Speciation of dissolved cadmium: Interpretation of dialysis, ion exchange and computer (GEOCHEM) methods

Equilibrium dialysis and ion exchange methods, as well as computer calculations (GEOCHEM), were applied for speciation of dissolved cadmium (Cd) in test solutions and leachate samples. The leachate samples originated from soil, compost, landfill waste and industrial waste. The ion exchange (IE) method separates dissolved Cd into free divalent Cd (Cd2+) and complexed Cd and furthermore separates the latter into the operationally defined forms: labile, slowly labile and stable complexes. The dialysis (ED) method determines high molecular weight Cd complexes (above 1000 mol. wt). For both method the reproducibility was good. By combining the results of the GEOCHEM calculations in terms of the inorganic complexes, and the IE results, the fractions of free and inorganically complexed Cd were estimated. The IE and ED results furthermore provided information about the organic complexes. Selected environmental leachates showed different Cd speciation patterns as expected. Some leachates were dominated by free divalent Cd (1–70%), some by inorganic complexes (1–87%), and some by organic complexes (7–98%).