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.     

Dissolution studies of mechanically activated Manavalakurichi ilmenite with HCl and H2SO4

The effect of the change in phase constitution, particle size distribution, surface area, crystallite size, strain and lattice parameters introduced by mechanical activation of the altered beach sand ilmenite from Manavalakurichi region, India on the dissolution kinetics of HCl and H₂SO₄ was investigated. The altered ilmenite showed different physico-chemical characteristics and was found to be more resistant to acid leaching than the less altered ilmenite from the Chatrapur beach sands, India investigated earlier. The dissolution behavior was also different in H₂SO₄ and HCl. For sulfuric acid leaching, the dissolution of Fe and Ti increased monotonically with time of milling and showed a continuous increase with time of leaching, whereas hydrolysis of titanium occurs in HCl medium, especially for the activated samples at lower acid concentration, lower solid to liquid ratio and higher temperature leading to lower solution recoveries. The dissolution kinetics in both H₂SO₄ and HCl prior to hydrolysis conforms initially to the reaction rate control model and for higher leaching times to the shrinking core model where diffusion through the product layer is rate controlling. It is postulated that the anatase formed by hydrolysis in milled samples impedes the further progress of leaching. The activation energies for the dissolution of Fe and Ti decreased with time of milling and were marginally lower in HCl than in H₂SO₄. An attempt has also been made to correlate the decrease in activation energy to the increase in the energy input to the material through high-energy milling. The relative contribution of the increase in surface area and structural disorder on the enhancement of the dissolution rates has been evaluated.     

Dissolution behaviour of a beryl ore for optimal industrial beryllium compound production

This study involves the leaching of the beryl ore with sulphuric acid (H₂SO₄) solution for predicting optimal beryllium extraction conditions with the aim of assessing the importance of leachant concentration, reaction temperature and particle size on the extent of dissolution. A kinetic model to represent the effects of these variables on the leaching rate was developed. It was observed that the dissolution of beryl ore increases with increasing H₂SO₄ concentration, temperature, decreasing particle size and solid to liquid ratio. At optimal leaching conditions, 89.3% of the ore was reacted by 1.25?mol/L at 75°C temperature and 120 minutes with moderate stirring, where 1612.0?mg/L Be²⁺, 786.7?mg/L Al³⁺, 98.1?mg/L Fe³⁺ and 63.4?mg/L Ag⁺ were found as major species in the leach liquor. The unleached products constituting about 10.7% were examined by X-ray diffraction (XRD) and found to contain primarily, siliceous compounds such as Xonotlite, Antigorite, Chrysolite and Kaolinite.     

Effect of mechanical activation on the leaching kinetics of pyrrhotite

BET, SEM, and particle size analysis was used for studying the changes in surface and bulk properties of mechanically activated pyrrhotite in a vibrating mill. The results showed that mechanical activation increased microstructure defects and specific surface area of pyrrhotite, and decreased powder particle size. And the formation of aggregates was very obvious. The influence of mechanical activation on leaching kinetics of pyrrhotite by FeCl₃–HCl solutions was investigated. When pyrrhotite was mechanically activated for 10 min, 20 min and 40 min, the apparent activation energy decreased from 133 kJ/mol to 33, 26 and 25 kJ/mol, respectively. Compared with the non-mechanical activation method, mechanical activation greatly improved the activity of pyrrhotite and decreased the apparent activation energy, so that the reaction speed was accelerated remarkably.     

Pyrite oxidation with ozone: stoichiometry and kinetics

One of the most frequent causes of refractoriness in precious metals leaching is their occlusion or fine dissemination into a pyritic matrix. This study experimentally explores the acid leaching of pyrite with ozone, suggests the stoichiometry of the reaction, estimates its activation energy and defines the effect of the main variables on the leaching kinetics. The results of stoichiometry tests allow establishing that one mole of pyrite requires 7.7 moles of ozone to produce one mole of ferric ion and 2 moles of HSO₄? ions. A decrease in the particle size, solution pH and solids’ concentration of the leaching system increases pyrite dissolution. The type of acid (nitric, sulphuric and hydrochloric) does not affect pyrite dissolution rate. Up to 60% of pyrite is dissolved when the optimal experimental conditions are employed (1?g pyrite (?25?µm), 800?mL of 0.18?M of H₂SO₄, 800?rev?min^?1, 1.2?L?min^?1 gas stream O₂/O₃ with 0.079?g O₃?L^?1 and 25°C). The apparent activation energy of the pyrite-ozone reaction is 14.92?kJ?mol^?1, and the absence of a passive layer on the pyrite surface and the linearity of the dissolution profiles suggest that the dissolution kinetics is controlled by the chemical reaction.     

