LITHIUM CHLORIDE FROM LEPIDOLITE GEORGE 0. G. LOFl
AND
WARREN K. LEWIS
Massachusetts Institute of Technology, Cambridge, Mass.
The reaction between gaseous hydrogen chloride and pulverized lepidolite at elevated temperatures was investigated with the object of determining the conditions required for a high recovery of lithium chloride. A t temperatures approaching the melting point of the ore (about 935' C.) lithium chloride could be distilled from the lepidolite and recovered in condensed solid form. A t these temperatures and at reaction times approaching 13 hours, essentially complete recovery of the lithium in the ore was obtained. The effects on lithium yield of variation in temperature, reaction time, hydrogen
chloride rate, quantity of ore, fineness of division of ore, and dilution of hydrogen chloride with air and water vapor were investigated. It was concluded that at high hydrogen chloride rates the reaction rate was controlling at the start of the heating period; but after 1 to 3 hours the diffusion of the reaction products from the ore particles controlled the production of lithium chloride. The hydrogen chloride requirements of the process have been calculated; a large excess of the gas is required, which necessitates a recycling system if economical operation is to be obtained.
HE low density and desirable alloying effects of metallic lithium, the hygroscopic character of the chloride, and the fluxing action of the carbonate are responsible for most of the important commercial uses of lithium and its salts. The use of pure lithium, made by the electrolysis of fused lithium chloride, is extremely limited; but as an alloying element the metal has gained considerable importance (11). As a deoxidant in iron and steel, a fraction of one per cent lithium results in increased strength and hardness; in copper and bronze, electrical conductivity is improved; and in bearing metals, lithium increases strength and wear resistance. When lithium is alloyed with aluminum, zinc, and magnesium, a group of strong, light, and corrosion-resistant materials is obtained. An alloy of 30 per cent lithium and 70 per cent magnesium, with a specific gravity of only 1.4, is said to be used in aircraft construction (18). I n glass and glazes lithium carbonate imparts low thermal expansion, high electrical resistance, high ultraviolet transmissivity, and other desirable properties. The dehumidification power of lithium chloride has been utilized in air-conditioning units, in which an aqueous solution of the chloride is contacted with the moist air. Drying of air at room temperature to 11per cent relative humidity is claimed ( 1 ) . This use of lithium, particularly in the field of industrial air drying, gives promise of expansion. Lithium is widely distributed throughout the world, but in only a few locations are there commercial deposits (IO). Although occurring in animal and vegetable matter, in a few springs, and in salt beds, its chief industrial source is in certain phosphate and silicate minerals (12). The complex phosphatic ores, such as amblygonite and triphylite, contain up to 9 per cent lithium oxide. Spodu-
mene, a feldspathic silicate, is the most important lithium ore in the United States (8) and contains from 3 to 7 per cent lithium oxide. Lepidolite, containing an average of 3.5 per cent lithium oxide, is a micaceous silicate; when pure it is represented by the formula Si309Alz(Li,K)z(B,OH)z (8). It is the most abundant ore in this country, but its low grade presents a drawback to economic utilization. South Dakota has been the chief producer of high-grade lithium minerals in this country (6). Most of the lepidolite production has been in New Mexico and California, but the tonnage has decreased markedly since 1920 (16). This decrease is due to the low lithium content of the ores and the uneconomical extraction methods in use. Some low-grade spodumene deposits have also been found in North Carolina. A recently developed source of lithium is the brine of Searles Lake in California (16). Most of the reported processes and all of the commercial methods for lithium extraction are modifications of two main types (4). The first involves the high-temperature reaction between the ore, usually a silicate, and a salt of the alkali or alkaline earth metals; and the second involves reaction a t a much lower temperature, about 300' C., between a silicate or phosphate ore and sulfuric or other acid. In the process of Filsinger (a), decomposition of lepidolite was effected by calcination with sulfuric acid at 340' C.; and the lithium salt was recovered by extraction with water. A modified form of this process is now in use. Wadman (I?') decomposed the silicate by sintering the ore with an equal quantity of potassium sulfate. A base exchange reaction occurred, and the lithium was ultimately recovered as the carbonate. The process has been modified so that the alkali requirement is one third the amount of ore, and less recycling of potassium sulfate (9, 14) is needed. Temperatures range from 700" to 950' C.
T
1 Present
address, University of Colorado, Boulder, Colo.
