Fig. 2. Effects of particle size, pH, and time on (a) B concentration and (b) B release rate for Morris illite, and (c) B concentration and (d) B release rate for Fithian illite. The B release rate is expressed as the difference in the amount of B in solution between two adjacent sampling time periods divided by the sample surface area, and plotted at the mean time of the two adjacent sampling events, excluding time zero and 5 d, that is, 10, 22.5, 45.75, 105, 135, and 165 d.