Experimental work in the recovery ofelemental sulphur by the Hall process

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Authors Michaelson, James Paul, 1913-

Publisher The University of Arizona.

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EXPERIMENTAL WORK IN THE RECOVERY OFELEMENTAL SULPHUR BY THE HALL PROCESS

by

James Paul Michaelson

A Thesissubmitted to the faculty of the

Department of Mining Engineering and Metallurgy

in partial fulfillment of the requirements for the degree of

Master of Science

in the Graduate College University of Arizona

1937

Approved: Major Profe < Date.

- . . . . ... . . . ■ .. . ... . ? Ess®Acknowledgments.......... 1Introduction............... 2Materials, apparatus, and experimental and

analytical methods.... ......................... 8Experimental w o r k .... ................. . . .......... 12Conclusions ............... 36

-CONTENTS

1

ACKHCF/fLEDGEENTSThe experimental work described in this thesis was per

formed in the laboratories of the U. S. Bureau of Mines, Southwest Experiment Station, Tucson, Arizona, by the author, who, for the year 1936-1937, was one of the Bureau of Mines Fellows at that station.

The author wishes to express his warmest thanks and appreciation to Mr. F. S. Wartman, Associate Metallurgist,U. S. Bureau of Mines, for his guidance and assistance on this research project throughout the year, and to Dr. T. Q. Chapman for his aid and advice in the preparation of this manuscript. ;

2

CHAPTER 1

Introduction

The important uses of the sulphur produced in the world comprise (1) the manufacture of sulphuric acid, (2) bleaching purposes as sulphur dioxide, (3) the manufacture of gunpowder and matches, and (4) the rubber industry.

The Sicilian deposits supplied 95 per cent of the world*s demands until 1901, when the Frasch hot water process was developed for the extraction of sulphur from such beds as those in Louisiana and Texas. In 1954 the world production of sulphur amounted to approximately 2.000,000- i 1 r“ - • - - - : , ’ •long tons, of which the United States supplies 75 per cent.In 1925, the estimated life of the Gulf sulphur fields was 20 years. The price of sulphur has been about $18.00 per long ton for the past 10 years. It is likely, however, that the demand for sulphur over long time periods is increasing, and this condition may result in an upward trend of price.

Elemental sulphur for the manufacture of sulphuric acid and sulphur dioxide has a strong competitor in the metallic

llj Lindgren, W., Mineral Deposits, p. 380, McGraw-fiill Book Co., Inc., New York, 1933.(2) Bacon, Raymond F., Engineering and Mining Journal Press, p. 382, Jan. 17, 1925.

(3) Minerals Yearbook, United States Government Printing Office, 1952-37.

3

sulphides., especially pyrite, copper, and zinc sulphides.Much pyrite is mined for its sulphur content alone, while the sulphur value in copper and zinc sulphides is secondary to the value of the metals. Industrial sulphuric acid is obtained from these metallic sulphides by two methods, first, the contact process, and, second, the chamber process. The contact process utilizes the oxidation of sulphur dioxide to sulphur trioxide by a suitable catalyst such as platinum; the chamber process employs nitre as the oxidizing agent.

If the demand for sulphuric acid is such that a profit cannot be made, sulphur dioxide resulting as a by-product from metallurgical processes is discharged to the atmosphere, resulting in considerable damage to nearby agricultural.dis-. tricts. At the Washoe plant of the Anaconda Copper Mining Company, the equivalent of l£ million tons of sulphuric acid was wasted, in 1912, as sulphur dioxide.^ If sulphur could be recovered in the elemental form rather than as sulphuric acid, several advantages as follows would result: (1) Thesulphur could be recovered in a form which could be more readily marketed than sulphuric acid; (2) Damage to surrounding agricultural districts would be eliminated; (3) Shipping weights would be reduced, as one pound of easily transported and easily stored sulphur is equivalent to four pounds of commercial sulphuric acid, which is difficult to transport or store. ’ ■ ■■ : ; -'

T4) Mellor, J.W., Modern Inorganic Chemistry, p. 519, Long- mans, Green and Co., London, 1930.

