Kemira Chemicals Oy

Jukka J&auml;k&auml;r&auml;

Reijo Aksela

Ilkka Renvall

Aarto Par&eacute;n

The invention relates to a process for the bleaching of chemical pulp, wherein the pulp is delignified and/or bleached with chlorine dioxide or with a combination of chlorine dioxide and a per-compound, and additionally the pulp is chelated in order to bind heavy metals, such as Fe, Mn and/or Cu, to a chelate complex. The chelate complex is selected from the group made up of N-bis-&lsqb;(1,2-dicarboxylethoxy)-ethyl&rsqb;-amine, N-bis&lsqb;(1,2-dicarboxylethoxy)-ethyl&rsqb;-aspartic acid and N-tris-&lsqb;(1,2-dicarboxylethoxy)-ethyl&rsqb;-amine, and the alkali metal and earth-alkali metal salts of these, and the chelating treatments are carried out simultaneously by combining the chelating chemical with the pulp in the same bleaching stage as chlorine dioxide.

Bleaching of chemical pulp and treatment with a chelating agent

A process for the bleaching of chemical pulp, in which process the pulp is delignified with a peracid and additionally the pulp is chelated in order to bind heavy metals, such as Fe, Mn and/or Cu, into a chelate complex. According to the invention, the chelating is carried out using a chemical which has been selected from a group consisting of N-bis-((1,2-dicarboxy-ethoxy)-ethyl)-amine, N-bis-((1,2-dicarboxy-ethoxy)-ethyl)-aspartic acid and N-tris-((1,2-dicarboxy-ethoxy)-ethyl)-amine, as well as the alkali metal and earth-alkali metal salts thereof, and the peracid and chelating treatments are carried out simultaneously by combining the peracid and the said chelating chemical in the same solution phase. In the bleaching sequence the treatment according to the invention may follow, for example, an ozone delignification and precede an alkaline peroxide step, and in the latter case a magnesium compound, such as MgSO,, may be added to the pulp before the alkali step.

Growing community of inventors

Vaasa, Finland

Jukka Jäkärä

Growing community of inventors

Vaasa, Finland

Jukka J&auml;k&auml;r&auml;

Jukka Jäkärä