Competitive and noncompetitive batch sorption studies of aqueous cd(ii) and pb (ii) uptake onto coffea canephora husks, cyperus papyrus stems, and musa spp. peels

Abstract

Coffea canephora, Cyperus papyrus, and Musa spp. were studied for competitive and noncompetitive removal of aqueous Cd2+ and Pb2+. The optimal conditions were pH 4.5 and agitation time 3.0 hours. Biomass constituent ions showed no interference effects whereas cation exchange capacity values corresponded to the sorption efficiencies. XRD spectroscopy revealed surface oxygen and nitrogen groups that provide binding sites for metal ions. The maximum sorption efficiency ranges for metal ions in noncompetitive media were 95.2–98.7% for C. canephora, 42.0–91.3% for C. papyrus, and 79.9–92.2% for Musa spp. and in competitive sorption 90.8–98.0% for C. canephora, 19.5–90.4% for C. papyrus, and 56.4–89.3% for Musa spp. The Pb2+ ions uptake was superior to that of Cd2+ ions in competitive and noncompetitive media. In competitive sorption synergistic effects were higher for Cd2+ than Pb2+ ions. The pseudo-second-order kinetic model fitted experimental data with 0.917 ≤ 𝑅2 ≥ 1.000 for Pb2+ ions and 0.711 ≤ 𝑅2 ≥ 0.999 for Cd2+ ions. The Langmuir model fitted noncompetitive sorption data with 0.769 ≤ 𝑅2 ≥ 0.999; moreover the Freundlich model fitted competitive sorption data with 0.867 ≤ 𝑅2 ≥ 0.989. Noncompetitive sorption was monolayer chemisorption whereas competitive sorption exhibited heterogeneous sorption mechanisms.