Institute of Paper Science and Technology
نویسنده
چکیده
The following study deals with the characteristics of the reaction to form BaSO4 and BaCO3 from Na2SO4 and Na2CO3, respectively, using BaS as the other reactant. These reactions would theoretically increase the efficiency of the chemical recovery process in papermaking to near 100% by completely converting Na2SO4 to Na2S and Na2CO3 to NaOH. Kinetic data were collected, and it was determined that both reactions were overall first order with rate constants of 0.037s for the formation of BaSO4 and 0.021s for the formation of BaCO3. Also, it was found that both reactions go to completion in under three minutes. The heats of reaction were studied and found to be negligible. BaSO4 particle sizes averaged approximately 4.5μm and remained steady with respect to time while BaCO3 particle sizes were approximately 21μm initially, but decreased over the course of several days. BaCO3 formed agglomerates which began to break down immediately, but BaSO4 did not form agglomerates at all. No explanation for why BaCO3 formed agglomerates and BaSO4 did not could be determined experimentally or found in the literature. Attempts to increase the particle size of BaSO4 included seeding the initial solution with BaSO4 crystals and increasing the concentration of reactants from 0.100M solutions each to 0.292M for BaS and 1.31M for the sodium salts. Both seeding and increased reactant concentration had no effect on particle size. The settling rates of BaSO4 and BaCO3 particles were also studied. BaSO4 exhibited mainly discrete and some flocculant settling characteristics, and the suspension as a whole settled quickly with some smaller particles remaining in suspension for a lengthy period of time. Hindered and mainly compression settling occurred with BaCO3 because of the agglomerates that formed due to strong particle-particle interactions. BaCO3 settled slowly, but virtually no particles remained in suspension after the bulk of the particles settled.
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