Biological Oxidation of Copper Sulfide Minerals

Brigham Young University BYU ScholarsArchive

Theses and Dissertations

1953-12-01

Biological oxidation of copper sulfide minerals

Delmar Boyd Davis Brigham Young University - Provo

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BYU ScholarsArchive Citation Davis, Delmar Boyd, "Biological oxidation of copper sulfide minerals" (1953). Theses and Dissertations. 8197. https://scholarsarchive.byu.edu/etd/8197

This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. BIOLOGICALOXIDATION OF COPPER SULFIDE MINERALS

A THESIS SUBMITTEDTO THE FACULTYOF THE DEPARTMENTOF CHEMISTRY BRIGHAMYOUNG UNIVERSITY

IN PARTIAL FULFILLMENT OF THE REQUIREMENTSFOR THE DEGREE MASTEROF ARTS

by DELMARBOYD DAVIS December., 1953 This Thesis by Delmar Boyd Davis is accepted in its present form by the Department of Chemistry as satisfying the Thesis requirement for the degree of Master of Arts.

Si gned ,

/ ACKNOWLEDGMENTS

The author wishes to take this opportunity to gratefully acknowledge the assistance of Dr. Loren C. Bryner in the planning and execution of this study. I wish to acknowledge Dr .• Jay V. Beck of the Bacteriology Department for the helpful suggestions regarding t he problem and the microorganisms used in the study. The sug gestions of the faculty of the Department of Chemistry are gratefully acknowledged. The author wishes to acknowledge the aid of the Utah Copper Division of the Kennecott Copper Corporation for support- ing this work. And to my wife, Marie, whose patience and inspiration contributed greatly to the completion of this work, I give my sincere thanks.

iii TABLE OF CONTENTS Page

LIST OF TABLES •••• . . . . . • • • • • • • • • • • V LIST OF ILLUSTRATIONS. . . . . • • • • • • • • • • vi Chapter I. INTRODUCTION.• . . • ...... 1 II. BASIS OF THE PROBLEM•...... 6 III. APPARATUSFOR THE PROBLEM ...... 9 IV. MICROORGANISM:SUSED IN THE STUDY.• . . . . . 12 v. METHODSOF ANALYSIS • • . . . . . • • • • 14 VI. EXPERIMENTALPROCEDURES AND RESULTS . 17 EXPERIMENTALPROCEDURE RESULTS Biological Oxidation of Chalcopyrite Biological Oxidation of Sorne Other Copper Sul.:('ide Minerals Bioiogical Oxidation of Reagent Grade Copper Sulfide Biological Oxidation of Bingham Canyon Float Concentrate Effect of Hydrogen Ion Concentration on the Leaching Action Ammonium Ion Studies Rate Studies of the Biolog ical Action VII. DISCUSSION OF RESULTS...... 39 BIBLIOGRAPHY...... • • • • • • • • • 41

iv LIST OF TABLES Table Page 1. Principal Copper Sulfides • ...... 2 2. Some United States Porphyry Copper Mines •••• 4 3. Nutrient Media for Microorganisms ••••• . . . 13 4. Biolo gical Oxidation of Chalcopyrite No. 1 . . . 19 5. Biological Oxidation of Chalcopyrite No. 2 19 • 6. Biological Oxidation of Other Sulfide Minerals • 23 7. Biological Oxidation of Reagent Grade CuS 28

8. Biological Oxidation of Bingham Canyon Float Concentrate ..•..••••.•..•• 31 9. Effect of pH on Leachin g Action. 31 10...... 34 11. Influence of Ammonium Ion Concentration on Biological Oxidation ••..••.•. 35

12. Hourly Soluble Copper. 37

V LIST OF ILLUSTRATIONS Figure Page 1. Air Lift Percolators ...... 11 2. Biological Oxidation of Chalcopyrite No. 1 • . . 20 3. Biolo gical Oxidation of Chalcopyri te No. 2 . . . 21 4. Biological Oxidation of Covellite ...... 24 5. Biological Oxidation of c'alcoci te ...... 25 6. Biolo gical Oxidation of Bornite ...... 2'6 7. Biological Oxidation of Tetrahedrite ...... 27

8. Biolo gical Oxidation of Reagent Grade CuS • . . 29 9. Biological Oxidation of Bingham Canyon Float Concentrate ...... 32 10. Effect of pH on Leaching Action ...... 33 11. Influence of NH Concentration Biolo gical 4+ on Oxidation ...... 36 12. Rate Study of Biological Oxidation . 38

vi CHAPTER I

INTRODUCTION

Copper is becoming increasingly important in maintain- ing our high standard of living. Methods of alloying it with other metals give an ever increasing horizon in which copper may be used. The advance of our technolo gical age with its industrial development creates an ever increasing demand for copper. Communication, household, industrial and military equipment consume more and more copper and its alloys each year. Copper is a heavy metal of characteristic color. This rudd y metal is ver y ductile, malleable and flexible, and is also fairly tou gh and strong. Copper has an atanic weight of 63.54, an atomic number of .29, and a specific gravity of 8.93 - 8.95. It is a very good conductor of heat and electricity and withstands corrosion. 1 Copper has been used since prehistoric time. It is believed that native copper has been mined for over five thou- s~nd years. 2 Native copper is found today in small amounts in several places in the world, 3 and some is still obtained from these sources.

