Physicochemical and environmental characteristics of alkali leaching residue of wolframite and process for valuable metals recovery

Physicochemical and mineralogical characteristics of an alkali leaching residue of wolframite were studied by XRD,SEM−EDS,chemical phase analysis,mineral liberation analyzer(MLA),and TG−DSC methods.Batch leaching tests,toxicity characteristic leaching procedure(TCLP)tests and Chinese standard leaching tests(CSLT)were conducted to determine the environmental mobility of toxic elements.The results show that,due to the high contents of W,Fe,Mn,Sn,and Nb,the residue is with high resource value,but the content of a toxic element,As,is also high.The existing minerals of the investigated elements mainly occur as monomer particles,but it is difficult to extract these valuable metals by conventional acid leaching due to their mineral properties.The release of As increases over time in acidic environment.The leaching concentration of all investigated harmful elements through TCLP is within the limiting value,while the leaching concentration of As through CSLT exceeds the limiting value by more than 4 times,so the residue is classified as hazardous solid waste based on the Chinese standard.A process for valuable metals recovery from this residue was proposed.Preliminary experimental results indicated that the main valuable metals could be extracted effectively.

Recovery of valuable metals from zinc leaching residue by sulfate roasting and water leaching

Zinc leaching residue(ZLR),produced from traditional zinc hydrometallurgy process,is not only a hazardous waste but also a potential valuable solid.The combination of sulfate roasting and water leaching was employed to recover the valuable metals from ZLR.The ZLR was initially roasted with ferric sulfate at640°C for1h with ferric sulfate/zinc ferrite mole ratio of1.2.In this process,the valuable metals were efficiently transformed into water soluble sulfate,while iron remains as ferric oxide.Thereafter,water leaching was conducted to extract the valuable metals sulfate for recovery.The recovery rates of zinc,manganese,copper,cadmium and iron were92.4%,93.3%,99.3%,91.4%and1.1%,respectively.A leaching toxicity test for ZLR was performed after water leaching.The results indicated that the final residue was effectively detoxified and all of the heavy metal leaching concentrations were under the allowable limit.

Processing, Recovery and Analysis of Precious Metals Using Molecular Recogntion Technology

IBC Advanced Technologies' Molecular Recognition Technology(MRT) products,trade named SuperLig,selectively and rapidly bind with target metal ions to remove them from solution.The MRT process can produce a high purity separation product of maximum added value at low cost.In this paper,applications of MRT in the precious metals industry,including selective commercial separations involving Au,Pd,Pt,Rh,and Ru,are described and discussed.Application of MRT to the analytical determination of precious metals is presented.Potential use of MRT in recovering precious metals from end-of-life(EOL) products is discussed.

Enhanced recovery of zinc and lead by slag composition optimization in rotary kiln

High-efficiency recovery of Zn and Pb from silicon-rich zinc leaching residues is realized in a rotary kiln.Characterizations by means of XRD,SEM,EDS and ICP reveal that the leaching residue contains 12.4 wt.%SiO_(2),16.1 wt.%Zn,and 7.4 wt.%Pb.Thermodynamic analysis shows that metallic vapor of Zn and Pb can be easily generated from the zinc leaching residue at 1150-1250°C inside the rotary kiln.Viscosities and melting points of 13 slag compositions were analyzed and three slag compositions(47wt.%SiO_(2)-23wt.%CaO-30wt.%FeO,40wt.%SiO_(2)-28wt.%CaO-32wt.%FeO,and 40wt.%SiO_(2)-30wt.%CaO-30wt.%FeO)possessed the desirable physical properties,with the melting point and viscosity in the range of 1150-1280°C and 0.2-0.5 Pa·s,respectively.The industrial tests show that adopting the optimized slag composition can contribute to very high recovery rates of Zn and Pb(97.3%for Zn and 94.5%for Pb),corresponding to slags with very low average contents of Zn and Pb(0.51 wt.%Zn and 0.45 wt.%Pb).The National-Standard leaching tests of the water-quenched slags result in 1.82 mg/L Zn,~0.01 mg/L Cu,0.0004 mg/L As,~0.01 mg/L Cd,0.08 mg/L Pb,and~0.02 mg/L Hg in the leachate,verifying the detoxification of the zinc leaching residue at the same time.

