Table 2
EDX analysis of decomposed products used throughout this study obtained by
converting elemental EDX analysis to oxides (wt.%)
Decomposed product Na2O MgO Al2O3 SiO2 CaO ZrO2
Unwashed product 38.6 – 0.6 20.5 – 40.1
Washed with water 7.1 0.8 0.9 8.9 1.2 81.0
Washed with 0.5 wt.%
H2SO4
6.5 0.7 0.3 13.2 0.8 78.5
Washed with 1 wt.% H2SO4 3.0 0.3 – 9.1 – 87.7
Washed with 5 wt.% H2SO4 1.0 – – 15.8 – 78.3
and small amount of decomposed products re-crystallised to
form synthetic zircon at 900 ◦C. As a consequence of this,
decomposition temperature for zircon into intermediate products
was selected to be 850 ◦C.
The chemical analyses of decomposed products determined
by using EDX are given in Table 2. As shown in this table,
decomposed intermediate product contains large amount of
Na2O (about 38.6 wt.%), which is in the form of Na2ZrSiO5,
Na2ZrO3 or Na2SiO3 as determined from XRD analysis. To
reduce Na2O based phases, decomposed product was washed
with water or H2SO4 solution. XRD patterns of decomposed
product showed that mainly Na2ZrSiO5 remain after washing
process, while the water-soluble (Na2ZrO3) and (Na2SiO3)
phases were removed (Fig. 2). Removed phases were confirmed
by XRD analysis of the dried powders obtained from washing
solutions. It was found that a 1 wt.% H2SO4 solution was most
effective in the removal of Na2O from the decomposed products.
Na2O can be fully eliminated from decomposed products
at higher acid concentration (5 wt.%H2SO4) but amount of ZrO2