Abstract: A pulp suspension is de-inked by way of flotation after the suspension is chemically treated to remove impurities. Air is supplied to the chemically treated suspension so as to generate a foam containing the impurities on the surface of the liquid level of the suspension. The foam is drawn off closely above the liquid level and quenched, and an upper layer of the pulp suspension beneath the foam is discharged so as to remove fiber fines contained in the upper layer. Accordingly, the pulp suspension is purified more quickly and effectively than with prior arrangements wherein the foam and the fiber fines were not separately removed.