Competitive and Noncompetitive Batch Sorption Studies of Aqueous Cd(II) and Pb(II) Uptake ontoCoffea canephoraHusks,Cyperus papyrusStems, andMusaspp. Peels
Coffea canephora,Cyperus papyrus,andMusaspp. 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% forC. canephora, 42.0–91.3% forC. papyrus,and 79.9–92.2% forMusaspp. and in competitive sorption 90.8–98.0% forC. canephora, 19.5–90.4% forC. papyrus,and 56.4–89.3% forMusaspp. 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 with0.917≤R2≥1.000for Pb2+ions and0.711≤R2≥0.999for Cd2+ions. The Langmuir model fitted noncompetitive sorption data with0.769≤R2≥0.999; moreover the Freundlich model fitted competitive sorption data with0.867≤R2≥0.989. Noncompetitive sorption was monolayer chemisorption whereas competitive sorption exhibited heterogeneous sorption mechanisms.