GB1463477A - Agglomeration of steel plant waste products - Google Patents

Abstract

1463477 Agglomeration of steel plant waste dust MICHIGAN TECHNOLOGICAL UNIVERSITY BOARD OF CONTROL 22 April 1975 16692/75 Heading C1K A hardened agglomerate is made from steel plant waste dust containing a hydratable material selected from overburned lime, a hydratable slag material or a mixture thereof, by (a) preparing a moistened mixture including the steel plant waste dust, 2 to 20 weight per cent of an oxide, hydroxide or carbonate of calcium or magnesium, or a mixture thereof, as a bonding agent, and 0À5 to 5 weight per cent of a silica-containing material capable of reacting with the bonding agent to form silicate bonds, therewith, the weight percentages being based on the total weight of dry solids in the moistened mixture, and the particle size of the solids in the moistened mixture being less than 10 Tyler mesh; (b) ageing the moistened mixture at an elevated temperature in an atmosphere containing water vapour, for a sufficient time to hydrate substantially all of the hydratable material therein; (c) forming the aged mixture into discrete compact masses; (d) drying the masses to a moisture content of 5 weight per cent or less, based on the total weight of the masses, the drying rate being below that at which bursting of the masses occurs; (e) hydrothermally hardening the masses by contacting them with saturated or substantially saturated steam at a temperature of 100 to 244‹ C. for a period of time sufficient to form hardened and integrally bonded masses, and (f) cooling the hardened masses. The term "steel plant waste dust" means finely divided, iron-rich, solid particulates and fines recovered as by-products from steel-making processes. It includes dust collected from the fumes from basic oxygen furnace, open hearth, blast furnace and electric furnace processes, mill scale fines, grit chamber dust, fines separating from pelletized iron and mixtures of these. The moistened mixture may also contain up to 3 weight per cent, based on the total weight of the dry solids in the mixture, of an oxide, hydroxide, carbonate, bicarbonate, sulphate, bisulphate or borate of an alkali metal, a quaternary ammonium hydroxide, a quaternary ammonium chloride, a quaternary ammonium amine or a mixture of two or more thereof, as a strengthening agent. In a further step (g) the hardened masses are dried immediately after the hydrothermal hardening step and prior to appreciable cooling, to remove at least a substantial portion of the moisture contained therein. The preferred bonding agent is calcium oxide or calcium hydroxide, the preferred strengthening agent is sodium hydroxide, sodium carbonate or sodium bicarbonate and the preferred silicacontaining material is silica.