The extraction of molybdenum fromwulfenite concentrates by a leaching method

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Authors Holmes, Donald Thomas, 1913-

Publisher The University of Arizona.

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The Extraction of Molybdenum From Wulfenlte Concentrates By A Leaching Method

byDonald Thomas Holmes

Submitted in partial fulfillment of the requirements for the degree of

Master of Science

in the Graduate College

University of Arizona

1935

A pproved:

577-7/H 3 Saa.

.2.

PREFACE.

The writer wishes to give grateful acknowledgement to Dr. ?. G. Chapman and Prof. J. 3. Cunningham, of the Department of Metallurgy, College of Mines and Engineering, University of Arizona, under whose direct supervision this work has been done.

To Dr. Robert Hugent, Mr. F. A. Jacobs, and all others who have aided the writer, acknowledgment and thanks are given.

99483

TABLE OF C05TESTS

Chapter Page1, Introduction . . . . . . . . . . . . . . . . . 12. Apparatus, Materials lise&, and Analytical

Methods . . . . . . . . . . ........ • • • • 6@. Leaching Experimental Work . . . . . . . . . . . 114. Experimental Work on Manufacture of Sodium

Sulphide. . . . .............. . . . . . . . 255. Experimental Work on The Calcium Chloride

Method of Precipitating MolybdenumDissolved from Wulfenite by AqueousSodium Sulphide • • • .......... .. gy

6. Experimental Work on the Precipitation ofDissolved Molybdenum as MoOg. . . . . . • • • 3g

7. Conclusions and Recommendations. . . . . . . . . 44

sodium sulphate and carhon follows:Na?S04 64C .HagS 4C0

Thenprospecta of obtaining sodium sulphate from

^McDermld, A. J., Engineering & Mining Journal, April 1934, p. 164

deposits within the State of Arizona are promising.

Testr.l.

Making Sodium Sulphide: The object of this test was todetermine the feasibility of making sodium sulphide byheating mixtures of sodium sulphate and coal,,and to got

#some idea of the amount of coal required to convert a giveniweight of sodium sulpate to sodium sulphide.

In studying the feasibility of this method and to determine the correct ratio of coal to sodium sulphate required toy|ield the maximum amount of sodium sulphide three 25-gram samples of powdered sodium sulphate were mixed with 8, 13, and 17 grams of powdered coal respectively The mixtures of coal and sodium sulphate were placed in three 20-gram fireclay crucibles.The covered crucibles wereplaced in a assay furnace and heated to a temperature of

oapproximately 900 C for thirty minutes. The sodium sulphide cakes resulting from this fusion were then analyzed for their sodium sulphide content by titrating a dissolved sample from each cako with standard iodine solution fsee p. 9$ The results of this test are given in Table 6.

-26-

. CHAPTER I.-— IHTRORUCTIOir

The world production1 of eolyMenum lacreoaed from 1,380,000 pounds in 1925 to 6,378,000 pounds in 1933.

I : 1 1 1 ~~ 1 1 ■“Kiasoek, Alan, Molybdenum - Mineral Industry, rol. 32, 1934,P, 409. _____________ ________:___________________________

The reasons for this increased production are, first, the Improvement a in the quality of molybdenum alloy steels; and, second, the fact that many now uses have been discovered for this metal.

The two important molybdenum minerals from the standpoint of production aro molybdenite (MoSg) and vralfonite (PbMoO^).

Prior to 1915 the wulfenite deposits of Arizona were the principle sources of this metal; but, with the advent of flotation, its adaptation to the concentration of molybdenite, together with the larger ore bodies of the latter, the wulfen­ite deposits became of minor importance.

