Adsorption of Cadmium and Cobalt on Montmorillonite as a Function of Solution Composition

Abstract

Abstract--Adsorption of Co 2+ and Cd ~+ on Wyoming montmorillonite was studied by the batch equilibration technique, as a function of salt concentration (0.01-4 M NaC1 and NaNO3), pH (5.0-6.5), adsorbate concentration (trace-10 -2 moles/liter), and presence of complexing ions. Comparison was made with the adsorbability of Sr 2+, known to follow simple ion-exchange equations. The distribution coefficients for Co and Cd in noncomplexing media varied with salt concentration (from -500 liters/kg in 0.01 M Na § to -10 liters/kg in 1 M Na+; pH = 5), but to a lesser extent than that of St. Adsorbability varied also with pH (-1 order of magnitude/pH unit), especially at high ionic strength, compared to a negligible pH effect on Sr. The distribution coefficients of Cd and Co decreased with increasing loading on the clay at a very low percentage (0.2%) of the ion-exchange capacity compared to Sr (20%). These data suggest two classes of sites participating in the adsorption of Cd and Co.The adsorbability of Cd in highly concentrated chloride solution (>1 M) was less than 1 liter/kg, presumably because of the chloride complex formation. This effect increased with increasing pH. The low adsorbability of Cd on montmorillonite from concentrated NaCI solution is promising with respect to its use as a tracer for monitoring flow through formations containing montmorillonite.

Sorption and desorption properties of Cadmium and Copper on soil clays in relation to charge characteristics

“…This fact may indicate that the edge surfaces of clays can be treated as oxides from the viewpoint of reaction kinetics. In a number of studies, the critical importance of edge surfaces for heavy metal adsorption has been suggested (Egozy 1980; Lackovic et al. 2003; Maes and Cremers 1975; O’Connor and Kester 1975).…”

Effect of Immobilizing Substances and Salinity on Heavy Metals Availability to Wheat Grown on Sewage Sludge-Contaminated Soil

“…In general, the decrease in positive charge on the complexed metal reduces adsorption to negatively charged surfaces (McLean and Bledsoe, 1992). In the presence of inorganic ligands Cl − and SO 2− 4 , the adsorption of Cd on soil was inhibited (O'Connor et al, 1984;Hirsch et al, 1989;Egozy, 1980;Benjamin and Leckie, 1982) due to the formation of cadmium complexes that were not strongly adsorbed by the soils. Downloaded by [UQ Library] at 14:23 05 November 2014 …”

Properties and structure of manganese oxide-coated clay

“…Montmorillonite, which belongs to the smectite group, is an important clay in soils and sediments, possesses a large specific surface area, and exhibits both variable and permanent surface charge [39,40]. Hence this clay is an important surface in the sorption of metals, radionuclides, and other fission and actinide products [4,39,[41][42][43][44][45][46][47][48][49]. Montmorillonite has a 2:1 layered aluminosilicate structure and is monoclinic consisting of a gibbsite plane (Al(OH) 6 ) sandwiched between two silica planes (SiO 4 ) [50]; it coexists with minerals such as Mn oxides, Fe oxides, and sands.…”