A. W. HENDERSON and S. L. MAY
U. S. Bureau of Mines, Albany, Ore.
K. B.
HlGBlE
Bureau of Mines, Washington, D. C.
Chlorination of Euxenite Concentrates Chlorination in
the
presence
of carbon and an alkali &loride additive is a method Of extracting and separating into three groups the component elements of multiple oxide minerals such as euxenite. Large scale tests indicate that the alkali salt additive is a practical addition to the direct chlorination procedure and should be suitable for production scale equipment.
one of the more valuable domestic sources of tantalum and columbium. Chemical and x-ray spectrographic tests indicated the following approximate composition (weight per cent): La
zzz6 28 Ti02
Ua08
:&& 47.0 7.8 0.8 11.0
YnOa Srn~01
Materials Starting material was a concentrate containing 70y0 euxenite from the placer deposits of Bear Valley, Idaho,
4:
19 10 Tho2 lo lo Zrosj *l2Oas Mgo, CaO, Si02 by difference
Gdz03
I N m m s m ~use of titanium, tantalum, niobium, uranium, thorium, and the rare earth elements has stressed the importance of developing methods of extracting these metals from the multiple oxide minerals and separating them into useful fractions. Euxenite, samarskite, polycrase, and pyrochlore contain all these valuable metals. This investigation was restricted to euxenite, but problems of extraction and separation of individual elements would be similar for the other minerals. As tantalum and columbium occur principally in multiple oxide types, this investigation is particularly significant to their extractive metallurgy. Chlorination was investigated as a possible technique for separating valuable metals into individual fractions that could be chemically purified. Previous low-temperature chlorination experiments with ores or concentrates that contain iron have indicated interference from the action of chlorine with iron, The volatile ferric chloride formed is a good chlorination agent and is subsequently reduced to the nonvolatile ferrous state while still in the charge zone, coating the charge material and reducing its amenability to further chlorination. Addition of sodium chloride to the charge reduces the volatility of the iron chloride through formation of a nonvolatile type of double salt. When added to euxenite, it lowers the volatility of the uranium chloride formed by a similar mechanism.
sa
CeO2
PrgO La203
L
s
27 3
10 1
6.8 0.7 0.8
ErzOa, DyzOa Nd203 4.8 Starting material for large scale tests. a L. 5. Starting material for small scale tests. Rare earth group.
Apparatus and Procedure Preliminary work was performed in a 1-inch Vycor tube 30 inches long, which acted as both reactor and condenser. The reaction and condensing zones were individually heated with split-tube furnaces, and temperatures were controlled electrically. Rubber stoppers and tubing were used for the gas connections to the Vycor tube. A quartz boat contained the charge mixture. Apparatus for large scale tests was of three main parts: a chlorinator (a 5-inch nickel tube 29 inches long supported in the vertjcal position), a horizontal condenser for high boiling point chlorides (a 5-inch nickel tube 18 inches long),
and a vertical, water-cooled nickel condenser which condensed a low-boiling liquid chloride and received in it a vessel attached at the bottom of the condenser. The chlorinator, horizontal condenser, and two crossover tubes were heated by Nichrome elements controlled independently. The oxides in the euxenite concentrate were converted to chlorides by the Oerstedt (3) method of oxide chlorination in the presence of carbon, expressed by the equation reported by Kroll ( 2 ): 3Me0
+ 2C + 3Cla - - - - - - - - - - 3 3MeC12 + CO/CO,
The concentrate, ground to -200mesh, was mixed dry with carbon, sugar, and in some tests, salt. Enough water was added to make the mixture suitable for extrusion into rods */2 inch in diameter and 1 to 3 inches long,*which were dried a t 51 C. and coked in the absence of air at 500' C. The coked rods were inserted into the chlorination reaction zone, and the desired temperature was reached under a flowing helium atmosphere. Chlorine was then admitted, and the resulting reaction continued for 1 to 4 hours in the small apparatus and for 16 to 60 hours in the large reactor. After the reaction was complete, the products were in 'three physical groups, each of which could be removed and treated separately. The two volatile portions (mixed tantalum and niobium chlorides which condensed in the heated condenser at 100' to 125' C., and liquid titanium tetrachloride which condensed
IO
, ,
.
7, Condenser no.2 Chlorinator charge 8. Gas outlet 9. Water jacket Resistor carbon IO. Cleanout Heating elements Condenser no. I I I, Receiver 12. Tic14 (Ta t C b ) CIS 13. Chlorine inlet
13 Euxenite chlorinator VOL. 50, NO. 4
APRIL 1958
61 1
60
i
50 40 30
20 10
'0
005 01 2 3 4 SODIUM CHLORIDE/ORE
Figure 1 . Effect of sodium chloride on the volatility of uranium and iron chlorides
in the water-cooled condenser) were removed and stored separately in an anhydrous condition. The residue, containing the water-soluble nonvolatile chlorides of mixed rare earths, thorium, uranium, iron, and unattacked ore, was removed from the reactor and treated by hydrometallurgical methods. The degree of attack was based upon the amount of insoluble unattacked ore present in the chlorination residue. The variablm investigated in the small scale tests were (1) ore-carbon ratio, (2) reaction and condenser temperature, and (3) ore-alkali salt ratio.