A novel process for the recovery of iron,titanium,and vanadium from vanadium-bearing titanomagnetite:sodium modification–direct reduction coupled process

A sodium modification–direct reduction coupled process was proposed for the simultaneous extraction of V and Fe from vanadium- bearing titanomagnetite. The sodium oxidation of vanadium oxides to water-soluble sodium vanadate and the transformation of iron oxides to metallic iron were accomplished in a single-step high-temperature process. The increase in roasting temperature favors the reduction of iron oxides but disfavors the oxidation of vanadium oxides. The recoveries of vanadium, iron, and titanium reached 84.52%, 89.37%, and 95.59%, respectively. Moreover, the acid decomposition efficiency of titanium slag reached 96.45%. Compared with traditional processes, the novel process provides several advantages, including a shorter flow, a lower energy consumption, and a higher utilization efficiency of vanadium-bearing titanomagnetite resources. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

Extraction of metals from complex sulfide nickel concentrates by low-temperature chlorination roasting and water leaching

The recovery of valuable metals from complex sulfide concentrates was investigated via chlorination roasting followed by water leaching. A reaction process is proposed on the basis of previous studies and the results of our preliminary experiments. During the process, various process parameters were studied, including the roasting temperature, the addition of NH4Cl, the roasting time, the leaching time, and the liquid-to-solid ratio. The roasted products and leach residues were characterized by X-ray diffraction and vibrational spectroscopy. Under the optimum condition, 95% of Ni, 98% of Cu, and 88% of Co were recovered. In addition, the removal of iron was studied in the water leaching stage. The results demonstrate that this process provides an effective approach for extracting multiple metals from complex concentrates or ores. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

Optimization of flotation variables for the recovery of hematite particles from BHQ ore

The technology for beneficiation of banded iron ores containing low iron value is a challenging task due to increasing demand of quality iron ore in India. A flotation process has been developed to treat one such ore, namely banded hematite quartzite （BHQ） containing 41.8wt% Fe and 41.5wt% SiO2,by using oleic acid, methyl isobutyl carbinol （MIBC）, and sodium silicate as the collector, frother, and dispersant, respectively. The relative effects of these variables have been evaluated in half-normal plots and Pareto charts using central composite rotatable design. A quadratic response model has been developed for both Fe grade and recovery and optimized within the experimental range. The optimum reagent dosages are found to be as follows： collector concentration of 243.58 g/t, dispersant concentration of 195.67 g/t, pH 8.69, and conditioning time of 4.8 min to achieve the maximum Fe grade of 64.25% with 67.33% recovery. The predictions of the model with regard to iron grade and recovery are in good agreement with the experimental results.

Comprehensive recovery of lead, zinc, and iron from hazardous jarosite residues using direct reduction followed by magnetic separation

Lead, zinc, and iron were recovered from jarosite residues using direct reduction followed by magnetic separation. The influence of the coal dosage, reduction temperature, and reduction time on the volatilization rates of lead and zinc and the metallization rate of iron were investigated. The results show that the volatilization rates of lead and zinc were 96.97% and 99.89%, respectively, and the iron metallization rate was 91.97% under the optimal reduction roasting conditions of a coal dosage of 25.0 wt% and reduction roasting at 1250°C for 60 min. The magnetic concentrate with an iron content of 90.59 wt% and an iron recovery rate of 50.87% was obtained under the optimum conditions in which 96.56% of the reduction product particles were smaller than 37 μm and the magnetic field strength was 24 k A/m. Therefore, the results of this study demonstrate that recovering valuable metals such as lead, zinc, and iron from jarosite residues is feasible using the developed approach.

