The effect of the elemental sulfur reaction product on the leaching of galena in ferric chloride media

The dissolution of galena in 0.3 M FeCl₃-0.3 M HC1 solutions containing 0 to 6 M LiCl was studied at 80 °C, and parabolic kinetics were observed at all LiCl concentrations. The leaching rate increases gradually with increasing LiCl concentrations to ≈4 M LiCl; the presence of >4 M LiCl results in a rapid increase in the leaching rate. The solubility of PbCl₂ in 0.3 M FeCl₃-0.3 M HC1 solutions containing 0 to 6.5 M LiCl was measured over the temperature range of 50 °C to 90 °C. The solubility increases systematically with increasing temperature and LiCl concentration. The parabolic kinetics, coupled with the correlation between the leaching rate and the solubility of PbCl₂, suggest that the dissolution of galena is controlled by the outward diffusion of the PbCl₂ reaction product through the constantly thickening layer of elemental sulfur formed during leaching. This conclusion is also supported by various morphological studies which consistently indicated a thin layer of PbCl₂ between the corroding galena and the porous elemental sulfur reaction product.     

Kinetics of galena dissolution in ferric chloride solutions

A leaching investigation of galena with ferric chloride has been carried out as a function of concentration of ferric chloride and sodium chloride, temperature, and particle size. Three size fractions were considered in this investigation, namely, 48 × 65, 35 × 48, and 28 × 35 mesh. The concentration ranges of ferric chloride and sodium chloride used in this investigation were 0 to 0.25 M and 0 to 3 M, respectively. The reaction rate mechanism has been discussed in terms of a shrinking core model developed for cubic systems. Mass transport of ferric chlorocomplex through the product sulfur layer appears to be responsible for establishing the overall leaching rate under most of the conditions used in this investigation. The apparent activation energy for the leaching of 28 × 35 mesh galena with 0.1 M FeCl₃, 1 M HC1, and 3.0 M NaCl was found to be about 8.05 kcal/mol (33.7 kJ/mol), which was partially contributed by diffusion and partially by the heat of reaction of the formation of ferric chlorocomplexes. Rate of dissolution at both 50° and 90 °C is greatly affected by ferric chloride concentration up to 0.2 M and is essentially constant with ferric chloride concentration above this value.     

The leaching of galena in cupric chloride media

The kinetics of dissolution of galena (PbS) in CuCl₂-HCl-NaCl media have been investigated using the rotating disk technique. Rapid nonlinear kinetics are observed over the temperature range 45 °C to 90 °C and for NaCl concentrations from 0 to 4.0 M. The leaching rate is in-dependent of CuCl₂ concentrations >0.1 M but increases with increasing concentrations of either HC1 or NaCl. The leaching rate decreases with the accumulation of either the PbCl₂ or CuCl reaction product in the leaching medium but is insensitive to the disk rotation speed. The apparent activation energy for the rate controlling process is 33 kJ/mol, and this value falls to about 15 kJ/mol when interpreted as a dissolution rate for PbCl₂, whose solubility increases with temperature. The above observations are shown to be consistent with rate control by the outward diffusion of the PbCl₂ and CuCl reaction products through the solution trapped in the pores of the constantly thickening elemental sulfur layer which forms on the surface of the galena. CANMET, Energy, Mines, and Resources Canada, 555 Booth Street, Ottawa, ON, K1A 0G1, Canada.     