209
210
INDUSTRIAL AND ENGINEERING CHEMISTRY FIGURE
I
DIAGRAM OF APPARATUS TO FUME LINE
F
IJ
G H
TO FUME LINE
uu K
C A B C D E F
---
C
K
D G - ELECTRIC RESISTANCE FURNACE H THERMOCOUPLE PROTECTION TUBE I - BOAT CONTAINING ORE J COOLING WATER DISTRIBUTOR K - ABSORBERS - . -- -
SULFURIC ACID DROPPING FUNNEL H C I GENERATING F L A S K SULFURIC ACID SCRUBBERS FLOWMETER THERMOCOUPLE LEADS SILICA REACTION-TUBE
FIGURE
-
2
DETAIL OF THERMOCOUPLE A N D H C t I N L E T D
n
E
B
- THERMOCOUPLE LEADS TO POTENTIOMETER B - HYDROGEN CHLORIDE I N L E T C - I N L E T MANIFOLD D - SILICA REACTION TUBE f. - SILICA THERMOCOUPLE PROTECTION TUBE
GH
J
F e (
A
I
= I INCH
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potentiometer. Figure 2 shows the details of the hydrogen chloride inlet and thermocouple assembly. Volatile chlorides which distilled from the ore were condensed and partially removed from the excess hydrogen chloride in the cooler portion of the quartz tube. The remaining solids suspended in the gas were recovered in two flasks containing water to absorb the hydrogen chloride carrier gas. To obtain data on the effect of mixing water vapor with hydrogen chloride, the apparatus was modified as shown in Figure 3. The gas mixture was generated by dropping aqueous hydrochloric acid into an electrically heated flaskin which complete vaporizationtook place. I n measuring the effect of diluting the hydrogen chloride with air, the air was metered, dried by bubbling through sulfuric acid, and mixed with hydro en chloride immediately downstream from t i e HC1 flowmeter. Temperature contrcl was effected by regulating the voltage on the furnace. Hydrogen chloride flow was controlled by regulating the rate of acid addition to the generating flask. The lepidolite used in the investigation contained 3.29 per cent lithium oxide. For all runs except those requiring coarser samples, the ore was pulverized in a ball mill to approximately 85 per cent through 200 mesh. When the furnace had been heated to the proper temperature, the thermocouple and gas inlet were removed and the sample boat was pushed to the center of the tube. The thermocouple was then reinserted, conneotion to the hydrogen chloride system made, and the gas started. Readings of the temperature and gas flow were made at intervals throughout the run.
Methods of Analysis
After completion of each run, the residue F - SILICA INSULATOR TUBE in the boat was removed and weighed. The G NO. 22 GA. CHROMEL WIRE loss in weight of the ore was used as a rough H NO. 22 GA. A L U M E L WIRE index of the extent of reaction, because in the I WELDED JUNCTION important ranges, extent of reaction paralleled J S I L I C A BOAT the amount of distillation. The residue was. then pulverized and extracted with hot water, and the insoluble final residue removed b y filtration. The filtrate was used for the determination of the soluble lithium salts remainin . in the ore residue after the reaction. Drawbacks inherent in the above processes are high acid $he distilled products which condensed in the cool portion of' requirement and difficult purification procedure in the modithe tube were dissolved in dilute hydrochloric acid and mixed fied Filsinger method, and high potassium sulfate requirewith the solution from the absorber flasks. This final solution ment and its expensive recovery system in the improved Wadwas then used for the determination of the lithium chloride volatilized from the ore. man process. For the lithium determination a spectroscopic method was em-. I n view of the costly methods for recovery of lithium comployed. No sensitive spectrograph or densitometer was available pounds from the ores, this investigation was undertaken to for a standard spectrographic analysis; therefore a method was devise and study a lepidolite decomposition process characdeveloped utilizing a relatively inexpensive spectroscope and. visual observation of the lithium line. terized b y high yields of lithium salt and, if possible, simplicIn a procedure of Skinner and Collins (15) a drop of dilute ity and economy of operation. It was decided t h a t the comlithium chloride solution was collected on a platinum loop and: mercial importance of the chloride merited the study of the the water evaporated. The lithium line (6708 A.) was observed. reaction between the ore and hydrogen chloride at temperavisually when the loop was inserted in a gas flame. By diluting, tures approaching 1000" C. and the distillation of the volatile the sample until the line failed to appear and comparing with the extinction concentration on known standards, the lithium, chloride from the ore residue. content of the solution could be easily computed. An accuracyof 10 per cent was claimed for this method. Considerable difficulty was experienced in recognizing the exDecomposition of Ore tinction point. hence a procedure was developed, based on thefact that the dime the spectrum line of the element is visible is a , The decomposition of lepidolite with hydrogen chloride function of the quantity of salt, deposited on a suitable support under varying experimental conditions was investigated in and vaporized in a gas flame. the