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The present work is focused on the recovery of pure copper metal from leach liquor of discarded printed circuit boards (PCBs) using solvent extraction and electrowinning techniques. Leach liquor containing copper was produced from PCBs of scrap computers using pretreatment followed by the leaching technique. The obtained leach liquor contained 19.35 g/L of copper and 6 M concentration of nitric media. From the obtained leach liquor, systematic solvent extraction and electrowinning studies were carried out for maximum extraction of copper, leaving other metals to be present as impurities. Various process parameters of solvent extraction viz. effect of pH, contact time, phase ratio, and so on were studied and optimized. McCabe–Thiele diagram was plotted, which shows that complete recovery of copper can be achieved in three stages using 40% LIX 84IC and O/A ratio 1/1 at equilibrium pH 2.2 in a mixing time of 20 min. The loaded copper was stripped using 10% H2SO4. The obtained strip solution containing 19.35 g/L Cu was electrowinned at the optimized condition, i.e., 8 hours' time and 205 A/m2 cathode density with 99.99% current efficiency. 99.8% pure copper metal was obtained. The developed process is environmentally sustainable and has potential to be commercialized after scale-up studies. [ABSTRACT FROM AUTHOR]

Electronic manufacturing industries use copper in highest proportion in metals due to its unique properties. But there is a gap in demand and supply of this metal to the industry due to its huge requirement and lack of its proper recycling of copper containing equipments. Also, effluent generated from these industries carries substantial amount of this metal, which get discharged, and loss of metals to the environment. Present paper discusses about valuable copper metal recovery from industrial effluent in powder form using novel process flow-sheet. At start, bio-adsorptiontechnique was used to recover copper from industrial effluent due to its advantages like low cost, feasible method showing faster kinetics. Datura root powder was found to be potential bio-adsorbent for copper recovery from effluent having 997 mg/g adsorption capacity. It follows second-order rate reaction and Freundlich adsorption isotherm with 0.9711 regression coefficient. Further, copper-enriched solution obtained from this technique was subjected to cementation process using scrap iron rods to get copper powder. This can be used to produce value added products using its ingots. This is one of the approaches towards waste to wealth creation having tremendous potential to get commercialized. [ABSTRACT FROM AUTHOR]

In the hydrometallurgical process of molybdenum using ammonia solution, ammonium paramolybdate tetrahydrate (APT: (NH4)6Mo7O24·4H2O) is produced as an intermediate product after a crystallization step. ATP is then thermally decomposed at a high temperature to give MoO3, which is reduced by hydrogen gas in a two-stage process to reduce molybdenum metal powder as the final product. If APT is pre-dried at an appropriately low temperature to remove the crystal water corresponding to 4 mol per mol of APT, it changes into (NH4)4Mo5O17, and the content of residual ammonia, which can be utilized as a reductant, in the ammonium molybdate increases. In this regard, the self-reducing potential of (NH4)4Mo5O17 was examined in this study through the effectiveness analysis of the residual ammonia component as a reductant for the primary hydrogen reduction step. In a series of experimental work on the thermal decomposition of (NH4)4Mo5O17 in an inert atmosphere, a maximum self-reduction degree of 18% was achieved. Based on this result, it can be expected that the metal powder can be manufactured in a more effective way than conventional processes in terms of hydrogen consumption and reaction time. [ABSTRACT FROM AUTHOR]

Vanadium in the vanadium-bearing titanomagnetite (VTM) exist by replacing iron in the magnetite crystal, and magnetite should be recovered separately from titanium components in the vanadium-bearing titanomagnetite. In the present study, a sensing system was proposed by measuring magnetic susceptibility of magnetite because the magnetic susceptibility can be easily and quickly measured. The effects of mixing ratio of magnetite and ilmenite with silica and the distance between the magnetic susceptibility meter and the sample bed on the magnetic susceptibility were investigated. The magnetic susceptibility of the mixture of magnetite and ilmenite with 0.1 g or 0.2 g of silica decreased with increasing the ratio of ilmenite in the mixture, but the effect of silica addition was not significant. When the distance between the magnetic susceptibility meter and the sample bed increased, the magnetic susceptibility of magnetite decreased, but the magnetic susceptibility decreased with increasing the thickness of magnetite sample bed of magnetite. Because the magnetic susceptibility depended strongly on the content of magnetite, the sensing system using the magnetic susceptibility measurement could be successfully applied to detect magnetite. [ABSTRACT FROM AUTHOR]

