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.     

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.     

A kinetic study on the pressure leaching of sphalerite

The dissolution of sphalerite (ZnS) in sulfuric acid solution under oxygen pressure was investigated. Effects of temperature, percent solids, agitation, sample size, oxygen partial pressure and foreign ions were evaluated. The effect of hydrogen pretreatment on sphalerite leaching rate was also examined. Leaching of sphalerite at 90°C and 150 psi oxygen pressure was found to occur at a constant rate. This rate was determined from the experimental data observed under the different leaching conditions mentioned above. The constant leaching rate was attributed to the chemical reaction occurring on the surface of the flat-plate type sphalerite sample. The rate-controlling step of the reaction was determined to be the oxidation of hydrogen sulfide to elemental sulfur. Oxidation of hydrogen sulfide was studied through the addition of iron and through the observation of the change in iron concentration during leaching. The oxidation was concluded to be by reaction with ferric ion rather than by direct oxygen oxidation. Leaching tests run with samples pretreated with hydrogen do not show any increase in the rate of zinc extraction. M. T. HEPWORTH, formerly with University of Denver.     

Kinetics of sphalerite bioleaching by Acidithiobacillus ferrooxidans

In the present study, the effect of some important parameters including particle size, pulp density and temperature on the rate of Zn dissolution from sphalerite concentrate by Acidithiobacillus ferrooxidans was investigated. The highest rate of sphalerite bioleaching was obtained at particle size, pulp density and temperature of 38–150 μm, 4% wt/vol and 33 °C respectively. The formation of a product layer over sphalerite concentrate particles was confirmed by SEM images whereas XRD, EDS and BET analysis showed that this layer is composed of elemental sulfur and is non-porous. Based on these results, it was decided that a kinetic model in which the rate of Zn dissolution is limited by diffusion of ions through a non-porous product layer is appropriate to describe the sphalerite bioleaching process. Determinations of ferrous iron ion concentration during bioleaching showed that the concentration of this ion varies significantly during bioleaching and hence the kinetic model was revised to take account of this fact. The predictions of this model had a good compatibility with the experimental data and the value of activation energy was determined as 39 kJ/mol.     

Reaction kinetics of the ferric chloride leaching of sphalerite—an experimental study

Chloride leaching processes have significant potential for treating complex sulfides. One advantage of chloride leaching is fast dissolution rates for most sulfide minerals. This experimental study is concerned with ferric chloride leaching of sphalerite, a common component of many complex concentrates. The effects of stirring, temperature, ferric ion concentration, and particle size have been examined. In addition, reaction residues at various levels of zinc extraction were examined by SEM, and the products of reaction were identified by energy dispersive X-ray analysis and X-ray diffraction. These observations indicated that the dissolution reaction is topochemical. Moreover, the leaching results fit a surface reaction control model. The activation energy was calculated to be 58.4 kJ/mole which is reasonable for a rate limiting surface reaction. The order of the reaction was 0.5 with respect to Fe³⁺ at low concentrations and zero at high concentrations. The change in reaction order occurred at similar Fe³⁺ concentrations for various particle sizes. This is believed to be indicative of an electrochemical reaction mechanism at low Fe³⁺ and an adsorption mechanism at higher Fe³⁺. A kinetic model for the ferric chloride leaching of sphalerite was also obtained for the lower Fe³⁺ concentrations and is given by: (ie5-01) This model is in excellent agreement with the experimental results for fractions of zinc extracted up to 0.95.     