1c. D. Hodgman, editor, "Handbook of Chemistry and Physics," 34th ed., Chemical Rubber Publishing Co., (1952),p.314. 2Ibid. 3Mack, et. al., "Text Book of Chemistry," Ginn and Company, New York, 1949, p. 662. 1 • 2 The importance of native copper in the production of the metal in the world toda y is very small. Copper is mostly obtained through the mining of ores containing its salts. The great bulk of the world's commercial copper is obtained today from the sulfide minerals.4 Many of which are ver y complex in nature. Copper sulfides usually contain other metals. The most common of these metals are iron, antimony and arsenic. These with others are combined together in a composition so varied that they are often referred to simply as cupriferous pyrite ores.5 TABLE I PRI NCIPAL COPPER SULFIDE MINERALSa

Name Formula Percent of Copper

Chalcocite Cu2S 79.8 Covellite CuS 66.4 Bornite Cu.5Fes 63.3 4 Enargite cu Ass 48.3 3 4 Chalcopyrite CuFes 2 34.5 Tetrahedrite Cu sb s 52.3 8 2 7

aErnest R. Lilley, "Economic Geology of Mineral Deposits," 2d ed., Henry Holt and Company, New York, 1938, p. 454. 4rb id. , p • 45 3 • 5Ibid. 3 The leadin g sulfide minerals from which copper is obtained in the United St ates are listed in Table 1. Copper produced fro m such ores show a continuous advance throu gh the years. Fro m some of t he latest yearl y data we find t hat in 1950; 909,343 tons of copper were produced from ore in the United States. 6 The ore fro m whi ch the co pp er was recovered had an avera ge of 0. 89 percent in 1950. 7 There has been an almost continual decrease in the percentage of copper found in the ore mined in t he last twenty years. Fi gures from the Bureau of Mines show an avera ge decrease from 2.11 % in 1933 to 0.89% 8 in 1950. This continual decrease in quality of ore has not gone unnoticed. Only throu gh the development of new methods along with the improvement of old methods is high production ac hieved. Due to the low qualit y of the ore, about 95% of all copper ore in t he United States is concentrated before it is sent to the smelter. 9 Present minin g techniques must also be changed to pro- duce lar ge volumes of the low grade ore cheaply. Open pit and cavin g methods are bein g extended to ac hieve quantity production.

6uni ted St a tes Department of ..,the Interior, "Minerals Yearbook, 1950, 11 United States Government Printin g Office, Washington D.C., 1953, p. 470. 7rbid. 8rt ia... ., 9A. M. Bate man, "Econo mic Mineral Deposits," 2d ed., John Wile y and Sons, Inc., New Yor k , 1950, p. 484. 4 Many of the main producing mines are, or could be, worked by the open pit method. This is possible because of the large quantity of ore lyin g relatively close to the surface of the ground. Some of these mines with their respective capa- cit y , ore depth, depth of overlay, and tennor of the ore, are 10 listed in Table 2.

TABLE 2

SOME UNIT ED STATES PORPhrRY COPPER MINES

Name Percent Annual Capacity Average Ore Thickness Copper Short Tons Cu Cap (feet) (feet)

Utah Copper 0.9 320,000+ 115 2,500 Nevada Copper 1.4 50,000 150 600 Consolidated 1.4 20,000 100 200 Copper Mines

Ray 1.6 16,000 250 150

Chino 1.22 75,000 150 700

New Cornelia 0.7 150,000 55 425 Miami 0.9 26,000 250 300 Insperation 1.3 30,000 250 300 Clay 0.99 150,000 220 850 Bagdad 1.4 150 100 San Manuel 0.7 8 .... 600 900 Castle Dome 0.7 25,000 50 135

These data show that it is necessary to move great quantities of low grade ore and rock to obtain free access to

lOibid., p. 487. 5 the richer ore. This overlay or cap, as it is called, consists of low grade ore. This is removed and p laced in large dumps in the vicinity of the mines . Waters flowing through these waste rock dumps are high in acidity and contain considerable quantities of iron and copper. The copper is removed by dis- placement fro m solution with scrap iron. This reaction takes place because of the relative positions of the iron to the copper in the electromotive series.

This leac hi n g process has become an important source of copper. Due to the gradual decrease in high g rade copper ore, it is possible that this process will play an ever in- creasin g role in the production of copper in the United States. CHAPTERII

BASIS OF THE PROBLEM

Until recently it has been assmned that molecular -~ oxy gen from the air was responsible for the oxidation of py- '? -, ,\ .., rites. This would account for the presence of soluble iron and copper in the acid mine waters and for the weathering of surface ores. Investigators working with pyrite ores report that the oxidation is very slight under c on trolled conditions. Ursenbach 1 and Jensen 2 both report that less than two-tenths of one percent of the pyrite sample used underwent oxidation. Carmichel3 supports these findin gs on pyrite and in addition reports that after thirteen days of continuous agitation in the presence of water and oxy gen, only two - hundreths of one percent of chalcop yr ite underwent oxidation. Mechener and Yates4

1ursenbach, "Factors Influencing the Moist Oxidation of Iron Pyrites," (Unpublished Master's Thesis, Department of Chemistry, Brigh am Young University, 1948). 2Jensen, "Factors Influencing the Solubility and Oxi- dation of Commercial Iron Pyrites," (Unpublished Master's Thesis, Department of Chemistry, Br igham Young University, 1949). 3carmichel, University of Toronto Studies, Geological Services, (1926). 4c. E. Michen er and A. B. Yates, Economic Geology, 39, (1944), pp. 506-514.

