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.     

Cathodic processes in the leaching and electrochemistry of covellite in mixed sulfate–chloride media

The cathodic processes that occur on a covellite (CuS) surface in mixed sulfate–chloride solutions in the absence and presence of copper(II) ions have been studied using potentiostatic transients and cyclic voltammetry at rotating disk electrodes in the potential range 0.3–0.7 V (versus SHE). This range is relevant to the oxidative leaching of this copper mineral in sulfate and chloride lixiviants. Variations in the concentrations of sulfate and chloride ions had a small effect on the cathodic reduction of covellite in the potential range of 0.5–0.3 V, although the presence of chloride ion resulted in a significant increase in the anodic current on the reverse sweep. On the other hand, addition of copper(II) ions resulted in enhanced cathodic currents and subsequent anodic currents in both sulfate and chloride solutions due to reduction of covellite to an undefined reduced copper sulfide species. Reduction of copper(II) to copper(I) ions becomes the preferred cathodic reaction as the concentration of chloride ions increases, becoming mass transport controlled at a rotating disc electrode at potentials below about 0.4 V. Potentiostatic measurements at potentials negative to the mixed potential in acidic chloride solutions have shown that reduction of copper(II) ions is reversible and have been used to estimate the rate of oxidative dissolution of the mineral which value agrees reasonably well with previously reported leaching rates under similar conditions. Reduction of dissolved oxygen has been found to be very much slower that that of copper(II) ions under ambient conditions.     

硝硫混酸与Ag、Cu反应的动力学

用失重法探讨了硝硫混酸此例、浸出温度和时间等因素对银的溶解和铜的钝化的影响。结果表明:在一定的[HNO_3]范周内,较高温度时,银的溶解符合一级反应规律;求得银的溶解量与时间、HNO_3起始浓度等的关系式和相应的反应活化能;铜在此条件时是钝化的。本实验再一次证实了银的溶解和铜的钝化机理的正确性,也为银、铜的分离提供了实验依据。     

Interaction Kinetics between Sn-Pb Solder Droplet and Au/Ni/Cu Pad

The interracial phenomena of the Sn-Pb solder droplet on and needle-like AuSn4 are formed at the interface after Au/Ni/Cu pad are investigated. A continuous AuSn2 the liquid state reaction （soldering）. The interracial reaction between the solder and Au layer continues during solid state aging with AuSn4 breaking off from the interface and felling into the solder. The kinetics of Au layer dissolution and diffusion into the solder during soldering and aging is analyzed to elucidate intermetallic formation mechanism at the solder/Au pad interface. The concentration of Au near the solder/pad interface is identified to increase and reach the solubility limit during the period of liquid state reaction. During solid state reaction, the thickening of Au-Sn compound is mainly controlled by element diffusion.     

Direct selective leaching of chalcopyrite concentrate

The ammonium persulphate (APS) leaching of chalcopyrite concentrate in the presence of ammonium carbonate was studied. The effects of ammonium carbonate concentration, APS concentration, leaching time, leaching temperature, solid/liquid ratio and stirring speed were investigated. Optimum leaching conditions were found as follows: APS concentration is 200 g L^?1; ammonium carbonate concentration is 200 g L^?1; leaching time is 180 min; leaching temperature is 60°C; solid/liquid ratio is 0·04 g mL^?1; and stirring speed is 400 rev min^?1. Under these conditions, copper extraction yield was obtained at about 72%. Furthermore, iron extraction yield decreased with increasing ammonium carbonate concentration and iron did not pass into solution under this condition. X-ray and SEM analysis also supported these results. It was determined that the copper extraction results were satisfactory by way of all experiments were performed under atmospheric conditions (i.e. low temperature and atmospheric pressure) and achieved selective copper leaching from chalcopyrite concentrate.

On a étudié la lixiviation au persulfate d’ammonium (APS) du concentré de chalcopyrite en présence de carbonate d’ammonium. On a examiné l’effet de la concentration du carbonate d’ammonium, de la concentration d’APS, de la durée et de la température de lixiviation, du rapport solide-liquide et de la vitesse d’agitation. Les conditions optimales de lixiviation suivent: concentration d’APS?=?200 g L^?1; concentration de carbonate d’ammonium?=?200 g L^?1; durée de lixiviation?=?180 min; température de lixiviation?=?60°C; rapport solide-liquide?=?0·04 g mL^?1; et vitesse d’agitation?=?400 rpm. Avec ces conditions, le rendement d’extraction du cuivre était d’environ 72%. De plus, le rendement d’extraction du fer diminuait avec l’augmentation de la concentration de carbonate d’ammonium, qui empêchait également le fer de passer en solution. L’analyse aux rayons x et au SEM supportait également ces résultats. Grâce à toutes les expériences effectuées en conditions atmosphériques (c’est-à-dire à basse température et à pression atmosphérique), on a déterminé que les résultats d’extraction du cuivre étaient satisfaisants et qu’on obtenait une lixiviation sélective du cuivre à partir du concentré de chalcopyrite.     

