Chemical speciation in natural and brine sea waters

A combined approach consisting of monitoring and thermodynamic modeling was used in order to calculate the concentration of trace element species in water samples of a broad salinity range and to explain their chemical behaviour. The study was performed on water samples (fresh, marine, hyper-saline) taken from the area of Burgas Bay, Bulgaria. The ion association model based on Debye-Hückel theory using the sst2008.dat database and the ion interaction model based on Pitzer theory using a new pit2010.dat database were compared and combined for the purposes of this study. The new pit2010.dat database combines the sst2008.dat database and the pitzer.dat database of the PHREEQCI computer program as well as the thermodynamic data for the elements Fe, Mn, Cu, Zn, Cd and Pb and their Pitzer ion interaction parameters. The results showed that: (1) the predominant species in fresh waters were free ions of Mn(2+) (73.6%), Zn(2+) (58.0%) and Cd(2+) ions (78.3%) as well as carbonate species CuCO⁰₃ (81.8%), PbCO⁰₃ (77.2%) and hydroxy species Fe(OH) ⁰₃(55.2%) and Fe(OH)+₂(35.6%); (2) an increase in chloride species MeCl²(n)-(n)(n = 1-4, Me = Mn, Zn, Cu, Pb and Cd) and of the hydroxy species Fe(OH)⁺₂ for Fe was calculated for sea and hyper-saline water.