At present (1935) wulfenite concentrates containing the equivalent of twenty per cent MoOg are bought for $0.25 per pound of contained Xo03, Tucson. Ho remuneration is usually made for the lead, silver, and gold contents which in some oases are appreciable. These concentrates are shipped to ohemieal plants in the East and treated, by methods unknown to the writer, to convert the molybdenum into calcium molybdate

-1-

or ferronolyMenma. In M&roh, 1935, oalcium molybdate oommanded a priae8 of $0.80 per pound molybdenum. Hew York, and forro- aolybdenum was quoted at $0.96 per pound of contained molybden­um, f.o.b., shipping point, v/hen the ferromolybdenum contained 60 to 60 per cent molybdenum.

% — 1 — :Metal and Mineral Markets, McGraw-Hill Publishing Co., Marsh 7. 1935. t>. 6._____________ _______________________ -

The wide margins in the prises paid for molybdenum in the forms mentioned, $0.37, $0.80, and $0.95 per pound of metallic molybdenum in wulfenite, caloium molybdate, and ferromolybdenum, respectively, warrants experimental work for the purpose of investigating new processes adaptable to the southwest which might be employed to recover molybdenum from wulfenite in the form of ealelum molybdate. The advantages of such a process, in addition to the higher unit price available for the molybdenum, would be savings in freight and the ability of the small wulfenite producer to market molybdenum as ealelum molybdate derived from concentrates too low grade to sell under current specifications. Either very little work has been dome on a process such as outlined or the results of experimental work, if done, are not available, since a survey of the literature on the subject revealed very meager and sketchy data. Such experi­mental work as is described in the literature has been mainly along smelting and leaching lines and a summary of such work follows. •

—B—

In the smelting process1 2 3 as described by Eonardl

r — -— :— ---- — — — — — ----------------—Bonardl, J. E.» Chemical and Metallurgical Engineer, vol* 21, September 15. 1919. pp. 064-369._______________ ____________

the wulfenlte concentrates (probably after brignetting) were charged into a blast furnace with carbon and a flux composed of soda ash and caustic soda. The lead was reduced to the metallic form and the molybdenum passed Into the slag no sodium molybdate. The sodium molybdate was leached from the slag with water, the resulting solution neutralized, and calcium chloride added. Upon heating the sodium molybdate solution to boiling calcium molybdate was precipitated. The metallurgical effici­ency of this process was high but the cost likewise.

Smelting

(1) Acid leaching: Wulfenlte is insoluble in dilutemineral acids, and soluble in concentrated mineral acids only when an excess of the aeld is present. The indicated high cost of a concentrated acid leaoh and the large quantity of alkaline reagent required to neutralize the excess acid in preparation for the precipitation of calcium molybdate pre­cludes the probable commercial success of such a method.

(2) Alkaline leaching: A test by the writer using onaqueous solution of ten per cent sodium carbonate as solvent at a temperature of 50°C dissolved about twenty-one per cent of the molybdenum content. A higher temperature and a more

concentrated solution might Increase the dissolution of the molybdenum; hut, as in the acid leach, the amount of acidic reagent necessary to neutralise the excess alkalinity in preparation for the precipitation of calcium molybdate would preclude this method,

Jacobs^ states that he obtained satisfactory dissolution

I----— ----- :--------- ------— ------ — -----—Oral communication. E, A, Jacobs, Tucson. Arizona.__________

of molybdenum from wulfenlte by using boiling, concentrated, aqueous mixtures of sodium hydroxide and sodium carbonate,but that the method was not commercially feasible.

(3) Sodium sulphide leaching; Bonar&i^ writes as follows

"5 ' ' ' ' ' : “ : :Bonardi, J. P,, Chemical &, Metallurgical Engineering, September 15. 1919, vol, 21. p, 365,of the sodium sulphide leach, "The sodium sulphide treatment offers an excellent method for treating wulfenlte", as the lead, together with the precious metals, will be found in the residue as sulphides in a concentrated form which can easily be shipped to tho smelters for farther treatments• The molyb­denum goes into solution as sodium molybdate• The same author in another paper6 devoted to analytical methods of determining

