Treatment of solid containing material derived from effluent of wastepaper treating plant

A method of treating solid containing material contained in or produced from an effluent or waste from a process for the treatment of waste paper, the solid-containing material comprising constituents of the waste paper and including organic material including cellulose fibers and inorganic particulate material including calcium carbonate and other inorganic particulate material included in the waste paper, the calcium carbonate constituting from 5% to 95% by weight of the inorganic particulate material, the method including the step of heat treating the solid-containing material to incinerate the organic material present and to leave a residue of the inorganic particulate material substantially free of organic material, the temperature of the treated solids containing material in the heat treating step being controllably maintained in the range of from about 600.degree. C. to about 800.degree. C. to cause incineration of the organic material without decomposition of more than 50% by weight of the calcium carbonate present, and resulting in the residue of the inorganic particulate material having reduced abrasiveness for use in making or coating paper.