Figure 2.

Plots of ln [Cr(VI)] vs. time show that the overall rate of Cr(VI) reduction is high with illite, low with kaolinite, and in the middle in the control without any mineral; and reaction rates decrease with increasing pH from pH 7.67 to pH 9.07. The initial concentrations of Cr(VI) and sulfide were 40 μM and 800 μM, respectively.