Evaluation of fly ash as a potential alkali for old newspaper de-inking

초록

Generally, fly ash from paper recycling mills is mainly composed of unburned carbon, magnesium, calcium and traces of heavy metals. In this study, fly ash from a paper recycling mill was tested as an alternative to alkali for the de-inking process of old newspapers (ONP). It was determined that 79% of fly ash passed through a 100 mesh screen and trace amounts of heavy metals were detected. The fly ash solution was analyzed as a strong alkali with a pH as high as 12.26. The pH and alkalinity of the fly ash solution increased with a decrease in its particle size. Better optical properties of a pulp pad formed after flotation were achieved when NaOH was used as chemical additive in de-inking process. High alkalinity of fly ash caused excessive fragmentation of ink in the pulping stage. High calcium hardness caused by fly ash was the reason for excessive generation of reject from froth-flotation. Except for low Hunter b* value of pulp pad, replacing common alkali (NaOH) with fly ash may not give any positive effect on optical properties of deinked pulp (DIP) from ONP.

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