Multi-metal System Research Articles

Hydrochar from sawdust and sewage sludge – a potential media for retaining heavy metals in sustainable drainage systems (SuDS)

ABSTRACT Waste valorization is an essential aspect of sustainable development. From this perspective, co-hydrothermal carbonization (Co-HTC) is a promising thermochemical process for converting organic waste into hydrochar. Hydrochar is a solid material whose physicochemical properties could make it suitable for adsorbing pollutants such as heavy metals. Accordingly, this work evaluated the hydrochar from Co-HTC of sawdust and non-dewatered sewage sludge as a potential adsorbent of heavy metals at low concentrations. In the context of sustainable drainage systems (SuDS), it is notable that heavy metals are present at very low but still potentially harmful concentrations, which presents a potential opportunity for the application of hydrochar. Thus, three hydrochars (H-180, H-215, and H-250), produced by Co-HTC at 180, 215, and 250 °C, were tested herein for their ability to retain lead (Pb2+). The H-180 presented better performance than other hydrochars (H-215 and H-250), suggesting that chemisorption could be the main adsorption mechanism. Interestingly, the presence of other cationic heavy metals (Cu2+, Zn2+, Cd2+, Cr6+, and Ni2+) did not hinder the Pb2+ adsorption, for which the removal efficiency remained close to 100%. In fact, in such a multi-metal system, hydrochar can be suitable for capturing both lead and cadmium. Therefore, the hydrochar from Co-HTC of sawdust and non-dewatered sewage sludge can be useful for removing heavy metals at low concentrations, such as those found in urban runoff waters. Although further studies are required, these findings suggest hydrochar as a potential material for application in SuDS.

Resourcization of Argillaceous Limestone with Mn3O4 Modification for Efficient Adsorption of Lead, Copper, and Nickel.

Argillaceous limestone (AL) is comprised of carbonate minerals and clay minerals and is widely distributed throughout the Earth's crust. However, owing to its low surface area and poorly active sites, AL has been largely neglected. Herein, manganic manganous oxide (Mn3O4) was used to modify AL by an in-situ deposition strategy through manganese chloride and alkali stepwise treatment to improve the surface area of AL and enable its utilization as an efficient adsorbent for heavy metals removal. The surface area and cation exchange capacity (CEC) were enhanced from 3.49 to 24.5 m2/g and 5.87 to 31.5 cmoL(+)/kg with modification, respectively. The maximum adsorption capacities of lead (Pb2+), copper (Cu2+), and nickel (Ni2+) ions on Mn3O4-modified argillaceous limestone (Mn3O4-AL) in mono-metal systems were 148.73, 41.30, and 60.87 mg/g, respectively. In addition, the adsorption selectivity in multi-metal systems was Pb2+ > Cu2+ > Ni2+ in order. The adsorption process conforms to the pseudo-second-order model. In the multi-metal system, the adsorption reaches equilibrium at about 360 min. The adsorption mechanisms may involve ion exchange, precipitation, electrostatic interaction, and complexation by hydroxyl groups. These results demonstrate that Mn3O4 modification realized argillaceous limestone resourcization as an ideal adsorbent. Mn3O4-modified argillaceous limestone was promising for heavy metal-polluted water and soil treatment.

The shells of edible freshwater snails as a biosorbent for multi-metal ions from wastewater: Implication in effluent purification and waste valorisation

