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.