Influence of organic additives on calcium carbonate precipitation during kraft pulping

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Abstract

In this study we monitored calcium during laboratory batch cooks to evaluate the influence of various organic additives on the precipitation of CaCO3 during kraft pulping. Included in the study were antiscalant chemicals thought to be capable of withstanding the harsh environment of kraft pulping and recovery operations. Results indicate significant differences in the way the tested chemicals inhibit calcium precipitation and their efficacy. For EDTA - an aminocarboxylic acid used to examine the effect of sequestrants - results were consistent with a reduction in dissolved calcium levels to slow nucleation and growth kinetics. EDTA used in molar excess of the released calcium prevented precipitation of CaCO3 during a kraft cook. For the carboxylic acid containing polymers tested, inhibition of calcium precipitation required concentrations similar to that used with sequestrants, in contrast to the high efficiencies demonstrated by these same polymers at lower temperatures. Even at concentrations well above that required for sequestering mechanisms, tested polymers could not completely prevent the precipitation of calcium at temperatures commonly used in kraft pulping reactions. In contrast, many of the organophosphonic acids tested demonstrated a significant inhibitory efficiency. Tests indicate a threshold effect with concentrations well below a stoichiometric match with dissolved calcium providing significant inhibition of calcium precipitation. This study identifies antiscalants that are effective under kraft pulping conditions. Future work will examine how best to apply this technology to control scale problems.

Original languageEnglish (US)
Pages21-27
Number of pages7
Volume1
No10
Specialist publicationTappi journal
StatePublished - Oct 1 2002

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