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 ulexite in acetic acid solutions

Ulexite is an important boron mineral used for the production of boron compounds. The aims of this study are to examine the dissolution kinetics of ulexite in acetic acid solutions, and to present an alternative process to produce boric acid. In order to investigate the dissolution kinetics of ulexite in acetic acid solutions, the concentration of solution, reaction temperature, solid-to-liquid ratio, and particle size were selected as experimental parameters. It was determined that the dissolution rate of ulexite increased with increasing solution concentration and temperature and decreasing particle size and solid-to-liquid ratio. The activation energy of the process was found to be 55.8 kJ/mol.     

Determination of the Optimum Conditions for Leaching of Malachite Ore in H2SO4 Solutions

The Taguchi method has been used to determine the optimum conditions for the dissolution of malachite ore in H₂SO₄ solutions. The chosen experimental parameters and their range were (i) reaction temperature: 15 to 45 °C, (ii) solid‐to‐liquid ratio: 1/10 to 1/3 g cm^–3, (iii) acid concentration (in weight): 2 % to 10 %, (iv) particle size: –40 to –3.5 mesh, (v) stirring speed: 240 to 720 rpm, and (vi) reaction time: 5 to 45 minutes. The optimum conditions were found to be reaction temperature: 40 °C, solid‐to‐liquid ratio: 1/3 g cm^–3, acid concentration (in weight): 10 %, particle size: –30 mesh, stirring speed: 480 rpm, and reaction time: 45 minutes. Under these optimum working conditions, the dissolution of copper and iron in malachite ore was 100 % and 58 %, respectively. Besides, alternative working conditions reducing the total cost and dissolution of iron were found.     

NaOH亚熔盐法分解钾长石矿

以高浓度NaOH溶液为亚熔盐介质分解钾长石矿精粉,考察了矿物粒径、NaOH溶液浓度、搅拌速度、反应时间、反应温度、液固比对K+溶出率的影响,并对分解过程动力学进行分析. 结果表明,100 mm粒径钾长石矿精粉的最佳反应条件为：NaOH初始浓度60%(w)、反应温度约160℃、搅拌速度400 r/min、液固质量比4:1、反应140 min,该条件下K+溶出率大于98%. 钾长石的分解符合粒径恒定的缩核模型,反应初期固相产物层内扩散为速控步骤. 80~140℃下,反应的表观活化能为110.42 kJ/mol.     

A Study on Recovery of Gold from Decopperized Anode Slime

A study was performed on the chlorination and cementation of gold from an anode slime. The gold from decopperized anode slime first was dissolved with chlorine gas in aqueous medium, later the dissolved gold was precipitated by using a rotational copper disc. The effects of reaction temperature, reaction period, stirring speed, solid‐liquid ratio and Cl₂ gas flow rate on the dissolution of gold were investigated. Increasing the solid‐liquid ratio decreases the dissolution, the solubility increases with increasing reaction temperature, reaction period and stirring speed. It was observed that the Cl₂ gas flow rate hasn't a significant effect on the dissolution. As to the precipitation of the gold in the solution, the effects of temperature and rotational speed were sought for. The experimental results showed that the gold recovery could be over 90 %. For the kinetics analysis of the cementation, the activation energy value was found to be 19.51 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 colemanite in ammonium hydrogen sulphate solutions

The aim of the study was to investigate the dissolution kinetics of colemanite in ammonium hydrogen sulphate solutions in a mechanical agitation system and to declare an alternative reactant to produce boric acid. Reaction temperature, concentration of ammonium hydrogen sulphate, stirring speed, solid/liquid ratio and particle size were selected as parameters on the dissolution rate of colemanite. 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 colemanite. The dissolution extent is highly increased with increase the stirring speed rate between 100 and 500 rpm and the dissolution extent is slowly increased with increase the stirring speed between 500 and 700 rpm in experimental conditions. The activation energy was found to be 32.66 kJ/mol. The leaching of colemanite was controlled by diffusion through the ash or product layer. The rate expression associated with the dissolution rate of colemanite depending on the parameters chosen may be summarized as follows: 1 ? 3(1 ? X)^2/3 + 2(1 ? X) = 8.99 × C^1.08 × W^1.39 × D^?1.27 × (S/L)^?0.54 × e^(?32.66/RT)t.     

