Optimization of the Dissolution of Tincal Ore in Phosphoric Acid Solutions at High Temperatures

The aim of the study was to investigate the optimization of the dissolution of tincal ore in phosphoric acid solutions at high temperatures in a batch reactor. The effect of the following parameters on the dissolution process was investigated: the reaction temperature, the phosphoric acid concentration, the particle size, and the solid-to-liquid ratio. The best conditions for the dissolution were determined using the 2⁴ factorial experimental design method. The optimum values of the parameters were experimentally determined. The effective parameters were the reaction temperature, the phosphoric acid concentration, the particle size, and the solid-to-liquid ratio. The optimum conditions resulted in the maximum boron dissolution at an acid concentration of 1 M, reaction temperature of 85°C, particle size of 4.75 mesh, and solid-to-liquid ratio of 1/6 g · mL^?1. Under these optimum conditions, the best dissolution yield was 98.26%.     

Investigation of selective leaching and kinetics of copper from malachite ore in aqueous perchloric acid solutions

In this study, the leaching kinetics of malachite in perchloric acid solutions was investigated. The dissolution behaviors of copper, zinc, and iron in the ore matrix were determined at different acid concentrations and reaction temperatures. It was observed that the concentration of perchloric acid had a major effect on the dissolution of copper, zinc, and iron. It was determined that the effect of temperature on the dissolution of these species was not as significant as concentration impact. The results obtained shown that copper in the ore matrix was completely leached while zinc and iron were partially dissolved in perchloric acid solutions. In addition, the effects of the acid concentration, reaction temperature, stirring speed, particle size, and solid-to-liquid ratio on the leaching of malachite were researched. In these experiments, it was observed that the leaching rate of copper increased with increasing solution concentration, stirring speed, and reaction temperature, and with decreasing solid-to-liquid ratio and particle size. A kinetic analysis was performed, and it was found that the rate of leaching reaction obeyed the mixed kinetic control model in the unsteady state. The activation energy of the leaching process was calculated to be 34.69 kJ/mol.     

Application of Taguchi method in the optimization of dissolution of ulexite in NH4Cl Solutions

The Taguchi method was used to determine optimum conditions for the dissolution of ulexite in NH₄Cl solutions. The ranges of experimental parameters were between 50–87 ‡C for reaction temperature, 0.05-0.20 gmL^-1 for solid-to-liquid ratio, 1–4 M for NH₄Cl concentration, 5–25 min for reaction time, and (-850+600)-(-90) Μm for particle size. The optimum conditions for these parameters were found to be 87 ‡C, 0.05 gmL^-1, 4M, (-300+212) Μm, and 18 minutes, respectively. Under these conditions, the dissolution percentage of ulexite in NH₄Cl solution was 98.37. Reaction products were found to be boric acid, ammonium tetraborates, sodium tetraborate decahydrate, calcium chloride, and sodium chloride.     

Dissolution of ulexite in ammonium carbonate solutions

The dissolution of ulexite in ammonium carbonate solutions is investigated. The effect of concentration, particle size, stirring speed, and reaction temperature is examined. It is found that the dissolution rate increases with increasing concentration and reaction temperature, and with decreasing particle size. No effect of stirring speed was observed on the conversion. It is determined that the dissolution rate fits to the first order pseudo-homogeneous reaction model.     

Kinetic Investigation of Reaction Between Colemanite Ore and Methanol

In the field of industry, it is very important that boron compounds are produced from boron ores. The aim of this study was to investigate the dissolution kinetics with carbon dioxide of colemanite in methanol medium in a pressure reactor and to derive an alternative process for producing boron compounds. Reaction temperature, stirring speed, solid/liquid ratio, pressure, and particle size were selected as parameters for the dissolution rate of colemanite. It was found that the dissolution rate increased with increase in pressure and reaction temperature, and with decrease in particle size and solid/liquid ratio. No effect of stirring speed was observed on conversion. The dissolution kinetics of colemanite were examined using both heterogeneous and homogeneous reaction models, and it was determined that the reaction rate can be described by a second-order pseudo-homogeneous reaction model. The activation energy was found to be 51.4 kJ/mol.     

