Copper desorption from Gelidium algal biomass

Desorption of divalent copper from marine algae Gelidium sesquipedale, an algal waste (from agar extraction industry) and a composite material (the algal waste immobilized in polyacrylonitrile) was studied in a batch system. Copper ions were first adsorbed until saturation and then desorbed by HNO3 and Na2EDTA solutions. Elution efficiency using HNO3 increases as pH decreases. At pH=1, for a solid to liquid ratio S/L=4 g l−1, elution efficiency was 97%, 95% and 88%, the stoichiometric coefficient for the ionic exchange, 0.70±0.02, 0.73±0.05 and 0.76±0.06 and the selectivity coefficient, 0.93±0.07, 1.0±0.3 and 1.1±0.3, respectively, for algae Gelidium, algal waste and composite material. Complexation of copper ions by EDTA occurs in a molar proportion of 1:1 and the elution efficiency increases with EDTA concentration. For concentrations of 1.4, 0.88 and 0.57 mmol l−1, the elution efficiency for S/L=4 g l−1, was 91%, 86% and 78%, respectively, for algae Gelidium, algal waste and composite material. The S/L ratio, in the range 1–20 g l−1, has little influence on copper recovery by using 0.1 M HNO3. Desorption kinetics was very fast for all biosorbents. Kinetic data using HNO3 as eluant were well described by the mass transfer model, considering the average metal concentration in the solid phase and the equilibrium relationship given by the mass action law. The homogeneous diffusion coefficient varied between 1.0×10−7 cm2 s−1 for algae Gelidium and 3.0×10−7 cm2 s−1 for the composite material.