Leaching Duration Research Articles

Microwave and Ultrasound Effect on Ammoniacal Leaching of Deep-Sea Nodules

The influence of ultrasound and microwaves on extraction of copper, nickel, and cobalt from manganese deep-sea nodules by reductive ammoniacal leaching in the presence of ammonium thiosulfate as a reducing agent was studied. The ultrasonic ammoniacal leaching provides higher metals extraction, while the effect of microwaves on the metals extraction under the studied leaching conditions is insignificant. In general, increasing leaching temperature increases significantly extraction of the metals of interest. At high temperatures, extraction efficiencies of copper, nickel, and cobalt decrease over longer leaching duration as a result of decomposition of the metals amino-complexes and reverse precipitation of metals. However, during the ultrasonic leaching at a temperature of 85 °C, the extraction of nickel remains almost unchanged over longer leaching durations and does not follow the decreasing course, observed in the extraction of copper and cobalt. The finding suggests that nickel can be selectively extracted from the nodules by the ultrasonic leaching. The maximal extraction efficiency of copper, nickel, and cobalt was 83%, 71%, and 32%, respectively, when the reductive ultrasonic ammoniacal leaching was carried out at 85 °C for 90 min. In the presence of microwaves, the maximal extraction efficiency of copper, nickel, and cobalt was 67%, 48%, and 8%, respectively, when the reductive ultrasonic ammoniacal leaching was carried out at the output power of 60 W for 210 min.

Influence of Thermal Treatment on Copper Extraction from Electronic Wastes

The results of studying the influence of the preliminary thermal treatment of crushed electronic waste (EW) at a temperature of 450°C on the copper extraction degree during the subsequent leaching of materials by solutions of nitric acid are presented. The waste of the electronic industry, in particular, automobile microcircuits and computer printed circuit boards, is chosen as a research object. It is experimentally determined that the percentage of the organic phase in the composition of the research object varies within the range of 20–25% of the mass of the crushed raw material. The results of thermogravimetric analysis (TGA) and X-ray fluorescence analysis (XRF) show that the maximum degree of organic removal and formation of oxide forms of metals are observed in the temperature range 400–450oC. A mathematical model of the copper leaching process from EW with nitric acid solutions is obtained. The optimum parameters for the process are found: the temperature in the system is 75°C, the duration of leaching is 150 min, and the concentration of acid is 4 M with the maximum copper extraction to the solution being 98%. A comparative analysis of leaching processes of two types of materials (after thermal treatment and without thermal treatment) was carried out. It is experimentally confirmed that, for materials after preliminary thermal treatment, more completed copper leaching from EW with nitric acid solutions of lower concentration is provided when compared to the leaching of raw materials without thermal treatment. It is proved that, due to the preliminary thermal treatment of the materials, phase changes occur in the composition of the research object, namely, the transition of metals to their oxide forms, which positively affects the degree of copper extraction from EW at the subsequent nitric acid leaching.

THERMAL TREATMENT INFLUENCE ON COPPER EXTRACTION FROM ELECTRONIC WASTE

The paper provides the results of studying the influence of preliminary thermal treatment of crushed electronic waste at a temperature of 450 °C on the copper extraction degree during subsequent material leaching by nitric acid solutions. Electronic industry waste, in particular automobile microcircuits and computer printed circuit boards, was chosen as a research object. It was experimentally determined that the percentage of the organic phase in the research object composition varies within 20–25 % of the crushed raw material mass. The results of thermogravimetric analysis (TGA) and X-ray fluorescence analysis (XRF) show that the maximum degree of organic removal and formation of metal oxides are observed in a temperature range of 400–450 °C. A mathematical model of copper leaching from electronic waste by HNO3 solutions was obtained. The optimum parameters for the process were found – the temperature in the system is 75 °C; leaching duration is 150 min; acid concentration is 4 M with a maximum copper extraction to the solution of 98 %. A comparative analysis of leaching processes for two types of materials (after thermal treatment and without it) was carried out. It was experimentally confirmed that copper leaching from electronic waste by nitric acid solutions with lower concentrations is more complete for materials after preliminary thermal treatment as compared to raw material leaching without thermal treatment. It was proved that preliminary thermal treatment leads to phase changes in the composition of the research object, namely, the transition of metals to their oxide forms, which positively affects the degree of copper extraction from electronic waste at subsequent nitric acid leaching.

UV-irradiation and leaching in water reduce the toxicity of imidacloprid-contaminated leaves to the aquatic leaf-shredding amphipod Gammarus fossarum.

