Abstract: The invention relates to a particularly energy efficient, two-step method and to a system for the continuous or semicontinuous production of crystalline calcium carbonate (precipitated calcium carbonate, PCC) by reacting calcium hydroxide with CO2, the calcium hydroxide being lime milk. In the first step of the germination, the CO2-source is exclusively flue gas having a CO2-content of between 4-25% <sb/><sb/>. In the second step, the complete conversion of the lime milk reacted in the first step to a maximum of 90%, preferably between 10-90%, is carried out exclusively using a rich gas which comprises 30-99% CO2, preferably using biogas.

Abstract: The invention relates to paper that contains scalenohedral precipitated calcium carbonate (s-PCC) of a certain specification. The invention further relates to the user of a s-PCC having a certain specification as filler material for paper.

Abstract: The invention relates to a particularly energy efficient, two-step method and to a system for the continuous or semi-continuous production of crystalline calcium carbonate (precipitated calcium carbonate, PCC) by reacting calcium hydroxide with CO2, the calcium hydroxide being lime milk. In the first step of the germination, the CO2-source is exclusively flue gas having a CO2-content of between 4-25% <sb/><sb/>. In the second step, the complete conversion of the lime milk reacted in the first step to a maximum of 90%, preferably between 10-90%, is carried out exclusively using a rich gas which comprises 30-99% CO2, preferably using biogas.

Abstract: Spherical, hard mono- or oligodisperse particles of diameter from 0.1 to 100 .mu.m are prepared by condensation of partially etherified melamine-formaldehyde precondensates which form a clear solution in water in every ratio, in an aqueous solution of a water-soluble polymer which has strongly acid groups and a K value of from 100 to 160, at pH 3 to 6 and at 20.degree. to 100.degree. C., and condensation of the resulting cloudy solution is continued until the precondensate has been consumed, resulting in a dispersion of the particles. The dispersion is neutralized. The particles can be used in the form of the aqueous dispersion or after isolation from the dispersion.The particles are spherical, hard and non-swellable and can be used, for example, as sizes for plastics, polishes, delustrants, extruders and/or as pigment.The process makes it possible to produce particles of predetermined size and size distribution.

Abstract: In an ultrafiltration of a liquid having a starting solids concentration, in which the liquid is pumped through a filtration circuit including at least one membrane filter, and the loss of liquid resulting from the continuous extraction of filtrate from the filtration circuit is compensated for by feeding unfiltered liquid into the filtration circuit from a separate concentrate container which is connected with the filtration circuit by a feedline and a return line for flow of liquid to and from the filtration circuit, the liquid in the filtration circuit is periodically and repeatedly supplemented by additions of fresh unfiltered liquid taken from a reservoir having the starting solids concentration so as to repeatedly bring the solids concentration in the filtration circuit closer to the starting concentration.