Influence of acid leaching of chips on eucalypt pulp production: Environmental and process performance

摘要

Acid leaching of chips is a promising technology for reducing non-process elements in kraft pulp manufacturing. The technique consists of pre-treating chips with an acid solution under appropriate time and temperature conditions prior to kraft pulping. The purpose of this study was to evaluate acid leaching of two eucalypts wood furnishes exhibiting very different characteristics prior to modified kraft pulping. The effects of acid leaching on oxygen delignification performance, pulp bleaching, and chemical properties of bleached pulps and on characteristics and treatability of effluents generated were determined. Reference chips (unleached) and chips leached with sulfuric acid or hot acid stage (A-stage) effluent were cooked by a modified kraft process then oxygen-delignified and ECF bleached using A/D(PO)DP and A(PO)DP sequences. Acid leaching considerably reduced metals contents in the chips. Pulps produced from leached chips showed improved performance during oxygen delignification and ECF bleaching over reference pulps. Pulp bleaching effluents after leaching had similar treatabilities to those of reference pulps. Treated effluents from A(PO)DP bleaching presented slightly higher organic loads and lower AOX than the treated effluents from A/D(PO)DP bleaching.