Systemic neonicotinoid insecticides such as imidacloprid are increasingly applied against insect pest infestations on forest trees. However, leaves falling from treated trees may reach nearby surface waters and potentially represent a neonicotinoid exposure source for aquatic invertebrates. Given imidacloprid's susceptibility towards photolysis and high water solubility, it was hypothesized that the leaves' toxicity might be modulated by UV-irradiation during decay on the forest floor, or by leaching and re-mobilization of the insecticide from leaves within the aquatic ecosystem. To test these hypotheses, the amphipod shredder Gammarus fossarum was fed (over 7 d; n = 30) with imidacloprid-contaminated black alder (Alnus glutinosa) leaves that had either been pre-treated (i.e., leached) in water for up to 7 d or UV-irradiated for 1 d (at intensities relevant during autumn in Central Europe) followed by a leaching duration of 1 d. Gammarids' feeding rate, serving as sublethal response variable, was reduced by up to 80% when consuming non-pretreated imidacloprid-contaminated leaves compared to imidacloprid-free leaves. Moreover, both leaching of imidacloprid from leaves (for 7 d) as well as UV-irradiation reduced the leaves' imidacloprid load (by 46 and 90%) thereby mitigating the effects on gammarids' feeding rate to levels comparable to the respective imidacloprid-free controls. Therefore, natural processes, such as UV-irradiation and re-mobilization of foliar insecticide residues in water, might be considered when evaluating the risks systemic insecticide applications in forests might pose for aquatic organisms in nearby streams.

Study on the release characteristics of chlorine in coal gangue under leaching conditions of different pH values

A series of leaching experiments were carried out for evaluation of release behavior of Cl in Chinese coal gangue from Yangquan Coal Mine in Shanxi province under different pH conditions (pH = 2.6, 4.2, 6.5, 8.1, respectively) and different leaching durations (up to 105 h). The modes of occurrence of Cl in the coal gangue and its post-leached residues were extracted with sequential chemical extractions; chlorine in solution was determined using IC (ion chromatography); chemical and mineralogical compositions in coal gangue and the post-leached residues were determined by XRD (X-ray diffraction), XRF (X-ray fluorescence spectrum) and FT-IR (Fourier infrared spectrum). The results indicated that kaolinite, quartz, calcite, pyrite and illite were the predominant minerals in coal gangue with a certain amount of organic matter and a little mica. Chlorine in coal gangue occurred in a descending order of significance, as forms of organic matter (P5), Fe-Mn oxides (P4), water-soluble (P1), residue (P6), carbonate (P3), and exchangeable (P2), which accounted for 41.56%, 37.87%, 14.65%, 3.26%, 1.33% and 1.31%, respectively. With the rise of acidity of leaching solution, the reaction rates of most of matrix compositions in coal gangue increased, and more Cl was leached out in a shorter time. Under the condition of pH 2.6, 4.2, 6.5 and 8.1 and leaching duration up to 105 h, the leaching rate of Cl were respectively 57.21% (11.98%, 1.31%, 1.33%, 23.03% and 20.06% for P1, P2, P3, P4 and P5, respectively), 35.97% (8.18%, 1.31%, 0.78%, 14.77% and 10.91% for P1, P2, P3, P4 and P5, respectively), 26.65% (7.52%, 1.31%, 0.42%, 9.87% and 7.53% for P1, P2, P3, P4 and P5, respectively) and 18.98% (5.32%, 0.60%, 1.33%, 7.61% and 5.45% for P1, P2, P3, P4 and P5, respectively). Chlorine in coal gangue may pose an environmental risk with the increase of acidity of environmental aqueous solution.

Recovery of valuable metals from waste diamond cutters through ammonia–ammonium sulfate leaching

Copper and zinc were recovered from waste diamond cutters through leaching with an ammonia–ammonium sulfate system and air as an oxidant. The effects of experimental parameters on the leaching process were investigated, and the potential–pH (E–pH) diagrams of Cu–NH3–SO42−–H2O and Zn–NH3–SO42−–H2O at 25°C were drawn. Results showed that the optimal parameters for the leaching reaction are as follows: reaction temperature, 45°C; leaching duration, 3 h; liquid-to-solid ratio, 50:1 (mL/g); stirring speed, 200 r/min; ammonia concentration, 4.0 mol/L; ammonium sulfate concentration, 1.0 mol/L; and air flow rate, 0.2 L/min. The results of the kinetics study indicated that the leaching is controlled by the surface chemical reaction at temperatures below 35°C, and the leaching is controlled by diffusion through the product layer at temperatures above 35°C.

