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.

Optimization of process parameters and kinetic modelling for leaching of copper from oxidized copper ore in nitric acid solutions

The leaching behavior of Tunceli malachite mineral was investigated in nitric acid solutions by two steps to evaluate the effect of various experimental parameters.In the first step,the optimal conditions for the leaching process were determined,while in the second step,a kinetic evaluation for the process was performed.In the optimization experiments,the concentration of nitric acid,temperature,stirring speed,and solid-to-liquid ratio were selected as the independent variables,and the central composite design method(CCD)was applied to the experimental data.At the end of the experiments,the optimal values for the concentration of nitric acid,temperature,solid-to-liquid ratio and stirring speed were determined to be 0.5 mol/L,50℃,0.004 g/m L and 500 r/min,respectively.Under the optimal conditions,the leaching rate was found to be 99%for 120 min of reaction time.In the kinetic evaluation tests,the effects of the concentration of nitric acid,temperature,stirring speed,solid-to-liquid ratio and particle size on the leaching rate of copper from malachite were investigated.In these tests,it was determined that the leaching rate increased with the increase in the temperature,acid concentration and stirring speed,and with the decrease in the particle size and solid-to-liquid ratio.In consequence of the kinetic analysis,it was observed that the leaching kinetics followed the mixed kinetic model,and a mathematical model for the leaching process was introduced.The activation energy for this process was calculated to be 36.23 k J/mol.

Mass transfer process of peanut protein extracted by bis(2-ethylhexyl)sodium sulfosuccinate reverse micelles

The liquid-liquid extraction method using reverse micelles can simultaneously extract lipid and protein of oilseeds,which have become increasingly popular in recent years.However,there are few studies on mass transfer processes and models,which are helpful to better control the extraction process of oils and proteins.In this paper,mass transfer process of peanut protein extracted by bis(2-ethylhexyl)sodium sulfosuccinate(AOT)/isooctane reverse micelles was investigated.The effects of stirring speed(0,70,140,and 210 r/min),temperature of extraction(30,35,40,45,and 50℃),peanut flour particle size(0.355,0.450,0.600,and 0.900 mm)and solidliquid ratio(0.010,0.0125,0.015,0.0175,and 0.020 g/mL)on extraction rate were examined.The results showed that extraction rate increased with temperature rising,particle size reduction as well as solid-liquid ratio increase respectively,while little effect of stirring speed(P>0.05)was observed.The apparent activation energy of extraction process was calculated as 10.02 kJ/mol and Arrhenius constant(A)was 1.91 by Arrhenius equation.There was a linear relationship between reaction rate constant and the square of the inverse of initial particle radius(1/r_(0)^(2))(P<0.05).This phenomenon and this shrinking core model were anastomosed.In brief,the extraction process was controlled by the diffusion of protein from the virgin zone interface of particle through the reacted zone and it was in line with the first order reaction.Mass transfer kinetics of peanut protein extracted by reverse micelles was established and it was verified by experimental results.The results provide an important theoretical guidance for industrial production of peanut protein separation and purification.

Recovery of zinc and lead by simultaneously leaching from lead slag fuming dust with ammonium chloride solution

The effects of leaching temperature(60−105°C),NH4Cl concentration(3−7 mol/L),liquid/solid ratio(4:1−12:1 mL/g),stirring speed(150−750 r/min),and leaching time(5−90 min)on the leaching rates of Zn and Pb were investigated.The leaching kinetics of Zn-and Pb-rich fuming dust with a NH4Cl solution was also studied.The leaching rates of Zn and Pb respectively reached 98.2%and 75.6%at leaching temperature of 100°C,an NH4Cl concentration of 7.0 mol/L,a liquid/solid ratio of 10:1 mL/g,a stirring speed of 450 r/min and leaching time of 60 min.The kinetics results indicate that the leaching of Zn and Pb conforms to the shrinking unreacted core model and is controlled by the internal diffusion of NH4Cl through the reacted fuming dust layer and external diffusion of NH4Cl through the leaching solution boundary layer,respectively.The apparent activation energies of Zn and Pb are 23.922 and 19.139 kJ/mol,respectively.This study demonstrates that the use of NH4Cl solution,without ammonia,is an environmentally friendly method for simultaneous extracting Zn and Pb from the fuming dust of lead blast furnace slag.

Preparation of bismuth subcarbonate by liquid ball-milling transformation method from bismuth oxide

In order to solve the problems of environment pollution and high cost in traditional process of bismuth subcarbonate preparation, a new process using ball-milling transformation method from NH4HCO3 and Bi2O3 was proposed. Additionally, the kinetics of bismuth subcarbonate preparation was studied. Effects of reaction temperature, particle size of bismuth oxide, solid-to-liquid ratio and concentrations of ammonium bicarbonate on the conversion rate of bismuth oxide were studied. The results indicate that the conversion rate of bismuth oxide significantly increased under the conditions of higher temperature, smaller particle size, higher concentration of ammonium bicarbonate and smaller solid-to-liquid ratio. The XRD and ICP-AES analyses show that the purity of product is high. The reaction kinetics with activation energy of 9.783 kJ/mol was analyzed by shrinking core model, and the whole transformation process is controlled by solid product layer diffusion. A semi-empirical kinetics equation was obtained to describe the conversion process.

