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Highlights: [•] We developed environmentally benign and low cost adsorbent from kraft mill lignin. [•] Specific gold selectivity and high gold uptake capacity of the adsorbent. [•] Reduction of adsorbed Au(III) to elemental Au and formation of gold aggregates. [•] Promising candidate for selective recovery of gold from base metals in aqueous environment. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biomass-based low cost and “green” adsorption materials. [•] Highly efficient and selective for the Cs+ over Na+ ions from aqueous solutions. [•] Materials with tremendous promise for the preconcentration and separation of Cs+ ions. [ABSTRACT FROM AUTHOR]

Highlights: [•] Low cost and environmentally green adsorption material. [•] Remarkable selectivity for adsorption of precious metals over base metal ions. [•] High efficient for preconcentration and separation of precious metals. [•] Superior performance over commercial anion exchange resin. [Copyright &y& Elsevier]

Abstract: A new adsorption gel has been developed by immobilizing N-aminoguanidine (AG), a chelating ligand, on persimmon tannin extract through consecutive reactions. Adsorption behavior of the gel was investigated for the adsorptive separation and recovery of precious metal ions from varying concentration of HCl medium. The adsorption isotherms of precious metal ions on the gel were described by the typical monolayer type of Langmuir model and the maximum adsorption capacities were evaluated as 8.90molkg−1 for Au(III), 2.01molkg−1 for Pd(II) and 1.01molkg−1 for Pt(IV). Real time applicability of the gel was examined for the recovery of precious metals from actual leach liquor of e-waste leached with chlorine containing hydrochloric acid. The gel was found to be highly efficient and selective for the uptake of targeted metal ions in the presence of excess base metal ions and also exhibited superior selectivity over commercially available anion exchange resins. [Copyright &y& Elsevier]

Abstract: A new approach of recovering precious metals from printed circuit boards (PCBs) of mobile waste by acidothiourea leaching followed by selective adsorption on low-cost and environmentally benign biomass sorbent prepared from easily available agricultural waste is suggested. The influence of various parameters like thiourea (TU) concentration, acid concentration, pulp density, temperature, and contact time were studied for gold and silver leaching using a batchwise method. It was found that the PCB sample with smaller particle size distribution (53 to 75μm) yielded higher amounts of gold and silver being leached into the solution. The optimum conditions for the leaching of gold were found to be 0.5M TU in 0.05M H2SO4 at 45°C, while that of silver were 0.5M TU in 0.01M H2SO4 at 60°C. Under the optimum leaching conditions, an average of 3.2mg/g of gold and 6.8mg/g of silver were extracted from incinerated sample of PCBs of mobile waste. Kinetic studies revealed that the complete leaching of silver was achieved in less than 2h, while it took approximately 6h at ambient temperature in the case of gold. Presence of 0.01M ferric ions facilitated the gold dissolution rate and complete leaching was achieved within 2h. Conventional copper cementation for recovery of gold and silver from pregnant leached liquor was not so effective. Adsorptive recovery of dissolved gold and silver using activated carbon as well as crosslinked persimmon tannin gel was also examined. Low-cost persimmon tannin extract crosslinked with sulfuric acid was found to be a promising material for the complete recovery of gold and silver from the leached liquor. This adsorbent not only adsorbed the dissolved precious metals selectively but also reduced the adsorbed cationic species of gold to the elemental gold. [Copyright &y& Elsevier]

Abstract: An adsorption gel was prepared by crosslinking the persimmon tannin with concentrated sulfuric acid and adsorption behavior of Au(III) from acidic chloride media on the crosslinked gel as well as crude persimmon tannin powder was evaluated. The crosslinked gel exhibited 100% adsorption of Au(III) over a whole concentration range of HCl from 0.1 to 6.0M (M=moldm−3) while crude persimmon tannin powder achieved 100% adsorption only in the low concentration region of HCl. The maximum adsorption capacity of the crosslinked gel for Au(III) was evaluated as high as 7.7mol/kg whereas it was only 5.8mol/kg for the crude tannin powder. The phenomenon of adsorption coupled reduction is considered to be responsible for the high adsorption of Au(III). The reduction of Au(III) to its elemental form was confirmed by XRD and digital micrograph of the adsorbents after the adsorption of Au(III). The reaction kinetics at different temperatures for both adsorbents was evaluated in terms of pseudo-first-order and pseudo-second-order kinetic models. As revealed by the high activation energy (E a) value, adsorption of Au(III) on both the adsorbents was found to be a chemical phenomenon. [Copyright &y& Elsevier]

Persimmon tannin was chemically modified to prepare a quaternary amine type of adsorption gel, named as quaternary amine modified persimmon tannin (QAPT) gel. The QAPT gel has been used to investigate the adsorption behaviors for Au(III), Pd(II), and Pt(IV) from HCl media. It was found that the gel exhibited good selectivity towards precious metals over a wide concentration range of HCl. However, it exhibited poor affinity towards base metals such as Cu(II), Fe(III), Ni(II), and Zn(II). The adsorption isotherms of the gel for precious metal ions were described by the Langmuir model. The maximum adsorption capacities for Au(III), Pd(II), and Pt(IV) were evaluated as 4.16, 0.84, and 0.52 mmol g−1, respectively. Although the anion exchange is the main mechanism for the adsorption of anionic species of Au(III), Pt(IV), and Pd(II), adsorption of Au(III) is followed by subsequent reduction, which results in the extraordinary high adsorption capacity for Au(III). Adsorption behavior of QATP gel for Au(III) was also compared to that of the persimmon tannin, the feed material. [ABSTRACT FROM PUBLISHER]

Abstract: Novel polyvinylcalix[4]arene resin has been synthesized by direct polymerization of calix[4]arene through vinylic groups at upper rim and an ion-exchange resin has been developed by appending carboxylic acid groups onto the resin. Adsorption behavior of the polyvinylcalix[4]arene carboxylic acid resin towards some divalent heavy metal ions has been investigated, together with its corresponding monomeric analogue as a control, in terms of effect of pH on selectivity, equilibrium time of adsorption and maximum uptake capacity. The calixarene resin was found to be superior to the monomeric analogue for adsorption ability and separation efficiency. Pb(II) ions were highly preferred over Cu(II), Zn(II), Co(II) and Ni(II) ions by calixarene resin. Size fit complementarity effect of the host cavity and the guest species was found to be the prevailing factor for specific lead ion selectivity of the resin. Surface reactive adsorption of cation on the resin due to ion exchange with carboxyl groups was sufficiently fast and significant adsorption of Pb(II) ions on the resin was achieved within 15min. However, the equilibrium of adsorption was achieved within 4h. Maximum lead loading capacity of calix[4]arene resin was found to be 1.82mmolg−1 while that of the monomeric analogue was 0.064mmolg−1 resin. Because of the resin''s sensitivity to change in pH, the loaded lead was easily eluted with dilute acid solution and the resin was regenerated without any physical and chemical damage. Separation of trace amount of lead in presence of excess of zinc ions was achieved in column chromatographic experiment. [Copyright &y& Elsevier]

Highlights: [•] A novel biosorbent was prepared from the microalgal waste after biofuel extraction. [•] Higher selectivity and adsorption efficiency of the adsorbent for Cs+ over Na+ ions from aqueous solutions. [•] Potential candidate and eco-friendly alternative to the commercial resins such as zeolite. [ABSTRACT FROM AUTHOR]