Cadmium adsorption effects

Van Riemsdijk et al. [53] were the first to show that electrostatic effects could explain non-stoichiometric exchange ratios. Predictions with the one-pKn SCG model and the two-pKn SGC model were both in a good agreement with experimentally observed proton/M ratios and metal ion isotherms at a series of pH values for rutile, hematite and amorphous iron oxide. In contrast with Benjamin and Leckie [86], Van Riemsdijk et al. [53] concluded that incorporation of surface heterogeneity is not required to describe cadmium adsorption on amorphous iron oxide. 

Neal, R. H., and Sposito. G. (1986). Effects of soluble organic matter and sewage sludge amendments on cadmium adsorption by soils at low cadmium concentrations. Soil Sci. 142, 164-172. 

Potassium, sodium, calcium and other positively charged ions present in the channel are exchangeable and get replaced by heavy metal ions. Heavy metals present in wastewater (chromium, mercury, lead and cadmium) are effectively adsorbed on zeolites. Clinoptilolite is a widely used zeolite for wastewater treatment due to its higher selectivity and ion exchange capability to remove heavy metal ions including strontium and cesium (Grant et al. 1987). Vaca Mier et al. (2001) studied the selectivity of zeolite for the removal of various heavy metals and observed that zeolites show higher selectivity for lead ions followed by cadmium, copper and cobalt. Table 2.2 (Bailey et al. 1999) shows the some of the reported adsorption capacities of zeolites. 

B. Prelot, S. Lantenois, C. Chorro, M.-C. Charbonnel, J. Zajac, J.M. Douillard, Effect of nanoscale pore space confinement on cadmium adsorption from aqueous solution onto ordered mesoporous sihca a combined adsorption and flow calorimetry study. J. Phys. Chem. C 115(40), 19686-19695 (2011). doi 10.1021/jp2015885... 

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. 

In their electrochemical surface properties, a number of metals (lead, tin, cadmium, and others) resemble mercury, whereas other metals of the platinum group resemble platinum itself. Within each of these groups, trends in the behavior observed coincide qualitatively, sometimes even semiquantitatively. Some of the differences between mercury and other. y- or p-metals are due to their solid state. Among the platinum group metals, palladium is exceptional, since strong bulk absorption of hydrogen is observed here in addition to surface adsorption, an effect that makes it difficult to study the surface itself. 

Bengtsson et al. [671] found that the high background adsorption of solutions of trace metals containing up to 400 mg/1 can be easily minimised by addition of 2% v/v nitric acid. Of the several agents added in an attempt to eliminate the decrease in sensitivity caused by the salt and the variability in sensitivity between graphite tubes, only lanthanum added at 1 g/1 was effective for both lead and cadmium. 

Cathodic stripping voltammetry has been used [807] to determine lead, cadmium, copper, zinc, uranium, vanadium, molybdenum, nickel, and cobalt in water, with great sensitivity and specificity, allowing study of metal specia-tion directly in the unaltered sample. The technique used preconcentration of the metal at a higher oxidation state by adsorption of certain surface-active complexes, after which its concentration was determined by reduction. The reaction mechanisms, effect of variation of the adsorption potential, maximal adsorption capacity of the hanging mercury drop electrode, and possible interferences are discussed. 

Benjamin, M.M. Leckie, J.O. (1981) Multiple-site adsorption of Cd, Cu, Zn, and Pb on amorphous iron oxyhydroxide. J. Colloid Interface Sci. 79 209-221 Benjamin, M.M. Leckie, J.O. (1981a) Competitive adsorption of Cd, Zn, Cu and Pb on amorphous iron oxyhydroxide. J. Colloid Interface Sci. 83 410-419 Benjamin, M.M. Leckie, J.O. (1982) Effects of complexation by Cl, SO4, and S2O3 on the adsorption behavior of cadmium on oxide surfaces. Environ. Sci. Tech. 16 162-170 Benjamin, M.M. (1978) Effects of competing metals and complexing ligands on trace metal adsorption. Ph.D. Thesis Benjamin, M.M. Hayes, K.E. Leckie, K.O. 

Hoins, U. Charlet, L. Sticher, H. (1993) Ligand effect on the adsorption of heavy metals. The sulphate-cadmium goethite case. Water, Air, Soil Pollution 68 241-255 Holm, G. (1985) Substitution selectivity of some transition elements (Cr, Mn, Co, Ni, Cu, Zn) during formation of P-FeOOH. Geologiska Foreningsi Stockholm Forhandlingar 107 297-300... 

It was found that the competitive adsorption of 1 and AN molecules on the Cd electrode affected the kinetics of the Cd(II) electroreduction [226]. The physicochemical properties of coatings and effects of organic additives on cadmium deposition from iodide-water-AN mixtures were also studied by Kuznetsov et al. [225]. 

The same authors have found that the inhibition effect of crown ethers [230] and crown esters [229] on cadmium electrodeposition from water-AN mixtures was caused by the competitive adsorption of macrocycles and organic solvents molecules. The effect of structure and concentration of crown ethers on the cadmium electrodeposition from aqueous sulfate solutions was also studied [231]. 

Properties dependent on adsorption are not confined to conductivity. Luminescence of materials may be affected, as Ewles and Heap (7) have shown for the case of silica, for which the luminescent peak at 4000 A. was shown to be associated with the adsorption of the OID radical. Many workers have demonstrated the dependence of the contact potential on the adsorption of gases. For example, Brattain and Bardeen (8) have shown that the contact potential of germanium varies with the adsorption of water vapor. Photoconductivity may be dependent on the adsorption. For example, Bube has shown (9) that the adsorption of water vapor has a marked effect on the photoconductivity of cadmium sulphide. He concluded (10) that the effect was indirect surface changes affect the lifetime of the excess carriers, thus affecting the photoconductivity. Melnick (11), however, working with zinc oxide, has produced evidence that part of the photoconductivity in this case is directly associated with excitation from adsorption levels. 

To verify the effect of the ions adsorption on the regularities of photoexcitation relaxation, we studied the temperature effect on the kinetics of the ultradispersed CdS photobleaching relaxation at the addition of electron acceptors of various nature. Fig. 2.13 presents the kinetic curves of the colloidal CdS photobleaching relaxation prepared with an excess of cadmium ions at different temperatures and at the addition of different... 

Martins, J.E., Pardo, R., and Boaventura, R.A.R. 2004. Cadmium (II) and zinc (II) adsorption by the aquatic moss Fontinalis antipyretica effect of temperature, pH and water hardness. Water Research, 38 693-9. 

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