Carbonate Sorption Capacity of Iron Hydroxide and Soil Material

Abstract

The ability of goethite and natural soil materials to sorb dissolved carbonate was demonstrated in this investigation. The sorption capacity of the laboratory-prepared material was shown to vary from 0.2 to 5.0 g C/kg Fe over the pH range from 3.9 to 7.8. Sorption capacities were higher at lower pH's and at higher dissolved carbonate concentrations. Measurable sorption capacities were detected for t he soil materials under conditions highly favourable for carbonate sorption, i. e. at high partial pressures of carbon dioxide and at pH's less than 4.7. These values range from 50 to 100 mg C/ kg soil and correspond to partition coefficients under the specified experimental conditions of 0.15 to 0.31 ml/g. Under pH conditions more typical of soil/water and groundwater flow systems (pH > 5.5 ), these values would be considerably less and it would seem unlikely that the sorbed carbonate reservoir would ever exceed several tens of percent of that carried in solution. Thus it can be concluded that soil material as investigated in this study would provide only a minor attenuating influence on 14C-carbonate during groundwater flow through such material.