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Pre-treatment of the paper pulp in the bleaching process using biodegradable chelating agents
Pinto, I. S. S.; Ascenso, O. S.; Barros, M. T. & Soares, H. M. V. M.
Abstract
The aim of this work was to study the application
of two biodegradable chelating agents, pyridine-2,6-
dicarboxylic acid (PDA) and methylglycinediacetic acid
(MGDA), in the treatment of the pulp, prior to hydrogen
peroxide bleaching. Such compounds must remove transition
metals (Mn, Fe and Cu) from pulp, that catalyze the
degradation of hydrogen peroxide, and Ca, which is also
problematic due to the formation of precipitates that
accumulate in the equipment. Computer simulations were
first performed to study the best conditions for metal
complexation, and optimum pH was defined as 5–5.5 for
PDA and 6.5–7 for MGDA. Metals removal from the pulp,
as well as the subsequent bleaching process (Q-P1-Paa-P2),
were tested experimentally, and performances were compared
to ethylenediaminetetracetic acid (EDTA). PDA
removed both Mn and Ca efficiently, leaving most Mg in
the pulp after first chelation stage, while MGDA had a
lower Ca removal, even using a higher pH and concentration.
Residual hydrogen peroxide and kappa number
after peroxide stages showed a similar bleaching efficiency
between the studied compounds and EDTA.
Keywords
Bleaching; Chelating agents; Methylglycinediacetic acid; Paper pulp; Pyridine-2,6- dicarboxylic acid (dipicolinic acid)
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