Fluoride leached through the disposal of untreated effluent in wastewater can contaminate ground water sources for human consumption. Hence it is essential that we use appropriate methods for the determination of fluoride so that the fluoride threat is minimized. In this article, I talk about the Spands method which helps achieve this.
The Spands method utilizes the reaction of the zirconium-dye lake with that of the F in wastewater as the basic reaction for the determination of fluoride in wastewater. During the reaction, the dye lake solution is broken down into two components, the dye and the anion ZrF^62, which is a complex anion in a colorless solution.
This disassociation of the dye and the anion is caused by the concentration of fluoride in wastewater. Since the strength of f in the solution plays an important part here, the stronger the concentration of fluoride, the lighter the color of the solution will be. The solution thus obtained from the reaction is further used for testing. These tests are identified by different names.
If this type of method is used for the determination of fluoride then one should remember that the level of acidity of the wastewater sample being tested, also plays a part in the outcome of the chemical reaction, i.e. the change in the color of the solution. This acidity level also controls the reaction of the zirconium ion with that of fluoride. And this level of acidity of the sample also determines the strength of the color of the solution.