Multi-metal Solutions Research Articles

Application of nanofiltration for the recovery of nickel glycinates from alkaline glycine-based solutions using polyamide membranes: A technical note

Glycine has been intensively investigated as a “green” lixiviant for precious and base metals. Alkaline glycine solutions to extract Ni from sulfide resources has shown promising results. However, a considerable amount of Ni will be lost in the wash solutions when leaching residues are washed during solid-liquid separation of the leachates from their respective leach residues. In this context, this study explored Ni recovery from alkaline glycine-based wash solutions using a polyamide nanofiltration membrane. In the tests using synthetic single and multi-metal solutions, the membrane achieved >95% rejection of Ni in the selected ranges of glycine/Ni molar ratio (up to 5), pressure (15–30 bar), initial nickel concentration (0.5–1.5 g/L), sodium sulfate background concentration (∼30 g/L) and under the use of different pH modifiers (aqueous ammonia and caustic soda). When using a real solution, the concentrations of Ni and other major elements (Cu, S, Co, Mg, Zn) in the final retentate increased by about 5 times at 80 wt% permeate recovery, leaving <3 mg/L major elements in permeate. The permeate stream could be recycled in the washing stage, and the retentate stream could be combined with the pregnant leach solution (PLS) for metals recovery. The investigation demonstrates some of the technical optionality for nickel recovery from filter wash solutions utilising nanofiltration within the context of alkaline glycine-based leach technology and preliminarily demonstrates where it can be used in the structure of flowsheets to recover valuable base metals and reagents for recycle. However, the increased membrane resistance causing a low permeate flux should be concerned due to the considerable dissolved salts, precipitation of gypsum and the increasing feed concentration over time.

Two electrochemical sensors based on pencil graphite electrodes modified with azo dye and a novel Schiff base for lead and cadmium ion quantification

This research introduces a cost-effective and straightforward approach to fabricating two novel electrochemical sensors. The initial novel sensor, termed AZOD/PLE, involves coating the surface of a pencil lead electrode (PLE) with the azo dye molecule (AZOD). The second novel sensor, named HDBE/PLE, is created by coating the pencil lead electrode (PLE) with a newly synthesized novel Schiff base molecule (HDBE), characterized through techniques such as IR, 1H NMR, and 13C NMR. The reason for the choice of the modifier materials in this research is their complexing ability with metal ions since they contain electron donor atoms such as O and N, which can form coordination bonds with the toxic heavy metal’s ions, cadmium and lead. This is the first time using the azo dye molecule (AZOD) and the novel Schiff base molecule (HDBE) as modifiers on PLE. The characterization of the electrode surfaces was made by energy-dispersive X-ray spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The surface morphology of the electrode was investigated by scanning electron microscopy (SEM). CV results indicate that the modified electrodes possess larger electroactive surface areas compared to the bare PLE. Square wave voltammetry (SWV) results demonstrate that both sensors exhibit high sensitivity in detecting low concentrations of Cd (II) and Pb (II) in tris-HCl buffer (0.1 M) for both single-metal and multi-metal solutions. These sensors can be easily produced in a single step and exhibit excellent selectivity, stability, reproducibility, and repeatability, making them well-suited for detecting Pb (II) and Cd (II) in aqueous environments.

Cadmium Removal by Adsorption on Biochars Derived from Wood Industry and Craft Beer Production Wastes

Cadmium pollution is a serious environmental issue that has an impact on both the ecosystem and human health. As a result, its removal from water is essential. Agro-industrial wastes are suggested as a sustainable adsorbent option, as they are among the most readily available renewable sources worldwide. Biochar is a carbonized biomass that has been shown to be a viable and novel adsorbent. This article compares the results of cadmium adsorption on biochars derived from wood industry and craft beer production wastes. Biochars were characterized before and after adsorption. Batch adsorption results of 0.18 mmol/L Cd(II) concentration solutions indicated adsorption percentages (A%) of 99.7% and 92.2% for sawdust biochar and barley biochar, respectively. For this cadmium concentration, the sawdust biochar presented an adsorption capacity (qm) of 0.0172 mmol/L, while the barley biochar presented a value of 0.0159 mmol/L. The influence of initial Cd(II) concentration on single and multimetal solutions was studied, and a decrease in Cd(II) adsorption on sawdust biochar was observed in the presence of Ni(II) and Zn(II). The Freundlich isotherm model was found to be the best fit to the data for Cd(II) adsorption isotherms on both biochars. According to the results of this article, sawdust biochar has the best performance as an adsorbent and can be safely disposed of in building bricks at the end of its useful life.

