Chaitanya Raj Adhikari

Selective recovery of precious metals by persimmon waste chemically modified with dimethylamine.

Persimmon waste was chemically modified with dimethylamine (DMA) to obtain a tertiary-amine-type gel, named DMA persimmon waste gel (DMA-PW). It was found to be effective for the adsorption of Au(III), Pd(II), and Pt(IV) in hydrochloric acid medium. In contrast, base metals such as Cu(II), Zn(II), Fe(III), and Ni(II) were not practically adsorbed. The formation of ion pairs of the metal chloro complex anions with the protonated adsorption gels was proposed as the main adsorption process. The gel exhibited selectivity only for precious metals with a remarkably high capacity for Au(III), i.e., 5.63 mol/kg dry gel and comparable capacities, i.e., 0.42 and 0.28 mol/kg for Pd(II) and Pt(IV), respectively. According to the kinetic and electrochemical studies, the adsorption rate of Au(III) was greatly enhanced by the chemical modification. Also, its excellent adsorption characteristics for the precious metals were confirmed by adsorption and elution tests using a column packed with the DMA-PW gel.

Recovery of precious metals by using chemically modified waste paper

Waste newsprint paper was chemically modified with p-aminobenzoic acid to prepare a sorption active gel. This gel proved useful for the selective uptake of gold, palladium and platinum over other coexisting metal ions such as copper, nickel, zinc and iron. A remarkably high capacity for Au(III) was observed together with a moderate uptake of Pt(IV) and Pd(IV). Furthermore, Au(III) was reduced to elemental gold which formed aggregates. A high percentage recovery of the precious metal ions (85–95%) and regeneration of the gel was attained by using a mixture of 0.15 M thiourea and 1 M HCl. Repeated cycles of uptake and elution by using a column packed with this new sorbent indicated that the gel is suitable for industrial application in continuous mode.

Chestnut pellicle for the recovery of gold

Recovery of Au(III) from hydrochloric acid medium by using crosslinked chestnut pellicle (CCP) gel was studied. Strong selectivity was observed for Au(III) showing negligible affinity for other precious metals and some base metal ions tested. The adsorption isotherm study exhibited the maximum loading capacity of the gel as high as 10.6 mol or about 2.1 kg gold per kg dry weight of gel. The reduction of Au(III) ion to elemental form during adsorption process is expected to be the reason of high selectivity and high capacity for Au(III). Kinetic studies at various temperatures confirm an endothermic adsorption process following the pseudo-first order rate law.

Pre-concentration and separation of heavy metal ions by chemically modified waste paper gel

Iminodiacetic acid was immobilized on waste paper by chemical modification in order to develop a new type of adsorption gel for heavy metal ions. Adsorption behavior of the gel was investigated for a number of metal ions, specifically Cu(II), Pb(II), Fe(III), Ni(II), Cd(II), and Co(II) at acidic pH. From batch adsorption tests, the order of selectivity was found to be as follows: Cu(II)>>Fe(III)>Pb(II)>Ni(II)>>Co(II)>Cd(II). Column tests were carried out for pairs of metal ions to understand the separation and pre-concentration behavior of the gel. It was found that mutual separation of Ni(II) from Co(II) and that of Pb(II) from Cd(II) can be achieved at pH 3. Similarly, selective separation of Cu(II) from Cu(II)-Fe(III) and Cu(II)-Pb(II) mixtures at pH 1.5 and 2, respectively, was observed by using this new adsorption gel. In all cases, almost complete recovery of the adsorbed metal was confirmed by elution tests with HCl.

Adsorption Behavior of Iminodiacetic Acid Type of Chelating Gel Prepared from Waste Paper

Abstract Adsorption gel was prepared from waste recycled paper by immobilizing iminodiacetic acid (IDA) functional group by chemical modification. The gel exhibited good adsorption behavior for a number of metal ions viz. Cu(II), Pb(II), Fe(III), Ni(II), Cd(II), and Co(II) at acidic pH. The order of selectivity was found to be as follows: Cu(II)>Pb(II)>Fe(III)>Ni(II)∼Cd(II)∼Co(II). From the adsorption isotherms, the maximum adsorption capacity of the gel for both Cu(II) and Pb(II) was found to be 0.47 mol/kg whereas that for Cd(II) was 0.24 mol/kg. A continuous flow experiment for Cd(II) showed that the gel can be useful for pre‐concentration and complete removal of Cd(II) from aqueous solution.