Adsorption of aqueous inorganic mercury and methylmercury on suspended kaolin: influence of sodium chloride, fulvic acid and particle content

The main tendencies in the adsorption of dissolved inorganic mercury (Hg2+) and methyl-mercury (MeHg+) on suspended kaolin particles have been investi gated in synthetic aqueous solutions. The influence of NaCl, fulvic acid (F A) and suspended particulate matter (SPM) in the system has been studied at a constant pH of 7.2, The experiments were arranged according to a full fa ctorial design with three factors (NaCl, FA SPM) at low (-) and high (+) le vels. A central point (0) was repeated four times to estimate the reproduci bility of the results. The low and high levels investigated were 0-35 g l(- 1) 0-10 mg l(-1) and 0.5-5 g l(-1) for the concentrations of NaCl, FA and k aolin respectively. In order to match the linear range of the analytical te chnique the total concentration of mercury (as Hg2+ or MeHg+) in the synthe tic suspensions was 25 ng mi After chemical stabilization of each suspensio n, the Hg2+ or MeHg+ content in the clear filtrate was determined by an aut omated hyphenated technique combining the following steps: (i) derivatizati on by hydride generation, (ii) preconcentration by cryogenic trapping, (iii ) separation by packed column gas chromatography and (iv) detection by quar tz furnace atomic absorption spectrometry, The removal of Hg2+ and MeHg+ fr om the solution via adsorption on particles ranged, respectively, from 12.4 to 94.9% and from 1.7 to 45.6% of the total mercury compound concentration , High concentrations of NaCl led to lower adsorption rates of both mercury species, The adsorption of MeHg+ was enhanced in the presence of FA, where as that of Hg2+ was clearly diminished. High levels of SPM promoted the ads orption of both Hg2+ and MeHg+ on kaolin particles. Several experiments wer e also conducted to check the adsorption rate of Hg2+ and MeHg+ on natural particles collected in the Gironde estuary, The results confirmed the gener al trends observed when using reference kaolin particles, The results prese nted here will be helpful for groups modelling the physico-chemical behavio ur of mercury in estuary conditions. Copyright (C) 2001 John Wiley & Sons, Ltd.