Bonardi, J. P., Analytical Methods for Certain Metals, U. S. Bureau of Mines. Bulletin 212. p. 77.___________________;___

molybdenum writes, "Sodium sulphide, however, is an efficientsolvent for wulfenlte in a boiling solution, so much so as

6

almost to offer a quantitative method of analysis•n

7Terriel states that a boiling ten per cent aqueous solu-

7 ‘ ' “ 1 “ “ "™ ' ' 'Mellor, J. W#, Inorganio and Theoretleal Chemistry, vol, 11, 1931. Longmans and Green Co.. Kow York, p, 569._____ _

tion of sodium sulphide deoomposes wulfenlte, forming a liquideontaining thiosulphate and molybdenum.

A further survey of available literature furnished no details of the reaction between wulfenlte and sodium sulphide. From Bonardi'o statements, the dissolution of molybdenum from wulfenlte with an aqueous solution of sodium sulphide is appar­ently sufficiently complete to make it interesting as the basis of a new method for the production of oaloium molybdate.

The object of the experimental work presented In this paper is to determine the feasibility of such a process.

6

CHAPTER II.-- APPARATUS, MATERIAL USED, Aim ANALYTICALEETEOBS .

Ap'pmratm® ■

The agitation of heated pulps was effected hy rcvolvlns rolls contained In an electrically heated, asbestos insulated oven shown In the photographic plate, page 7.

Referring to page 7 the rolls (A) wore directly connected hy a belt and revolved at a speed of 50 R.P.M. The tenperatnre within the oven was indicated by a centigrade thermometer (B) protruding through the top of the oven, and was controlled by regulating a "make cmd break" contact (0 ) in the some circuit with the heating units (D).

The ore and leaching solution were first heated separately within the oven to the temperature at which the test was to be made then mixed in a 350 oo. stoppered bottle and placed upon the revolving rolls.

Methods of Analyses

Molybdenum analyses were made by a method described by Bonardl.®

Bonardl, J. P., Analytical Methods for Certain Metals, U. 3. Bureau of Mines. Bulletin 212. p . 786._______ _____________

Bonardl,a method consists in decomposing the ore by acid into soluble molybdate and residue. The molybdate solution

-• •• ••» .'jr r.Ovon for heating and agitating pulps. (Bight

hand door removed)

-7-

In filtcroa and Interfering elements, especially Iron, ar­senic, vanadium, and copper, are removed. The resulting molybdate solution is then acidified and passed through a Jem##* redactor where the molybdenum is reduced from the sci:- ivalent to the trivalcnt state'. The solution containing tho trivalent molybdenum compound is titrated with standard petaaeiun permanganate solution and the per cent molybdenum present calculated.

the determination of sodium sulphide in solutions gave considerable difficulty as various methods described by ethers did not give reliable results;,

A method9 based bn oxidation by bromine and the preoipl-

Seott, \ u ?/., Standard Methods of Chemical Analysis, Fourth Edition, vol. 1, p. 506, 1925, D. Van Eorstrand & Go., Hew York.

tation of the resulting sulphate ion by barium chloride failed to give satisfactory results.

A method9 based on evolution of hydrogen sulphide worked satisfactorily on the steelc solutions but failed to give reliable results on filtrates.

■ . , -vrIn this method the sample is placed in a distilling flask,

sulphuric sold added, and the resulting hydrogen sulphide removed by boiling. The evolved hydrogen sulphide is passed through a neutral solution of cadmium sulphate and the follow-

i m reaction t&kos place •cdS04 + e2s — ̂ cas + h 2so4

The titration of the resulting solution with standard sodium hydroxide solution reveals the equivalents of sulphur­ic acid formed end the equivalent of hydrogen sulphide evolved from the sample*

As previously mentioned, an attempt to use this method for determining the sodium sulphide content in the effluents from the leaching tests gave disappointing results. These efflu­ents contained molybdenum compounds which formed insolubley V ■ . .... . - ' ■■■ ■molybdenum sulphide upon acidifying. Concentrated sulphuric aoid and heating failed to decompose the molybdenum sulphide.

