MEASUREMENT OF SORPTION ISOTHERMS WITH FLOW-THROUGH REACTORS

A simple flow-through reactor technique is described for measurements of sorption isotherms on solid environmental materials such as soils, crushed rocks, aquifer materials, or peat. The applicability of the method was established by determining copper sorption isotherms at effectively constant pH for two different soil samples. The experimental results compare favorably with independent batch and column studies. Potential advantages of the flow-through technique are exemplified by studying the sorption behavior of one soil sample that shows in batch experiments a pronounced dependence on the solid concentration (particle concentration effect). Comparison of these results with the flow-through reactor technique and independent column experiments confirms unequivocally that in this case the influence of the solid concentration is an artifact due to insufficient prewashing of the soil with the background electrolyte solution and has nothing to do with the shaking process in batch experiments. The present results indicate that incomplete removal of preadsorbed ions may often represent a major source of error in sorption studies and may be difficult to recognize in batch experiments.