Abstract
The sorption of phosphate on soils is studied by radioisotopic tracer method. Two consecutive processes with rather different rates were differentiated: namely the heterogeneous isotope exchange between the phosphate in the soil solution and the weakly sorbed phosphate (fast reaction), and the transformation of weakly sorbed phosphate to tightly sorbed phosphate (slow reaction). In this paper, it is shown how the rate constants of these two processes can be determined by a radiotracer with a relatively short half-life.
Highlights
Interactions in solid/liquid systems are determined by chemical environment and physical, physicochemical, chemical processes
The dissolved in soil solution and weakly sorbed phosphate is considered as utilized by plants
Since all experimental conditions were the same during the incubation and batch studies, except that carrier-free phosphate was added to the soil or to the solution, the plots for non-radioactive and radioactive incubations should coincide when the heterogeneous isotope exchange and dissolution reach the equilibrium state
Summary
Interactions in solid/liquid systems are determined by chemical environment and physical, physicochemical, chemical processes. The quantity of water soluble/weakly sorbed phosphate as well as the fast transport rate of phosphate in a steady state between the soil and soil solution can be determined by heterogeneous isotope exchange. The fast process is the heterogeneous isotope exchange between the phosphate dissolved in the soil solution and weakly sorbed phosphate under a steady state. The non-radioactively incubated soil samples (1 g) was equilibrated with water (200 cm3) to reach a steady state (120 min mixing), than carrier-free 32P (as H3PO4) solution was added to the non-radioactive samples; that is the heterogeneous isotope exchange of phosphate between the dissolved and weakly sorbed phosphate was studied. The dissolution of phosphate, including weakly and tightly sorbed species, of the radioactively incubated soils was studied by batch technique (1 g soil and 200 cm solution).
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