apparatus shown in Figure 1: The distillate solution and residue extracts were analyzed; for lithium chloride by first diluting to known volumes. A drop Concentrated sulfuric acid was dropped into a flask containing of the solution was then collected in a platinum loop and the strong hydrochloric acid. The resulting gaseous hydrogen water gently evaporated over a gas flame. When the loop was. chloride was dried by bubbling through strong sulfuric acid. placed in the burner flame, the time the lithium line was visible After the rate was measured in a flowmeter, the gas was passed in the spectrum was measured. Comparison with the time the to a fused quartz tube in which had previously been placed a silica line was visible using solutions of known concentration enabled. boat containing a small sample of pulverized lepidolite. The rethe computation of the lithium chloride content of the sample. action tube was heated in a tubular electric resistance furnace, The accuracy of the determination by this procedure was found: the temperature of which was measured by thermocouple and to be about 3 per cent of the lithium present and was consideredi
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INDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1942
A - ELECTRIC HOT PLATE B HYDROCHLORK ACID VAPORIZING FLASK
-
C
- HYDROCHLORIC ACID DROPPING FUNNEL D - ELECTRICALLY HEATED
c
E F
-
-
CONNECTION TUBE SILICA REACTION TUBE THERMOCOUPLE LEADS
FIGURE 3 DIAGRAM OF APPARATUS FLASH HC! VAPORIZER
satisfactory for the purpose. Four total balances made by comparing the lithium in the distillate, soluble residue, and insoluble residue with that in the original sample gave differences of -0.6, -2.4, f2.2, and -2.0 per cent. Rough approximations of the potassium contents were made by depositing the samples on a graphite ring held inside the loop. An accuracy greater than 20 per cent could not be obtained on this analysis. A carbonate fusion of the residue was made and dissolved, and most of the other salts were separated. Insoluble lithium in the residue was then determined spectroscopically. Alumina and silica were determined by standard methods.
Effect of Temperature on Lithium Yield When conditions of hydrogen chloride flow rate, reaction time, and quantity of sample are maintained essentially constant, the yields of lithium chloride in the distillate vary with temperature (Figure 4A) Lithium yields increase rapidly from low values at 600" C. to maxima a t about 935" C. Melting of the ore causes yields to decrease rapidly between 950" and 960" because of the decreased rate of diffusion through the ore. The slow rise above 1000" is due to the increase in reaction rate with increase in temperature. Figure 4B shows the corresponding yields of lithium in the residue. These yields increase rapidly from relatively low values a t 600' C. to maxima a t 750-800" C. Removal of lithium chloride above 900" by distillation causes a rapid decrease in residue yields. The rising portion of the curves indicates that rate of formation of lithium chloride is exceeding the rate of removal by distillation. The reverse is true at temperatures above 800". The maxima of these curves correspond to equal rates of formation and distillation. When the low residue yield is reached at tomperatures between 900" and 1000" C., distillation is removing lithium chloride from the solid as fast as it is being formed. Combined yields of lithium chloride in distillate and residue (Figure 4C) are found to show the same general trends as the distillate yields. I
FIGURE4. PLOTSOF YIELDus. TEMPERATURE A , distillate yield. B residue yield: C , t o t h yjeld
ZIP
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Effect of Reaction Time on Lithium Yield
0
I
e
3
4
6
6
REACTION
7 8 9 IO TIME HOURS
-
II
I2
FIGURE 5. PLOTS OF YIELDvs. TIME A , distillate yield; B , residue yield; C,total yield
13
When conditions of temperature, hydrogen chloride flow rate, and quantity of sample are maintained essentially constant, the yields of lithium chloride in the distillate vary with reaction time as shown in Figure 5A. These curves were made by plotting values read from the temperature-yield curves. That nearly constant distillation rates prevail at temperatures up to 935" C. is shown by the nearly straightline character of the curves. This is particularly true in the runs at temperatures up to 800" C. As 100 per cent yield is approached, the rates decrease only slightly. The slightly decreasing rate observed in the 900" and 935' C. runs after about 8 hours is believed due to the decreased diffusion rate of lithium chloride out through the now porous crystals. This decrease in rate is caused by the greater distance through which the product vapors must diffuse. The distillate yield curves a t 1000" and 1100" C. lie below the 900" curve because of lower diffusion rate through the ore mass. The distillation rate is also lower than that for the 900" runs and decreases more rapidly as the reaction proceeds. This is thought to be due to change in diffusion rate through the molten ore, caused, in turn, by decreasing concentration of alkali and change in the viscosity brought