Abstract
The aim of this work was to study the ability of two biodegradable chelating agents, nitrilotriaceticacid (NTA) and ethylenediiminopropanedioic acid (EDDM) to complex metals, in the treatment of the pulp,prior to a totally chlorine free (TCF) bleaching process, and compare with the ethylenediaminetetraacetic acid(EDTA) performance. Firstly, speciation efficiency index (SEI) was calculated by computer simulations inorder to evaluate the best pH conditions for metal chelating removal: pH range 6.5-7.0 for NTA and EDDMand pH range 5-5.5 for EDTA. After implementation of the bleaching Q-P1-Paa-P2 sequence, NTA andEDDM removed transition metals (Cu, Fe and Mn) from the pulp more selectively than EDTA. The treatmentwith either NTA or EDDM resulted in a final bleached pulp with residual lignin contents similar to the oneobtained with EDTA. A higher peroxide consumption was recorded when EDDM was used, while equivalentperoxide consumptions were registered when NTA or EDTA were applied.
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