Bioleaching and dissolution kinetics of pyrite,chalcocite and covellite

In this work,the bioleaching process of pyrite,chalcocite and covellite which were the main phase compositions for Zijin copper mineral was comprehensively studied.The influence parameters,such as leaching temperature,Fe^(3+)concentration,pH of solution and bacteria concentration were investigated.The leaching kinetics of the pyrite,chalcocite and covellite under the studied conditions was successfully modeled by an empirical diffusion-like equation,respectively.The apparent activity energy of pyrite leaching,chalcocite leaching(stage Ⅱ)and covellite leaching was calculated to be 69.29,65.02 and 84.97 kJ/mol,respectively.

Selective leaching of vanadium from V-Ti magnetite concentrates by pellet calcification roasting-H_(2)SO_(4) leaching process

A novel method of pellet calcification roasting-H_(2)SO_(4) leaching was proposed to efficiently separate and extract vanadium(V)from vanadium-titanium(V-Ti)magnetite concentrates.The leaching rate of V is as high as 88.98%,while the leaching rate of impurity iron is only 1.79%.Moreover,the leached pellets can be used as raw materials for blast furnace ironmaking after secondary roasting.X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy with energy dispersive X-ray spectrometry(SEMEDS)analyses showed that V^(3+)was oxidized to V^(5+)after roasting at 1200℃,and V^(5+)was then leached by H_(2)SO_(4).X-ray diffraction(XRD)analyses and single factor experiment revealed a minimal amount of dissolved Fe_(2)O_(3) during H_(2)SO_(4) leaching.Therefore,a high separation degree of V and iron(Fe)from V-Ti magnetite concentrate was achieved through H_(2)SO_(4) leaching.Compared with the traditional roastingleaching process,this process can achieve a high selectivity of V and Fe,and has excellent prospects for industrial production.

Well-controlled stirring tank leaching to improve bio-oxidation efficiency of a high sulfur refractory gold concentrate

For the high sulfur refractory gold concentrate with 41.82%sulfur and 15.12 g/t gold,of which 82.11%was wrapped in sulfide,a well-controlled stirring tank leaching was carried out to improve the bio-oxidation efficiency.Results show that bio-oxidation pretreatment can greatly improve the gold recovery rate of high-sulfur refractory gold concentrate,and at the optimum pH 1.3 in this study,compared with the process without pH control,the oxidation rate of sulfur increased from 79.31%to 83.29%,while the recovery rate of gold increased from 76.54%to 83.23%;under this condition the activity of mixed culture could be sustained and the formation of jarosite could diminish.The results also displayed that for the high sulfur refractory gold concentrate,the recovery of gold is positively correlated with the oxidation rate of sulfur,and the recovery rate of gold increases with the increase of sulfur oxidation rate within a certain range.

Application of response surface methodology in optimization of bioleaching parameters for high-magnesium nickel sulfide ore

The response surface methodology(RSM)was used to optimize the operating parameters during the bioleaching of Jinchuan high-magnesium nickel sulfide ore.The particle size,acid addition,pulp density and inoculation amount were chosen as the investigated parameters.To maximize the leaching efficiency of nickel,copper,cobalt and minimize the dissolution of magnesium and iron ions,the model suggested a combination of optimal parameters of particles less than 0.074 mm being 72.11%,sulfuric acid addition being 300 kg/t,pulp density being 5%and inoculation amount being 12.88%.Under the conditions,the average results of three parallel experiments were 89.43%of nickel leaching efficiency,36.78%of copper leaching efficiency,84.07%of cobalt leaching efficiency,49.19%of magnesium leaching efficiency and 0.20 g/L of iron concentration.The model indicated that the most significant factor in response of the leaching efficiency of valuable metal is the particle size,and the most significant factor in response to the leaching efficiency of harmful ions(Mg2+)is the amount of sulfuric acid addition.And according to the suggested models,no significance of the interaction effect between particle size and acid addition was shown.Under the optimized parameters suggested by models,the valuable metals could be separated from harmful ions during the bioleaching process.

Electrochemistry of Hf(Ⅳ)in NaCl-KCl-Na-K_(2)HfF_(6) molten salts

The cathodic reduction mechanism of Hf(Ⅳ)ions in a fused Na Cl–KCl–Na F–K_(2) HfF_(6) salt system was studied in various Na F concentrations at 1073 K to obtain a purified dendritic Hf metal.The results of cyclic voltammetry and square wave voltammetry indicated that the reduction process comprised two steps of Hf(Ⅳ)→Hf(Ⅱ)and Hf(Ⅱ)→Hf at low Na F concentrations(0<molar ratio of[F-/Hf 4+]≤17.39)and one step of Hf(Ⅳ)→Hf at high Na F concentrations(17.39<molar ratio of[F-/Hf 4+]<23.27).The structure and morphology of the deposits obtained in potentiostatic electrolysis in the one-step reduction process were analyzed and verified by X-ray diffraction,scanning electron microscopy,and energy dispersive X-ray spectrometry.In the one-step reduction process,the disproportionation reaction between the Hf metal and Hf complex ions was inhibited,and a large dendrite Hf metal was achieved in molten salt electrorefining.