Investigation of kinetics of coal based reduction of oolitic iron ore

Abstract

An oolitic iron ore was isothermally reduced by coal at 1423–1573 K, and the reduction kinetics was investigated in detail. The degree of reduction and reduction rate increased with increasing temperature and C/O molar ratio to some extent at the same reduction time. In the entire reduction process, the reduction mechanism changes with changing experimental conditions. The degree of reduction under different experimental conditions should be represented by different reduction kinetic models. The reduction rate curves are similar in shape and could be analytically divided into initial, intermediate and final stages. The apparent activation energies of the three stages are 48·26, 69·80 and 127·58 kJ mol^?1 respectively. The rate controlling mechanism in the reduction process was determined by analysing the reduction process and apparent activation energy. The rate controlling steps of these stages are combined gas diffusion and interfacial chemical reaction, surface chemical reaction and combined solid state diffusion and boundary reaction.     

The catalytic action of cupric and ferric ions in nitric acid leaching of Ni3S2

The kinetics of dissolution of synthetic Ni₃S₂ in nitric acid solution containing ⩽ 2.0 M HNO₃ in the presence of cupric and ferric ions was investigated. The effects of stirring, particle size, temperature and concentration of cupric and ferric ions were examined. Solid residues at various levels of nickel extraction were examined by SEM, X-ray diffraction, electron microprobe and chemical analysis. The constant dissolution rate of Ni₃S₂ was attributed to the electrochemical reaction occurring on the surface of flat-plate type Ni₃S₂ particles. The reaction kinetics were found to be independent of both cupric and ferric ion concentrations up to 1 mM. Cupric ion did not act as a catalyst at temperatures below 60°C. At 80°C cupric and ferric ions show the same catalytic activity. The activation energy in the presence of ferric ions was 103.6 ± 4.2 kJ/mol. A mechanism for Ni₃S₂ dissolution in the presence of cupric and ferric ions is proposed.     

A kinetic study on nonoxidative dissolution of sphalerite in aqueous hydrochloric acid solutions

The nonoxidative leaching of sphalerite in aqueous acidic solutions was studied from a kinetic point of view. Also the selective nonoxidation leaching in a hydrochloric acid solution containing a large amount of sodium chloride was examined for a Pb-Zn sulfide bulk concentrate. The dissolution rates of sphalerites from five different mines appeared to be controlled by a chemical reaction on the surface of sphalerite. The dissolution rate of sphalerite is of the first order with respect to the hydrogen ion activity of the solutions. It is also considerably affected by the iron content of the sphalerite sample; a linear relationship was observed between iron content of the sphalerite and its dissolution rate. The addition of sodium chloride to the hydrochloric acid solutions greatly enhanced dissolution rates. Compared to the dissolution rates of galena, which were reported in a previous paper, the dissolution rates of sphalerite were found to be far slower. The difference in the dissolution rates between these two minerals becomes greater with the addition of sodium chloride to the hydrchloric acid solutions. Based on these findings, the selective leaching of Pb-Zn bulk concentrate in a hydrochloric acid solution containing a large amount of sodium chloride was examined. The experimental results clearly showed that the galena was selectively leached, leaving a residue of sphalerite. NORIO MISAKI formerly Graduate student, Kyoto University     

Leaching of bornite in acidified ferric chloride solutions

In an acidified ferric chloride solution, bornite leaches in two stages of reaction with the first being relatively much more rapid than the second; the first terminates at 28 pct copper dissolution. The first-stage dissolution reaction is electrochemical and is mixed kinetics-controlled; ferric-ion transfer through the solution boundary layer and reduction on the surface to release Cu²⁺ into solution are both important in controlling the rate. The concentration of labile Cu⁺ in the bornite lattice governs the potential of the surface reaction, and, once Cu⁺ is depleted from the original bornite, stage-I reaction ceases. The solid reaction intermediate formed is Cu₃FeS₄. Minute subcrystallites formed at the latter part of stage I leach topochemically in stage II. This reaction which commences at 28 pct Cu dissolution is characterized by a change in mechanism at about 40 pct copper dissolution, though the overall chemical equation for reaction is unchanged in stage II; cupric and ferrous ions and sulfur as a solid residue are products of reaction. The region 28 to about 40 pct Cu dissolution is designated as a transition period to stage-II reaction. Reaction rate in this period is interpreted as being controlled by reduction of Fe³⁺ on active product sulfur surface sites, and hence the reaction rate is controlled by the rate of nucleation and growth of sulfur on the Cu₃FeS₄ intermediate surfaces. Strain in the Cu₃FeS₄ crystal lattice is released during this period by diffusion from the lattice of Cu⁺ remaining from the labile copper initially present in the bornite. After about 40 pct Cu dissolution the rate of reaction is controlled by diffusion through the fully formed sulfur layer in an equiaxial geometrically controlled reaction.     

