ELECTROCHEMICAL DETERMINATION OF CADMIUM SORPTION ON KAOLINITE

Two alternative methods, based on voltammetric (OSWSV, Osteryoung Squa re Wave Stripping Voltammetry, OSWV, Osteryoung Square Wave Voltammetr y) 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 techni ques is that filtration step, of the classical ''batch equilibration m ethod'' for liquid-solid separation, can be skipped and metal equilibr ium concentration determined directly in the suspension without releva nt problems. Some limitation are evidenced during the experiments: pH dependence of the electrode response for the potentiometric determinat ions and reproducibility of the measures at very low concentrations (l ess-than-or-equal-to 100 mug L-1) for voltammetric methods. The comput er code MINTEQA2 was used to simulate solid-liquid phase equilibria of the cadmium-kaolinite systems for the interpretation of the interacti ve phenomena. A combination of the ion exchange and surface complexati on models was adopted for data interpretation.