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.     

硼精矿加压碱解制备水合偏硼酸钠

采用NaOH-H2O体系加压溶出硼精矿制备水合偏硼酸钠．正交实验结果表明,影响硼溶出的因素顺序为,碱浓度>时间>液固比>温度. 考察了初始NaOH溶液浓度、液固比、反应时间、反应温度、矿石粒度和搅拌速度对硼溶出的影响,最优条件[初始NaOH浓度25%(w)、液固比4:1(w)、反应时间2 h、反应温度140℃、搅拌速度500 r/min、高压釜表压0.2 MPa]下,硼转化率达95.91%. 湿硼泥经三级逆流浆化洗涤(各级洗涤温度90℃、洗水与湿硼泥质量比3:1、时间1 h)可实现Na2O和B2O3的高效回收,烘干的终硼泥Na2O和B2O3含量分别为0.35%和0.45%(w),含42.91%(w) MgO的终硼泥可作为提镁的优质原料. 溶出液添加CaO苛化并高温放置陈化脱色除杂,再降温至25~30℃,恒温结晶6 h后抽滤,结晶率大于70%,晶体用无水乙醇、饱和偏硼酸钠溶液洗涤,40℃烘干12 h,物相为NaB(OH)4,纯度约为90%.     

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.     

Electric‐oxidation kinetics of molybdenite concentrate in acidic NaCl solution

The electric‐oxidation kinetics of molybdenite concentrate in NaCl electrolyte was investigated in this study. The effects of liquid‐to‐solid ratio, stirring speed, and concentration of NaCl on the dissolution rate were determined. It was found that the dissolution rate increases with increase in liquid‐to‐solid ratio, stirring speed, and concentration of NaCl. A shrinking particle model is presented to describe the dissolution and to analyse the data. The apparent activation energy of this dissolution process was found to be 8.2 kJ/mol; it was established that the leaching process is mainly controlled by diffusion, and the kinetics formula of this research system can be expressed as: .     

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.     

NaHCO3溶液浸出硼精矿中硼的工艺

研究了NaHCO3溶液提取硼精矿熟料中硼的工艺,考察了液固比、NaHCO3用量、浸出温度、浸出时间和搅拌速率对硼提取率的影响. 结果表明,最佳提取工艺条件为液固质量比2.1:1,NaHCO3用量为理论用量的150%,反应温度100℃,反应时间1 h,搅拌速率400 r/min,该条件下硼浸出率达92.88%. 硼精矿熟料的晶形大多是柱状和扁平状,并有微小颗粒附着其表面;终硼泥为很多小晶体堆叠在一起,与硼精矿熟料相比,终硼泥颗粒变小,因此可用收缩核模型描述硼精矿熟料中硼在NaHCO3溶液中的浸出过程. 金云母、遂安石、利蛇纹石和橄榄石是硼精矿熟料的主要物相,而终硼泥出现了MgCO3和Na2Mg(CO3)2物相,遂安石消失.     

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。     

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.     

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.     

低品位铌钽矿高浓碱性介质浸出过程动力学研究

The leaching kinetics of niobium from a low-gr~te niobium-tantalum ore by concentrated KOH solution under atmospheric pressure has been studied. Significant effects of reaction temperature, KOH concentration,stirring speed, particle size and mass ratio of alkali-to-ore on the dissolution rate of niobium were examined. The experimental data of the leaching rates and the observed effects of the relevant operating variables were well interpreted with a shrinking core model under diffusion control. By using the Arrhenius expression, the apparent activation energy for the dissolution of niobium was evaluated. Finally, on the base of the shrinking core model, the rate equation was established.     

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.     

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%.     

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%.