The generation of waste shells of edible freshwater snails, Filopaludina bengalensis and Pila globosa, following human consumption and use in aquaculture, encourages their utilisation as a potential biomaterial. In this experiment, we employed the shell dust derived from F. bengalensis (FSD) and P. globosa (PSD) shells as a biosorbent of Cd2+, Co2+, Cr2O72- and Cu2+ from single- and multi-metal solutions. The results of batch adsorption experiments and characterisation of FSD and PSD using SEM, EDS, ICP-OES, FTIR, and XRD indicated that the metal ion removal process involved chemical adsorption (formation of CdCO3, Cu2CO3(OH)2 and CoCO3), ion exchange (reduced quantity of various elements on the shell dust following their release into the solution during adsorption) and surface precipitation. The best-fitted Langmuir isotherm specified monolayer adsorption with maximum adsorption capacity for Cd2+ (in single-metal system: FSD- 254.42, PSD- 327.76 mg/g; in multi-metal system: FSD: 93.79, PSD: 94.45 mg/g) and Cu2+ (in single-metal system: FSD- 234.63, PSD- 289.71 mg/g; in multi-metal system: FSD: 150.01, PSD: 160.51 mg/g). In multi-metal systems, the adsorption of Cd2+ and Cu2+ was antagonistic, and the adsorption of Co2+ and Cr2O72- was synergistic in nature. The thermodynamic parameters suggest that the adsorption is endothermic, feasible and spontaneous. The successful removal of metal ions from single- and multi-metal solutions and real wastewater recommended FSD and PSD as eco-friendly and low-cost biosorbent for wastewater amelioration with implication in waste valorisation.

Wetting mechanisms in the mass transfer process of CuSi3 droplets on the TC4 and 304SS multi-metal system controlled by the hybrid shielding gas atmosphere

To explore the synergistic wettability of the Ti-Cu-Fe multi-metal system, the wetting behaviors of CuSi3 droplets on the TC4 and 304SS plates during the cold metal transfer welding process in various gas atmospheres were studied in this work. The effects of Ti, Fe, Si, C, and O on the spreading dynamics of liquid Cu were analyzed in detail. The results reveal that the CO2 + Ar hybrid gas shielding atmosphere significantly affects the interfacial mass transfer. The sufficient interfacial reaction and increased element diffusion promoted the formation of Ti2Cu/TiCu multiphase microstructure at the Cu/Ti interface instead of a continuous Ti2Cu layer, and a thicker and loose Fe (s, s) layer was formed at the Cu/Fe interface. The variations of surface phase composition and the generation of inward flow weakened the wettability of CuSi3/TC4 and CuSi3/304SS systems. The dissolution of Si and surface adsorption of O decreased the σlv of liquid Cu, whereas Ti and Fe had the opposite effect. When the shielding gas changed from pure Ar to CO2 + Ar hybrid gas, the potential spreading model of the CuSi3/TC4 system changed from reaction-limited to diffusion-limited, and the wetting activation energy increased from 46 kJ/mol to 57 kJ/mol. Removing oxide film, forming Ti2Cu and diffusion of Ti controlled the wetting. Whereas for the CuSi3/304SS system, the potential spreading model changed from diffusion-limited to a molecular dynamics model. Removing oxide film, diffusion of Fe and interfacial adsorption were the dominant factors for wetting.

Adsorption studies of a multi-metal system within acetate media, with a view to sustainable phosphate recovery from sewage sludge

Phosphate shortages and the ensuing pressures on food security have led to an interest in processed sewage sludge as a substitute for commercial fertilisers. The presence of heavy metals in this nutrient source causes concerns around environmental release and pollution. This work builds towards a resin-in-pulp sludge detoxification process. It showcases the kinetic and thermodynamic adsorption capabilities of the ion-exchange resins C107E (carboxylic acid functionality), MTS9301 (iminodiacetic acid) and TP214 (thiourea), with respect to Cu(II), Fe(II), Pb(II) and Zn(II), within a simulated sewage sludge weak acid (acetate) leachate. The isotherms produced in this complex system were quite different to those generated when single metals were investigated in isolation, with desorption of lower affinity species clearly observed at higher equilibrium concentration values. Mixed-metal isotherm data were fitted to common two-parameter isotherm models and also a novel modified Langmuir model, which better accounted for the effects of desorption and competition. Kinetic data were also fit to common two-parameter models; results suggesting the system was likely film diffusion-controlled and followed pseudo-2nd-order kinetics. C107E displayed rapid adsorption of lead (t1/2 = 26 ± 3min), and significant uptake of all metals. MTS9301 showed high affinity for copper ions, with concurrent desorption of all the other metals, and also displayed the fastest kinetics (t1/2 = 14.1 ± 0.9, 130 ± 20, 25 ± 5 and 49 ± 6 min for copper, iron(II), lead and zinc, respectively). C107E and MTS9301 showed far slower adsorption for iron(II) than the other three metals, which invited the possibility of kinetic separations. TP214 had reasonable effectiveness in removal of copper, but poor affinity for all other metals. The greatest difficulty in modelling the multi-metal system was the two-stage trends observed in equilibrium experiments, as metal-proton exchanges become metal-metal exchanges. While not having the highest capacity, MTS9301 was recommended as the most appropriate resin for rapid and efficient removal of Cu, Pb and Zn from the acetate medium.

