Influence of organic additives on calcium carbonate precipitation during kraft pulping.Application: This study identifies antiscalant chemicals that are effective for controlling calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral. scale problems in kraft process liquors. In this study, calcium was monitored during laboratory batch cooks to evaluate the influence of various organic additives on the precipitation of calcium carbonate during kraft pulping. Included in the study were antiscalant chemicals thought to be capable of with standing 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 nu·cle·a·tion n. 1. The beginning of chemical or physical changes at discrete points in a system, such as the formation of crystals in a liquid. 2. The formation of cell nuclei. and growth kinetics. EDTA EDTA: see chelating agents. used in molar excess of the released calcium prevented precipitation of CaC[O.sub.3] during a kraft cook. For the carboxylic acid carboxylic acid: see carboxyl group. carboxylic acid Any organic compound with the general chemical formula −COOH in which a carbon (C) atom is bonded to an oxygen (O) atom by a double bond to make a carbonyl group (−C=O; see 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 those required for sequestering Particle Physics In particle physics, sequestering is a procedure of isolating different types of physical processes or different particle species by separating them geometrically in additional dimensions of space. 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 stoi·chi·om·e·try n. 1. Calculation of the quantities of reactants and products in a chemical reaction. 2. The quantitative relationship between reactants and products in a chemical reaction. 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. Guo is a graduate student and Severtson is an assistant professor with the Department of Wood and Paper Science, University of Minnesota (body, education) University of Minnesota - The home of Gopher. http://umn.edu/. Address: Minneapolis, Minnesota, USA. , Kaufert Laboratory, 2004 Folwell Avenue, St. Paul, MN 55108, USA; email Severtson at sever018@tc.umn.edu. |
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