A view of pulp washing in bleaching

The main purpose of this article is to explore current knowledge of pulp wa shing as part of the bleaching process. The between pulp washing in bleachi ng and brown stock washing are emphasized and the need for appropriate meas urement of wash loss is pointed out. The literature concerning brown stock washing is vast, and research in this area has been carried out for many de cades. In contrast, pulp washing as part of bleaching has been neglected, a nd there ore surprisingly few significant publications on this subject. The authors claim that pulp washing during bleaching is not well known today a nd that the existing knowledge is mainly based on information gained from b rown stook washing. This approach is no longer sufficient, as the chemical environments in these two forms of washing are quite different. One difficu lty is how to measure wash loss in bleaching. In brown stock washing this c an be done easily by measuring the sodium loss or chemical oxygen demand (C OD). COD has also been used as a wash loss indicator in bleaching, but it i nvolves a long delay and the method is not repeatable. Whether or not this is the right indicator of wash loss is also open to question. The differenc es highlighted between pulp washing and brown stock washing clearly indicat e that further research is required into washing during bleaching.