Reaction mechanism for the acid ferric sulfate leaching of chalcopyrite

The acid ferric sulfate leaching of chalcopyrite, CuFeS₂ + 4Fe⁺³ = Cu⁺² + 5Fe⁺² + 2S⁰ was studied using monosize particles in a well stirred reactor at ambient pressure and dilute solid phase concentration in order to obtain fundamental details of the reaction kinetics. The principal rate limiting step for this electrochemical reaction appears to be a transport process through the elemental sulfur reaction product. This conclusion has been reached in other investigations and is supported by data from this investigation in which the reaction rate was found to have an inverse second order dependence on the initial particle diameter. Furthermore, the reaction kinetics were found to be independent of Fe⁺³, Fe⁺², Cu⁺² and H₂SO₄ in the range of additions studied. The unique aspect of this particular research effort is that data analysis, using the Wagner theory of oxidation, suggests that the rate limiting process may be the transport of electrons through the elemental sulfur layer. Predicted reaction rates calculated from first principles using the physicochemical properties of the system (conductivity of elemental sulfur and the free energy change for the reaction) agree satisfactorily with experimentally determined rates. Further evidence which supports this analysis includes an experimental activation energy of 20 kcal/mol (83.7 kJ/mol) which is approximately the same as the apparent activation energy for the transfer of electrons through elemental sulfur, 23 kcal/ mol (96.3 kJ/mol) calculated from both conductivity and electron mobility measurements reported in the literature. formerly Metallurgy Graduate Student, University of Utah.     

The Dissolution of Sphalerite in Ferric Chloride Solutions

The kinetics of dissolution of both sintered sphalerite disks and untreated sphalerite particles in ferric chloride-hydrochloric acid solutions have been investigated. Over the temperature interval 25 to 100°C, the dissolution occurred according to a linear rate law and with an associated apparent activation energy of about 10 kcal/mole. Most of the oxidized sulfide ion reported as elemental sulfur in the leach residues. The leaching rate was independent of the disk rotation speed and this fact, together with various hydrodynamic calculations, indicated that the reaction was chemically controlled. The dissolution rate increased as the 0.36 power of the ferric chloride concentration and it also increased substantially in the presence of dissolved CuCl₂. The accumulation of the ferrous chloride reaction product severely retarded the leaching reaction, but the presence of dissolved zinc chloride only slightly impeded it. The leaching rate was relatively insensitive to low levels of HC1 (>1 M), but increased dramatically at higher acid concentrations because of direct acid attack of the ZnS.     

The kinetics of leaching galena with ferric nitrate

The kinetics of leaching galena with ferric nitrate as oxidant has been studied. Experimental results indicate that the rate of galena dissolution is controlled by surface chemical reaction. Rate is proportional to the square root of the concentration of ferric ion. The addition of more than one mole/liter sodium nitrate decreases reaction rate. With nitrate additions below this concentration, rate either remains constant or is slightly enhanced. An activation energy of 47 kJ/mol was measured, and rate is proportional to the inverse of the initial size of galena particles. These results are explained in terms of mixed electrochemical control. The anodic reaction involves the oxidation of galena to lead ion and elemental sulfur, and the cathodic reaction involves the reduction of ferric ion to ferrous ion.     

The leaching of galena in ferric sulfate media

The leaching of galena (PbS) in ferric sulfate media was investigated over the temperature range 55 °C to 95 °C and for various Fe(SO₄)_1.5, H₂SO₄, FeSO₄, and MgSO₄ concentrations. Relatively slow kinetics were consistently observed; in most instances, the 1-2/3α-(1−α)^2/3 vs time relationship, indicative of a diffusion-controlled reaction, was closely obeyed. The diffusion-controlled kinetics were attributed to the formation of a tenacious layer of PbSO₄ and S⁰ on the surface of the galena. The generation and morphology of the reaction products were systematically determined by scanning electron microscopy, and complex growth mechanisms were illustrated. The leaching rate increased rapidly with increasing temperature, and the apparent activation energy is 61.2 kJ/mol. The rate increases as the 0.5 power of the ferric ion concentration but is nearly independent of the concentration of the FeSO₄ reaction product. The rate is insensitive to H₂SO₄ concentrations <0.1 M but increases at higher acid levels. The presence of neutral sulfates, such as MgSO₄, decreases the leaching rate to a modest extent.     

