Study of the Performance of Nitrilotriacetic Acid and Ethylenediiminopropanedioic Acid as Alternative Biodegradable Chelating Agents for Pulp Bleaching

Document Type : Original Research Paper

Authors

1 REQUIMTE, Departamento de Química da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto. Portugal

2 REQUIMTE, Departamento de Química, Faculdade de Ciência e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal

3 ITQB, Universidade Nova Lisboa, P-2780157 Oeiras, Portugal

Abstract

The aim of this work was to study the ability of two biodegradable chelating agents, nitrilotriacetic
acid (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 in
order to evaluate the best pH conditions for metal chelating removal: pH range 6.5-7.0 for NTA and EDDM
and pH range 5-5.5 for EDTA. After implementation of the bleaching Q-P1-Paa-P2 sequence, NTA and
EDDM removed transition metals (Cu, Fe and Mn) from the pulp more selectively than EDTA. The treatment
with either NTA or EDDM resulted in a final bleached pulp with residual lignin contents similar to the one
obtained with EDTA. A higher peroxide consumption was recorded when EDDM was used, while equivalent
peroxide consumptions were registered when NTA or EDTA were applied.

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