The method11 finally used for the determination of sodium sulphide content in the effluents from the leaching test was the iodine titration using starch solution for an indicator. The principle equation of this reaction follows:

Ka2S + I2 --- » SKal + S

H "" ' ' ' ' *wScott, R. %.* Standard Methods of Chemical Analysis, Fourth Edition, vol. 1, p, 509, P, Van Iioratrand & Co,, hew York,

This method is satisfactory for freshly made solutions but it is not to be rooomended for stale solutions which contain thiosulphate 1̂2 formed by decomposition of the sodium sulphide, which also reacts with the iodine.

Mellor, J. \7., Modern Inorganic Chemistry, 1920, p* 408, longman^ Green & Co.. Kew York* _______________

The material with which the majority of the leaching testa were made was a Deis ter table concentrate of an ore furnished by the Tombstone Development Company, Tombstone,- Arisons, This material was the highest grade wulfenlte con­centrate whioh could be obtained by concentrating this ore. The concentrate analyses as reported by E. A. Jacobs wore as follows:

H003. . . . . . . Au. , . ^ per tonV206. . . . . . . . . 0.12 Ag. . .. .9.20 « »Pb. . . . . . . . .54.20

Insoluble. . . . . . . . 4.60Total determined . 66,96

Unless otherwise mentioned the material described in the material referred to in this paper as wulfenlte rfcimte.'

CHAPTER III.--LEACHING EXPERIMENTAL WORK

Hie experimental leaching work involved studies of the fundamental reaction, and the variblas which follow:(a) temperature, (b) time of contact, (o) strength of solution* (d) consumption of solvent, (e) size of grinding, (f) consump­tion of solvent by impurities, and (g) percolation method of leaching.

Reaction Involved

A survey of the available literature did not reveal an equation for the reaction between sodium sulphide and lead molybdate. From Bonardi’s statement (page 5) it is evident that the products of this reaction are lead sulphide and sodium molybdate. The reaction evidently is as follows:

PbMoO* + NagS t-- PbS 4 NagMoO^

Terriel states (page 5) that molybdenum goes into solution along with thin sulphate. Whether or not the thiosulphate is a produot of the reaction between sodium sulfide and lead molybdate was not investigated by the writer.

Bacon"1'3 sulphidized the surface of wulfenite in preparation

13 ' ' ' ' ' ' : “Bacon, Ira P., ma Study of Certain Oxidized Lead & Zinc Minerals" Master of Science Thesis, University of Arizona 1988, p. 61

n

for flotation experl;mat,, By X-ray analysis he proved that lead sulphide was one of the products formed v/hon sodium sulphide and milfenito react.

' Test 1.

Tiira of Contact end Tamperatures of Leachim:: The object ofthe tiiso and toia|»ratures tests was to determine the effect of time duration of leach upon rate of dissolution of the molybdenum and the lowest feasible temperature which would give a satis factory dissolution rate of the molybdenum.

In studying the effect of time of contact at various temperatures tliree samples, weighing 50 grams each and ground to -100 raosh, wore placed into three 350 eo. bottles for each temperature dotormlned. TIioso bottles and 500 cc» of a 10 per cent aqueous solution of sodium sulphide were placed in the oven until they were heated to tho required temperatures.When the desired temperature was reached the heated solution (150 eo.) was poured into each bottlo• 52m stoppered bottles were placed upon the revolving rolls within the oven. The bottles were removed at 15, 30, end 60 minute intervals. Upon removing a bottle its contents wore poured immediately upon a filter and the residue washed eight times with warm water (60°C). The total volume of wash water used for each residue being about 150 oo. The washed residues were then dried at 106°C and analyzed for their molybdentsa contents. Throe time tests

•12- -

were made for each of the following temperatures: 92°, 78°,62°, 45°, and 25°C. The results of these tests follow in Table I.

