Adsorptive separation of heavy metals from an aquatic environment using orange waste

Preparation of adsorption gel for metal ions from orange wastes by simple chemical modification was investigated. Two types of adsorption gels, Ca2+-form and H+-form gels, were prepared by saponifying orange juice residues with calcium hydroxide and its subsequent acid treatment, respectively. Both gels were adequately stable against dissolution in aquatic environment. The Ca2+-form gel was effective for the complete and selective removal of Pb(II), Cu(II) and Fe(III) compared with other divalent metal ions. The selectivity order for metal ion uptake by the gel is Pb(II) > Fe(III) > Cu(II) > Cd(II) ≈ Zn(II) > Mn(II). Among these metal ions, the maximum loading capacities for divalent metal ions such as Pb(II), Cd(II) and Zn(II) were evaluated as 1.1 mol/kg-dry gel while that for Fe(III) was 1.55 mol/kg-dry gel. The H+-form gel showed a different adsorption profile for Fe(III) compared to the Ca2+-form gel. The experimental results clearly suggest that both gels are quite effective for removing heavy metal ions in acidic pH ranges.