2010 Volume 1 Issue 2 Pages 2_33-2_39
Calcium hydrogen phosphate dihydrate (DCPD) reacts with fluoride ion in aqueous solution and forms stable fluorapatite (FAp). This reaction has been investigated on prevention of dental caries. We have applied this reaction to immobilize fluoride in the environment. In this paper, we investigated applications reaction of DCPD to treatment of fluoride in waste water and waste gypsum board. We appeared that addition of calcium ion is effective to inhibit remaining phosphate ion in effluent and improvement of removal efficiency of fluoride in the wastewater. In order to confirm these phenomena, experiments using real wastewater under coexistence of calcium ion were carried out not only by measuring the fluoride concentration in the effluent, but also by characterizing the properties of the formed sludge. As a result, the DCPD method is suggested to be a very promising method for treatment of wastewater containing fluoride from the viewpoint of ecotechnology. On the other hand, immobilize fluoride in waste gypsum board were also examined. Mixing DCPD is very effective to immobilize fluoride in recycled soil made from construction sludge and recycled waste gypsum for long term.