Removal of metal ions from a petrochemical wastewater using brown macro-algae as natural cation-exchangers

Abstract

Four brown macro-algae, Ascophyllum nodosum, Fucus spiralis, Laminaria hyperborea and Pelvetia canaliculata, were investigated as natural cation exchangers for the removal of transition metals from a petrochemical wastewater. The wastewater presents a high conductivity due to chloride, sulfate, sodium, calcium and residual concentrations of copper, zinc and nickel species. According to all-inorganic species evaluated, the molar fraction of Zn2+, Cu2+ and Ni2+ is near 92% and the remaining species are ZnCl+, ZnSO4, CuSO4, NiCl+ and NiSO4. A Langmuir multicomponent model was able to predict the ion-exchange equilibrium data for Cu, Ni, Zn and Ca species present in the petrochemical wastewater. L. hyperborea showed a higher uptake capacity than the other brown algae tested. The equilibrium affinity constants for the functional groups decreased in the following order: Cu > Zn > Ni approximate to Ca, except for L. hyperborea, which presents a lesser affinity for Ca. Ion-exchange breakthrough curves obtained from a fixed-bed column packed with raw L. hyperborea, led to an operating capacity of 0.22, 0.10 and 0.05 mEq/g for Cu, Zn and Ni, corresponding to 1558, 515, 528 BV (7.2 BV/h), respectively. The treatment strategy consisted in the operation of two consecutive columns, the first one for copper ions removal (operating capacity of 1558 BV - 7.2 BV/h) and the second one for zinc and nickel removal (operating capacity of 163 BV-7.3 BV/h). The elution of Cu, Zn and Ni from the natural resin was achieved with 10 and 6 BV of HCl (0.4 M, 1.2%) (150 and 90 g HCl/L of resin), using a flow rate of 3.6 BV/h, respectively for the first and second columns.