Abstract: The calcium carbonate is prepared by:(a) slaking quicklime in an aqueous medium;(b) carbonating and neutralising the suspension of slaked lime formed in step (a) using a gas comprising carbon dioxide; and(c) separating the precipitated calcium carbonate formed in step (b) from the aqueous medium in which it is suspended. There is added 0.1% to 2% by weight, based on the weight of dry calcium oxide, of a reagent having one or more active hydrogen atoms (or a salt thereof), to the aqueous medium in which the quicklime is slaked in step (a).

Abstract: There is disclosed a process for separating fine solids from water in the used water recovery system of a sheet forming mill, wherein the used water recovery system includes at least one stage in which an alkaline earth metal carbonate is precipitated in the aqueous suspension constituting the used water whereby the particulate material present in the used water becomes entrained in the alkaline earth metal carbonate precipitate. By the invention it is possible to recover the water and the fine solid materials which pass through the wire mesh belt of a paper or board forming machine, and optionally recycle those recovered materials.

Abstract: A method of preparing precipitated calcium carbonate which comprises slaking quicklime in an aqueous medium, passing the suspension of calcium hydroxide through a sieve having an aperture size in the range of 40 to 70 microns, carbonating the calcium hydroxide and separating the calcium carbonate from the aqueous medium in which it is suspended. The sieved calcium hydroxide is subjected to high energy, high shear agitation which is terminated prior to carbonation. During the carbonation, the suspension of calcium hydroxide is subjected to relatively lower energy and shear agitation compared to the previous high energy, high shear agitation.

Abstract: The calcium carbonate is prepared by:(a) slaking quicklime in an aqueous medium;(b) carbonating and neutralizing the suspension of slaked lime formed in step (a) using a gas comprising carbon dioxide; and(c) separating the precipitated calcium carbonate formed in step (b) from the aqueous medium in which it is suspended. There is added 0.01% to 15% by weight, based on the weight of dry calcium oxide, of a reagent having one or more active hydrogen atoms (or a salt thereof), to the aqueous medium in which the quicklime is slaked in step (a).The reagent is selected from the group consisting of triethanolamine, mannitol, diethanolamine, bicine, morpholine, tri-isopropanolamine, N-ethyl diethanolamine, N,N-diethylethanolamine and sodium boroheptonate.

Abstract: Raw bentonite is beneficiated by treating a substantially iron oxide-free bentonite, as an aqueous suspension, with an alkali at a temperature of at least 60.degree. C.; washing the alkali treated bentonite at least once with water; and then subjecting a suspension of the alkali-treated and washed bentonite to shearing, attrition and impact forces in a homogenizer of the type wherein the suspension is forced in the form of a film through a thin, hard-surfaced gap under a pressure of at least 1.7 MPa, and at high velocity. The suspension of bentonite thus obtained can then be dried to a product which has a good white color and is more resistent to bacteriological growth.