Kinetics of zinc sulfide concentrate direct leaching in pilot plant scale and development of semi-empirical model

The direct leaching kinetics of an iron-poor zinc sulfide concentrate in the tubular reactor was examined.All tests werecarried out in the pilot plant.To allow the execution of hydrostatic pressure condition,the slurry with ferrous sulfate and sulfuric acidsolution was filled into a vertical tube(9m in height)and air was blown from the bottom of the reactor.The effects of initial acidconcentration,temperature,particle size,initial zinc sulfate concentration,pulp density and the concentration of Fe on the leachingkinetics were investigated.Results of the kinetic analysis indicate that direct leaching of zinc sulfide concentrate follows shrinkingcore model(SCM).This process was controlled by a chemical reaction with the apparent activation energy of49.7kJ/mol.Furthermore,a semi-empirical equation is obtained,showing that the order of the iron,sulfuric acid and zinc sulfate concentrationsand particle radius are0.982,0.189,-0.097and-0.992,respectively.Analysis of the unreacted and reacted sulfide particles bySEM-EDS shows that insensitive agitation in the reactor causes detachment of the sulfur layer from the particles surface in lowerthan60%Zn conversion and lixiviant in the face with sphalerite particles.

Statistical evaluation and optimization of zinc electrolyte hot purification process by Taguchi method

The neutral zinc sulfate solution obtained from hydrometallurgical process of Angouran zinc concentrate has cadmium, nickel and cobalt impurities, that must be purified before electrowinning. Therefore, cadmium and nickel are usually cemented out by addition of zinc dust and remained nickel and cobalt cemented out at second stage with zinc powder and arsenic trioxide. In this research, a new approach is described for determination of effective parameters and optimization of zinc electrolyte hot purification process using statistical design of experiments. The Taguchi method based on orthogonal array design（OAD） has been used to arrange the experimental runs. The experimental conditions involved in the work are as follows： the temperature range of 70-90 ℃ for reaction temperature（T）, 30-90 min for reaction time（t）, 2-4 g/L for zinc powder mass concentration（M）, one to five series for zinc dust particle size distributions（S1-S5）, and 0.1-0.5 g/L（C） for arsenic trioxide mass concentration. Optimum conditions for hot purification obtained in this work are T4（85 ℃）, t4=75 min, M4=3.5 g/L, S4（Serie 4）, and C2=0.2 g/L.

The Influence of Morphology on Photo-catalytic Activity and Optical Properties of Nanocrystalline ZnO Powder

ZnO nano-particles were synthesized via an ammonical ammonium carbonate solution by precipitation method in presence of some additives such as urea, oleic and stearic acid. The morphology and crystallinity of the obtained zinc oxide particles depend critically on the type of additive which was used. Additives also affected the crystal orientation of precipitate nano-particles. SEM, XRD, BET and UV-visible were used to characterize morphology, microstructure, specific surface area and optical properties of the products.Photo-catalysis properties of the as-prepared ZnO powders were evaluated by degradation of methyl red(acid red) in aqueous solution exposed to UV-light. Results suggested a close relationship among the morphology,size and surface area on photo-catalysis and optical properties of the particles. The widest Egvalue(3.56 e V),highest degradation and decolorization efficiency(99%) were obtained from a sample with the smallest grain size(largest surface area) which were used urea as an additive.

Enhanced selectivity of hydrolytic precipitation of Zn from Zn-Ni sulfate solution via chelation of Ni

The selective precipitation of zinc from zinc-nickel sulfate solution with the Zn/Ni molar ratio of20:1was studied.Dropwise addition of0.5mol/L NaOH solution into the zinc-nickel sulfate solution containing0,0.01,0.02,0.03and0.04mol/L ethylene diamine tetraacetate(EDTA)as a chelating agent was done.The equilibrium analysis of precipitation pathway was performed using Visual MINTEQ program.The equilibrium analysis showed that the presence of small amounts of EDTA can prevent nickel precipitation in alkaline conditions without any negative effect on zinc precipitation.On this basis,more than90%of zinc could be precipitated as a product with about50%Zn and only0.11%Ni at pH=9.0merely as a result of the presence of0.03mol/L EDTA in the solution.The stirring time of120min after precipitation was found to be essential for more complete separation.The X-ray diffraction studies on the precipitate revealed that the precipitated phase was Zn4(OH)6SO4.4H2O.

