Removal of calcium sulfate deposits from waste acid treatment facilities

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Virginia Polytechnic Institute

The object of this research was to investigate and evaluate three methods for determination of sulfate and to use the obtained information as a guide in selecting an accurate analytical method with which to conduct a complete analysis of calcium sulfate deposits.

The investigation of the analytical methods revealed that the gravimetric method is most accurate for high sulfate concentrations. This method was selected for all analytical work conducted in the study of the deposited material and in the development of a sodium hydroxide-alcohol-water solution for the removal of the calcium sulfate deposits.

The initial phases of the development of the sodium hydroxide-alcohol-water solution were discouraging in that the results were inconsistent and could not be reproduced. It was believed that such inconsistencies resulted, primarily, from the method of mixing the solutions, since all mixing was done by weight percentages. The method of mixing was revised, and all subsequent mixing was governed by titration of the solution in order to determine the sodium hydroxide concentration. The alcohol was added after the solution was adjusted to the desired sodium hydroxide concentration.

The investigation revealed that, following the immersion period, “air drying" the material had an effect upon the behavior of the sample during the second immersion period. It was seen that the disintegration of more resistant materials could be facilitated by employing such a period for drying the material before a second immersion period.

A cost study revealed that application of the proposed method for removal of calcium sulfate deposits from treatment facilities is economically sound and that the cost of application of the method is very small compared to the cost of replacement of facilities.