Kinetic Investigation of Reaction Between Metallic Silver and Nitric Acid Solutions

In this study, the reaction kinetics between metallic silver and nitric acid solutions was investigated by taking into consideration the parameters of temperature, solid‐to‐liquid ratio, stirring speed, nitric acid concentration, particle size and addition of sodium nitrite. It was determined that the dissolution rate of the process increased with decreasing particle size and solid‐to‐liquid ratio, and increasing nitric acid concentration, reaction temperature and the amount of the sodium nitrite in the solution. In addition, it was observed that the stirring speed had more effect on the dissolution rate at low stirring speeds than at high stirring speeds. In the present study, the examination of shrinking core models of fluid‐solid systems showed that the dissolution of metallic silver in the nitric acid solutions was controlled by the reaction on the surface. A semiempirical model, which represented well the process, was developed by statistical methods. The activation energy of the process was found to be 57.66 kJ mol^–1.     

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.     

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.     

硫酸浸出硼泥中镁离子过程研究

对硫酸浸出硼泥中镁离子工艺过程进行了研究,考察了硼泥颗粒粒径、硫酸稀释比、酸浸温度对浸出镁离子的影响。结果表明,当硼泥颗粒粒径为62~77 μm、硫酸稀释比为1∶2、酸浸温度为60 ℃时,得到镁离子最高浸出率为64.61%。通过动力学分析得出,当硼泥颗粒粒径为62~77 μm 时,硫酸浸出硼泥中的镁由表面反应控制和固膜扩散控制共同作用,酸浸活化能为14 kJ/mol。     

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 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.     

EVALUATION OF LEACHING CONDITIONS FOR DISSOLUTION OF PYRITE IN CHLORINE-SATURATED WATER

The optimum leaching conditions for the dissolution of pyrite in water saturated with chlorine gas were investigated. Reaction temperature, solid-to-liquid ratio, reaction time, and particle size were selected as the leaching parameters. 2ⁿ factorial experimental design and orthogonal central-composite design methods were used. A mechanical stirring speed of 500 rpm and chlorine gas-flow rate of 1379 mL/minute were chosen as the fixed parameters in all experiments. The degrees of effectiveness from high to low were found to be, in respective order, the particle size, the reaction temperature, the solid-to-liquid ratio, and leaching time. A reaction temperature of 30°C, solid-to-liquid ratio of 0.167 g/mL, particle size of 150–212 μm, and reaction time of 360 minutes were found to be the optimum leaching conditions. The dissolution yield of iron from pyrite was 98.4% under optimal leaching conditions.     

硫铁矿烧渣酸浸铜反应动力学研究

研究了硫酸烧渣的硫酸浸铜过程中,搅拌速率、浸出剂初始质量浓度、固液比、浸出温度和矿物粒径对浸出率的影响,并对硫铁矿烧渣浸取铜过程动力学进行了分析。研究结果表明,该浸出过程符合收缩芯模型,与化学反应控制动力学方程式相吻合,浸出反应的表观活化能为39.19 kJ/mol,浸出过程控制步骤为化学反应控制。     

Dissolution of colemanite in (NH<Subscript>4</Subscript>)2SO<Subscript>4</Subscript> solutions

Turkey is the country having the richest boron ores in the world, and colemanite, tincal and ulexite are the ores being mined mostly in Turkey. These ores are used in the production of various boron compounds of which the production methods are generally patented. Colemanite ore also is reacted with sulfuric acid to product boric acid. Produced by this method, boric acid contains various impurities which reduce the market value and are difficult to remove. This study investigated the reaction between colemanite and ammonium sulfate as an alternative method to produce boric acid. Particle size, ammonium sulfate concentration, solid to liquid ratio and reaction temperature were chosen as parameters. In results, the conversion rate was increased by decreasing particle size and solid to liquid ratio, by increasing ammonium sulfate concentration and temperature. A semi-empirical model with 40.46 kJmol⁻¹ activation energy representing this process was found as follows: 1−(1−X)^1/3=2.12×10²·C^1.38·R^−0.75·(S/L)^−0.44·e^−4866/T·t^0.61.     

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.     

低冰镍转炉渣中钴的氧压酸浸行为及其动力学

研究了转炉渣中钴氧压硫酸体系选择性浸出过程的行为及其动力学。通过改变搅拌速度、反应温度、硫酸浓度、氧分压、物料粒度以及反应时间等浸出条件,考察钴浸出率的变化及影响,获得转炉渣中钴的浸出动力学规律。结果表明,钴的浸出率随着温度、酸度、氧分压的增加而增加;硫酸质量浓度大于0.4 mol·L^-1会导致铁大量溶出;浸出过程符合未反应芯收缩核模型,前期受化学反应控制,然后转变为混合控制,后期受固体产物层扩散控制。化学反应控制和固体产物层扩散控制过程的活化能分别为43.19 kJ·mol^-1 和10.49 kJ·mol^-1。化学反应控制过程对硫酸浓度、氧分压及粒度的反应级数分别为0.79、0.85和 -0.95。     