6 7 found that although other nickel and iron containing ores changed considerably on lon g exposure to air, chalcopyrite showed only a sli ght change. It would appear from these reports that the presence of copper in the acid waters coming from the mine dumps could not be caused by the oxidation of molecular oxy gen reacting directly on the copper bearin g pyrite ore. The presence of iron and sulfuric acid in certain coal mine waters has been studied by Leathen5, 6 and co-workers. Their results indicate that the iron and acid in coal mine waters was due to the oxidation of sulfuritic material by mi croor ganisms in the mine waters. Beckwith 7 has reported the action of certain Thiobacilli on iron sulfide. The pH studies in his work show the possibility of oxidative action on iron pyrite, c halcopyrite, marcasite , and pyrrhotite, by micro- or ganisms. Wils on8 separated a culture of microorganisms from the mine waters of Bingham Canyon, Utah. He showed that the oxidation of iron pyrite was largely due to biological action. He also demonstrated that the micr oor ganisms could tolerate copper ion concentrations up to 1500 ppm.

5Leathen, Braley , and McIntyre, Applied Micr obiology, I, (1953), pp . 61-64. 6Ibid., pp. 65-68. 7T. D. Beckwith, Gas, 21, No. 12, (1945), pp. 47-L~8. 8wilson, "Studies on the Biolo gical Oxidation of Iron Pyrite," (Unpublished Master 's Thesis, Department of Chemistry, Brigham Young University , 1952). 8 At Bingham Canyon, Utah, the copper in the mine waters comes from leachin g of porphyry type mineral deposits. Inasmuch as the oxidation of these materials by molecular oxygen has been reported as very slight, the oxidative process is probably due to biological action.

Therefore, it is the express pu rpose of this study to dete~nine the role of the mine water microorganisms on the oxidation of these copper sulfide minerals. It was desired to see if the copper ore was dissolved by the leac h in g action of the sulfuric acid in the water or through t he oxidation of sulfide min erals by microorganisms. Also to determine how the oxidative process could be controlled. CHAPTERIII

APPARATUS FOR THE PROBLEM

The apparatus used in this investi gation was developed by Wilson 1 in his stud y on pyrite. It consisted of an air-lift percolator constructed from 30 or 40 mm glass tubing and was approximately 200 mm in len gth. The tube was constricted at one end, and a perforated porcelain disk resting on the bottom he~d the samples in th e l ar ge t ube. An exterior circuit was made of 5 mm glass tubing and attached to a controlled source of compressed air. This served as t he lifting mechanism. A one-holed rubber stopper fitted wit h a 100 mm calcium chloride tube filled with cotton plu gged the top of the percolator to keep out forei gn material. Figure 1 is a photo graph of the apparatus used. Air re gulated at constant pressure was bubbled throu gh an aerator containin g distilled water to reduce the amount of eva p oration fro m the percolators. The air was then passed throu gh a cotton filled 20 X 200 mm glass tube to purify the air. Then it was passed into a gas distributin g tube and from there into the percolators. The air for eac h percolator was controlled by pinch clamps placed on t he rubber tubin g comin g from the gas

1Wilson, .££• cit., pp. 14-17.

9 10 distributin g tube. Once regulated the percolators needed very little atte n tion.

The sample to be analyzed was suspended in Ottawa sand.

This sand is inert che mically, and serves as a dispersing a g ent for the finely divided pyrite. It also furnishes a surface for the bacteria to grow on. 11

Fig. 1.--Air Lift Percolators CHAPTER IV

MICROORGANISMS USED IN THE STUDY

The microor ganisms used in this study were taken from the same culture used by Wil son. 1 In order to insure an active culture of the or ganis ms for this study, the culture was allowed to grow freely on iron pyrite. An air-lift percolator was used to make t hi s possible. The percolators were charged in the same way as those used throughout this study. About every two to three months as t he pyrite was used up in one percolator, a new one was set up and sterilized. Then the newly char ged percolator was inoculated from the old one, which was discontinued. In this manner cons tant active cultures were maintained throu ghout the study. The nutrient media was the same as used by Leathen in his work. 2 The composition is gi ven in Table 3. This media was used in nearly all of the work done in this study. To maintain the tolerance of the microorganisms to copper, five hundred ppm of copper ion was added in the form of cupric su lfate to the solution in Table 3. Organis ms grown in this solution were able to tolerate t he co pp er ion in the solutions obtained in this investi gation.

1 Ibid • , p • 8 •

2Leathen, McIntyre, and Braley, Science, 114, pp. 280, 281, (1951).

