SPECIATION OF DISSOLVED CADMIUM - INTERPRETATION OF DIALYSIS, ION-EXCHANGE AND COMPUTER (GEOCHEM) METHODS

Equilibrium dialysis and ion exchange methods, as well as computer cal culations (GEOCHEM), were applied for speciation of dissolved cadmium (Cd) in test solutions and leachate samples. The leachate samples orig inated from soil, compost, landfill waste and industrial waste. The io n exchange (IE) method separates dissolved Cd into free divalent Cd (C d2+) and complexed Cd and furthermore separates the latter into the op erationally defined forms: labile, slowly labile and stable complexes. The dialysis (ED) method determines high molecular weight Cd complexe s (above 1000 mol. wt). For both methods 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 ino rganically complexed Cd were estimated. The IE and ED results furtherm ore provided information about the organic complexes. Selected environ mental leachates showed different Cd speciation patterns as expected. Some leachates were dominated by free divalent Cd (1-70%), some by ino rganic complexes (1-87%), and some by organic complexes (7-98%).