Recovering metals from printed circuit board scrap by a mechanical separation process

A mechanical separation process was developed for recovering metals from printed circuit board(PCB) scrap;it included three steps:impact crushing,sieving and fluidization separation.The mechanism of the technique was based on the difference in the crushabilities of metallic and nonmetallic materials in the PCBs that led to the concentrated distribution of metals in particles of larger sizes and nonmetals mostly in particles of smaller sizes.It was found that crushed PCB particles from 0.125 mm to 1.000 mm contained about 80% of metals in the PCBs.Metals acquired satisfactory liberation in particles smaller than 0.800 mm.The crushed PCB particles were sieved into fractions of different size ranges.Each fraction separately went through a gas-solid fluidized bed operating at a selected optimal gas velocity for the specific size range.Approximately 95% of metals in printed circuit board particles from 0.125 mm to 0.800 mm was recovered by the gas-fluidized bed separator at the selected optimal gas velocity.However,separation of metals from particles smaller than 0.125 mm was not satisfactory.Further study is needed on metal recovery from fine particles.

Influence of Relative Electrode-Electrolyte Movement over Productivity for Silver Recovery from Diluted Solutions

The paper presents the influence of relative electrode-electrolyte movement over productivity for silver ions recovery by electrodeposition from diluted solutions. Wasted photographic fixing agent solution in various concentrations was used. For each concentration three regimes were studied： stationary, electrode rotation with 100 rpm and electrode rotation with 300 rpm. Polarization curves were drawn and working conditions from silver recovery point of view were discussed.

Microbial Community with Potential for Metal Release Isolated from Palca Mine Tailings Pond in Peru

The improvement of microbial characterization has increased the comprehension of microbial population and their ability in the microbiological metal dissolution. Bioleaching processes have been expanded to use microorganisms for the recovery of metals from ores and wastes. This study introduces Palca mine tailings pond in Peru which turned into acid mine drainage (AMD). AMD is a source of microbial communities whose microorganisms may support the aqueous extractive metallurgy for metal recovery. Four samples of AMD were collected from different locations and the elemental characterization showed concentrations of metals, such as Cu, Zn, Al, Mn, and Fe. The pH of the samples showed variation between 1.9 - 6.8. Twenty-one microorganisms were isolated and selected according the cell morphology. 16s rRNA gene sequences identified five species of which three belong to the bacterial kingdom and two to the Fungi kingdom. Two of the bacterial species were ferrous ion oxidizing bacteria, identified as Acidithiobacillus ferriphilus and Acidithiobacillus ferridurans;and the other one a ferric ion reducing bacteria identified as Acidiphilium acidophilum. The fungi species identified were Rhodotorula sinensis and Exophiala xenobiotica, a filamentous fungus isolated for the first time from an AMD.

Electrochemical recycling of Pd and Ag from simulated high-level liquid waste

For the recycling of Pd and Ag from high-level liquid waste(HLLW), the electrochemical behaviors of Pd and Ag in the simulated HNO_(3) solutions were investigated by cyclic voltammetry and potentiostatic deposition.Scanning electron microscopy(SEM) and X-ray diffraction(XRD) were used to-observe the deposits morphology and to evaluate their composition. The results indicate that the formation of NO_(2)^(-)electrodeposited. When Pd and Ag are electrodeposited together, more metals are gained in the same time, and the deposited Ag does not dissolve in this situation. The metals are electrodeposited completely at the potentials from -0.4 to -0.6 V(vs MSE) and the deposits contai-n Ag and PdHx. The electrodeposition of Pd can boost h-ydrogen evolution,and then the reaction between H;and NO_(2)^(-)is sped up, thereby lowering the concentration of NO_(2)^(-)and inhibiting the dissolution of Ag.

Recovery of Metals from Anodic Dissolution Slime of Waste from Electric and Electronic Equipment（WEEE） by Extraction in Ionic Liquids

The recovery of metals from a multi-component alloy obtained by crushing, melting and anodic dissolution of waste from electric and electronic equipment（WEEE） was investigated. The anodic dissolution of the alloy was carried out in an electrolysis cell with one copper cathode and a central cast anode, immersed in the electrolyte formed by choline chloride-ethylene glycol-iodine. The temperature of the electrolyte during the process was 343 K. Depending on the electrolysis parameters（current density and cell voltage）, cathodic deposits of Sn, Pb and Zn of 〉99% purity were obtained. Cyclic voltammetry was used in order to determine the deposition potentials of the studied metals. The obtained metallic deposits were subject of determination of XRD, SEM/EDX and AFM in order to evidence the deposits structure and morphology. The experiments performed demonstrated the possibility of separating/selective recovery of metals from the multi-component alloy resulted from the waste from electrical and electronic equipment by anodic dissolution in ionic liquids.

