Use of Pitzer equations to examine the formation of mercury(II) hydroxide and chloride complexes in NaClO₄ media

The thermodynamic stability constants for the hydrolysis and formation of mercury (Hg²⁺) chloride complexes Hg²⁺ + nH₂O = Hg(OH)_n^(2-n)+ + nH⁺ β_n Hg²⁺ + nCl^- = HgCl_n^(2-n)+ β_i have been used to calculate the activity coefficients for Hg(OH)_n^(2-n)+ and HgCl_n^(2-n)+ complexes using the Pitzer specific interaction model. These values have been used to determine the Pitzer parameters for the hydroxide and chloro complexes β_ML⁽⁰⁾, β_ML ⁽¹⁾ and C_ML). The values of λ_ij and ζ_ijk have been determined for the neutral complexes (Hg(OH)₂ and HgCl₂). The resultant parameters yield calculated values for the measured values of log β* to ±0.01 from I = 0.1 to 3 m at 25°C. Since the activity coefficients of Hg(OH)_n^(2-n)+ and HgCl_n^(2-n)+ are in reasonable agreement with the values for Pb(II), we have estimated the effect of temperature on the chloride constants for Hg(II) from 0 to 300°C and I = 0-6 m using the Pitzer parameters for PbCl_n^(2-n)+ complexes. The resulting parameters can be used to examine the speciation of Hg(II) with Cl^- in natural waters over a wide range of conditions.