Selective recovery of lithium from spent coin cell cathode leachates using ion imprinted blended chitosan microfibers: Pilot scale studies provide insights on scalability

We report an approach on specific and scalable recovery of lithium ions from coin cells using functionalized chitosan microfibers. Low swelling ratios and high degree of crosslinking resulted from a dual combination of blended viscosities and crosslinking. Owing to their defined structure (pore diameter: 2.29±0.31 µm; fiber diameter: 176.5±3.44 µm; ion exchange capacity: 8.45 meq/g), imprinted microfibers exhibited high lithium uptake potential (100 mg/g), high distribution coefficient (6969.7 mL/g) and high separation factors (90) in a multi-metal system generated from leachates (co-ions: Co(II), Ag(I), Mn(II), Cu(II), Al(III), Ni(II), Na(I), K(I) and Ca(II)). The uptake phenomena followed a homogeneous monolayer adsorption mode and a spontaneous endothermic nature (ΔG:-20.3 KJ/mol). High values of relative lithium sorbed (RLS) (>20) and relative lithium released (RLR) (>9) in case of imprinted microfibers suggested high selectivity. Batch conditions showed a selective recovery of 45.7%/g/L of leachates (< 50 cathodes) at pH of 6.1. However, packed bed column studies showed that 14.3 g of biosorbent could recover up to 99.1% lithium (recovered lithium of up to 971.19 mg/L) over 9 cycles (250 cathodes; CoLi: 976.33 mg/L). The present study suggested blended and imprinted chitosan microfibers as a useful matrix towards scalable lithium recovery.

Thermodynamic and Kinetic Adsorption Studies of a Multi-Metal System within Acetate Media, with a View to Sustainable Phosphate Recovery

Thermodynamic and Kinetic Adsorption Studies of a Multi-Metal System within Acetate Media, with a View to Sustainable Phosphate Recovery

High-efficiency removal of lead/cadmium from wastewater by MgO modified biochar derived from crofton weed

The adsorption performance and mechanisms of Pb2+ and Cd2+ in wastewater using MgO modified biochar derived from crofton weed (MBCW600) are investigated. The Pb2+ and Cd2+ adsorption capacities of MBCW600 by the Hill model reach 384.08 mg/g and 207.02 mg/g, respectively, which is larger than that of original biochar. Pb2+ could be more easily captured by MBCW600 compared to Cd2+ in the multimetal system. Mg2+ contributes to Pb2+ and Cd2+ adsorption among coexisting cations. The exhausted MBCW600 could be well regenerated by simple method after use. The adsorption mechanism study indicates that Pb2+ and Cd2+ removal are primary contributed to mineral precipitation and ion exchange. The effective treatment volumes of Pb2+ and Cd2+ wastewater achieve 3050 mL and 2150 mL in the fixed-bed column experiment, respectively. Therefore, MBCW600 presents remarkable adsorption capability, excellent recoverability and large throughput, which shows the potential application in future treatment of wastewater containing heavy metal.

Competitive adsorption and mechanism of hexahydroxy metallic system by aminated solution-blown polyacrylonitrile micro/nanofibers