Core-shell design of UiO66-Fe_(3)O_(4) configured with EDTA-assisted washing for rapid adsorption and simple recovery of heavy metal pollutants from soil

The coupling of washing with adsorption process can be adopted for the treatment of soils contaminated with heavy metals pollution.However,the complex environment of soil and the competitive behavior of leaching chemicals considerably restrain adsorption capacity of adsorbent material during washing process,which demands a higher resistance of the adsorbents to interference.In this study,we synthesized strongly magnetic,high specific surface area(573.49 m^(2)/g)UiO66 composites(i.e.,UiO66-Fe_(3)O_(4))using hydrothermal process.The UiO66-Fe_(3)O_(4) was applied as an adsorbent during the ethylene diamine tetraacetic acid(EDTA)-assisted washing process of contaminated soil.The incorporation of UiO66-Fe_(3)O_(4)results in rapid heavy metal removal and recovery from the soil under low concentrations of washing agent(0.001 mol/L)with reduced residual heavy metal mobility of soil after remediation.Furthermore,UiO66-Fe_(3)O_(4)can quickly recollect by an external magnet,which offers a simple and inexpensive recovery method for heavy metals from contaminated soil.Overall,UiO66-Fe_(3)O_(4)configuration with EDTA-assisted washing process showed opportunities for heavy metals contaminated sites.

Nickel solvent extraction from cold purification filter cakes of Angouran mine concentrate using LIX984N

Cold purification filter cakes generated in the hydrometallurgical processing of Angouran mine zinc concentrate commonly contain significant amounts of Zn, Cd, and Ni ions and thus are valuable resources for metal recovery. In this research, a nickel containing solution that was obtained from sulfuric acid leaching of the filter cake following cadmium and zinc removal was subjected to solvent extraction experiments using 10vol%LIX984N diluted in kerosene. Under optimum experimental conditions （pH 5.3, volume ratio of organic/aqueous （O：A） = 2：1, and contact time -5 min）, more than 97.1% of nickel was extracted. Nickel was stripped from the loaded organic by contacting with a 200 g/L sulfuric acid solution, from which 77.7% of nickel was recovered in a single contact at the optimum conditions （pH 1-1.5, O：A =5：1, and contact time =15 min）.

Surface modification of phosphate ion to promote photocatalytic recovery of precious metals

Photocatalytic recovery,a novel precious metal recycling technology,dedicates to solving the environmental and energy consumption problems caused by traditional technologies.The activation of molecular oxygen (O_(2)) is one of the most critical steps in the whole process.Herein,we regulated the different adsorption intensity of oxygen on the surface by designing phosphate (PO_(4)^(3-)) modified titanium oxide(TiO_(2)).The results show that the adsorption of oxygen on the photocatalyst surface is gradually enhanced,which effectively improves the dissolution rate of precious metals.PO_(4)^(3-)modification increased the photocatalytic dissolution rate of gold (Au) by 2.8 times.The photocatalytic activity of other precious metals dissolution (such as palladium (Pd),platinum (Pt),rhodium (Rh),ruthenium (Ru) and iridium (Ir)) was also significantly improved.It is applied to the recovery of precious metals from spent catalysts and electronic devices to significantly promote the recovery efficiency.This indicates the direction for designing more efficient photocatalysts for precious metal recovery.

A mathematical model for the distribution balance of extraction processes from waste batteries

The experiments of metal Cd extraction were carried out three times at oil phase/aqueous phase （O/A） = 1 and pH 2.2 by using 1.3 mol/L di（2-ethylhexyl）phosphoric acid （DEHPA） as the agent, with an extraction rate of 99.5%. Experiments on metal Co extraction were done three times at O/A = 0.5 and pH 4.7 by using 0.4 mol/L Cyanex 272 as the agent, with an extraction rate of 99.2%. By using equilibrium data and massive calculations to analyze and predict the interaction among the extraction systems, this paper came out with the polynomials of the empirical model as well as their parameter values for the equilibrium concentration of the above two extraction looos.

