Leaching kinetics of ulexite in sodium hydrogen sulphate solutions

The aim of this study was to investigate the dissolution kinetics of ulexite in sodium hydrogen sulphate solutions in a mechanical agitation system and to declare an alternative reactant to produce boric acid. Reaction temperature, concentration of sodium hydrogen sulphate solutions, stirring speed, solid/liquid ratio and ulexite particle size were selected as parameters of the dissolution rate of ulexite. The experimental results were successfully correlated by linear regression using Statistica program. Dissolution curves were evaluated in order to test shrinking core models for solid-fluid systems. It was observed that increase in the reaction temperature and decrease in the solid/liquid ratio cause an increase in the dissolution rate of ulexite. The dissolution extent is highly increased with increase in the stirring speed rate between 100 and 700 rpm experimental conditions. The activation energy was found to be 36.4 kJ/mol. The leaching of ulexite was controlled by diffusion through the ash or product layer. The rate expression associated with the dissolution rate of ulexite depending on the parameters chosen may be summarized as: 1–3(1 − X)^2/3 + 2(1 − X) = 6.17 × C^0.97 × W^1.17 × D^−1.72 × (S/L)^−0.66 × e^(−36.4/RT)·t.     

Leaching kinetics of magnesium extraction from boron mud in ammonium bisulphate solutions

In this study, the leaching kinetics of magnesium of boron mud (BM) is evaluated using NH₄HSO₄ solution. The effects of leaching temperature, leaching time, ammonium bisulphate solution concentration and liquid–solid ratio on the extraction ratio of magnesium are investigated. Optimum leaching parameters are determined through an orthogonal test based on single factor experiments. Under the optimum leaching temperature (333 K), leaching time (40 min), NH₄HSO₄ concentration (2.8 mol · L⁻¹), and liquid–solid ratio (9:1 mL · g⁻¹), the extraction ratio of magnesium was 76.73%. In addition, the leaching kinetics data of magnesium from BM are analyzed through graphical and statistical approaches, which reveal that the leaching process conforms to the grain model. The leaching process is diffusion-controlled with an activation energy of 41.67 kJ · mol⁻¹.     

Dissolution kinetics of colemanite in HCl solutions by measuring particle size distributions

Dissolution kinetics of colemanite in hydrochloric acid solutions was investigated in this study. Particle size distribution data was, for the first time in the literature, utilized to investigate dissolution kinetics of colemanite. The size distribution of colemanite particles was measured in the reaction vessel during reaction, and the kinetic models were applied to particle size data. For comparison, the kinetic models were also fitted to the fractional conversion data, calculated from Ca concentration of the medium. Additionally, electrical conductivity and pH of the reaction medium were also recorded while measuring particle size distribution. Among the heterogeneous and pseudo-homogeneous models, Avrami model was found to be the best model to fit the particle size and fractional conversion data.     

Leaching kinetics of calcined magnesite in acetic acid solutions

The leaching kinetics of calcined magnesite by using acetic acid solutions was investigated in a batch reactor by using the parameters such as temperature, acid concentration and particle size. The experimental results were successfully correlated by linear regression using Statistica Package Program. Dissolution curves were evaluated in order to test shrinking core models for fluid–solid systems. It was concluded that the leaching of calcined magnesite was controlled by chemical reaction. In addition, the fact that leaching was controlled by the chemical reaction was also supported with the relationship between the reaction rate constant and the particle radius. The apparent activation energy of dissolution process was found as 34.60 kJ mol^?1.     

Leaching kinetics of Chevreul's salt in hydrochloric acid solutions

The aim of this study was to investigate the dissolution kinetics of Chevreul's salt in hydrochloric acid [HCl] solutions in a mechanical agitation system and to precipitate Chevreul's salt [Cu₂SO₃·CuSO₃·2H₂O] using ammonium sulfide [(NH₄)₂SO₃] solutions at various concentrations from synthetic aqueous copper(II) sulfate [CuSO₄] solutions. Reaction temperature, concentration of HCl, stirring speed and solid/liquid ratio were selected as parameters. The experimental results were successfully correlated by linear regression using Statistica Package Program. Dissolution curves were evaluated in order to test shrinking core models for solid–fluid systems. It was observed that increase in the reaction temperature and decrease in the solid/liquid ratio causes an increase the dissolution rate of Chevreul's salt. The dissolution extent is highly increased with increase the concentration of HCl solutions in the experimental conditions. The activation energy was found to be as 57 kJ/mol. The leaching of Chevreul's salt was controlled by diffusion through the ash or product layer.     

