| 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 the pulp is treated with a peroxide and/or a peracid in the presence of an activating Ti-, V- or Cr-group transition metal, such as molybdenum, vanadium or tungsten. The essential idea in the invention is that, before this peroxide and/or peracid treatment, heavy metals derived from the wood raw material, such as iron, manganese and/or copper, are removed from the pulp by chelation. In the chelation the heavy metals are converted to soluble complex salts which are removed along with the chelating solution or washing water. The chelation and the peroxide and/or peracid treatment constitute parts of a bleaching sequence which contains as possible other treatment steps, for example, a treatment with oxygen, a second chelation step, and an alkaline peroxide treatment. |
