Production of concentrated carbonate suspensions

This application is a 371 of PCT/GB 99/04249, filed Dec. 23, 1999, which claims priority based on United Kingdom 9828514.1 filed Dec. 23, 1998 and United Kingdom 9910038.0 filed Apr. 30, 1999. A method of producing a rheologically stable concentrated aqueous suspension of a particulate alkaline earth metal carbonate which method comprises the following steps: (a) preparing a dilute aqueous suspension of the carbonate having a solids content of not more than 40% by weight; (b) dewatering the dilute aqueous suspension to form a carbonate suspension having a solids content in the range of from 45% to 65% by weight; (c) optionally mixing with the dewatered suspension formed in step (b) a dispersing agent for the carbonate to form a fluid suspension; (d) further dewatering the fluid suspension formed in step (b) by thermal evaporation under reduced pressure to raise the solids content of the suspension by a further differential amount of at least 5% by weight; and (e) after at least some of the dewatering in step (c) treating the suspension by a mechanical working process in which at least 1 kW.hr per tonne of carbonate on a dry weight basis is dissipated to refluidise the suspension.