Preparation of NiO nanoparticles from Ni(OH)_2·NiCO_3·4H_2O precursor by mechanical activation

A mechanical activation process was introduced as a facile method for producing nickel oxide nanopowders. The precursor compound Ni（OH）2-NiCO3-4H2O was synthesized by chemical precipitation. The precursor was milled with NaCl diluent. A high-energy ball milling process led to decomposition of the precursor and subsequent dispersal in NaCl media. Nickel oxide nanocrystalline powders were produced by subsequent heat treatment and water washing. Milling rotation speed, milling time, ball-to-powder ratio （BPR）, and nickel chlo-ride-to-precursor ratio were introduced as influential parameters on the wavelength of maximum absorption （λmax）. The effects of these pa-rameters were investigated by the Taguchi method. The optimum conditions for this study were a milling rotation speed of 150 r/min, a mill-ing time of 20 h, a BPR of 15/1, and a NaCl-to-powder weight ratio （NPR） of 6/1. In these conditions,λmax was predicted to be 292 nm. The structural properties of the samples were determined by field emission scanning electron microscopy, X-ray diffraction, and energy dispersive spectrometry.

Simple separation method of Zn(Ⅱ) and Cd(Ⅱ) from brine solution of zinc plant residue and synthetic chloride media using solvent extraction

In this work,the possibility of separation of Zn^2+and Cd^2+metal ions from chloride(brine)solutions was examined.For this purpose,simple solvent extraction(SX)experiments by di-2-ethylhexyl phosphoric acid(D2EHPA)in kerosene as a diluent was performed on synthetic and industrial chloride solution obtained from brine leaching of zinc filter cakes(by-product of zinc hydrometallurgical processing).The optimal conditions for separation were determined.The zinc extraction efficiency was 99%with negligible co-extraction of cadmium.Therefore,a highΔpH0.5 value for Zn(Ⅱ)and Cd(Ⅱ)was achieved.FT-IR and slope analysis indicated that ZnClA·3HA and CdClA·3HA species were probably extracted.

Green synthesis,characterization and physiological stability of gold nanoparticles from Stachys lavandulifolia Vahl extract

The synthesis of nontoxic stable gold nanoparticles is important for medical applications. An aqueous extract of the plant Stachys lavandulifolia Vahl was used to synthesize gold nanoparticles. This green method involved the S. lavandulifolia Vahl extract acting as a reducing and stabilizing agent. The nanoparticles were characterized by transmission electron microscopy, dynamic light scattering analysis and UV-vis absorption and Fourier transform-infrared spectroscopies. Stability under physiological conditions is important for medical applications. The stability of the nanoparticles was compared with that of conventional citrate-capped nanoparticles, under both synthetic and physiological conditions. The nanoparticles synthesized from the S. lavandulifolia Vahl extract were stable under physiological conditions, in contrast with conventional citrate-capped nanoparticles.

A new approach to zinc–nickel separation using solution alkalinization method:application to a zinc plant residue

The present investigation involves the separation of zinc and nickel from a sulfate solution using the acidic leaching of zinc plant residue after cadmium removal step as precursor(42.88 wt%Zn,8.50 wt%Cd and 2.33 wt%Ni).Separation of nickel from the solution was done by pouring it into a strong alkaline sodium hydroxide solution due to precipitation of nickel hydroxide and conversion of zinc to the soluble Zn(OH)_(4)^(2-)complex.Higher degrees of separation were reached by pouring more diluted solutions into the stronger alkaline media.To clear pursue of the process,design of experimental methodology was applied for experiments.Scrutinizing different washing steps on nickel-rich precipitates shows that the washing process decreases zinc content and thereby increases overall selectivity coefficient.Outcomes show that,at the optimized condition,Ni/Zn weight ratio in the solid product becomes about 104 times higher than the initial ratio in the initial feed solution and a nickel concentrate with 29.98 wt%Ni and 5.99 wt%Zn is achieved.At the same time,the chemical analysis of filtrate shows only 4.4 mg·L^(-1)Ni in the alkaline zinc solution,which means that over 99%nickel is recovered.The study on changes of zinc concentration with time shows that the process could be completed only after few minutes.