A Critical Review of the Ferric Chloride Leaching of Galena

Abstract Ferric chloride leaching is a potentially attractive method of processing lead concentrates, and many studies have been carried out on the kinetics of dissolution of galena (PbS). In this paper, the extensive literature on galena dissolution is critically reviewed and the various results are compared on a consistent basis. There is a consensus that the leaching reaction is rapid and that elemental sulphur is the dominant reaction product. Although quantitative agreement among the various studies is lacking because of differences in galena purity, experimental procedures and methods, and data interpretation, the overall trends indicate a shallow temperature dependence, a direct total chloride concentration effect and a modest influence of solution agitation. Furthermore, there is an abrupt change in the reaction mechanism at FeCl3 concentrations less than ∼0.1 M. The experimental observations are consistent with rate control either by the outward diffusion of the PbCl2 reaction product through the...

A Critical Review of the Ferric Chloride Leaching of Galena

A Critical Review of the Ferric Chloride Leaching of Galena