12 13

TABLE 3 NUTRIENTMEDIA FOR MICROORGANISMS Component Amount

Ammonium sulfate, • • • • • • • • • 0.15 g

Potassium chloride, KCl •• • • • • • • • • • • • • 0.05 g . . • • • • • • •• 0.50 g Potassium hydrogen phosphate, K HPo .. • 0.05 g 2 4 • • • • • Calcium nitrate, Ca(N0 ) • • •• 0.01 g 3 2 • • • • • • • • • Distilled water •••• • . . . . . • • • • • 1000 ml CHAPTER V

METHODSOF ANALYSIS

To follow the oxidative process, it was necessary to analyze the solutions for the ions formed. The usual products found in solution from the min erals used in these experiments were sulfuric acid and the ions of copper and iron. The concentration of the acid was followed by pH measurements . Determination of iron. - Iron was determined by a meth od given by Scott. 1 This is an accurate, rapid, volumetric method . Ferrous iron in solution is titrated with potassium dichromate solution. An indicator solution of barium diphenyl- aminesulfonate2 gave a very sensitive end point. To insure consistent accuracy, the potassium dichromate solutions were checked frequently against standard iron wire. Procedure for the iron determination. - Solutions taken from the percolators were treated with two ml of concentrated hydrochlor ic acid and heated to boiling. To the clear, yellow colored, solution obtained , a stannous chloride solution,

{6g SnC12 in 60 ml HCl, 40 ml H20), was added drop by drop to

1scott, "Standard Methods of Chemical Analysis," Vol. 1, D. Van Nostrand and Co., Inc., New York, 1938, p. 473. 2Pierce and Haenisch, "Quantitative Analysis,n 3rd ed., John Wiley and Sons, Inc., New York , 1948, p. 490. .. 15

a three drop excess over the amount needed to dissipate the iron color. An equation for this reaction is as follows -:

2Fe~++ + sn++ ---➔ 2Fe++ + sn++++. After cooling in a cold water bath, 15 ml of a satu- rated mercuric chloride solution was added to oxidize any re- maining stannous chloride. The reaction is as shown below -:-

SnC12 ~ 2HgC1 2 --➔ SnC14 + 2HgCl. Meeurous chloride formed as above does not interfere with the reaction. Fifteen ml of sulfuric acid - phosphoric

acid solution, (150 ml H2 S04 , 150 ml H3 P0 4 , 700 ml H2 0), were added, followed by drops of the diphenylarninesulfonate indicator. This solution was diluted to 200 ml and titrated with constant stirring to an intense purplish or violet color. The reaction for the analysis is as follows:

Determination of copper. - The determination of copper was accomplished by the use of a Beckman Flame Photometer (Model DU). This instrume nt provided a very dependable and •rapid means of analyzing for copper in solution. The flame photometer was used at a wave lengt h of 325.8 mu and a slit width of .418 mu. The oxygen was set at the pressure of 32 inches of water with the air pressure at 15 lbs. per square inch. A standard solution of 100 ppm copper

ion was used as 100 percent• transmissence. At this concentration 16 the Beckman Flame Photometer can give an accuracy of better than five percent.3 Procedure for the copper determination . - By using a standard solution of 100 ppm copper ion as 100 percent transmissence , a calibration curve was made of concentrations between zero and 100 ppm copper ion. This curve was determined with the instrument settin g s listed above. These proved to give the maximum optical density for the wave len gth used. The solutions to be analyzed were carefully subjected to the same conditio ns as those used for the calibration curve. When the transmissence of the unknown solution was compared to the curve the cor responding concentration could be read directly. The solutions to be anal yzed were diluted to a constant volume of 100 ml. Care was taken to adjust the pH to that of the standard solutions since the pH value is known to affect the trans mission reading. Determination of pH values. - ~he pH values were deter mined by a commercial pH meter usin g a glass electrode. Standard buffer solutions were used to check the electrode. These values were used to follow the reaction and control conditions for the other determinations.

3willard, Merritt , and Dean, "Instrumental Meth ods of Analysis," 2d ed., D. Van Nostrand Company, Inc., New York, 19.51, p. _50. CF..APrER VI

EXPERJJ,,1ENTAL PROCEDURESAND RESULTS

Experimental Procedure

The air-lift percolators were charged with 190 g of

Ottawa sand mixed with 1 or 10 g of finely divided ~Jperal, ---- depending upon the experiment. The charged percolators and the copper free nutrient media (Table 3) at different hydrogen ion concentrations were sterilized in an autoclave at 140° C for thirty minutes. The percolators were attached to the sterile air source and 50 ml of media were transferred asepticly into each percolator. From this point on every precaution was taken to avoid contamination of the controls. Half of the percolators were inoculated from the culture growing on pyrite in the presence of 500 ppm copper ion. The other percolators were run as sterile controls.

At the end of seven days the solutions were drained from the apparatus for analysis. The content of the percolator was rinsed with three, five ml portions of sterile media and 50 ml of fresh media were transferred asepticly into each percolator. The apparatus was run again for seven days and the process repeated.

When each solution was drained from the percolator for anal y sis the pH value was checked. The solution was then

17 18 diluted to 100 ml at the desired pH and aliquots were taken for analysis. The results of the experiments are recorded in the tables and represented graphi cally. Results Biological oxidation of chalcopyrite. - Two chalcopyrite samples were used in the exp eriment; one containing mor e iron than copper, the other more copper than iron. The chalcopyrite samples were obtained throu gh the courtesy of Mr . Zimmer l y of the Utah Copper Division Kennecott Copper Corpora- tion. Analysis of chalcopyrite No. 1 showed that it contained 20.2 percent copper, 35.9 percent iron, 33.54 percent sulfur, and 10.36 percent insol and others. Chalcopyrite No. 2 tested gave the analysis of copper 32.15 percent, iron 18.55 percent, . sulfur 33.45 percent, and 15,85 percent insol and other. Teng of each of the chalcopyrite samples were run according to the general procedure given. Chalcopyrite No. 1 was run in a media at pH of 3 and the results are recorded in Table No. 4 and Figure No. 2. The Chalcopyrite No. 2 was tested in media at a pH of 2. The results are found in Table 5 and l?igure 3. After seventy days the cumulative soluble copper from the inoculated percolator was 56.5 mg and that from the sterile control was 3.54 mg. The pH readings of the inoculated percolator showed a consistent decrease each week, while those of the sterile control increased each week . Bi olo gi cal oxidation of some other copper sulfide minerals. - Several of the co1Tu~oncopper sulfide mine rals were 19

