Recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation: process optimization and mineralogical study

Currently, the majority of copper tailings are not effectively developed. Worldwide, large amounts of copper tailings generated from copper production are continuously dumped, posing a potential environmental threat. Herein, the recovery of iron from copper tailings via low-temperature direct reduction and magnetic separation was conducted; process optimization was carried out, and the corresponding mineralogy was investigated. The reduction time, reduction temperature, reducing agent (coal), calcium chloride additive, grinding time, and magnetic field intensity were examined for process optimization. Mineralogical analyses of the sample, reduced pellets, and magnetic concentrate under various conditions were performed by X-ray diffraction, optical microscopy, and scanning electron microscopy-energy-dispersive X-ray spectrometry to elucidate the iron reduction and growth mechanisms. The results indicated that the optimum parameters of iron recovery include a reduction temperature of 1150A degrees C, a reduction time of 120 min, a coal dosage of 25%, a calcium chloride dosage of 2.5%, a magnetic field intensity of 100 mT, and a grinding time of 1 min. Under these conditions, the iron grade in the magnetic concentrate was greater than 90%, with an iron recovery ratio greater than 95%.

Deep cleaning of a metallurgical zinc leaching residue and recovery of valuable metals

Huge quantities of zinc leaching residues(ZLRs) generated from zinc production are dumped continuously around the world and pose a potential environmental threat because of their considerable amounts of entrained heavy metals(mainly lead). Most ZLRs have not been properly treated and the valuable metals in them have not yet been effectively recovered. Herein, the deep cleaning of a ZLR and recovery of valuable metals via a hydrometallurgical route were investigated. The cleaning process consists of two essential stages: acid leaching followed by calcium chloride leaching. The optimum conditions for extracting zinc, copper, and indium by acid leaching were a sulfuric acid concentration of 200 g·L^(-1), a liquid/solid ratio of 4:1(m L/g), a leaching time of 2 h, and a temperature of 90°C. For lead and silver extractions, the optimum conditions were a calcium chloride concentration of 400 g·L^(-1), a pH value of 1.0, a leaching time of 1 h, and a temperature of 30°C. After calcium chloride leaching, silver and lead were extracted out and the lead was finally recovered as electrolytic lead by electrowinning. The anglesite phase, which poses the greatest potential environmental hazard, was removed from the ZLR after deep cleaning, thus reducing the cost of environmental management of ZLRs. The treatment of chlorine and spent electrolyte generated in the process was discussed.

Electrochemical behavior and corrosion resistance of IrO2–ZrO2 binary oxide coatings for promoting oxygen evolution in sulfuric acid solution

In this study,we prepared Ti/IrO2–ZrO2 electrodes with different ZrO2 contents using zirconium-n-butoxide(C16H36O4Zr)and chloroiridic acid(H2IrCl6)via a sol–gel route.To explore the effect of ZrO2 content on the surface properties and electrochemical behavior of electrodes,we performed physical characterizations and electrochemical measurements.The obtained results revealed that the binary oxide coating was composed of rutile IrO2,amorphous ZrO2,and an IrO2–ZrO2 solid solution.The IrO2–ZrO2 binary oxide coatings exhibited cracked structures with flat regions.A slight incorporation of ZrO2 promoted the crystallization of the active component IrO2.However,the crystallization of IrO2 was hindered when the added ZrO2 content was greater than 30at%.The appropriate incorporation of ZrO2 enhanced the electrocatalytic performance of the pure IrO2 coating.The Ti/70at%IrO2–30at%ZrO2 electrode,with its large active surface area,improved electrocatalytic activity,long service lifetime,and especially,lower cost,is the most effective for promoting oxygen evolution in sulfuric acid solution.

Leaching kinetics of calcium molybdate with hydrochloric acid in presence of phosphoric acid

Calcium molybdate(CaMoO4)is the main component of powellite and is a predominant intermediate in the pyrometallurgical and hydrometallurgical process of molybdenum.The extraction of Mo from CaMoO4 by a combination of phosphoric acid and hydrochloric acid was investigated.For further understanding of the leaching mechanism,the effects of five key factors were studied to describe the leaching kinetics.The results indicated that the dissolution rate of CaMoO4 was independent of the stirring speed.Mo extraction significantly increased with increasing HCl concentration and temperature,but decreased with increasing particle size.A shrinking core model with surface chemical reaction was found to withstand the dissolution of CaMoO4.The apparent activation energy was calculated to be 70.879 kJ/mol,and a semi-empirical equation was derived for the rate of reaction.

Cobalt recovery and microspherical cobalt tetroxide preparation from ammonia leaching solution of spent lithium-ion batteries

A process for recovering Co and preparing microspherical Co_(3)O_(4)through NH_(3)distillation and phase transformation from ammoniacal solution was investigated.As the basis of thermodynamics,the solubility of Co at different NH_(3)and CO_(3)^(2-)concentrations was studied,and then the effects of different NH_(3)distillation conditions on Co recovery rate were discussed.Over 94%Co and 96%NH_(3)were recovered through NH_(3)distillation,and the cobalt was precipitated in form of cobalt carbonate ammonium compound salt.Through the analysis of the formation mechanism of the precursor,the precipitation process of cobalt could be divided into two stages,and the cobalt precipitation rate was significantly accelerated in the second stage.In phase transformation,the effect of temperature on the roasted product was investigated.The microspherical Co_(3)O_(4)with a microporous structure was prepared at 300°C,and Co_(3)O_(4)with a mesoporous structure and high-spin state was obtained at 750°C.

Pressure nitric acid leaching of alkali-pretreated low-grade limonitic laterite

The pressure nitric acid leaching of alkali-pre- treated low-grade limonitic laterite, as well as removing impurity AI（III） and preparing intermediate product of nickel/cobalt sulphide from leaching liquor were investi- gated. After pretreatment, iron exists in the form of amorphous iron oxides, while nickel is adsorbed on the surface of iron oxides in the form of nickel oxide. The preferable pressure leaching conditions are determined as follows： leaching temperature of 458 K, leaching duration of 60 min, initial acidity of nitric acid of 1.90 mol.L-~ and liquid to solid ratio of 3：1 （volume to mass ratio）. Under these conditions, the leaching efficiencies of Ni, Co and A1 are 95 %, 88 % and 55 %, respectively, and that of Fe is less than 1%. The loss rates of Ni and Co are 1.8 % and 1.5 %, respectively, during the step of removing impurity AI（III）. The sulphide precipitation process produces the interim production of nickel/cobalt sulphides, recovering greater than 99 % of Ni and Co in the purified solution. The iron-rich （〉60 %） pressure leaching residue with low Cr, S can be further reclaimed as the raw materials for iron making.