On precipitated calcium and magnesium phosphates during synthetic hard waters softening by monosodium phosphate

Abstract

Phosphates were largely used to soften process or drinking waters. We have investigated the precipitation of Ca²⁺ and Mg²⁺ ions by monosodium phosphate dehydrate. Magnesium phosphate starts precipitating at pH₀ = 8.6. The obtained solids have been identified by chemistry analyses, FTIR spectroscopy, X-ray diffraction, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA). The solid phases obtained vary with pH₀. It shows that DCPD (dicalcium phosphate dehydrate, ) precipitated within pH₀ 5 to 6.6, the TCP (tricalcic phosphate) and other apatite appear below pH₀ = 7. The DCPD (dicalcium phosphate dihydrate, ,) precipitated was a pure product that can be used in nanotechnology and biomedical technology. We are presently testing these solids for natural waters defluoridation.

Keywords:

• Softening
• synthetic hard waters
• settling time
• calcium
• magnesium
• phosphates
• solid phases