Recovery of rare earth elements from mining wastewater with aminomethylphosphonic acid functionalized 3D-printed filters

Herein we report the use of nylon-12-based 3D-printed filters incorporating α-aminomethylphosphonic acid as an active additive for the recovery of Y, Nd, and Dy from the mining waste solution containing Al, K, Ca, Sc, Fe, Co, Cu, Zn, Y, Nd, Dy, and U. Nylon-12 was chosen for the polymer matrix of the filter due to its inactivity towards the studied metals. The micrometer-level structure of the filters was studied with a scanning helium ion microscope and X-ray tomography to reveal the porosity, pore size, and active additive distribution in the filters. Furthermore, FTIR spectroscopy was used to analyze the compositional changes in the 3D-printed filters after the printing and adsorption processes. Adsorption of the metals was studied at a pH range of 1–4, and the following adsorption trend Sc > Fe > U > Y, Nd, Dy > Al, Cu, Zn > K, Ca, Co was observed in each of the studied pH values. The sequential recovery process for metals was studied at pH 2, and desorption of the metals from the filters was performed with 6 M HNO3. 100 % adsorption of REEs, Fe, and U was achieved during the recovery process, and on average, over 88 % of the adsorbed Y, Nd, and Dy were desorbed from the filters. In contrast to Y, Nd, and Dy, the desorption of Sc, Fe, and U was minimal (Fe and U) or negligible (Sc) with 6 M HNO3 due to their strong coordination to the active additive. Maximum adsorption capacities for Y, Nd, Dy, and U were determined by using linear Langmuir adsorption isotherm. The best maximum adsorption capacity was determined for Sc, Qmax = 0.51 mmol/g followed by U, Nd, Dy, and Y with capacities of 0.47, 0.24, 0.23, and 0.17 mmol/g, respectively. Overall, this study achieved a complete removal of Sc, Fe, and U from the simulated mining waste solution leaving a final eluate that mainly contained Y (320 μg), Nd (350 μg), Dy (330 μg), and Al (710 μg) demonstrating the applicability of the 3D-printed filters in the recovery of Y, Nd, and Dy from the multimetal solution.

Semi-continuous cultivation of EPS-producing marine cyanobacteria: A green biotechnology to remove dissolved metals obtaining metal-organic materials

Given the necessity for bioprocesses scaling-up, the present study aims to explore the potential of three marine cyanobacteria and a consortium, cultivated in semi-continuous mode, as a green approach for i) continuous exopolysaccharide-rich biomass production and ii) removal of positively charged metals (Cu, Ni, Zn) from mono and multi-metallic solutions. To ensure the effectiveness of both cellular and released exopolysaccharides, weekly harvested whole cultures were confined in dialysis tubings. The results revealed that all the tested cyanobacteria have a stronger affinity towards Cu in mono and three-metal systems. Despite the amount of metals removed per gram of biomass decreased with higher biosorbent dosage, the more soluble carbohydrates were produced, the greater was the metal uptake, underscoring the pivotal role of released exopolysaccharides in metal biosorption. According to this, Dactylococcopsis salina 16Som2 showed the highest carbohydrate productivity (142 mg L−1 d−1) and metal uptake (84 mg Cu g−1 biomass) representing a promising candidate for further studies. The semi-continuous cultivation of marine cyanobacteria here reported assures a schedulable production of exopolysaccharide-rich biosorbents with high metal removal and recovery potential, even from multi-metallic solutions, as a step forward in the industrial application of cyanobacteria.

