Effects of pH, Temperature, and Water Quality on Chloride Removal with Ultra-High Lime with Aluminum Process

Ultra high-lime with aluminum process (UHLA) is an innovative technology for treating recycled cooling water that has the ability to remove sulfate and chloride in addition to other scale forming materials. Laboratory experiments have demonstrated that the UHLA process can achieve high chloride removal from recycled cooling water and an equilibrium model was developed to describe chemical behavior during chloride removal. This paper describes the influence of pH, temperature, and initial chloride concentration on chloride removal by UHLA and identifies the precipitated solids formed during treatment. Optimum pH for maximum chloride removal efficiency was found to be 12 ± 0.2. Chloride removal efficiency at water temperatures above 40 °C was substantially lower than that at lower temperatures. Chloride removal efficiency was higher at high initial chloride concentration than at low initial chloride concentration with the chemical doses employed. Solids formed during UHLA treatment were identified by XRD as calcium chloroaluminate, tricalcium hydroxyaluminate, and tetracalcium hydroxyaluminate. This supports the assumption of the equilibrium model that these compounds are present and form a solid solution. In addition to these, calcium hydroxide or aluminum hydroxide can form when calcium or aluminum dose is above the stoichiometric ratio.