Development of novel sericin and alginate-based biosorbents for precious metal removal from wastewater

Biosorption of europium and erbium from aqueous solutions using crosslinked sericin-alginate beads

Critical metals such as rare earths are essential for important industrial applications and for producing high-tech materials. Currently, the development of alternative and non-conventional biomaterials has gained significant interest. This work investigated the use of crosslinked sericin-alginate-based natural polymeric particles for the removal of rare earths from water. Affinity tests showed that sericin-alginate/polyethylene glycol diglycidyl ether had the highest potential for capturing europium (0.258 mmol/g and 94.33%) and erbium (0.259 mmol/g and 94.55%). Next, erbium was selected based on the affinity with sericin-alginate/polyethylene glycol diglycidyl to investigate the effect of dose/pH, biosorption kinetics, isothermal equilibrium, desorption/reuse, and selectivity. The effect of dose and pH showed that 8.0 g/L (95.91%) and pH 5.0 (97.53%) were more efficient in capturing erbium. The biosorption kinetics showed that the equilibration time was reached within 210 min. The PSO and EMTR models effectively represented the kinetics data. The isothermal equilibrium revealed that the maximum uptake capacity for erbium was 0.641 mmol/g. The isothermal curves better fit the Dubinin-Radushkevich (55 °C) and Langmuir (25 and 40 °C) models. Thermodynamic quantitates indicated that erbium uptake was spontaneous, governed by entropic changes, and endothermic. The recovery of Er3+ was greater than 98% and the reuse of the eluent in the cycles enriched the Er3+ load 10-times (1.0 to 9.91 mmol/L). The beads also showed better performance for capturing Er3+ and Eu3+ with other coexisting ions. Characterization analyzes revealed the ion exchange mechanism between Ca2+/Er3+ prevailed in the Er3+ removal. Thus, the results pointed out that crosslinked sericin-alginate can be used as an alternative and promising biosorbent to remove and recover rare earths.

Metal ions guide the production of silkworm silk fibers

Silk fibers' unique mechanical properties have made them desirable materials, yet their formation mechanism remains poorly understood. While ions are known to support silk fiber production, their exact role has thus far eluded discovery. Here, we use cryo-electron microscopy coupled with elemental analysis to elucidate the changes in the composition and spatial localization of metal ions during silk evolution inside the silk gland. During the initial protein secretion and storage stages, ions are homogeneously dispersed in the silk gland. Once the fibers are spun, the ions delocalize from the fibroin core to the sericin-coating layer, a process accompanied by protein chain alignment and increased feedstock viscosity. This change makes the protein more shear-sensitive and initiates the liquid-to-solid transition. Selective metal ion doping modifies silk fibers' mechanical performance. These findings enhance our understanding of the silk fiber formation mechanism, laying the foundations for developing new concepts in biomaterial design.

A spherical adsorbent produced from a bagasse biochar chitosan assembly for selective adsorption of platinum-group metals from wastewater

This study addresses the challenge of platinum-group metal scarcity by exploring the adsorption of these metals from industrial wastewater. An inexpensive adsorbent with selective platinum-group metal adsorption capacity, named chitosan/citric acid@diatomaceous earth-sugarcane bagasse (CTS/CA@DE-SBS), was newly synthesized. The material features a double coating of chitosan and diatomite on bagasse biochar, and it exhibits an excellent adsorption performance for platinum-group metals due to the synergistic effects of the biochar and chitosan-diatomaceous earth intercross-linked coatings. CTS/CA@DE-SBS achieved an 81 % adsorption efficiency and a static saturated adsorption capacity of 217 mg/g for Pt (IV) in water. Notably, the material exhibited selective adsorption properties for platinum-group metals dissolved in diverse aqueous solutions. The potential for the secondary recovery of platinum-group metals in complex aqueous bodies further underscores the significance of this adsorbent. In conclusion, this research introduces a promising solution for platinum-group metal shortages, offering a cost-effective and selective adsorbent with potential applications in the secondary recovery of these metals from industrial wastewater.

