Process for increasing pulp brightness with zeolites and easily decomposable organic chelating agents

A process for increasing pulp brightness of a bleached raw material selected from the group consisting of wood pulp, cellulose, used paper and mixtures thereof comprising pretreating said raw material at a consistency of from 1.5% to 25% prior to bleaching with a natural or synthetic zeolite or a layer lattice silicate and simultaneously with an easily decomposable organic chelate forming agent;

• wherein the complex forming constant of said natural or synthetic zeolite or said layer lattice silicate with heavy metal ions is larger than that of lignin in said raw material and the complex building constant of said easily decomposable organic chelate forming agent is lower than that of said zeolite or said layer lattice silicate and wherein said pretreating step results in an improved pulp brightness.