Kinetic investigation of dissolution of CaWO4 in oxalic acid solution

Abstract

In this study, the effects of stirring speed, temperature, H₂C₂O₄ concentration and particle size on the dissolution rate of CaWO₄ in H₂C₂O₄ solutions were investigated. CaWO₄ was dissolved in H₂C₂O₄ solutions as series parallel type reaction. In the first step which took place according to Langmuir-Hinshelwood Mechanism, H₂C₂O₄ was adsorbed as a mobile adsorption layer on the surface of CaWO₄, reacted to form adsorbed calcium aqua oxalato tungstate (Ca[WO₃(C₂O₄)H₂O]) intermediate product and the adsorbed Ca[WO₃(C₂O₄)H₂O] was desorbed into the solution. In the second step, Ca[WO₃(C₂O₄)H₂O] hydrolysed and formed H₂WO₄ which reacted with H₂C₂O₄ to form hydrogen aqua oxalato tungstate (H₂[WO₃(C₂O₄)H₂O]) as end product together with solid CaC₂O₄H₂O. Model kinetic equations were derived which showed the relationships of the fractional conversion of CaWO₄, the concentration of Ca[WO₃(C₂O₄)H₂O] and the concentration of H₂[WO₃(C₂O₄)H₂O] with time. The diagrams drawn according to the model kinetic equations were in good agreement with the experimentally obtained diagrams (R²>0·99).

Dans cette étude, on a examiné les effets de la vitesse d’agitation, de la température, de la concentration d’H₂C₂O₄ et de la taille de particule sur la vitesse de dissolution de CaWO₄ dans des solutions d’H₂C₂O₄. On a dissous le CaWO₄ dans des solutions d’H₂C₂O₄ en une réaction de type série-parallèle. Dans la première étape, qui avait lieu d’après le Mécanisme de Langmuir-Hinshelwood, l’H₂C₂O₄ était adsorbé en une couche mobile d’adsorption à la surface du CaWO₄, réagissait pour former le produit intermédiaire adsorbé, aqua oxalato tungstate de calcium (Ca[WO₃(C₂O₄)H₂O]), et ce Ca[WO₃(C₂O₄)H₂O] adsorbé était désorbé dans la solution. Dans la seconde étape, le Ca[WO₃(C₂O₄)H₂O] était hydrolysé et formait l’H₂WO₄ qui réagissait avec l’H₂C₂O₄ pour former de l’aqua oxalato tungstate d’hydrogène (H₂[WO₃(C₂O₄)H₂O]) comme produit final avec le CaC₂O₄H₂O solide. On a dérivé les équations cinétiques du modèle, lesquelles montraient les relations de la conversion fractionnelle du CaWO₄, de la concentration de Ca[WO₃(C₂O₄)H₂O] et de la concentration d’H₂[WO₃(C₂O₄)H₂O] en fonction du temps. Les diagrammes dessinés d’après les équations cinétiques du modèle étaient en bon accord avec les diagrammes obtenus expérimentalement (R²>0·99).     

The mechanical properties of directionally solidified aluminum-based eutectic castings

Abstract

The mechanical properties for directionally solidified Al-Al₃Ni, Al-Si, and Al-Al₂Cu eutectic castings have been determined and it is shown that the properties of castings (solidified at approximately 80 cm/hour) compare favourably to those obtained for slowly solidified eutectics (solidified at approximately 2 cm/hour). The strengths of Al-Al₂Cu and Al-Si eutectic castings are higher than those obtained for slowly solidified alloys while the strengths for the Al-Al ₃Ni eutectic castings are somewhat lower than for the slowly solidified alloys. The Al-Al₃Ni and Al-Al₂Cu cast eutectics essentially maintain their yield strength up to 300°C whereas the yield strength of the Al-Si eutectic decreases continuously with increasing temperature. It is concluded that the high strengths reported result from a combination of the fine micro-structure obtained from the relatively rapid solidification rate and by strengthening of the intermetallic phase.

Réesumé

Les auteurs ont déterminé les propriétés mécaniques d'alliages eutectiques Al-Al₃Ni, Al-Si et Al-Al₂;Cu solidifiésdirec-tionnellement. Ils montrent que les propriétés des coulées (solidi-fiées à environ 80 cm/h) se comparent favorablement à celles d'eutectiques solidifiés lentement (à environ 2 cm/h). Les résistances mécaniques des coulées eutectiques de Al-Al ₂Cu et Al-Si sont plus élevées que celles obtenues pour des alliages solidifiés lentement tandis que les résistances mécaniques des coulées eutectiques Al-Al₃Ni sont légèrement plus basses que celles des alliages solidifiés lentement. Les limites d'élasticité des alliages eutectiques coulés d'Al-Al₃Ni et Al-Al₂;Cu demeurent élevées jusqu 'à des tempéraptures de 300°C, tandis que lalimite d'élasticité de l'alliage eutec tique Al-Si diminue continuellement quand la température croft. Les auteurs conc1uent que les bonnes propriété s mécaniques obtenues ré sultent de la combinaison de l'effet de la microstructure fine produite par le taux de solidification relativement élevéet de l'effet de fibres produit par la phase intermétallique.     