AbstractAdsorptive properties for Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) onto amidoxime-functionalized polyacrylonitrile (APAN) micro/nanofibers were systematically investigated in a hexahydroxy metallic solution system using batch experiments. The interactive effect of multi-metal ions in multi- metal systems was antagonistic in nature, and the adsorption capacity in a multi-metal system was lower than that in a single-metal system. The Langmuir isotherm model could explain respectively the isotherm and kinetic experimental data for the hexahydroxy metallic system with much satisfaction. The maximum adsorption capacity in hexahydroxy metallic for Cd(II), Cr(III), Cu(II), Ni(II), Pb(II) and Zn(II) was calculated to be 98 mg/L, 158 mg/L, 80 mg/L, 76, 312 and 58 mg/L individually. The APAN micro/nanofibers possessed good selectivity toward Pb(II) and Cr(III), over Cd(II), Cu(II), Ni(II), and Zn(II), having the highest selectivity coefficients at 17.52 and 6.07 in the test range. The five adsorption-desorption cycle experiments exhibited that APAN micro/nanofibers adsorbent are readily reusable, and have potential for heavy metal removal from wastewater. The adsorption behavior in multi-metal systems was shown to be complex, including surface complexation, antagonistic competition and displacement reactions. The diversity and selectivity in metal ion adsorption onto the micro/nanofibers relate mainly to the stability constants, and the microscopic coupling mechanism between the heavy metal ions and the functional groups on the fiber surface. This interaction mechanism between the favorable component and other metal ions could contribute significantly to the direct displacement impact illustrated schematically.

Evaluación de la tolerancia de Aspergillus terreus a metales tóxicos

Introduction: Metal pollution is one of the major environmental problems. Some metals are toxic at very low concentrations, bioaccumulate and do not decompose to non-toxic forms. Objective: To isolate a strain of microscopic fungus in a site contaminated with toxic metals and to evaluate the tolerance to these substances. Materials and methods: Fungi were isolated from the soil of an abandoned lead mine. Tolerance index of fungi to cadmium, mercury and lead was evaluated individually at concentrations of 50, 100, 250, 350 and 500 ppm; in addition, a multimetal system (mixture) with cadmium, chromium, mercury and lead was evaluated at 4, 8, 16, 64, 80, 120, 200 and 400 ppm. The minimum inhibitory concentration (MIC) was also determined. Results and discussion: The isolated fungi were identified as Aspergillus terreus, which showed high tolerance indices for lead (0.9) at all concentrations tested and indices of 0.8 at most mercury concentrations. Cadmium was the most toxic metal; tolerance indices of 0.56 and 0.2 were observed at 50 ppm and 100 ppm, respectively. High tolerance indices (0.9) were observed in the multimetal system up to 64 ppm. MIC was greater than 500 ppm with lead and mercury, less than 250 ppm with cadmium and greater than 400 ppm with the multimetal system. Conclusion: A. terreus showed high tolerance to lead at all concentrations tested. The level of tolerance is influenced by the type of metal.

Functionalized agro-waste for toxic metal remediation from water bodies: A green pre-treatment process

A site-specific functionalized novel bio-adsorbent (seed composite; MOLL) was used for the remediation of toxic metal ions from the water bodies. The graft co-polymerization using acrylic acid has been carried out onto the polyvinyl alcohol encapsulated seed composite to enrich the bio-adsorbent surface with numerous active carboxylic functionalities responsible for the enhancement in the remediation of cationic metal ions from aqueous system. The morphology, surface area, porosity, presence of functionalities and thermal stability were characterized using SEM-EDX, BET, FTIR and TGA. The functionalized bio-adsorbent (AA-g-PVA-SC-en) exhibited excellent remediation of metals (Pb2+, Cd2+, Cr3+and Ni2+) in the range (90% − 98%) with adsorption capacity (22.44 – 24.73 mg/g). The adsorption capacities in both a single metal and multi-metal system far exceeds from other bio-adsorbents reported so far. The regeneration of functionalized bio-sorbent remained up to six cycles. The findings open up new avenues for the development of a green pre-treatment approach for water remediation, prior to the large scale chemical treatment.

Lead and cadmium clean removal from wastewater by sustainable biochar derived from poplar saw dust

Biochar is produced at 400–800 °C by pyrolysis of poplar saw dust, which is used as the sustainable adsorbent to investigate the adsorption performance of Pb2+/Cd2+ from wastewater. The adsorption kinetics and isotherms of Pb2+/Cd2+ on biochar were determined. The maximum adsorption amount of Pb2+ is 62.68 mg/g, while that of Cd2+ is 49.32 mg/g at pH of 5 based on Langmuir equation. The Cd2+ adsorption was seriously inhibited, while the uptake of Pb(II) was not significantly affected in the multimetal system. The adsorption performance of Pb2+/Cd2+ was also investigated in different water systems. Mineral precipitation with Pb2+ is predominant mechanism for Pb2+ removal with the contribution proportion of 51.76%. Coordination with π electrons is the primary mechanism for Cd2+ adsorption, at 59.36% of the total adsorption capacity. Our findings provide a successful example of poplar saw dust converting into the sustainable adsorbent for Pb2+/Cd2+ removal from wastewater to implement the concept of “clean production”, which is worthy of further study.

