A Study of Bleach Effluents from Oxidative Extraction

During the 1970\u27s oxygen delignification was primarily undertaken before the bleaching stages in a pulp mill. However, towards the end of the 1970\u27s further research was done to promote the use of oxygen as a decoloring agent within the bleaching stages. This was warranted because oxygen delignification was known to promote decreased chemical consumption, mainly chlorine. The process that was developed came to be known as oxidative extraction. This process has become very popular due to the fact that it is easier to install and operate than the conventional oxygen delignification system. Some other advantages that this process offers are its applicability to all pulps and the reduction in the number of bleaching stages in some instances. Oxidative extraction involves the addition of oxygen to an alkaline pulp stream following a C-stage washing but ahead of the first extraction stage in a bleaching sequence. The oxygen acts to further delignify the pulp which in turn reduces the demand for bleaching chemicals in the following stage or stages. One major advantage of the decreased usage of chemicals is the improvement of the effluent quality from the bleaching sequences. My project involves the Kraft cooking of a typical species of a hardwood common to Michigan. The pulp was cooked to a low and high kappa number, then each Kappa number pulp bleached to a common kappa number. The bleaching stages include a chlorinechlorine dioxide stage (Cd) followed by an oxidative extraction (Eo) or extraction {E) stage. The effluents from this stage was then tested for COD, color, pH, chlorides, and total solids