4

One of the earliest processes for recovering sulphur from metallic sulphides utilized the preferential combination of oxygen from steam with the associated metal, resulting in the formation of a metallic oxide and hydrogen sulphide as indicated in equation (1). The hydrogen sulphide was either partially burned, releasing sulphur and water as in equation (2), or it reacted with sulphur dioxide which was present as indicated in equation (3).

(1) CuS * HgO — CuO * HgS(2 ) 2H2S «■ Og = 2HgO f 2S

(3) 2H2S -h S02 = 2H20 > 3SBeginning in 1911, W. A. Hall was granted a series of

patents for a process disclosing the recovery of sulphur'from metallic sulphide ores by the combined action of steam and a reducing flame or gas,5 6 or by the use of a hydrocarbon gas.7 8 9 In the latter case the hydrocarbon supposedly furnished e- nough steam frcan its partial combustion to make the addition of accessory steam unnecessary. Hall also developed two furnaces, one of the mechanically rabbled type,® and the other of the Dwight and Lloyd type.®

(5) Wilkes, J. P., British Patent 3,087; Septi 9, 1874.(6) Hall, W. A., United States Patent 1,083,246; 1914.(7) Hall, V/. A., United States Patent 1,083,250; 1914.(8) Hall, W. A., United States Patent 1,083,251; 1914.(9) Hall, W. A., United States Patent 1,083,252; 1914.

5

A surrey of the literature revealed that Hall wrote a paper for publication describing his process, excerpts of which follow:^

"The sulphur existing in the ore as a sulphide is removed and discharged from the ore in the elemental condition and when the furnace operation is properly adjusted, there is substantially no discharge from the furnace of combined sulphur, either as SOo, S03, HgS or COS. Staall mechanically rabbled reverberatory furnaces and multiple-hearth furnaces have been operated with the entire fumes discharged into a small room and no odor of these gases was discernible, even when the operation was continued

. for many hours.- "The Hall process of desulphurizing, sulphide

ores..•..is based on the principle of removing; the 1 fixed* sulphur atom of a sulphide by distillation and without permitting any considerable portion of the sulphur thus discharged to pass into any of the combined forms, such as S0 or SO*.

• ".....gas analyses have been made of the fumes discharged. These analyses have been made over continuous runs of several hours, and the total amount of combined sulphurous gas of any condition has been found to average under 0.25% by volume without the admixture of any extraneous air.

, "..... The distillation is obtained by the. directapplication to the ore of a burning-gas flame of slightly reducing or at least non-oxidizing character, accompanied by sufficient H?0, either in the shape of water of formation (from the combustion of hydrogen) or by the addition of small amounts of

; extraneous water in the shape of steam. This H«0, ...... is decomposed by the hot ore, the nascentoxygen going to the metal and the nascent hydrogencombining with any free oxygen.... thus creating asort of cycle of HgO decomposition and water formation

(ioj Hall, W. A., The Hall Ore Desulphurizing Process,Engineering and Mining Journal, Volume 96, July 5, 1913,

; .p. 35. ; ■.. . ■ : ■ . ' : '.

6

from the combustion of the hydrogen so derived.It appears that nascent hydrogen has more affinity for oxygen than it has for sulphur.

"A large variety of ores have been experimented with, including pyrites, various pyrrhotites, copper concentrates, crude blende, zinc concentrates and even chemically pure FeS, the action appearing to be the same on each and the only difference being in the mount of sulphur discharged, according to the amount contained. In order to prove that the 'fixed* atom is removed by distillation, the furnace has been operated on chemically pure FeS, which, of course, contains no feeble or free atom and no SOp or HoS was discernible in the discharge, but only yellow elemental sulphur vapor.

“The temperature maintained in the furnace must be slightly above 700 C., as that is about the distillation point of the S of a metallic sulphide, and it must be maintained below 900 0., the fusing point....

