Metal Ion Content of Material Removed from the Surface of Unbleached Kraft Fibres

Abstract

Distribution and attachment of metal ions to the pulp components in kraft pulps can affect the possibilities to achieve a metal ion profile favourable for total chlorine free bleaching. By enrichment and analysis of different morphological fractions of the pulp, such as material from the fibre surface and ray cells, the metal ion distribution (Fe, Cu, Mn. Mg and Ca) in a commercial unbleached softwood kraft pulp (kappa number 32) was investigated. Material removed from the surface of unbleached kraft fibres and the fraction containing the ray cells were found to have a considerably higher metal ion content than the rest of the pulp. There was good correlation between the content of manganese and calcium and the content of lignin and carboxy groups. Distribution patterns of metal ions in the pulp appear to resemble those found in the wood. The metal profile in the pulp was studied also following EDTA treatment. Metal ions remaining in the pulp after the EDTA treatment were still unevenly distributed, with high levels in the surface material and the ray cell enriched fraction