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.     

Rate of dissolution of solid nickel in liquid tin under static conditions

The dissolution kinetics of solid nickel in liquid tin have been investigated under static conditions. The cylindrical nickel specimens were immersed in liquid tin over the temperature range of 551 to 803 K in the reaction time range of 0.9 to 6.0 ks. A natural convection model for mass transfer and the dissolution rate equation derived by considering intermetallic compound layer formation were used to interpret the experimental dissolution data. A larger dissolution at the upper part of specimen causing natural convection and an intermetallic layer formation with a linear relationship at solid/liquid interface occurred. Below 628 K, the dissolution rate appears to be controlled by chemical reaction of an intermetallic compound layer. At mid-range temperatures (of 681 K), the dissolution process was governed by a mixed control mechanism involving diffusion in liquid tin and chemical reaction of the intermetallic compound layer. At temperatures above 735 K, the rate seems to be controlled by diffusion across a concentration boundary layer in liquid tin. The formation of an intermetallic compound layer did not interfere with the dissolution.     

微纳米氧化铁粉低温还原特性的研究

研究了低温还原微纳米氧化铁粉的还原特性与机理。用高能球磨法获得的微纳米氧化铁粉在280～400 ℃内用氢气还原,并测定还原后粉末中氧、计算氧化铁粉末的还原率,通过扫描电子显微镜来观察还原铁粉的形貌;找出了氧化铁粒度、还原温度和还原时间等参数对氧化铁还原率、铁粉粒度和粒度分布、铁粉形貌等的影响。从动力学的角度,探讨了粉末细化对低温氢气还原氧化铁活化能的影响。研究结果指出,微纳米氧化铁粉的还原反应遵循吸附自动催化理论,反应动力学遵循界面化学反应理论,研究获得了反应所对应的反应机制函数和相应的动力学方程。     

微纳米氧化铁粉低温还原特性的研究

研究了低温还原微纳米氧化铁粉的还原特性与机理。用高能球磨法获得的微纳米氧化铁粉在280～400 ℃内用氢气还原,并测定还原后粉末中氧、计算氧化铁粉末的还原率,通过扫描电子显微镜来观察还原铁粉的形貌;找出了氧化铁粒度、还原温度和还原时间等参数对氧化铁还原率、铁粉粒度和粒度分布、铁粉形貌等的影响。从动力学的角度,探讨了粉末细化对低温氢气还原氧化铁活化能的影响。研究结果指出,微纳米氧化铁粉的还原反应遵循吸附自动催化理论,反应动力学遵循界面化学反应理论,研究获得了反应所对应的反应机制函数和相应的动力学方程。     

Leaching studies of chalcopyrite and sphalerite with hypochlorous acid

Laboratory studies have been conducted on the leaching of chalcopyrite and sphalerite with hypochlorous acid. The effects of stirring speed, temperature, pH, and hypochlorous acid concentration on the leaching rates have been determined. In addition, the leaching mechanisms have been resolved by analyzing the concentrations of the reaction products. It has been found that more than 90 pct extraction of both chalcopyrite and sphalerite can be achieved in one hour using less than 0.3 molar hypochlorous acid at room temperature. The primary leach products of chalcopyrite and sphalerite were sulfur and sulfate in the mole ratios of 1 to 1 and 2 to 1, respectively. A mixed kinetic model was applied to explain the leaching rates of chalcopyrite while a diffusion model was applied to explain the leaching rates of sphalerite. The mixed kinetic model involved steady-state diffusion of hypochlorous acid through the sulfur layer by a chemical reaction at the reaction interface. Good agreement between these models and the leaching rates of both minerals was obtained.     