Biosorption of Cu2+, Pb2+, Cd2+ and their mixture from aqueous solutions by Michelia figo sawdust

The study aimed at investigating copper, lead, and cadmium removal from both single and mixed metal solutions by Michelia figo (Lour.) Spreng. wood sawdust treated with 0.5 mol l−1 NaOH for four hours. In order to evaluate the effects of each factor and interactions between factors on metal ion biosorption, a 23 factorial experimental design was applied. FTIR results showed that the metal ions would bind to the hydroxyl and carboxyl groups of M. figo wood sawdust biomass. The main effects and interactions of three factors pH (3 and 5), initial metal ion concentration (C0, 0.157 and 1.574 mmol L−1), and dosage of biomass (D, 4 and 10 g L−1) at two levels were analyzed. The most significant variable regarding Cu2+ and Pb2+ biosorption was initial metal iron concentration. For Cd2+, pH was found to be the most significant factor. The maximum removal efficiencies were 94.12 and 100% for Cu2+ and Cd2+, respectively, at conditions of (+ 1, − 1, + 1): pH 5, initial metal concentration 0.157 mmol L−1 and dosage of biomass 10 g L−1, while 96.39% for Pb2+ at conditions of (− 1, − 1, + 1): pH 3, initial metal concentration 0.157 mmol L−1 and dosage of biomass 10 g L−1. There were some interactions between factors: pH*C0 and C0*D for Cu2+, pH*C0, pH*D and C0*D for Pb2+, pH*C0 and C0*D for Cd2+. Biosorption from a multi metal system showed that the presence of Cu2+ and Cd2+ had no significant influence on the Pb2+ removal, while Pb2+ in solution significantly decreased the removal efficiencies of the other two metals.

Recovery of Gold in Au/Cu/Mg System from SH/Fe3O4@SiO2 as a Magnetically Separable and Reusable Adsorbent

The recovery of Au(III) in the Au/Cu/Mg system from mercapto-silica hybrid coated magnetite (SH/Fe3O4@SiO2) adsorbent has been investigated. This adsorbent characterized using FT-IR to determine functional groups, crystallinity study using XRD, surface morphology using SEM, material compositions with XPS, surface area using nitrogen adsorption, and TGA to study thermal stability. Adsorption of metal ions carried out with batch system for 30 minutes at a pH of 3. In the Au/Cu/Mg multi-metal system, Au(III) ions were easily desorbed (approximately 85%) by SH/Fe3O4@SiO2 adsorbent based on HSAB (Hard Soft Acid Base) theory that Au(III) ion is a softer metal than Cu(II) and Mg(II) where Au(III)&gt;Cu(II)&gt;Mg(II). The recovery of Au(III) ions was easily desorbed using thiourea 7% in 0,1 M HCl solution with the percentage of 79%. The process of SH/Fe3O4@SiO2 adsorbent separation after adsorption and recovery was very easy. The adsorbent could perfectly separate in 5 minutes using an external magnet. The SH/Fe3O4@SiO2 adsorbent can be reused on the adsorption-desorption process of Au(III) in the Au/Cu/Mg system approximately four times of cycle reactions.

