22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Plasma chemical titan dressing of silica-leucoxene concentrate via plasma-arc
treatment
D.E. Kirpichev, A.A. Nikolaev, A.V. Nikolaev and A.V. Samokhin
Russian Academy of Sciences, A.A.Baikov Institute of Metallurgy Science,, Russia
Abstract: Results of the thermo dynamical calculation and experiment of silica extraction from
silica-leucoxene concentrate with titan dressing of concentrate via plasma-arc treatment with
carbon are cited.
Keywords: silicon oxide, titanium oxide, carbothermal reducing, plasma-arc treatment
1.Introduction
Russian considerable titan resources concentrate in
heavy oil mined at the Yarega deposit. Silica-leucoxene
concentrate after hydrocarbon distillation and flotation
dressing has fine interpenetrating silica and titanium
dioxide structure.
Silica and titanium dioxide
concentrations alter on different regions of deposit in
wide range (TiO 2 50-70%, SiO 2 20-40%). Alternating
concentration and fine interpenetrating structure do not
allow to apply classical hydrometallurgical technologies
for silica extracting and titan production executing from
source of the deposit. Silica and titanium dioxide physicchemical properties are close and their combined in
concentrate heat treatment has not titan dressing result.
Silica reduced with carbon to volatile SiO and removal it
with exhaust gas is possible with plasma-arc treatment.
Titanium oxide stays in melt. This allows to simplify
technological scheme and to refuse to dangerous reagents
of hydrometallurgy use. The work had an aim to
determine plasma-arc titan dressing of silica-leucoxene
concentrate parameters based on the thermodynamical
calculation and experimental data.
Ti
Si
Si
where m Ti
m , m m mass Ti, Si in the melt, m c , m c
mass Ti, Si in the initial concentrate.
Total silicon component transfer to gas phase and
absence titanium component less via vaporization
correspond to value of separation degree equal 100%.
Initial increase of separation degree value with
temperature increase is explained by the decrease of
silicon content in the melt due to vaporization of SiO, the
second item decreases in (1). Decrease to zero in the high
temperature range explained by the titanium vaporization,
the first item decreases (1)).
2.Thermodynamical calculation of the energy and
material process parameters
The aim of the calculation is to determine temperature,
carbon concentration in the charge and energy
consumption, by which titan dressing is fullest.
The calculation was made via thermodynamical
equilibrium program TERRA at atmospheric pressure,
alter temperature in the range 2000-4000 K and carbon
concentration in the charge in the range 0-17 mass%. The
calculation is based on the second thermodynamical
principle, in which the system reaches the equilibrium
when entropy is maximum. Calculated model of oxide
system agrees with main components silica-leucoxene
concentrate chemical composition: TiO 2 – 50 %, SiO 2 –
45 %, Al 2 O 3 – 3%, Fe 2 O 3 – 2%.
The separation degree was calculated:
SR =
P-II-12-9
mTi
m
mTi
c
−
mSi
m
mSi
c
,
(1)
Fig. 1. Calculated dependences of silicon and titanium
separation degree SR (%) from temperature T (K) with
different carbon concentration in the charge %С
1
The complete separation of silica-leucoxene concentrate
to silicon and titanium components is possible when
carbon concentration in the charge %С = 13% and
temperature Т = 2200 К (Fig .1). Titanium in the melt is
in quantity 74% as lower oxides TiO and Ti 2 O 3 .
Calculated necessary energy consumption to concentrate
separation is 9,2 GJ/t in this case.
Titanium concentration in the melt can be increased by
increase carbon concentration in the charge, to the point
of complete titanium reducing. But in this case titan
losses due to vaporization (Fig. 2).
plasma-arc 100kW DC furnace with copper water cooled
crucible 1 (Fig. 3).
The produced materials were analysed by the following
methods: X-ray diffraction (XRD) analysis was done
using difractometer RIGAKU Ultima – 4 with
monochromatic CuK radiation and high-speed detector
D/teX, PDXL software and PDF-2 database; Specific
Surface Area (SSA) measurements were done using
Micromeritics TriStar 3000 porosity analyser; particle
morphology was studied using Helios 650 NanoLab
(SEM + EDX) with Apollo X SDD analyzer.
Fig. 3. Experimental setup.
Fig. 2. Calculated temperature T,K dependences of
titanium concentration in the melt C m Ti and titanium mass
in the melt related to its mass in the charge m m Ti/m c Ti at
different carbon concentrations.
