Deinking flotation: influence of calcium soap and surface-active substances

The removal of ink particles from recycled paper appears to be an important stage in the pulp treatment process, since it allows for the production of material with suitable characteristics for reuse. Although, the deinking of paper pulp is usually conducted in a flotation cell with agitation, into which air is injected countercurrent to the feed. Recent studies have focused on columns without agitation and on reactor/separators. The work reported on here involved an investigation into the use of dissolved air flotation (DAF) to remove ink from old newspaper and comparative studies with induced air flotation (IAF). Before the flotation treatment, the old newspapers were physically and chemically treated to detach the ink from the pulp. The flotation experiments were conducted using Ca(oleate)2, CaCl2, sodium oleate, SDS (sodium dodecyl sulfate) and SBDS (sodium benzene dodecyl sulfate). The experimental results demonstrated that ink removal was more efficient with the concomitant use of Ca(oleate)2 and SDS in the two processes studied. The efficiency of the process was measured by the pulp's brightness and yield.