Experimental study and modelling of inorganic Cd2+ speciation in natural waters

Abstract

Environmental contextCadmium(II) is considered as one of the most dangerous pollutants in natural waters. We performed a complete study on the interactions of cadmium(II) with inorganic components of natural waters, by using new experiments and some literature data. The body of results can be considered an improvement in modelling the inorganic speciation of cadmium(II) in natural waters. AbstractAn analysis of literature data together with new potentiometric and voltammetric studies on the interaction between Cd2+ and the common environmental inorganic ligands, such as OH–, Cl–, F–, CO32– and SO42–, was reported at t = 25°C. New formation constant values for CdCl+, CdCl20, CdCl(OH)0, CdSO40, CdCO30 and CdF+ species at different ionic strengths (0.1 ≤ I ≤ 1 mol L–1) were determined. The cumulative seawater ligand capacity was evaluated by using a model in which synthetic seawater is expressed as a single salt BA, where the major cations (Na+, K+, Ca2+ and Mg2+) are represented by a single cation Bz+ and the anions (Cl– and SO42–) by a single anion Az– (|z| = 1.117). The formation of CdA0.883+ and CdA(OH)0.117– species was proposed and formation constants are reported at different salinities (5 ≤ S ≤ 45). The ionic strength dependence of the stability constants was studied by means of Pitzer and SIT (Specific ion Interaction Theory) equations.