Surface complexation modeling of Hg(II) adsorption at the goethite/water interface using the charge distribution multi-site complexation (CD-MUSIC) model.
OBJECTIVE
Previous attempts to describe Hg(II) adsorption onto mineral surfaces using surface complexation models (SCMs) have proven unsuccessful and/or require the use of hypothetical surface species. Given that metal ion adsorption at the mineral-water interface is greatly influenced by mineral surface heterogeneity and the presence of competing adsorbates in solution, it stands to reason that estimating the crystal face composition (CFC) of the mineral surface and the extent of carbonate contamination in the experimental system will improve SCM predictions.


METHODS
The Charge Distribution Multi-Site Complexation (CD-MUSIC) model was used to simulate experimental Hg(II) adsorption data, collected on the iron hydroxide mineral goethite, in the presence and absence of competing adsorbates and complexing ligands as a function of pH and ionic strength. The CFC of each goethite sample studied was predicted using a newly discovered relationship between goethite's proton reactive site density (N(H)) and specific surface area (SSA). Carbonate's presence in the experimental systems was determined utilizing a novel methodology developed in this work.


RESULTS
The CD-MUSIC model developed in this study accurately predicted Hg(II) adsorption onto goethite over the entire range of experimental conditions investigated while only employing surface species consistent with spectroscopic evidence.
The University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering, 301 E Dean Keeton Street Stop C1786, Austin, TX 78712-1173, USA. Electronic address: jmangol@clemson.edu.
Jeremiah E
JE
Mangold
The University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering, 301 E Dean Keeton Street Stop C1786, Austin, TX 78712-1173, USA. Electronic address: changmin.p@samsung.com.
Chang Min
CM
Park
The University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering, 301 E Dean Keeton Street Stop C1786, Austin, TX 78712-1173, USA. Electronic address: liljestrand@mail.utexas.edu.
Howard M
HM
Liljestrand
The University of Texas at Austin, Department of Civil, Architectural and Environmental Engineering, 301 E Dean Keeton Street Stop C1786, Austin, TX 78712-1173, USA. Electronic address: lynnkatz@mail.utexas.edu.
Lynn E
LE
Katz
Adsorption; BAR76; BON15; CD-MUSIC model; CFC; Carbonate; Charge Distribution Multi-Site Complexation model; Chloride; EXAFS spectroscopy; Goethite (α-FeOOH); Goethite sample used by Barrow and Cox [5]; Goethite sample used by Bonnissel-Gissinger et al. [6]; Goethite sample used by Villalobos and Leckie [32,33]; Mercury; N(H); N(S); VIL70; all carbonate present in the solid – solution system from both surface and aqueous species; crystal face composition; extended X-ray absorption fine structure spectroscopy; proton reactive site density (sites/nm(2)); site density (sites/nm(2))