Impurity controlled diffusion reaction in thorium-vanadium system

The effect of ppm level impurities present in the thorium metal on the diffusion reaction in thorium-vanadium system has been investigated by making “sandwich” type diffusion couples and annealing them in the temperature range of 900 to 1200°C. The microstructure of the diffusion zone has been examined by optical and electron microscopy. X-ray powder techniques have been employed to detect the presence of secondary intermetallic phases in thorium metal and in the diffusion zone. The chemical composition of these phases and the elemental distribution in the diffusion zone have been established by using an electron microprobe analyzer. The time and the temperature dependence of the diffusion zone width is used to evaluate the kinetics of layer growth. Present studies have shown that impurities like iron, copper and aluminum form low melting point intermetallic compounds in thorium metal and segregate at the grain boundaries. Further in a diffusion reaction at the elevated temperatures, these thorium rich secondary phases melt and form a liquid film between the thorium and the bonding metal, vanadium in the present case. The rate controlling process appears to be an interfacial chemical reaction involving dissolution of vanadium in the thorium rich liquid.     

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.     

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 kinetics of dissolution of bornite in acidified ferric sulfate solutions

Sintered disks of synthetic bornite were dissolved in acidified ferric sulfate solutions at temperatures ranging from 5δ to 94δC. The dissolution occurs in two stages; in the first a nonstoichiometric bornite with up to 25 pct deficiency of copper is formed. In the second, the nonstoichiometric bornite is converted to chalcopyrite and elemental sulfur, which accumulates on the disk surface. At temperatures below 35°C, the reaction follows parabolic kinetics and stops at the nonstoichiometric bornite stage. At higher temperatures it continues through to chalcopyrite and follows linear kinetics. Both the parabolic and linear processes have activation energies of 5 to 6 kcal per mole. At higher temperatures the sensitivity of the reaction rate to changes in stirring velocity indicates control by diffusion through the liquid boundary layer. Natural and synthetic bornite dissolve by the same process and at essentially the same rate.     

Treatment of a Nigerian covellite ore. Part I: Dissolution kinetics study by ammonia solution

In the present work, the leaching kinetics of covellite ore in ammonia solution was studied and the following variables, the solution concentration, reaction temperature and particle size were considered. A kinetics model representing the effects of these variables on the leaching rate was developed and it was ascertained that the leaching rate increases with increasing solution concentration, reaction temperature and decreasing particle size. At optimal conditions, 75.1% of covellite ore was reacted within 120 min and the leaching reaction was diffusion controlled by surface chemical mechanism. The calculated activation energy of 56.98 kJ/mol supported the proposed dissolution process.     

弱磁性铁矿物的表面自磁化

利用菱铁矿和赤铁矿在酸性体系中的溶解特性,无需添加任何铁离子,只需调节矿浆的pH值,然后通过控制反应温度即可实现矿物表面的自磁化.实验考察了反应时间、铁离子浓度、过氧化氢添加量和反应温度等因素对菱铁矿在酸性体系中溶解行为的影响.在100℃条件下,通过表面自磁化反应,菱铁矿磁选回收率从53.8%提高到94.6%,因此可以确定反应温度是影响自磁化的重要因素.利用赤铁矿和菱铁矿的混合矿物重复菱铁矿单矿物的自磁化实验,混合矿物回收率从66.8%提高到了72.6%.最后利用含有赤铁矿和菱铁矿的实际矿石进行自磁化实验,结果与单矿物实验和混合矿物实验相一致,磁选回收率从46.3%提高到了63.1%,实现了样品的自磁化.