Porous carboxymethyl cellulose nanocrystalline imprinted composite aerogels for selective adsorption of gadolinium

Gadolinium is widely applied in medical and high-tech materials because of special magnetic properties. Recovery of gadolinium from waste rare earth products has both economic and environmental value. In this experiment, honeycomb porous composite aerogels were constructed using sericin and sodium alginate mixed with functionally modified carboxymethylated cellulose nanocrystals for the adsorption and separation of gadolinium ions. There were large numbers of carboxyl groups as well as hydroxyl groups on the surface of sodium alginate and filamentous protein, which provided more sites for the adsorption of gadolinium ions. Besides, a stable honeycomb structure appeared on the surface of composite aerogels when the mixture of filamentous protein and sodium alginate was 1:1, which increased the specific surface area of materials to 140.65 m2 g-1. Additionally, the imprinted composite aerogels Ic-CNC/SSA were prepared by virtue of the imprinting technology, enhancing the adsorption selectivity of composite aerogels for gadolinium. The adsorption experiments revealed that the maximum adsorption capacity of Ic-CNC/SSA reached 93.41 mg g-1 at pH 7.0, indicating good selective adsorption of gadolinium ions. In summary, such composite aerogels provide great potential and reference value for the selective adsorption of gadolinium ions in industry.

Polyelectrolyte and polyelectrolyte complex-incorporated adsorbents in water and wastewater remediation - A review of recent advances

In recent years, polyelectrolyte-incorporated functional materials have emerged as novel adsorbents for effective remediation of pollutants in water and wastewater. Polyelectrolytes (PEs) are a special class of polymers with long chains of repeating charged moieties. Polyelectrolyte complexes (PECs) are obtained by mixing aqueous solutions of oppositely charged PEs. Herewith, this review discusses recent advances with respect to water and wastewater remediation using PE- and PEC-incorporated adsorbents. The review begins by highlighting some water resources, their pollution sources and available treatment techniques. Next, an overview of PEs and PECs is discussed, highlighting the evolving progress in their processing. Consequently, application of these materials in different facets of water and wastewater remediation, including heavy metal removal, precious metal and rare earth element recovery, desalination, dye and emerging micropollutant removal, are critically reviewed. For water and wastewater remediation, PEs and PECs are mostly applied either in their original forms, as composites or as morphologically-tunable complexes. PECs are deemed superior to other materials owing to their tunability for both cationic and anionic pollutants. Generally, natural and semi-synthetic PEs have been largely applied owing to their low cost, ready availability and eco-friendliness. Except dye removal and desalination of saline water, application of synthetic PEs and PECs is scanty, and hence requires more focus in future research.

Cerium biosorption onto alginate/vermiculite-based particles functionalized with ionic imprinting: Kinetics, equilibrium, thermodynamic, and reuse studies

Cerium is an essential element for several applications in industry, therefore, recovering it from secondary sources is a promising strategy from an economic and environmental perspective. For this purpose, biosorption is a low-cost and effective alternative. The present work evaluated the recovery of Ce³⁺ from aqueous solutions using alginate/vermiculite-based particles (ALEV) functionalized by ionic imprinting. From the kinetic assays, it was verified that the uptake of Ce³⁺ followed the pseudo-second-order model and was mainly controlled by external diffusion. The Langmuir model better described the equilibrium data, and a maximum biosorption capacity of 0.671 mmol/g at 45 °C was attained. The evaluation of the thermodynamic quantities revealed that the process occurs spontaneously and endothermically. The particles reuse and Ce³⁺ recovery were achieved using 0.1 mol/L HCl or 1.0 mol/L CaCl₂ solutions for up to four cycles of biosorption/desorption. The biosorbent was characterized before and posted Ce³⁺ biosorption to investigate the morphology, textural properties, crystallinity, thermal resistance, composition, and functional groups of the biosorbent.

Biosorption of rare-earth and toxic metals from aqueous medium using different alternative biosorbents: evaluation of metallic affinity