“The calculation of the cost of producing sulphur by this method in American smelting works is placed at from $3 to $5 per ton of the crude sulphur derived .** 'Later references reveal that at the Balaklala smelter,

at Coram, Shasta County, California, during July, 1913, an experimental plant composed of two McDougall roasters was contemplated. The plans indicated that one of the furnaces was to be heated with oil, the other with a fixed oil gas fuel."^" A brief note in October, 1915, stated: “The actualtests that were delayed by the incompleteness of the gasplant at the Coram works.....will be resumed.... soon.....*^Ho later reference with respect to the process was found.

(11) Engineering and Mining Journal, July 26, 1913, Volume 96, p, 188.

(18) Engineering and Mining Journal, October 11, 1915, Volume 96, p. 709.

7

Although the original object of the experimental work planned for this paper was to experiment with the possibilities of recovering metals from calcines produced by the Hall process, it developed that the writer was unable to obtain satisfactory sulphur recovery with the Hall process, and therefore the experimental work described is more or less concerned with verification of claims for the Hall process.

8

CHAPTER 2

Materials, Apparatus, and Experimental and Analytical Methods

The mineral used for the experimental work was chaleo- pyrite obtained from the United Verde Mine, Jerome, Arizona. It was fairly pure, containing only small amounts of pyrite and biotite. The chalcopyrite was crushed in a chipmunk jaw crusher, and ground in stages in a Braun pulverizer to approximately 35-mesh, and the minus 35 plus 80 mesh portion was used. . .- A sample of the material prepared as described was

placed in a pyrex glass or silica tube, and roasted in an 8-inch diameter electric combustion tube furnace. Temperatures were determined by a platinum, platinum-rhodium thermocouple equipped with a millivoltmeter, and were controlled by a rheostat and alternating current ammeter.

Various gases used in roasting comprised one or more of the following: Air, water vapor, nitrogen, sulphur dioxide, and natural gas. An analysis of the natural gas used follows:

Per cent by volume

Carbon DioxideOxygenNitrogen

MethaneEthane

82.0312.880.260.24.63

9

The rate of flow of gases except water vapor was governed by calibrated capillary tube flow meters. To supply water vapor to the furnace in governed amounts, a gas was passed at a known rate through a saturating bulb containing distilled water held at a definite temperature. Knowing the vapor pressure of the water at that temperature and the total gas pressure, then the volume of the water vapor may be determined frcm the fact that the ratio of the volume of water vapor to the total volume of gases is the same as the ratio of the vapor pressure of water to the total gas pressure. As the gases were forced through the heated ore, the possible gaseous products were sulphur, sulphur dioxide, hydrogen sulphide, nitrogen, oxygen, and water vapor.

The cooled and precipitated sulphur discharged from, the furnace was retained in a tube filled with asbestos fibre.The increase in weight of the moisture free tube filter represented the sulphur recovered. The hydrogen sulphide and sulphur dioxide were retained in an adsorption bulb filled with sodium hydroxide solution. The remaining gaseous constituents were not determined.

The total sulphur remaining in the roasted ore was determined by the standard acid barium sulphate m e t h o d , a s was the water soluble sulphur c o n t e n t . T h e sulphur content of the sodium hydroxide solution was determined by a standard method, using hydrogen peroxide as the oxidizing agent.

(l3) Low, Albert H., Technical Methods of Ore Analysis,John Wiley & Sons, New York, 1914, p. 239.

14) Ibid. p. 308.115) Scott, Wilfred W., Standard Methods of Chemical Analysis,

D. Van Nostrand & Co., New York, 1922, p. 511.

10

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18

• CHAPTER 5

Experimental Work Series 1

In the first series of experiments, air and water vapor were used as gases. The purpose of this series was twofold. First, to determine, by carefully controlling the amount of oxygen supplied, if the metallic constituents of the chaloo- pyrite could be oxidized, leaving the sulphur in elemental form. Secondly, to determine by the use of controlled volumes of water vapor if the water vapor acted as a catalyst, in the preferential oxidation of the metals.