Solvent extraction of heavy metals contained in phosphoric acid solutions by 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline in kerosene diluent

The solvent extraction of zinc, cadmium and chromium contained in 5.5 mol/L phosphoric acid solutions (30% P₂O₅) was investigated using 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline-Kelex 100® as extractant and treated kerosene as diluent. At organic-to-aqueous phase ratio (1/1) and at room temperature, 58% of zinc, 34% of chromium and 15% of cadmium were recovered in 240 min. In order to improve the kinetics of extraction, a modifier reagent was added to the organic phase. The addition of n-decanol (10 vol.%) increased the rate metals extraction by reducing the equilibrium time from 240 min to 30 min, along with 60% recovery of metals. Extraction of metal ions increased with increasing aqueous phase pH. The pH_0.5 values difference of 0.1 M with Kelex 100® indicates the possible separation of cadmium, zinc and chromium. Increasing the concentration of Kelex 100® increased the percentage extraction of metal ions. The loading capacity values were found to be 83%, 80% and 71% for zinc, chromium and cadmium, respectively, at 0.4 M Kelex 100® concentration, indicating that the extractant is highly selective for the metal ions considered.     

Kinetic Investigation of Reaction Between Mineral Ulexite and Citric Acid

In this study, the dissolution kinetics of ulexite, a sodium-calcium-borate hydrate (Na₂O·2CaO·5B₂O₃·16H₂O) in citric acid solutions was investigated in a batch reactor. The rate of dissolution can be expressed according to surface chemical reaction controlling with changing fluid reactant concentration. The activation energy of the process was found to be 39.4 kJ/mol.     

碰撞反应界面—电感耦合等离子体质谱法测定磷酸中15种痕量杂质元素

使用传统的电感耦合等离子体质谱法（ICP-MS）测定磷酸中杂质元素存在严重的多原子离子干扰,本文利用碰撞反应界面技术(CRI)有效地消除或降低了多原子离子干扰。实验表明,直接稀释磷酸样品后,采用⁸⁹Y-¹¹⁵In-²⁰⁹Bi三内标元素可补偿仪器的信号漂移和基体效应;采用无CRI模式可直接测定Mg、Al、Sr、Cd和Pb;采用He作为碰撞反应气可消除V、Cr、Mn、Co、Ni、Cu、Zn和As的质谱干扰,并确定最佳He流量为90 mL/min;采用H₂作为碰撞反应气可消除Fe和Se的质谱干扰,并确定最佳H₂流量为70 mL/min。方法检出限为0.5~10 ng/g,加标回收率为80%~120%。采用本方法测定工业和食品级磷酸样品,测得结果和其它方法一致,相对标准偏差不大于6.6%（n=6）,适用于大批量样品的分析。     

Synergistic extraction of rare earth by mixtures of 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester and di-（2-ethylhexyl） phosphoric acid from sulfuric acid medium

The extraction of Nd^3＋ and Sm^3＋, including the extraction and stripping capability as well as the separation effect of Nd^3＋ or Sm^3＋, from a sulfuric acid medium, by mixtures of di-（2-ethylhexyl） phosphoric acid （HDEHP, H2A2（0）） and 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester （HEH/EHP, H2L2（0）） were studied. The distribution ratios and synergistic coefficients of Nd^3＋ and Sm^3＋ in different acidities were also determined. A synergistic extractive effect was found when HDEHP and HEH/EHP were used as mixed extractants for Sm^3＋ or Nd^3＋. The chemical compositions of the extracted complex were determined as Nd.（HA2）2-HL2 and Sm.（HA2）2-HL2. The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined.     

高硅氧化铅锌矿加压酸浸中锌的浸出动力学

探讨了高硅氧化铅锌矿加压酸浸中锌的浸出反应动力学。考察了温度、硫酸浓度、搅拌速度、压力对锌浸出的影响。结果表明:氧化铅锌矿加压酸浸过程遵循未反应核缩减模型,浸出过程属于固体膜层扩散控制,表观反应级数为1.09,在试验选取的温度范围内,浸出的扩散活化能14.3kJ/mol。     

Pressure acid leaching of arid-region nickel laterite ore: Part II. Effect of ore type

A comparison of the leach chemistry and residue mineralogy has been carried out on the pressure acid leaching of nontronite, limonite and saprolite ores, using hypersaline water. Results are also compared with a typical arid-region laterite feed from Bulong, which consists of a blend of these ore types. Particular emphasis is placed on the influence of ore type on liquor analysis of iron, aluminium and magnesium, residue mineralogy and nickel extraction. Microprobe evidence is presented that incomplete nickel extraction results from the presence of unreacted minor phases present in the original ore, or from the presence of nickel in the amorphous silica, in apparent association with magnesium.     

