NEWDEF ®Hydroxyapatite – Fluoride removal
Hydroxylapatite, also called hydroxyapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. Hydroxylapatite is the hydroxylendmember of the complex apatite group. The OH− ion can be replaced by fluoride, chloride or carbonate, producing fluorapatite or chlorapatite. It crystallizes in the hexagonalcrystal system. Pure hydroxylapatite powder is white. Naturally occurring apatites can, however, also have brown, yellow, or green colourations, comparable to the discolourations of dental fluorosis.
It is one of the most effective adsorbents of fluoride with much faster reaction times than Activated Alumina.
1. Defluoridation Capacity
The defluoridation capacity of hydroxapatite is about 2~4 mg/g which is superior compared to most medias under the same conditions. The capacity is impacted by different raw water quality including fluoride concentration、 temperature、co-existing ions etc..
Hydroxyapatite Features and Benefits
- High capacity and shorter contact time
- Very safe to use; no dissolution of toxic and hazardous substances
- High efficiency, hydroxyapatite can remove up to 99% fluoride in raw water.
- Limited competing interference by other ions
- Lower regeneration cost and simple regeneration process
- Not only restricted to Fluoride ,but can remove iron and manganese as well
Fig below demonstrates that the NEWDEF® media( Hydroxapatite) outperforms other common defluoridation materials under the same conditions. The treated water volume before fluoride breakthrough of NEWDEF® is About 5.09—11.7 times of activated alumina and 12.9—23 times of activated clinoptilolite.
Figure 1．The volume of water treated by different medias under the same conditions, the initial concentration of fluoride is 6mg/L in raw water
Figure 2. The volume of water treated by different media under the same conditions, the concentration of fluoride is 2mg/L in raw water
Sodium hydroxide regeneration: It’s the reverse reaction of the defluoridation mechanism. OH– replaces F– on the particle surface. Regeneration is carried out using 0.5 to 1 % caustic solution which is recirculated for 6-12 hours.