Crystallization and agglomeration kinetics of nickel ammonium sulphate in an MSMPR crystallizer

Precipitation of nickel ammonium sulphate achieved by mixing solutions of nickel sulphate and ammonium sulphate in a 5 1 MSMPR crystallizer is used to investigate both crystallization and agglomeration kinetics from the steady-state crystal size distribution. An iterative non-linear parameter estimation procedure is used to deduce the kinetic rate parameters in the solution of the agglomeration model suggested by Liao and Hulburt from the data-set obtained by size analysis of the product crystals. The results obtained are correlated in terms of conventional power law kinetic expressions.     

Dissolution kinetics of calcined ulexite in ammonium carbonate solutions

The leaching kinetics of calcined ulexite in ammonium carbonate was studied in this work. The effect of parameters of ammonium carbonate concentration, solid/liquid ratio, stirring speed, calcination temperature and reaction temperature was determined in the experiments. It was found that the conversion rate increased with increasing ammonium carbonate concentration, reaction temperature and decreasing solid/liquid ratio. However, the effect of stirring speed on the conversion rate was insignificant. The experimental data practised the heterogeneous and homogeneous models, and an acceptable model for the conversion rates of ulexite was determined to be a first-order pseudohomogeneous reaction model. The activation energy of dissolution process was determined to be 35.3 kJ/mol.     

Dissolution mechanism of colemanite in sulphuric acid solutions

Boron compounds are very important raw materials in many branches of industry and their uses have been increasing and expanding continuously. Colemanite, one of the most common boron minerals, has a monoclinic crystal structure with a chemical formula of 2CaO·3B₂O₃·5H₂O and is used usually in the production of boric acid. The present study concerns and investigation of the dissolution mechanism of colemanite in H₂SO₄ solution and the effect of acid concentration, the effect of SO₄⁻² ion on the dissolution process, using H₂SO₄, HCI+H₂SO₄ and H₂SO₄+Na₂SO₄ solutions. The analysis of the experimental data shows that increasing H₃O⁺ acid concentration increased the dissolution rate, but increasing SO₄⁻² concentration reduced dissolution rate because of the precipitation of a solid film of CaSO₄ and CaSO₄·H₂O.     

Leaching kinetics of copper flotation tailings in aqueous ammonia/ammonium carbonate solution

The experiments of agitation leaching were carried out in aqueous ammonia/ammonium carbonate solution, to recover copper from the flotation tailings of waste copper oxide residue. The main copper minerals contained in the flotation tailings are chrysocolla, malachite, and cuprite, with the copper grade of 1.12%. Effects of lixiviant concentration, solid‐to‐liquid ratio, stirring speed, and reaction temperature on copper leaching ratios at various time were investigated. It is found that the leaching ratio almost cannot be affected by time after 90 min of leaching. The optimised processing conditions have been determined, under which the leaching ratio of 70.6% is obtained. Kinetics analysis indicates that the copper leaching ratio is controlled by diffusion through the product layer in the initial 60 min of leaching, and corresponding measures to strengthen the copper extraction is proposed, with the activation energy of 32.3 kJ/mol. © 2012 Canadian Society for Chemical Engineering     

Extraction of zinc from ammoniacal/ammonium sulphate solutions by LIX 54

The extraction of zinc from ammoniacal/ammonium sulphate aqueous media using LIX 54 has been studied. The metal extraction rate has been examined and also the effect of temperature on the extraction of zinc (ΔH° = −8·8 kJ mol⁻¹). The effect of the aqueous pH, and therefore zinc ammine complex formation, on the extraction of zinc was studied. Stripping of the metal from loaded organic phases was carried out at various rates, temperatures (ΔH° = 3·2 kJ mol⁻¹) and sulphuric acid concentrations. The results obtained were compared with others obtained from the literature wherein different extractants were used. © 1998 SCI.     

Dissolution kinetics of colemanite in water saturated by carbon dioxide

The dissolution kinetics of original and calcinated samples of the boron containing mineral colemanite, in CO₂-saturated water were studied. Effects of particle size, calcination temperature and reaction temperature were evaluated. It was observed that the dissolution is chemically-controlled. The reaction rate decreased with increase in particle size, and increased with increase in the calcination and reaction temperatures. The activation energy for solution of the sample calcinated at 400°C as calculated as 57.7 kJ mol^?1.     