Hydrometallurgical Purification of Metallurgical Grade Silicon with Hydrogen Peroxide in Hydrofluoric Acid

The effect of adding hydrogen peroxide (H2O2) as an oxidizing agent on purifying metallurgical grade silicon (MG-Si) by leaching with hydrofluoric acid (HF) was studied as a function of leaching temperature, particle size, leaching duration and concentration of leaching agents. It was found that the extraction capacity for metallic impurities could be significantly enhanced with introducing H2O2 into HF lixiviant showing litter dependence on HF concentration. By leaching with 1 mol· L-1 HF plus 2 mol· L-1 H2O2 for only 0.25 h at 55 ℃, the MG-Si purity could be upgraded from 99.74% to 99.96%, to 99.99% with further prolonging leaching duration. The sensitivity sequences of precipitates to each etchant were obtained through revealing the micro-structural evolution of MG-Si before and after etching. With the help of Raman spectrometry, it was reasonable that etching silicon starts with first oxidizing reaction by H2O2 and then dissolved by HF. Like Si-Si bonds, some Si-F and Si-O bonds could also be found on silicon surface after acid etching with HF plus H2O2 etchant. After acid leaching, the zigzag silicon surface had been detected by using transmission electron microscopy analysis and the formation mechanism was further discussed. Figure 1

Nontarget Analysis via LC-QTOF-MS to Assess the Release of Organic Substances from Polyurethane Coating.

A novel approach was investigated for the assessment of leaching from a one-component polyurethane (1C-PU) coating used for hydraulic structures using nontarget analysis via LC-QTOF-MS. Leaching behavior of the 1C-PU coating was studied using experiments in which the coating was exposed to water for defined periods (6 h, 24 h, 3 d, 14 d). Three hardening durations for the 1C-PU coating were tested (0 h, 24 h, 14 d) as well as two water matrices (ultrapure water and river water), including a successive water renewal. Dissolved organic carbon, total nitrogen bound and nontarget measurements via LC-QTOF-MS showed that under all tested conditions organic substances were leached out of the 1C-PU coating. The shorter the hardening duration and the longer the leaching duration, the higher were the number and quantities of the eluted substances, while the influence of the water matrix was minor with respect to substance elution. Based on the MS2 spectra from the LC-QTOF-MS measurements, 30 substances released from the 1C-PU coating were tentatively identified. These substances belong to five chemical groups: derivatives of (i) N-(tosyl)carbamate, (ii) p-toluenesulfonamide (PTSA), (iii) 4,4'-methylenediphenyl diisocyanate (4,4'-MDI), (iv) toluenediisocyanate (TDI), and (v) oligo(ethylene) ([C2H4O]n) as well as p-toluenesulfonic acid. The identity of seven substances was confirmed by authentic reference standards, all of which exhibited an elevated bacterial toxicity to Aliivibrio fischeri. p-Toluenesulfonic acid was present in a German canal (Teltowkanal) with concentrations of up to 11 μg L-1.

Low-Temperature Pressure Leaching of Converter Matte in Sulfuric Acid Solutions

During treatment of copper-cobalt ores with a high nickel content of one of the domestic deposits by standard technology, it is expected to obtain converter matte containing, wt.%: 60–68 Ni, 7–9 Cu, 4–6 Fe, 2–3 Co, 21–23 S. It has been established for a model sample (wt. %: 62 Ni, 7.1 Cu, 3.7 Fe, 2.2 Co, 18 S) that processing converter matte under conditions of increased oxygen pressure is much more effective than under atmospheric conditions, and this is indicated by a reduction in the duration of pressure leaching (1.3–1.5 h) compared with leaching under atmospheric conditions (4–8 h), and also indices for extraction of economic components into solution (wt. %: 67 Ni, 99 Cu, 99 Fe). Due to the use of special experiment planning programs, a more complete study is achieved for the effect of oxygen pressure and temperature on leaching nickel, and also determination of the most effective production parameters for performing the process. In view of the low copper content, flotation separation of this converter matte is ineffective. Separation of copper and nickel is accomplished by selective pressure leaching of nickel from converter matte. It is established that as a result of selective leaching of nickel from copper-nickel converter matte the initial acid concentration has a considerable effect. It is possible to extract nickel into solution at the level of 50–55% and copper and iron are concentrated in cake (concentration in final solution is mg/dm3: 0.06 Cu and 0.62 Fe). A method is proposed for processing leaching products.

