Flotation deinking with magnesium oxide as the alkali source.

Application: This study supports the use of magnesium oxide as an alternative alkali in flotation deinking to reduce salinity and sodium adsorption concerns.

Concerns over the environmental problems of highly saline effluent and high sodium adsorption ratios from RCF plants and paper mills has meant that paper mills need to find alternative strategies to reduce the problem, One solution is to reduce the amount of sodium hydroxide used or replace it with an alternative alkali such as magnesium oxide. This paper describes the results of laboratory work and mill scale trials undertaken to assess the viability of MgO as an alternative alkali source in flotation deinking.

Laboratory experiments using a Lamort deinking unit showed that the deinking efficiency and final pulp brightness of the MgO system were not as sensitive to changes in chemical levels as the NaOH system. Increasing the soap addition in the pulper did appear to improve the brightness and ink removal efficiency of the process. A dual alkali system of MgO and NaOH was also investigated with promising results in the laboratory.

A number of mill trials in which NaOH was partially replaced by MgO showed promising results in reducing the salinity and high SAR from the mill. The RCF pulp brightness was slightly lower compared to normal operations with NaOH as the alkali source, but this did not significantly affect the final paper brightness.

Stack is associate lecturer; Featherstone is research assistant, and Baptist is a student in the School of Chemistry at the University of Tasmania, GPO Box 252-75, Hobart, Tasmania 7001, Australia," Kirk is technical account manager, ORICA Australia Ply. Ltd., 1 Nicholson St., Melbourne 3000, Australia. Email Stack at [e-mail].