Download A New Energy Efficient Chemical Pathway For Extracting Ti From Ti

Supporting information for
“A New Energy Efficient Chemical Pathway For Extracting Ti From
Ti Minerals”
Zhigang Zak Fang*, Scott Middlemas*+, Jun Guo*, and Peng Fan*
*Metallurgical Engineering, University of Utah, Salt Lake City, UT 84112
+
Now with Army Research Laboratory, Aberdeen, MD 21005, USA
Experimental Method:
Ti-slag was ball milled with chloride salt mixture in a stainless steel jar in a high energy planetary
ball mill for 2 hours, and then mixed with MgH2 for an hour in a laboratory tumbler. The chloride salt
mixture in this particular example was an eutectic of 50 wt% NaCl -50 wt% MgCl2, which was melted,
cooled, and crushed prior to adding into the slag. This composition was chosen after experiments with a
series of other salt mixtures including both monolithic and mixed chloride salts. This particular composition was chosen for its melting point below the reaction temperature. It composed 20 wt% of the initial
reaction mixture. The slag-reductant mixture was charged in a crucible and held in a tube furnace with
flowing hydrogen at 500 °C for 12-48 hrs.
The reduced powder was first leached in NH4Cl (1.0 M) / NaC6H7O7 (0.77 M) solution at 70ºC for 6
hours. This was sufficient to remove most of the MgO with no dissolution of TiH2 or Ti, as determined
by analysis of the leach solution. Leaching times of 30-60 minutes have yielded similar results. Any remaining MgO is removed with HCl in the final leaching stage. The powder after NH4Cl leaching was
thoroughly rinsed with water and ethanol and then leached with NaOH (2 M) solution for 2 hours at
70ºC. After another rinsing, the powder was further leached with HCl (0.6 M) for 4 hours at 70ºC. The
leaching parameters are currently being optimized.
S１
Dissolved metal concentrations were determined using an ICP Agilent 7500ce quadrupole massspectrometer. X-ray diffraction was performed with a Philips 1140 diffractometer.
Analysis of Energy Consumption:
The approximate energy consumption of the proposed direct reduction process of Ti slag with MgH2
(DRTS process) on an industrial scale was calculated and compared with the conventional Kroll process. A schematic diagram of the cradle-to-gate boundary comparison of the DRTS and the Kroll processes is shown in Figure S1. Based on a typical industrial production target of 10,000 metric tons per
year, a model plant was designed that would employ the proposed process. The energy required for each
step (in the form of electrical power or natural gas) in the process was calculated based on the
WC phase
Figure S1. Cradle-to-Gate energy boundary comparison of the DRTS and Kroll processes.
process parameters from initial experimental results. The system boundary for the process calculation
includes the milling and blending of slag with MgH2 and salts, direct reduction, leaching, filtering, dry-
S２
ing and dehydrogenation of TiH2 powder. The energy required to make slag as well as recover and regenerate MgH2 is calculated.
In order to reach the annual production goal, 1.19 tph (ton per hour) of Ti must be produced, which
requires 2.56 tph of slag as feed. In order to prevent overgrinding, the as-received slag is sized using a
20 HP dual-fan air classifier, with only the oversized material being sent to the ball mill. The energy required to mill the slag to the desired particle size can be determined using Bond’s law [S1] which states
that the required specific energy input, E (kWhr/ton), is proportional to the size reduction ratio to be
achieved, according to the following equation:
E= 10* Wi [(1/ P80)0.5 – (1/ F80)0.5]
(S1)
where F80 and P80 are the particle sizes (80% passing) of the feed and product, respectively, and Wi is
the Bond work index, which is a material specific index of “grindability.” Titania slag has a Bond work
index of 17.6 kWhr/ton [S2]. The size distribution of the slag was experimentally determined using a
series of sizing sieves, and the F80 and P80 were determined to be 600 µm and 1 µm, respectively. Grinding slag thus requires 220 kWh/ton, which will require a 11.5’D x 14.5’L ball mill driven by a 753 HP
motor [S3]. The blending of 2.56 tph slag with 1.10 tph salts and 1.46 tph MgH2 requires 50 kWhr/ton
[S4], or a total of 256 kWhr.
The energy required for the reduction reaction was calculated using HSC Chemistry 5.11 software.