Kinetics of nitric acid leaching of low-grade rare earth elements from phosphogypsum

Phosphogypsum(PG)is a potential resource for rare earth elements(REEs).Several studies have been carried out on REE leaching from PG.However,few in-depth studies have investigated the kinetics of this leaching process.In this study,the leaching kinetics of REEs from PG in nitric acid at different temperatures were explored in depth.The experiments show that the maximum leaching recovery for ΣREE was 58.5%,75.9%and 83.4%at 30,60 and 80℃,respectively.Additionally,among La,Ce,Y and Nd,Y had the highest leaching rate.A new shrinking core model(SCM)based on the dissolution reaction of a cylindrical solid particle with interfacial transfer and diffusion across the product layer as the rate-controlling step was deduced and could well fit the leaching process of REEs from PG.The activation energies for the leaching of La,Ce,Y and Nd were determined on the basis of the new cylindrical SCM.In summary,the cylindrical SCM was a more suitable fitting model than the spherical SCM,and the interfacial transfer and diffusion across the product layer were the rate-controlling step for REE leaching from the PG sample.

Process optimization and kinetics for leaching of cerium, lanthanum and neodymium elements from iron ore waste's apatite by nitric acid

The leaching of rare earth elements （REEs） including cerium, lanthanum and neodymium from apatite concentrate obtained from iron ore wastes by nitric acid was studied. The effects of nitric acid concentration, solid to liquid ratio and leaching time on the recoveries of Ce, La and Nd were investigated using response surface methodology. The results showed that the acid concentration and solid to liquid ratio have significant effect on the leaching recoveries while the time has a little effect. The maximum REE leaching recoveries of 66.1%, 56.8% and 51.7% for Ce, La and Nd, respectively were achieved at the optimum leaching condition with 18% nitric acid concentration, 0.06 solid to liquid ratio and 38 min leaching time. The kinetics of cerium leaching was investigated using shrinking core model. It was observed that the leaching is composed of two stages. In the first stage a sharp increase in cerium leaching recovery was observed and at the longer time the leaching became slower. It was found that in the first stage the diffusion of reactants from ash layer is the rate controlling mechanism with an apparent activation energy of 6.54 kJ/mol, while in the second stage the mass transfer in the solution is the controlling mechanism.

Numerical Analysis of Blast Furnace Performance Under Charging Iron-Bearing Burdens With High Reducibility

The reducibility of iron-bearing burdens was emphasized for improving the operation efficiency of blast furnace. The blast furnace operation of charging the burdens with high reducibility has been numerically evaluated using a multi-fluid blast furnace model. The effects of reaction rate constants and diffusion coefficients were investigated separately or simultaneously for clarifying the variations of furnace state. According to the model simulation results, in the upper zone, the indirect reduction of the burdens proceeds at a faster rate and the shaft efficiency is enhanced with the improvement under the conditions of interface reaction and intra-particle diffusion. In the lower zone, direct reduction in molten slag is restrained. As a consequence, CO utilization of top gas is enhanced and the ratio of direct reduction is decreased. It is possible to achieve higher energy efficiency of the blast furnace, and this is represented by the improvement in productivity and the decrease in consumption of reducing agent. The use of high-reducibility burdens contributes to a better performance of blast furnace. More efforts are necessary to develop and apply highreducibility sinter and carbon composite agglomerates for practical application at a blast furnace.

Kinetics of Silver Dissolution in Nitric Acid from Ag-Au_(0.04)-Cu_(0.10) and Ag-Cu_(0.23) Scraps

Kinetics of dissolution of silver present in precious metal 26～85℃. Dissolution rate of silver was much faster than scraps in HNO3 was studied in temperature range of that of copper at all temperatures. Effects of particle size, stirring speed, acid concentration and temperature on the rate of dissolving of silver were evaluated. Dissolution rate decreases with particle size and increases with temperature. Dissolving was accelerated with acid concentrations less than 10 mol/L. Concentrations greater than 10 mol/L resulted in slowing down of the dissolution rate. Shrinking core model with internal diffusion equation t/τ=1-3（1-x）^2/3＋2（1-x） could be used to explain the mechanism of the reaction. Silver extraction resulted in activation energies of 33.95 kJ/mol for Ag-Au0.04-Cu0.10 and 68.87 kJ/mol for Ag-Cu0.23 particles. Inter-diffusion of silver and nitrate ions through the porous region of the insoluble alloying layer was the main resistance to the dissolving process. Results were tangible for applications in recycling of the material from electronic silver-bearing scraps, dental alloys, jewelry, silverware and anodic slime precious metal recovery.

