Study of Ni(II) sorption on chlorite - a fracture filling mineral in granites

摘要

Chlorite is an Fe(II)-containing phyllosilicate which is often present as a fracture filling mineral in e.g. granitic rocks. It may therefore be significant in influencing redox conditions and sorption processes in granitic groundwaters. The sorption properties of chlorite may therefore be important when modelling the migration of radionuclides under reducing conditions around nuclear waste repositories or in sites contaminated by mining waste. The sorption behaviour of Ni(II) onto a natural chlorite (Karlsborg, Sweden) was investigated using a batch technique. The effects of three different background electrolyte concentrations (0.01 M, 0.1 M and 0.5 M NaClO_4), different pH values (ranging from 4 to 11) and different Ni(II) concentrations (10~(-6) and 10~(-8) M) were studied under anoxic conditions in a glove-box. Ni(II) solutions were spiked with ~(63)Ni and β-Liquid scintillation counting (LSC) was used to determine the concentration of nickel in the bulk solution, allowing the calculation of solid-water distribution coefficients for the metal ion. The results of the sorption experiments show strong pH dependence at pH > 5, but the sorption is independent of ionic strength. The maximum adsorption is found in the pH range between 7 and 11 with K_d values ≈10~3 cm~3/g. A diffuse double layer model has been used to describe the experimental results.