example in accordance with the invention illustrates the surprising and unexpected progress in particular in the improvement of the whiteness which changes from 45 to 57 example 3 is repeated but the disintegration and the first flotation are carried out at a neutral ph in other words without adding any product likely to acidify the treated solution the whiteness obtained after flotation is 42 and after bleaching 49 the same second flotation in an alkaline medium is carried out a whiteness of 55 is obtained example 3 is repeated but after bleaching with peroxide the pulp is diluted to approximately 5 and treated for five minutes in a laboratory disintegrator the second flotation as described in example 3 is carried out the final whiteness of the pulp is 62 example 5 is repeated in which sodium hydrosulphite na 2 s 2 o 4 in a proportion of 1 5 by weight of dry substance is introduced into the mixture during the detachment in the pulper in the course of phase i the mixture is left to stand for half an hour the whiteness obtained after the flotation in an acid medium is 47 the final whiteness after flotation in an alkaline medium is 63 example 5 is repeated but using only newspapers printed using the offset method a final whiteness of 64 is observed thus representing a significant improvement inherent in the treatment.