about by alkali removal. The residue yields (Figure 5B) can be looked upon as the difference between the total and distillate yields. At temperatures up to 825" C. these yields increase with reaction time, but at higher temperatures they pass through maxima and drop off to low values. The rising yields are due to the fact that at the lower temperatures, rate of formation of lithium chloride exceeds distillation rate, but as the temperature is raised above 825", the distillation rate exceeds formation rate after the first two hours. The rapid initial rise of the curves is caused by the high rate of formation of lithium chloride a t the start of the run. After this initial high rate, there is a more uniform increase in yields at temperatures up to 825" C. and a decrease a t higher temperatures. These facts are further brought out in Figure 5C. The high initial rate of production in all runs above 600" C. is considered to correspond to the reaction between the gas and the surface of the ore particles; thus, no diffusion of the products through the particle is necessary The rate of reaction is therefore the controlling rate in the production of lithium chloride during this period. Following the first hour, diffusion of the reaction products out through the particles must take place. As pointed out below, a fresh unreacted surface of lithium silicate is continually presented to the gas, so that rate of reaction should decrease very little as the reaction proceeds. Thus, the rate of diffusion is considered to be the controlling rate for the balance of the run. This rate decreases only slightly as the reaction progresses. The diffusion of the products is controlling rather than hydrogen chloride diffusion, because at all times practically pure hydrogen chloride is in contact with the reacting surface. At 600' C., however, reaction rate is so low that i t is the controlling factor over the entire heating period. At this temperature the vapor pressure of lithium chloride is negligible, and the chloride remains as a solid in the ore particles. The water vapor can diffuse from the particles, however, and this rate is high enough to remove it from within the crystal. The constant rate of reaction a t this temperature, shown by the straight-line relation. is good evidence that in the mechanism of the ore-gas reaction a fresh ore surface is presented to the gas a t all times. This could be attained by a continuous invasion of hydrogen chloride into the ore crystal, which causes reaction to take place in a rather sharply defined front of unreacted lithium silicate.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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213
In the 1000" and 1100" C. runs, lithium chloride production rate is lower because of the decreased diffusion rates through the viscous molten ore. Reaction is believed to take place at the ore-gas interface, and diffusion of the lithium oxide or silicate to the surface to be the controlling rate.
Effect of Hydrogen Chloride Flow on Lithium Yield Under conditions of constant temperature, reaction time, and quantity of sample, the yields of lithium chloride vary with hydrogen chloride flow, as shown in Figure 6. Total yields increase with increase in gas rate to practically a constant value. At 910' C. and 7 hours reaction time, the yields increase from 33 to 56 per cent as the gas rate is increased from 10 to 40 cc. per minute. Since removal of the metal chloride and water vapor takes place at the surface of the ore change, a concentration gradient of these compounds is present from the bottom to the top of the layer. The diffusion of these products to and through the surface gas film is therefore affected by change in gas flow rate. The driving force increases with gas flow and therefore increases the yield. Removal of products from the reaction zone causes the equilibrium,
RzO
+ 2HC1
2RC1
+ HzO
to be displaced toward the formation of more alkali chloride. However, when the gas rate is increased to a sufficient degree, the driving force is high enough to remove effectively all the products diffusing from the individual particles, and no appreciable increase in driving force is obtained by using higher gas flows. At this point diffusion inside the particles becomes the controlling rate, as previously stated. Increase in gas rate has no effect on this diffusion, and a constant yield is obtained at gas flows above this critical value. When the total yields of the two runs using samples larger than those generally employed are plotted on a basis of hydrogen chloride flow per unit thickness of ore layer, the points are fairly near the curve. This fact lends support to the theory that diffusion of the reaction products through the charge is the controlling factor a t the low gas rates. The increased layer thickness of these two samples requires diffusion through a greater distance, which results in a lowered rate of lithium chloride production. When correlated on the same basis, total yields from samples smaller than the standard (not shown in the plot) lie on the extended horizontal portion of the curve. It must be recognized that this correlation