Abstract
Calcium hydroxide was used to remove ferric ions from waste iron (III) oxalato complexes in solution which were generated from the chemical leaching of clay minerals with oxalic acid, other industrial processes. In this study, the iron (III) oxalato complex solution which was prepared with iron (III) chloride and oxalic acid, was studied on various factors such as temperature, oxalic acid concentration, initial pH and amount of calcium hydroxide. The pH of the solution depended on the concentration of calcium hydroxide. More than 0.054mol/l of calcium hydroxide was needed for the treatment of 0.010mol/l of Fe dissolved in 0.100mol/l of oxalic acid at 25°C. Fe(OH)3 was formed from the iron (III) oxalato complex by Ca(OH)2, and this reaction was completed within 15 minutes. The concentration of calcium hydroxide added was dependant upon the initial pH and Fe concentration in the oxalic acid solution. When the precipitated sludge was reused repeatedly two or more times, the efficiency decreased sharply due to the inert nature of CaC2O4・H2O and a small amount of Ca(OH)2. The reaction temperature did not play an important role on the removal of iron from the ferric oxalato complex solution, but the temperature was effective in removing Fe (III) and Al (III) from the clay leaching solution by adjusting the pH to alkaline range using calcium hydroxide.
