Bleaching method for bleaching deinked waste pulp

Abstract

The invention discloses a bleaching method for bleaching deinked waste pulp. The bleaching method has the advantage of avoiding the environment pollution caused by the conventional bleaching using sodium hydrosulfite and thiourea dioxide. The method is an environment friendly reducibility bleaching method which has great improvement on the whiteness of the waste pulp and low cost. The method can overcome the defect of a yellow color system lying in the conventional bleaching through the sodium hydrosulfite. In addition, sulphate used in the method can selectively be sodium bisulphite or sodium pyrosulfite so as to further improve the whiteness after the waste pulp is bleached and reduce the dosage of sodium borohydride. A chelating agent is at least one of sodium silicate, disodium edta or tetrasodium salt, and diethylene triamine pentacetic acid or sodium tripolyphosphate. Additives and the dosage of the additives can be adjusted according to the actual metallic ion content in the waste pulp so as to improve the bleaching efficiency and reduce the cost of the bleaching medicine for unit whiteness improvement.

Description

technical field [0001] The invention relates to a method for treating waste paper pulp used in papermaking industry, in particular to a bleaching method for bleaching deinked waste paper pulp. Background technique [0002] my country is a big country in the production and consumption of paper. In 2006, the national output of paper and cardboard was 65 million tons, and the consumption was 66 million tons, both ranking second in the world, second only to the United States. However, my country is a country with poor forest resources, with many people and little land. Although after years of hard work, my country's forest area and coverage have been greatly improved, but the per capita forest area is only 0.132 hectares, which is less than 1 / 2 of the world's average level. 4. The per capita forest stock volume is 9.421 cubic meters, which is less than 1 / 6 of the world average level. Therefore, the supply of papermaking raw material resources is the biggest problem in the develop...

AI Technical Summary

Problems solved by technology

However, replacing wood pulp fibers with waste paper will inevitably bring about various properties of the pulp (especially a decrease in whiteness), thereby affecting the quality of the paper

In order to improve the whiteness of waste paper, many enterprises use sodium hydrosulfate or methyl sulfonic acid to reductively bleach waste paper pulp. Dangerous goods, whose reaction products are mainly sulfite and sulfate or sulfur-containing gas, will cause serious pollution to the environment; It is relatively stable and has a good bleaching effect, but the reaction mechanism is similar to that of hydrosulfite, and other by-products such as sulfites will inevitably be produced during the reaction process, which will also pollute the environment, and the price of methylsulfonic acid is relatively expensive