TABLE 4 BIOLOGICALOXIDATION OF CHALCOPYRITENO. 1

-...I I-R0cula ted ii!:,!!!e: B~,- Sterile Control Time in Days pH Cumulative pH Cumulative Soluble Copper (mg) Soluble Copper (mg)

7 2.16 3.2 3.8 .6 14 2.35 _5.6 4.1 1.0 21 2.15 8 .3 3.7 2.0 28 1.8 15.0 3 .l~ 3.0 35 1.9 23.3 3.4 3.0 42 2.2 32.6 3.2 3.0 49 2.2 41.0 3.6 3.2 56 2.2 48.8 3.4 3.2 63~:- 2.2 56.3 3.6 3.54

70 2.6 56.5 • • • 3.54 ~}Autoclaved

TABLE 5 BIOLOGICALOXIDATION OF CHALCOPYRITENO. 2

Cumulative Copper (mg) Cumulative Iron (mg) Time in Days Inoculated I noculated 28t ~J2 ay Sterile 28th Day Sterile

\I; 14 9~4 ✓ 8.1 1.0 1.0 2t) 16.6 16.2 1.3 1.5 42 68.8 20.9 2.3 1.5 56 160. 8 25.0 20.0 1.8 70 192.8 26.2 3~.o 2.0 84 229. 8 29.1 43.4 2.4 20

70 0 Inoculated

• Sterile Control 60

bD 13 -~ 50 s.. co ~ 0 t) 40 G) -~ "'& 13 30 0

1'1mein Days ~. 2.-- Biological Oxidation of Chalcopyrite No. 1 21

InocuJ. ated 28t1~ j)c_~· Steri le Co!ltrol

280 o Copper

• Iron 240

~ 200 -~

+>t) .g 0 160 it «> ~ ~ ~ ]20 8

40'

0 ~•~t.1:::::::::L-L..-L...... L.----L----L----1-~IIA=:t::::a::c::::IR:=:::dt:::::c:R:c:::L.....1..-.L.....J b 20 40 6o Bo 0 . 20 40 6o Bo

Time in Days \ - Fig. 3.- Btological Oxidation of Ghalcopyrite No. 2 22 obtained through the courtesy of Dr. Keith Rigby of the Depart- ment of Geolo gy, Bri g ham Youn g University. These minerals were hi gh grade museum specimens and in all cases were representative of the species. Cove l lite (CuS), chalcocite (Cu s), bornite (cu Fes ), 2 5 4 and tetrahedrite (cu sb s ) were the minerals tested. They 8 2 7 were ground ina porcelain mill to a particle size that would pass through a 60 mesh screen and yet the large portion was re- tained on a 200 mesh screen.

Two charges of eac h mineral were placed in the percolators. The c h ar g e consisted of one gram of the mineral and

190 g of Ottawa sand. The char g ed percolators and nutrient media adjusted to a pH of 2 were sterilized in the autoclave, inoculated and tested as described b efore. The other percolators were held as sterile controls.

The results of the experi ment with these copper sulfides are recorded in Table 6. Results of the or ganis ms on covelli te are also shm ·m in Fi gu re 4; while ~lcoci te, borni te and tetrahedrite can be found in Fi gures 5, 6, and 7 respective- ly. They all showed p ositive action.

Biological oxidation of reagent grade copper sulfide. -

Since covellite and ~lcocite do not contain iron to any extent, it was dee med a dvisable to test a copper sulfide which was free from iron. Rea g ent grade cupric sulfide was used. The analysis from the manufacture indicated that the maximum limits of im- purities were; alkali salts 1.0 %, chloride (Cl) 0.01 %, and iron (Fe) 0.10 %. '

-I- TABLE6 BIOLOGICALOXIDATION OF OTHERSULFIDE MINERALS

Cumulative Soluble Copper (mg) Time in Covellite c§.1cocite Bornite Tetrahedrite

Days Inoc. Sterile Inoc. Sterile Inoc. Sterile Inoc. Sterile

I\) 7 13.5 4.6 12.0 6.o 15.o .8 . 8 0 vJ 14 39.0 10.1 23.4 12.8 23.0 2.2 1.7 0 21 79.0 14.1 52.4 19.0 31.0 2.6 2.1 0

28 112.0 17.7 83.4 26.6 38.0 3.9 2.9 0 35 126.4 20.5 91.4 33.8 41.4 4.7 2.9 0 42 134.s 22.4 99.6 39.2 46.1 5.1 2.9 0 24

0 Inoculated

• Sterile 120

-~100 r.. (I) ~ 0 80

0 W;::::;;;.._....,11..... __ ...... ____ -'----"""----a.....-----,1----- 0 7 21 28 35 42 - Time in Days j Jig. 4.-- Rl.ological Oxidation of Covellite 25