3.Methodology and experiment results.
Experimental investigations was realized on the labor
2
The crucible is in the steel water cooled hermetic
150 dm3 chamber 2 and connects to power supply positive
pole. Graphite electrode 3 is over in alignment in
crucible. It is fixed in copper water cooled holder 4.
Electrode can be axial moved without chamber seal
failure. Arc 5 is excited due to move electrode down to
contact with crucible or electroconductive material 7.8 in
the crucible. Spatial stabilization is realized by axial
magnetic field, which is made with electromagnetic coil 6
on the crucible lateral outside.
Initial concentrate represents bulk material with particle
size ≈1mm and consists of 53.3 % TiO 2 , 40.2 % SiO 2 and
admixtures – mainly Fe 2 O 3 and Al 2 O 3 . The concentrate
7 in quantity of 293 g was loaded into lower crucible part.
Graphite disc 8 with mass of 38.6 g was laid over the
concentrate, this imitated carbon concentration in charge
%С = 12%. There was 15 mm hole in the disc center and
few 8-10 mm holes in the disc periphery. The disc was
carbon source for silicon reduce and prevent concentrate
ejection on the initial melting stage. The disc holes were
made for gaseous reduce products escape and contact
plasma arc with oxide melt.
The melting was realized in two stages in order to
decrease of raw material eject from crucible at arc gaskinetic pressure. First stage included heating and surface
melting of material with current 200 A and voltage 25 V
during 8 minutes. Thereafter arc current was increased to
400 A with voltage 60 V and began second stage wich
included complete material melting and its interaction
with carbon. Arc length was near 1 sm. On the first stage
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the arc had an constricted anode tie, which shifted by the
edge of graphite disc central hole under the influence of
magnetic field. On the second stage constricted tie was
supplemented with diffuse tie on the material surface in
the hole limits.
As experimental result there was solidified oxide as
black ingot with mass 206.8 g in the crucible. The ingot
includes scar with thickness near 2 mm and mass 40.5 g
and graphite disc refuse with hard separable slag
inclusions. Total disc mass was 55.0 g, included not less
then 20 g of slag. Inside chamber was coated of gray
powder deposit. Mass of the collected powder was
29.0 g.
X-ray analyze shown that titanium was in the oxide
ingot as Ti 3 O 5 ; silicon wasn`t found out (Fig. 4).
Titanium was not found out in powder from chamber
walls, but silicon as SiO 2 and Si was found out. Tailing
and higher background are evidence about particles small
size up to amorphous state.
SiO2
SiO2
Si
powder from
chamber walls
3,6
SiO2?
2,4
Ti3O5
Ti3O5
Ti3O5
material from crucible
1,2
SiO2
initial concentrate
Fig. 5. Re-condensed powder from the chamber walls
(72.7 m2/g).
TiO2
SiO2
0
10
15
20
25
30
35
40
45
2θ
50
Fig. 4. Results of X-ray material analysis of crucible and
powder from the chamber walls.
Powder from chamber walls was re-condensation
product. This was confirmed by a great heat quantity
which passed to cooling chamber water and a thin fiber
structure (Fig. 5), characterized for condensed from gas
phase powder.
Titanium oxides began to condense from higher
temperatures, then silicon oxides, while cooling it became
crystallization centers for silicon oxide. Chamber walls
powder specific surface was 72.7 m2/g.
Output materials chemical element analyze shown that
silicon and titanium are presented in oxide ingot from
crucible in qualities 15.0% and 37.4%. In the powder
from chamber walls silicon and titanium are contained in
qualities 30.0% and 12.5% correspondingly.
Evidently there was overheating in the arc anode tie. As
result not only silicon oxide vaporized, but also titanium
oxides. At the same time melt temperature was near
T = 2000 K and titanium stayed in the melt as TiO 2
(C m Ti =30%). The separation degree was calculated (1)
on the base of the chamber walls powder analyze. It
equals 11.2%.
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4.Conclusion
On the base thermodynamical calculation was shown
that complete separation of silica-leucoxene concentrate
to silicon and titanium components is possible when
carbon concentration in the charge %С = 13% and
temperature Т = 2200 К. Calculated necessary energy
consumption to concentrate separation is 9,2 GJ/t in this
case. Under kinetic restrictions received experimental
data differs to calculation results. Persistent row material
feed to the arc anode tie during the process allows to clear
of kinetic restrictions and overheating in the anode tie.
3