Display omitted
► A novel copper oxidate catalyst activated persulfate to generate SO4- was investigated. ► Dissolved Cu2+ was regarded as the key factor activating the persulfate at pH 3.0. ► ...Heterogeneous catalysis played the main role in the oxidation of p-chloroaniline at pH 5 and 7. ► p-Chloroaniline removal would occur on the boundary-layer of solid surface at pH 7. ► Base activation of persulfate and heterogeneous catalysis was occurred at pH 11.
Oxidation of p-chloroaniline (PCA) by persulfate (PS) performed with a novel supported copper oxidate catalyst in an aqueous solution at ambient temperature (i.e. 20°C) was investigated in this study. This study focused mainly on determining the proportions of heterogeneous catalysis in the copper oxidate/PS combined system. There existed a more remarkable effect on the degradation of PCA in the copper oxidate/PS combined system than in the Cu2+/PS or only PS system. The effects of copper oxidate dosage, persulfate concentration, and initial solution pH on the oxidation of PCA were also evaluated. Higher copper oxidate dosage and persulfate concentration resulted in higher PCA degrading rates, the optimal initial pH was determined as 7.0. Moreover, the change in the degradation of PCA by pH was also investigated in terms of the contribution of dissolved copper ion in leaching solution. We inferred that homogeneous catalysis was of increasing importance and the copper ion dissolved from the copper oxidate was regarded as the key factor activating the persulfate under acidic conditions (pH 3.0), heterogeneous catalysis played the main role in the oxidation of PCA at pH 5–7. However, both heterogeneous catalysis and base-activated persulfate contributed to the degradation of PCA under alkaline conditions (pH 11). In addition, the radical mechanism was studied and three radical scavengers (phenol, methanol (MA) and Tert-butanol (TBA)) were used to determine the kind of major active areas taking part in the PCA degradation at pH 7.
This paper focused on optimizing the process conditions of direct acid leaching process to enhance the leaching efficiency of leaching vanadium from the stone coal. Orthogonal experiments and single ...factor experiments were conducted to investigate the effect of the influential factors of direct acid leaching on vanadium leaching ratio. The results showed that the vanadium leaching ratio reached the maximum value of 89.22 % under the optimal process conditions of CaF
dosage 5 mass%, H
SO
dosage 40 mass%, leaching temperature 95 °C and leaching time 10 h. Furthermore, the reaction mechanisms of the main influencing factors were analyzed. Finally, the two-stage counter-current leaching process was adopted to decrease the consumption of sulfuric acid and neutralizer, and the results indicated that the consumption of sulfuric acid decreased 12.50 % as well as neutralizer decreased 35.80 %.
Extracting valuable elements from coal gangue is an important method for the utilization of coal gangue. In order to obtain the suitable technological conditions and the acid leaching kinetic model ...of leaching aluminum and iron ions from high-iron and low-aluminum coal gangue, the effects of calcination temperature, calcination time, and acid types on the leaching results of aluminum and iron ions are studied. The results show that when the gangue is calcined at 675 °C for 1 h, then the calcined gangue powder is leached by 6 mol/L hydrochloric acid at 93 °C for 4 h, the leaching ratio of iron ions is more than 90%, and that of aluminum ions is more than 60%. Furthermore, the acid leaching kinetic equations at 30 °C, 50 °C, 70 °C, and 90 °C are studied by three kinetic models, and the apparent activation energies of the reactions are calculated by the Arrhenius formula. The results show that the leaching behavior of aluminum and iron ions conformed to the “mixing control” model equation: “(1 − x)−1/3 − 1 + 1/3ln(1 − x) = kt + b”. The apparent activation energies of aluminum and iron ions are 55.5 kJ/mol and 55.8 kJ/mol, respectively. All these indicate that the acid leaching process is controlled by the “mixing control”.