Carbothermic reduction-roasting tests of NCM (nickel, cobalt, and manganese) cathode active materials with carbon sources such as activated carbon and graphite followed by sulfuric acid leaching were performed to investigate the effects of roasting temperature, molar mixing ratio of cathode active materials and carbon sources, and type of cathode active materials. When the virgin NCM622 materials were roasted with activated carbon, the peaks of Ni and Co metals were observed in the XRD data. The leaching efficiencies of Li, Ni, Co, and Mn increased to over 99.9% within 120 min in all samples roasted at 600 °C–900 °C, but, at the beginning of leaching, the leaching efficiencies increased more slowly with increasing roasting temperature. The leaching efficiencies of Ni and Co decreased with decreasing the molar mixing ratio of active cathode materials and carbon sources, but the leaching efficiencies were more than 99.9% in all ratios. These results indicate that roasting can enhance the leaching of cathode active materials and improve the conventional leaching process using hydrogen peroxide. [ABSTRACT FROM AUTHOR]

The mineralogy of beach sand, which was sampled from an island, Jumundo of South Korea, was investigated and beneficiated using gravity and magnetic separation processes. Ilmenite was determined to be a major heavy mineral and, as minor heavy minerals, zircon, monazite, and sphene were observed. Quartz, biotite, microcline, kaolinite, hornblende, and chlorite were present as gangue minerals. The Ilmenite was concentrated with a Humphrey spiral concentrator and shaking table followed by magnetic separators (drum and cross belt types). As a final product, 18% of the Humphrey spiral system concentrate was recovered, and the grade of final product was determined to be 93% ilmenite. The electron probe microscope analysis indicates that ilmenite was a solid solution of major FeTiO3, minor MgTiO3 (geikielite), and MnTiO3 (pyrophanite). [ABSTRACT FROM AUTHOR]

The leaching behaviors of tin (Sn), antimony (Sb), iron (Fe), and lead (Pb) from non-magnetic fraction of Pb dross, which was obtained from magnetic separation process to remove As components, were investigated using HCl solution. The leaching efficiencies of Sn, Fe, and Pb increased with increasing agitation speed, temperature, and HCl concentration and with decreasing pulp density, but Sb was dissolved only in the 3 and 5 M HCl solutions. The leaching efficiencies of metals increased to 100% in the 5 M HCl solution at 400 rpm and 70°C with 1% pulp density within 120 min. In the case of leaching test with 1 M HCl, Sb components could be recovered as leach residue. After leaching test, Pb could be recovered as PbCl2 from the solution by lowering temperature. Tin ions were extracted selectively by solvent extraction with tri-butyl phosphate, remaining Fe and Pb ions in the solution. The process consisting of HCl leaching, precipitation, and solvent extraction recovers successfully Sb, Pb, and Sn from non-magnetic fraction of Pb dross. [ABSTRACT FROM AUTHOR]

Electrowinning process to regenerate Sn4+ from Sn2+ in HCl solution using an electrowinning cell with anion exchange membrane was proposed to suggest a novel recycling process to recover Sn. During the tests, the effects of initial Sn2+ concentration on the regeneration of Sn4+ were investigated under the following condition; 7,000 mg/L, 10,000 mg/L, and 13,000 mg/L of Sn2+, 1 M HCl, 250 A/m2 of current density, graphite anode, titanium cathode, room temperature, and 2 h. Electro-deposited Sn on the cathode showed dendritic structure regardless of the Sn2+ concentration and no change of Sn concentration was observed in the anolyte. Leaching tests were performed using the anolyte, obtained from the electrowinning tests, to examine the amount of regenerated Sn4+ concentration during electrowinning process. Based on the results of Sn leaching tests, it was found that 84.44%, 81.03%, and 79.43% of Sn4+ were regenerated from 7,000 mg/L, 10,000 mg/L, 13,000 mg/L initial concentration of Sn2+ solution, respectively. Consequently, it was found that the regeneration of Sn4+ can occur during the electrowinning process at the same time with Sn recovery and Sn4+ can be reused as an oxidant to leach Sn successfully. [ABSTRACT FROM AUTHOR]

South Korea imports 99% of its mineral metal resources, so it is important to recover valuable metals from metal-containing waste for sustainable domestic industry development. The Korean government launched a 10-year recycling research project, 'Valuable Recycling', in May 2011 with $180 million funding ($150 million from the government). The objectives of the project were to develop highly efficient technologies that improve the resource recycling ratio and quality of life, and meet international environmental regulations for enhancing the competitiveness of domestic industries. The project includes 26 sub-projects classified into four categories: electrical & electronics, automotive, metals & inorganics, and organics. The main research achievements and recycling processes are presented in this article. [ABSTRACT FROM AUTHOR]