The dissolution of sphalerite in ferric sulfate media

The dissolution of sphalerite, (Zn,Fe)S, in ferric sulfate media was investigated using closely sized fractions of crushed sphalerite crystals. Linear kinetics were observed, and the rate increased in proportion to the surface area, as the average particle size of the sphalerite decreased. The predominant reaction products are ZnSO₄, FeSO₄, and elemental sulfur. The leaching rate increases with increasing temperature, and the apparent activation energy is 44 kJ/mol. The relatively high apparent activation energy suggests that the rate is chemically controlled, a conclusion supported by the insensitivity of the rate of the rotation speed that was observed in complementary rotating disk experiments. The rate increases as the 0.3 to 0.4 power of the Fe(SO₄)_1.5 concentration, and is nearly independent of the pulp density, in the presence of a stoichiometric excess of ferric sulfate. In 0.3 M Fe(SO₄)_1.5 media, the rate increases with increasing acid concentrations >0.1 M H₂SO₄, but is insensitive to more dilute acid concentrations. In the absence of ferric ions, the rate increases rapidly with increasing H₂SO₄ concentrations, and relatively rapid rates are observed in solutions containing >0.5 M H₂SO₄. The rate decreases with increasing initial concentrations of ZnSO₄, MgSO₄, or FeSO₄ in the ferric sulfate leaching solution, and this emphasizes the importance of maintaining the dissolved iron in a fully oxidized state in a commercial leaching operation.     

An investigation of the thermodynamics and kinetics of the ferric chloride brine leaching of galena concentrate

The solution thermodynamics of acidified ferric chloride brine lixiviants and the dissolution kinetics of a galena concentrate in such solutions have been investigated. The distribution of the various metal chloro complexes calculated from available thermodynamic data shows that the distribution is shifted to the higher complexes, predominantly FeCl ₃ ^o , FeCl ₂ ^o , and PbCl ₄ ⁼ , as the total Cl^? concentration increases, and that the distribution is unaffected by the extent of reaction. The dissolution of PbS concentrate is presented as a competition between a nonoxidative reaction with H⁺ and the oxidative reaction with ferric ion. Acid dissolution of PbS predominates when the activity ratio of hydrogen ion to ferric ion is high. Under these conditions H₂S is produced. When the activity ratio of hydrogen ion to ferric ion is low, and especially when the concentration of Fe³⁺ is greater than 0.15 M, oxidative dissolution of PbS becomes the controlling reaction. The dissolution can be represented by a shrinking core model with a surface chemical reaction as the rate controlling step. This is supported by the activation energy of 72.1 kJ/mole and the dependence of the rate on the inverse of the particle radius. The following rate equation was found to be in excellent agreement with the experimentally observed leaching behavior for 0.15 to 0.6 M [Fe⁺³] _T up to approximately 90 to 95 pet extraction: $$1 - \left( {1 - \alpha } \right)^{1/3} = \left[ {\frac{{2.3 x 10^{12} }}{{r_0 }}\left[ {{\text{Fe}}^{{\text{ + 3}}} } \right]_T^{0.21} \exp \left( {\frac{{ - 72100}}{{{\text{R}}T}}} \right)} \right]t$$ The rate deviates from the 0.21 order for Fe⁺³ concentrations greater than 0.6 M. The deviation from the surface model at higher values of PbS conversion is due to the presence of solid PbCl₂ in the pores of the reacting particles.     

氯化铁溶液浸出低冰镍提取镍铜的研究

利用三价铁离子(Fe3+)的氧化性,采用氯化铁溶液浸取低冰镍,提取其中的镍、铜元素。本研究考察了浸出液固比、浸出温度、浸出时间、氯化铁溶液浓度对镍和铜浸出率的影响。动力学研究表明:氯化铁溶液浸出低冰镍时,镍元素的浸出过程由化学反应控制,铜元素的浸出过程由混合反应控制,经计算镍的浸出活化能为70.26 kJ/mol、铜元素的浸出活化能为38.62 kJ/mol。低冰镍和浸出渣的物相分析结果表明,浸出反应发生时,低冰镍中的硫元素被氧化成单质硫。本研究避免了传统工艺中的含硫气体污染问题。      

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 S^o 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 S^o layer, the system is shown to exhibit parabolic behavior as long as the S^o layer is built up primarily at the PbCl₂-S^o interface. For the mechanism considered in this study, negative deviation from parabolic behavior is observed to increase as the amount of S^o forming at the external S^o-solution interface rises. When the system is controlled by surface reaction kinetics, the model predicts linear rates under all circumstances.     