The time of heating for this series varied from 2.5 to 5 hours. Temperatures used were 550, 650, 750, and 850 degrees C. At each temperature, four tests were made, one using air with no water vapor, and three employing air with increasing amounts of water vapor. Air was supplied at the rate of 50 cc. per minute.

Results are given in Table 1 and Graphs 1 and 2. Since the results obtained from tests made at 550 degrees C. were erratic with respect to total sulphur and water soluble sulphur contents, these results have been neglected in seme of the curves as indicated on the graphs.

13

Table 1 - Detailed data of series 1.

Test : Time,:Temp. No. : hours: °C.

WaterPressuremm.

Sulphur:SulphurRecovered

Recovered

grams :as SOg,Sulphur in ore, grams

WaterSolubleSulphur,grams: : ; :______ : grams

5 :: 4 550 - 0.34 2.25 0.78 0.456 : 5 550 16.8 0.34 2.27 0.80 0.457 2 3 550 149.4 0.31 2.07 0.95 0.269 2 2.5 550 289.1 0.26 1.83 1.21 0.4310 2 3.25: 550 610.9 0.53 2.02 1.02 0.3411 : 4 650 - 0.25 2.13 0.82 0.0612 2 3 650 149.4 0.26 2.07 0.66 0.0514 2 3 650 433.6 0.34 2.68 0.09 0.0215 2 4 650 610.9 0.58 2.68 0.08 0.0316 2 3.5 750 - 0.39 2.28 0.39 0.0217 2 3 750 149.4 0.38 2.74 0.06 0.0218 : 3.5 750 433.6 1.00 2.18 0.11 0.0219 2 3.5 750 610.9 0.36 2.63 0.12 0.0520 2 3.5 850 - 0.70 : 2.10 0.38 : 0.02 -22 2 3.75 850 149.4 1.04 1.96 0.37 0.0023 2 5 850 433.6 . 0.97 1.44 0.57 0.0224, 2

23.75 850 610.9 1.57 1.88 0.21 o.oo

The results of series 1 indicated that the recovery of sulphur tended to increase with higher temperatures as well as with greater partial pressuresof water vapor.

The total sulphur remaining in the calcine decreased markedly with increase of temperature, and reached a minimum at 750 degrees 0. Above this temperature the total sulphur of the calcine increased, indicating a partial fusion of the particles of ohelcopyrite and a consequent decrease in the extraction of sulphur. The total sulphur remaining in the calcine decreased more or less regularly with increased partial pressures of water vapor.

650 850

16

The water soluble sulphur of the calcine was apparently hot influences by variations in the partial pressure of water vapor, and aside from the temperature, 550 degrees C., was practically constant at the remaining temperatures. The increase in water soluble sulphur at 550 degrees was probably due to undecomposed sulphates.

Summarizing, the data presented for series 1 showed that the preferential oxidation of the metallic constituents of the chalcbpyrfte particles, which released free sulphur, was only partially complete and that water vapor acted in the roll of a catalyst.

Series 2

The tests of series 2 were made using natural gas and air in varying proportions. Theoretical products of the partial oxidation of methane, the principal constituent of

I \natural gas, are carbon monoxide, water vapor, carbon dioxide, and hydrogen as indicated in equations 4.and 5.

(4) 2CH4 ♦ 502 = 200 * 4HaO(5) CH4 + Og = COg * 2H2The water of combustion, according to Hall, would react

with ohalcopyrite. Any sulphur dioxide which might be formed would be reduced by carbon monoxide or hydrogen to elemental sulphur as indicated in equations 6 and 7.

(6) SOg + 200 = S + 2C0g(7) SOg + 2Hg = 2HgO ♦ S

17

In series 8, temperatures of 550, 650, and 750 degrees C. were used, and 850 degrees 0. was attempted, tut resulted In slight fusion of the ohaloopyrite. Ratios of natural gas to air used were 1/3, 1/6, 1/10, 1/12, 1/16, 1/20. Results of series 2 tests are shown in Table 2, and in Graphs 5 and

Table 2 - Detailed data of series 2.

TestNo.

