Chemical equilibrium of nonprocess elements in the kraft recovery cycle Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fq977x75n

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  • Non-process elements are present in all kraft recovery systems. Non-process elements are defined as those elements which are not essential to the chemical process, i.e., are neither active pulping chemicals (e.g., NaOH and Na₂S in the kraft process), nor compounds present as a result of incomplete conversion of makeup chemicals to active pulping chemicals. Problems associated with the build up of these elements include scaling, fouling and corrosion of heat exchangers, and various operating problems in the preparation of pulping liquors. A better understanding of the solubility of these elements in solutions similar to recovery cycles would facilitate the elimination of these problems. The solubility of aluminosilicates was measured in aqueous solutions of high ionic strengths and hydroxide ion concentrations. Temperature, ionic strength, hydroxide ion concentration and Al/Si ratio were varied to determine their effect on the solubility of aluminum and silicon. Several cations (Ca,Mg,Mn,V,Fe,K) were also studied to determine their effect on the solubility of aluminum and silicon. The results show that the solubility of aluminum and silicon increases with increasing hydroxide ion concentration and temperature, and decreases with increasing ionic strength. The solubility of aluminum and silicon was found to be a complicated function of Al/Si ratio at varying hydroxide ion concentrations and ionic strengths. Magnesium salts were found to decrease the solubility of aluminum when no silicon was present, but increase it when silicon was present. The other salts had no effect on the solubility of aluminosilicates, although calcium aluminosilicates were formed under some conditions. A thermodynamic model was developed using parameters that were obtained from the experimental solubility data. The model gives a reasonable fit to the data at 0.1 and 1N hydroxide ion concentration and can be used to estimate the solubility of aluminum and silicon in aqueous solutions where data are not available. Limitations to the model are discussed.
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