Chemical speciation in fresh, saline and hyper-saline waters

Abstract

A thermodynamic model is proposed, which combines the ion association and the ion interaction models using the extended database pit2010.dat for a more precise modeling of the chemical species of micro components in natural waters of varying ionic strength (fresh, saline and hyper-saline). Compared to the ion association model, the proposed combined model more adequately describes the complex character of the ionic interactions. The performance of the combined ion association/ion interaction model compared to that of the ion association model is illustrated in case studies of several Bulgarian natural water systems of different ionic strength and type of pollution. The results are interpreted in terms of the chemical behavior of the metals and of their chemical species in the water systems, which is defined by the redox potential, pH, cationic and anionic organic and inorganic composition of the water systems and by the ability of the metals to preferentially coordinate with some anions, as well as by the stability of the corresponding species. The affinity of the transition metals towards the ligands is explained by the "hardness-softness" factor and the crystal field stabilization energy (CFSE).