The per cent of MoOg dissolved as given in Table I was calculated as the difference between MoOg in tiie heads and residues. An attempt to calculate the per cents MoOg dissolved from the determinations of per cent molybdenum in the filer at es from the leaching tests gave an extraction of more than 100 per cent. This was probably due to the presence of vanadium"1'* which is also soluble in sodium sulphide.

•‘•^Fester, 0. ̂ Chemical Abstracts of the American Chemical Society, vol. 12, p. 852

The indicated difference in per cent dissolved, calculated as MoOg contents of beads and residue, and beads and flIterates, was approximately 5 per cent.

From Table I it may be seen that the dissolution of molybdenum from wulfenite is nearly complete at room temperature in 15 minutes when an excess of a 10 per cent aqueous solution of sodium sulphide is used as solvent and that the rate of dissolution is therefore rapid.< The reason that the entire series was run in view of the high per cent of molybdenum dissolved at room temperature was because the experimental work started at 92°C rather than 25°C.

IS-

Tablo I— Leaching for 15, 30, m d 60 Llinute Intervalsat Various Teaperaturo a

: : $ :TestHo»

Mulfaniteconcentraten m d

Sodiumsulphidesolution

Rationsolution to solid#

Tinoalas.

2ip:2 :>:MoOg :ito03 lin ;dis-

wt»gms.

per cent HOpfl __

used oc. (10%)

2:

:resi~:solved :dues :

1 50 8.04 150 3:1 15%•12

: :10.15 198.13: ' : • ':0.18_:97.762 W 8.04 150 3:1 15 :78

3 50 0.04 150 3:1 15::62

: ' : ' :0.12 :98.51

4 50 8,04 150 3:1 15 V':45 : ' ■ ' ':0,1s :98.39 : :$0.16 :98.01- * *5 50. 8.04 150 3:1 15 :25

6 50 E . ' .8.04 150 3 si 30 :92 ♦0.21 :97.39 : ::0.17 :97.88 : ::0.16 :98.01 : ::0.08 :99.01

9 50 8.04 150 !i3:l :$30 :788 :$50 8.04 150 3:1 :30 :689 50 0.04 150 !$3:1 30 :45

10 50 8.04 150 3:1 30 :25 :0.14 -98.26 ̂ : ’ ::0.3B :96.0211 50 8.04 150 3:1 60 :92

12 §0 8.04:150 3:1

$: 60 ::78

: : - :0.18 :97.76

13 50 8.04 150 3:1 60 •62 :0.13 -90.39. ' . e *14 50 8.04 150 3:1 60 :45 •0.09 :90.88

:; ::d.l3 :98.39 -15 50 8.04 •150 3:1 60 •25

14

. ; T##t 2.

LoachinR with Varying Strength of Solvent: The object ofthis test was to determine the variation in the rate of dlesoluticn of the molybdenum from the wulfonite concentrate using aqueous solutions of different sodium sulphide contents.

In studying the rate of.dissolution of the molybdenum with solutions of different sodium sulphide contents» leach­ing and washing operations were carried out as described in Test 1. Biree 50-gran, sample a of vmlfeiiito concentrate, ground to -100 mesh, wore loached with three 150 ec. volumes of an aqueous sodium sulphide solution, amtaiming 2, 4, and 6 per cent by weight of sodium sulphide respectively for 50 minutes at a temperature of 45°C.