The effect of chloride ion on the ferric chloride leaching of galena concentrate

Previous investigations of the ferric chloride brine leaching of galena concentrate have shown that additions of chloride ion result in accelerated dissolution rates. The current study has provided the necessary information to extend and modify these previous results by incorporating the important effect of chloride ion on the dissolution kinetics. As part of this study the solubility of lead chloride in ferric chloride-brine solutions has been determined and results indicate that additions of either FeCl₃ or NaCl increase the PbCl₂ solubility. This is attributed to the effect of complexing on the level of free chloride ion. In addition, the dissolution kinetics of elemental lead and lead chloride were also determined and compared with the kinetics of PbS dissolution. It is significant that the rate of dissolution of PbCl₂ decreases as the concentration of Cl⁻ is decreased and as the concentration of dissolved lead increases. These results along with SEM examination of partially reacted Pb shot show that solid PbCl₂ forms on the surface long before the bulk solution is saturated with lead. The PbCl₂ is proposed to form by a direct electrochemical reaction between Cl⁻ and PbS prior to the formation of dissolved lead. The reaction was determined to be first order with respect to Cl⁻ and closely obeys the following kinetic model based on a rate limiting charge transfer reaction at the surface: The model is in excellent agreement with experimental results up to about 95 pct reaction as long as the solubility of PbCl₂ is greater than about 0.051 M. Where these conditions are not met, deviation from the surface reaction model occurs due to the extremely slow dissolution rate of PbCl₂. Therefore the effect of Cl⁻ on the brine leaching of PbS is attributed to two factors, the direct reaction of Cl⁻ with the pbS surface and the effect of Cl⁻ on the dissolution rate of PbCl₂. The overall dissolution process is viewed as occurring in three stages; in the first stage the reaction is controlled by the surface reaction and described by the model above, then as solid PbCl₂ is produced the diffusion of Cl⁻ would be equal in importance with the surface reaction,i.e, the second stage. As the reaction proceeds further, a shift in the rate-limiting step from surface reaction to product layer or pore diffusion occurs, the third stage. Thus the rate-determining step would no longer be just the surface reaction as observed experimentally at longer reaction times. The practical implications of these results for the processing of a complex sulfide concentrate using sequential, selective, or total leach approaches are also discussed.     

Oxidative leaching of an offgrade/complex copper concentrate in chloride lixiviants

Laboratory studies have been conducted on chloride leaching as a possible route for the simultaneous recovery of copper, zinc, and lead from an off grade and complex chalcopyrite concentrate (from Sikkim, India) associated with appreciable amounts of sphalerite, galena, and pyrite. The effects of temperature, concentration, and quantity of ferric chloride, stirring speed, and leaching time on metal dissolution have been investigated. Leaching tests have also been conducted with in-dividual (HC1, NaCl, CuCl₂, FeCl₃) and mixed chlorides (two-, three-, and four-component mix-tures). Results show the possibility of recovering not only 99 pct Cu and 89 pct Zn but also 82 pct Pb and 58 pct elemental S by treatment of the concentrate with 4 M FeCl₃ at 383 K (110 °C) for 7.2 ks (2 hours) employing 25 pct excess FeCl₃ and a stirring speed of 700 rev min⁻¹. Though 64 pct iron of the concentrate is found to dissolve, the pyrite seems to remain unattacked. Kinetic studies indicate that the chalcopyrite, sphalerite, and galena of the concen-trate dissolve simultaneously in the FeCl₃ lixiviant as if each mineral is separately leached, and the Cu and Zn dissolution reactions are under chemical control (linear kinetics). The addition of NaCl to the chloride lixiviants is found to be beneficial only up to a common salt concen-tration of 100 g/l. Leaching of the copper concentrate with CuCl₂ or mixed FeCl₃-CuCl₂-NaCl has not been as effective as its direct leaching with 4 M FeCl₃. N.V. NGOC, formerly Visiting Scientist with the Department of Metallurgical Engineering, Institute of Technology, Banaras Hindu University.     