Micronization of cilostazol using supercritical antisolvent (SAS) process: Effect of process parameters

The aim of this study was to improve dissolution rate of poorly water-soluble drug, cilostazol, using supercritical antisolvent (SAS) process. The effect of process variables, such as pressure, temperature, drug concentration, type of solvents, feed rate ratio of CO₂/drug solution, on drug particle formation during SAS process was investigated. Particles with mean particle size ranging between 0.90 and 4.52 μm were obtained by varying process parameters such as precipitation vessel pressure and temperature, drug solution concentration, solvent type, feed rate ratio of CO₂/drug solution. In particular, mean particle size and distribution were markedly influenced by drug solution concentration during SAS process. Moreover, the drug did not change its crystal form and the operating parameters might control the ‘crystal texture’ due to the change in crystallinity and preferred orientation during SAS process, as confirmed by differential scanning calorimetry and powder X-ray diffraction study. In addition, the dissolution rate of drug precipitated using SAS process was highly increased in comparison with unprocessed drug. Therefore, it is concluded that the dissolution rate of drug is significantly increased by micronization of cilostazol, leading to the reduction in particle size and increased specific surface area after SAS process.     

Electrochemical behaviour and corrosion of lead in some carboxylic acid solutions

The electrochemical behaviour and corrosion of lead in various concentrations of acetic, lactic (0·01 M –1·0 M ), oxalic and tartaric (0·01 M –0·15 M ) acid solutions were studied at 25°C by a potentiodynamic method. The lead anode is readily soluble both in acetic and lactic acid solutions up to 2000 mV. In these two acid solutions, the anodic dissolution of lead increases with increases in the acid concentration and the dissolution process is under charge transfer control. Lactic acid is more corrosive than acetic acid. However, in oxalic and tartaric acid solutions, the E/i profiles depend on the acid concentration. Above a certain specific concentration, the profiles exhibit an anodic current peak associated with a dissolution of the metal and the formation of a passivating lead salt film and a cathodic peak which is related to the reduction of the film. The active dissolution of the lead increases with the acid concentration, the scan rate and stirring of the solution. The passivation of lead in these two acid solutions occurs by a dissolution–precipitation mechanism and the process is controlled by diffusion. X-ray diffraction analysis confirmed the presence of a passivating salt film (either lead oxalate or lead tartrate) on the electrode surface. © 1998 SCI     

硝酸分解钠硼解石制备硼酸的工艺研究

以玻利维亚钠硼解石矿为原料,采用硝酸酸解硼矿制备硼酸。考察了钠硼解石的洗矿和酸解工艺,结果表明：在洗矿工艺中,控制液固体积质量比为6 mL/g和洗矿时间为20~30 min,氯离子的脱除率达到92.17%;在酸解工艺中,控制硝酸用量为理论用量的90%、液固质量比为5、反应温度为60 ℃和反应时间为40~60 min,硼的浸出率达到98%以上。在上述工艺条件下进行硼酸母液循环研究,结果显示,随着循环次数的增加,虽然母液中的硝酸钙和硝酸钠不断积累,其质量浓度不断增加,但硼酸的质量浓度保持稳定。合适的循环次数有利于硼的回收和母液中硝酸盐浓度的提高,使母液可以用于生产硝酸钠和碳酸钙等附加值高的副产品。     

Determination of the Optimum Conditions for Copper Leaching from Chalcopyrite Concentrate Ore Using Taguchi Method

The optimum conditions for the extraction of copper from chalcopyrite concentrate into SO₂-saturated water were evaluated using the Taguchi optimization method. High level copper recovery was obtained in an environmentally friendly process that avoids sulfur dioxide emission into the atmosphere because SO₂ forming in the roasting is used in the dissolution. Experimental parameters and their ranges were chosen as follows: reaction temperature, 293–333 K; solid-to-liquid ratio, 0.025–0.15 g/mL; roasting time, 30–90 min; roasting temperature, 773–973 K; stirring speed, 400–800 rpm; and reaction time, 10–60 min. The particle size and gas flow rate were 63 µm and 10 cm³/min, respectively. The optimum conditions of the dissolution process were determined to be reaction temperature of 318 K, a solid-to-liquid ratio of 0.025 g mL^?1, a roasting time of 75 min, a roasting temperature of 773 K, a stirring speed of 400 rpm, and a reaction time of 30 min. Under optimum conditions, dissolution yield of copper was 91%.