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Adsorption of Pb(II) at calcite-water interphase, revisited

Introduction An important anthropogenic pollutant Pb(II), now monitored in natural waters and sediments, has been intensively studied under controlled laboratory- and estuarine- conditions [1 - 8]. The aim of the work is to discuss on example of Pb(II) in carbonate solutions, what we have learned in 35 years, changing experimental and calculation techniques. Results, Discussion and Conclusions Complex formation between Pb(II) and hydroxide or carbonate ions started with electroanalytical methods [1 - 6]. Later, radiotracer [7] and EXAFS analyses [8] were performed. The last method provided direct spectroscopic evidence for formation of Pb(II) inner-sphere complexes with calcite, what could not be evidenced using electroanalytical methods. Conclusions in reference [8], obtained by advanced PHREEQC computer calculations, utilizing the MINTEQ database, do not give any new finding since the quoted early works of the two giants of mineral surface chemistry, Stumm and Schindler. Complex PbCO3 0 (aq) via which dissolved Pb is transported to calcite surface, and the combination of mononuclear adsorption complex combined with precipitation of hydrocerrusite and cerrusite in concentrations above their solubility limit could be obtained by simple calculation and using constants from earlier works [1– 5]. It can be concluded that besides development of advanced analytical and calculation techniques, exact and time consuming determination of equilibrium constants in heterogeneous systems should be continued for other elements. [1] Stumm & Bilinski (1973) Adv. Wat. Poll. Res. Sixth Int. Conf. Jerusalem, Pergamon, 39-49. [2] Bilinski & Stumm (1973) EAWAG News 1, 2-3. [3] Bilinski et al. (1974) Vom Wasser 43, 107-116. [4] Bilinski et al. (1976) Anal. Chim. Acta 84, 157-164. [5] Bilinski & Schindler (1982) Geochim. Cosmochim. Acta 46, 921-928. [6] Bilinski et al. (1991) Mar. Chem. 32, 225-233. [7] Rouff et al. (2002) Aquat. Geochem. 8, 203-228. [8] Ashaki et al. (2004) Environ. Sci. Technol. 38, 1700-1707.

adsorption; Pb(II); calcite-water interphase; equilibrium constants

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