O InOCl''.la ted

120 • Sterile

b.O s 100 -~ M (I) & 0 0 80

(I) ~

60 10

0 0 10 20 30 40 50 60

. Time in Days Fi g . ~.--B:Lolo~ical Oxidation of cli.lcocite 26

70 o Inoculated

• Sterile 60

~ 50 -.~ H (I) g; 0 0 40 Q) I> •rl 16 30 10

'1'1.mein Days

Fig. 6 ~-- Bi.ological Oxidation of Ibrnite 27

3 o Inoculat ed

• St er ile

l 0

(

\ 0 7 21 28 35 42 Time in Days

Fig. 7 .- Biolo gical Oxidation of Tet.rahedrite 28 A charge of one gram of CuS was mixed with 190 g of Ottawa sand and this to gether with the nutrient media adjusted to a pH of 2 was sterilized and tested in the usual manner. TABLE 7 BIOLOGICAL OXIDATION OF REAGENTGR.tillE CuS

Inoc u lated 17th Day Sterile Control

Ti me in Days Cumulative Cumulative Soluble Copper 6:ng)Time in Days Soluble Copper (mg)

7 7.8 7 8.2 14 14.8 l~- 15.2 21 19 .2 21 20.8 25 23.0 28 25.6 32 41.0 35 28.6 35 55.0 42 30. 6 39 69.0 49 31.6 46 89 .0 56 32.6 52 112.0 63 33.6

55 135.0 • • • • • • 60 153.0 ...... 67 172.5 ......

73 182.5 • • • • • •

The results recorded in Figure 8 and Table 7 show that after 60 days 153 mg of copper had gone into solution from the inoculated s ample whereas only 33 mg had dissolved in the control. The pH re mained fairly constant indicatin g that copper sulfate was being formed. 29

21'.j o Inoculated 17t.";1 ..Jay

• Sterile Control 180

~ :.;:J -~ H Q) ~ 0 l2CJ b Q) ~ ~ r'I § 90 0

0 ~----L. ___ _.______.___ .....______....______0 28 42 70 84

Time in Days

Fig. 8 .- Bi.ological Oridatj_on, of Reagent Grade CuS 30 Biological oxidation of Bingham Canyon Float Concen- trate. - The concentrated ore from Bi ngham Canyon, Utah, con- tains most of the minerals used in t his study. However, the principal minerals are chalcopyrite and chalcocite. The concentrate used in the study came from the Arthur mill of the Kennecott Copper Corporation in March, 1952. It had a composition of 29.67 percent copper, 22.00 percent iron, 27.52 percent sulfur, 18.11 percent insol, and 1.74 percent molybdenum sulfide. Ten gra ms of the sample were mixed with 190 g of Ottawa sand and run in a nutrient of pH of 2 by the procedure described. The results can be found in Table 8 and are illus- trated in Figure 9. The cumulative soluble copper from the inoculated sa mple at the end of 98 days was over 5 times as much as that from the sterile control. Because of the extremely small particle size of the float conc ent rate, it is likely that some particles were p0ptized and carried off in the solutions to be analyzed. Effect of hydro1,en ion concentration on the leaching action. - A series of eight percolators were charged with 10 g Chalcopyrite No. 1 and 190 g Ottawa sand. These were sterilized and run in the usual manner. Two samples were run at each of four initial hydro gen ion concentrations as follows: PH's of 1.0, 2.0, 4.0, and 6.5. One percolator at each pH was inoculated and the other was run as a sterile control. The total cumulative copper after 90 da ys is recorded in Table 9 and Figure 10. 31

TABLE 8 BIOLOGICALOXIDATION OF BINGHAMCANYON FLOAT CONCENTRATE

Cumulative Copper (mg) Cumulative Iron (mg) Time in Days Inoculated Inoculated Sterile Sterile 21st Day 21st Day

14 19.5 18.2 2 .5 2.0 28 50.2 42.9 2.5 2.5 42 169.2 65.2 8.6 2.9 56 314.2 86 .0 20.9 3.7 46 6 .2 108.6 27.6 4.1 70- . 84 6,36.2 131.5 34. 7 4.8 98 775.2 149.1 38.2 5.5

112 891.2 • • • 42.2 •••

126 981.2 • • • 46.3 • • •

TABLE 9 EFFECT OF PH ON LEACHING ACTION

Total Copper After 90 Days (mg) Percolator PH 1 PH 2 PH 4 PH 6.5

Inoculated 32.8 55.o 50.8 52.9 Sterile 11.9 8 .2 4.8 3.2

The results indicat e that the hydrogen ion concentration had a slight leaching effect on the sterile samples. Microorganism~produced much more soluble copper at all hydrogen I ion concentrations tested than the ste~±le samples. However, 32

Inoculated 21st Day Sterile Contro 1

980 o Copper

• Iron 840

260

lhO

84 ll2 b •- 28 56 84 112

Fig. :,,.-- Biological Oxidation of Blngham Canyon Float Concentrate 33

X Inoculated 6 - Sterile

pH 1 pH 2 pH 4 pH 6.5 Fig. 10.- Ul'$R of pH on ·reaching Action 34 at pH of 1 the or ganisms showed a decreased leaching action because of their in ability to tolerate the higher acidity. Ammonium ion studies. - Sin ce nitrogen is necessary for cell growth, an experiment was conducted to dete~mine the effect of the ammonium ion concentration on the amount of soluble copper produced. A series of percolators were set up each with a char ge of 1 g of Chalcop yrite No. 2 and 190 g of