A recycling process consisting of HCl leaching with Sn 4 + followed by solvent extraction is proposed to recover Cu, Sn and Pb from photovoltaic (PV) ribbon. During HCl leaching with Sn 4 + , Sn and Pb were removed from PV ribbon whereas Cu remained as plate. The leaching efficiency of Sn increased with increasing temperature, initial Sn 4 + concentration or decreasing pulp density. In the case of leaching test performed in the 1 M HCl solution at 400 rpm and 70 °C with 5% pulp density and 5000 mg/L Sn 4 + , the leaching efficiency of Sn increased to > 99% within 60 min, whereas 71.9% of Pb was recovered as PbCl 2 powder after settling the leach solution for 24 h at room temperature. A solvent extraction with tri-butyl phosphate (TBP) was performed to extract selectively Sn from leach solution. The extraction efficiency of Sn increased with increasing the contents of TBP in kerosene, and < 1% of Pb was extracted. Therefore, the separation of Sn, Cu, Pb was achieved successfully by the recycling process. [ABSTRACT FROM AUTHOR]

A recycling process consisting of swelling, ammonia leaching and hydrochloric acid leaching was developed to recover Sn, Bi, Cu, and resin from Pb-free Sn-Bi-Cu solder paste. The resin was separated from metal powder by swelling the solder paste in methyl ethyl ketone at 30 °C, 200 rpm and 5% pulp density. The addition of distilled water precipitated the resin from methyl ethyl ketone. The recovered resin was confirmed to be epoxy resin by FT-IR analysis. Ammonia leaching followed by hydrochloric acid leaching was performed to separate Cu, Sn, Bi sequentially from metal powder. Copper was solubilized easily with leaching efficiency reaching 100% within 15 min under the following conditions: 5 M NH 3 solution, 1 M (NH 4 ) 2 CO 3 , 0.1 M CuCO 3 , 50 °C, and 1% pulp density. Tin and bismuth were recovered as leach residue in the ammonia leaching. Tin was selectively leached in 0.5 M HCl solution with 10,000 mg/L Sn 4 + and 1% pulp density at 50 °C and 400 rpm, while Bi was not detected in the leach solution. The recycling process has successfully separated Sn, Cu, Bi and resin. [ABSTRACT FROM AUTHOR]

A recycling process consisting of hydrochloric acid leaching with ferric chloride as an oxidant and cementation using Sn powder followed by solvent extraction was proposed to separate Sn from Pb-free solder. Leaching tests showed that the effect of HCl concentration on the leaching efficiency of Sn was negligible in 1.0–2.0 kmol · m − 3 HCl, and the efficiency was lower at 0.5 kmol · m − 3 HCl. Higher temperature yielded higher dissolution rates of Sn and Cu in the beginning of leaching; the leaching efficiencies of Sn and Cu increased to more than 99% within 90 min, but Ag was not detected, indicating that Ag could be separated successfully from Sn and Cu. When more than 1 g of Sn powder was added to 100 ml of leach solution containing 98.1 g · m − 3 Cu, Cu ions could be removed from the leach solution by the cementation reaction. In the solvent extraction test using tri-butyl phosphate (TBP) diluted with kerosene, the extraction efficiency of Sn increased with increasing TBP volume ratio in the organic phase, and 99.9% of Sn was extracted selectively by 3-time solvent extraction with 15% TBP and 1:1 O/A ratio at 30 °C. [ABSTRACT FROM AUTHOR]

Abstract: The effect of chloride on chalcopyrite leaching has been investigated by performing batch leaching tests with three kinds of leaching solutions and using Hiroyoshi’s model, which suggests that a zone of rapid leaching exists between the critical potential (Ec , equilibrium redox potential for the reduction of CuFeS2 to Cu2S) and the oxidation potential (Eox , equilibrium redox potential for the oxidation of Cu2S). The results of the leaching tests show that the leaching rate in hydrochloric acid solution is the fastest and that the relationship between the Cu leaching rate and oxidation–reduction potential (ORP) follows Hiroyoshi’s model. Thermodynamic calculations indicate that, with an increase in the chloride concentration, the concentration of cuprous ions increases as the chlorocuprate(I) complex ions are formed and the contribution of cuprous ions to the critical potential is greater than that of cupric ions, even though the concentration of cuprous ions is lower than that of cupric ions. This fact suggests that the formation of chlorocuprate(I) ions in a chloride solution may improve the chalcopyrite leaching rate by increasing the critical potential. [Copyright &y& Elsevier]