Time, hours

Tgmp.,: iSulphur::Ratio,: Reoov- :Gas to: ered,: Air : grams : :

Sulphur Recovered

as S02, grams

Sulphur in ore, grams

WaterSolubleSulphur,grams

1 6 550 ; 1/3 : 0.39 2.11 0.78 0.473 5 650 : 1/6 : 0.46 2.78 0.04 0.026 4.25 550 : 1/6 : 0.54 2.20 0.24 0.219 6 750 ; 1/6 : 0.81 :i 0.78 0.36 0.0010 5.75 750 2 1/10: 0.88 1.10 0.28 0.0011 6 750 2 1/12: 1.37 1.23 0.26 0.07 ;12 6 750 2 1/16: 1.03 : 1.07 0.21 0.0413 4 750 2 1/20: 0.95 1.33 0.13 0.0214 6 550 2 1/12: 0.60 1.14 0.63 0.3715 7 650 2 1/12: 0.80 2.23 0.51 0.0718 8 750 2 1/16: 1.03 1.78 0.85 : 0.0019 6 550 * 1/16: 0.39 2.07 0.98 : 0.4921 5 550 2 1/20; 0.40 2.21 0.92 : 0.55: :____ : : :

The results of Series 2 indicated that the recovery of sulphur tended to increase with higher temperatures employed. The sulphur recovery also improved with an increasing proportion of air to gas until it reached a maximum at the ratio 1/12, and thereafter decreased. The recovery of sulphur at various temperatures when employing natural gas was greater than that obtained by using water vapor, as indicated on

/?&/'o .

G

20

Graph 3. The fact that some fusion tdok place at 850 degrees when using natural gas and air, and only slight fusion took place with air and water vapor at this temperature, may be explained-by local overheating due to the burning of natural gas in contact with the ohalcopyrite particles.

The amount of sulphur recovered as sulphur dioxide decreased with increasing proportions of air to gas until the ratio l/l2 was reached, afterjwhich it remained about constant.

..The sulphur remaining. in the calcine increased with an increasing proportion of air to gas, and reached a maximum at a ratio of 1/12.

- The amount of water soluble sulphur, as in Series 1, was solely dependent upon the temperature.

-Summarizing, the extraction of sulphur and the amount of sulphur combined as sulphur dioxide decreased, and the recovery of sulphur increased, with increasing ratios of air to gas until a ratio of about 1/12 was reached. With greater ratios than 1/12, the extraction was less, recovery was.less, and the amount of combined sulphur was about the same.

Series 3

Series 3 was run using air and water vapor for gases as in Series 1. However, instead of varying the. temperature of the. furnace and the degree of water saturating the air, as in Series 1, the temperature of each test was 650 degrees, and the degree of saturation was about 149 millimeters of partial

21

pressure of water vapor, the only variation being in. the rate of flow of air. TJiis was varied between 25 and 200 cubic centimeters per minute in 25 cubic centimeter steps. Results given in Table 3, are erratic.

Table 3 - Detailed data of series 3

• :: / . ■ : I : Sulphur. i WaterTest Air, : cc/min.:

Time, Recov : Recov- : S in SolubleNo. hours ered, : ered :Calcine, S in

: grams :as S02, : grams Calcine,: : grams 2 grams1 :100 : 5 0.73

:: 1.93 2 0.73 0.312 125 : 5 0.70 : 2.35 2 0.46 0.225 150 : 4 0.54 : 1.85 : 0.60 0.304 175 : 4 0.99 I 2.01 : 0.80 0.33‘ 5 ; 75 : 8 1.12 : 1.90 : 0.70 it 0.416 200 : 4 0.94 : 1.77 : 0.93 0.367 50 :: 8 0.53 : 1.06 2 1.32 0.368 25 : 8 0,59 : 0.17 : 3.02 0.12 .• • ' • • - - 2 ! 2 - ' -*

: ; In general, the results showed no particular change forvariations in the rates of flow of air and water vapor. Since no evidence of new disclosures was noted, the series was a- bandoned without an attempt at repeating the tests until the results became more continuous^

Series 4 - " .