Optimization of recovering cerium from the waste polishing powder using response surface methodology

Abstract Recovery of rare earth from the waste rare earth polishing powder is of great importance to improve the process economics. The current recovery methods result in the generation of large quantities of polluted discharge necessitating waste treatment systems. The present work attempts to extract cerium from rare earth slurry waste by thiourea reducing and hydrochloric acid leaching, towards which central composite technique of the response surface methodology is adopted to design the experiments and to optimize the process conditions to maximize the recovery rate. The effects of four major parameters such as temperature, duration of leaching, dosage of thiourea, and the concentration of HCl were assessed, and the optimal process conditions were identified. Analysis of variance (ANOVA) was utilized to identify the suitable model and to eliminate the insignificant model parameters. The optimized process conditions for maximizing the recovery rate are identified to be a leaching temperature of 90°C, duration of 150 min, thiourea dosage of 0.2 g/g, and HCl concentration of 3.5 mol/l. A recovery of 91.23% could be achieved and validated through repeat experimental runs at the optimized process conditions. The optimized process samples are characterized utilizing XRD to validate the recovery.

Evaluation of temperature-time conditions for the chemical abrasion treatment of single zircons for U–Pb geochronology

Partial loss of radiogenic Pb and presence of older grains or cores (inheritance) are the main obstacles for accurate and precise U–Pb geochronology of magmatic zircons by ID-TIMS (isotope dilution thermal ionisation mass spectrometry). Sequential annealing and leaching (chemical abrasion, (Mattinson 2005)), restores crystallinity to zircons with low to medium radiation damage, and removes parts of the zircon with strongly radiation damaged crystal lattice, effectively eliminating Pb loss. The original version of chemical abrasion (Mattinson 2005) was designed for determination of precise 206Pb–238U plateau ages of multi-grain zircon populations, free from inheritance, using multiple dissolution steps. However, the main application of chemical abrasion is to date zircon populations potentially affected by both Pb loss and inheritance, which is commonly achieved by analysis of single zircon grains. Chemical abrasion of single zircon grains involves only one high temperature leaching step, since stepwise leaching is rarely possible or practical due to the small sample size. Despite the widespread use of single zircon chemical abrasion, the optimal temperature and duration of annealing and single step leaching have not been reported thus far. Furthermore, the temperature and time durations of chemical abrasion (apparently an ad-hoc adaptation of the findings of multi-grain, multi-step leaching experiments) vary substantially between published geochronological studies, leaving the possibility of incomplete removal of Pb loss and hence a potential bias in comparison of the ages. Here we report the results of a systematic study aimed at determination of optimal conditions for chemical abrasion of single zircon grains to ensure complete removal of zones that were affected by Pb loss in a single high temperature leaching step. The tests were performed on three different zircon standards with various ages (~418 to 3465Ma) using a three step partial dissolution technique. The optimal conditions for low to moderately radiation damaged zircons are annealing at 900°C for 48h and subsequent leaching at 190°C or slightly higher in concentrated HF in a pressurized vessel for 15h. Leaching at a lower temperature does not completely remove Pb loss. Annealing at higher temperature might be restoring crystallinity in the parts of zircon crystals that were affected by Pb loss.

NH4Cl selective leaching of basic oxygen furnace slag: Optimization study using response surface methodology

The basic oxygen furnace slag (SL) was selectively leached by NH4Cl. Response surface methodology and the central composite design (CCD) were employed in determining the optimal condition. The process parameters such as leaching duration, NH4Cl concentration, liquid solid ratio (LSR), and leaching temperature were chosen as independent variables in CCD. The quadratic model was developed for process optimization and statistical experimental designs. It is found that the leaching duration, NH4Cl concentration and liquid solid ratio are significant to the extraction of Ca2+ and Mg2+. The optimal conditions with setting maximum extraction of calcium and magnesium cations from SL are as following: 68 min (X1), 1.8 mol/L NH4Cl (X2), LSR 12 mL/g (X3), 53°C (X4), with the predicted Ca2+ and Mg2+ concentration reaching 13.3 and 3.2 g/L, respectively. The proposed simplified leaching mechanism indicates a two‐stage leaching. The prone leachable MgFe2O4 and Ca2Fe2O5 are extracted in the fast stage, while the extraction of CaO occurs throughout slow stage. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1387–1394, 2016