Abstract: Wastewater produced during recycling of spent lithium primary battery was biologically treated with Acidithiobacillus ferrooxidans to decrease the pH and metal concentration. Since the wastewater contains high concentrations of Cr, Ni, and Li, the effects of these metals on the bacterial activity in a 9K medium were also investigated. Samples of the medium with different metal concentrations were treated, and the oxidation ratio of Fe2+ ions was measured to examine the activity of bacteria. In the treatment of simulated wastewater, the presence of Cr and Ni ions with concentrations of 8000gm−3 and 13,000gm−3, respectively, did not inhibit the bacterial activity, whereas the oxidation ratio of Fe2+ ions was observed to be low in the medium when Li ion was present with a concentration at 5000gm−3. This observation suggested that at this concentration, Li ion suppressed the bacterial activity. In the case of treatment of real wastewater containing Cr, Ni, and Li, the oxidation ratio of Fe2+ to Fe3+ was observed to be low while the Fe concentration and pH decreased to 21,633gm−3 and 1.8, respectively. Thus, the wastewater produced during the recycling of spent lithium primary batteries can be effectively treated biologically for re-circulating in the recycling process. [Copyright &y& Elsevier]

Nickel metal hydride (NiMH) batteries are extensively used in the manufacturing of portable electronic devices as well as electric vehicles due to their specific properties including high energy density, precise volume, resistance to overcharge, etc. These NiMH batteries contain significant amounts of rare earth metals (REMs) along with Co and Ni which are discarded due to illegal dumping and improper recycling practices. In view of their strategic, economic, and industrial importance, and to mitigate the demand and supply gap of REMs and the limited availability of natural resources, it is necessary to explore secondary resources of REMs. Therefore, the present paper reports a feasible hydrometallurgical process flowsheet for the recovery of REMs and valuable metals from spent NiMH batteries. More than 90% dissolution of REMs (Nd, Ce and La) was achieved using 2 M H2SO4 at 75 °C in 60 min in the presence of 10% H2O2 (v/v). From the obtained leach liquor, the REMs, such as Nd and Ce, were recovered using 10% PC88A diluted in kerosene at eq. pH 1.5 and O/A ratio 1/1 in two stages of counter current extraction. La of 99% purity was selectively precipitated from the leach liquor in the pH range of 1.5 to 2.0, leaving Cu, Ni and Co in the filtrate. Further, Cu and Ni were extracted with LIX 84 at equilibrium pH 2.5 and 5, leaving Co in the raffinate. The developed process flow sheet is feasible and has potential for industrial exploitation after scale-up/pilot trails. [ABSTRACT FROM AUTHOR]

Non-availability of rich primary resources of rare earth metals (REMs) and the generation of huge amounts of discarded magnets containing REMs, compelled the researchers to explore the possibilities for the recovery of REMs from discarded magnets. Therefore, the present paper reports the recovery of REMs (Nd, Pr, and Dy) from discarded Nd-Fe-B magnets. The process consists of demagnetization, pre-treatment, and hydrometallurgical processing to recover REMs as salt. Leaching studies indicate that 95.5% Nd, 99.9% Pr, and 99.9% Dy were found to be dissolved at the optimized experimental condition i.e., acid concentration 2 M H2SO4, temperature 75 °C, pulp density 100 g/L, and mixing time 60 min. Solvent extraction technique was tried for the selective extraction/separation of REMs and Fe. The result indicates that 99.1% (24.42 g/L) of Nd along with 90% (1.08 g/L) of Pr and total Fe were co-extracted using 35% Cyanex 272 at organic to aqueous (O/A) ratio 1/1, eq. pH 3.5 in 10 min of mixing time. It requires multistage separation and therefore, not feasible in view of economics. Thus, direct precipitation of REMs salt and iron oxide as pigment was studied using two stages of precipitation at different pH. The obtained precipitate of REMs and Fe hydroxides were dried separately to remove the moisture and further treated at elevated temperature to get pure REMs oxide and red oxide. [ABSTRACT FROM AUTHOR]

In the present paper, the leaching of copper from printed circuit boards (PCBs) using sulfuric acid with Cu2+ and O2 is proposed. The effects of various process parameters such as agitation speed, temperature, the type and the flow rate of gas, initial Cu2+ concentration, and pulp density were investigated to examine the dissolution behavior of Cu from PCBs in 1 mol/L sulfuric acid. The kinetic studies were performed using the obtained leaching data. The leaching rate of Cu from PCBs was found to be higher on addition of Cu2+ and O2 to the leachant in comparison with the addition of O2 or both Cu2+ and N2 in the leachant. The leaching efficiency of Cu was found to be increased with increasing agitation speed, temperature, O2 flow rate, and initial Cu2+ concentration and decreasing pulp density. The 96% of Cu leaching efficiency was obtained under the following conditions: sulfuric acid concentration, 1 mol/L; temperature, 90 °C; agitation speed, 600 rpm; pulp density, 1%; initial Cu2+ concentration, 10,000 mg/L; and O2 flow rate, 1000 cc/min. The leaching data and analyses indicate that the Cu leaching from PCBs followed the reaction-controlled model satisfactorily and determined that the activation energy was found to be 23.8 kJ/mol. Therefore, these results indicate that the sulfuric acid solution with Cu2+ and O2 as a mild leach medium without strong oxidants such as HNO3, H2O2, and Fe3+ is valid for Cu leaching from PCBs. [ABSTRACT FROM AUTHOR]