磷酸在燃煤型塔式锌精馏炉砌筑中的应用

介绍了燃煤型锌精馏炉的基本炉型、耐火材料的选择及磷酸在筑炉中的应用.生产实践表明,添加适量的磷酸砌筑碳化硅塔盘,有利于延长塔体寿命.     

Determination of Optimum Ingredients for Phosphogypsum Composite Stability under Marine Conditions-Response Surface Analysis with Process Variables

The construction of mixture designs and the methods of response surface analysis of mixture data are discussed and applied for determining the optimum ingredients for stabilized phosphogypsum (PG) composites conducive to marine application. Of particular importance is the ability of the composites to maintain physical integrity when submerged. Therefore, potential indicators for the survivability of the stabilized PG composites were also screened. The triangular coordinate system was used to present the three ingredient components of the PG composites as well as their dependent variables. The augmented simplex centroid design with pseudocomponents was used in determining mixture ingredient composition. A quadratic model with two process variables was used to analyze the experimental results and predict the optimum ingredient composition. The model predicts that a series of PG: class C fly ash:portland type II cement ingredients, such as 62%:35%:3% PG:class C fly ash:portland type II cement and 65%:31%:4% PG:class C fly ash:portland type II cement composites with class C fly ash content (30.7–36.6%) and portland type II cement content (2.7–4.2%), can survive in marine environments for more than two years. The indicator screening for the survivability of the stabilized PG composites in the marine environment showed that the minimum wet leached surface hardness, minimum wet control surface hardness, and maximum effective diffusion coefficient may serve as indicators.     

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.     

微波辅助硫酸浸出红土镍矿的研究

以红土镍矿为原料,研究了微波辅助硫酸浸出镍钴的工艺条件。考察了硫酸浓度、微波功率、微波温度、辐射时间、液固体积质量比对镍钴浸出率的影响。结果表明,在硫酸浓度3.0mol/L、微波功率700 W、微波温度90℃、辐射时间2.5 h、液固体积质量比4:1的最佳工艺条件下,镍浸出率达91%,钴浸出率65%以上。     

变色酸偶氮试剂在动力学光度分析中的应用

对变色酸偶氮试剂在催化动力学光度法测定过渡金属、贵金属及非金属含量方面的应用和速差动力学光度法测定混合稀土中单一稀土含量的方法进行了综述     

含碳酸盐脉石氧化铜矿的酸浸动力学

针对碳酸盐脉石对氧化铜矿酸浸动力学的影响进行探讨,研究了温度、酸度、矿石粒径、液固质量比、振荡速度等因素对含碳酸盐脉石氧化铜矿浸出的影响.结果表明,高温、高酸度、高液固质量比、小粒径和高振荡速度利于矿石的浸出,但碳酸盐脉石使得酸耗增加.考虑浸出成本确定合理的浸出条件为温度303 K、酸度35 g·L^-1、矿石粒径0.074~0.125 mm、液固质量比3∶1以及振荡速度180 r·min^-1,浸出180 min后铜浸出率达53.6%.对浸出前后矿石表面形貌进行分析.结果显示碳酸盐脉石与酸反应后在矿石表面形成CaSO₄·2H₂O沉淀,覆盖在颗粒表面,限制了矿石颗粒孔裂隙的发育.基于收缩未反应核模型对浸出动力学进行分析,发现碳酸盐脉石反应生成的沉淀阻碍了浸出反应,固体产物层扩散为浸出反应的控制步骤,反应的表观活化能为8.65 kJ·mol^-1.     

Kinetic investigation of sulfuric acid leaching of Zn-containing wastes from nonferrous metalworking plants

The kinetics of the dissolution of Zn-containing waste of brass production in sulfuric acid is investigated. It is proved that dissolution proceeds in two stages. Optimal conditions of obtaining zinc sulfate from mentioned waste are found. According to proposed recommendations, zinc vitriol of commercial grade corresponding to GOST (State Standard) requirements is obtained.     

混凝法处理酸性磷化废水

介绍了混凝法在处理汽车配件加工生产酸性磷化废水中的应用，在原水pH、CODCr、磷酸盐(P)分别为2．93-4．81、621．2mg／L、72．911mg／L情况下，出水相应指标分别为6．62-8．85、15．5mg／L、0．435mg／L，CODCr、磷酸盐(P)的平均去除率达到97．50％和99.40％。     

乳酸直接缩聚制备聚乳酸的动力学

研究了乳酸直接缩聚制备聚乳酸的反应动力学,结果表明:在常压和无催化剂条件下,当温度达到124℃时,乳酸单体开始缩聚,在反应程度为14.15%～62.75%的范围内缩聚反应符合3级反应,其动力学方程式为-d[COOH]/dt=1.057×10-5[COOH]3.还计算了在不同温度下的反应速率常数k,并根据ARRHENNIS公式求得反应活化能E=4.34 kJ·mol-1.最后,比较了理论计算与实际测量的数均分子量与时间的关系.