Currently, the world faces difficulties related to the quantity and quality of water because of industrial expansion, population growth, and urbanization intensification. Biosorption is considered a promising technology that can be applied to remove toxic metals (TMs) and rare-earth metals (REMs) in wastewater at low concentrations, due to its efficiency and low cost. In this work, we investigated different non-conventional biosorbents to remove metallic ions (TMs and REMs) in biosorptive affinity tests. Metallic affinity assays among lanthanum and different biosorbents showed that greater affinities were found for sericin-alginate beads crosslinked with polyvinyl alcohol (SAPVA) (0.280 mmol/g) and polyethylene glycol diglycidyl ether (SAPEG) (0.277 mmol/g), expanded vermiculite (0.281 mmol/g), Sargassum filipendula seaweed (0.287 mmol/g), and seaweed biomass waste (0.289 mmol/g). Among the biosorbents evaluated, SAPVA and SAPEG beads, besides to sericin-alginate beads crosslinked with proanthocyanidins (SAPAs) were selected for affinity assays with other REMs and TMs. Compared to other particles, SAPVA beads showed higher potential for biosorption by REMs with the following order of affinity: Yb3+ > Dy3+ > Nd3+ > Ce3+ > La3+. Additionally, the biosorptive affinity of TMs by SAPVA beads followed the order: Al3+ > Cr3+ > Pb2+ > Cu2+ > Cd2+ > Zn2+ > Ni2+.

Selective recovery of gold from dilute aqua regia leachate of waste printed circuit board by thiol-modified garlic peel

Garlic peel (GP) was chemically modified by using thiourea under hydrothermal treatment, which could selectively adsorb gold ions from the 1/10 dilute aqua regia media directly without needing the dangerous evaporation operation. The synthetic chloroauric solution and practical leach liquor of the waste PCB (printed circuit board) powder in dilute aqua regia were employed to assess the adsorption performance on the thiol-GP and the commercial quaternary ammonia anion resin of D201, respectively. It was experimentally confirmed that the adsorption efficiency of gold onto the thiol-GP and D201 resin both reached 100%, and the maximum adsorption capacity of thiol-GP gel was evaluated as 42.59 mg Au/g that was much larger than that of D201 resin (3.33 mg Au/g). The thiol-GP gel adsorption efficiency of other coexisting base metal ions like Cu²⁺, Ni²⁺, Al³⁺, and Fe³⁺ from dilute aqua regia leach liquor of the waste PCB powder was near zero, and only gold could be enriched by selective adsorption onto the thiol-GP gel. At least 3 cycles of adsorption/elution could be obtained without decreasing the adsorption efficiency drastically. The adsorbed gold on the thiol-GP was able to be eluted effectively by using the mixture solution of 0.1 M thiourea and 0.1 M hydrochloric acid, and finally the solid gold could be recovered by sodium borohydride through a reduction process. This study demonstrated a green, environmentally friendly, low-cost, and efficient method for selective recovery of gold from the dilute leach liquor (aqua regia) of waste circuit boards.

Research trend and dynamical development of focusing on the global critical metals: a bibliometric analysis during 1991-2020

Critical metals are indispensable to a world seeking to transition away from carbon. Yet their extraction, processing, and application leave an unsustainable global environment and climate change footprint. To capture the development dynamics and research emphases of critical metals throughout their life cycle, this paper adopts bibliometrics to analyze the various stages of global critical metal flow in multiple dimensions to reveal the hot issues and future strategic trends. The research results indicate that the number of research papers on critical metals is annually rising, with remarkably rapid growth after 2010. Judging from the number of articles published by the authors and the citations, among the authors, Kawakita, Poettgen, Anwander, Inoue, and Dongmei Cui have a significant influence on critical metal research fields. The institutions with the most research on critical metals are universities, not research institutes. In addition, the focus has extended from a single discipline to the interdisciplinary development of multiple disciplines. Analysis of keywords shows that "rare metals" and "precious metals" are the most popular metals among the researched metals. The researched buzzwords of critical metals are disappearing, convergent, and merging over time. The research has focused on the mining and the whole life cycle process of extraction, treatment, and application. Based on the above characteristics, this paper tries to understand the dynamic development and evolution of global critical metals from multiple dimensions, resorting to giving a reference for follow-up-related research scholars.

Effective recovery of ytterbium through biosorption using crosslinked sericin-alginate beads: A complete continuous packed-bed column study

