Selective adsorption of Au³⁺ from aqueous solutions using persimmon powder‐formaldehyde resin

Abstract

A new adsorption resin has been developed by immobilizing persimmon powder with formaldehyde, and its adsorption properties to Au 31 were investigated in detail. The resin exhibited outstanding selective adsorption capacity towards Au 31 from acidic aqueous solutions (pH 2.0), which the equilibrium adsorption capacity was high up to 3025.20 mg g 21 at 323 K. The resin exhibited 100% adsorption of Au 31 within 8 h, and the experimental data were well fitted with the pseudo-first/second-order rate model. The adsorption isotherms could be well described by Freundlich equation. The column studies suggested that the resin was effective for the adsorption of Au 31 from aqueous solutions, and the loaded Au 31 could be easily desorbed by acidic thiourea solution. The adsorption of Au 31 was an endothermic reductive adsorption process. This suggested that the resin can be used as an active biosorbent for the recovery of Au 31 from aqueous environment. R 2 : correlation coefficient.Initial conc. of Au 31 = 100 mg L 21 , pH = 2.0, adsorbent dose = 0.3 g L 21 , temperature = 303, 313, and 323 K, respectively, shaking speed = 200 r min 21 , and shaking time = 0.5212 h. ARTICLE WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP

Tannin-based biosorbents for environmental applications – A review

“…Tannin resins have also showed a selective uptake for gold, against negligible uptakes of other metals from the solution (Fe 3+ , Pb 2+ , Cu 2+ , Zn 2+ , Ni 2+ Pd 2+ , Pt 4+ ) [42,43,53,95]. In general, literature has been focused in batch adsorption studies, with few studies reporting results in continuous mode fixed-bed columns [53,94]. The column studies carried out by Xie et al [53] suggested that the resin was effective for the uptake of Au (III) from aqueous solutions but, during the adsorption step and even after 8000 bed volumes, adsorption equilibrium (saturation) was not achieved.…”

“…Weibull black tannins, for instance, were successfully gelified with formaldehyde amounts of 1 and 3.68 mmol g À1 , but did not gelified with acetaldehyde dosages of 1.3 and 4.85 mmol g À1 [32]. In order to simplify the synthesis procedures, some works [42,53,56] report the preparation of tannin-gels using the vegetable materials (e.g. : persimmon powder, raw peels) without extracting the tannins.…”

“…The optimum pH conditions for gold uptake are usually in a narrow acidic range (practical interest conditions), using HCl solutions or HNO 3 /HCl mixtures (acids of aqua regia, commonly used in leaching processes). Optimum uptake of gold in tannin-derived resins has been found at pH 2 [38,53] or 3 [89]. In addition to the pH, the acids present in solution (HCl or HNO 3 ) are also variables to be considered, exerting different effects on the amount of gold adsorbed.…”

“…Insolubilization of tannins can be achieved through their reaction with formaldehyde (or other aldehyde), a step-growth polymerization reaction that can be either acid-or base-catalyzed [32,52,53]. In such reaction, an aldehyde compound establishes links between the tannin monomers, acting as a cross-linking agent.…”

“…An example of such wastes are the obsolete electric and electronic devices, or e-wastes, which contain large amounts of precious metals. Indeed, e-wastes contain more gold per ton of scrap than gold ores do per ton of ore, being considered a secondary ore of gold [53].…”