Hall stated that the water *....•is decomposed by the hot ore, the nascent oxygen going to the metal and the nascent hydrogen combining with any free oxygen... It appears that nascent hydrogen has more affinity for than it has for

22

sulphur.” From, the previous three series, the theory was advanced that the sulphur as well as the metal content of the ore is oxidized. It was postulated that instead of the sulphur being distilled and remaining in the elemental form, as stated by Hall, the sulphur was oxidized to sulphur dioxide, and was subsequently reduced by the ehaloopyrite particles to sulphur, as well as reacting with hydrogen sulphide and carbon monoxide, if present.

To test this hypothesis, a series of experiments was made using nitrogen and sulphur dioxide as gases. The purpose of using sulphur dioxide was to eliminate the first reaction of oxygen with the ehaloopyrite to produce sulphur dioxide, and to determine if ehaloopyrite did reduce the sulphur-dioxide to sulphur. Results are given in Table 4.

Table 4 - Detailed data of series 4

16

Test : Time, No. : hours

:

Temp., °C.

Nitrogenoc/min

SO®, ;Sulphury oc/min.: grams

S as SO®, grams

WaterSolubleSulphur,grams

1 i 3 750 100 35 ; 2.60 i: 11.40 2.402 : 4 750 75 21 i 2.57 7.59 2.84. 6 : 4: ....

750 50 i! 5 : 0.56: :

1.94 2.02

This series of three tests indicated that the sulphur dioxide reacted with metallic sulphides to form sulphur, as more sulphur was recovered than was extracted from the chalco pyrite.

Tl6) Hall, T%. A., Ibid. '

23

A test was made similar to test number 6 in fable 4, except it was run in two periods of one hour each, with different sulphur filter tubes used for each period. The sulphur recovered in the second period was less than that recovered in the first. This indicated either a decreased distillation of the free atom of sulphur frcm pyrite as an impurity in the chalcopyrite, or a decreased chemical reaction due to surface alteration.

. Series 5

To determine what the rate of extraction would be on fine particles of chalcopyrite such as would be used in practise in a mechanically rabbled furnace, as well as to determine the ratio of sulphur, dioxide to free sulphur which might be expected in practice, a separate series was run. In this series, a test was made using an atmosphere of nitrogen. This was followed by a separate test in which nitrogen and sulphur dioxide were the gases employed. The increase in sulphur recovered in the roast employing sulphur dioxide over that employing nitrogen alone was considered as the amount obtained by the reaction of sulphur dioxide with the metallic sulphides. To determine the amount of sulphur which could be recovered by roasting a very finely divided chalcopyrite, extrapolation of results down to zero time was desired, but the results as shorn in table 5 and graph 5, while within the limits of error of the experimental method, particularly that of weighing

25

the sulphur tube filter with a triple beam balance, were practically useless for extrapelation purposes.

Table 5 - Detailed data of series 5

Test Time,co/min.

: SOc, . Typ;; : .so*.No. hours icc/iniii* «c. : grams : grams1 i 50

!-s : 0 750 : 0.61

:. : : 0.042 1 50 r '- '-5 - 750 : 0.81 r- 0.513 0.5 : 50 •t 0 750 $ 0.62 : 0.035 : 0.5 50 : 5 750 : 0.80 0.24

6 0.25 50 : 0 750 : 0.48 ! 0.027 0.25 50 5 750 ; 0.60 : 0.078 1 50 0 750 : 0.61 : 0.099 1 50 : 5 750 : 0.77 i 0.2910 0.5 50 : 0 750 : 0.66 : 0.0211 0.5 50 : 5 750 : 0.74 % 0.2412 0.25 i 50 : 0 750 : 0.57 : 0.0214 0.25 : 50 5 750 : 0.69 2 0.06

: r $ : i

Series 7A

In series 7A, the gases used were nitrogen and sulphur dioride as in Series 5. Instead of first determining the amount of sulphur obtained by roasting with an atmosphere of nitrogen, and then running a separate test using nitrogen sued sulphur dioxide as gases, the charge of chaloopyrite was roasted with nitrogen for a definite period of time, and then the residue was roasted for the same period of time with nitrogen and sulphur dioxide. Sulphur and sulphur dioxide were determined separately for the two testing periods. Sulphur recovery was determined bn a balance accurate to ten milligrams. Results are given in Table 6, and Graph 6.

