Deinking of high-quality offset papers : Influence of consistency, agitation speed, and air flow rate in the flotation stage

Flotation deinking of high-quality offset printed papers was studied using a laboratory cell with a nominal capacity of 50 L. Disintegration conditions prior to flotation were held constant to facilitate study of operating conditions during the flotation stage. The analyzed process variables were pulp consistency (0.75 %, 1%, 1.25%), air flow rate (500, 750, 1000 L/h), and agitation speed (850, 1150, 1450 rpm). A deinkability factor - based on handsheet brightness after flotation - was used to evaluate process efficiency and establish the optimum flotation conditions. Analysis of the results showed excellent correlation between deinkability factor and flotation operating conditions, and the proposed empirical equation had a regression coefficient r 2 of 0.90. The change in deinkability factor with operating conditions is explained by applying probability theory to predict the frequency of collisions between air bubbles and ink particles. Application : a laboratory investigation to determine optimum operating conditions for efficient flotation deinking of high-quality offset printed papers.