Deinking of newsprint by flotation method

There is much current interest in development of processes which lead to . greater utilisation of secondary fibres in papermalcing operations, both in Australia and overseas. The removal of ink from paper (deinking) is a major step in these processes. After repulping, ink can be removed from aqueous suspension by a number of techniques, one of which is flotation. Most commercial deinking facilities use flotation as the principle method of ink removal. Studies have been made on the effects of flotation conditions, feedstock composition, and surfactant during flotation deinking of newspaper (ONP) and magazines (OMG). Type of surfactant and amount of surfactant appear to affect deinking performance. Temperature, pH, and furnish also appear to affect deinking efficiency of the various surfactants investigated. There is an optimum pH of 8.5 for flotation deinking of a 70/30 mixture of ONP/OMG using a fatty acid type deinking surfactant. Increasing proportions of magazines (ash content of 26%) in the feedstock results in a deinked pulp with higher brightness. However, it was found that the higher brightness attained is largely due to the addition of higher brightness materials from the magazines, rather than a more efficient mechanism of ink removal from the ONP. Addition of Ca2+ in the pulping stage at low level of addition seem to improve the brightness response for deinking of newspaper with fatty acids. High level of addition of Ca2+ seems to have detrimental effect. An attempt is made to explain the results in terms of a model describing the flotation deinking process and the interactions occurring between surfactant molecules, ink particles, fibres, and air bubbles.