Title page for ETD etd-10022001-110024

Type of Document Master's Thesis
Author Parks, Jeffrey Lynn
Author's Email Address jparks@vt.edu
URN etd-10022001-110024
Title Effect of Calcium on Arsenic Release From Ferric and Alum Sludges and Lagoons
Degree Master of Science
Department Environmental Engineering
Advisory Committee
Advisor Name Title
Edwards, Marc A. Committee Co-Chair
Novak, John T. Committee Co-Chair
  • Calcium
  • Arsenic
  • Leachability
  • Ferric
  • Sludge
  • Alum
  • Drinking Water
Date of Defense 2001-09-18
Availability unrestricted
The dewatering of arsenic-containing residuals is a process that has received little study in the past. Arsenic that has been removed from water by sorption to ferric or aluminum hydroxides can accumulate in residuals to concentrations many times higher than in the source water. The first part of this study evaluates the effectiveness of lime conditioning as a method for immobilizing this arsenic. As the pH is increased with addition of caustic soda or soda ash, soluble arsenic concentration increases dramatically. However, as the pH is increased with lime, very little arsenic is released back into the water. On the basis of previous research this phenomenon might be attributed to the formation of a calcium arsenate solid. However, this study indicates it is more likely that the soluble calcium neutralizes the negative surface charge on the hydroxide solids at high pH and enhances arsenic sorption compared to when calcium was absent.

In many cases arsenic-containing residuals are stored in lagoons and allowed to reside there for months or even years. Many parameters may affect the soluble arsenic concentration and speciation in these lagoons. The second portion of this study gives some baseline conditions for these lagoons, both with and without microbial activity and biological organic matter. In these practical situations it appears that lime can assist in keeping arsenic sorbed to the solids and prevent its release to the environment.

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