Preparation and electrochemical behaviour of Ti/Mn_(2)O_(3)coating anode

Owing to the excellent electrocatalytic activity,corrosion resistance and high cell potential of the dimensionally stable anodes(DSA),DSAs have great application potential in metallurgical electrolysis industry.In this research,the Ti/Mn_(2)O_(3)DSA anode was prepared by the thermal decomposition method.

Electrochemical dissolution behavior of gold and its main coexistent sulfide minerals in acid thiocyanate solutions

Electrochemical tests were developed to investigate the electrochemical dissolution behavior of gold and its main coexistent sulfide minerals in acid thiocyanate solutions.The optimal leaching conditions for gold in acidic thiocyanate system were pH 2,0.15 mol·L^(-1) thiocyanate and 0.2 g·L^(-1)Fe^(3+).Fe^(3+) addition to the acidic thiocyanate system promoted gold dissolution significantly,arsenopyrite dissolution was inhibited,chalcopyrite dissolution was increased,and the dissolution behavior of other associated minerals remained mostly unchanged.Thiocyanate made gold and associated mineral leaching easier.The galvanic corrosion effect of gold and its main coexistent sulfide minerals in an acidic thiocyanate-free system was that the chalcocite,arsenopyrite and pyrite acted as a cathode to reduce anodic gold dissolution;galena as an anode undergoes oxidation to inhibit anodic gold dissolution.There was almost no galvanic corrosion behavior between stibnite,yellow sphalerite and black sphalerite and gold.Thiocyanate addition changed the galvanic corrosion behavior of stibnite and yellow sphalerite in the thiocyanate system,which inhibited anodic gold dissolution.In the acidic thiocyanate system in the presence of ferric iron,the arsenopyrite promoted anodic gold dissolution,the chalcocite and gold were mostly free of galvanic corrosion,and the remaining minerals inhibited anodic gold dissolution.

A novel approach to extract Nb,Y and Ce from a niobium-bearing ore of low grade by roasting KHSO_(4)-H_(2)SO_(4) system

In this work,a novel approach of leaching valuable metals,such as niobium,yttrium and cerium,from a niobium-bearing ore of low grade by roasting KHSO_(4)-H_(2)SO_(4)system was experimentally studied.Through the work,the effects of roasting temperature,roasting time,mass ratio of agents to ore and the types of leaching agents on the extraction of Nb,Y and Ce were investigated,and the roasting KHSO_(4)-H_(2)SO_(4)-ore system was thought as an effective method to extract these valuable metals.It was found that the recovery of Nb,Y and Ce can,respectively,reach 90.20%,97.22%and 98.41%in condition of roasting temperature of 300℃,roasting time of 2 h,mass ratio of KHSO_(4)-to-H_(2)SO_(4)to ore of 0.5:1:1,particle size of-74 lm(~95%),leaching solution of oxalic acid(30 g·L^(-1)),leaching temperature of 90℃and leaching liquid-to-solid ratio of 5:1.The leaching kinetics of the calcined Nb-bearing ore in oxalic acid solution was successfully modeled by chemical reaction model,and the apparent activity energy was obtained to be14.16 kJ·mol^(-1).The results generated from this work will provide the fundamentals for extracting Nb,Y and Ce from a niobium-bearing ore of low grade and have potential applications value in future.

Electrochemical adsorption and passivation on gold surface in alkaline thiourea solutions

An electrochemical method was used to examine Au surface absorption and passivation under the most commonly employed pH conditions in an alkaline Au leaching system.The polarization at different pH values was obtained through the current step curve.At pH 10,no absorption layer was formed.When the pH was increased to 11,an absorption layer was formed through the Au electrode reaction.At pH 12,the entire system could not be stabilized,even after long durations because of the thiourea oxidation and decomposition.The samples were analyzed by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),and atomic force microscopy(AFM).AFM observations of the Au plating surface and SEM-EDS analyses for the Au-coated graphite surface indicated that a passivation membrane was formed on the Au surface after its use in the alkaline thiourea Au leaching system.Two-step leaching was used to confirm the conclusions drawn from the experimental results.The twostage experimental results further confirmed the existence of a passivation membrane.

Electrolytic silicon/graphite composite from SiO_(2)/graphite porous electrode in molten salts as a negative electrode material for lithium-ion batteries

Nano-silicon(nano-Si)and its composites have been regarded as the most promising negative electrode materials for producing the next-generation Li-ion batteries(LIBs),due to their ultrahigh theoretical capacity.However,the commercial applications of nano Si-based negative electrode materials are constrained by the low cycling stability and high costs.The molten salt electrolysis of SiO_(2)is proven to be suitable to produce nano-Si with the advantages of in-situ microstructure control possibilities,cheap affordability and scale-up process capability.Therefore,an economical approach for electrolysis,with a SiO_(2)/graphite porous electrode as cathode,is adopted to produce nano-Si/graphite composite negative electrode materials(SGNM)in this study.The electrolytic product of the optimized porous electrode is taken as the negative electrode materials for LIBs,and it offers a capacity of 733.2 mAh·g^(-1)and an initial coulombic efficiency of 86.8%in a coin-type cell.Moreover,the capacity of the SGNM retained 74.1%of the initial discharging capacity after 50 cycles at 0.2C,which is significantly higher than that of the simple mixture of silicon and graphite obtained from the formation of silicon carbide(SiC)between nano-Si and graphite particles.Notably,this new approach can be applied to a large-scale production.