The recovery of rare-earth from secondary sources is essential for cleaner production. The development of natural biocomposites is promising for this purpose. Sericin is a waste protein from silk manufacturing. The highly polar groups on the surface of sericin facilitate blending and crosslinking with other polymers to produce biocomposites with improved properties. In this work, we investigate ytterbium recovery onto a natural biocomposite based on sericin/alginate/poly(vinyl alcohol) (SAPVA) in packed-bed column, aiming to establish a profitable application for sericin. Effects of flow rate and ytterbium inlet concentration showed that the highest exhaustion biosorption capacity (128.39 mg/g) and lowest mass transfer zone (4.13 cm) were reached under the operating conditions of 0.03 L/h and 87.95 mg/L. Four reusability cycles were performed under the optimum operating conditions using 0.3 mol/L HNO₃. Ytterbium recovery was highly successful; desorption efficiency was higher than 97% and a final ytterbium-rich concentrate (3870 mg/L) was 44 times higher than input concentration. Regenerated beads characterization showed that the cation exchange mechanism plays a major function in continuous biosorption of ytterbium. SAPVA beads also showed higher biosorption/desorption performance for ytterbium than other competing ions. These results suggest the application of SAPVA may be an alternative for large-scale ytterbium recovery.

Application of alginate extraction residue for Al(III) ions biosorption: a complete batch system evaluation

The residue derived from the alginate extraction from S. filipendula was applied for the biosorption of aluminum from aqueous medium. The adsorptive capacity of the residue (RES) was completely evaluated in batch mode. The effect of pH, contact time, initial concentration, and temperature was assessed through kinetic, equilibrium, and thermodynamic studies. The biosorbent was characterized prior and post-Al biosorption by N₂ physisorption, Hg porosimetry, He pycnometry, and thermogravimetry analyses. Equilibrium was achieved in 60 min. Kinetics obeys pseudo-second-order model at aluminum higher concentrations. Isotherms followed Freundlich model at low temperature (293.15 K) and D-R or Langmuir model at higher temperatures (303 and 313 K). Data modeling indicated the occurrence of both chemical and physical interactions in the aluminum adsorption mechanism using RES. The maximum adsorption capacity obtained was 1.431 mmol/g at 293 K. The biosorption showed a spontaneous, favorable, and exotherm character. A simplified batch design was performed, indicating that the residue is a viable biosorbent, achieving high percentages of removal using low biomass dosage.

Equilibrium, Thermodynamic, Reuse, and Selectivity Studies for the Bioadsorption of Lanthanum onto Sericin/Alginate/Poly(vinyl alcohol) Particles

In a scenario of high demand, low availability, and high economic value, the recovery of rare-earth metals from wastewater is economically and environmentally attractive. Bioadsorption is a promising method as it offers simple design and operation. The aim of this study was to investigate lanthanum bioadsorption using a polymeric bioadsorbent of sericin/alginate/poly(vinyl alcohol)-based biocomposite. Batch system assays were performed to evaluate the equilibrium, thermodynamics, regeneration, and selectivity of bioadsorption. The maximum capture amount of lanthanum at equilibrium was 0.644 mmol/g at 328 K. The experimental equilibrium data were better fitted by Langmuir and Dubinin-Radushkevich isotherms. Ion exchange mechanism between calcium and lanthanum (2:3 ratio) was confirmed by bioadsorption isotherms. Thermodynamic quantities showed that the process of lanthanum bioadsorption was spontaneous (-17.586, -19.244, and -20.902 kJ/mol), endothermic (+15.372 kJ/mol), and governed by entropic changes (+110.543 J/mol·K). The reusability of particles was achieved using 0.1 mol/L HNO₃/Ca(NO₃)₂ solution for up to five regeneration cycles. The bioadsorbent selectivity followed the order of lanthanum > cadmium > zinc > nickel. Additionally, characterization of the biocomposite prior to and post lanthanum bioadsorption showed low porosity (9.95 and 12.35%), low specific surface area (0.054 and 0.019 m²/g), amorphous character, and thermal stability at temperatures up to 473 K. This study shows that sericin/ alginate/poly(vinyl alcohol)-based biocomposites are effective in the removal and recovery of lanthanum from water.

Crosslinked alginate/sericin particles for bioadsorption of ytterbium: Equilibrium, thermodynamic and regeneration studies