Separation of heavy metals from dilute solutions using D2EHPA carrier fixed onto the outer surface of coaxially electrospun core-sheath fibers

In this study, porous membranes based on core-sheath fibers covered with fixed carriers were prepared by coaxial electrospinning for the separation of heavy metal ions from dilute solutions. Cellulose triacetate (CTA) and an extractant di(2-ethylhexyl)phosphoric acid (D2EHPA) were mixed to prepare a sheath-layer solution and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was adopted to prepare a core-layer solution for electrospinning. The morphological and textural properties as well as chemical composition of the fabricated core-sheath fibers were first analyzed to determine the optimal preparation conditions. The ability and selectivity of such fixed D2EHPA carriers were evaluated via the adsorption of Zn2+, Cu2+, and Ni2+ ions from dilute solutions. Dynamic tests revealed that the adsorption of metal ions on the core-sheath fibrous membrane made of 52 wt% PVDF-HFP, 18 wt% D2EHPA, and 30 wt% CTA (on a dry basis) reached equilibrium within 8 h. As expected, all adsorption isotherms at specific equilibrium pH values were well described by the Langmuir equation, ascribed to the chemical reaction nature between metal ions and D2EHPA carrier. The crossflow permeation-adsorption tests of a multi-metal solution in a total recycling mode revealed the adsorption selectivity of Zn2+ over Cu2+ and Ni2+, as observed in conventional liquid–liquid extraction. Four repeated adsorption-regeneration experiments revealed an adsorption efficiency beyond 95 % relative to the first route, demonstrating the satisfactory reusability and stability of the as-prepared core-sheath fibrous membranes for this purpose.

Effect of metals on recovery of gold from ammoniacal thiosulphate leach solutions by precipitation using trimercapto-s-triazine (TMT)

There are significant technical challenges/shortcomings in recovering gold from thiosulphate leach solutions. This study presents a new approach for the recovery of gold from ammoniacal thiosulphate leach solutions using an environmentally friendly organo-sulphide reagent, trimercapto-s-triazine (TMT; C3N3S33−). Precipitation of gold by TMT was investigated using synthetic gold and multi-metal solutions (Au-Ag, Au-Cu, Au-Ag-Cu) to investigate the effect of the co-presence of metals commonly present in thiosulphate leach solution. The effect of TMT concentration (by up to 115 mM), temperature (25–60 °C) and ammonia (0.25–1 M NH3) on the precipitation of gold was also investigated. The results showed that gold precipitation with TMT was relatively low (i.e., limited to only 37.7% over 15 min) from the solution containing only gold. However, the presence of silver and/or copper significantly improved the precipitation of gold. Silver concentrations at ≥20 mg/L led to a complete recovery of gold in 15 min, producing stable gold precipitates. The results have also indicated that silver readily precipitates when compared to gold. The effectiveness of the TMT precipitation process was also tested on a real leach solution from which complete recovery of gold and silver was readily achieved. The findings demonstrated that gold could be readily but unselectively recovered by precipitation with TMT from ammoniacal thiosulphate leach solutions containing silver, in particular, at the expense of co-precipitation of other metals such as copper and zinc.

Preparation of novel CS/SiO2-EDTA nanocomposite from ash of rice straw pellets for enhanced removal efficiency of heavy metal ions in aqueous medium

The production valuable materials from waste for environmental treatment have attracted considerable attention worldwide. In this study, porous silica was produced from the ash of rice straw pellets. The porous silica was then modified with chitosan (CS) and ethylenediaminetetraacetic acid (EDTA) to produce novel CS/SiO2-EDTA nanocomposites for the removal of heavy metals in aqueous medium. The adsorption of Pb2+ was investigated to evaluate the effectiveness of the composite and the effects of reaction parameters on the adsorption process were extensively explored. The adsorption is fast in the initial 5 min, then almost reaches equilibrium in 10 min. The conditions for the highest adsorption capacity are an EDTA content of 1.0 M, a pH of 6, an adsorbent dosage of 0.1 g/L, and a Pb2+ concentration of 100 ppm. The removal efficiency, adsorption capacity, and rate constant are 70.39 %, 703.9 ± 21.1 mg/g, and 0.012 ± 0.003 g/mg·min, respectively. The conditions for the highest adsorption efficiency are an EDTA content of 1.0 M, a pH of 6, an adsorbent dosage of 0.5 g/L, and a Pb2+ concentration of 40 ppm, where the adsorption efficiency, adsorption capacity, and rate constant are 89.88 %, 71.91 ± 1.86 mg/g, and 0.013 ± 0.002 g/mg·min, respectively. The selectivity of the composite was investigated by using Ni2+, Cu2+ and Fe2+ ions under the same experimental conditions. In multi-metal solutions, the adsorbent showed the highest affinity for Pb2+. In addition, the adsorption isotherms and thermodynamics were investigated and an adsorption mechanism was proposed.

