Interaction between aqueous chromium solutions and layer silicates

The interactions between Cr in aqueous solutions and phyllosilicates were s tudied to determine: (a) the amount of Cr(VI) to Cr(III) reduction in aqueo us solutions by Fe(II)-bearing phyllosilicates; (b) the removal of the Cr s pecies from solution by interaction with phyllosilicates, as a function of Cr(III) concentration and anionic environment. Chlorite, corrensite and mon tmorillonite were reacted with solutions containing Cr(VI) (1.62 x 10(-3) N , 5.77 x 10-3 N and 1.32 x 10(-1) N, respectively). The sorption/desorption of Cr(III) by saponite was investigated in different anionic environments (Cl-, NO3- and CH3COO-) and at different initial Cr(III) concentrations (3. 21 x 10(-3) N, 5.49 x 10(-3) N and 8.49 x 10(-3) N). The extent of Cr(VI) reduction and the amount of Cr removed by phyllosilica tes were measured by analysis of the liquid portion separated by centrifuga tion after controled periods of exposure. The minerals were studied by chem ical, thermal and X-ray powder diffraction analyses. The results show that: (i) Fe(II)-bearing phyllosilicates sorb Cr and reduce Cr(VI) to Cr(III); ( ii) the extent of reduction depends on the solution concentration and on mi neral crystal chemistry; (iii) Cr(III) sorption isotherms show that the deg ree of uptake depends both on the initial concentration of metal in solutio n and on the anionic environment, the order of effectiveness being Cl- cong ruent to NO3- > CH3COO-; (iii) Cr(III) is retained in the mineral substrate and its release is difficult. (C) 2000 Elsevier Science Ltd. All rights re served.