Shenghai Yang

Dissolution kinetics of low grade complex copper ore in ammonia-ammonium chloride solution

The leaching kinetics of Tang-dan refractory low grade complex copper ore was investigated in ammonia-ammonium chloride solution. The concentration of ammonia and ammonium chloride, the ore particle size, the solid-to-liquid ratio and the temperature were chosen as parameters in the experiments. The results show that temperature, concentration of ammonia and ammonium chloride have favorable influence on the leaching rate of copper oxide ores. But, leaching rate decreases with increasing particle size and solid-to-liquid ratio. The leaching process is controlled by the diffusion of the lixiviant and the activation energy is determined to be 23.279 kJ/mol. An equation was also proposed to describe the leaching kinetics.

Extraction of indium from indium-zinc concentrates

Abstract A new process for extracting indium from indium-zinc concentrates was proposed. The process can directly extract indium from removed copper solution by D2EHPA, and cancel the stage of removing iron in the traditional process because of using iron and part of zinc in the In-Zn concentrates for direct preparing high quality Mn-Zn soft magnetic ferrites. The technologies in the processes, such as leaching the neutral leached residues with high concentrated acid at high temperature, reduction ferric and removing copper, and extracting indium, were investigated. The results show that total recovery ratio of indium is increased from less than 70% in the traditional process to more than 95%. This process has the advantages of largely simplifying the procedure of indium extraction, zero draining off of iron residue and zero emitting of SO2. So this is a clean production process.

Heavy metal removal and crude bio-oil upgrade from Sedum alfredii Hance harvest using hydrothermal upgrading.

In this study, heavy metals were removed and crude bio-oil was yielded from a heavy metal hyperaccumulator harvest, Sedum alfredii Hance, through hydrothermal upgrading process. This paper reports on the optimization of process parameters for the removal of heavy metals (zinc, lead, and copper) and for the upgrading of crude bio-oil from this biomass in an autoclave. Parameters such as granularity, temperature, pressure, and duration were examined for their effect on the removal efficiency of heavy metals and upgrading efficacy of crude bio-oil. Maximum heavy metal removal efficiency of >99% and crude bio-oil upgrading efficiency of >60% were attained with an 18 mesh (1 mm) granularity, and 22.1 MPa at 370 degrees C in the presence of 10 mg/L additives (K(2)CO(3)) for 60 s. Under these optimized conditions, an oil phase (mostly composed of phenolic hydrocarbons and derivatives), a water phase raffinate (containing Zn(2+) (0.39 g/L), Pb(2+) (0.10 g/L), Cu(2+) (0.15 g/L)), and a solid phase (the hydrothermal upgrading residue, which completely satisfies the limit set by China legislation related to biosolids disposal) were obtained.

Preparation of high-purity tantalum ethoxide by vacuum distillation

Abstract Effects of reflux ratio, water addition and content of water in ethanol on the purity and yield of tantalum ethoxide during vacuum distillation were investigated under the operational conditions of pressure of 1 kPa, oil bath temperature of 210–230 °C, and outlet temperature of 190 °C. The condensate sample was characterized by FTIR, 1 H-NMR spectroscopy and Raman spectra, respectively. The contents of tantalum, carbon and hydrogen in the sample were also determined with elemental analysis instrument. The obtained results consistently demonstrate that the condensate is tantalum ethoxide. The content of impurity, such as Al, As, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Sn, Ti, V and Zn, in tantalum ethoxide is less than 0.000 05%, while Nb content is less than 0.000 5%. The content of impurities in tantalum ethoxide sample excels that of Epichem Groups requirement for Ta(OC 2 H 5 ) 5 of 99.999%.

Thermodynamics of solubility of Cu2(OH)2CO3 in ammonia-ammonium chloride-ethylenediamine(En)-water system

Abstract In order to decrease the evaporating rate of ammonia and increase the solubility of copper in the solution, ethylenediamine was added into the ammonia-ammonium chloride system to leach the copper-containing oxide ores. The thermodynamic model was constructed and the solubility of malachite Cu 2 (OH) 2 CO 3 in the ammonia-ammonium chloride-ethylenediamine(En)-water system was calculated using the exponential computation method based on both mass balance and charge balance. It is found that the solubility of copper can be increased and the free ammonia concentration can be decreased by submitting partial ammonia with ethylenediamine. The lower free ammonia concentration in the solution is a guarantee to the lower evaporating rate of ammonia. The conditions of malachite Cu 2 (OH) 2 CO 3 converting to atacamite Cu(OH) 1.5 Cl 0.5 were also studied. A group of experiments were designed to validate the veracity of the results of the thermodynamic calculation. It is found that the thermodynamic model is reliable and it can guide the leaching process.