The energy required to heat the reactants from 25 ºC to 500 ºC and the energy of the reaction at 500 ºC
was calculated separately, and is shown in Table S1. It is evident that the net reaction is exothermic.
The energy required for dehydrogenation of 1.27 tph of the purified TiH2 in Ar at 400 ºC was also
calculated using HSC, and is shown in Table S2. Once again, a 10% conductive heat loss in the furnace
was assumed. It is evident that the reaction is endothermic and requires a total energy input of 3,943
MJ/ton Ti. It should be noted that the amount of heat released during the exothermic reduction reaction
is approximately 10% greater than the heat required for the endothermic dehydrogenation reaction. The
S３
heat from the hot hydrogen gas that must be vented from the reduction furnace can easily be captured
using a thermal storage refractory material and used for the dehydrogenation reaction.
Table S1. Energy required to heat reduction reactants from 25ºC to 500ºC and energy released by
reduction reaction at 500ºC
MJ
MJ/ton Ti
Heating Reactants
4408
3704
Reduction reaction
-5137
-4316
Total
-729
-613
Table S2. Energy required to heat TiH2 and Ar from 25ºC to 400ºC and dehydrogenate at 400ºC
MJ
MJ/ton Ti
Heating TiH2
486
408
Dehydrogenating TiH2
4207
3535
Total
4692
3943
After reduction, 5.14 tph of reduced powder will be leached for two hours with NH4Cl solution in a
series of four closed 7,400 gallon leaching tanks each agitated with a 5.5’D mixing blade driven by a 15
HP motor [S5]. The energy required to heat the solution will be provided from boiler steam and will require 3.7 MBTU of natural gas or 3890 MJ/ton. The leached powder is then thickened to 50% solids in a
75’D bridge thickener with a 5 HP motor, with the overflow being sent to the Mg recovery process. The
underflow is sent to a three stage countercurrent washing circuit, with each stage occurring in a 50’D
high capacity thickener driven by a 2 HP motor [S3]. The rinsed powder is then filtered using an 8’D x
8’L drum filter driven by 10 HP motor. Each of the subsequent leaching stages follows a similar procedure with nearly identical equipment. Pumps were sized for conveying the solution to and from each
process and were also included in the energy tally.
S４
After the final rinsing and filtration, the TiH2 powder still contains 10% by weight water (312 lbs)
that must be removed prior to dehydrogenation. The moist powder is fed to a 3’D x 10’L rotary drying
kiln driven by a 10 HP motor. Drying requires 1800 BTU/lb of water [S3], therefore the drying will require 562 kBTU per hour, or about 500 MJ/ton Ti.
The energy consumption for each step in the DRTS process as well as total energy is summarized in
Table S3. The most power intensive step of the new process is the milling and blending of the slag,
while leaching consumes the most natural gas due to the energy required to heat solutions. After further
optimization of the process, it is likely that lower solution temperatures could be used and the process
would require significantly less energy.
TABLE S3. Energy consumption of each step in the proposed DRTS process
Process
Electricity
(MJ/ton)
% Total
Electricity
Natural
Gas
(MJ/ton)
% Total
Natural
Gas
Total
% Total
Energy
Milling/Blending
7751
81.7
-
-
7751
38.7
Reduction/Dehydrogenation
35
0.4
4240
40.1
4275
21.3
Leaching
1218
12.8
5824
55.1
7042
35.1
Drying/Filtering
488
5.1
498
4.7
986
4.9
Total
9492
10562
20054
The total energy consumption for the process from slag to Ti powder was calculated to be 20,054
MJ/ton Ti. The energy to produce raw Ti sponge from raw ilmenite using a combination of the Becher
and Kroll processes has been reported as 360,000 MJ/ton Ti (100 kW-hr/kg) [S6], which includes the
energy for upgrading to synthetic rutile, which has been reported to consume 35,000 MJ/ton TiO2[S7].
