The effect of process parameters on kinetics and mechanisms of Co2+ removal by bone char
Smičiklas, Ivana D.
Šljivić-Ivanović, Marija Z.
Plećaš, Ilija B.
Slavković-Beškoski, Latinka J.
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Bone char powder, composed mainly of poorly crystalline hydroxyapatite (Ca-10(PO4)(6)(OH)(2)), carbon and CaCO3, has potential applicability in the removal of Co2+ ions from contaminated effluents. In the present study, the influence of process parameters: particle size, agitation speed, initial pH and initial sorbate concentration, onto kinetics and mechanism of Co2+ sorption was studied and discussed. In order to describe and compare time evolution of the process under different conditions, the experimental data were analyzed using pseudo-first, pseudo-second and Vermeulens kinetic models. Generally, experimental results were best fitted with the pseudo-second-order model, which accurately predicted the equilibrium sorbed amounts. The pseudo-second-order rate constant was the most influenced by variations in initial metal concentration and pH, in the investigated ranges. The conclusions about sorption mechanism were derived based on Co2+ amounts sorbed during time, as well as conside...ring solution pH changes, changes of Ca2+ amounts released into liquid phase and Ca2+/Co2+ molar ratios. It was concluded that rapid sorption stage was governed by surface complexation reactions, whereas the contribution of the ion-exchange mechanism increased with time and became more significant in the second, slower phase. Experimentally determined maximum sorption capacity towards Co2+, under optimal conditions, was found to be 0.38 mmol/g. The results show that bone char represents cost-effective alternative to synthetic hydroxyapatite sorbent.