Preconcentration Method of Fluoride Ion in Natural and Environmental Waters by Activated Carbon Loaded with Zirconium for the Purpose of Simple Field Analysis

Abstract

The authors have just started a study to develop simple analytical methods of natural and environmental waters which can be widely used without any expensive instruments. As a part of the study, a preconcentration method for fluoride ion in aqueous solution has been investigated.
An effec tive and simple method for preconcentration of fluoride ion in aqueous solution has been developed by use of activated carbon loaded with zirconium (Zr-C*). The Zr-C* was prepared by mixing 100 ml of zirconium(W) nitrate oxide solution (1 g Zr, pH 1.6)with 10 g of activated carbon at room temperature for three days, filtering and drying the residue in air. Ten grams of the resulting activated carbon included O.5 to 0.6 g of zirconium.
The established method for concentration of fluoride ion in aqueous solution is as follo ws: Af ter adjusting the pH of sample solution (O.1 to 10l) to 3.7±0.3, the solution is passed through the Zr-C* bed (0.5 g) with the aid of a device as shown in Fig.1. The fluoride adsorbed on the Zr-C* is eluted with 40 ml of 0.02 moldm^-3 sodium hydroxide solution, then the recovered fluoride ion was determined photometrically with lanthanum alizarin complexon.
As seen in Fig.2, Zr-C* adsorbs fluoride ion quantitatively at the pH 4.5 or below and scarcely at the pH above 9.0, and the desorption of fluoride ion from Zr -C* occurs quantitati vely at the pH 9.0 or above. Thus, the adsorption and desorption only depend on the pH of the solution. Because the adsorption and desorption of -fluoride ion are accomplished instantaneously, zirconium seems to be loaded only on the surface of activated carbon. These characteristics of Zr-C* are favorable for rapid concentration of fluoride ion in a large volume of sample solution (10 1/2 h). Large amounts of phosphate and sulfate which react with zirconium give a low recovery of fluoride. In the presence of metal ions which form the complex with fluoride ion such as aluminum and iron ions, addition of acetylacetone is recommended as a demasking agent.