CSIRO PUBLISHING - Australian Journal of Chemistry

Chemical Speciation of Hg(ii) with Environmental Inorganic Ligands

Kipton J. Powell ^A ^, ^H , Paul L. Brown ^B , Robert H. Byrne ^C , Tamas Gajda ^D , Glenn Hefter ^E , Staffan Sjöberg ^F and Hans Wanner ^G

^A Department of Chemistry, University of Canterbury, Christchurch, New Zealand.
^B Australian Sustainable Industry Research Centre, Monash University, Churchill VIC 3842, Australia.
^C Department of Marine Science, University of South Florida, St. Petersburg, FL 33701-5016, USA.
^D Department of Inorganic and Analytical Chemistry, A. József University, Szeged 6701, Hungary.
^E School of Mathematical and Physical Sciences, Murdoch University, Murdoch WA 6150, Australia.
^F Department of Inorganic Chemistry, Umeå University, 90187 Umeå, Sweden.
^G Swiss Federal Nuclear Safety Inspectorate, 5232 Villigen, Switzerland.
^H Author to whom correspondence should be addressed (e-mail: kip.powell@canterbury.ac.nz).

Abstract

Complex formation between Hg(ii) and the common environmental ligands Cl^-, OH^-, CO₃^2-, SO₄^2-, and PO₄^3- can have profound effects on Hg(ii) speciation in natural waters with low concentrations of organic matter. Hg(ii) is labile, so its distribution among these inorganic ligands can be estimated by numerical modelling if reliable values for the relevant stability constants are available. A summary of critically reviewed constants and related thermodynamic data is presented. Recommended values of log₁₀β_p,q,r° and the associated reaction enthalpies, Δ_rH_m°, valid at I_m = 0 mol kg^-1 and 25°C, along with the equations and specific ion interaction coefficients required to calculate log₁₀β_p,q,r values at higher ionic strengths and other temperatures are also presented.

Under typical environmental conditions Hg(ii) speciation is dominated by the reactions Hg²⁺ + 2Cl^- ↔ HgCl_2(aq) (log₁₀β₂° = 14.00 ± 0.07), Hg²⁺ + Cl^- + H₂O ↔ Hg(OH)Cl_(aq) + H⁺ (log₁₀β° = 4.27 ± 0.35), and Hg²⁺ + 2H₂O ↔ Hg(OH)_2(aq) + 2H⁺ (log₁₀*β₂° = -5.98 ± 0.06).

Australian Journal of Chemistry 57(10) 993–1000 doi:10.1071/CH04063
Submitted: 16 March 2004 Accepted: 12 July 2004 Published: 1 October 2004