Copper (Cu) has been recovered from speiss generated from top submerged lance furnace process, but it was reported that the leaching efficiency of Cu in sulfuric acid solution decreased with increasing antimony (Sb) content in the speiss. Scanning electron microscopy (SEM)–energy-dispersive X-ray spectroscopy (EDS) results indicate that Sb exists as CuSb alloy, which would retard the leaching of Cu. Therefore, hydrochloric acid leaching with aeration was performed to investigate the leaching behaviors of copper and antimony. The leaching efficiency of Cu increased with increasing agitation speed, temperature, HCl concentration, and the introduction ratio of O2, but also with decreasing pulp density. The leaching efficiency of Cu increased to more than 99% within 60 min in 1 mol/L HCl solution at 600 rpm and 90 °C with 10 g/L pulp density and 1000 cc/min O2. The leaching efficiency of Sb increased and then decreased in all 1 mol/L HCl leaching tests, and precipitate was observed in the leach solution, which was determined to be SbOCl or Sb2O3 by XRD analyses. However, in 2 mol/L–5 mol/L HCl solutions, the leaching efficiency of Sb increased to more than 95% (about 900 mg/L) and remained, so more than 2 mol/L HCl could stabilize Sb ion in the HCl solution. [ABSTRACT FROM AUTHOR]

The addition of ferrous sulfate as a depressant for Ca-bearing minerals such as calcite and fluorite during scheelite flotation was investigated to recover scheelite from tungsten mine tailings, using Hallimond-tube flotation tests, zeta-potential measurement and Fourier-transform infrared (FT-IR) analyses. The flotation tests indicate that the selectivity of scheelite recovery was the largest over calcite and fluorite under the following conditions: 0.5 g sample, 50 g/ton AF65, 1 × 10−3 M sodium oleate, 1200 g/ton SF2 (sodium silicate and ferrous sulfate) depressant with the 8:2 ratio of sodium silicate and ferrous sulfate, 50 mL/min air injection rate, 5 min flotation time, and pH 8. The selectivity of scheelite flotation increased when the amount of SF2 depressant addition increased to 1200 g/ton, but it decreased by adding 1400 g/ton SF2, which would result from the precipitation of iron components. In the zeta potential results, the zeta potentials of scheelite with the collector show similar results regardless of the addition of SF2, while the change of zeta potentials of calcite and fluorite by adding NaO collector diminished when SF2 was added. In FT-IR analyses, the spectrum of NaO in scheelite results was observed regardless of the addition of SF2, while the spectra of NaO in calcite and fluorite results disappeared when SF2 was added. These results suggest that the addition of SF2 prevents the adsorption of NaO on the surface of calcite and fluorite. Therefore, the addition of SF2 could enhance the selectivity of scheelite flotation over calcite and fluorite. [ABSTRACT FROM AUTHOR]

Dry gravity separation using a vibrating zirconia ball bed is proposed in this study to separate aluminum (Al) and stainless steel (STS) scraps obtained from spent hard disk drive recycling. The effects of zirconia ball sizes and vibrating power (vibration amplitude) on the separation efficiency of Al and STS scraps were investigated. The zirconia balls moved down at the center of the vessel and rose with the wall during the vibration test. Although more STS scraps sunk than Al scraps did, the separation efficiency was not maintained because Al scraps also sunk along with balls' movement. The separation efficiency increased to 86.6% using 1-mm zirconia balls with a 2.5-mm vibration amplitude at 4 min, but it decreased rapidly by ball moving. Therefore, when a ball bed of mixed sizes (2:1 ratio of 1 and 3 mm) was used and arranged, whereby the 3-mm zirconia balls were above the 1-mm ball bed, the separation efficiency increased to 100% for more than 2 min. This dramatic improvement was because the 3-mm ball bed acted as a barrier to prevent sunken STS scraps from rising, and Al scrap cannot sink through the 3-mm ball bed. These results indicate that the separation of Al and STS scraps could be achieved successfully using the dry gravity separation method. [ABSTRACT FROM AUTHOR]