with the different sized samples is not strictly rigorous, because the rate of diffusion of the products from the surface of the layer depends upon the actual gas flow rate and not upon the thickness of the charge. Dividing the hydrogen chloride flow rate by the layer thickness fa&, therefore, to take this into consideration. An additional variable is introduced with the largest sample (4.26 grams) because the ore waB packed tight in the boat. Thus, three times the standard ore quantity was used which gave a layer thickness of only twice the standard. Ratio of ore quantity t o gas quantity undoubtedly has an effect on the yield, but the predominant effect seems to be that of layer thickness. The true effective gas flow rate for use in this correlation probably lies between the actual measured rate and the value obtained by multiplying the measured rate by the ratio of the standard sample layer thickness to the thickness used in each run. Below the gas rate of 10 cc. per minute, the rate of lithium chloride distillation is evidently high enough to remove nearly all of it from the charge. Decrease in the gas rate toward zero should be expected to reduce the distillate curve asymptotic
HCI FLOW
-
CC. PER MINUTE
FIGURB 6. LITHIUMYIELDAND SATURATION us. HYDROGEN CHLORIDE FLOW Temperature 910° C., reaction time 7 hours. yields 1.42-gram sample 2 6 mm. thick. LiCl Laturation, 1.42 gdrns, 2.6 mm. 2.6 0 Large samples, HC1 flow X of layer 1.42 AALaree samples, HCI flow X weight of
0
$
to the straight line representing the distillate yield if the gas were saturated with lithium chloride. This is shown by the dotted curves in Figure 6. Since no data were taken at gas rates below 10 cc. per minute, the exact shape of the curve below this rate is not known. However, at an infinitesimal flow, the main body of the gas should be saturated with lithium chloride; this would cause an initial rise in the distillate curve along the saturation line. The total yield curve probably lies slightly above the saturation line at this very low rate because of the presence of lithium chloride in the residue. As the gas rate is increased by a small amount, saturation with lithium chloride is not attained, and the distillate yield curve bends away from the saturation line. As the gas rate is increased above 10 cc. per minute, the rate of production of lithium chloride exceeds the rate of distillation, and the lithium chloride content of the residue increases (Figure 6). I n this region the rate of distillation rises with increasing gas flow because of the more effectiveremoval of lithium chloride from the surface of the charge. This removal of lithium chloride from the surface induces faster diffusion through the mass. The rising gas rate is thought to have the combined effect of lowering the effective thickness of the stagnant gas film covering the surface of the charge, of lowelting the concentration of the lithium chloride in the gas immediately above the film, and thereby increasing the diffusion driving force. Further increase in the hydrogen chloride rate causes the rate of distillation to exceed the rate of formation of lithium chloride, and the lithium chloride in the residue decreases. Using the vapor pressure of lithium chloride a t this temperature, about 0.01 atmosphere (6,7), the percentage saturation of lithium chloride in the gas was calculated and plotted on the same figure. Thus, the distillate yields are of such magnitude that the gas is 55 per cent saturated with lithium
TABLE I. EFFECT OF SIZE OR SAMPLE O N LITHIUMCHLORIDE YIELD
Temperature, C. Time, hours Sample weight, grams Layer thickness, mni. HC1 flow Cc./min. Cc./min./1.42 grams ore Cc./min./2.6-mm. layer thickness Distillate yield, Residue yield, % Total yield, S a t n . of LiCl4in gas, Yo a
'J1g 0.35 0.7
$, 190 56 0.4 5:
9l: 0.71 1.3
89; 1.42 2.6
01: 2.84 5.2
59 54 0.6 55 1.5
30 51 2.6 54 28
::
1:$ 104
56 0.6 5;
4.26
5.8"
i: i: 27 40 15 56 34
Sample packed tight in boat.
TABLE 11. EFFECTO F ORE PARTICLE SIZEO N LITHIUMCHLORIDE
YIELD Fine Orea
Coarse Ores
Temperature, C. Reaction time, hours HC1 flow, cc./min. Yield in distillate, % Yield in residue, % T o t a l yield, T o t a l yield cor. t o 910' C.. % a
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Particle size distribution was as follows: Tyler Screen Size, Size of Opening, Inch Mesh (Mm.) 3 5 0 n 48 0.0164 (0.417) 4 8 o n 65 0.0116 (0.295) 65 on 100 0.0082 (0.208) 100 ,on 200 0,0058 (0.147) Passing 200 0,0029 (0,074)
Fine Ore, 70
..
14 86
Coarse Ore, % 27 20 15 23 15
chloride a t a rate of 10 cc. per minute, and 25 per cent saturated a t the 40 cc. rate. The two large samples also fall on the distillate yield and per cent saturation curves, when the flow rate is taken to be the rate per 1.42 grams of ore used. This is considered the best method of correlation since the actual quantity of lithium chloride issuing into the gas stream should, if resistance to diffusion through the ore is insignificant, be proportional to the amount of gas used per unit weight of sample. There is again the question of using sample quantity, layer thickness, or actual gas flow rate as the basis for the correlation.