In-situ leaching assisted by geophysical techniques were used to exploit previously leached and long-abandoned copper sulphide heaps. The technology was first piloted for five months at the 59 kt ...scale with up to three injection wells. This was followed by a 14-month industrial pilot at the 1.2 Mt. scale with 97 injection wells. In-situ leaching was then fully implemented, drilling more than one thousand injection wells on 16 abandoned heaps over a period of almost three years. Geophysical surveys were used to visualize the movement of the injected leaching solutions in-situ. Geophysical imaging was also used to avoid flooding and prevent geotechnical instability. The imaging indicated the injection wells had a radius of influence of 11 to 13 m, and that well injection flows should not exceed 1.5 L/s. Oxidative conditions were facilitated in-situ by encouraging air entry from the heap drainage system and alternating periods of injection with rest periods that allowed air entry through the injection wells. This work introduces some concepts and terms related to in-situ leaching operations.
•In-situ leaching of copper from an abandoned heap of secondary sulphides was piloted and demonstrated.•More than 1000 injection wells were used to produce 7600 t of copper from material abandoned as waste.•The injection wells were found to have a radius of influence of 11 to 13 m.•60% of the copper extracted was attributed to oxidative bacteria-assisted leaching.•Copper recovery based on sequential copper assay was approximately 20% per 1 m3/t injection ratio.
Display omitted
•Microwave (MW) assisted chloride leaching extracted valuable and heavy metals from two zinc plant residues.•Microwave irradiation allowed for short leaching times (e.g. 10 min) at ...200 °C.•Microwave NaCl leaching selectively extracted Cd, Cu, Pb, and Zn from goethite sludge.•For Zn-leach product, MW NaCl leaching was selective (Bi, Pb) and HCl addition increased leachability (Ag, As, Bi, Sb, Zn).•One stage leaching tests showed improved environmental characteristics for the residues after MW chloride leaching.
Microwave (MW) assisted chloride leaching was studied to remove valuable and heavy metals from two zinc plant residues, i.e. goethite sludge and Zn-leach product.
For both materials, NaCl leaching parameters, such as temperature, NaCl concentration, leaching time and addition of acid, were optimized. For goethite sludge, the best efficiencies for Cu (45–47 %), Pb (83–90 %), and Zn (47–58 %) extraction, with a minimal dissolution of matrix elements, were obtained at 200 °C, 300 g/L NaCl and L/S 10. At short leaching times (5 min) the maximal leachability of Cu and Zn was reached, while at longer leaching time (60 min) the Pb extraction increased to 90 ± 1%. Zn leaching was limited due to the presence of stable franklinite (ZnFe2O4).
NaCl (280 g/L) leaching of Zn-leach product required the addition of 1 M HCl to improve metal leaching to Ag 52 ± 3 %, Bi 83 ± 1 %, Cd 82 ± 4 %, Sb 39 ± 1 %, Zn 71 ± 2 % at 200 °C, L/S 10 for 30 min. Consequently, matrix dissolution was enhanced. Metal associations in Zn-leach product were statistically investigated. The environmental impact of the MW leached materials was evaluated by a one stage leaching test, which showed a significant overall reduction in heavy metal leachability compared to untreated materials.
Leaching in cement-based materials and dissolution in rocks are important problems in civil engineering. In the past century, concrete damage caused by leaching have occurred worldwide. And, rock ...dissolution is usually the main cause of karst rock erosions. This paper provides a review of the causes, influencing factors, and effects on engineering properties of dissolution of rocks and leaching of cement-based materials. The applied experimental methods for leaching and dissolution have been sorted out and discussed. In situ field experiments can be used to study dissolution under natural conditions, while the laboratory experiments can effectively shorten the experiment time length (by changing pH, temperature, pressure or other factors that affect the leaching or dissolution) to quickly investigate the mechanism of dissolution and leaching. Micro tests including XRD, SEM, EDS, and other testing methods can obtain the changes in material properties and microstructures under leaching and dissolution. In addition, with the advances in technologies and updated instruments, more and more new testing methods are being used. The factors affecting the leaching and dissolution include environmental factors, materials, and solvent parameters. The mechanisms and deterioration processes of leaching and dissolution varies according to the types of material and the compositions.