Selective recovery of lead from zinc oxide dust with alkaline Na2EDTA solution

Abstract The selective recovery of lead from the zinc oxide dust using an alkaline Na2EDTA solution was investigated. The effects of temperature, leaching time, Na2EDTA concentration and initial NaOH concentration on the leaching rates of lead and zinc were studied. The following optimized leaching conditions were obtained: liquid-to-solid ratio 5:1 mL/g, stirring speed 650 r/min, Na2EDTA concentration 0.12 mol/L, initial NaOH concentration 0.5 mol/L, leaching temperature 70 °C, leaching time 120 min. Under the optimized conditions, the average leaching rates of lead, zinc, fluoride and chloride are 89.92%, 0.94%, 62.84% and 90.02%, respectively. The filtrate was used to electrowin lead powders. The average current efficiency of electrowinning is about 93% and lead content is higher than 98% under the conditions of temperature of 60 °C, current density of 200 A/m2, H3PO4 concentration of 1.5 g/L, and lead ion concentration of above 5 g/L. The consumption of Na2EDTA and the direct current are about respectively 0.218 kg and 0.958 kW·h for per kilogram of lead powder.

Electrochemical Behaviors of Tantalum in Anhydrous Ethanol Containing Hydrogen Sulfate Ions

The electrochemical behaviors of Ta in tetrabutylammonium hydrogen sulfate (TBAHS) ethanol solutions were studied using potentiodynamic polarization, cyclic voltammetry, potentiostatic current time transient and impedance techniques. The results revealed that no active-passive transition is presented in the cyclic voltammogram, and the anodic current density increases with the increase of solution temperature, TBAHS concentration, potential scan rate and water content. The apparent activation energy is about 43.389 kJ/mol and the dissolution process is diffusion-controlled. Potentiostatic measurements showed that the current density gradually decays to a steady value when the potential is low; however, when the potential is higher than a certain value, the current density initially declines to a minimum value and then increases gradually. The resistance of passive film decreases with increasing potential, and inductive loops are presented when the potential is higher than 2.0 V.

Thermodynamics and technology of extracting gold from low-grade gold ore in system of NH4C1-NH3-H2O

Abstract According to the principles of simultaneous chemical equilibrium and electronic charge neutrality, the thermodynamics of Au-NH 4 Cl-NH 3 -H 2 O system was studied by using the exponential computation method and through MATLAB programming, and the solid figure of potential-c(NH 4 Cl)-c(NH 4 OH) was drawn. The results show that when the sum concentration of Au + and Au 3+ is equal to 5 × 10 −5 mol/L, φ(Au + /Au) is about −0.2 V; when the sum comes up to 0.5 mol/L, the value of φ(Au + /Au 3+ ) increases to 0.2 V. In this case, φ(O 2 /OH − ) is as high as 0.7 V. This means that it is feasible to extract gold in this system. In addition, to predict the feasibility of reducing gold from the Au(I)-NH 4 Cl-NH 3 -H 2 O system with copper or zinc powder, the solid figures of potential-c(NH 4 Cl)-c(NH 4 OH) for both systems of Cu-NH 4 Cl-NH 3 -H 2 O and Zn-NH 4 Cl-NH 3 -H 2 O were also drawn. The results indicate that both copper and zinc powders can reduce Au + into metal gold, and zinc powder can also reduce H 2 O into H 2 , while copper powder can not. The leaching results of a cuprous gold ore show that the extraction of gold can reach 80% in this system. The preliminary results of reduction with copper and zinc powders show that with deoxygenizing, the reduction effects are relatively good.

Electrochemical Behavior of Tantalum in Anhydrous Ethanol

The electrochemical behaviors of Ta in Et 4 NCl ethanol solutions were investigated using potentiodynamic polarization, cyclic voltammetry, and potentiostatic current-time transient techniques, complemented with a scanning electron microscope (SEM). The potentiodynamic anodic polarization curves did not exhibit an active dissolution region due to the presence of a thin oxide film on the electrode surface, which was followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of Cl - anions. SEM images confirmed the existence of pits on the electrode surface. The pitting potential (E b ) decreased with the increase in solution temperature, but increased with increasing potential scan rate. The potentiostatic current-time transients showed that the incubation time slightly decreased with increasing Et 4 NCl concentrations. The pitting growth current density agreed well with Hillss model.

Electrochemical synthesis and characterization of tantalum alkoxides

Abstract Tantalum(V) propoxide (Ta(OPr n ) 5 ), isopropoxide (Ta(OPr i ) 5 ) and butoxide(Ta(OBu n ) 5 ) were synthesized by electrochemical reactions of corresponding alcohol at sacrificial tantalum anode in the presence of tetraethylammonium chloride as a conductive additive. The pure products were isolated by reduced pressure distillation under 5 kPa. The crystal of Ta(OPr i ) 5 was obtained by recrystallization from hexane at −10 °C. These samples were characterized by Fourier transform infrared spectra (FT-IR), Raman spectra, nuclear magnetic resonance spectra (NMR), TG/DTA and ICP-MS. The results show that direct electrochemical synthesis of metal alkoxides has a high current efficiency and electrolysis yield. These alkoxides have a high purity of 99.97% and can be directly used as the precursor of Ta 2 O 5 films.