Kinetics of silver leaching from manganese-silver associated ores in sulfuric acid solution in the presence of hydrogen peroxide

Kinetics of silver leaching from a manganese-silver associated ore in sulfuric acid solution in the presence of H₂O₂ has been investigated in this article. It is found that sulfuric acid and hydrogen peroxide have significant effects on the leaching rate of silver. The reaction orders of H₂SO₄ and H₂O₂ were determined as 0.80 and 0.68, respectively. It is found that the effects of temperature on the leaching rate are not marked, the apparent activation energy is attained to be 8.05 kJ/mol within the temperature range of 30 °C to 60 °C in the presence of H₂O₂. Silver leaching is found to be diffusion-controlled and follows the kinetic model: 1−2x/3−(1−x)^2/3=Kt. It is also found that particle size presents a clear effect on silver leaching rate, and the rate constant (k) is proportional to d ₋₂ ⁰ .     

Leaching of a sphalerite concentrate with H2SO4–HNO3 solutions in the presence of C2Cl4

The enhanced leaching of sphalerite concentrates in H₂SO₄–HNO₃ solutions and the extraction of sulfur with tetrachloroethylene were studied. Variables of the process were investigated including leaching temperature, reaction time, liquid / solid ratio, and tetrachloroethylene concentration. The number of cycles that tetrachloroethylene could be recycled did not have a significant effect on zinc extraction. The results indicated that 99.6% zinc extraction was obtained after three hours of leaching at 85 °C and 0.1 MPa O₂, when 20 g of sphalerite concentrate were leached in a 200 ml solution containing 2.0 mol/L H₂SO₄ and 0.2 mol/L HNO₃, in the presence of 10 ml C₂Cl₄. Leaching rates were significantly improved under these conditions.     

Leaching of a sphalerite concentrate with H2SO4–HNO3 solutions in the presence of C2Cl4

The enhanced leaching of sphalerite concentrates in H₂SO₄–HNO₃ solutions and the extraction of sulfur with tetrachloroethylene were studied. Variables of the process were investigated including leaching temperature, reaction time, liquid / solid ratio, and tetrachloroethylene concentration. The number of cycles that tetrachloroethylene could be recycled did not have a significant effect on zinc extraction. The results indicated that 99.6% zinc extraction was obtained after three hours of leaching at 85 °C and 0.1 MPa O₂, when 20 g of sphalerite concentrate were leached in a 200 ml solution containing 2.0 mol/L H₂SO₄ and 0.2 mol/L HNO₃, in the presence of 10 ml C₂Cl₄. Leaching rates were significantly improved under these conditions.     

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.     

Kinetics of leaching selenium from Ni-Mo ore smelter dust using sodium chlorate in a mixture of hydrochloric and sulfuric acids

The kinetics of leaching selenium from Ni-Mo ore smelter dust in H₂SO₄-HCl-H₂O system was investigated. The effects including leaching temperature and time, particle size of the smelting dust, stirring speed, acid concentration and the coefficient β (the molar ratio of sodium chlorate to selenium in the smelter dust) on leaching of selenium were studied. The results indicated that the leaching of selenium increased sharply with the increase of temperature. The leaching of selenium reached 98% at 95 °C and stirring speed of 350 rpm for 150 min with the particle size of − 0.15 mm, initial [H⁺] concentration of 8 mol/L, the solid/liquid ratio of 1:5 g/mL and the coefficient β of 3.33. The leaching process was controlled by the surface chemical reaction and the kinetics of leaching selenium from Ni-Mo ore smelter dust followed the model of “shrinking core”. The apparent activation energy of leaching selenium was determined to be 44.4 kJ/mol, which was consistent with the values of activation energy reported for the surface chemical reaction control. The kinetics equation of leaching selenium from Ni-Mo ore smelter dust was expressed as , which coincided with the experimental results.     