Time, Hours

27

Table 6 - Detailed results of series 7A

TestNo.

Time,hours cc/min. cc/min. S,grams

as SOg, grams

2a 1 50 0 0.745 0.042b 1 50 5 0.095 0.41sa 0.5 50 0 0.515 0.043b 0.5 • 50 5 0.160 0.215a 0.25 50 0 0.540 0.015b 0.25 50 5 0.150 0.346a 0.25 50 0 0.605 0.036b 0.25 50 5 0.2557a 0.25 50 : 0 0.565 0.037b 0.25 50 5 0.145 0.734a 0.5 50 0 1.218 tr4b 0.25 50 5 0.190 0.2010a 0.5 50 0 0.595 0.0110b 0*5 50 . .. 5 0.116 0.12

Test 7B .

Subsequently, several tests were made consisting of four stages each. In the first stage nitrogen was passed for one hour through the chaleopyrite heated to 750 degrees. Then sulphur dioxide and nitrogen were passed through the chalco- pyrite in three stages of 15, 15, and -50 minutes. The rate of flow of nitrogen was 50 cubic centimeters per minute; where sulphur dioxide was used, the rate was 5 cubic centimeters per minute.

It was noted from the results that the second 15-minute period using sulphur dioxide resulted in more sulphur dioxide being retained in the caustic solution than was the case during the first 15-minute period.

28

A test was run by F. S. Wartman to determine the amount of sulphur dioxide which could be expected to be retained in the sulphur tube filter and thus not be included in the previous results. Results of this test were as follows:

Stage Time, minutes Sulphur as SOp1 60 Neglected2 • : , - 15 "' 0.01113 15 0.1080

; 30 0.0122Average - 0.0113

The figures used in column 7 of table 7 were obtained by adding the average figure frcm Wartman* s test to the figures of column 6 of the same table. Results are shown in Table 7 and Graph 7.

On addition of the average value to the results given in column 6 of Table 7, column 7 of the same table results.

Table 7B - Detailed data of series 7B

TestNo. Time,hours oo/Sin. oo/mtn. grams

; S in802,grams

S in S02, (Corrected) gramsda 1 50 — - 0.52m 0.609b 0.25 50 5 0.158 0.062 0.0733c 0.25 50 5 0.161 0.126 0.1393d 0.50 50 5 0.183 0.115 0.126311a 1 50 - 0.680 0.009 -b 0.25 50 5 0.113 0.062 0.0733c 0.25 50 5 0.115 0.120 0.1313d 0.50: 50 5 0.148 0.293 0.5043

Referring to tables 7A and 7B and the graphs 6 and 7, the results indicated that the recovery of elemental sulphur

50

was approximately equal to the recovery of sulphur as sulphur dioxide, and that surface alteration Imd hut slight Influence upon the rate of extracting the sulphur,

", Series 70

A test was made using water vapor and nitrogen as gases. Nitrogen was passed through the chaloopyrite for one hour after vtolch nitrogen, saturated with water vapor at 27 degrees C., was passed throu$i the residue in 4 periods of 15, 15,30, and 60 minutes respectively. Results are given in Table 8 , and in graph 8.

Table 8 -Detailed results of series 70

Stage ■ :■. : %0?ime,Min.

: Nitrogen, : oc/mln# ;:

Sulphur,grams : Sulphur as S0o, grams

- ■' " * ■ : - : :: ' a :■ 15 : 50 . : 0.079 : 0.063b : r: 15 : 50 : 0.032 ■ s 0.0080 : 30 : 50 : 0.058 ; 0.03660 : 50 : 0.083 : 0.055- : : !

