Effects of Various Chelating Agents on FAS Bleaching Efficiency, for Brightening of Secondary Fiber in a Flotation Deinking Process, 1999 Recycling Symposium Proceedings

Robert C. Taylor

Degussa Corporation

Carol R. Morrison

Formamidine Sulfinic Acid (FAS) color stripping and bleaching has had a significant impact in upgrading recycled fiber. When used as an active bleach stage, in a tower or disperser, FAS can provide a large degree of brightness gain and color reduction.

As in all bleaching processes economics is of paramount importance.

This paper addresses the use of chelating and sequestering agents in the pulper and with the FAS in the bleach stage. With the information developed in this detailed laboratory investigation, one may utilize FAS more efficiently, thereby providing overall cost savings for the bleach stage.

Evaluation of the effects of aminopolycarboxylates, organophosphonates, and sodium silicate use in the pulper and with FAS is the focus of this paper. Two furnish compositions were used for this study, an eighty-five percent printed mixed office paper (MOP) with fifteen percent unprinted color ledger, and a seventy-three percent MOP with fifteen percent colored ledger and twelve percent groundwood.

Dramatic brightness results of 10 - 12 points of ISO occurred using DTMPA in a split chemical addition between the pulper and FAS stage. Similar results were obtained when a small charge

of sodium silicate (0.25%) introduced in the pulper produced an increase in brightness of two to three points ISO over no silicate usage. Additionally, sodium silicate can be used as the alkali source for the activation of FAS. Considerable cost savings could be realized by such a combined chemical strategy.