DELIGNIFICATION OF CHEMICAL PULP WITH PEROXIDE IN THE PRESENCE OF A TRANSITION METAL

摘要

The invention relates to a process for the delignification of a chemical pulp,such as a sulfate or sulfite pulp, in which process thepulp is treated with a peroxide and/or a peracid in the presence of anactivating Ti-, V- or Cr-group transition metal, such as molybdenum,vanadium or tungsten. The essential idea in the invention is that a compoundcontaining at least one heteroatom, such as Si, P or B, whichis capable of forming a heteropolyacid with the activating transition metal,is added to the pulp. The feeding of the activating transitionmetal and the heteroatom into the pulp may take place in one and the samealkaline solution, for example introduced into the solution or inthe form of a compound of the silicomolybdenic acid type, formed in thesolution. The peroxide and/or peracid treatment may constitutepart of the bleaching sequence, which contains as potential other treatmentsteps, for example, a treatment with oxygen and a chelation forthe removal of heavy metals such as iron, manganese and/or copper.