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

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.