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.     

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.     

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 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.     

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.     

The economics of hydrogen and carbon monoxide separation with cuprous ammonium lactate solutions

A process is proposed for making hydrogen from coal which completely eliminates low temperature and reduces the amount of high temperature shift conversion. The resulting 1:1 H₂CO mixture is separated by absorption and reaction in a cuprous ammonium lactate solution at 1000 p.s.i.a. The hydrogen is used for large scale coal liquefaction. Regeneration of the cuprous ammonium lactate solution results in a sulfur and particulate free carbon monoxide stream suitable for electric power generation.A comparison of the economics of this alternative with conventional high and low temperature shift conversion shows an increase in the process efficiency as well as reduction in the amount of capital required. This, plus other savings, results in carbon monoxide costing 0.988 $/MSCF or 3.095 $/MM Btu. On an equivalent Btu basis, this is 70.9% of the cost of hydrogen by conventional coal conversion. Thus, substitution of separation for shift conversion results in a substantial product cost reduction.     

Electrodeposition of iron in sulphate solutions

The kinetics of iron electrodeposition from acid sulphate solutions onto a platinum electrode was investigated by means of stationary polarisation curves and electrochemical impedance spectroscopy. Together with interfacial pH data previously obtained, the effect of pH was analysed. The formation of at least three adsorbed intermediates at the cathode surface was evidenced in all pH values. The relative rate of their formation and its surface concentration depend on the solution pH as well as on the electrode potential. It is suggested that two of these species catalyses the H⁺ reduction whereas the other one may have a blocking effect on this reaction.     

电解锰生产中硫铵渣的处理

硫铵渣是在电解锰生产过程中产生的一种废渣,如何处理硫铵渣是现在电解锰企业亟待解决的问题。简要介绍了几种可用于硫铵渣的处理、回收利用的参考方法,对各个处理方法的优缺点进行分析,并对以后处理利用硫铵渣的手段进行了展望。     

Modification of alumina bubbles with ammonium aluminum sulphate

Ammonium aluminum sulphate was introduced to modify alumina bubbles by the wet chemical method. Distribution of ammonium aluminum sulphate, in situ decomposition characteristics, microstructure and mechanical properties of the modified alumina bubbles were investigated by SEM, XRD, BET and by a purposely designed experimental device for the measurement of compressive resistance. Experimental results showed that an ammonium aluminum sulphate thin film was formed on the surface of the alumina bubbles, at the same time, ammonium aluminum sulphate also infiltrated into the flaws and cavities of the alumina bubbles. After heat-treated at 900 °C, the ammonium aluminum sulphate on the alumina bubbles could be in situ decomposed to γ-Al₂O₃ with high activity. The compressive resistance of the modified alumina bubbles was enhanced from 15.6N to 38.7N after heat-treatment at 1700 °C for 2 h.     

The anodizing of aluminium in sulphate solutions

The morphology of films formed in H₂SO₄---Na₂SO₄ mixtures for different times at various constant cds has been studied as a function of electrolyte concentration, pH and temperature, using electron microscopy. At low pH, local preferential film dissolution competes with the film-forming reaction, producing typical porous films whereas, as the pH is raised towards neutrality, pitting by metal dissolution becomes a progressively more important competitive process, probably initiating at the base of flaws in the film. For porous films, it is shown that the pore diameter, cell diameter and barrier-layer thickness are all proportional to the formation voltage, there being evidence that pore initiation and development are largely controlled by field-assisted oxide dissolution, with possible lesser contributions from Joule heating effects. Severe anodizing conditions produce pore widening and merging, as well as general roughening, at and near the outer surface but, although the film appears less regular and compact, there is no evidence of major pore widening throughout its thickness.     

从铋冶炼浸渣制取三碱式硫酸铅的工艺研究--碳酸氢铵转化工艺的影响

介绍了铋冶炼浸渣采用碳酸氢铵转化-硝酸浸出-硫酸沉铅-氢氧化钠反应合成三碱式硫酸铅的工艺原理。探讨了铋冶炼浸渣采用碳酸氢铵转化过程中，碳酸氢铵与浸渣配比、碳酸氢铵及醋酸加入量、反应时间、液固质量比等因素对铅的转化率的影响。通过正交试验找出了转化反应的最佳制备条件：碳酸氢铵与铅的物质的量比为2．5：1，室温条件下反应时间2，5h，不加醋酸，液固质量比为3：1，浸渣粒径≤90μm。     

硫酸铵与氯化钾生产硫酸钾的研究

研究了氨法脱硫副产的硫酸铵溶液直接与氯化钾进行复分解反应生成K2SO4结晶的工艺参数.离心分离K2SO4结晶,经干燥后制得合格的农用化肥硫酸钾产品.试验表明：反应时间3h、反应温度30℃、L/G为1.2,KCl与（NH4） S04质量比1.10条件下,采用硫酸铵与KCl定量配比投料能生产出硫酸钾合格品.     

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.