Patent ID: 8282780

Claim:
Method for precipitating mineral particles on fibres to be used for manufacturing paper, paperboard or the like, which method consists essentially of: (a) a fibre material containing the fibres to be used in manufacturing is fed into a precipitation reactor; (b) a reactive mineral substance is fed into the precipitation reactor; (c) the reactive mineral substance and fibre material are mixed to form a fibre suspension in the precipitation reactor and/or before these substances are fed into the precipitation reactor; (d) the fibre suspension in the precipitation reactor is exposed to a substance which precipitates at least partially said reactive mineral substance, in which case at least part of the precipitated mineral substance thus formed precipitates on fibres residing in the fibre suspension, (e) the thus treated fibre suspension is led out of the precipitation reactor, (f) a gas which contains carbon dioxide is fed into the precipitation reactor, for forming a gas space containing said precipitant in the precipitation reactor, and (g) the fibre suspension that has been fed and/or that is formed in the precipitation reactor is disintegrated as small solid particles or liquid drops and/or particles into said gas space, wherein the fibre material is activated in an activation zone before the precipitation so that the ability of the fibres to bind with each other and to bind precipitated mineral substance increases, and that the dwell-time of the fibre material in the activation zone is <10 seconds, and wherein the activation zone of the precipitation reactor comprises an impact mill, having several coaxially arranged rings equipped with blades, of which at least every other ring operates as a rotor, and the adjacent rings of these rings as stators or rotors, and in which the difference in speed between the rotors and the stators and rotors of adjacent rings is 10-500 m/s, and wherein the fibre suspension is supplied so as to move from the centre of the impact mill radially outwards through its rings, in which case the blades on the rings direct recurrent impacts, double impacts, shear forces and/or over- and underpressure pulses on the fibre suspension flowing outwards, which all together activate the fibres, and optionally precipitating additional mineral particles onto said treated fibre suspension by repeating (a)-(q) at least once.