Selectivity of lanthanum and ytterbium in binary and multi-component system by modified sericin/alginate/poly (vinyl alcohol) adsorbent beads

Rare earths are essential for important industrial applications and for producing high-tech materials. Its recovery from secondary sources is fundamental from an environmental and economic perspective. Biosorption is a promising method that can be used to remove and recover rare earth at low concentrations in an aqueous medium due to its low cost, simplicity, and efficiency. Recently, natural biomaterials based on sericin/alginate began to be investigated as a biosorbent for rare-earths uptake. Sericin is a natural protein of silkworm cocoons, usually discarded along with silk industry effluents, and alginate is a natural carbohydrate extracted from abundant sources of brown algae. The particles produced by the sericin/alginate blend were crosslinked with poly (vinyl alcohol) (PVA), which promotes better properties to this biomaterial. In this study, modified beads of a sericin/alginate/PVA blend were produced by ionic imprinting (Ca(NO3)2, Ca(NO3)2/La(NO3)3, or La(NO3)3) and leaching with HNO3 (0.1 mol/L). The developed particles were applied to remove ytterbium and lanthanum from aqueous solutions through adsorptive affinity and selectivity tests. The results indicated that the modified particles showed superior removal efficiency for lanthanum. For ytterbium, the highest removals were obtained for sericin/alginate/PVA-La(NO3)3 (94.33 ± 0.05%), sericin/alginate/PVA-Ca(NO3)2/La(NO3)3 (94.05 ± 3.12%), and sericin/alginate/PVA-Ca(NO3)2 (92.06 ± 2.01%). For lanthanum, higher removal values were obtained for sericin/alginate/PVA-La(NO3)3 (100.71 ± 0.77%), sericin/alginate/PVA-Ca(NO3)2/La(NO3)3 (99.21 ± 0.28%), and sericin/alginate/PVA-Ca(NO3)2 (98.45 ± 2.98%). In the binary system of rare earths, selectivity between the metals was not observed, however the modified beads showed great selectivity performance for lanthanum and ytterbium in multi-metal solution. Additionally, the modified beads with ionic imprinting were characterized by SEM, EDS, FTIR, XPS, and TGA/DTG. Thus, the results indicated that modified sericin/alginate/poly(vinyl alcohol) beads could be used as an alternative and promising biosorbent to remove and recover rare earths.

Smart Sorption: Novel applications of cellulosic nanomaterials for selective critical metal recovery from black mass leachates through multibatch processes

Selective critical metal recovery from black mass leachates (BML) is a great challenge for the Li-ion batteries recycling sector. This paper shows the potential of nanocellulose products as green adsorbents for a selective recovery of critical metals through multibatch sorption processes. Cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) of 0.4 and 1.5 meq/g cationic demand, respectively, have been produced and used as biosorbents. Metal leaching from non-pyrolyzed black mass with HCl presented the highest critical metal extraction yield, obtaining up to 10 g/L of Co and more than 1 g/L of Cu, Mn and Ni. The adsorbents were tested under different dosages and pH conditions for the treatment of both synthetic multimetal solution (MMS), with Mn, Cu, Co, and Ni, and real BML, through a multiple step batch treatment to increase the selectivity towards each critical metal. For MMS treatments, the lowest pH (1–2) conditions are favorable for Co separation, reaching 135 g/g, while higher pH values (4–5) are better to recover Cu and Ni. Selectivity indexes between metals could reached values above 40 for the optimal conditions. For the treatment of BML, pH around 3 enhanced the selectivity of Al and pH of 5 of the Li. In this case, metal recoveries were higher than 30 g/g. When CNCs were used, more than 4 g/g of Co was adsorbed, recovering more than 99 % of the Co present in the waste. 99 % of Co purity was obtained at the optimal Co selective recovery conditions. Although the studied critical metals were strongly sorbed onto the nanocelluloses, a solution with a concentration of 2.5–5 g/L of these metals could be extracted from desorption tests.

