Interaction of Hg(II) with kaolin-humic acid complexes

Abstract

A B S T R A C T : The adsorption and desorption of Hg(II) by humic acid (HA) previously adsorbed on kaolin was studied. In the range of HA concentration investigated (0.0 -26.9 mg g -1 ), the Hg(II) adsorption capacity of kaolin at pH 4 is enhanced by the presence of HA. For the complexes with the highest HA concentration and for low Hg(II) initial concentrations, adsorption was lower, i.e. as HA concentration on the complexes increases, Hg(II) equilibrium concentration also increases. This behaviour is due to the increasing presence of dissolved organic matter as the HA concentration on the complexes increases. The dissolved organic matter is able to form a soluble complex with Hg, thus decreasing adsorption. Hg(II) adsorption from a 2.5610 -5 MHg(II) solution was influenced by pH. For kaolin, a pH max (pH where maximum adsorption occurs) of 4.5 was observed. At pH values >pH max retention decreased with increasing pH. This same behaviour was observed for the kaolin-HA complex containing the lowest HA concentration (6.6 mg g -1 ). For the other kaolin-HA complexes there was little effect of pH on Hg(II) adsorption between pH 2.5 and pH 6.5. The presence of HA increased the adsorption of Hg(II) on kaolin all along the pH range studied. Desorption experiments showed that the amount of Hg(II) desorbed was quite low (<1%) for all the HA and Hg(II) concentration range studied, except for the kaolin at acid pH (pH 2.5) where the Hg(II) released was >50% of Hg(II) previously adsorbed. The presence of HA dramatically reduced this percentage of desorption to values of <3%, indicating reduced risk of toxicity problems in surface and subsurface waters. The addition of Cu(II) did not favour any Hg(II) desorption, even though Cu exhibits a strong affinity for organic matter.

Distribution and Speciation of Mercury in Mine Waste Dumps

“…The suspension was vigorously shaken at room temperature for 1 h, then left intact for 24 h. After supernatant removal by centrifugation, the obtained solid material was rinsed with distilled water and dried at 60°C. Adsorption of Hg(II) to humic acid (Sigma Aldrich) was prepared according to Arias et al (2004).…”

Effect of carboxylic and thiol ligands (oxalate, cysteine) on the kinetics of desorption of Hg(II) from kaolinite

“…Numerous studies have been reported on adsorption of Hg(II) by various particles, e.g., clay minerals (Hamilton et al 1995;Sarkar et al 2000;Singh et al 1996), oxides (Bonnissel-Gissinger et al 1999;Gunneriuson and Sjoberg 1993;Gunneriuson et al 1995;Sarkar et al 1999;Thanabalasingam and Pickering 1985;Tiffreau et al 1995;Walcarius et al 1999;Weerasooriya et al 2006Weerasooriya et al , 2007, and soils (Schluter 2000;Schuster 1991;Yin et al 1996;Yin et al 1997a, b). Desorption of Hg(II) from particles has also received attention (Arias et al 2004;Yin et al 1997b), yet the literature in this regard has remained limited.…”

Development of an Enhanced Hydro-geochemical Model to Address Mercury-speciation Fate and Transport in Aquatic Environments

“…Hg has also been found to be in high concentration in sediment, from high absorption in clay (Arias et al, 2004;Reddy and Aiken, 2001); transport of Hg can thus occur through its attachment to sediment (Lui et al, 2008). The latter implies that site stratigraphy, sediment type, and distribution coefficient (K d ) are important factors for estimating Hg transport in sediment (Reddy and Aiken, 2001).…”

“…In addition, speciation also depends on the mixture of metals and complexing agents, pH, temperature, redox, salinity, major ion composition and sorbing solids (Arias et al, 2004;Wang et al, 1991;Wnalin et al, 2007).…”

“…Nevertheless, the sorption capability of the minerals mainly depends on their surface area properties (Arias et al, 2004;Miretzky et al, 2005;Martell and Smith, 2001) (Table 11). (Table 12) documented in various studies (Elliott and Huang, 1981;Meng and Letterman, 1993;Riese, 1982;Singh and Mattigod, 1992).…”