LEACHING BEHAVIOUR OF A TURKISH LATERITIC ORE IN THE PRESENCE OF ADDITIVES

This paper investigates the dissolution mechanism of a lateritic nickel ore from the Caldag Region of Manisa in Turkey. The ore sample contained 1.2% Ni, 24.8% Fe, and 0.062% Co. The optimum leaching conditions were found to be temperature 80 o C, particle size -74 µm, H2SO4 concentration 200 g/dm 3 , solids ratio (by weight) 10% and leaching duration 8 h. The extractions of 98.2% Ni, 98.6% Fe and Co 98.9% were obtained under these conditions. Additionally, the effects of additional substances such as NaCl, Na2S2O5, Na2SO4, and KCl were investigated in order to decrease the leaching duration. The results showed that the additives accelerated the leaching kinetics and achieved nearly the same nickel and cobalt extractions at the end of 4 h compared to the results obtained after 8 h without the additives. If the additives containing chlorine were used, it was determined that the iron extraction showed no increase, although both the nickel and cobalt extractions increased.

Tuning of textural properties of germanosilicate zeolites ITH and IWW by acidic leaching

The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions (e.g. temperature, pH, duration) of acidic leaching was shown. While the growth of the temperature of acid treatment caused the increasing amount of leached Ge atoms and enhancing volumes of both micro and mesopores at 80 °C, the mesopore volume in ITH (Si/Ge = 3.4 and 5.8) and IWW (Si/Ge = 3.3) zeolites changed with the duration of the treatment (pH = 2; T = 80 °C) as follows: 96 h < 1 h < 24 h. Independently on the chemical composition and zeolite topology, the treatment of germanosilicate zeolites at pH = 2–7 resulted in development of both micro and mesoporosity accompanied by the extraction of substantial amount of Ge atoms, while the increasing acidity up to pH = 0 resulted in some reduction of Ge extraction and in the development of mesopores at maintained value of micropore volume when compared with initial germanosilicates. The higher activity (i.e. number of reactant molecules converted per active site) of germanosilicate with modified micro-mesoporous channel system in comparison with parent IWW zeolite in esterification of levulinic acid was attributed to enhanced accessibility of active sites.

Comparison of ultrasonic-assisted and regular leaching of germanium from by-product of zinc metallurgy

A major source of germanium recovery and also the source of this research is the by-product of lead and zinc metallurgical process. The primary purpose of the research is to investigate the effects of ultrasonic assisted and regular methods on the leaching yield of germanium from roasted slag containing germanium. In the study, the HCl–CaCl2 mixed solution is adopted as the reacting system and the Ca(ClO)2 used as the oxidant. Through six single factor (leaching time, temperature, amount of Ca(ClO)2, acid concentration, concentration of CaCl2 solution, ultrasonic power) experiments and the comparison of the two methods, it is found the optimum collective of germanium for ultrasonic-assisted method is obtained at temperature 80°C for a leaching duration of 40min. The optimum concentration for hydrochloric acid, CaCl2 and oxidizing agent are identified to be 3.5mol/L, 150g/L and 58.33g/L, respectively. In addition, 700W is the best ultrasonic power and an over-high power is adverse in the leaching process. Under the optimum condition, the recovery of germanium could reach up to 92.7%. While, the optimum leaching condition for regular leaching method is same to ultrasonic-assisted method, except regular method consume 100min and the leaching rate of Ge 88.35% is lower about 4.35%. All in all, the experiment manifests that the leaching time can be reduced by as much as 60% and the leaching rate of Ge can be increased by 3–5% with the application of ultrasonic tool, which is mainly thanks to the mechanical action of ultrasonic.

Reductive acid leaching of cadmium from zinc neutral leaching residue using hydrazine sulfate

Zinc neutral leaching residue (ZNLR) from hydrometallurgical zinc smelting processing can be determined as hazardous intermediate containing considerable amounts of Cd and Zn which have great threats to the environment. The ZNLR contained approximately 35.99% Zn, 15.93% Fe and 0.26% Cd, and Cd mainly existed as ferrites in the ZNLR in this research. Reductive acid leaching of ZNLR was investigated. The effects of hydrazine sulfate concentration, initial sulfuric acid concentration, temperature, duration and liquid-to-solid ratio on the extraction of Cd, Zn and Fe were examined. The extraction efficiencies of Cd, Zn and Fe reached 90.81%, 95.83% and 94.19%, respectively when the leaching parameters were fixed as follows: hydrazine sulfate concentration, 33.3 g/L; sulfuric acid concentration, 80 g/L; temperature, 95 °C; duration of leaching, 120 min; liquid-to-solid ratio, 10 mL/g and agitation, 400 r/min. XRD and SEM-EDS analyses of the leaching residue confirmed that lead sulfate (PbSO4) and hydrazinium zinc sulfate((N2H5)2Zn(SO4)2) were the main phases remaining in the reductive leaching residue.