Effect of Quantity of Sample The effect of the quantity of sample and thickness of ore layer on yields is shown in Table I. The distillate yield in the first three samples is practically independent of the sample quantity and layer thickness; and when correlated on the basis of equivalent hydrogen chloride flow per unit weight of sample (Figure 6), the yields from the two large samples fall in line. The yield of lithium chloride in the residue is also independent of the quantity of sample and layer thickness, provided enough hydrogen chloride is used to distill it from the ore. If the gas flow is low, lithium chloride normally appearing in the distillate remains in the residue. That the two small samples give no higher yields than the standard sample is excellent evidence that the yields have reached essentially a maximum value a t gas flows above 40 cc. per minute. This also shows the maximum yield to be independent of the total gas flow or the gas-ore ratio, provided they are above the critical values. The independence of the asymptotic yield on the layer thickness shows that above the gas rate for maximum yield, diffusion of reaction products out through the ore crystal is the controlling factor, rather than diffusion through the ore mass. The two samples larger than the 1.42-gram standard did not give such high distillate yields as the three smaller ones; but as explained in the preceding section, this is to be ex-
pected because of the use of gas-ore quantity ratio lower than that dictated by the value of the maximum yield. When this rough correlation is applied, yields fall in line with those on the standard size samples. This indicates the independence of yield from sample thickness in the range below the maximum, provided the gas flow is based on either a unit quantity of ore, a unit thickness of the layer, or a suitable combination of the two if they are not proportional to each other. The twelvefold variation in quantity of sample with only slight variation in the total yield is good evidence supporting the theory that diffusion rates within the crystals are the controlling factor in the production of lithium chloride a t reperiods above 3 hours and temperatures above 700° C,
Effect of Ore Particle Size on Lithium Yield The effect of variation in the ore particle size on yields is shown in Table 11. Variation in particle size from 0.0029 t o 0.0164 inch (0.074 t o 0.417 mm.) in diameter is seen to have only slight effect on the yields of lithium chloride. At the start of the reaction a t temperatures above 700" C., rapid production of lithium chloride occurs, during which time the rate of reaction is controlling. After the rapid initial reaction of lithium silicate in and very near the surface of the crystals, diffusion of the reaction products through the crystal is the controlling rate. Furthermore, the rate of production of lithium chloride as the time is increased above 3 hours decreases only slightly (Figure 5 C ) ; this indicates that the diffusion rate decreases little as the run proceeds. Since the surface area of the larger particles is less than that of the finely powdered material, production of lithium chloride during the early part of the run should be somewhat less when the coarse ore is used. Hoxever, as soon as the surface material has reacted, diffusion controls, and the rate of production should differ only slightly between the two samples. The data, when corrected to the same temperature, show this slight difference in yields, but it must be noted that the accuracy of the analytical method is not high enough t o show a difference of l per cent in 56 per cent.
Effect of Diluting Hydrogen Chloride with Air and Water Vapor The effect on lithium yield of diluting the hydrogen chloride with air is shown in Table I11 and that of water vapor dilution in Table IV. Comparison of the yields with those obtained using pure hydrogen chloride shows a moderate decrease with air dilution and an extreme decrease with mater vapor dilution. The presence of air would be expected to reduce the yield
TABLE 111. EFFECTO F 4IR DILUTION ON LITHIUMCHLORIDE YIELD Temperature, C. Time, hours HC1 flow cc./min. Air flow 'cc./min. H C I in ;as, 70 Distillate yield yo Residue yield, !% Total yield, %
909 7 55 271 17 41 0.6 42
808 7 59 0 100 54 0.6 55
TABLEIV. EFFECT OF WATERVAPORDILUTIOX O N LITHIUM CHLORIDE YIELD
Temperature, C. Time, hours HC1 flow, cc./min. HpOin gas $6 HCI in gas: % Distillate yield, % Residue yield, yo Total yield, %
810 5 44 0 100 17 30 47
813 5 64 78 22 5.4 4.2 9.6
914 3 58 0
100 25 9.1 34
919 8 57 78 22 6.1 2.1
8.2
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somewhat because of the diluent action in lowering the concentration of hydrogen chloride in contact with the ore particles. Water vapor causes a great decrease in yield because of its reversal effect on the reaction. Its presence in such quantity markedly reduces the diffusion of water vapor from the ore particles and thereby reduces the yield. These data are additional evidence that rate of diffusion of reaction products from the ore particles is the controlling factor a t sufficiently high gas rates and after the first hour or two of reaction time.
