Effect of air volume and air bubble size distribution on flotation in injector-aerated deinking cells

Air bubbles are essential in flotation deinking. After their collision with ink particles, the air bubble-ink particle agglomerate floats, followed by its removal with the flotation froth. Commercial flotation deinking cells cover a great range of airflow rates (from 20% up to 1000%) but most units operate at a rate below 100%. However in flotation, not only the volume of air but the average size of the air bubbles as well as their distribution is of significance. For an injector-aerated pilot plant flotation cell, various injectors were developed to control the introduction of air into the suspension. The airflow rate was increased in water and stock from 30 to 180% by variation of the injector types, the pulp flow and the airflow. The effects on air bubble size distribution in water as well as in suspension are demonstrated by utilizing a recently developed measuring device. In addition, the influence of airflow rate and injector design on flotation efficiency (ISO brightness gain, yield) was evaluated.