Heavy metals retention

Jaber, M., M-Brendle, J., Michelin, L. and Delmotte, L. (2005) Heavy metal retention by organoclays synthesis, applications, and retention mechanism. Chemistry of Materials, 17, 5275-5281. 

Salim, I.A., Miller, C.J. and Howard, J.L. (1996) Sorption isotherm-sequential extraction analysis of heavy metal retention in landfill liners. Soil Sci. Soc. Am.f., 60, 107-114. 

The multireaction approach, often referred to as the multisite model, acknowledges that the soil solid phase is made up of different constituents (clay minerals, organic matter, iron, and aluminum oxides). Moreover, a heavy metal species is likely to react with various constituents (sites) via different mechanisms (Amacher et al 1988). As reported by Hinz et al. (1994), heavy metals are assumed to react at different rates with different sites on matrix surfaces. Therefore, a multireaction kinetic approach is used to describe heavy metal retention kinetics in soils. The multireaction model used here considers several interactions of one reactive solute species with soil matrix surfaces. Specifically, the model assumes that a fraction of the total sites reacts rapidly or instantaneously with solute in the soil solution, whereas the remaining fraction reacts more slowly with the solute. As shown in Figure 12.1, the model includes reversible as well as irreversible retention reactions that occur concurrently and consecutively. We assumed that a heavy metal species is present in the soil solution phase, C (mg/L), and in several phases representing metal species retained by the soil matrix designated as Se, S, S2, Ss, and Sirr (mg/kg of soil). We further considered that the sorbed phases Se, S, and S2 are in direct contact with the solution phase (C) and are governed by concurrent reactions. Specifically, C is assumed to react rapidly and reversibly with the equilibrium phase (Se) such that... 

Cabral, A. R., and Lefebvre, G. (1998). Use of sequential extraction in the study of heavy metal retention by silty soils. Water Air Soil Pollut. 102, 329-344. 

The second-order approach was successfully used for Cr retention and transport predictions by Selim and Amacher (1988) and for Zn retention by Hinz et al. (1992). This model was recently modified such that the total adsorption sites Smax were not partitioned between Sc and Sk phases based on a fraction of sites/(Selim Amacher, 1997 Ma Selim, 1998). Instead it was assumed that the vacant sites are available to both types of Se and Sk. Therefore,/is no longer required and the amount of solute adsorbed on each type of sites is only determined by the rate coefficients associated with each type of sites. As a result, sites associates with equilibrium or instantaneous type reactions will compete for available sites prior to slow or kinetic type sites are filled. Perhaps such mechanism is in line with observations where rapid (equilibrium type) sorption is first encountered and followed by slow types of retention reactions. We are not aware of the use of this second-order approach to describe heavy metal retention kinetics and transport in soils. 

Several sorption isotherms representing the total amount of Cu retained (5) vs. Cu in soil solution (C) are shown in Fig. 6-2. These results were obtained for selected reaction times from the batch experiments and show the kinetics of Cu retention in this soil. In addition, Cu retention is not only time dependent but nonlinear in nature. Similar kinetic and nonlinear behavior of other heavy metal retention has been observed by numerous investigators. The concave sorption nonlinearity implies that Cu mobility in the soil solution tends to increase as the concentration increases. A simple way to describe the above sorption isotherms is by use of the Frcundlich equation ... 

Hinz, C., B. Buchter, and H.M. Selim. 1992. Heavy metal retention in soils Application of multisite models to zinc sorption, p. 141-170. In I.K. Iskandar and H.M. Selim (ed.) Engineering aspects of metal-waste management. Lewis Publ., Boca Raton, FL. 

Cardenas, G., Orlando, P., and Edelio, T. 2001. Synthesis and applications of chitosan mercaptanes as heavy metal retention agent. Int. J. Biol. Macromol. 28, 167-174. 

Removal of Metal Ions. The natural capacity of peat for heavy metal retention has been recognized in many studies which have investigated the removal of Hg, Cd, Zn, Cu, Fe, Ni, Cr(VI), Cr(lll), Ag, Pb, and Sb. These studies found sorption to be quite high due to the polar character of peat and its weak acid ion exchange properties (Zhipei et al., 1984 Sharma and Forster, 1993 Ho et al, 1994, 1995 Gosset et al, 1986 Chen et al., 1990). 

Table 1. Heavy metal retention by some clay minerals...

Galvez, R. Phadungchewit, Y. 1993. Selective sequential extraction analysis of heavy metal retention in soil. Canadian Geotechnical Journal, 30, 834-847. 

Kolay, P.K., Singh, D.N. Characterization of alkali activated lagoon ash and its application for heavy metal retention. Fuel 8, 483-489 (2002)... 

Kolay and Singh [15] have investigated the alkali activated lagoon fly ash for its heavy metal retention capacity. It has been opined that a 12 h interaction of activated ash samples which contains zeolite Na-Pl, with 0.0005 M Pb(N03)2 can result into 100 % removal of Pb from similar type of industrial sludge which has initial pH from 2 to 8 and ion concentration of the order of 3885 ppm. 

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