Effects of Cation Exchange Material on Zinc Adsorption by Soils

Abstract

The adsorption of Zn by soils which are different in their major cationexchange materials was measured at equilibrium Zn concentrations up to lo-' M in lo-' to l O -' M CaCl,. The results are interpreted on K$;-[Zn],,il plots, where KE; is the selectivity coefficient defined by the equation All natural samples except those containing halloysite exhibited no or very small specific Zn adsorption. AU Ca-saturated samples exhibited specific Zn adsorption dependent oncation-exchange materials. The cationexchange sites with high selectivities for Zn (K3: > 10) constitute more than 40 per cent of the total exchange sites in soils containing allophane, imogolite, and halloysite, whereas those with moderate to low selectivities for Zn (K$; < 10) predominate in montmorillonitic, vermiculitic, and humic soils. Differences in the contribution of the respective cationexchange materials to specific Zn adsorption are discussed relating t o differences in the origin of their negative charge.

Effects of pH and Ionic Strength on Zinc Sorption by a Variable Charge Soil

“…The values of K and b constants for pH and ionic strength values are shown in Table 2. [24] Maximum zinc adsorption was always higher in the surface soil than in the subsoil ( Table 2). A good fit of adsorption data by Langmuir and Freundlich equations for soils of the State of Sa˜o Paulo, Brazil, was also observed by others.…”

Selective Adsorption of Zinc on Halloysite

“…It is considered that Zn is adsorbed at first on sites with "higher selectivity" and then on sites with "lower selectivity." The proportion of "high" and "low" selectivity sites differ from clay to clay, and their differences broadly parallel those between the soils containing these clays as major cation-exchange materials (Wada and Abd-Elfattah, 1979). However, some soils tend to adsorb Zn more q I000 I , The K~vs.…”

“…In an earlier study (Wada and Abd-Elfattah, 1979) on Zn adsorption by soils which differ in their major cation-exchange materials, halloysite was found to be a very selective adsorbent for Zn. Halloysite and kaolinite are widespread products of hydrothermal alteration and weathering and are common constituents of soils and sediments.…”

Purification of Waste Water Using Alumina as Catalysts Support and as an Adsorbent

“…For example, weakly bound outer-sphere adsorption complex are more rapidly exchangeable than more strongly bound inner-sphere adsorption complexes. This explains socalled specific adsortpion, which suggests alumina can adsorb heavy metal ions 1,000 to 10,000 times more readily than alkaline or alkaline earth metal ions (Wada & Abd-Elfattah, 1979).…”