Ottawa sand. A nutrient media was made up containin g all the necessar y minerals for growth with the exception of nitrogen. The composition of the media is listed in Table 10. To t his basic media sufficient (NH ) SO was added 4 2 4 to give the concentrations of ammonium ion desired. Percolators containing various amounts of ammonium ion were inoculated from the culture in the usual manner. The soluble copper produced at each concentration (0 to 700 ppm) was deter mined and recorded eac h week. The res ults are given in Table 11 and represented graphically in Figure 11. The ammonium ion concentration had an affirmative effect on the production of soluble copper. The optimum ammonium ion concentration is about 300 ppm. TABLE 10

CaC12 •••• • • • • ••• 0.025 g • • • • • • • • • • 0.05 g ...... • 0 .5 g

Distilled Water • • • • •• 1000 ml Rate st ud ies of the biological oxidation. - A deter- mi nation of the rate of the production of soluble copper was desired. This would show the best time to re move the solution 35

TABLE 11 INFLUENCE OF AMMONIUMION CONCENTRATION ON BIOLOGICAL OXIDATION

NH4+Concentrationmg/liter Total Cumulative Copper at 28 days (mg)

o.o. • • • • • • • .... 0.3 -l;-41.0 • • • • • • • • • • • • 1.7

Bo. o . . • • • • • • • . . • 4. o 100. 0 • • ...... 12.0 1_50.0. • • • • • • • • • • .14. o 200.0 • ...... 15.0

300.0 • • • • • • • • • • • .29.4 400.0 • ...... • •• 29.1 500. 0 • • • • • • • • • • • .27.8 600.0. • • • • • • . . • 26.2 700.0 • • • • • • • • • • • • 23. 5 Sterile • • . . . . • • • • • o.8 -i:•This was the amm.onium ion concentration used in the standard media; see Table 3. for analysis to obtain the maximum activity. A percolator showing normal action was chosen to be used in this study. The leaching solution was withdrawn from the percolator and the charge was washed in the usual manner.

Fresh nutrient was added and from t his 1 very small samples were removed at intervals of time for analysis for a 10 day period. The results given in Table 12 and represented graphically in Figure 12 indicate that a seven day interval was a favorable time for analysis. 36

~--;,p ._:;, (/) so ...~ d q

C,_) (') +' Cil )10 fu p,~ 0 0 ,-1 (ij 30 +l eS

') , · ; '- ,

0 :i_O

0 ~--.....l..---.&...---.....I..---.L...-----L---..______. 0 100 200 JOO 400 500 600

im4• Concentration in mg/liter Fig. -...• - Influence of im1• Concentration on •Biological Ox:t&l:tion of C'.«:.i.lco.:v.,,,:;_te Ilo.2 37

TABLE 12 HOURLYSOLUBLE COPPER

Cumulative Soluble Copper Time in Hours (mg/100 ml)

0 • ...... • • • • 10 24 . . • • • . . . . • • 18

49. • • • • • • • • • • 25 72...... • • • • • 41

109. • • • • • • • • • • 74

142 • • • • • • • • • • • 118 164 •• ...... 150 178 ...... 180 202...... • • 200 226 ...... 215 250. . . . • • • • • • • 220 38

280

240 1 0 0 Fl ...... b.? I;, 200 -~ s:: 0 •r-1 ~ ct! 160 .fj

(!)s:: g 8 ::s 120 0

0 40 80 120 160 200

Time in Hours

F.i.G. ....q- Rate Study of Biological Oxidation on Jir._; har . Sanyon Flc

DIS CUSSI ON OF RESUL'rS

The several experi me n ts conducted i n t his stu dy provided conclusive evidence that most of t h e solu b le copper found in acid mine leachin g is a product of biolo g ical oxidation of cop p er sulfide ores.

Soluble copper was readily produced from all copper containing sulfides investi g ated. These varied greatly in com- p osition from high to low concentrations of cop p er and iron.

The minerals studied were Bin gham Canyon Float Concentrate, chalcop yr ite (CuFeS 2 ), covellite (CuS), dalcocite (cu 2 s), bornite (cu Fes ), tetrahedrite (Cussb s )~ and reagent grade 5 4 2 7 CuS.,

The production of soluble cop per fro m a c halcop y rite ore was increased many times by inoculation with microorganisms obtained from acid water of Bin gham Canyon,Utah. Autoclaving t h e inocuiated percolator slowed t he oxi d ation to the rate of a sterile control. The pH readi ng s i ndicated a deviatio n from t h e ini tial pH of 3 in b ot h percolators used. The i no culated percolator s h owed an increase in the hyd ro g en ion concentration while the sterile control decreased.

