DEFLUORIDATION OF DRINKING-WATER WITH POTTERY - EFFECT OF FIRING TEMPERATURE

Excessive fluoride (F) in drinking water should be removed, but simple , inexpensive methods of fluoride removal are not readily available. T his study examines the F--binding capacity of clay and clayware, espec ially the effect of the firing temperature on the F--binding process. A series of pots were made from ordinary potter's clay and fired at 50 0-1000 degrees C. Likewise, small clay bricks were fired and then crus hed and sieved. NaF solutions containing 10 mg/l F- (10 ppm F-) were p repared. Suitable aliquots of the solutions were poured into clay pots or exposed to powdered clayware. Samples were taken at storage period s of 30 min to 20 days and analyzed for F- by ion-selective electrodes . The rate and capacity of F--binding in the clayware varied with the firing temperature. Clay fired at approximately 600 degrees C was most effective. Temperatures over 700 degrees C caused a decline in F--bin ding, and pottery fired at 900 degrees C and above seemed unable to re move F- from water. Pots fired at 500 degrees C or less cracked in wat er. The findings indicate that clayware, fired at an optimal temperatu re, may be of practical value for partial defluoridation of drinking w ater.