Options for Metals Removal to Improve Peroxide Bleaching, 1995 Pulping Conference Proceedings

Hasan Jameel, Huaiyu Zhan, Hou-min Chang

North Carolina State University

P.M. Hoekstra

Buckman Laboratories

Bijan Amini

E. I. Dupont de Nemours

It is well known that transition metals such as manganese, iron and copper catalyze the decomposition of hydrogen peroxide under alkaline conditions. It has also been demonstrated that the decomposition of hydrogen peroxide is accompanied by the formation of hydroxyl and superoxide anion radicals, resulting in low pulp viscosity and poor pulp strength properties. As a result, it will be very important to measure and control the metal ion profile in pulps to optimize the performance of all oxygen based bleaching chemicals. Methods for controlling the metal profile have included pretreatments with an acid (A) or a chelant (Q). Another method that has been proposed includes an acid pretreatment followed by a peroxide stage with DTMPA, A(PDTMPA ). In this paper another technique for controlling metals has been developed. It consists of combining an acid and chelation stage without interstage washing (AQ). Higher brightnesses were measured as compared to a Q stage. The pH in the A stage needs to be about 2 for 5 minutes followed by a Q stage at pH 5 - 6. All the three options (A(PDTMPA ) QP and (AQ)P) improve the performance of an pressurized peroxide stage. A brightness of 81+% ISO can be achieved using the (AQ)P sequence with 4% hydrogen peroxide. This is higher than that achieved with either a QP or an A(PDTMPA ) sequence. The option that will be chosen will depend on the brightness, the pulp strength desired, the economics, the limitations of the particular application with respect to equipment and capital, and the metal content of the starting pulp...