Recovery of Gold in Au/Cu/Mg System from SH/Fe3O4@SiO2 as a Magnetically Separable and Reusable Adsorbent

The recovery of Au(III) in the Au/Cu/Mg system from mercapto-silica hybrid coated magnetite (SH/Fe3O4@SiO2) adsorbent has been investigated. This adsorbent characterized using FT-IR to determine functional groups, crystallinity study using XRD, surface morphology using SEM, material compositions with XPS, surface area using nitrogen adsorption, and TGA to study thermal stability. Adsorption of metal ions carried out with batch system for 30 minutes at a pH of 3. In the Au/Cu/Mg multi-metal system, Au(III) ions were easily desorbed (approximately 85%) by SH/Fe3O4@SiO2 adsorbent based on HSAB (Hard Soft Acid Base) theory that Au(III) ion is a softer metal than Cu(II) and Mg(II) where Au(III)&gt;Cu(II)&gt;Mg(II). The recovery of Au(III) ions was easily desorbed using thiourea 7% in 0,1 M HCl solution with the percentage of 79%. The process of SH/Fe3O4@SiO2 adsorbent separation after adsorption and recovery was very easy. The adsorbent could perfectly separate in 5 minutes using an external magnet. The SH/Fe3O4@SiO2 adsorbent can be reused on the adsorption-desorption process of Au(III) in the Au/Cu/Mg system approximately four times of cycle reactions.

Targeted recovery of Ag-Pd alloy from polymetallic electronic waste leaching solution via green electrodeposition technology and its mechanism

Electronic waste (e-waste), as hazardous waste, is a promising secondary resource of precious metals. The extraction of precious metals from e-waste has great environmental and economic benefits. Most of the existing methods have high energy consumption, environmental pollution or low recovery efficiencies. This study proposed the application of green electrodeposition technology to realize targeted recovery of Ag-Pd alloy from Ni, Cu, Ag, Pd, Bi polymetallic e-waste leaching solution. Linear sweep voltammetry was conducted to determine the feasibility of targeted extraction. The high purity of Ag-Pd alloy was realized by controlling the potential. The recovery efficiencies of Ag and Pd were 97.72% and 98.05% after 5 h in 0.5 mol/L HNO3 with applied potential of 0.35 V. The results indicated the formation of monophase Ag-Pd alloy. Besides, the effect of acidity and potential on the particle size of alloy was analyzed. Chronoamperometric method was applied to study the electrodeposition mechanism. The Ag-Pd electrodeposition followed three-dimensional instantaneous nucleation and growth mechanism analyzed with Scharifker-Hills model, thus producing a solid solution. The nucleation site increased with the overpotential. This study provides a novel, efficient and green approach for the targeted recovery of Ag and Pd from the complex multi-metal system of e-waste.

Facile indium recovery from waste liquid crystal displays: Chloride-facilitated indium electroreduction and stepwise Cu/MoO2 and indium electrodeposition

With a huge amount of waste liquid crystal displays (LCDs) generated annually, their proper recycling raises continuous concern to realize pollution control (heavy metal and liquid crystal) and resource recovery (indium). However, due to their multi-metal feature, traditional hydrometallurgy lacks of sufficient selectivity, which makes the recycling route lengthy, costly, and generate more waste. Electrodeposition acts as a promising technique for selective metal extraction from multi-metal system due to its high selectivity and electron as clean reagent. To fully develop its application in metal recovery, stepwise Cu/MoO2 and In electrodeposition from In-Cu-Mo-Fe waste LCD leachate is explored in depth. Electrochemical behavior analysis shows Cu and MoO2 can be first electrodeposited for their higher electroreduction potential. Cl- plays a key role in accelerating indium electroreduction kinetics, which largely shortens the extraction time without the sacrifice of current efficiency. This accelerating effect is attributed to the increased concentration of electroactive species or collision frequency. Under optimized condition, 99.41% of indium (> 99% purity) can be electrodeposited within 13 h with high current efficiency. This study provides a cleaner approach for waste LCDs recycling and gives implications for the potential application of electrochemical technique in e-waste recycling.

