|dc.description.abstract||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⁻¹ for the formation of BaSO₄ and 0.021s⁻¹ 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.||