جستجوی مقالات مرتبط با کلیدواژه « leaching » در نشریات گروه « شیمی »

The hydrochloric acid leaching of cadmium, nickel, and cobalt from the dismantled powder of spent rechargeable nickel-cadmium batteries was optimized by the response surface methodology. The optimized parameters included HCl concentration, powder mass, temperature, and solid/solution contact time. The optimal values were 100 mL of 2.6 M HCl, 4.4 g of powder, temperature 48.6 °C, and time 3.19 h. The concentrations of Cd, Ni, and Co in the leach solution were 13500, 12150, and 900 mg/L, respectively. The designed process involved a two-step solvent extraction/back-extraction procedure using 0.5 mol/L trioctylamine (TOA) in dichloromethane as the organic phase. The first step consisted of four successive extraction experiments of the metals from the aqueous phase into the organic phase. The results of this step showed that 92.7% of cadmium and 26.7% of cobalt are extracted into the organic phase. In contrast, nickel ions remain quantitatively in the source phase. The different stability of the anionic chloride complexes of cadmium and cobalt leads to different extractability of these metals. By employing an appropriate back-extraction procedure a selective separation of these ions was achieved. The extracted Cd(II) and Co(II) ion pairs (i.e. [TOAH+][MCl¯3], M is Cd or Co) were back-extracted into the stripping phase by using ammonia solutions as a suitable complexing reagent for these metal ions. Selective back-extraction of cadmium (86.3%) from the organic phase by using 0.5 M NH3 solution has resulted. The second step included five consecutive extraction experiments on the raffinate of the preceding step. The total extraction of cobalt into the accumulated organic phase reached 83.0%. Efficient recovery of the extracted cobalt (79.3%) was obtained by a single back-extraction experiment using 7 M NH3. The investigated design allows for improving Ni/Co ratio from 13.9 in the starting aqueous solution to 106 in the ultimate raffinate.

Taguchi Method is used as a statistical approach to optimize the process parameters and improve the quality of components that are produced. The present study aimed to illustrate the leaching optimization of Sarcheshmeh copper concentrate using Taguchi’s experimental design. Various operating parameters such as acid concentration (CA), temperature (T), solid percentage (%S), O2 flow rate (O2), extra oxidizing agent (OxA), NaCl concentration(CNaCl), and contact time (t), each at three levels, were selected and their effect on the copper extraction (R%) was analyzed. L27 Orthogonal Array (OA) was employed as the experimental design and the results were analyzed using analysis of variance (ANOVA) and analysis of mean (ANOM). The experiment results indicated that (T) variable was the most significant parameter with 81% contribution to the response. It is also observed that the interactions between (CA and OxA), (CA and Cox), (CA and CNaCl) had no significant effect on the copper dissolution process. Furthermore, (T), (%S), (O2), (CNaCl) and (t) parameters were found to be statistically significant at 95% confidence level for the desired response. The study showed that Taguchi’s method was suitable to optimize the experiments for increasing leaching efficiency.

An experimental study was conducted to determine the effects of the leaching parameters on impurity ion concentrations of the liquid phase in ulexite leaching. Powdered ulexite ore was leached in an aqueous medium with sulfur dioxide. The Taguchi experimental design approach and statistical methods were used to evaluate the effects of the leaching parameters (solid/liquid ratio, temperature, pH, particle size, time) on impurity ion concentrations (concentrations of magnesium, calcium, iron ions) in the liquid phase. The average B2</sub>O3</sub> leaching ratio of ulexite ore was found as 98.56 % (± 0.95). Statistically effective leaching parameters on impurity concentrations (and delta values for concentrations) were found as pH (770 ppm) for magnesium, solid/liquid ratio (372 ppm) </em>for calcium ion concentrations. The examined parameters were not found effective for iron ion concentrations.

The leaching kinetics of smithsonite ore in acetic acid solutions, an environmental friend, and natural reagent was investigated. The influence of parameters such as reaction temperature, particle size, solid-liquid ratio and acid concentration was studied in order to reveal the leaching kinetics of smithsonite ore. In this study, experimental and statistical methods were carried out in order to analyze the kinetics data to investigate a kinetics model which describes the dissolution. The results indicate that the unreacted shrinking core model for fluid-solid heterogeneous reactions was favorable for the leaching process. The apparent activation energy of the leaching process was found as 74 kJ/ mol. It was determined that the leaching rate of smithsonite was controlled by the chemical reaction below.

This study investigated the optimum conditions for the leaching of manganese-rich iron ore for subsequent beneficiation studies in laboratory scale. The experiments were carried out by varying the concentration of H2SO4 solution and the leaching temperature. The properties of the iron ore was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) as well asphoto-micrographic examination. The leaching experiments showed that the ore leaching increases with increasing acid concentration and temperature. About 78.9% of the iron ore was reacted within 120 minutes by 4M H2SO4 solution at a temperature of 80oC. The activation energy (Ea) and the order of reaction were determined to be 31.14kJ/mol and 0.979, respectively. The leaching data were fitted to the shrinking core model and the experimental results followed a diffusion controlled mechanism. The residual product at optimal leaching was appropriately characterized and was found to contain silicate compound.

The optimization of vegetable oil leaching from spent nickel catalyst is reported in this work. Different solvents including; methyl ethyl ketone (MEK), acetone, hexane and toluene were employed. The leaching time in the range 1 to 5 h was studied. The leaching optimization shows that the use of MEK for 3 h provides the best results.
This was followed by the recovery of nickel from spent catalysts in the form of nickel sulfate. In pursue of finding a robust, inexpensive, simple and fast technique for on-line concentration measurement of nickel solution from leaching, the spectrophotometer technique was evaluated. The findings were then validated against titration method using EDTA.

Leaching of molybdenite concentrate with hydrogen peroxide in sulfuric acid solution was investigated to determine the effects of reaction time, reaction temperature, H2O2 concentration, H2SO4 concentration, pulp density and rotation speed on molybdenum extraction and molybdenite dissolution kinetics, using the Taguchi method. From analysis of variance (ANOVA) for molybdenum extraction, the most significant factors were H2O2 concentration, pulp density and reaction temperature. The optimal factor levels to maximize extraction were determined. As the leaching process does not result in an ash layer, only chemically controlled kinetic model was applied. ANOVA for the reaction rate constant showed that H2O2 concentration made the greatest contribution to the model, and reaction time and temperature were also statistically significant factors. The reaction rate constant increased with increasing temperature and H2O2 concentration. The order of reaction with respect to H2O2 and activation energy for the dissolution were determined to be 1.21 and 46.5 kJ/mol, respectively, and a semi-empirical rate equation was derived.

Computer circuit boards (CCBs) are valuable because of their precious metal contents. In this regard، the recovery of gold from CCBs has attracted great interest. In this work، we report the recovery of gold from CCBs with different reductants. The CCBs were first crushed mechanically to obtain particles with sizes less than 0. 1 mm. The powders were then leached with nitric acid to remove undesired metals. The remaining was then treated with aqua regia to dissolve gold ion. The dissolved gold was then precipitated from the leachate with hydrazine، ferrous sulfate or oxalic acid and the effect of these reductants on the recovery of gold was studied. We were able to recover more than 99% of gold from CCBs with purity of about 99. 5%.