Recycling for newsprint manufacture : deinking fundamentals

• Main Author: Harrop, Nicholas M.
• Published: University of Manchester 1999
• Subjects: 676
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616284

It has long been known that waste newsprint can be deinked effectively only if a proportion of coated waste is added to it. Coated waste paper is not always in good supply, and can cost more than waste newsprint. The present research has thrown new light on why coated waste is required. In flotation deinking, two distinct processes act to separate ink from pulped stock. Firstly, air bubbles rising through the liquid phase collect ink particles and carry them to the surface. The ink particles are then retained by the foam on the surface until it is removed. The commercial deinking plant that was the subject of the present study uses a proprietary chemical, which is intended to act effectively in both processes. Chemical speciation has shown that the chemical species in the foam and in the bulk solution have similar thermodynamic properties. This implies that the chemical process operates independently of the presence of coated waste. Comparison of results gathered in full-scale and in pilot deinking equipment has shown that the foam is more stable when the waste paper being deinked contains coated waste. The key role of coated material is therefore to stabilise the foam, and so prevent re-mixing of ink with the deinked fibre slurry. These facts suggest that to achieve good deinking without having to use coated waste, other means of maintaining foam stability must be sought.