A flow-through reactor with an infinite sink for monitoring desorption processes

The assessment of elemental release processes in soils are of large interest in soil research. A technique is presented where the advantages of a flow-through reactor are combined with a specific infinite sink. Between the two reactors an electrolyte solution (pH 6) acting as a transport carrier was circulated continuously in a closed-loop setup. To demonstrate the capability of the new technique, phosphate desorption kinetics from different synthetic Fe and Mn hydroxides coated on silica sand were studied. The relative amount of P desorbed increased in the order ferrihydrite (10% of the initially sorbed P) < goethite (20%) <<hematite (65%) < Mn dioxide (80%). We suggest that this technique can also be adapted to other issues, for example, desorption of other anions and cations from solid phases (soils and sediments) because the composition of the infinite sink is variable.