Characterization of zinc adsorption sites in two mineral soils

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 CaCl₂.

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 as defined by the equation:

was calculated for each adsorption equilibrium and plotted against the amount of Zn adsorbed. This [Zn]_soil plot was used to estimate the capacities of the soil to adsorb Zn with specified affinities. The value varied between 1 and 1,000, whereas the corresponding value varied only between 0.5 and 1. The 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.     

Influence of pH,dispersion methods,and different compounds on adenosine triphosphate recovery from soil

We studied the recovery of ATP from soil. A soil-water suspension was prepared by two different methods (simple stirring or ballottini mill treatment) at different pH levels and in the presence of different chemicals [Na₂SO₄, Na₃PO₄, Na₅P₃O₁₀, adenosine, ethylenediaminetetra-acetic acid (EDTA), TRIS]. The ATP recovery was evaluated by adding [³H]-8 ATP to the solution and comparing the values obtained by radioactivity measurements with those obtained by an enzymatic assay. Strongly acidic (pH lower than 1.0) or alkaline (pH 10.0) extractions yielded the best ATP recoveries compared with intermediate pH values. At pH 10.0, the addition of Na₃PO₄ or Na₅P₃O₁₀ gave a high level of ATP recovery, 68 and 96%, respectively. No ATP hydrolysis occurred under alkaline extraction conditions. Under acidic extraction conditions, the addition of adenosine, EDTA, Na₂SO₄, or Na₅P₃O₁₀ improved ATP recovery but it was never higher than 34%. The results were discussed in terms of the effects of different physical and chemical conditions on cell disruption, ATP stability, ATP interactions with soil components, and ATP solubilization.