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.

To remove the radioactive cesium from the polluted environment, tea leaves were chosen as cheap, and abundantly available environment-friendly bio-adsorbents to investigate the alkali metals adsorption. Fresh and used tea leaves (FT and UT) were found to have high efficiency and selectivity for cesium adsorption, after the crosslinking with concentrated sulfuric acid. Calculation of the proton-exchanged amount suggested adsorption mechanism of three alkali metals on crosslinked tea leaves involve a cationic exchange with a proton from the hydroxyl groups of the crosslinked tea leaves, as well as coordination with ethereal oxygen atoms to form the chelation. Further, considering the practical application of the polluted water treatment, the competitive adsorption of Cs⁺ and Na⁺ ions was investigated by the batch-wise method and column chromatography separation. Unlike the conventional ion exchange and chelate resins with less selectivity for Cs⁺ coexisting cations, both crosslinked fresh tea leaves (CFT) and crosslinked used tea leaves (CUT) exhibited Cs selectivity over Na. In addition, batch adsorption studies revealed that the cesium adsorptions were driven by the Langmuir isotherm model; the capacity of both crosslinked tea leaves for cesium adsorption was determined to be around 2.5 mmol g⁻¹. The adsorption capacities are sufficiently higher in comparison with those of synthetic polymers, inorganic ion-exchangers, and other bio-adsorbents.

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. 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. By using these biosorbents, recovery of gold from actual samples of printed circuit boards of spent mobile phones and Mongolian gold ore was investigated. Recovery of trace concentration of gold(I) from simulated spent alkaline cyanide solution was also investigated using the bioadsorbent. Application of bioadsorbents to some recovery processes of gold from cyanide solutions was proposed.

The present study investigates a new adsorbent for Cs(I) removal from green tea extract. An extract of green tea rich in polyphenolic compounds was simply cross-linked using concentrated sulfuric acid to reduce aqueous solubility and improve Cs(I) adsorption. Dissolution of total organic carbon (TOC) from non-modified tea extract (TE, 4,324 mg/L) was drastically suppressed in cross-linked tea extract (CLTE, 13.6 mg/L). The adsorption performance of CLTE for Cs(I) was compared with TE, the feed material, using the batch-wise method. Kinetic study showed that the adsorption equilibrium can be reached within 4 h for native TE and 12 h for CLTE. The maximum adsorption capacity of Cs(I) using non-modified tea extract (TE, 0.20 mmol/g) was drastically increased after cross-linking (CLTE, 1.23 mmol/g). The Cs(I) ion was selectively adsorbed onto CLTE from a mixture containing a trace amount of Cs(I) and a high concentration of Na(I). Therefore, the CLTE adsorbent investigated in this study can be expected to be a potential efficient; and environmentally benign adsorbent for the treatment of water polluted with Cs(I) ion.