A new concept for copper (Cu) metal leaching by the simultaneous use of cupric ions (Cu2+) and oxygen (O2) was proposed to improve Cu metal leaching in sulfuric acid. According to this concept, Cu2+ oxidizes Cu metal into cuprous ion (Cu+), and O2 oxidizes Cu+ into Cu2+. The improvement in Cu leaching efficiency from Cu metal was investigated experimentally in the sulfuric acid solution using Cu2+ and O2 simultaneously. Furthermore, the result was compared with that for the sulfuric acid solution containing neither Cu2+ nor O2 and with the sulfuric acid solution without Cu2+ and O2. When both Cu2+ and O2 were used in the leaching solution, the leaching rate of Cu from Cu metal powder was higher than at other leaching conditions, and the leaching efficiency of Cu increased to more than 99.9% in 1 mol/L sulfuric acid solution at 400 rpm and 50 °C with ≤75 µm Cu metal powder, 1% pulp density, 10,000 mg/L initial Cu2+ concentration, and 100 cc/min O2 introduction. These results indicated that the leaching of Cu from Cu metal could be accelerated by adding Cu2+ and O2 in the sulfuric acid solution. [ABSTRACT FROM AUTHOR]

• Co was separated from leach solution with Mn by cementation process with Zn powder. • After magnetic separation, Co was concentrated in a magnetic fraction. • Unreacted Zn powder was recovered as a non-magnetic fraction. • The unreacted Zn powder could be reused as a cementation reagent. A cementation process with Zn powder followed by magnetic separation was conducted to separate Co as precipitate from leach solution containing Mn ions and to recover unreacted Zn and concentrated Co from cementation precipitate. The separation of Co component from Mn could be achieved successfully by a cementation process performed under the following conditions; 200 mg/L Cu, 140 mg/L Sb, pH 3.3–3.7, temperature 85 °C, and 1% Zn powder, where Cu and Sb were used as cementation activators to avoid the redissolution of Co. Magnetic separation of the cementation-precipitate was performed using 2000 G magnetic rod, and the results showed that Zn distributed more in non-magnetic fraction while Co, Cu, Sb were contained more in magnetic fraction. The Co was concentrated to 8.3% in magnetic fraction of the precipitate obtained from 60 min-cementation test. The non-magnetic fraction contained the unreacted Zn powder, which could be reused for cementation test for precipitating Co. [ABSTRACT FROM AUTHOR]

The removal of the cyanide and copper (Cu) from the waste printed circuit boards (WPCBs) cyanide leach solution through the alkaline chlorination using electro-generated hypochlorite (NaOCl) followed by magnetite (Fe3O4) adsorption is investigated. The efficiency of the destruction of cyanide and precipitation of Cu was increased with increasing the concentration of free available chlorine in NaOCl. More than 99% of free cyanide and 76% of Cu were removed under the following conditions: concentration of chlorine in electro-generated NaOCl, 5.2 g/L; volume ratio of NaOCl/leach solution, 1; pH, ~9.8; ambient temperature for 12 h. Then, magnetite adsorption for selective removal of remaining Cu (50.5 mg/L) was selected and more than 99% of copper ion was successfully removed with dosage 10g/100mL, shaking speed 150 rpm within 30 min. The results revealed that the alkaline chlorination using electro-generated NaOCl followed by magnetite adsorption could completely remove the cyanide and Cu, remaining Au in the final solution. [ABSTRACT FROM AUTHOR]

The present paper reports an improved process using cheaper reagent at atmospheric conditions compared to the expensive pressure leaching technique (Temperature = 140 °C) as well as other processes available at higher temperature. An effective baking reagent, potassium hydroxide (KOH) was used to dephosphorize monazite. Roasting studies were carried out to optimize various process parameters such as temperature, time and doses of baking reagents. The dephosphorization of monazite was completed in 30 min at temperature 250 °C and monazite:KOH ratio of 1:1 (wt/wt). The experimental data was validated scientifically using TG-DTA. Further, leaching studies with selected lixiviant was carried out to optimize various process parameters viz. leachant concentration, time, pulp density, temperature and dosage of hydrogen peroxide (H 2 O 2). More than 90% rare earth metals (REMs) were found to be leached from dephosphorized and washed residue using hydrochloric acid (HCl) at optimized condition i.e. 1 M HCl with 10% H 2 O 2 (v/v), temperature 80 °C, time 120 min and pulp density 50 g/L. The novel process flow-sheet after scale-up studies can be used for monazite processing in industries. Unlabelled Image • Energy saving atmospheric leaching process • Developed process can replace the conventional pressure leaching. • Effective baking reagent KOH is used to dephosphorize monazite. • From pre-treated monazite, >90% REMs was leached out. [ABSTRACT FROM AUTHOR]

