Gypsum scale formation and control during continuous sulphuric acid neutralization.
Published: 2004
Language: eng
Number of pages: 143
Description: A fundamental study on gypsum scale formation and control during neutralization was performed. Through the use of the OLI simulation software and a solubility study, it was shown that it is possible to accurately model gypsum solubility (and hence, predict scaling potential) in Ni, Mg, and even Zn containing solutions over a wide range of temperatures (25&deg;C--90&deg;C) and solution concentrations (0--6 m).The model also was extended to model several different neutralization configurations. The optimum configuration determined using the model was a two stage neutralization with all the base added in the first stage. Seeding was effective up to a 100% seed recycle. A non-base-added final polishing stage (reactor) added at the end of any neutralization configuration was modelled to be the most effective for ensuring that the outlet stream had a minimum supersaturation.The OLI software package was used to predict calcium sulphate conductivity over a range of concentrations, temperatures, and slurry densities through the use of the modified mean spherical approximation equations. Ion size parameters for the calcium and sulphate ion pair were determined by regressing experimental conductivity measurements, in order to predict conductivities in undersaturated, saturated, and supersaturated calcium sulphate solutions. The effect of solids on conductivity was modelled using Maxwell's equation.The conductivity model was used to convert conductivity measured  in situ during pure sulphuric acid neutralization into supersaturation. This enabled the elucidation of the mechanism of gypsum scale growth and demonstrated the relationship between reactor conditions and scale growth. A gypsum growth equation of the form GCaSO4= = k(S-1)2.5 relating growth to supersaturation was found to best fit experimental data. The activation energy for growth was found to be 86 kJ/mol. The effect of seeding (adding extra solid gypsum seed to the neutralization reactor) also was proven with the new conductivity technique.The kinetics in the continuous neutralization reactor, determined using the conductivity technique, were used to build a population balance model for gypsum crystallization during neutralization. This model is able to explain many of the trends in gypsum scale growth.
Notes: Adviser:  Vladimiros G. Papangelakis.

Thesis (Ph.D.)--University of Toronto, 2004.

Electronic version licensed for access by U. of T. users.

Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 5262.