A simple method for physical purification of bentonite

• A bentonite with 44% montmorillonite was purified adopting a simple method.
• Purified bentonite with montmorillonite content of 96.5% and montmorillonite yield of 70% was obtained.
• Appropriate grinding of raw bentonite and dispersant are very important for the centrifugal separation.
• Under the optimal condition, bentonite with different montmorillonite content and yield can be obtained by adjusting the centrifugal speed.

Impurities limit the application of low-grade bentonite, resulting in a large waste of resources. A simple physical method composed of grinding, dispersion and centrifugation was adopted to purify a low-grade bentonite from Zhejiang, China. This experiment increased the montmorillonite content of the bentonite from 44% to 96.5% with montmorillonite yield over 70%. The influence of the grinding time of raw bentonite, the dispersant dosage in bentonite dispersion, and the centrifugal speed on the purification of bentonite were investigated. Results indicate that appropriate grinding is crucial to the dissociation of bentonite aggregates. The particle size of raw bentonite decreases with increasing the grinding time but it is needed to stay within a certain range to avoid excessive grinding that hinders the purification. A suitable amount of dispersant can change the surface potential of minerals and enlarge the flottability and stability differences between montmorillonite and impurities, which is important for their separation by aqueous dispersion. Centrifugal speed is also critical as too low speed decreases the purity level of the purified bentonite and too high speed lowers the yield of montmorillonite.