Sericin is a soluble globular protein, present in Bombyx mori silkworm cocoons. Sericin's properties can be improved to expand its application by producing blends with other substances, such as alginate polysaccharide and crosslinking agent poly(vinyl alcohol). This study evaluates the use of alginate and sericin particles chemically crosslinked with poly(vinyl alcohol) (SAPVA) for batch bioadsorption of rare-earth element ytterbium from aqueous medium. The equilibrium study showed that the maximum bioadsorption capacity for ytterbium was 0.642 mmol/g at 55 °C. Equilibrium data fit both Langmuir and Dubinin-Radushkevich models. The estimation of thermodynamic parameters showed that there was an increase in the entropy change, and that the bioadsorption process is endothermic and spontaneous. Characterization analyzes revealed that SAPVA particles, even after ytterbium bioadsorption, showed spherical shape, homogeneous composition, amorphous structure, low surface area, macropores, and low porosity. After the first regeneration cycle, the amount of captured ytterbium ions showed a slight increase (about 0.01 mmol/g) and calcium ions were completely released by SAPVA particles. Bioadsorbent particles separated selectively ytterbium from synthetic effluent containing different toxic metal ions. These results show that the SAPVA particles can be used as an effective bioabsorbent to remove and recover ytterbium from wastewater.

Facile preparation of L-cysteine-modified cellulose microspheres as a low-cost adsorbent for selective and efficient adsorption of Au(III) from the aqueous solution

A facile method to synthesize adsorbent based on cellulose modified by amino acid was developed. The novel L-cysteine-functionalized adsorbent for Au(III) recovery was synthesized via radiation grafting technique. Glycidyl methacrylate (GMA) was grafted on the surface of microcrystalline cellulose microsphere (MCC); next, ring-opening reaction was performed to immobilize L-cysteine. The adsorption abilities of the adsorbent (CysR) were tested. Batch experiments suggested that the maximum adsorption capacity of Au(III) is 714.28 mg/g calculated by Langmuir model. The adsorption kinetic data was followed by pseudo-second-order model. CysR showed excellent selectivity for Au(III) even the concentration of competing ions was all ten times than that of Au(III). The column experiments revealed that Au(III) could be efficiently adsorbed by CysR competition with equal amounts of Ni(II) and Zn(II). Moreover, XPS analysis demonstrated that the adsorbed Au(III) was reduced to Au(I) and Au(0). The adsorption performance certified that CysR was a promising adsorbent for Au(III) recovery.

Competitive biosorption of Cu2+ and Ag+ ions on brown macro-algae waste: kinetic and ion-exchange studies

The application of biosorption operation has gained attention in the removal and retrieval of toxic metal ions from water bodies. Wastewater from industrial activity generally presents great complexity due to the coadsorption of cations to the inactive biomass binding sites. In this work, the competitive biosorption of Cu(II) and Ag(I) ions was studied in batch systems. A kinetic study applying a non-acidified and acidified waste of Sargassum filipendula in equimolar and non-equimolar metal samples was carried out and the acidified biosorbent was selected due to higher removal rates and selectivity of silver ions. The assays were performed with 2 g L^-1 of biosorbent concentration at 25 °C for 12 h and pH was controlled at around 5.0. Copper presented higher affinity for the biosorbent and a fast biosorption kinetic profile, while silver equilibrium times exhibited dependence on the copper concentration. External diffusion is the rate-limiting step in Cu(II) ion removal and it might also limit the kinetic rates of Ag(I) ions with intraparticle diffusion, depending on the initial concentration of metal cations. The ion-exchange mechanism is evidenced and complexation and electrostatic attraction mechanisms might be suggested, explained by simultaneous chemisorption and physisorption processes during the operation. Calcium and sodium were released in considerable amounts by the ion-exchange mechanism. Characterization analyses confirmed the role of several functional groups in the competitive biosorption accompanied by a homogenous covering of both metal ions on the surface of the particles. Particle porosity analyses revealed that the material is macroporous and an appreciable amount of macropores are filled with metal cations after biosorption.

Biosorption technology for removal of toxic metals: a review of commercial biosorbents and patents

In last decades, the biosorption process has become one of the main alternative treatment technologies for the removal of pollutants from dilute aqueous solution. Among these pollutants, toxic metals have drawn attention due to their negative effects in human body and food chain. Even though biosorption is considered a cost-effective and eco-friendly technology to remove toxic metals from dilute wastewaters, there are still obstacles that restrain its commercialization. For this reason, various scientific articles and patents have been published each year to make more effective and economical this technology. This review reports an overview of past achievements, current research of biosorption studies, and future trends for the development of the biosorption as sustainable cleaner technology. Mechanisms of metal uptake, recovery and biosorbent regeneration, process design, commercial application of biosorbents, and patents registered are presented. Finally, future aspects in biosorption research and suggestions for its application will be discussed.