KINETICS OF ION REMOVAL FROM AN IRON-RICH INDUSTRIAL COPRODUCT .1. CHLORIDE

An industrial TiO2 extraction process results in a Fe-rich material (I RM) that contains substantial chlorides. Recent investigations showed that washed IRM may serve as a soil amendment for agricultural use. Ye t, washing processes at the industrial production facility are current ly problematic and costly, and it is essential to devise effective pro cedures for CI removal. This study was conducted to determine the mech anism of CI retention, and to ascertain whether the rate of Cl removal was governed by time-dependent surface-chemical kinetics or diffusion (transport)-controlled kinetics. The IRM samples we used throughout t he study were homogenous. It was physicochemically characterized and c oncentrations of heavy metals were determined. The IRM batch studies r evealed negative CI adsorption, even though its point of zero charge w as 8.3. Column studies showed that 92% of the CI was removed with the first pore volume. Additionally, the salt removal decreased the electr olyte concentration, caused dispersion, and, ultimately, lowered the h ydraulic conductivity. Stirred-how kinetic studies established that Cl leaching was a function only of the total volume that flowed through the chamber, and that no chemical kinetics were involved.