For example, in the cases of ion-exchange resins, they deteriorate through the formation of many cracks and clogging of micropores of the resins by fine particles present in actual solutions, both of which impede smooth operation using packed columns.įor the effective separation and concentration in hydrometallurgical processes, high selectivity and high loading capacity for targeted metals are strongly required for solvent extraction reagents and adsorbents.
Of these processes, precipitation and solvent extraction are suitable for the recovery from solutions of high concentration, while adsorption and ion-exchange are suitable from those of low or trace concentration.ĭuring long operation, solvent extraction reagents, adsorbents, and ion-exchangers gradually deteriorate and finally they are discarded. For the separation and concentration of the targeted metals, various processes such as precipitation, solvent extraction, ion-exchange including chelating ion-exchange and adsorption have been employed.
Hydrometallurgical processes consist of leaching of metals from solid feed materials into aqueous solutions, separation and concentration of the targeted metals from other metals, and final recovery as solid metals of high purity such as ingot metals. The typical wastes containing valuable metals are those of spent electric and electronic appliances, i.e., e-wastes.įor the recovery of valuable metals from such poor and complex feed materials, hydrometallurgical processes are more suitable than pyrometallurgical processes. Under such situation, not only poor and complex natural resources but also secondary resources, i.e., various wastes containing valuable metals in low contents, have to be employed as feed materials to recover valuable metals. In recent years, accompanied by huge consumption of various metals, metal contents or grade of metal ores have become poor and complex. Application of bioadsorbents to some recovery processes of gold from cyanide solutions was proposed. Recovery of trace concentration of gold(I) from simulated spent alkaline cyanide solution was also investigated using the bioadsorbent. By using these biosorbents, recovery of gold from actual samples of printed circuit boards of spent mobile phones and Mongolian gold ore was investigated. These bioadsorbents exhibited high selectivity only to gold over other metals and extraordinary high loading capacity for gold(III), which were elucidated to be attributable to the selective reduction of gold(III) ion to elemental gold due to its highest oxidation-reduction potential of gold(III) of metal ions, catalyzed by the surface of bioadsorbents prepared in boiling sulfuric acid. Bioadsorbents were prepared in a simple manner only by treating in boiling concentrated sulfuric acid from various biomass materials such as various polysaccharides, persimmon tannin, cotton, paper and biomass wastes such as orange juice residue and microalgae residue after extracting biofuel.
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