The flocculation and de-watering of kimberlite clay slimes

The crushing of kimberlite at certain diamond mines produces a very persistent “slime” which is exceptionally difficult to filter or de-water. The colloidally stable component has been identified as a swelling clay, saponite, which carries a strong negative charge in alkaline media.Methods of coagulating or flocculating these slimes have been investigated; the most convenient method found was the combined use of magnesium sulphate and an anionic polyacrylamide (A-130 from B.T.I. Chemicals Ltd.). Optimal results were obtained only in a narrow range of conditions but with these it was possible to build flocs of any required size.The permeability and de-watering of coagulated or flocculated kimberlite slimes has been investigated with a hydraulic apparatus and in the capillary suction time (c.s.t.) apparatus. Typically compressible filter-cakes are obtained, their character varying greatly with the flocculation conditions.