Effect of Organic Ligands on Copper(II) Removal from Metal Plating Wastewater by Orange Peel-based Biosorbents

Copper(II) biosorption in the presence of complexing agents (CA) onto orange peel (OP) and chemically modified OP (OPH+, OPNa+, and OP(Na+)(H+)) was studied. The study of the effect of pH showed that OPH+ presented a copper(II) uptake similar to OP in the pH range 1.5–6.0, whereas OPNa+ and OP(Na+)(H+) showed the highest copper(II) uptake in the pH range 4–6. Copper(II) sorption isotherms were obtained with Cu(II)/CA mass ratios of 1:0 and 1:2 at pH 5. The Sips model fitted best the isotherms without CA, whereas the Freundlich and Brunauer-Emmett-Teller (BET) models fitted best the isotherms in the presence of ethylenediaminetetraacetic acid (EDTA) and citrate, respectively. The CA reduced the copper(II) uptake due to the presence of copper(II)-chelated species, though the interference of citrate was less important than that of EDTA. OPNa+ and OP(Na+)(H+) showed a higher copper(II) uptake capacity than OP, also in the presence of CA in solution. Copper(II) sorption mechanisms were studied using energy-dispersive X-ray and Fourier transform infrared spectroscopy and revealed ion exchange as one of the mechanisms. Biosorption reversibility and biosorbent reuse were evaluated in sorption/desorption cycles. Reversibility of copper(II) sorption was obtained (90 % metal recovery), though an important reduction of the metal uptake was observed in the second cycle.