Cation transport and partitioning during a field test of electroosmosis

Field experiments were conducted to evaluate the effects of soil properties , such as the cation exchange capacity and mineral content, on pH, soluble ion concentrations, and electrical conductivity during electroosmosis in a silty clay soil. The soil is composed mainly of quartz (60%) and smectite/i llite (20-29%). The measured cation exchange capacity of the test site soil ranged from 11 to 22 cmol kg(-1), which was consistent with the contributi on from the clay contents. The exchangeable cations and reserve acidity mea surements suggest that the majority of protons that were generated at the a node by electrolysis not only exchanged;the base cations but also were adso rbed on the soil minerals. Protons also reacted with the soil minerals and caused the release of dissolved Al3+, which was then exchanged and adsorbed by the soil minerals. The exchange and adsorption of proton and Al3+ resul ted in the decrease of the exchangeable base cations and ion concentrations of the pore fluid. Sorption (exchange and adsorption) and reaction signifi cantly retarded the transport of protons. The apparent retardation factor f or protons calculated from the movement of the pH front was of the order of 1000, whereas retardation factors calculated by assuming a Langmuir isothe rm ranged from 30 to 6700 in the pH range of 3.6-4.8. The electrical conduc tivity of the soil also was influenced and dominated by the sorption and re action of protons. In the region close to the anode where protons were sorb ed, the electrical conductivity at the end df the test decreased to 0.37 of the initial value despite the fact that the proton concentration in pore f luid increased by 1-2 orders of magnitude. The results of this study show t hat soil properties, such as cation exchange capacity and mineral content, have a pronounced effect on solution chemistry and hence the utility of ele ctroosmosis.