Biosorption of cadmium, copper and zinc in binary and ternary systems

A biosorbent prepared from Ascophyllum nodosum seaweed biomass, designated as FCAN2, was examined for its sorption capacity. Equilibrium batch sorption studies were performed using two-metal systems respectively comprised of (Cd + Cu), (Cd + Zn), (Cu + Zn) and a three-metal system comprised of (Cd + Cu + Zn). In the evaluation of the two-metal sorption system performance, simple sorption isotherm curves had to be replaced by three-dimensional sorption isotherm surfaces. In order to describe the isotherm surfaces mathematically, three Langmuir-type models were evaluated. The apparent one-parameter Langmuir constant was used to quantify FCAN2 'affinity' for one metal in the presence of another one. In order to represent the equilibrium data of the ternary system, a multicomponent Langmuir model was adopted and triangular equilibrium diagrams were used. Mathematical models for the two- and three-metal sorption systems enabled quantitative estimation of one metal sorption inhibition due to the influence of the other metal(s). For biosorption on FCAN2 at pH 4.5, the inhibition dominance observed in the two- and three-metal systems was Cu $>$ Cd $>$ Zn