Effect of Competing Cations (Pb, Cd, Zn, and Ca) in Fixed-Bed Column Biosorption and Desorption from Citrus Peels

Citrus peels were utilized for dynamic biosorption of Pb, Cd, and Zn from mono-and bi-component solutions in fixed-bed columns at feed concentrations of 0.1 meq/L. Uptake at breakthrough and saturation followed the order Zn<Cd<Pb in single-metal biosorption. An overshoot of the Zn or Cd effluent concentration was observed in Pb-Zn and Pb-Cd bimetal systems, where Pb displaced initially bound Zn and Cd. The desorption efficiency of the saturated column using 0.1 N nitric acid was 74 to 100 %, achieving a concentration factor (CF) of 34 to 129, based on the average desorbed metal concentration. The common practice of defining the concentration factor based on the peak concentration overestimates the CF value. Increasing Ca concentrations in Pb-Ca and Cd-Ca systems reduced target metal uptake, especially for Cd which had a lower affinity than Pb. Actual mining effluent was treated successfully. A sigmoid function was applied to describe experimental breakthrough data. A novel simple two-parameter model was introduced to simulate overshoot and desorption curves.