Abstract:
Mineral sands deposits represent the most promising and profitable future resources for
the country. The crude heavy minerals at Pulmudai-Sri Lanka contain about 60% to 70%
of heavy minerals having composition of 70% to 75% ilmenite (about 52% of titanium
dioxide and 48 % iron oxide), 10% rutile (about 95% titanium dioxide) and 8 to 10%
zircon (65% zirconium dioxide and 35% silica). Titanium dioxide is an important
inorganic chemical material, especially the best-quality white pigment.
The objective of this project was to apply a simple and very effective method to produce
nano particles of titanium dioxide and iron oxide powders from beach mineral sands. Low
cost environmental friendly hydrothermal technique was used to breakdown well
structured mineral of Ilmenite, with a composition of FeTiO3. Breaking down of ilmenite
structure into TiO2 is normally done at 850 C using 70% H2SO4. It is assumed that this can
be done at a relatively low temperature with saturated vapor pressure or high pressure
under hydrothermal conditions since near critical state condition of water which facilitate
to fabricate most of inorganic compounds.
In the acidic media, ilmenite could was mixed with a strong acid such as HCl or H2SO4 in
different ratios of ilmenite to water then the mixture was reacted under hydrothermal
conditions at different temperatures and pressures. Ilmenite was decomposed completely
after several hours. Nano-particles of TiO2 could be obtained by hydrolysis and low
temperature calcinations of the hydrothermally derived product. The effect of pH on the
size and morphology of particles in nano-powders were also investigated.
Our results showed after the hydrothermal treatment of ilmenite, black-colored granules
changed into swelled yellowish-white product. The HCl solution was also colored
yellowish, indicating the Fe-ion leaching from the natural source. This phenomenon
implies the hydrothermal treatment for natural rutile can be used not only as a reaction
step but also as a semi-purification step. The further research on evaluation and
optimization should be conducted in detail; this preliminary results are encouraging
toward the present cost-effective process. The results demonstrated that the process is
inexpensive, environment friendly and promising in preparing high-purity TiO2 from
ilmenite with a high content of gangues.