Referring to table 8 and graph 8 , the results indicatedthat more elemental sulphur was recovered than that combined' ' ' ' . - : - ' - ' . .. . ' ::as sulphur dioxide• • However, the elemental sulphur recovered may be partly due to the continued distillation of the feebly held atom of sulphur in the impurity pyrite contained in the chaloopyrite particles, or to distillation of the sulphur content of the chaloopyrite over that required to form CugS and FeS. '. . " .

: : ; 9«rl®» 7D . ■ V ' . " .

Series 7D test vma made using air and. water vapor as gases. Nitrogen was passed through the ohalcopyrlte for one hour / after which airsaturated with water vapor at ZZ degrees C. was passed through the ohalcopyrlte in 4 stages of 15, 15/30, and 60 iQinutes fespectively. Results of the recovery of sulphur and sulphur dioxide in this test are shown in Table 9, and in Graph 9.

Table 9 - Detailed data - of. series 7D.

Stage Time, Nitrogen, : Sulphur, : Sulphur asMin. oe/min. ■'■-.'fflraas. ■: SO?. gramsa

... : . ■15 50 0.074 : 0.1565b 15 50 0.018 : 0.1147: 0 30 50 0.078 ! 0.2130

a 60 50 0.026 : 0.2948: - . ,

Referring to table 9 and graph 9, the results indicated that using air and water vapor, the amount of sulphur oxidized to sulphur dioxide was very much more than that which was recovered as elemental sulphur. These results were in contrast to those of tests using either water vapor and nitrogen, or sulphur dioxide and nitrogen, in which cases the recovery of elemental sulphur was higher than the sulphur oxidized to sulphur dioxide.

77/7

7,

Af/

ryc/

fes

54

Series 6

In series 6, gypsum or gypsum anhydrite was used either in the discharge side of the roasting tube or mixed with the chalcopyrite charge. Nitrogen, at the rate of 50 cubic centimeters per minute, was used in all tests. Water vapor was used in one test, and sulphur dioxide in the remainder. The results of this test are given in Table 10.

Table 10 - Detailed results of series 6

TestNo.

Time, hours

Gypsumused,grams

o o W • Sulphur,: Sgrams :as SOg, : grams S inCalcines,grams5 5 5 3.80' : 1.88 2.584 • 5 5 1.84 : 2.29 2.985 3 (G) 1 18.5 1.19 : 3.73 3.506 3 (G 2 12.5 1.10 : 3.70 3.537 3 (A) S 12.5 1.13 : 1.891 ' 4 (1)611 1.80 : 1.65

: 0.38

Gr - gypsum A - gypsum anhydrite(1) water vapor partial pressure, ram.

These results indicated that gypsum aided in the extraction of sulphur from chalcopyrite.

35

CHAPTER 4

Conclusions

1. Although the original object of the experimental work planned for this paper was the recovery of the metallic constituents of a calcine produced by the Hall process, it developed during the course of the experimental work that the recoveries of elemental sulphur obtained by the writer were so incomplete that verification of the Hall process became necessary, and therefore the experimental data presented deals only with attempts to verify claims made for the Hall process.

2. Briefly, the results indicate that the writer was unable to obtain appreciable commercial recoveries of elemental sulphur by the Hall process as he interpreted the process, but that the use of either water vapor or reducing gas did have a beneficial effect upon the recovery of sulphur as elemental sulphur from chalcopyrite.

3. Experimental results have been discussed in detail after presenting each series of tests.

4. Hall claimed that the recovery of elemental sulphur was from the preferential oxidation of the metallic constituents of a sulphide, and the direct distillation of the sulphur content. It is possible that Hall misinterpreted the situation and that the recoveries he obtained were due to the

56

atmosphere prevailing "being sufficiently reducing in the discharge end of the furnace to cause the reduction of sulphur dioxide to elemental sulphur. The reaction of a reducing gas such as carbon monoxide with sulphur dioxide to release sulphur is well known and relatively complete.^

117) Lewis, Gilbert Newton, and Randall, Merle., Thermo- ' dynamics and the free energy of chemical substances., p. 548. McGraw-Hill Book Co., New York, 1923.