Suspensions of a microparticulate boron adsorbent Dowex XUS can be effectively concentrated by microfiltration (MF) to relatively high concentrations of about 24 mass% of dry adsorbent. This is important for formation of a hybrid process combining adsorption or ion-exchange and MF. A tubular ceramic membrane with the mean pore size of 0.1 mu m and the ground boron adsorbent with the mean particle size of 4.7 mu m have been used. Analysis of the flux decline data revealed that the dominant membrane fouling mechanism is cake formation. A more detail analysis showed that a pore blocking by initial layer of deposit is dominant at the beginning of MF and the resistance of growing cake becomes more important with increasing filtration time. With the increasing suspension velocity, the permeate flux significantly increases. The velocity of suspension above 2 m s(-1) should be used to achieve a reasonable flux. The limiting flux was reached at a pressure difference of about 60 kPa at higher suspension concentrations. The critical permeate flux was achieved at pressure difference below about 40 kPa. Even at concentrations as high as 20 mass% of dry adsorbent in the suspension, the permeate flux of about 43 dm(-3) m(-2) h(-1) was achieved.