Cadmium sorption

Hill WR, Bednarek AT, Larsen XL (2000) Cadmium sorption and toxicity in autotrophic biofihns. Can J Fish Aquat Sci 57 530... 

Collins, C.R. Ragnarsdottir, K.V. Sherman, D.M. (1999) Effect of inorganic and organic ligands on the mechanism of cadmium sorption to goethite. Geochim. Cosmochim. Acta 63 2989-3002... 

Zachara, J.M., Smith, S.C., Resch, C.T. and Cowan, C.E. (1992) Cadmium sorption to soil separates containing layer silicates and iron and aluminium oxides. Soil Sci. Soc. Am. J., 56, 1074-1084. 

For example, 1 retains a high affinity for mercury even in the presence of electrolytes. This is illustrated by the Kd values of Hg " and Cd " ions uptake hy the TiP as a function of sodium nitrate concentration in solution (Fig. 6). The Kd values are very high (>10000 mL g" ) in the presence of a 100-fold excess of the sodium ion. Even higher Kd values were found for cadmium sorption. A gradual decrease in the Kd values as the concentration of NaNOs increases suggests that Hg and Cd " ions are taken up by the ion-exchange mechanism. 

Cadmium sorption in soils is known to be a fast process, with 95% of the Cd sorption taking place in the first 10 minutes and reaching equilibrium in 1 hour (Christensen, 1984). Although the initial sorption of trace elements is rapid, further sorption is usually quite slow, which was ascribed to inter or intraparticle diffusion in pores, sites of low reactivity, and surface precipitation (Waychunas et al., 1993 Sparks, 1999). An important factor affecting the degree of slow sorption of trace elements is the resident time of the sorbate with the sorbent. 

Naidu, R.. and Harter. R. D. (1998). Effect of different organic hgands on cadmium sorption by and extractability from soils. Soil Sci. Soc. Am. J. 62, 644-650. 

Schulte, A., and F, Beese. 1994. Isotherms of cadmium sorption demsity. J. Environ. Qual. 23 712-718. 

Nonequilibrium transport of solutes through porous media occurs when ground-water velocities are sufficiently fast to prevent attainment of chemical and physical equilibrium. Chemical reactions in porous media often require days or weeks to reach equilibrium. For example. Fuller and Davis Q) reported that cadmium sorption by a calcareous sand was characterized by multiple reactions, including a recrystallization reaction that continued for a period of days. Sorption of oxyanions by metal oxyhydroxides often occurs at an initially rapid rate the rate then decreases until steady-state is achieved (2-4). Unless ground-water velocity in such a situation is extremely slow, nonequilibrium transport will occur. 

P-06 - Crystal structure of a cadmium sorption complex of dehydrated fully Cd(II)-exchanged zeolite X... 

Apart from the high selectivity for the cadmium sorption, the hyper-crossHnked cation exchanger MN-500 is characterized by the highest rate ofH+/Cd + exchange, while the slowest diffusion was found to be pecufiar to the macroporous resin C-150 [390], This result is quite predictable, because in the open-work-type matrix of hypercrossfinked resins there are no dense domains. On the contrary, the pore walls in the macroporous matrix present a dense polymer phase in which the bivalent metal ions could hardly diffuse. 

EPS aggregates rapidly sorbed up to 90% of cadmium from solution. Changes in pH affected cadmium sorption, with Ae proportion of freed Cd to sorbed Cd changing from 90% at pH 5 to 5% at pH 9 desorption was enhanced with increasing salinity. 

Van Gestel, C.A., and J.E. Koolhaas. 2004. Water-extractabihty, free ion activity, and pH explain cadmium sorption and toxicity to Folsomia Candida (CoUembola) in seven soil-pH combinations. Environ. Toxicol. Chem. 23 1822-1833. 

Dzul Erosa, M. S., Saucedo Medina, T. I., Navarro Mendoza, R., Avila Rodriguez, M., and Guibal, E. (2001) Cadmium sorption on chitosan derivatives. Hydrometallurgy 61(3), 157 167. 

Uryash, V.F., Gruzdeva, A.E., Pletneva, N.B., Maslova, E.A., Potemkina, E.V., Demarin, V.T., Investigation of lead and cadmium sorption with a number of vegetable raw products, Khimiya, tekhnologiya i promyshlennaya ekologiya neorganicheskikh soedinenii, Perm Perm. SUniv. Press, 1999, vyp. 2, pp. 56-59 (in Russian). 

FIG. 5 pH-dependent cadmium sorption. The line is the behavior predicted using as input a imidentate binding of Cd with A1 sites on the siuface. (From Ref. 12.)... 

Benguella and Benaissa (2002) studied the adsorption of cadmium from a 100 mg/L aqueous solution onto chitin at initial pH between 5.7 and 6.4. The maximum cadmium removal capacity of chitin was 12.5 mg/g at a load of 2 g/L. They followed this study by evaluating the effect of several ions (Na+, Mg +, Ca +, CL, SO , and CO ") on the kinetics of cadmium sorption onto chitin. The authors found that Ca and C03 had a large inhibitory effect over cadmium adsorption, while Mg + and had a weak inhibitory effect. At the same time, Na and CL were found to have no effect on cadmium adsorption. Most of these studies focused on either single metal removal or on the effect of competitive ions on metal removal. 

The kinetie and equilibrium studies were done on the removal of cadmium Ifom aqueous solutions using chitin as an adsorbent by Benguella and Benaissa (2002). The effect of particle size of chitin on the cadmium removal was studied using six particle size groups such as 0- 0.20 0.20-0.63 0.63-1.25 1.25-2.50 2.50-4.10 4.10-6.30 mm. The increase in cadmium sorption capacity at the equilibrium with the decrease of ehitin partiele sizes indicates that cadmium ion sorption occurs by a surface meehanism. Similar results have been reported for the sorption of metal ions by natural polymers and their derivatives [211]. 

Consequently, the time needed to reach equilibrium gets increased with increasing particle size. These observations suggest that the cadmium sorption kinetic by chitin is largely determined by the particle size. 

Benaissa, H., Benguella, B. Effect of anions and cations on cadmium sorption kinetics from aqueous solutions by chitin experimental studies and modeling. Environmental Pollution. 2004, 130, 157-163. 

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