Fluoride remediation with calcide as a function CO₂partial pressure

At Hydro Aluminium located in the Hunter Valley, NSW, Australia, spent potliner (SPL) waste has contaminated the local ground water aquifer with concentrations of fluoride up to 2,000 mg/L. The ability of calcite (CaC0₃) to remove this fluoride was studied in a batch reactor as a function of C0₂partial pressure and fraction size. Results show that fluoride removal at equilibrium is independent of fraction size, but the rate at which equilibrium is achieved is faster for smaller sized fractions (larger surface area). The optimum partial pressure of C0₂was between 7% and 15% with ~95% & 98% F removal achieved respectively in experiments using pure fluoride solutions. Results using actual SPL contaminated groundwater indicate removal by calcite is dependent on at leasttwo different chemical pathways (mechanisms) that can adversely affect defluoridation and that geochemical models require rigorously defined kinetic data before they can be used to accurately predict results in this system .