Biosorbents for remediating aquatic environmental media polluted with hazardous heavy metals and metalloids such as Pb(II), Cr(VI), Sb(III and V), and As(III and V) were prepared from lignin waste, orange and apple juice residues, seaweed and persimmon and grape wastes using simple and cheap methods. A lignophenol gel such as lignocatechol gel was prepared by immobilizing the catechol functional groups onto lignin from sawdust, while lignosulfonate gel was prepared directly from waste liquor generated during pulp production. These gels effectively removed Pb(II). Orange and apple juice residues, which are rich in pectic acid, were easily converted using alkali (e.g., calcium hydroxide) into biosorbents that effectively removed Pb(II). These materials also effectively removed Sb(III and V) and As(III and V) when these were preloaded with multi-valent metal ions such as Zr(IV) and Fe(III). Similar biosorbents were prepared from seaweed waste, which is rich in alginic acid. Other biosorbents, which effectively removed Cr(VI), were prepared by simply treating persimmon and grape wastes with concentrated sulfuric acid.

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

Germanium in solution was recovered on an anion-exchange membrane after complexation with 3-methylcatechol. The complex was transferred to the anion-exchange membrane by convection, which meant diffusion was not the rate-determining step as in conventional resin recovery. In batch mode, the optimum solution pH was 8, and at this pH the method was selective for germanium against silicate ion. In continuous mode at pH 11.0 and 2.0, the germanium ion was selectively adsorbed as a complex ion in the membrane. This system could be applied to hydrometallurgy processes for the recovery of germanium.

Gold was selectively precipitated with solution of persimmon extract which contains persimmon tannin, a kind of polyphenol. Quantitative recovery of gold was achieved in the concentration range of hydrochloric lower than 0.5 mol · dm⁻³. X-ray diffraction analysis and a digital micrograph of the filtered cake indicated the formation of gold particle during recovery process. High selectivity of persimmon extract is ascribed to the reduction of Au(III) to elemental form.