Competitive heavy metal adsorption on pinecone shells: Mathematical modelling of fixed-bed column and surface interaction insights

Pinecone shells are assessed as a cost-effective biosorbent for the removal of metal ions Pb(II), Cu(II), Cd(II), Ni(II), and Cr(VI) in a fixed-bed column. Influent concentration, bed height, and flowrate are studied to improve efficiency. The breakthrough data is well fitted by the Sips adsorption model, suggesting a surface complexation mechanism, with maximum adsorption capacities of 11.1 mg/g for Cu(II) and 66 mg/g for Pb(II).In multimetal solutions, the uptake sequence at breakthrough and saturation is Pb(II) > Cu(II) > Cd(II). Characterization via FTIR and XRD reveals carboxyl and hydroxyl functional groups interacting with metal ions. Ca(II) does not compete with Pb(II), Cu(II), and Cd(II) adsorption, highlighting the ability of pinecone to adsorb heavy metals via surface complexation. Its application in the treatment of industrial effluents containing Cu(II), Ni(II), and Cr(VI) is explored.The study investigates bed media regeneration via eluting adsorbed metal ions with hydrochloric acid solutions. The potential of pinecone shells as an efficient biosorbent for removing toxic metal ions from industrial wastewater is emphasized. These findings enhance our understanding of the adsorption mechanism and underscore the fixed-bed column system's applicability in real-world scenarios, addressing environmental concerns related to heavy metal contamination of industrial effluents.

Enhanced selective adsorption capacity of lead (II) from complex wastewater by aminopropyltriethoxysilane-functionalized biochar grafted on the MXene based on anion-synergism

The simultaneous elimination of dyes and metal ions from wastewater is essential for industrial wastewater treatment. In the current work, a novel adsorbent, aminopropyltriethoxysilane-functionalized biochar grafted on MXene (APTES/BC/MXene composite), was synthesized and utilized to increase the selectivity of the uptake of lead from a complex multi-metal solution based on anion-synergism. The surface area of the APTES/BC/MXene composite (164 m2/g) was higher as compared to the BC (90 m2/g), APTES (87 m2/g), and APTES/BC (151 m2/g). The outcomes of selective adsorption of metal ions were altered by the composite before (APTES = 52.98 mg/g, APTES/MXene = 58.65 mg/g, and APTES/BC = 313.86 mg/g) and after grafting aminopropyltriethoxysilane-functionalized biochar on the MXene (APTES/BC/MXene = 323.17 mg/g). In this investigation, the composite showed remarkable selectivity for the adsorption of lead. The adsorption capacity of composite for Pb2+ (323.17 mg/g) was superior compared to Cd (16.45 mg/g), Sr (10.99 mg/g), Zn (25.37 mg/g), Ni (7.82 mg/g, Ca (20.79 mg/g), and Ag (58.47 mg/g). Interestingly, the selective uptake of lead by the composite was enhanced from 446.85 to 1072.04 mg/g as coexisting methyl blue dosages increased from 0 to 100 mg/L at a pH value of 6.0. In the lead-methyl blue complex binary system, lead and methyl blue indicated synergistic phenomena, in which the existence of methyl molecules generated new unique sites for lead adsorption, while methyl blue uptake was also increased by the existence of lead. The experiment's findings demonstrate that the prepared APTES/BC/MXene exhibited excellent stability and regeneration capabilities (96.2% and 95.1% adsorption efficacy after 5th cycles for Pb2+ and MB respectively), suggesting it can be employed as a quick and efficient uptake adsorbent for the elimination of MB and Pb2+ in a single pollutant system. Hydrogen bonding, electrostatic interaction, synergistic penetration, and ion exchange processes were primarily involved in the uptake of lead and methyl blue. This investigation offers useful insights for the development of composite that indicate outstanding performance and easy recovery for the synergistic and simultaneous uptake of heavy metal ions and organic dyes. The results also reveal the remarkable enhancement of selective heavy metal uptake from complex wastewater by utilizing anion-bye interactions.