Effect of the composition of some sulphide minerals on cyanidation and use of lead nitrate and oxygen to alleviate their impact

An investigation was carried out on synthetic ores containing high purity pyrite, pyrrhotite and chalcopyrite and on two gold ores currently processed to evaluate the impact of cyanicides on cyanidation and to improve the leaching performance by using a pre-leaching, injecting oxygen and adding lead nitrate. With regard to the synthetic ores, it was found that pyrrhotite did not generate a high cyanide consumption while pyrite and chalcopyrite were detrimental. Pre-leaching was deleterious for the ore containing chalcopyrite while pre-leaching with lead nitrate was very efficient to decrease the reactivity of the ore containing pyrite. The two gold ores studied had very different compositions. The low sulphide ore had a low sulphide content (1.36% S), present as pyrrhotite while the second had a very high sulphide content (20.2% S), in the form of pyrite, pyrrhotite and chalcopyrite. The efficiency of the process conditions was peculiar to the ores. The high sulphide ore required a stronger, longer pre-leaching period (12 h) with greater amounts of lime (7.0 kg/t) and lead nitrate (600 g/t) than the low-sulphide ore. The ore with a low sulphide content required a pre-leaching of only 1 h with a small quantity of Pb(NO₃)₂ (50 g/t) and leaching can be performed at 360 ppm NaCN to allow a recovery of 96.4% Au and a low cyanide consumption at 0.18 kg/t. As for the high sulphide ore, cyanidation had to be conducted at 560 ppm NaCN to recover 88.4% Au with a cyanide consumption of 0.80 kg/t. An increase in the amount of lime enhanced oxidation of soluble sulphides. Lead nitrate stabilized copper and iron dissolution by forming a passivation layer at the surface of sulphide minerals. Lead nitrate also prevented the formation of a passive layer at the surface of gold.     

强碱三元复合驱结垢现象

采用现场举升系统结垢统计、室内铸体薄片,结合SEM和电子探针分析了强碱三元复合驱过程中垢成分的变化和储层结垢类型与形成机理。结果表明,垢的主要类型随着强碱三元复合驱体系注入PV数的增加发生变化,注入初期以碳酸盐垢为主并含有少量硅垢和有机物,注入中期3种垢成分含量相当,注入后期结垢类型转变为与初期相同类型。铸体薄片分析表明,垢形态为白色云雾状和褐色胶结状,部分孔隙阻塞造成孔隙结构发生变化,面孔隙率平均下降6.45%。研究区垢的类型主要为钙垢和硅垢,含有少量的钡/钛垢和铁垢。由于强碱的溶蚀作用,地层和井筒中容易出现结垢现象,建议在能够实现相同提高采收率幅度的前提下可以考虑采用弱碱三元复合驱。     

岩盐溶解速率的研究

在岩盐溶解速率及其影响因素的实验研究基础上,建立了岩盐溶解速率的计算公式。研究的结果可为岩盐开采和其他水溶法矿物开采提供参考。     

Experimental investigation of a pilot-scale jet bubbling reactor for wet flue gas desulphurisation

In the present work, an experimental parameter study was conducted in a pilot-scale jet bubbling reactor for wet flue gas desulphurisation (FGD). The pilot plant is downscaled from a limestone-based, gypsum producing full-scale wet FGD plant. Important process parameters, such as slurry pH, inlet flue gas concentration of SO₂, reactor temperature, and slurry concentration of Cl⁻ have been varied. The degree of desulphurisation, residual limestone content of the gypsum, liquid phase concentrations, and solids content of the slurry were measured during the experimental series.The SO₂ removal efficiency increased from 66.1% to 71.5% when the reactor slurry pH was changed from 3.5 to 5.5. Addition of Cl⁻ (in the form of CaCl₂·2H₂O) to the slurry increased the degree of desulphurisation to above 99%, due to the onset of extensive foaming, which substantially increased the gas-liquid contact area. An increase in the inlet flue gas SO₂ concentration from 502 to led to a decrease in the SO₂ removal efficiency from 80.1% to 69.4%. A temperature increase from 296 to caused a reduction in the degree of desulphurisation from 69.4% to 68.1%, but this result is almost within the experimental uncertainty. The residual limestone level in the gypsum formed increased with increasing values of reactor slurry pH, inlet flue gas SO₂ concentration, and slurry concentration of Cl⁻.     

High-pressure fluidized bed coating utilizing supercritical carbon dioxide

Various particles with sizes between 100 and 200 μm were encapsulated with waxes commonly used in technical coating applications. For this, a homogeneous mixture of molten paraffin and supercritical carbon dioxide was prepared in an autoclave and injected into the high-pressure fluidized bed through a nozzle from the bottom. Due to the different conditions in the mixing autoclave and the fluidized bed, the paraffin precipitated in the vicinity of the nozzle and adhered to the solid particles. A complete, thin, uniform, and solvent-free coating was produced. The use of two paraffins with different alkane compositions resulted in dissimilar spreads on glass beads due to their different glass transition temperatures. A smaller pressure drop across the nozzle led to more uniform and even coatings. Glass beads, ceramic spheres, potassium chloride, and lactose showed similar coating results, whereas different morphologies were observed with a plastic material, characterized by a rougher surface and a lower surface energy. The high quality of the coating was confirmed by standard dissolution tests with coated potassium chloride crystals and lactose agglomerates.