Potassium, Alumina, and Silica Yields The yields of potassium are shown in Table V. Comparison with lithium yields (Figure 4) shows that they are approximately the same but usually somewhat smaller. Because of the secondary importance of the potassium analysis, only an approximate method was used, and the difference in the potassium and lithium yields is not significant. Comparable yields should be expected because of the similar position of the two elements in the crystal and their similar chemical properties. TABLEV. POTASSIUM CHLORIDE YIELD Temperature, C. Time hours HCl bow cc /min Distillati yigld. %' Rerridue yield, % Total yield, %
712 9 54 10 33 43
911 13 53 86 0.6 87
934 11 53 65
... ...
I n a representative test a t 911" C. and 13 hours of heating, the respective distillate yields of alumina and silica were 7.2 and 9.4 per cent of the amounts in the sample. Neither was present in the residue in soluble form.
Distillate Composition and Hydrogen Chloride Consumption At 911" C. and 13-hour reaction tim'e, the distillate yields and hydrogen chloride consumption are as shown in Table VI. The potassium percentage yield is here considered to be the same as the lithium yield. TABLE VI.
DISTILLATE COMPOSITION AND HYDROGEN CHLORIDE CONSUMPTION % Recovery
Lithium Potassium Aluminum Silicon
96 96
7 9
% Total Dist. as: Oxides Chlorides 17 21 36 49 9 11 25 32
Constituent 25
24 13 38
Although these product compositions were determined only on the 911" C. 13-hour sample, they should represent fairly well those under other conditions, particularly in the important high-yield region. Although the chlorides other than that of lithium are of some value, their production is considered an economic disadvantage because they consume hydrogen chloride and require a purification process to separate them from the desired lithium chloride. Separation of the chlorides of aluminum and silicon from the alkali chlorides can easily be accomplished by distillation above 315" C. At this temperature the small quantity of ferric chloride is also removed. Separation of the alkali chlorides can then .be effected by means such as fractional crystallization or solvent extraction. The consumption of hydrogen chloride by the alkalies was about 50 per cent of the total hydrogen chloride consumed, the lithium accounting for half of this figure. If the three other
215
components are considered waste products, the hydrogen chloride efficiency of the process is thus only 25 per cent. If profitable markets for the by-products could be found, this low hydrogen chloride efficiency would not be a serious drawback to industrial utilization. Table VII, based on the data presented above, shows the hydrogen chloride requirements of the process. TABLEVII. HYDROQEN CHLORIDE REQUIREMENTS Total vol. of gas (S.T . P.), cc. Total gram moles of gas ' Gas oonsumed, % Moles of as circulated: Per mofe of gas reacted Per mole of LiCl formed Pounds of gas circulated: Per pound of LiCl formed Per pound of ore
Used 41,400 1.85 0.64
Minimum 31,200 1.39 0.86
165 615
117 463
529 47
397 36
The hydrogen chloride rate was 53 cc. per minute; and since at 910" C. a rate of 40 cc. per minute was found to be adequate for obtaining the highest possible yield, the hydrogen chloride requirement a t this minimum rate is also tabulated. Although the quantity of hydrogen chloride used was in the ratio of 155 moles t o every mole which reacted, and the minimum quantity required was 117 moles, this great excess would be recirculated to the ore if the process were used on a large scale. Suitable means would of course be necessary to remove volatile chlorides and water vapor from the gas.