Metal selectivity and effects of co-existing ions on the removal of Cd, Cu, Ni, and Cr by ZIF-8-EGCG nanoparticles

Recently, the developments of MOFs and their applications on heavy metal removal have attracted much attention. In this paper, we focused on the influence of co-existing ions on the adsorbability of epigallocatechin gallate (EGCG) modified ZIF-8 in a multi-metal system (Cd(II), Cu(II), Ni(II), and Cr(VI)). It was found that the adsorption of Cd(II), Cu(II), Ni(II), and Cr(VI) on the ZIF-8-EGCG fitted well with the pseudo second-order kinetic model and Langmuir isotherm. The adsorption selectivity of ZIF-8-EGCG in the mixed metal solution followed the order of Cu(II) ≫ Cr(VI) > Cd(II) > Ni(II). Besides, Cu(II) was the most attractive substance with a maximum capacity of 232.97 mg·g−1. Copper also disturbed the adsorption of Cd(II) and Ni(II) and contributed the most to the Cr(VI) removal. The natural anions (e.g., Cl−, NO3–, AsO2−, SO42−) significantly impeded Cr(VI) adsorption, while low concentrations of natural cations (e.g., K+, Na+, Ca2+, and Mg2+) facilitated the adsorption of Cd(II), Cu(II) and Ni(II).

Separation of metals from Ni-Cu-Ag-Pd-Bi-Sn multi-metal system of e-waste by leaching and stepwise potential-controlled electrodeposition

Electronic waste, as hazardous waste, contains a large amount of metals, which is of great recovery value. However, they are difficult to separate due to wide variety and complex distribution. Most of current recycling methods are environmentally-unfriendly or complicated. In this study, a simple, efficient and green approach for metals separation from Ni-Cu-Ag-Pd-Bi-Sn multi-metal system of e-waste was proposed combining mild leaching and stepwise potential-controlled electrodeposition. The leaching efficiencies of Ni, Ag, Pd, Cu and Bi were 99.16%, 99.09%, 94.91%, 99.61% and 23.76% with 1 mol/L HNO3 at 80 °C. The leaching process was analyzed. It showed that the existence of Ag-Pd continuous solid solution in the alloy lowered the oxidation potential of Pd, which facilitated its leaching. Sn precipitated as SnO2. Then Ag-Pd alloy and Cu-Bi alloy were separately extracted from the leaching solution by stepwise electrodeposition. 97.72% of Ag and 98.05% of Pd were recycled after 5 h with potential of 0.35 V. The recovery efficiencies of Cu and Bi were 97.87% and 97.33% after 7 h with potential of 0.05 V. The EDS results showed high purity property of Ag-Pd and Cu-Bi alloy. This process can achieve cleaner and efficient extraction of metals from multi-metal system in e-waste.

Competitive adsorption of Cu2+ in Cu2+, Co2+ and Ni2+ mixed multi–metal solution onto graphene oxide (GO)–based hybrid membranes

Graphene oxide (GO)–based hybrid membranes (GHMs) were synthesized by sol–gel reaction of GO with N-[3-(trimethoxysilyl)propyl] ethylene diamine (KH792). Some methods including XRD, TGA and DSC thermal measurements, surface FE–SEM and EDS images, FTIR, and XPS are applied to characterize their performance properties. Especially, competitive adsorption of Cu2+ onto these GHMs in Cu2+, Co2+ and Ni2+ mixed multi–metal aqueous solution was considered to inspect the selectivity of Cu2+ adsorption in mixed multi–metal system. Typical theoretical equations are modelled to search the adsorption mechanism. Both TGA and DSC curves showed that the thermal stability of these GHMs could exceed 500 °C. XPS spectra confirm the formation of hybrid matrix in GHMs. Competitive adsorption of Cu2+ in mixed multi–metal solution proves that Cu2+ adsorption onto these GHMs had better selectivity. Adsorption mechanism suggests that the adsorption of Cu2+, Co2+ and Ni2+ ions followed Lagergren pseudo 2nd–order kinetic model and diffusion–chemisorption model, respectively. Moreover, Langmuir isotherm model indicates that the adsorption of metals on the surface of GHMs was monolayer process and the Qm values can be arrived at 4.338, 3.339, and 3.160 mg/g for Cu2+, Co2+ and Ni2+, respectively. These results unveil that these GHMs have prospective applications in the separation and recycle of Cu2+ from Cu2+, Co2+ and Ni2+ ternary mixed multi–metal wastewater by stepwise separation technique. As a practical application, the adsorption separation of metals from synthetic laterite leach solution was examined. The outcome demonstrates that Cu2+ can be removed preferentially from the synthetic laterite leach solution by these GHMs, exhibiting potential usages in the removal of metals from industrial wastewater by multistage operation method.