Thermal decomposition of ammonium sulphate

The thermal decomposition and vaporisation of ammonium sulphate, (NH₄)₂SO₄, is shown to take place via two distinct sets of reactions. In the first, ammonium pyrosulphate, (NH₄)₂S₂O₇, is the primary condensed phase product: 2(NH₄)₂SO₄ ← (NH₄)₂S₂O₇+2NH₃+H₂O The second stage concerns the decomposition of the pyrosulphate. Ammonia, sulphur dioxide, nitrogen and water are the major products, the dominant reaction being 3(NH₄)₂S₂O₇ ← 2NH₃+6SO₂+2N₂+9H₂O     

Leaching kinetics of iron from low grade kaolin by oxalic acid solutions

Kaolin is a clay with important industrial applications. Unfortunately, with iron oxides depositing on mineral particles during kaolin formation, much of this clay has become unusable for industrial applications. Two of the most important factors that affect the value of this raw material are its iron concentration and brightness. The goal of this work was to examine the leaching kinetics of iron from low grade kaolin using oxalic acid solutions. The effects of particle size, acid concentration, and reaction temperature were studied. It was determined that the iron dissolution rate increases with oxalic acid concentration, temperature, and decreased particle size. Leaching data showed that iron dissolution from low grade kaolin is due to diffusion through the product layer. The activation energy of the process was 46.32 kJ/mol.     

Leaching of raney ni-a1 alloy with alkali: kinetics of hydrogen evolution

Kinetics of leaching of Raney Ni-AI alloy (Ni: 50% w/w) with alkali has been studied in an agitated reactor by measuring the rate of H₂ evolved in the leaching process at constant alkali concentrations. The effects of various process parameters such as temperature, type and concentration of alkali, particle size of the alloy and stirring speed, on the leaching process have also been investigated. The kinetic data could be fitted to the empirical expression: q=α+βlog(t) Where, q is the amount of H₂ evolved in the leaching process; t, the reaction time; and a and β, the constants. The order of reaction with respect to alkali concentration and the activation energy for the leaching process were determined from the analysis of the initial rates. An appreciable fraction of the hydrogen, which is formed in the leaching process, has been found to be retained on the solid product(s).     

Zinc electrowinning from acidic sulphate solutions. Part III: Effects of quaternary ammonium bromides

The effects of the organic additives cetyltrimethylammonium bromide (CTABr) and tetrabutyl ammonium bromide (TBABr) on the electrowinning of zinc from acidic sulphate solutions were studied in the presence and absence of trace amounts of antimony(iii). The results indicated that CTABr has similar properties to the commonly used industrial additive glue with respect to current efficiency, power consumption, polarization behaviour, and the crystallographic orientation and surface morphology of the zinc deposits. TBABr was generally less useful with respect to all these properties. Voltammetric studies indicate that polarisation for zinc electrodeposition decreased in the order CTABr > glue > TBABr. The nature of the electrode reactions were investigated through measurements of exchange current densities, Tafel slopes and transfer coefficients.     

Leaching calcium from phosphogypsum desulfurization slag by using ammonium chloride solution: Thermodynamics and kinetics study

Phosphogypsum(PG) desulfurization slag is a calcium-rich residue from reductive decomposition of PG using sulfur as the reductant. We proposed a technology of preparation light calcium carbonate with PG desulfurization slag, which mainly contains two steps: leaching and carbonizing. In this work, we concentrated on the former, in which ammonium chloride aqueous solution was utilized as leaching agent to extract calcium from the slag, and conducted thermodynamics and kinetics study on it. Fact Sage software was employed to do thermodynamic and phase equilibrium diagram calculations. The influence of leaching conditions including agitation speed, initial concentration of leaching solution, reaction temperature, and liquid/solid ratio on the calcium leaching rate was discussed in detail by means of experiment optimal design. A kinetic model developed from the shrinking core model was given to describe the leaching process. The apparent kinetic activation energy(Ea) of the leaching reaction was calculated to be 10.58 k J·mol~(-1).     

Investigating dissolution of colemanite in sulfuric acid solutions by particle size measurements

Dissolution properties of colemanite and gypsum formation in sulfuric acid were investigated by measuring size distribution of particles in the reaction cell with time. After termination of the reaction, the remained material in the cell was analyzed to find out unreacted and reacted fractions. The results showed that the reaction of colemanite particles with sulfuric acid led to reduction in particle sizes and the degree of reduction depended on acids concentration and reaction time. The dissolution period and point of gypsum formation were clearly distinguished and marked on particle size plots.