Column flotation is an emerging technology in the deinking of recycled paper. Deinking efficiency depends primarily on the effect of four physical variables: gas and accepts flowrates, bubble size distribution, and pulp consistency. Experiments to establish operating ranges for these variables by determining their effect on gas holdup were conducted in a laboratory column installed at Bowater's Gatineau (Quebec) mill which processes a pulp (70% ONP/30% OMG) with about 1% consistency. The results showed the general trends expected from a review of previous studies: gas holdup increases with gas and accepts flowrates and with smaller bubble size, and decreases for higher pulp consistencies. However, the review also demonstrated that the published information is of limited application as the bubble size was much larger than that encountered in industrial flotation practice, primarily because of the use of pure water. Industrial pulps contain in most cases surface active agents which have a substantial effect on forming and preserving a small size bubble population.La flottation en colonne est une technologie en emergence pour le desencrage du papier recycle. L'eficacite de desencrage depend principalement de I'effet de quatre variables physiques : les debits de gaz et d'alimentation, la distribution de taille des bulles et la consistance de la plte. Afin de determiner les g a m e s de fonctionnement et leur effet sur la retention de gaz, des experiences ont ete menees dans une colonne de laboratoire installee a l'usine de Bowater a Gaineau (Quebec) qui traite une plte a papier (70% ONP/30% OMG) d'une consistance de 1%. Les resultats illustrent les tendances generales previsibles d'apres un examen d'etudes anterieures : la retention de gaz augmente avec les debits de gaz et d'alimentation et avec la diminution de la taille des bulles, et elle diminue avec I'augmentation de la consistance de la plte. Toutefois, I'etude bibliographie revele que les donnees publiees sont d'une application limitke du fait que la taille des bulles est plus grande que celle qu'on rencontre dans la pratique industrielle en matiere de flottation, surtout a cause du recours a de I'eau pure. Dans la plupart des cas, les pltes industrielles contiennent des surfactifs qui ont un effet significatif pour former et conserver une population de bulles de petite taille.
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