Pure and low-cost bentonite was prepared by a simple procedure, different from that previously reported by sedimentation and centrifugation. In this case, the raw clay has been purified by the hydrocyclone procedure. The effect of sodium carbonate on the removal of the impurities and the proprieties of the clay phase has been investigated by XRD and FTIR analysis. The results showed a considerable reduction of quartz and calcite amounts. The best viscosity has been detected for the clay–Na2CO3 mixture 5 wt%. The use of the purified clay as an adsorbent of methylene blue showed the increases in the quantity removed from 118 mg/g for the raw clay to 184 mg/g for the purified clay with hydrocyclone.