Activity was ob ser ved in the ot h er minerals test e d, even thou gh t heir co mposition varied. No obvious difference was detected between min erals containing oxidiza b le iron and

39 40 those containing only copper and sulfur. Results show that soluble copper was produced from the oxidation of minerals containing no iron. This demonstrat es that these or ganisms found in the mine water will oxidize sulfide sulfur in the presence or absence of iron. It was demonstrated that the hydrogen ion concentration increases the sterile leac hing of chalcopyrite type ores. How- ever, the amount of soluble copper produced by the hi ghest con- centratio n was less than that produced by inoculated systems with comparable initial hydrogen ion concentrations. The biological oxidation showed a decrease at a pH of 1. This was due to the inability of the ni croor ganisms to tolerate the higher hydrogen ion concentration. Studies on the a~monium ion concentration show an optimum in the neighborhood of 300 ppm. In the absence of soluble nitrogen the organisms failed to gr ow. The rate study on the production of soluble copper shows that the optimum is reached in 7 to 10 days. · This ini'or- mation was useful in deter.mining the time interval for analysis. Although these results were obtained from a synthetic media under controlled conditions, they have shown that the natural weathering and leaching action in the waste rock dumps in Bingham Canyon, Utah, is due lar gely to the action of iron- sulfur oxidizing microorganisms . BIBLIOGRAPHY

Bateman , A. M., Economic Mineral De osits, 2d Ed., John Wiley and Sons, Inc., New York, 19 O.

Beckwith, T. D., n Corrosion of Iron by Biological Oxidation of Sulfur and Sulfides,n Gas Vol. 21, No. 12, 1945, pp. 47-48. Carmichel, Terge, "Oxidation of Sulfides," University of Toronto Studies, Geological Services, 1926. Hodgman, C. D., editor, Handbook of Chemistry and Physics, 3L~th Ed., Chemical Rubber Publishing Co., Cleveland, Ohio, 1952. Jensen, Neldon L., "Factors Influencing the Solubility and Oxi- dation of Commercial Iron Pyrites," Unpublished Master's Thesis, Department of Chemistry, Brigham Young Univer- sity, 1949. J Leathen, W. w., L. D. McInt yre, and S. A . Braley , ttA Medium for the Study of the Bacterial Oxidation of Ferrous Iron," Science, 114, 1951, pp. 280-281. Leathen, W. W., S. A. Braley Sr., and L. D. McIntyre , "The Role of Bacteria in the Formation of Acid from Certain ' Sulfuritic Constituents Associated with Bituminous Coal," A~plied Microbiology , Vol . 1, No. 2, 1953, pp . 61-6 . Lilley, E . R., Economic Geology of Mineral Deposits, 2d Ed ., Henry Holt and Company , New York , 1938. Mack, E . Jr., A. B. Garrett , J. F . Haskens, and F . H~ Verhoek, Textbook of Chemistry, Ginn and Company, New York , 1949. Michener , C. E., and A. B. Yates, "Oxidation of Primary Nickel Sulfides," Economic Geology , 39, No. 7, 1944, pp. 506-514. United States Department of the Interior, Minerals Year Book , 1950, United States Government Printing Office, Washing - ton D. C., 1953. Ursenba ch, Wayne O., "Factors Influencing the Moist Oxidation of Iron Pyrites," Unpublished Master 's Thesis, Depart- ment of Chemistry, Brigh&~ Young University , 1949.

41 Willard, H. H., L. L. Merritt Jr., J. A. Dean, InstrUJ.nental Methods of Analysis, 2d Ed., D. Van Nostrand Company, Inc., New York, 1951. Wilson, Dean G., "Studies on the Biological Oxidation of Iron Pyrite, 11 Unpublished Master's Thesis, Department of Chemistr y , Brigham Young University, 1952. ABSTRACTOF THESIS

BIOLOGICALOXIDATION OF COPPER SULFIDE MINERALS

This work represents a stud y of the biolo gical oxidation of copper sulfide minerals. The principal objective of

\,,.. -~ the stud y was to determine the extent of bacterial oxidation + on copper containin g sulfide minerals. It was also desirecf1-to dete~ mi ne if the bacteria could oxidize copper sulfides in the abse n ce of iron. A better understa ndin g of the nitrogen re- quire ments of the or ganisms was desired. Minerals used in this stud y were Bin gh am Canyon Float Concentrate, chalco pyrite, covellite, c?cllcocite, bornite, tetrahedrite, and rea gent grade cop per su lfide. The bacteria used were obtained from the mine waters of Bin gha m Ca..~yon, Utah. To study the proble m the a pparatus used consisted of an air-lift percolator whic h contained the finely divided ore dispersed in Ottawa sa nd. A nutrient media was used to supply the in gredients necessar y to su pp ort growth. The studies were conducted by comparin g the amount of soluble copper produced in the presence of the or ganisms with that of a sterile control. The effect of the mine water bacteria was studied on all of the minerals listed above. The soluble copper in each was determined and recorded. A study on ammonium ion concentration was conducted and also the effect of acid concentrations on sterile leaching. The results of the exp eriments provided conclusive proof that the microorganisms are able to oxidize copper sulfide ores in the presence or absence of soluble iron. Nitrogen is essential for bacterial growth. By varying the ammonium ion concentration, the optimum was deter mined. Although the hydrogen ion concentration was found to have a positive effect upon the sterile leaching of chalcopyrite, the amount of soluble copper produced at the highest concentration was far less than that produced by the action of bacteria. Although these results were obtained from a synthetic m.edia under controlled conditions, they have shown that the natural weathering and leachin g action in the waste rock dumps in Bingham Canyon, Utah, is due largely to the action of iron- sulfur oxidizing microorganisms.