The ferric fluosilicate leaching of lead concentrates: Part I. Kinetic Studies

A new hydrometallurgical leaching process, which dissolves lead concentrates with acidified ferric fluosilicate solution, has been investigated for the selective extraction of lead and zinc from lead concentrates containing galena. The leaching of the Pine Point lead concentrate by ferric fluosilicate solutions was studied under various experimental conditions in the temperature range 20 °C to 95 °C. Temperature had a pronounced effect on the dissolution of the concentrates. The rates of lead leaching are very rapid over the temperature range 38 °C to 95 °C. The kinetics of zinc extraction are much lower than those of lead extraction. The reaction rates for the dissolution of galena were found to be controlled by surface chemical reaction. The apparent activation energy of the leaching reaction was calculated to be 62.1 kJ/mol. The initial concentrations of Pb²⁺, H⁺, and Fe³⁺ in the lixiviant do not have a significant effect on the rate or extent of lead extraction under the experimental conditions in this study.     

The dissolution of chalcopyrite in ferric sulfate and ferric chloride media

The literature on the ferric ion leaching of chalcopyrite has been surveyed to identify those leaching parameters which are well established and to outline areas requiring additional study. New experimental work was undertaken to resolve points still in dispute. It seems well established that chalcopyrite dissolution in either ferric chloride or ferric sulfate media is independent of stirring speeds above those necessary to suspend the particles and of acid concentrations above those required to keep iron in solution. The rates are faster in the chloride system and the activation energy in that medium is about 42 kJ/mol; the activation energy is about 75 kJ/mol in ferric sulfate solutions. It has been confirmed that the rate is directly proportional to the surface area of the chalcopyrite in both chloride and sulfate media. Sulfate concentrations, especially FeSO₄ concentrations, decrease the leaching rate substantially; furthermore, CuSO₄ does not promote leaching in the sulfate system. Chloride additions to sulfate solutions accelerate slightly the dissolution rates at elevated temperatures. It has been confirmed that leaching in the ferric sulfate system is nearly independent of the concentration of Fe³⁺, ka[Fe³⁺]^0.12. In ferric chloride solutions, the ferric concentration dependence is greater and appears to be independent of temperature over the interval 45 to 100 °C.     

The kinetics of dissolution of chalcopyrite in ferric ion media

The kinetics of dissolution of chalcopyrite (CuFeS₂) in ferric chloride-hydrochloric acid and in ferric sulfate-sulfuric acid solutions have been investigated using the rotating disk technique. Over the temperature range 50 to 100‡C, linear kinetics were observed in the chloride media while nonlinear kinetics were noted in the sulfate system. The apparent activation energy in the chloride system was about 11 kcal/mole. The rate increased with increasing ferric chloride concentrations but was insensitive to the concentrations of hydrochloric acid, the ferrous chloride reaction product and “inert≓ magnesium or lithium chlorides. Cupric chloride substantially accelerated the rate. Small amounts of sulfate in an otherwise all chloride system greatly reduce the chalcopyrite leaching rate; still larger amounts of sulfate make the system behave essentially like the slower-reacting ferric sulfate medium.     

The kinetics of dissolution of chalcopyrite in ferric ion media

The kinetics of dissolution of chalcopyrite (CuFeS₂) in ferric chloride-hydrochloric acid and in ferric sulfate-sulfuric acid solutions have been investigated using the rotating disk technique. Over the temperature range 50 to 100?C, linear kinetics were observed in the chloride media while nonlinear kinetics were noted in the sulfate system. The apparent activation energy in the chloride system was about 11 kcal/mole. The rate increased with increasing ferric chloride concentrations but was insensitive to the concentrations of hydrochloric acid, the ferrous chloride reaction product and “inert? magnesium or lithium chlorides. Cupric chloride substantially accelerated the rate. Small amounts of sulfate in an otherwise all chloride system greatly reduce the chalcopyrite leaching rate; still larger amounts of sulfate make the system behave essentially like the slower-reacting ferric sulfate medium.     

