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.

Microstructure refinement,mechanical and biocorrosion properties of Mg–Zn–Ca–Mn alloy improved by a new severe plastic deformation process

In this study,the microstructural evolution,mechanical properties and biocorrosion performance of a Mg–Zn–Ca–Mn alloy were investigated under different conditions of heat treatment,extrusion,one pass and two passes of half equal channel angular pressing(HECAP)process.The results showed significant grain refinement of the homogenized alloy after two passes of HECAP process from 345μm to 2μm.Field emission scanning electron microscopy(FESEM)revealed the presence of finer Mg_(6)Zn_(3)Ca_(2)phase as well asα-Mn phase after HECAP process.The results also showed that mechanical characteristics such as yield strength,ultimate tensile strength and elongation of the HECAPed samples improved by~208%,~144%and~100%compared to the homogenized one,respectively.Crystallographic texture analysis indicated that most of the grains at the surface were reoriented parallel to the(0001)basal plane after HECAP process.Electrochemical corrosion tests and immersion results indicated that the sample with two passes of HEACP had the highest biocorrosion resistance confirming that the basal planes had the lowest corrosion rate compared to the non-basal ones.The mechanical behavior and bio-corrosion evaluation demonstrated that the HECAPed Mg–Zn–Ca–Mn alloy has great potential for biomedical applications and a mechanism was proposed to explain the interrelations between the thermomechanical processing and bio-corrosion behavior.

Effect of filler metal on microstructure and mechanical properties of manganese-aluminum bronze repair welds

The repair welding of UNS C95700manganese?aluminum bronze plates was done using different filler metals.Themicrostructure and mechanical properties of welds were studied.The main microstructural constituents wereα,βandκphases withdifferent morphologies.The addition of manganese decreased the percentage ofαphase in the microstructure of weldments from80%(Mn-free weld)to57%(12.5%Mn weld,mass fraction).The morphology ofκphase was lamellar in high nickel specimens andit was changed to a globular morphology for high manganese welds.Although the application of high manganese filler metal yieldedthe higher tensile and bending strengths of weldment compared with the weld using high nickel filler material,the optimummechanical properties of repair welds were obtained using a non-alloy filler material(ERCuAl-A2)for the underlay and highmanganese filler metal(ERCuMnNiAl)for filling passes.This weld presented an increase of39%in tensile strength compared withthe base metal,and no cracking was observed after bending test.

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.

Characterizations of dissimilar S32205/316L welds using austenitic, super-austenitic and super-duplex filler metals

UNS S32205 duplex stainless steel plates were welded to AISI 316 L stainless steel using the pulsed gas tungsten arc welding process with three different filler metals: ER2594, ER312, and ER385. The microstructures of the welds were characterized using optical and scanning electron microscopy, and all of the specimens were evaluated by ferrite measurements. The mechanical properties were studied through hardness,tensile, and impact tests. In addition, the pitting resistance equivalent number was calculated and cyclic polarization tests were performed to evaluate the corrosion resistance of the weld metal. The results showed that chromium nitride was formed in the heat-affected zone of the duplex side,whereas no sigma phase was detected in any of the specimens. The ferrite number increased from the root pass to the final pass. The absorbed energies of the impact test decreased with increasing ferrite number, whereas the tensile strength was enhanced. The fully austenitic microstructure of the specimen welded with ER385 exhibited the highest resistance to pitting corrosion at 25°C, and the super-duplex weld metal presented superior corrosion resistance at 50°C.

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.

Super Strength Aluminum Produced by Traditional Metallurgy and Nanotechnology

This paper investigates the production of pure aluminum by using traditional metallurgy and nanotechnology. To make a pure aluminum stronger, extremely cold and mechanical manipulation process was employed and followed by carefully heat treatment cycle. The practical produetion and testing showed that the higher the stored dislocation＇s density after rolling was, the finer the recrystallized grains during heating were. In aluminum, these new grains were only a couple of nanometers in size, several hundred times smaller than the original crystals, making the aluminum much stronger than its original form.