A hydrochloric acid (HCl) leaching process with stannic chloride (SnCl 4 ) was proposed to leach Sn from waste Pb-free solder containing Sn, Ag, and Cu, where the oxidant stannic ion (Sn 4 + ) oxidizes Sn metal into stannous ion (Sn 2 + ). When Sn reagent-grade powder was leached in HCl solution with SnCl 4 , the leaching efficiency of Sn increased rapidly and the oxidation-reduction potential decreased with leaching time. In the leaching tests of Pb-free solder, the effect of factors such as the agitation speed, HCl concentration, pulp density, and temperature on the leaching behaviors of metals was investigated. The leaching efficiencies of Sn increased rapidly in the beginning of leaching with increasing agitation speed, HCl concentration, and temperature. The difference in the leaching efficiencies was negligible after 90 min under the following conditions: HCl concentration of 1–3 kmol m − 3 , agitation speed of 300–600 rpm, and temperature of 50 °C or 70 °C. Although the pulp density was increased from 1% to 2%, the Sn concentration dissolved did not exceed 10,500 g m − 3 because of the lack of oxidant, and the increase in the initial concentration of Sn 4 + as the oxidant could accelerate the leaching of Sn. A Sn leaching efficiency of greater than 99% was achieved in 1 kmol m − 3 HCl with 10,000 g m − 3 Sn 4 + at 400 rpm and 50 °C with 1% pulp density within 90 min. Ag was not detected in any of the leaching tests. Although the leaching solution contained 24.5 g m − 3 of Cu, the addition of Sn powder was successful in removing Cu from the solution via a cementation reaction. Thus, a Sn leaching solution was successfully obtained from Pb-free solder via HCl leaching with SnCl 4 . [ABSTRACT FROM AUTHOR]

The potential sweep method, adsorption kinetics and isotherm studies, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) after adsorption tests of copper(I) and gold(I) ions using magnetite were performed to investigate the mechanism of selective copper(I) adsorption over gold(I) ion from chloride solution with small amount of cyanide. The electrochemical analysis reveals that the reduction potential is −0.81 V for Au and + 0.38 V for copper (vs. Ag/AgCl) which lead to selective adsorption of Cu over Au from chloride solution with cyanide because the adsorption could be achieved when the reduction potential of the metal ion is higher that of Fe 2 O 3 /Fe 3 O 4 pair in the magnetite. By the kinetics and isotherm studies, the chemisorption was found to be well fitted to the pseudo-second-order model and monolayer adsorption of Cu ions on the surface of magnetite. The XPS and TEM results indicates that the ratio of Fe(II) in the iron of the magnetite decreased from 74% to 43% due to the oxidation. Consequently, the mechanism of adsorption using magnetite was depends on the reduction potential of metal ions to selectively receive electrons generated during the oxidation of magnetite in the chloride solution with cyanide. • Cu ion was adsorbed selectively on magnetite particle over gold ion. • Addition of cyanide ion decreased the reduction potential of Au ion. • The adsorption was found to be fitted to the pseudo-second-order model. [ABSTRACT FROM AUTHOR]

This study examined the reaction mechanism of arsenite, As(III), and antimonite, Sb(III), with iron sulfide and compared their pH-dependent reaction behaviors under strictly anoxic environments. The comparison of Sb(III) with As(III), based on their chemical similarity, may provide useful insight into understanding the geochemical behavior of the less studied Sb(III). The pH-dependent batch sorption studies revealed that As(III) and Sb(III) displayed similar removal trends with pH in terms of the removal efficiency. However, the aqueous As(III) species transformed to thioarsenite species, while aqueous Sb(III) species remained inert under the highly sulfidic anoxic system. An X-ray absorption spectroscopy study demonstrated the reaction of As(III) and Sb(III) at acidic pH was closely related to the precipitation of sulfide minerals As 2 S 3 and Sb 2 S 3 , respectively, as a consequence of the reaction with sulfide produced through mackinawite dissolution. Meanwhile, the removal at basic pH was inferred as a surface reaction, possibly through surface complexation, surface-precipitation, or both. In this study, the pH-dependent Sb(III) uptake mechanisms proved to be similar to the corresponding mechanisms for As(III) uptake, with mackinawite demonstrating a superior capacity to scavenge Sb(III) in ferrous and sulfide-rich reducing environments. [ABSTRACT FROM AUTHOR]

Present paper reports the systematic scientific studies for extraction of lanthanum (La) and neodymium (Nd) from chloride solution containing rare earth metals (REMs). The chloride leach liquor was generated by dissolving rare earth mineral and found to contain 0.53 g/L La and 1.01 g/L Nd along with other REMs. Initial extraction studies were carried out from a model solution containing La and Nd using 10% Cyanex 272 diluted in kerosene along with 2% isodecanol (ID) as phase modifier. Various process parameters viz. effect of pH, time, O/A ratio, loading capacity, etc. were optimized for maximum extraction. More than 97% La and Nd were extracted at an equilibrium pH of 3.3 and 2.7, respectively at phase ratio (O/A) 1:1 and mixing time of 5 min in two stages. 10% HCl was used to strip La as well as Nd from the loaded extractant. Moreover, 99.99% separation of La and Nd could also be achieved by stripping the loaded organic phase with pure Nd scrub solution. The optimum condition for extraction was validated with the actual solution. The result revealed that 99.49% La and 95.04% Nd can be extracted in 5 min at an equilibrium pH of 3.3 and 2.7, respectively at phase ratio 1:1. [ABSTRACT FROM AUTHOR]