Effects of mechanical activation on the HCl leaching behavior of plagioclase, ilmenite and their mixtures

Plagioclase (NaAlSi₃O₈–CaAlSi₂O₈) is one of the dominant impurity minerals in the ilmenite concentrate from the Panxi area of China. The effects of mechanical activation on the structural changes of plagioclase and ilmenite single minerals from Panxi were investigated using X-ray diffraction (XRD), particle size analysis, and scanning electron microscope (SEM). Hydrochloric acid leaching behaviors of mechanically activated plagioclase and ilmenite single minerals and their mixtures were also studied. The results show that with increasing milling time, the crystallite size, lattice strain and the particle size changed continuously but differed between plagioclase and ilmenite. Mechanical activation enhanced the leaching reactivity of plagioclase and ilmenite with 20% HCl at 105 °C, consistent with the lattice disorder and decreased particle size. The leaching of plagioclase was hardly affected by the existence of ilmenite, but the leaching of ilmenite was inhibited when plagioclase co-existed in the sample which is attributed to silica gel produced from leached plagioclase blocking the surface of unleached ilmenite.     

Recovery of valuable metals from jarosite by sulphuric acid roasting using microwave and water leaching

In this paper, jarosite residue (JR) blended with concentrated H₂SO₄ was subjected to a process comprising microwave roasting and water leaching. The effects of H₂SO₄/JR weight ratio, microwave roasting temperature and time, water leaching conditions on the recovery of Fe, Zn, In, Cu, Cd, Ag and Pb were investigated utilising a series of experiments.

Based on energy conservation and environmental protection, optimum conditions for metals recovery from JR were determined as: H₂SO₄/JR weight ratio?=?0.36, microwave roasting temperature, 250°C; roasting time, 30?min; leaching temperature, 50°C; leaching time, 1?h; and liquid–solid ratio, 4:1 (mL/g), thus, the extraction of Fe, Zn, In, Cu, Ag and Cd were 89.4, 80.7, 85.1, 90.7, 61.3 and 48.8% respectively, while the Pb was concentrated in the final residue. Scanning electron microscope-energy dispersive spectrometer (SEM-EDS) patterns were used to characterise and analyse the transformation of valuable metals in the residue after roasting and leaching.     

Reductive leaching of manganese from low-grade manganese ore in H2SO4 using cane molasses as reductant

Manganese extraction from a low-grade ore was investigated using cane molasses as a reducing agent in dilute sulfuric acid medium. The effects of concentrations of cane molasses and sulfuric acid, leaching temperature as well as reaction time were discussed. The results showed that high manganese recovery with low Fe and Al extraction yield could be obtained by analyzing the leaching efficiencies of Mn, Fe and Al during the leaching process. The optimal leaching condition was determined as 1.9 mol/L H₂SO₄ and 60.0 g/L cane molasses for 120 min at 90 °C while using particles smaller than 0.147 mm. The leaching efficiencies were 97.0% for Mn, whereas 21.5% for Al and 32.4% for Fe, respectively.     

Leaching of copper(I) sulphide by sulphuric acid solution with addition of sodium nitrate

Finely grained samples of copper(I) sulphide were leached by H₂SO₄ solution with added NaNO₃. The occurrence probability of chemical reactions was analysed based on literature data and products which were formed during the process and the overall leaching reaction was defined. The effect of temperature, concentration of NaNO₃ and H₂SO₄, stirring speed, phase ratio and time, on the leaching degree of copper was studied. The quantity of copper dissolved increases with growth of the values of all the parameters. Kinetic analysis shows that the leaching mechanism is very complex. By using appropriate mathematical kinetic models, it is found that the leaching rate is chemically controlled. It was concluded that the leaching reaction is first order with respect to the concentration of NaNO₃ and second order with respect to the concentration of H₂SO₄.     

Removal of ash from low grade Indian coal by chemical leaching technique

In this work leaching of low grade Indian coal was investigated. Coal samples of pre-treated and treated were characterized to quantify the quality of coal. An attempt has been made in this work to reduce the mineral matter from low grade coal of particle size 250 μm by leaching with H₂SO₄, HCl, Na₂CO₃ and NaOH solution as leaching agent at a temperature of 100°C for 3 h. It was found that the final ash content of treated coal was 22% from 38% of ash of feed raw coal by NaOH treatment alone compared to rest of the solvents.     

Removal of Iron From Quartz Ore Using Different Acids: A Laboratory-Scale Reactor Study

The purification of quartz using chemical processes is extremely important for many industries, including the glass, electronic, detergent, ceramics, paint, refractory, and metallurgy industries, as well as for advanced technology products. The purpose of this work was to investigate the removal of iron as an impurity from quartz ores using a chemical leaching method with different reagents.

