Flocculants made of natural volcanic ash soils can be used to purify turbid water in reservoirs. Imogolites in the flocculants seem to play an important role when the flocculants are applied. To clarify the mechanism of imogolite-induced flocculation, we studied the flocculation and charging of latex particles as a function of the ratio of the concentration of imogolites (CI) to that of latex particles (CL) at three different pH. The mechanisms at each pH are found as follows. At pH4, flocculation occurs only around CI/CL=0.01, where the particles are uncharged found from electrophoretic mobility. Thus, the mechanism at pH4 is charge neutralization. At pH6.5, the suspensions flocculate when CI/CL is higher than 0.01; the particles flocculate due to charge neutralization as well as sweep flocculation, by which latex particles are enmeshed by the flocs of imogolites. At pH10, where imogolites and latex particles bear negative charge, the suspensions flocculate when CI/CL exceeds 0.1. Only the sweep flocculation acts at pH 10.
