A study of pulping and flotation processes in deinking of office waste with block copolymers

A two-stage deinking process of pulping followed by flotation has been examined for office copier waste. Experiments were performed on a simple chemical formulation comprised of one of three PEO-PPO-PEO block copolymer surfactants to evaluate the separate effects of surface chemical and mechanical processes in pulping and in flotation. The deinking results were reported as the percentage fiber lost, the brightness of the deinked sheets, and the amount of residual ink left behind; the development of a novel image analysis technique facilitated the measurement of this ink.;Tests on variations in pulping conditions indicated that the amount of residual ink increased dramatically when the pulping speed was decreased in the presence of a hydrophobic copolymer, whereas a hydrophilic copolymer caused a decrease or no noticeable change in residual ink with decreasing impeller speed.;Tests in which flotation conditions were varied showed that foam thickness and stability increased with increasing hydrophilic character of the copolymer and increasing flotation impeller speed. The amount of paper lost increased as foam stability increased. The maximum amount of ink removed did not occur at the same conditions corresponding to maximum fiber removal; ink removal was greatest when flotation speed was low and air flow into the cell was moderate.;The removal of material from a batch flotation cell has been modeled by others as a first-order rate process. Pseudo-rate constants (kcalc ) were calculated for each experiment by arranging the process variables into groups that represented one of several different removal mechanisms. Comparison of kcalc with the k values from experiment indicated that regardless of how the process variables were arranged to represent the removal mechanisms, kcalc was a poor fit of kexp. The fit did not improve as the variables in the calculation were replaced with other variables. Our analysis was flawed mainly because the tests were performed at one constant time scale, so there was no time dependence to the data. The use of a wider range of test conditions may also indicate a stronger dependence of ink or fiber removal on changes in test variables.