ELECTROCHEMICAL DETERMINATION OF CADMIUM SORPTION ON KAOLINITE

Two alternative methods, based on voltammetric (OSWSV, Osteryoung Square Wave Stripping Voltammetry, OSWV, Osteryoung Square Wave Voltammetry) and potentiometric (ISE, Ion Selective Electrode), are proposed for the determination of adsorption isotherms of metals in natural porous systems (soils, subsoils). The main advantage of the reference techniques is that filtration step, of the classical ''batch equilibration method'' for liquid-solid separation, can be skipped and metal equilibrium concentration determined directly in the suspension without relevant problems. Some limitation are evidenced during the experiments: pH dependence of the electrode response for the potentiometric determinations and reproducibility of the measures at very low concentrations (less-than-or-equal-to 100 mug L-1) for voltammetric methods. The computer code MINTEQA2 was used to simulate solid-liquid phase equilibria of the cadmium-kaolinite systems for the interpretation of the interactive phenomena. A combination of the ion exchange and surface complexation models was adopted for data interpretation.