Characterization of zinc adsorption sites in two mineral soils

Abstract

The adsorption of Zn, as compared with Mg, on two mineral soils, which differed in their major cation-exchange materials and with and without Ca-saturation, was measured in the presence of free CaCl a •The adsorption of Zn as well as Mg occurred on cation-exchange sites. The Zn adsorption data conformed to a two-term Langmuir equation. The presence of two kinds of adsorption sites and their numbers and bonding energies were deduced. However, the Langmuir approach was not adopted on the basis of comparison between the total number of the adsorption sites for Zn deduced and the CEC of the soils.As an alternative approach, the selectivity coefficient K~~, as defined by the equation:was calculated for each adsorption equilibrium and plotted against the amount of Zn adsorbed. This K~:-[Zn]80i! plot was used to estimate the capacities of the soil to adsorb Zn with specified affinities. The K~: value varied between 1 and 1,000, whereas the corresponding K~arz value varied only between 0.5 and 1. The K~: value was dependent upon the amount of Zn adsorbed, the status of exchangeable cations, and the major cation-exchange materials (montmorillonite VS. allophane-imogolite) in the soils. The importance of surface OH groups in allophane-imogolite as specific adsorption sites for Zn was suggested.

Modeling the Effect of Temperature on Adsorption of Lead(II) and Zinc(II) onto Goethite at Constant pH

“…Similar values for these which a single hydrated metal species from solution is replaced ratios have been found for the two-site Langmuir equation by more than one hydrogen ion. The fact that the entropies are for adsorption of phosphate on soils (14), Zn(II) on soils similar in magnitude for adsorption of Zn(II) under all condi- (16), and cadmium on goethite (3).…”

Effects of Cation Exchange Material on Zinc Adsorption by Soils

“…This finding is important in its implication on the effect of liming on the availability of Zn in the soil. This effect of Ca saturation being actually the effect of raising pH was shown in our previous paper (Wada and Abd-Elfattah, 1978).…”

Advances in Soil Science

“…According to Watanabe et al (1977), these cyanobacteria play the greatest role in N2 fIXation in tropical paddy soils. In Japanese paddy soils, the atlrobic N 2 -flXing bacteria and not the cyanobacteria are believed to contribute most to biological N2 assimilation (Wada et al, 1978). Average rates of biological N2 ftxation in flooded soils (paddy) are in a range of 50 kg N ha-1 yr-1 and thus are much higher than the rates in arable soils that amount to about 12 kg N ha-1 yr-1 (see also Table 4).…”