Experimental Results The carbon requirement for chlorination of this concentrate was found, by experiment, to be between 15 and 20% of the ore-carbon mixture. The variation of reaction temperature in the small scale tests indicates that below 500" C. the reaction is slow, between 500' and 600" C. there is little difference in the extent of attack, and at 750' C. over 99% of the ore is converted to anhydrous chlorides. The unattacked concentrate in the chlorination residue from the runs in which the reaction temperature ranged from 500' to 600' C. contained little of value. Apparently, in this range the undesirable elements, such as silicon, aluminum, and calcium, are only slightly chlorinated. The location of uranium and iron chlorides was affected by the temperature of the reaction and salt additions. At40O0C.,where salt was not present, the bulk of the uranium chlorides remained with the rare earth and thorium chlorides in the residue; a t 750' C. the major portion of the uranium was contained with the tantalum and niobium chlorides in the volatile product. At 500" and 600" C. uranium chloride was evenly distributed between the volatile and nonvolatile fractions. I n the large scale runs at 500" C. where salt was not added, uranium and iron were distributed between
61 2
the residue and sublimate as predicted in the smaller tests. The need for the alkali-salt additive became more apparent when attempts were made to chlorinate large charges. Hindrance of the reaction by ferrous chloride resulted in low yield and poor chlorine efficiency. However, with addition of sodium chloride to the charge mixture, reduction of ferric to ferrous iron was prevented by the formation of a stable, complex, nonvolatile double salt of ferric chloride and sodium chloride. This double-salt mechanism ( 7 ) eliminated formation of ferrous chloride coating on unreacted ore particles and reduced volatility of uranium chloride to increase chlorination efficiency and degree of separation. Figure 1 shows the effect of varying the amount of sodium chloride in the charge. Experimental data indicate that 17 to 28% sodium chloride in an ore-carbonsodium chloride mixture restricted uranium and iron to the nonvolatile fraction through the double-salt mechanism,
Table 1.
The use of sodium chloride in the chlorination change permitted lower chlorination temperatures, to effect a high yield and acceptable chlorine efficiency. The volatile portions were free of uranium and iron. Because there was only slight variation in the analysis of the products, the analytical data for run 4 are presented in Table I as typical of all the alkali additive runs. Titanium tetrachloride, having a low boiling point, was easily separated from tantalum and niobium pentachlorides by regulating the condenser temperatures. The data for the experimental work are shown in Tables I1 and 111.
literature Cited (1) Horrigan, R. V., J . Metals 7 , 1118 (1955). (2) KGoll, (V. J., Metal Ind. (London) 81, 243 (1952). ( 3 ) Oerstedt, Pogg. Ann. 5 , 132 (1825). RECEIVED for review April 3, 1957 ACCEPTEDSeptember 20, 1957
Analysis of Chlorination Products
'CYeight Producta (Ta Nb)20j
+
TiOa
R ~ ~ ~Ratio, ~ , Product ____ ery, ____ Ore Ti02 % 99 96
0.31 0.17
0.01 98.0
99
0.43
1.0
Analysis, Wt. % Sb206 Fen03 u308
Tan06 6.0
...
90.0
...
0.1 0.1
...
...
3.4
Chlorination residue 0.05 1.0 0.3 a Analyzed after chlorides were converted to oxides
0.5
ThOn
0.5
...
19.0
9.0
... ...
1.0
0.7
Table II. Small Scale Chlorination Data Ituii NO.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1 2 3
4 5 6 7 8 9 10 11 12 13 14 16
Ore, G. 10 10 10 10 10 10 10 10 10
10 10 10 10 10 10
Weight Ratio _C _ - NaCl Ore Ore 0.10 0.15 0.20 0.25 0.30 0.16 0.16 0.16 0.16 0.16 0.40 0.40 0.40 0.40 0.40
... ... ... ... .,. ... ... ... ... ... ...
> Ore
0.85 2.0 2.0 3.16 3.02
0.19 0.20 0.20 0.25 0.25
.
0.10 0.20 0.40
F,
4 emu.$
c.
:.-.-
70
... ... ... ...
73 89 91 92 84 87 80 93 93 99 96 95 83 96 96
-
Distribution lies. Subl.
99 72 64 56 1 49 61 95 99.5 >99
* . a
... .
I
,
...
... 1
28 36
44 99
51 39
5 0.5
