Towards environmentally sustainable bleaching of kraft pulp. Evaluating the possible role of ozone

摘要

In this paper, contemporary bleaching is discussed in an environmental context. Both Totally Chlorine Free (TCF) and Elemental Chlorine Free (ECF) bleaching concepts are covered, and the literature on the toxicity of various concepts is reviewed. Special attention is paid to ozone, considering how to use it in both an efficient and a selective way. It is concluded that ozone could be used in both ECF and TCF sequences, but that the most attractive implementation of ozone bleaching is in a TCF sequence for hardwood kraft pulp. Moreover, laboratory trials seem to indicate a better selectivity of medium consistency over high consistency ozone bleaching, probably because water acts as a protective layer around the pulp fibres. In comparison with hot chlorine dioxide bleaching technology, ozone seems not to be the first choice for the bleaching of hardwood kraft pulp as long as TCF bleaching is not considered an end in itself.