Modelling and numerical simulation of isothermal oxidation of an individual magnetite pellet based on computational fluid dynamics

A mathematical model based on the computational fluid dynamics method,heat and mass transfer in porous media and the unreacted shrinking core model for the oxidation reaction of an individual magnetite pellet during preheating was established.The commercial software COMSOL Multiphysics was used to simulate the change in the oxidation degree of the pellet at different temperatures and oxygen concentrations,and the simulated results were compared with the exper-imental results.The model considered the influence of the exothermic heat of the reaction,and the enthalpy change was added to calculate the heat released by the oxidation.The results show that the oxidation rate on the surface of the pellet is much faster than that of the inside of the pellet.Temperature and oxygen concentration have great influence on the pellet oxidation model.Meanwhile,the exothermic calculation results show that there is a non-isothermal phenomenon inside the pellet,which leads to an increase in temperature inside the single pellet.Under the preheating condition of 873-1273 K(20%oxygen content),the heat released by the pellet oxidation reaction in a chain grate is 7.8×10^(6)-10.8×10^(6) kJ/h,which is very large and needs to be considered in the magnetite pellet oxidation modelling.

Absorption mechanism of SO_(3)on various alkaline absorbents in the presence of SO_(2)

Sulfur trioxide(SO_(3))as a condensable particle matter has a significant influence on atmospheric visibility,which easily arouses formation of haze.It is imperative to control the SO_(3)emission from the industrial flue gas.Three commonly used basic absorbents,including Ca(OH)_(2),MgO and NaHCO_(3)were selected to explore the effects of temperature,SO_(2)concentration on the SO_(3)absorption,and the reaction mechanism of SO_(3)absorption was further illustrated.The suitable reaction temperature for various absorbents were proposed,Ca(OH)_(2)at the high temperatures above 500°C,MgO at the low temperatures below 320°C,and NaHCO_(3)at the temperature range of 320–500°C.The competitive absorption between SO_(2)and SO_(3)was found that the addition of SO_(2)reduced the SO_(3)absorption on Ca(OH)_(2)and NaHCO_(3),while had no effect on MgO.The order of the absorption selectivity of SO_(3)follows MgO,NaHCO_(3)and Ca(OH)_(2)under the given conditions in this work.The absorption process of SO_(3)on NaHCO_(3)follows the shrinking core model,thus the absorption reaction continues until NaHCO_(3)was exhausted with the utilization rate of nearly 100%.The absorption process of SO_(3)on Ca(OH)_(2)and MgO follows the grain model,and the dense product layer hinders the further absorption reaction,resulting in low utilization of about 50%for Ca(OH)_(2)and MgO.The research provides a favorable support for the selection of alkaline absorbent for SO_(3)removal in application.

Adsorptive separation of La(Ⅲ)from aqueous solution via the synthesized[Zn(bim)_(2)(bdc)]_(n) metal-organic framework

Lanthanum is one of the rare earth metals which due to specific chemio-physical properties,has wide applications in different industries.In this research,the ability of the synthesized metal-organic framework(MOF),[Zn(bim)_(2)(bdc)]_(n)(ZBB) for the removal of lanthanum ions from the aqueous stream was investigated in the batch and column processes.The synthesized MOF was characterized by using scanning electron microscopy(SEM),Brunauer-Emmett-Teller(BET),Fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis(TGA).The effect of pH on lanthanum ions adsorption was evaluated in the range from 1 to 7.Moreover,isothermal,kinetic,and thermodynamic parameters for adsorption of La(Ⅲ) ions onto the synthesized MOF were evaluated.The adsorption capacity of lanthanum ions onto the synthesized MOF was calculated to be about 130 mg/g.Thermodynamic studies demonstrate the endothermic and chemical nature of lanthanum adsorption,while kinetic studies suggest the pseudo-first-order of reaction.In column mode,the effect of solution flow rate passing through the fixed-bed was studied.Experimental data confirm that increasing the bed flow rate causes a decrease in the adsorption capacity of lanthanum ions on the synthesized MOF.

Effect of pressure on gasification reactivity of three Chinese coals with different ranks

The gasification reactivities of three kinds of different coal ranks(Huolinhe lignite,Shenmu bituminous coal,and Jincheng anthracite)with CO_(2) and H_(2)O was carried out on a self-made pressurized fixed-bed reactor at increased pressures(up to 1.0 MPa).The physicochemical characteristics of the chars at various levels of carbon conversion were studied via scanning electron microscopy(SEM),X-ray diffraction(XRD),and BET surface area.Results show that the char gasification reactivity increases with increasing partial pressure.The gasification reaction is controlled by pore diffusion,the rate decreases with increasing total system pressure,and under chemical kinetic control there is no pressure dependence.In general,gasification rates decrease for coals of progressively higher rank.The experimental results could be well described by the shrinking core model for three chars during steam and CO_(2) gasification.The values of reaction order n with steam were 0.49,0.46,0.43,respectively.Meanwhile,the values of reaction order n with CO_(2) were 0.31,0.28,0.26,respectively.With the coal rank increasing,the pressure order m is higher,the activation energies increase slightly with steam,and the activation energy with CO_(2) increases noticeably.As the carbon conversion increases,the degree of graphitization is enhanced.The surface area of the gasified char increases rapidly with the progress of gasification and peaks at about 40%of char gasification.