Novel ZIF-8/CNC Nanohybrid with an Interconnected Structure: Toward a Sustainable Adsorbent for Efficient Removal of Cd(II) Ions.

Water pollution, especially by heavy metals, continues to pose significant challenges, emphasizing the urgency to develop sustainable processes to remove pollutants while developing sustainable materials derived from renewable sources. In the present research, a nanoscale adsorbent was prepared to remove cadmium (Cd(II)) ions from wastewater by hybridizing zeolitic imidazolate framework-8 (ZIF-8) with a cellulose nanocrystal (CNC). The prepared nanohybrid exhibited an interconnected structure in which the ZIF-8 particles were connected to each other via CNC nanoneedles. The hybridization of ZIF-8 with CNC caused a significant enhancement in the adsorption performance of the fabricated nanohybrid compared to pure ZIF-8, increasing its adsorption capacity by nearly 36%. The adsorption of ZIF/CNC followed the Langmuir isotherm model and pseudo-second-order kinetics models, remarking homogeneous adsorption onto the surface of ZIF/CNC, where chemisorption controlled the rate of adsorption. The thermodynamic study uncovered that the adsorption is spontaneous, endothermic, and entropy-governed as the randomness was increased at the solid-liquid interface. Additionally, the influence of operating variables, such as temperature, adsorbent dosage, pH, and ionic strength, was studied to mimic the adsorption capabilities of the adsorbent in real conditions. Accordingly, the optimum conditions were found to be at 45 °C and pH = 7 with a dosage of 0.4 g/L for the adsorbent. Moreover, the adsorption in a multimetal solution showed that the ZIF/CNC nanohybrid can remove various heavy metals, including Cd(II), Fe(III), Cu(II), and Pb(II) ions simultaneously. Finally, the regeneration study confirmed the great potential of the ZIF/CNC nanohybrid, which retained 94% of its initial adsorption capacity after 5 consecutive adsorption/desorption cycles.

Development of novel biopolymer membranes by electrospinning as potential adsorbents for toxic metal ions removal from aqueous solution

This work aims to develop novel biomembranes based on PLA, PBS, or their blend and composites, with the Cloisite® 20A nanoclay, as adsorptive materials for metal ions removal. To obtain a membrane with good morphology and thinner diameter of the fibers, a series of nonwoven mats were prepared by electrospinning. To improve the adsorption performance of the electrospun membranes, thermal and acid modifications were carried out in the nanoclay before the electrospinning process, and the final electrospun membranes were applied in the removal of Cr(VI), Cu(II), Cd(II), Zn(II), Ni(II), and Mn(II) ions present in a multi-metal solution. The PBS/PLA/C20A (80/10/10) membrane obtained with an injection flow rate of 3 mL/h, needle tip-to-collector distance of 15 cm, and voltage of 20 kV were selected for the synthesis of the adsorptive membranes, which has the best morphology due to the small average diameter of the fiber and bead-free structures. The characterization techniques (TGA, BET, helium pycnometry, RMN, and DMA) results proved that the addition of PLA and nanoclay resulted in the formation of a material more resistant and with high porosity and specific surface area than the neat PBS. It can be seen that the membranes prepared with the nanoclay after thermal modification showed high metal removal efficiency than the mats designed with the raw nanoclay and after acid modification. It was also possible to conclude that PBS and PLA present the capacity to gradually release organic carbon compounds, which can be used directly as electron donors for Cr(VI) reduction.

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.

Metal tolerance and biosorption capacities of bacterial strains isolated from an urban watershed.