Rare earth metals are essential ingredients for the development of modern industry as well as designing and developing high technology products used in our daily lives. Consequently, the worldwide demand of rare earth metals is rising quickly and predicted to surpass the supply by 40,000 tons annually. However, their availability is declining, mainly due to the export quotas imposed by the Chinese government and actions taken against illegal mining operations. This has laid emphasis to exploit and expand technologies to meet the future necessities of rare earth metals. Bastnasite, monazite, and xenotime are their chief mercantile sources, which are generally beneficiated by flotation, gravity or magnetic separation processes to get concentrates that are processed using pyro/hydrometallurgical routes. To develop feasible and eco-friendly processes, R&D studies are being conducted for the extraction of rare earth metals from leached solutions (chloride, nitrate, sulfate, thiocyanate, etc.) using different cationic, anionic and solvating solvents or ions depending on material and media. Commercial extraction of rare earth metals has been carried out using different extractants viz. D2EHPA, Cyanex 272, PC 88A, Versatic 10, TBP, Aliquat 336, etc. The present paper reviews the methods used for the recovery of rare earth metals from primary as well as secondary resources, with special attention to the hydrometallurgical techniques, consisting of leaching with acids and alkalis followed by solvent extraction, ion exchange or precipitation. The piece of comparative and summarized review will be useful for the researchers to develop processes for rare earth recovery under various conditions. [ABSTRACT FROM AUTHOR]

Abstract: Chromobacterium violaceum (C. violaceum), a cyanide generating bacterium has been used to leach out gold and copper from the waste mobile phone printed circuit boards (PCBs) containing ∼34.5% Cu and 0.025% Au in YP (yeast extract and polypeptone with glycine) medium. The bioleaching was carried out in an incubator shaker (150rpm) at 30°C and 15g/L pulp density in the pH range 8–11. Dissolution of gold and copper increased from 7.78% (0.225ppm) to 10.8% (0.46ppm) and 4.9% (419ppm) to 11.4% (879ppm) in 8days with increase in pH from 8 to 11 and 8 to 10 respectively. Supplementing oxygen with 0.004% (v/v) H2O2 increased the copper leaching to 24.6% (1743ppm) at pH 10 in 8days whereas improvement in gold leaching was insignificant with the recovery of 11.31% Au at pH 11.0. The waste PCBs can thus be recycled in environmental friendly manner. [Copyright &y& Elsevier]

Abstract: Huge amounts of effluent of low copper content are generated in electrical and electronic parts manufacturing industries. Here we report an adsorption process using strongly acidic exchanger Dowex G-26 for copper recovery from dilute sulfate solution containing 0.5–0.7 g/L copper, which is similar to the chemical and mechanical polishing (CMP) waste generated in electronic industries. The structures of activated and copper-loaded resins were compared by FT-IR spectroscopic characterization to confirm the adsorption phenomena. Various process parameters viz. contact time, solution pH, resin dose were investigated for copper recovery from the waste effluent. Copper adsorption from the solution was complete within a contact time of 14 min for an aqueous/resin (A/R) ratio of 100 mL/g and equilibrium pH of 2.5. The mechanism for copper adsorption by Dowex G-26 resin was found to follow a Langmuir isotherm and second-order reaction rate. 99.7% of the copper was eluted effectively from the loaded resin by 10% sulfuric acid at an A/R ratio of 25 in a contact time of 20 min to produce a copper-enriched solution. After copper recovery, the raffinate generated could be disposed safely without affecting the environment. [Copyright &y& Elsevier]

Abstract: In the present study, the leaching of copper using electro-generated chlorine in hydrochloric acid solution has been carried out. The behavior of cuprous ions during the electro-leaching of copper has been extensively investigated. During the leaching of copper with the electro-generated chlorine, the copper leached out as cuprous ions which were accumulated in the solution and affected the oxidation–reduction potential of the leaching solution. The increasing rate of cuprous concentration linearly decreased with current density, which was verified by the retardation of the oxidation–reduction potential drop. At a current density 400Am−2, the leaching rate of copper increased linearly with increase in stirring speed and became saturated at stirring speeds of more than 600rpm. When the supplement of cuprous ions to the anode was rapid enough to consume the applied charge, the anodic reaction changed from chlorine generation to cuprous oxidation. The change of the anodic reaction retarded the leaching of copper. Therefore, the cuprous ions generated from copper leaching simultaneously affected the leaching of copper and the anodic reaction. [Copyright &y& Elsevier]