Recovering noble metals from waste streams using porous organic frameworks for heterogeneous catalysis

Recovering noble metals from waste resources and incorporating them into catalysts stands out as a promising strategy for advancing sustainability within the catalysis field. This review provides a comprehensive overview of recent investigations into noble metal recovery from waste streams, specifically employing porous organic frameworks(POFs). Additionally, the study delves into the utilization of the resultant composites, enriched with noble metals, in heterogeneous catalysis. Moreover, we offer insights into the challenges faced and outline prospects for the practical implementation of extracting noble metal catalysts from waste streams using POFs, aiming to develop cost-effective, sustainable, and efficient heterogeneous catalysts.

Metal distribution characteristic of MSWI bottom ash in view of metal recovery

Bottom ash is the major by-product of municipal solid waste incineration（MSWI）, and is often reused as an engineering material, such as road-base aggregate. However, some metals（especially aluminum） in bottom ash can react with water and generate gas that could cause expansion and failure of products containing the ash; these metals must be removed before the ash is utilized. The size distribution and the chemical speciation of metals in the bottom ash from two Chinese MSWI plants were examined in this study, and the recovery potential of metals from the ash was evaluated. The metal concentrations in these bottom ashes were lower than that generated in other developed countries. Specifically, the contents of Al,Fe, Cu and Zn were 18.9–29.2, 25.5–32.3, 0.7–1.0 and 1.6–2.5 g/kg, respectively. Moreover,44.9–57.0 wt.% of Al and 55.6–75.4 wt.% of Fe were distributed in bottom ash particles smaller than 5 mm. Similarly, 46.6–79.7 wt.% of Cu and 42.9–74.2 wt.% of Zn were concentrated in particles smaller than 3 mm. The Fe in the bottom ash mainly existed as hematite, and its chemical speciation was considered to limit the recovery efficiency of magnetic separation.

Recovery of rare-earth metal neodymium from aqueous solutions by poly-γ-glutamic acid and its sodium salt as biosorbents:Effects of solution pH on neodymium recovery mechanisms

For recovery of metals from low-concentration sources, biosorption is one of promising technologies and poly-γ-glutamic acid（γ-PGA） has been known as a potential biosorbent for recovery of heavy metals from aqueous solutions. Effects of solution pH on recovery of rare-earth metal Nd are systematically examined to clarify mechanisms of Nd recovery by y-PGA and its sodium salt（y-PGANa）. The recovery efficiency of Nd by y-PGA increases from 2.4 to 19.6% as pH increases from 2 to 4. Subsequently the Nd recovery efficiencies for y-PGA and y-PGANa remain almost constant in the range of pH from 4 to 7. For pH 〉 7 the increase in Nd recovery is significant and 100% recovery of Nd is achieved at pH 9. The pH dependency on Nd recovery by y-PGANa is similar to that by y-PGA. Contributions of adsorption and precipitation/coagulation to Nd recovery process are quantified. Whereas the adsorption dominates Nd recovery at lower pH（〈～4）, the precipitation/coagulation controls Nd recovery process for pH 〉 7. At higher pH, purple gel precipitates are observed. The maximum adsorption capacities for γ-PGA and yPGANa are 215 mg-Nd/（g-γ-PGA） at pH 4 and 305 mg-Nd/（g-y-PGANa） at pH 3, respectively. From the spectra of FT-IR and XPS, the biosorption of Nd onto y-PGA and y-PGANa via electrostatic interaction with carboxylate anions at pH 3 is verified. The Nd complexation with amide and carboxylate anion groups on γ-PGA and γ-PGANa may also contribute to the Nd recovery. The biosorption isotherms for Nd recovery by γ-PGA and γ-PGANa can be satisfactorily fitted by the Langmuir model. The thermodynamic studies suggest that the biosorptions of Nd by γ-PGA and γ-PGANa are endothermic. The utilization of γ-PGA and γ-PGANa as potential and eco-friendly biosorbents for the highly effective recovery of Nd from aqueous solution is confirmed.