Rapid industrialization and urbanization have led to widespread metal contamination in aquatic ecosystems. This study explores the metal tolerance and biosorption characteristics of four bacterial strains (Serratia sp. L2, Raoultella sp. L30, Klebsiella sp. R3, and Klebsiella sp. R19) isolated from Saint Clair River sediments. These strains effectively removed various metal cations (As3+, Pb2+, Cu2+, Mn2+, Zn2+, Cd2+, Cr6+, and Ni2+) in single and multi-metal solutions. Minimum inhibitory concentration (MIC) assays revealed strain-specific variations in metal tolerance, with L2 and L30 exhibiting higher tolerance. Surprisingly, R3 and R19, despite lower tolerance, demonstrated superior metal removal efficiency, challenging the notion that tolerance dictates removal efficacy. In single-metal solutions, R3 and R19 excelled at extracting various metal ions, while competitive binding in multi-metal solutions hindered removal. However, R3 and R19 retained higher removal efficiencies, possibly due to enhanced flocculation activities facilitating metal-ion contact. Comprehensive Fourier-transform infrared (FTIR) analysis highlighted the strains' metal-binding capabilities, with novel peaks emerging after metal exposure, indicative of extracellular polymeric substance (EPS) production. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) confirmed metal accumulation on bacterial surfaces and within cytoplasmic regions and revealed morphological changes and metal adsorption patterns, emphasizing the strains' ability to adapt to metal stress. Scanning transmission microscopy (STEM) and EDX analysis uncovered metal accumulation within bacterial cells, underscoring the complexity of microbial-metal interactions. This study also confirms that the simultaneous presence of an aqueous solution may cause a mutual inhibition in the adsorption of each metal to the EPS resulting in reduced metal uptake, which emphasizes the need to select specific bacterial strains for a given metal-containing effluent. The differences in metal distribution patterns between Klebsiella sp. R19 and Raoultella sp. L30 suggest species-specific metal accumulation strategies driven by environmental conditions and metal availability. The heavy metal-removing capabilities and the ability to grow over a wide range of metal concentrations of the strains used in this study may offer an advantage to employ these organisms for metal remediation in bioreactors or in situ.

Experimental study of competitive heavy metals removal from multimetal solution using wheat bran as a biomaterial: Response surface methodology

AbstractBatch and continuous adsorption studies were performed for heavy metal removal from the ternary metal system using wheat bran as an adsorbent. An adsorbent pellet was prepared using clay and chitosan as a binder. For batch adsorption experiments, the Box–Behnken design of response surface methodology was used to optimize the process parameters for adsorption. In our mixed metal continuous study, cadmium (70%–80%) and chromium (74%–80%) had shown a synergistic effect on copper removal leading to an increase in breakthrough and exhaustion time. In a continuous study, a higher breakthrough time was obtained for copper at a bed height of 0.15 cm, a flow rate of 5 mL/min and an initial metal concentration of 100 mg/L. The modeling and simulation of the continuous adsorption process were performed. The breakthrough curve obtained from the model and from experiments was compared and high R2 values up to 0.99 and low chi‐square and MAPE values up to 0.018% and 0.037% indicate good fitting of model and experimental data. Regeneration studies results show that good desorption efficiency is obtained using regenerated wheat bran. The adsorbent was regenerated and reused up to five cycles and it showed good desorption efficiency of up to 95% for copper, 79% for cadmium and 80% for chromium.

Improving the sorption properties of mesoporous carbons for the removal of cobalt, nickel and manganese from spent lithium-ion batteries effluent

