Regeneration of a chemically improved peat moss for the removal and recovery of Cu(II) and Pb(II) from aqueous solution

Unabated research into biosorption technology is fueled by the prospect of a low-cost solution to the unrestrained discharge of heavy metal effluents. However, the resulting spent biosorbents can become an environmental burden, and thus, the ability to remove and recover metal contaminants from spent biosorbents can reduce disposal risk. A suitable desorption process should, therefore, generate a rapid sorbate release, a high metal concentrated effluent, provide minimal physico-chemical damage to the biosorbent, as well as, produce little or no change in biosorbent capacity upon re-use. In this study, an improved peat biosorbent produced by hot-alkali pretreatment was subjected to individual and sequential desorption, desorption kinetics, and regeneration studies using various eluents. Elution studies using distilled water, calcium chloride (CaCl2), ethylenediaminetetraacetic acid (EDTA), and hydrochloric acid (HCl) to release Cu(II) and Pb(II) ions exposed the involvement of multi-mechanistic attachment. Cu(II) sorption was attributed to 3% physisorption, 26% ion exchange and 71% complexation while Pb(II) sorption was attributed to 50% ion exchange and 50% complexation. Desorption kinetics was examined to elucidate the rate of release of the metal ions and was best modeled by the pseudo-second-order equation. Regeneration tests revealed after 4 biosorption/desorption cycles, EDTA washes delivered an increased sorbent capacity. However, HCl offered the most rapid release of metal ions, a marginal increase in sorbent capacity and more significant, the greatest release of bound ions, thus producing a safer biosorbent for disposal.