Hydrometallurgical Recovery of Precious Metals and Removal of Hazardous Metals Using Persimmon Tannin and Persimmon Wastes

Abstract

Novel and environmentally benign adsorbents were prepared via a simple sulfuric acid treatment process using the wastes of astringent persimmon, a type of biomass waste, along with persimmon tannin extract which is currently employed for the tanning of leather and as natural dyes and paints. The effectiveness of these new biosorbents was exemplified with regards to hydrometallurgical and environmental engineering applications for the adsorptive removal of uranium and thorium from rare earths, cesium from other alkaline metals such as sodium, hexa-valent chromium from zinc as well as adsorptive recovery of gold from chloride media. Furthermore, reductive coagulation of gold from chloride media for the direct recovery of metallic gold and adsorptive recovery of palladium and platinum using chemically modified persimmon tannin extract were studied. OPEN ACCESSMetals 2015, 5 1922

Selective Adsorption of AuIII from Aqueous Solution Using 2,5‑Dimercapto‑1,3,4‑thiadiazole Modified Persimmon Tannin

“…As shown in Figure 3, for DMTD-PT, when the pH was lower than that of the isoelectric point, DMTD-PT had relatively higher Au III adsorption because the positively charged surface (as a result of protonation of the N-functional groups on the surface) was beneficial for attracting AuCl 4 − via electrostatic interactions. However, when the pH was higher than that of the isoelectric point, ).…”

“…As shown in Figure 1, under acidic conditions (that is, for pH values lower than the isoelectric point) the nitrogen atoms of DMTD-PT are easily converted into positively charged centers as a result of protonation, and this favors the adsorption of the anionic AuCl 4 − via electrostatic interactions.…”

“…III adsorption on DMTD-PT slightly decreased because the negatively charged surface of the adsorbent (as a result of deprotonation) repelled the adsorption of AuCl 4 − via electrostatic interactions.…”

“…2 Such a technology is also vitally crucial in terms of sustainable development because it would undoubtedly decrease the consumption of virgin materials and energy. 3 Over the past decade, persimmon peels and residues, whose main composition is persimmon tannin (PT), 4 have attracted a great deal of attention among waste agricultural byproducts because of the plentiful resources and moderate conditions for chemical modification. 4 Relevant work has mainly focused on grafting amine-and thiourea (TU)-based modifiers on the PT matrix [5][6][7] to improve both adsorption capacity and selectivity for precious metals.…”

Magnetic Adsorbents for the Recovery of Precious Metals from Leach Solutions and Wastewater

“…Due to their unique physical and chemical properties, precious metals (PMs) are used extensively not only in traditional jewelry and ornamental purposes but also in a variety of advanced applications, such as electronics, chemical and environmental catalysis, dentistry and medicine, and pharmaceutical industries. Since these metals are scarce and exist only in small amounts in the earth's crust, they should be recovered effectively from their natural ores and also from various wastes and secondary sources through recycling [2].…”