A method and apparatus for the beneficiation of a contaminated particulate solid comprising a particulate solid and a contaminant including forming a feed slurry of the contaminated particulate solid in a mixing apparatus (22), passing the feed slurry to shear means (25) in fluid connection with the mixing apparatus and subjecting the feed slurry therein to conditions of shear in such manner as to disperse at least some of the contaminant in the feed slurry to provide a dispersed slurry, passing the dispersed slurry through a settler-type separator (32-36) which is in fluid connection with the shear means and collecting from an underflow outlet (49) of the settler-type separator a product slurry enriched in the particulate solid and collecting from an overflow outlet (47) of the settler-type separator a waste slurry enriched in the contaminant. In particular, the contaminated particulate solid is diatomaceous earth contaminated with clay and the beneficiated product has negligible cristobalite. The feed slurry may be formed by wet attriting of diatomite or diatomaceous earth in a high shear mixing apparatus and a dispersing agent may be used.