Activation and regeneration of a soil sorbent for defluoridation of drinking water

Geomaterials can be cost-effective sorbents for use in water treatment. In this study, a heavily-weathered Tertiary soil from Xinzhou. China was used as a sorbent for defluoridation of high-fluoride drinking water. The soil i s composed of quartz, feldspar, illite and goethite? with an Fe oxide conte nt of 6.75%. Batch and column experiments were done to characterize the F- removal properties and to develop an optimal activation and regeneration pr ocedure. The soil can be regenerated following a simple base-acid rinsing p rocedure. This can be performed in situ, i.e., by passing the rinsing solut ions directly through the treatment column. The same regeneration procedure can be used to activate the pristine soil. Fluoride sorption is described by a Freundlich isotherm model and the bulk of the uptake occurs within 1.5 h. Iron oxide coatings on soil particles and perhaps =FeOH surface groups at particle edges of illite grains are likely responsible for the soils F-s orption property. As collected in the field, the soil has a low permeabilit y and is thus unsuitable for direct use in a flow-through column. Heat-trea tment at 400-500 degreesC for 2 h, however, produces a granular and permeab le sorbent. Although the soil's sorption capacity (150 mug/g) is about a qu arter of the low end range of values reported for commercially-available ac tivated alumina, the sorption for F- is specific. A batch sorption experime nt in the presence of Cl-, SO42- and HCO3- shows little or no competition f rom these other anions. (C) 2001 Published by Elsevier Science Ltd.