Pre-treatment of the paper pulp in the bleaching process using biodegradable chelating agents

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.

Improving manganese circular economy from cellulose by chelation with siderophores immobilized to magnetic microbeads

“…Dry cellulose was analyzed for determination of initial total metal concentration. Per kg of dry cellulose, 14.5 ± 0.7 mg Mn was determined via ICP-OES, with an iron content of 6 ± 4 mg Fe per kg of dry cellulose, similar to previously reported values (Kujala et al 2004;Pinto et al 2015). The Mn and Fe content from the dry cellulose and pulp suspension samples was measured via ICP-OES, and results are shown in Tables 2 and 3, respectively.…”

“…Samples were prepared as described by Pinto et al (2015) with minor modifications. To proceed with the Mn removal present in the pulp, 2% (m/v) pulp suspensions were mixed with the aqueous complexing agents [50 mg mL −1 DFOB, 50 mg mL −1 DFOE or 1 mg mL −1 PratA (kindly provided by Prof. Dr. J. Nickelsen, LMU Munich); 0.01 mg mL −1 EDTA used as control] and incubated at 50 °C overnight.…”

“…Mn, Fe and Cu). Mn(II) has a negative impact on the efficiency of bleaching with oxygen-based chemicals due to its decomposing effect through peroxide, worsening overall pulp quality and causing darkening of the pulp (Pinto et al 2015). Removal of Mn adsorbed to the fiber phase is characteristically carried out at pH values between 4.5 and 6.…”

“…At pH > 7, Mn(II) is chelated less effectively, and hence, its removal cannot be performed by dewatering and washing in subsequent steps in the pulp manufacturing. Between 14 and 50 mg Mn per kg of dry pulp can be extracted with almost complete removal of Mn at pH values as low as 5.5 and as high as 9.5 (Elofson and Nordgren 1996;Pinto et al 2015).…”

“…Consequently, other chelating alternatives have been proposed. Hitherto, some substitutes for EDTA in the paper pulp industry studied are novel amino acid derivatives like ethylenediamine-N,N'-disuccinic acid (EDDS), iminodisuccinic acid (IDS), pyridine-2,6-dicarboxylic acid (PDA), methylglycinediacetic acid (MGDA) or siderophores [like desferrioxamine B (DFOB) or desferrioxamine E (DFOE)] (Hyvonen et al 2006;Metsarinne et al 2007;Pinto et al 2015;Wilkesman et al 2019).…”