Mechanochemical leaching of chalcopyrite concentrate by sulfuric acid

This study aimed to introduce a new cost-effective methodology for increasing the leaching efficiency of chalcopyrite concentrates at ambient temperature and pressure. Mechanical activation was employed during the leaching（mechanochemical leaching） of chalcopyrite concentrates in a sulfuric acid medium at room temperature and atmospheric pressure. High energy ball milling process was used during the leaching to provide the mechanochemical leaching condition, and atomic absorption spectroscopy and cyclic voltammetry were used to determine the leaching behavior of chalcopyrite. Moreover, X-ray diffraction and scanning electron microscopy were used to characterize the chalcopyrite powder before and after leaching. The results demonstrated that mechanochemical leaching was effective; the extraction of copper increased significantly and continuously. Although the leaching efficiency of chalcopyrite was very low at ambient temperature, the percentages of copper dissolved in the presence of hydrogen peroxide（H2O2） and ferric sulfate（Fe2（SO4）3） after 20 h of mechanochemical leaching reached 28% and 33%, respectively. Given the efficiency of the developed method and the facts that it does not require the use of an autoclave and can be conducted at room temperature and atmospheric pressure, it represents an economical and easy-to-use method for the leaching industry.

Comparison of the morphology and structure of W03 nanomaterials synthesized by a sol-gel method followed by calcination^or hydrothermal treatment

Tungsten （VI） oxide （WO3） nanomaterials were synthesized by a sol-gel method using WC16 and C2HsOH as precursors followed by calcination or hydrothermal treatment. X-Ray diffraction （XRD）, scanning electron microscopy （SEM） and high resolution transmission electron microscopy （HRTEM） equipped with energy dispersive X-ray spectroscopy （EDX） were used to characterize the structure and morphology of the materials. There were significant differences between the WO3 materials that were calcinated and those that were subjected to a hydrothermal process. The XRD results revealed that calcination temperatures of 300℃and 400℃ gave hexagonal structures and temperatures of 500℃ and 600℃ gave monoclinic structures. The SEM images showed that an increase in calcination temperature led to a decrease in the WO3 powder particle size. The TEM analysis showed that several nanoparticles agglomerated to form bigger clusters. The hydrothermal process produced hexagonal structures for holding times of 12, 16, and 20 h and monoclinic structures for a holding time of 24 h. The SEM results showed transparent rectangular panicles which according to the TEM results originated from the aggregation of several nanotubes.

New insights into microstructural changes during transient liquid phase bonding of GTD-111 superalloy

The effects of joining temperature(TJ)and time(tJ)on microstructure of the transient liquid phase(TLP)bonding of GTD-111 superalloy were investigated.The bonding process was applied using BNi-3 filler at temperatures of 1080,1120,and 1160℃ for isothermal solidification time of 195,135,and 90 min,respectively.Homogenization heat treatment was also applied to all of the joints.The results show that intermetallic and eutectic compounds such as Ni-rich borides,Ni−B−Si ternary compound and eutectic-γcontinuously are formed in the joint region during cooling.By increasing tJ,intermetallic phases are firstly reduced and eventually eliminated and isothermal solidification is completed as well.With the increase of the holding time at all of the three bonding temperatures,the thickness of the athermally solidified zone(ASZ)and the volume fraction of precipitates in the bonding area decrease and the width of the diffusion affected zone(DAZ)increases.Similar results are also obtained by increasing TJ from 1080 to 1160℃ at tJ=90 min.Furthermore,increasing the TJ from 1080 to 1160℃ leads to the faster elimination of intermetallic phases from the ASZ.However,these phases are again observed in the joint region at 1180℃.It is observed that by increasing the bonding temperature,the bonding width and the rate of dissolution of the base metal increase.Based on these results,increasing the homogenization time from 180 to 300 min leads to the elimination of boride precipitates in the DAZ and a high uniformity of the concentration of alloying elements in the joint region and the base metal.