The iron content of the quartz ore sample was 310 ppm, and the iron was in the form of Fe₂O_3. In the first step, pre-enrichment studies were conducted based on the particle size, and the Fe₂O₃ content of the quartz ore was decreased to 88 ppm. A statistical design of the experiments and an ANOVA (analysis of variance) were performed in the second step to determine the main effects and interactions of the researched factors, which were the concentration of the leaching reagent (H₂SO₄, HCl, H₃PO₄, HClO₄, and NTA [Nitrilotriacetic acid]), solid/liquid ratio, leaching temperature, and leaching time. The highest Fe₂O₃ removal was 86.6%, and a 11.8 ppm Fe₂O₃ content quartz product with a whiteness index (WI) value of 90.6 was obtained after 120 min of treatment at 90°C with a 10% S/L ratio and 1 M H₂SO₄.     

Preparation of Industrial Manganese Compound from a Low-Grade Spessartine Ore by Hydrometallurgical Process

The increasing global demands for pure manganese in steel production and manganese compound as dietary additives, fertilizer, pigment, cells and fine chemicals production cannot be over-emphasized. Thus, continuous efforts in developing low cost and eco-friendly route for purifying the manganese ore to meet some defined industrial demands become paramount. Therefore, this study focused on reductive leaching and solvent extraction techniques for the purification of a Nigerian manganese ore containing admixture of spessartine (O_96.00Mn_24.00Al_16.00Si₂₄.₀₀) and quartz (Si_3.00O_6.00). During leaching, parameters such as leachant concentration and reaction temperature on the extent of ore dissolution were examined accordingly for the establishment of extraction conditions. At optimal leaching conditions (1.5 mol/L H₂SO₄?+?0.2 g spent tea, 75 °C), 80.2% of the initial 10 g/L ore reacted within 120 min. The derived dissolution activation energy (Ea) of 35.5 kJ/mol supported the diffusion reaction mechanism. Thus, the leachate at optimal leaching was appropriately treated by alkaline precipitation and solvent extraction techniques using sodium hydroxide and (di-2-ethylhexyl) phosphoric acid (D2EHPA) respectively, to obtain pure manganese solution. The purified solution was further beneficiated to obtain manganese sulphate monohydrate (MnSO₄.H₂O, melting point?=?692.4 °C: 47-304-7403) of high industrial value. The unleached residue (~?19.8%) analyzed by XRD consisted of silicileous impurities (SiO₂) which could serve as an important by-product for some defined industries.     

Mechanism and Kinetics of the Thermal Oxidation of Natural Sphalerite

The oxidation of natural sphalerite on heating in an oxidative medium is studied by thermogravimetry coupled with scanning calorimetry, mass spectrometry of released gases, and X-ray powder diffraction analysis. The mechanism of sphalerite oxidation when the particle surface is equally accessible and sulfur dioxide is removed from the reaction zone is the formation of ZnO, ZnFe₂O₄, and SO₂. The process is found to be one-stage, as determined by a nonisothermal kinetic method. The activation energies are from 293 to 317 kJ/mol depending on the model used. Natural sphalerite is oxidized in the kinetic regime, and the rate-determining steps are the formation and growth of new-phase nuclei.     

Leaching of sulfide copper ore in a NaCl–H2SO4–O2 media with acid pre-treatment

A study was made of the leaching of a sulfide copper ore in a NaCl–H₂SO₄–O₂ media after pre-treatment by agglomeration with H₂SO_4(conc) and NaCl. The leaching variables evaluated included the amount of NaCl to be employed, the percentage of solids in the leaching solution, particle size of the raw mineral to be leached, and the preferable method of agitation in the leaching system. Mineralogical characterization of the material to be leached included analysis of the raw ore and of the leached ore residue using reflected-light microscopy, X-ray diffraction, and scanning electron microscopy. The soluble species included djurleite and digenite. The most important parameters in the leaching process proved to be particle size and type of agitation. A total percentage of copper extraction of 70% was achieved using mechanical stirring, which increased to 78% when using compressed air agitation. The best extraction of the copper was achieved when leaching with 3 g/L of chloride, room temperature of 20 °C, and when all particles were < 1.65 mm in diameter.