Iron cadmium adsorption

A study of iron, cadmium and lead mobility in remote mountain streams of California by Erel et al. (1990) showed that the excess of atmospheric pollution-derived lead and cadmium is rapidly removed downstream. The comparison of truly dissolved, colloidal, and surface particle concentrations measured in the stream with the results of a model of equilibrium adsorption indicates that the mechanism of removal in this organic-poor environment is essentially by uptake onto hydrous iron oxides. The experimentally determined partition coefficients (Dzomback and Morel, 1990) explain the behavior of lead however, they fail to explain the cadmium removal. It is proposed by the authors that cadmium is taken up by surfaces other than hydrous iron oxides. 

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. 

Cowan, C. E., Zachara, J. M., and Resch, C. T. (1991). Cadmium adsorption on iron oxides in the presence of alkaline-earth elements. Environ. Sci. Technol. 25, 437-446. 

Benjamin, M. M. and Leckie, J. O. (1981). Multiple-site adsorption of cadmium, copper, zinc, and lead on amorphous iron oxyhydroxide, J. Coll. Inter/. Sci., 79, 209-221. 

Heavy metals such as copper, zinc, lead, nickel, silver, arsenic, selenium, cadmium and chromium may originate from many sources within a rehnery and may, in specihc cases, require end-of-pipe treatment. Some agencies have set discharge limits that are beyond the capability of common metals removal processes such as lime precipitahon and clarihcation to achieve. Other treatment processes such as iron coprecipitation and adsorption, ion exchange, and reverse osmosis may be required to achieve these low effluent concentrations [52]. 

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. 

Specific adsorption of zinc and cadmium by iron and aluminum hydrous oxides. In Proc. 15 Hanford Life Sci. Symp. on Biol. Implications of Metals in the Environment, Hanford,Washington, USERDA-NTIS, 231-239... 

Petersen,W. Wallmann, K. Schroer, S. Schroeder, F. (1993) Studies on the adsorption of cadmium on hydrous iron (III) oxides in oxide sediments. Anal. Chim. Acta 273 323-327... 

Many different chemical treatment systems have been developed to reduce the leachability of lead and cadmium compounds in flue dust. These systems usually rely on stabilization/solidification, adsorption, chemical reduction, or pH control. Chemical reduction employing the use of metallic iron has been successful in reducing the leachability of lead to below EP-Toxicity levels. Adding a 5 percent by weight dose of iron filings to cupola furnace emissions control sludge, for instance, reduced lead leaching from 28.6 mg/1 to less than 0.1 mg/1 (Stephens 1984). 

Reprecipitation A drastic but effective way to minimize the effects of adsorption is reprecipitation. In this process, the filtered solid is redissolved and reprecipitated. The first precipitate ordinarily carries down only a fraction of the contaminant present in the original solvent. Thus, the solution containing the redissolved precipitate has a significantly lower contaminant concentration than the original, and even less adsorption occurs during the second precipitation. Reprecipitation adds substantially to the time required for an analysis but is often necessary for such precipitates as the hydrous oxides of iron(III) and aluminum, which have extraordinary tendencies to adsorb the hydroxides of heavy-metal cations such as zinc, cadmium, and manganese. 

Marshakov et al. studied the effect of an ultrasonic field on the anodic dissolution of a variety of metals [120]. Anodic polarization curves were measured in 0.1—0.5 N HC1, NaCl, H2S04, and NajSC solutions in an ultrasonic field of 20 kHz frequency. The effect of ultrasound was different for various metals due to differential effects on the rate-controlling process. Anodic dissolution of Fe was actually slowed down in the presence of ultrasound because the rate-controlling adsorption of anions at the iron surface was inhibited. At a cadmium anode, the energy of metal atoms in a lattice was increased in the presence of ultrasound and, therefore, the ionization of cadmium was accelerated. Anodic dissolution of copper and silver... 

The effects of electrolyte concentration. Okazaki et al. [26] reported no effect of electrolyte concentration on adsorption of copper and zinc by iron and aluminium oxides. Similarly, from their own work, and from a survey of the literature, Hayes and Leckie [27] concluded that there was little effect of electrolyte concentration on metal adsorption. However, a wider view of the literature shows that there are indeed effects on surfaces which are probably negatively charged - for example, for adsorption of nickel on kaolinite [31], for zinc on soil [32], for copper, cadmium and lead on kaolinite [33] and for cadmium on soil [34]. This discrepancy probably arises because metal adsorption on oxides often... 

Consider now the adsorption of cations. Two kinds of explanations are possible within the model. One is that reaction is dominated by the first hydrolysis product - the monovalent MOH" " ions. Provided the pH is more than about one unit below the pK for this reaction, the concentration of MOH ions increases 10-fold for each unit increase in pH. An extra effect of pH is produced from the decrease in electrical potential as the pH is increased. Thus, this explanation requires that there must be at least a ten-fold increase in the effectiveness of ions in inducing adsorption with each unit increase in pH. This is consistent with the conclusions of Kinniburgh and Jackson [58] who reported effects of pH which were more than ten-fold for reaction of cobalt, copper, zinc and cadmium with iron oxide. The values were Co, 25 fold Cu, 33 fold Zn 45 fold and Cd 50 fold. 

In general, pHpzc values for silica and manganese oxides are below pH 7 and values for aluminum and iron oxides are greater than pH 7. Therefore, the electrostatic attraction of a divalent metal ion for a particular mineral will vary with pH. The adsorption of divalent cations is expected to increase with increasing pH as the surface becomes less positively charged. For example, Fig. 7-1 demonstrates the shift in the fractional pH adsorption edge of cadmium (Cd(II)) with pHpzc of the sorbent. Reported pHpzc values of rutile, ferrihydrite and corundum (a-Al203) are 5.8, 8.5 and 8.9, respectively (Davis Kent, 1990 Stumm, 1992 Hayes et al., 1990). Adsorption of Cd(II) for all of the minerals shown occurs below its reported pHpzc-... 

Sudha et al. (2008) and Dinesh Karthik et al. (2009) reported on the removal of heavy metal cadmium and chrominm from industrial wastewater using chitosan-coated coconut charcoal and chitosan impregnated polyurethane foam, respectively. Adsorption and determination of metal ions such as zinc (11) and vanadium (II) onto chitosan from seawater have been studied (Muzzarelli et al. 1970, Muzzarelli and Sipos 1971, Muzzarelli and Rocchetti 1974). Adsorption of strontium (II), cobalt (11), zinc (11), and iron (III) on chitosan from sodium chloride solution have been reported (Nishimura et al. 1995). Adsorption behavior of Cu (II) (Minamisawa et al. 1996, Wu et al. 2000) and cobalt (11) (Minamisawa et al. 1999) were investigated. The amount of cadmium removed by chitin increases with increase of these parameters at a specific time. The application to experimental results of the Langmuir and Freundlich models shows that the Langmuir model gives a better correlation coefficient. 

FIGURE 7.29 Integrated adsorption process for recovery of iron, copper, zinc, lead and cadmium from Berkeley pit waters. (Reproduced from N. V. Deorkar, L. L. Tavlarides. Environ. Progress 17 120-125, 1998. With permission.)... 

In wastewater treatments, special attention is given to removal of dangerous inorganic material such as the heavy metals, including mercury, chromium, molyMenum, cobalt, nickel, copper, cadmium, lead, uranium, gold, arsenic, barium, iron and vanadium. Whereas the forces of adsorption from the gas phase are well understood, adsorption from solution of inorganic species is not so well understood. So, it is most pertinent to enquire about the sites which are responsible for adsorption of inorganic species. 

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