Summary and Conclusions The results show the essential characteristics of the reaction between hydrogen chloride and lepidolite. They show that practically complete recovery of the lithium values in the ore can be attained under conditions which are possible on a large scale. The yield of lithium chloride increases with rise in temperature and reaction time, provided the ore is not melted. If the gas is used in sufficient excess, recovery is practically independent of hydrogen chloride flow, and the ratios of hydrogen chloride to ore quantity and layer thickness. A minimum of approximately 117 parts hydrogen chloride is required per part which reacts, for a 95 per cent recovery of the lithium a t 910" C. The yield is also independent of the particle size in the range studied. Presence of air or water vapor in the gas lowers the yield, however. Percentage yields of potassium chloride are approximately equal to the lithium yields, whereas alumina and silica yields at the optimum conditions are below 10 per cent of the amounts in the ore. Per unit of lithium chloride recovered under the optimum conditions, the distilled product mixture contains approximately 1.7 parts potassium chloride, 0.5 part aluminum trichloride, and 1.5 parts silicon tetrachloride. These products consume a total of 4 parts hydrogen chloride per part appearing in the distillate as lithium chloride. The excessive quantity of hydrogen chloride required in the reaction would not be a great disadvantage in a large-scale installation, because a suitable gas-recycling system could be employed to recover all the hydrogen chloride not actually consumed in the reactions. The hydrogen chloride reacting with oxides other than lithia would probably not be recovered. Separation of the products could be effected (a) by removal of the chlorides of aluminum (iron) and silicon by a simple distillation process operating a t a temperature as low as 315" C., and (b) by separation of the lithium chloride from potassium chloride by fractional crystallization, solvent extraction, or other means. I n this work all the runs were made with the same ore.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Although other lepidolite ores would probably give similar results, small variations should be expected. The melting point would no doubt vary somewhat with the distribution of the constituents and thus change the optimum temperature for the reaction. Since the ratio of total alkali to ore is fairly constant, and since the lithium and potassium have nearly identical behavior in the reaction, the percentage yields of the chlorides should not change materially. At hydrogen chloride rates below the value required for the maximum yield, rate of production of lithium chloride was controlled by the rate of diffusion of the reaction products from the mass of ore. At higher gas rates the reaction rate of the mineral with hydrogen chloride was the controlling factor during the first two or three hours at temperatures between 700” and 935’ C. After the first two or three hours, rate of diffusion of the products from the individual ore particles is controlling.
Literature Cited (1) Bichowsky and Kelly, IKD.ENG.CHEM.,27, 879-82 (1935). (2) Chambers and Enck, Chem. Industries, 34, 405-8 (1934).
Vol. 34, No, 2
(3) Filsinger, Arch. Pharm., 208, 198 (1876). (4) Gmelins Handbuch der anorganisohen Chemie, 8th ed., No. 20. pp. 2-8,
(5) (6) (7) (8)
Berlin, Verlag Chemie, 1927.
Hess, Eng. Mining J., 137, 339-42 (1936). Kelly, U. S. Bur. Mines, Bull. 383, 63-4 (1935). Maier, U S. Bur. Mines, Tech. Paper 360 (1929).
Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry”, Vol. 11, pp. 425-6, London, Longmans, Green and Co., 1922. (9) Metallbank und Metallalurgische Ge3. A.-G., Brit. Patent
269,878 (1927). (10) Meyer, IND.ENG.CHEM.,30, 431-6 (1938). (11) Osborg, Trans. Electrochem. Soc., 66, 91-105 (1934). (12) Pascal, “Trait6 de chimie min&ale”, Vol. 11, p. 727, Paris, Masson et Cie., 1934. (13) Sanderson, Can. Mining J.,60, 546-51 (1939). (14) Scieffelin and Cappon, J. SOC.Chem. Ind., 27, 549 (1908). (15) Skinner and Collins, U. S. Dept. -4gr,, Bur. Chem., Bull. 153 (1912). (16) U. S. Bur. Mines, Minerals Yearbook for 1939, p. 1404, Washington, Govt. Printing Office, 1939. (17) Wadman, German Patent 207,845 (1909). PRESENTEDbefore the Division of Industrial and Engineering Chemistry a t the lOlst Meet ing of the AMERICAN CHEMICAL SOCIETY, S t . Louis, Mo.
HOCUS POCUS BY
Thomas Rowlandson
AGAIN
we are indebted to Prof. E. C . Watson of the California Institute of Technology for a photograph of his original color print. This we are reproducing as No. 134 in the Berolzheimer series of Alchemical and Historical Reproductions. This print has the sub-title “Searching for the Philosopher’s Stone”. It was published March 12, 1800, at R. Ackerman’s Repository of the Arts,No. 101 Strand, London. Under the portrait on the back wall is the inscription “Count Caliastro (sic) Discoverer of the Philosopher’s Stone”. On the book in the foreground are the legends “Transmutation of Metal” and “Animal Heat/Blood Warm”. Thomas Rowlandson was born in 1756 in London. H e studied at the Royal Academy and in Paris. After losing his
fortune in gambling, he settled down in London to paint portraits and landscapes. These were exhibited at the Royal Academy and gained Rowlandson much fame. He then turned t o caricature and illustration. While not as prolific as his contemporary Gillray, his work has more artistic merit. H e died in London in 1827.
D. D. BEROLZREIMER 50 East 41st Street
New York, N. Y . The lists of reproductions and directions for obtaining copies appear as foUows: 1 t o 96, January, 1939, page 124; 97 tp.120, January, 1941, page 114; 121 to 132, January, 1942, page 119. An additional reproduction appeara each month.