Are we getting accurate measurements of Ksat for sodic clay soils?

In this paper we discuss the use of a series of column experiments to improve understanding of the effect irrigation water chemistry (saline solutions) has on measurements of saturated hydraulic conductivity (Ksat) of a sodic clay soil. We highlight in particular the use of extended leaching periods to determine whether the duration of leaching affects the results.In the experiments, mixed cation solutions of two different salinity levels, 50meq/L and 100meq/L, were applied under constant head to columns of a repacked sodic clay soil using three replicates for each treatment. The maximum Ksat measured during leaching with the 100meq/L solution was approximately double the maximum Ksat measured during leaching with the 50meq/L solution. Measured flow rates were found to increase rapidly after flow commenced then decrease gradually until flow rates became stable. The final, stable flow rate was roughly 80% less than the maximum flow rate measured. Reasons for these changes in saturated hydraulic conductivity are discussed. The key finding from these experiments is that long term leaching, involving significantly more pore volumes than is commonly reported in the literature, is required to obtain a ‘stable’ Ksat. We recommend that further studies be carried out to (1) determine whether similar behaviour in Ksat occurs in a wide range of sodic clay soils and (2) to help build a better understanding of the causes and implications of the observed behaviour in Ksat.

THE INFLUENCE OF PRE-AERATION ON CYANIDE LEACHING OF A NON-REFRACTORY SULPHIDE GOLD AND SILVER ORE

The leaching behaviour of a sulphide gold-silver ore was investigated in terms of a relationship between gold and silver extractions and cyanide consumption. Ninity five Au % and 88.0% Ag extractions were obtained under the determined conditions of 24 h leaching duration, -74 µm particle size, 40% solids ratio, 4 g/dm 3 NaCN concentration, and 450 rpm stirring speed with NaCN consumption of 3.35 g/dm 3 . Since the NaCN consumption was higher than in industrial applications, Pb(NO3)2 and H2O2 additions and aeration using an air pump were tested during leaching in order to decrease the consumption. While Pb(NO3)2 addition with aeration caused a decrease in the metal extractions, the individual or combined additions of H2O2 and aeration could not provide a reduction in the cyanide consumption. Therefore, the effect of the pre-aeration followed by cyanidation was tested. Eventually, applying 4 h of pre-aeration before a shorter leaching duration of 12 h provided 92.0% Au and 90.5% Ag extractions with a reduced NaCN consumption of 2.44 g/dm 3 .

Selective extraction of Mo from a Ni–Mo ore using pressure alkaline leaching

Pressure alkaline leaching of a Ni–Mo ore for selective extraction of Mo was investigated. Thermodynamic analysis of Mo–S–H2O and Ni–S–H2O indicated that pressure alkaline leaching of Ni–Mo ore is technically feasible for selective extraction of Mo. The effects of NaOH concentration, temperature, leaching duration, liquid/solid ratio and particle size on the leaching of Mo and Ni were studied. The results showed that Mo extraction was improved significantly by NaOH concentration, temperature or leaching duration, but not by liquid/solid ratio or particle size. The optimum parameters were: NaOH concentration of 100g/L, temperature of 120°C, leaching duration of 5h, liquid/solid ratio of 3mL/g and particle size of 74–98μm. Under these conditions, about 95.7% of Mo and 1.3% of Ni could be extracted.

Copper leaching from waste electric cables by biohydrometallurgy

This study examines the leaching of copper from waste electric cables by chemical leaching and leaching catalysed by Acidithiobacillus ferrooxidans in terms of leaching kinetics and reagents consumption. Operational parameters such as the nature of the oxidant (Fe3+, O2), the initial ferric iron concentration (0–10g/L) and the temperature (21–50°C) were identified to have an important influence on the degree of copper solubilisation. At optimal process conditions, copper extraction above 90% was achieved in both leaching systems, with a leaching duration of 1day. The bacterial leaching system slightly outperformed the chemical one but the positive effect of regeneration of Fe3+ was limited. It appears that the Fe2+ bio-oxidation is not sufficiently optimised. Best results in terms of copper solubilisation kinetics were obtained for the abiotic test at 50°C and for the biotic test at 35°C. Moreover, the study showed that in same operating conditions, a lower acid consumption was recorded for the biotic test than for the abiotic test.