THERMAL DEHYDRATION MECHANISM OF ULEXITE FROM XIAO CHAIDAN SALT LAKE

Thermal dehydration process of ulexite,NaCa[B_(5)O_(6)(OH)_(6)] 5H_(2)O,was investigated by the isothermal-isobaric method,thermal analysis(DTA),X-ray and IR-spectral methods at 50-500 ℃.It was found that there mainly existed three solid phases during dehydration of ulexite: 1) NaCa[B_(5)O_(6)(OH)_(6)]·3H_(2)O was formed as a result of losing the first two water molecules coordinated with Na;2) release of another two water molecules coordinated with Ca,leading to the formation of NaCa[B_(5)O_(6)(OH)_(6)]·H_(2)O;and 3) loss of a last water molecule coordinated with Na and release of water coming from OH groups,causing the formation of amorphous phase.