Competitive and noncompetitive batch sorption studies of aqueous Cd uptake onto Coffea canephora husks, Cyperus papyrus stems, and Musa spp. peels

Coffea canephora, Cyperus papyrus, and Musa spp. were studied for competitive and noncompetitive removal of aqueous [Cd.sup.2+] and [Pb.sup.2+]. 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 [Pb.sup.2+] ions uptake was superior to that of [Cd.sup.2+] ions in competitive and noncompetitive media. In competitive sorption synergistic effects were higher for [Cd.sup.2+] than [Pb.sup.2+] ions. The pseudo-second-order kinetic model fitted experimental data with 0.917 [less than or equal to] [R.sup.2] ≥ 1.000 for [Pb.sup.2+] ions and 0.711 ≤ [R.sup.2] ≥ 0.999 for [Cd.sup.2+] ions. The Langmuir model fitted noncompetitive sorption data with 0.769 ≤ [R.sup.2] ≥ 0.999; moreover the Freundlich model fitted competitive sorption data with 0.867 ≤ [R.sup.2] ≥ 0.989. Noncompetitive sorption was monolayer chemisorption whereas competitive sorption exhibited heterogeneous sorption mechanisms.