Effect of vacuum degree in VIM furnace on mechanical properties of Ni-Fe-Cr based alloy

In order to investigate the effect of the vacuum degree in vacuum induction melting （VIM） furnace on the mechanical properties of Ni-Fe-Cr based alloy, four samples were prepared under different conditions. The chemical analysis results show that under the argon atmosphere, there is more dissipation in Al and Ti, whereas it is reduced by establishing the vacuum atmosphere. The gas analysis results show that the oxygen and nitrogen contents of the samples decrease with increasing vacuum degree. However, there is no dissipation in the gas content of the samples in higher degree of vacuum. In addition, the thermodynamic calculations show that the probability of TiO2 and Al2O3 formation is high due to the small value of the equilibrium oxygen. Higher vacuum degree reduces the tensile and yield strength of the alloys, while it enhances the elongation and reduction of area values due to the lower amount of the inclusions and evaporation of Al and Ti under higher vacuum. On the other hand, increasing vacuum degree changes the fracture mode from brittle to ductile.

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.

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.

Characterization of Spent Household Zinc-Carbon Dry Cell Batteries in the Process of Recovery of Value Metals

Spent zinc-carbon dry cell batteries were characterized to assess the environmental impacts and also, to identify the potentials of recovering the metal values from these batteries. Different component parts of both new and spent batteries of all the five types (AAA, AA, C, D and 9V) were examined. The outer steel casings were found to be tin plated. Steel, zinc and manganese constituted 63 percent of the total weight of the battery. Average zinc and manganese contents were about 22 and 24 percent of the total weight of spent batteries. The electrolyte paste of the spent batteries contained 22 wt. percent zinc and 60 wt. percent manganese. The rest was chlorine, carbon and small amounts of iron and other impurity elements. The major phases in the fresh batteries were carbon, MnO2 and NH4Cl, while Zn(NH3)2Cl2, ZnO.Mn2O3, Mn3O2 and Mn2O4 were the prominent phases in the spent batteries. Presence of mercury and cadmium were not detected and a small percentage of lead was found in both the zinc anode and in the electrolyte paste.

A new method to determine the synergistic effects of area ratio and microstructure on the galvanic corrosion of LAS A508/309 L/308 L SS dissimilar metals weld

The synergistic effects of area ratio and microstructure on the galvanic corrosion of A508/309 L/308 L dissimilar metals weld(DMW)are studied by a multi-analytical approach.It was demonstrated that decreasing the anode/cathode surface area ratio obviously enhances the corrosion rate of A508,both locally and globally.Deeper analyses of the AFM results enabled quantitative comparison of the corrosion behaviour of the different surface constituents.It was revealed that in the galvanic interaction of the DMW,the grain refined region corrodes most,followed by the partial grain refined region and base metal matrix of the A508,respectively.The electrochemical localization index(LI)estimation method and AFM analysis both confirmed the presence of a mixed(localized and uniform)corrosion phenomenon occurring on the surface of the A508 anode metal in the galvanic interaction of the dissimilar metals.Finally,the degree of synergism equation was utilized to describe the synergistic effects of anode/cathode area ratio and the microstructure of the samples on the galvanic corrosion of LAS A508/309 L/308 L SS DMW.

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.

The effect of calcination temperature on the capacitive properties of WO3-based electrochemical capacitors synthesized via a sol-gel method

Electrochemical capacitor （EC） is a promising energy storage device which can be hybridized with other energy conversion or energy storage devices. One type of ECs is pseudocapacitor made of metal oxides. WO3 is an inexpensive semiconductor metal oxide which has many applications. However the application of WO3 as an EC material was rarely reported. Therefore in this research EC was prepared from WO3 nanomaterial synthesized by a sol-gel process. The WO3 gel was spin-coated on graphite substrates and calcined at various temperatures of 300~C, 400℃, 500℃ and 600℃ for 1 h. Cyclic voltammetry （CV） measurements were used to observe the capacitive property of the WO3 samples. SEM, XRD, FTIR and Brunauer-Emmett-Teller （BET） analyses were used to characterize the material structures. WO3 calcined at 400~C was proved to have the highest capacitance of 233.63 Fo g^-1 （1869 mFo cm-2） at a scan rate of 2 mVo s-1 in 1 mol/L H2SO4 between potentials -0.4 and 0.4 V vs. SCE. Moreover it also showed the most symmetric CV curves as the indication of a good EC. Hence WO3 calcined at 400℃ is a potential candidate for EC material of pseudocapacitor type.