The making of slag has been reported to consume at 35,500 MJ/ton TiO2[S7]. Based on the TiO2 content
of the slag, the proposed process will require 2.15 tons of slag per ton Ti. The total amount of energy
from slag production is calculated to be 60,900 MJ/ton Ti as shown below:
S５
(S2)
Adding this amount to the calculated energy consumption from slag to Ti powder, a total of 80,954
MJ/ton Ti (22.5 kWhr/kg) is obtained. It appears that the system boundary considered by Norgate et al
[S6] also included the energy to recover and regenerate Mg through electrolysis, therefore it shall also
be included in this analysis. The electrolysis of MgCl2 to form Mg and Cl2 gas has been reported to consume 13.0 kWhr of electrical energy per kg of Mg. The energy required for producing Mg used in this
process can be calculated as follows:
(S3)
The addition of this value brings the total energy consumption for the DRTS process to 137,700
MJ/ton Ti (38.2 kWhr/kg). Based on this preliminary assessment, the proposed process would consume
~62 % less energy than the Kroll process, which for an annual domestic Ti production rate of 18,000
tons would result in 4,000 TJ of annual energy savings.
S６
Results of Thermodynamic Analysis
E quilibium am ount, log(m ole)
1
0.5
H 2(g)
MgO
0
TiH2
Mg
MgH2
-0.5
-1
Fe2Ti
Fe
TiAl
Fe3Si
-1.5
FeSi
-2
TiAl3
-2.5
Ti5Si3
V
CaAl2
Mn
Al
-3
FeTi
Cr
V5Si3
CaO
Mg(g)
Cr3Si
ZrH 2
CaH 2
-3.5
MnSi
-4
100
Mn3Si
200
300
TiSi
Mg 2Si
400
500
600
700
Temperature, °C
Figure S2. Relative equilibrium amounts of reaction products of Ti slag reacted with MgH2 in 1 bar H2
atmosphere at different temperatures. MgO and TiH2 are the major predicted phases at equilibrium for
the entire temperature range. Data calculated using HSC Chemistry 5.11.
S７
TABLE S4. Typical oxygen content in Ti or Ti powders
ASTM standard of O2 in Powder Metallurgy (PM) Ti [S8]
O2 content (ppm)
Grade 1 PM Ti
1800
Grade 2 PM Ti
2500
Grade 3 PM Ti
3500
Measured* O2 of Sponge Ti from Kroll process
O2 content (ppm)
Sponge Ti - 30 µm
3500
Sponge Ti - 75 µm
2000
Sponge Ti - 150 µm
1570
*Measured by Leco TC600 Nitrogen/Oxygen Analyzer
Reported O2 in Ti powder from other developing processes
O2 content (ppm)
FFC process [S9]
<1000
Armstrong process [S9]
<1000
TABLE S5. Energy consumption of Ti production processes
Processes
Total energy
consumption
(kWhr/kg)
Kroll process [6]
100.3
FFC process [6]
88.1
Armstrong process [10]
48.4
DRTS process
38.2
S８
References
[S1] Wills BA, Napier-Munn T. Will's Mineral Processing Technology Handbook. 7th ed. Oxford,
U.K.: Butterworth-Heinemann; 2006.
[S2] Penney WR, Fair JR. Chemical Process Equipment: Selection and Design. Oxford, U.K.:
Butterworth-Heinemann; 2012.
[S3] Infomine. Mine an Mill Equipment Costs Estimators Guide: Capital and Operating Costs.
Vancouver: Infomine; 2012.
[S4] Kirchain R, Roth R. The Role of Titanium in the Automobile. Cambridge, MA: Camanoe
Associates; 2002. p. 43.
[S5] Baasel WD. Preliminary Chemical Engineering Plant Design. 2nd ed. New York City: Van
Nostrand Reinhold; 1990.
[S6] Norgate TE, Jahanshahi S, Rankin WJ. Assessing the Environmental Impact of Metal Production
Processes. Journal of Cleaner Production. 2007;15:838-48.
[S7] Reck E, Richards M. Titanium Dioxide - Manufacture, Environment and Life Cycle Analysis: The
Tioxide Experience. Surface Coatings International Part B: Coatings International.
1997;80(12):568-72.
[S8] ASTM B988-13 standard. Standard Specification for Powder Metallurgy (PM) Titanium and
Titanium Alloy Structural Components, 2013.
[S9] US DOE report. Summary of Emerging Titanium Cost Reduction Technologies, 2004.
[S10] William HP, et al. Solid State Processing of New Low Cost Titanium Powders Enabling
Affordable Automotive Components, 13th Diesel Engine-Efficiency & Emissions Research
Conference, 2007.
S９