The electrocatalyst with cost effective and high performance towards hydrazine electrooxidation is critical to promote the practical application of direct hydrazine fuel cell (DHFC). Herein, an ...effective approach is developed to study the Ni-Zn alloy as promising hydrazine electrocatalyst by the combined experimental and theoretical investigations. 3D nanosheet Ni-Zn alloy with single α-NiZn phase was successfully synthesized on Ni foam (NF) substrate through the electrodepostion of Ni-Zn alloy and followed electrochemical leaching. The Ni-Zn catalyst exhibits the synergetic capabilities of impressively high activity with a superior current density of 370 mA cm−2 at 0.3 V, excellent durability with a retention rate of 88.7% after 5000 s and almost 100% selectivity for the complete electrooxidation of hydrazine, which is at the top level among the reported electrocatalysts for hydrazine oxidation up to now. The reason for the excellent durability of Ni-Zn catalyst was studied. Specially, first principles calculations were employed to shed light on the catalytic mechanism of high performance Ni-Zn catalyst.
Copper plant residue (CPR) is a hazardous industrial by-product possessing both high toxicity and valuable metal content, necessitating its high value-added utilization. Traditional practices in ...smelters involve stockpiling and landfilling of CPR, leading to substantial land occupation and water contamination. This study focused on the preparation of PbO and Pb3O4 using the HCl–NaCl leaching–conversion–thermal decomposition process, employing CPR as the primary raw material. The effect of various leaching process conditions on the metal leaching rate was explored. A maximum lead leaching rate of 87.65% was achieved under optimal conditions including leaching temperature, liquid–solid ratio, leaching time, HCl molar concentration, NaCl mass concentration, and particle size. The lead content in the leachate was 15.85 g/L. Experimental data indicated that ash diffusion control served as the rate-limiting step in the HCl–NaCl leaching process. The apparent activation energy was determined to be 18.374 kJ mol−1, with a reaction order of 0.8986 concerning the HCl concentration and an L/S ratio of 0.8124. Additionally, response surface methodology enabled the determination of technological parameters for refining PbCl2 into PbCO3 precursors, yielding a conversion rate exceeding 96.50%. Moreover, the technical indicators of PbO and Pb3O4 obtained through low-temperature thermal decomposition of PbCO3 were investigated. The fabricated PbO and Pb3O4 exhibited purities of 99.65% and 99.26%, respectively, effectively transforming CPR from hazardous waste residue into valuable products. The process ensures the efficient recovery of lead to its maximum extent and promotes residue recycling.
Display omitted
•The High purity lead oxide and lead tetroxide were prepared.•The Pb leaching kinetics (kinetics) and mechanism were studied.•PbCO3 precursor preparation parameters were determined in the case of RSM model.•The optimum technical parameters of technology for the disposal of LCR was studied.•A process was proposed for the high-value utilization of LCR.
Barite ore is typically associated with difficult-to-remove vein minerals, but commercial barite products require a high BaSO4 content. We investigated the occurrence state of fluoride in barite ore ...using various analytical techniques, which indicated that elemental fluorine in barite predominantly exists as fluorite. Fluoride was then leached from barite ore via complexation. The effects of HCl and AlCl3 concentrations, temperature, time, and liquid-solid ratio on the leaching rate were examined, and the leaching conditions were optimized using an orthogonal array method. The fluorine leaching rate approached 93.11% after stirring for 30 min at 90 °C and 300 rpm with 3 mol/L HCl, 0.4 mol/L AlCl3, a liquid-solid ratio of 10:1 mL/g, and an ore sample size of −75 μm + 48 μm. According to the leaching kinetics, the process conformed to the solid membrane diffusion control model at a high temperature and the joint chemical reaction-diffusion control model at a low temperature. The apparent activation energy was 56.88 kJ/mol. Furthermore, aluminum and fluorine coordination numbers increased with increasing Al3+/F− molar concentration ratios. Competing complexation reactions of Al3+, H+, and F− occurred at three levels. This complexation approach effectively leaches fluoride from barite, improves barite product quality, and reduces environmental pollution.
Display omitted
•Fluoride occurrence state in barite ore is studied before and after leaching.•Fluoride leaches from barite ore via HCl–AlCl3 complexation reactions.•Chemical reaction-diffusion and solid membrane diffusion jointly control leaching.•Competing complexation reactions of Al3+, H+, and F− are observed at three levels.
PDF