Leaching and kinetic modelling of low-grade calcareous sphalerite in acidic ferric chloride solution

The leaching kinetics of a low grade-calcareous sphalerite concentrate containing 38% ankerite and assaying 32% Zn, 7% Pb and 2.2% Fe was studied in HCl–FeCl₃ solution. An L₁₆ (five factors in four levels) standard orthogonal array was employed to evaluate the effect of Fe(III) and HCl concentration, reaction temperature, solid-to-liquid ratio and particle size on the reaction rate of sphalerite. Statistical techniques were used to determine that pulp density and Fe(III) concentration were the most significant factors affecting the leaching kinetics and to determine the optimum conditions for dissolution. The kinetic data were analyzed with the shrinking particle and shrinking core models. A new variant of the shrinking core model (SCM) best fitted the kinetic data in which both the interfacial transfer and diffusion across the product layer affect the reaction rate. The orders of reaction with respect to (C_Fe³⁺), (C_HCl), and (S/L) were 0.86, 0.21 and − 1.54, respectively. The activation energy for the dissolution was found to be 49.2 kJ/mol and a semi-empirical rate equation was derived to describe the process. Similar kinetic behavior was observed during sphalerite dissolution in acidic ferric sulphate and ferric chloride solutions, but the reaction rate constants obtained by leaching in chloride solutions were about tenfold higher than those in sulphate solutions.     

Leaching of sulfidized chalcopyrite with H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaCl-O<Subscript>2</Subscript>

The recovery of copper from chalcopyrite by leaching is complex not only due to the slow dissolution kinetics of this mineral in most aqueous media but also due to the production of solutions that are heavily contaminated with iron. On the contrary, the leaching of sulfidized chalcopyrite is very attractive because of a faster and more selective dissolution of copper compared to the leaching of the untreated chalcopyrite. In this work, the results of leaching in H₂SO₄-NaCl-O₂ solutions of sulfidized chalcopyrite concentrate are discussed. Experiments were carried out with chalcopyrite concentrates previously reacted with elemental sulfur at 375 °C for 60 minutes. The results showed that the concentration of chloride ions below 0.5 M, temperature, and leaching time are important variables for the extraction of Cu. On the other hand, Fe extraction was little affected by the same variables, remaining below 6 pct for all the experimental conditions tested. Microscopic observations of the leached particles showed that the elemental sulfur produced by the reaction does not form a coherent layer surrounding the particle, but rather concentrates in certain locations as large clusters. The leaching kinetics can be accurately described by a nonreactive core-shrinking rim topochemical expression for spherical particles 1 − (1 − 0.45X)^1/3=kt. The activation energy found was 76 kJ/mol for the range 85 °C to 100 °C.     

The solubility of silver chloride in ferric chloride leaching media

The solubility of silver chloride in various FeCl₃-FeCl₂-HCl solutions has been measured over the temperature range 20–100°C; the densities of the associated saturated solutions have also been determined. The solubility increases systematically with either rising temperature or increasing concentrations of the constituent chlorides. The solubility is higher in a ferrous chloride medium than in an equivalent ferric chloride solution. The presence of CuCl₂ systematically raises the AgCl solubility, but increasing ZnCl₂ concentrations cause the solubility to decrease slightly to about 1.5 M ZnCl₂ and subsequently to increase gradually. The addition of NaCl to the iron chloride media substantially increases the AgCl solubility under all conditions. Although the solubility of AgCI is only a few mg/L in cold water, this increases to over 1 g/L in hot, moderately concentrated chloride media. Silver chloride solubilities at elevated temperatures are sufficiently high that silver solubility limitations should not be a problem in most commercial ferric chloride leaching processes.