The competitive sorption of Co2+, Li+, Ni2+, and Mn2+, strategic metals from spent lithium-ion batteries and their leachates, was studied using activated mesoporous carbons. The mesoporous carbon was synthesized by the replica method using silica gel as a template and exhibited a high surface area with an accessible pore volume due to mesopores (Vmeso > 95%). Fast kinetics and high sorption capacities of these metals were achieved with the chemical activation of mesoporous carbons. The surface modification of the mesoporous carbon was carried out by physical activation with O2 at 450 °C and chemical activation under mild conditions (room temperatures) with NaClO2/H2O2 as oxidizing agents. FTIR analysis and conductimetric titration showed that the combination of an initial physical activation step, followed by chemical functionalization, maximized the formation of carboxylic acids (from 0.2 to 0.9 meq/g), due to the complete oxidation of the weakly acidic groups. Those carbons were tested in sorption experiments of the lithium-ion battery metals in monometallic solutions, where physically activated and chemically reactivated mesoporous carbon selectively removed over 80% of Co2+, Ni2+, and Mn2+, with sorption capacities over 20 mg/g, while only 20% of Li+ was removed. This carbon stood out amongst the others studied (2 to 11-fold increase in sorption capacities depending on the metal) and was tested in multimetallic solutions, showing fast removal rates, reaching equilibrium within the first 15 min, as well as selectivity towards divalent cations (18 mg/g of Co2+) with insignificant lithium sorption (qLi = 0.33 mg/g). Desorption of metals was carried out using H2SO4, which allowed the recovery and twofold of the initial concentrations of Co, Ni, and Mn.

Enhanced adsorption selectivity of Au(III) over Cu(II) from acidic chloride solutions by chitosan/palm kernel fatty acid distillate/magnetite nanocomposites

This work aimed to develop a modified chitosan adsorbent with enhanced adsorption selectivity for Au(III) over Cu(II) from acidic chloride solutions using low-cost and green raw materials. Various adsorbents, i.e., chitosan powder, chitosan microbeads, chitosan/palm kernel fatty acid distillate (PKFAD) microcomposites, magnetite nanoparticles, and chitosan/PKFAD/magnetite nanocomposites (CPMNs), were first evaluated for their ability to adsorb Au(III) and Cu(II) from single- and binary-metal solutions across different pH levels, followed by parametric analysis of Au(III) and Cu(II) adsorption from binary- and multi-metal solutions onto CPMNs, Au(III) desorption from Au(III)-loaded CPMNs, and reusability of CPMNs. Finally, Au(III)-loaded CPMNs were characterized with SEM-EDX, XRD, FTIR, and XPS to confirm the proposed adsorption mechanisms. Among all the adsorbents studied, CPMNs exhibited outstanding performance in adsorbing Au(III) from an equimolar binary Au(III)-Cu(II) solution, achieving the highest equilibrium adsorption capacity of 0.479 mmol/g (94.4 mg/g) without reaching saturation. Under optimal adsorption conditions of pH 3, 1 g/L CPMN dosage, and 90 min contact time, CPMNs adsorbed 96 % of Au(III) with a selectivity over Cu(II) exceeding 99 %. CPMNs demonstrated excellent reusability, maintaining over 80 % adsorption and desorption efficiencies for 5 cycles. The proposed adsorption mechanisms of CPMNs for Au(III) encompass electrostatic attraction, hydrogen bonding, solvation, and reduction.

Quantifying metal-binding specificity of CcNikZ-II from Clostridium carboxidivorans in the presence of competing metal ions

Many proteins bind transition metal ions as cofactors to carry out their biological functions. Despite binding affinities for divalent transition metal ions being predominantly dictated by the Irving-Williams series for wild-type proteins, in vivo metal ion binding specificity is ensured by intracellular mechanisms that regulate free metal ion concentrations. However, a growing area of biotechnology research considers the use of metal-binding proteins in vitro to purify specific metal ions from wastewater, where specificity is dictated by the protein's metal binding affinities. A goal of metalloprotein engineering is to modulate these affinities to improve a protein's specificity towards a particular metal; however, the quantitative relationship between the affinities and the equilibrium metal-bound protein fractions depends on the underlying binding mechanisms. Here we demonstrate a high-throughput intrinsic tryptophan fluorescence quenching method to validate binding models in multi-metal solutions for CcNikZ-II, a nickel-binding protein from Clostridium carboxidivorans. Using our validated models, we quantify the relationship between binding affinity and specificity in different classes of metal-binding models for CcNikZ-II. We further illustrate the potential relevance of data-informed models to predicting engineering targets for improved specificity.