Table 2a— Leaching with Solutions of Different Strongths-Constant Volume

* J : ' . I ; •TcstjWulfonito HagS Time tTaap. :>$ Mo03 ■ idisoolyod. Ho. :oon©mtrato:in 150 mine,:OQ sin resi-:uaed :co of idues s: wt .ras :Si oima ol uti on s :

1 :50 : s ' -:8.04; 2- 50 50:; 5,50 $s 31.50

: s . s2 :50 z8e04?4 50 50 :1.72 : 78.61

: s : s $3 :50 :8.04:6 30 50 :0.19 z97.64

: : : S ' ;z

-15-

From Tabid 2a it may be seen that the rate of dissolution of molybdenum from wulfenite, using equal volumes of an aqueous solution of sodium sulphide as solvent , varied almost directly with the per cent? sodium sulphide contained.

Referring again to Table 2a attention Is directed to the rate at which a given weight of sodium sulphide in an aqueous seOLution will dissolve molybdenum from wulfenite concentrate. The data indicate that the rates of dissolution should vary inversely with the volumes of solution containing constant weights of sodium sulphide.With this point in mind two more tests were under similar conditions as the tests of Table 2a. Two 50-gram samples of the wulfenite concentrate, ground to a -100 mesh, were leached with 150 oo. and 60 oc. volumes respectively of an aqueous solution of sodium sulphide, both volumes of solution contained 6 grams of sodium sulphide. The leaching period was thirty minutes at a temperature of

16-

Table 8b— Leatiilng with Solutions of DifferentStrengths but Containing Same Weights of Na2S

: ■. : : . s : %Test:Wulfenite :Volume of :TimeNo. .-Concentrate :solution mins

J used : containing:i Wt gms:$ MoEJ£:6 gms. of :: : :Kaj>S :

$ $T#mp, ,:6C : .$$

$55 MoOg tin resi­due ::

$% MoOg tdis- $solved

: : $ $ ; •*1 :S0 :8.04 $150 :30 $50 $1.78 $78.61

' : $ $ $ • $ :8 :50 :8.04 $100 $30 $50 $0.79 $90.17t " : . 1 . $ ' ■ :v $qS $50 $8.04 $ @0 $30 $60 $0*08 $99.01

■' : ' •' : - ■ : ' 2From Test 8, Table- 8a.

From Table 8b and the acooi^panylng graph, Figure 1,It may be seen that the rate at which a given weight of

- ' ' sodium sulphide in an aqueous solution will dissolvemolybdenum from wulfenite varies inversely as the volumeof solution, the weight of sodium sulphide remaining constant.

17

l/o /o/ne (CCj o f So/c/f'OS? CO/t/a/fr/STy S'* jrams <f ̂oc//um scs//oA/t/e

Fig.1-Relations between dissolution rates and concentrations of sodium sulphide.

Teat 3.

Consumption of Sodium Sulphide by Wuifenite: Theobject of this experiment was to approximately determine the consumption of sodium sulphide from an aqueous solution of sodium sulphide per unit weight of MoOg dissolved from the wulfenite concentrate.

The calculation from the equation indicating the reaction between sodium sulphide and wulfeaite (p. II) showed, that at the completion of the reaction 0.528 grams of sodium sulphide will be consumed per gram of M0O3 dissolwed.

In studying the consumption of sodium sulphide by the wulfenite concentrate three 50-gram sample s of wulfe- ni te ground to -100 mstii' were placed in three 350 eo. bottles along with three 60 ec. volumes of an aqueous sodium sulphide solution containing 8.3, 6.6, and 5.0 per cents of sodium sulphide respectively. The leaching was carried out at a temperature of 45°C for a time interval of 30 minutes. The pulps were filtered and the residues washed eight times using 150 cc. of water for each residue. The results of this test are given in Table 3.

18-

Table 5— C m sumption of Sodium Sulphide per Oram of M0O5 Dissolved from Wulfenlto C cnc ent rate

TestNo.

Wulfenlteconcentrate

ed 6W

: ■ : . ■ : ;:.Per o®it$per cent:Per cent :Gms NagS •NagS^in^iMoGs ln :Mo03 :*AgmsMoOs!solution:

iconsunsd60 co.of.pesiduesidlssolvediper gm

:of MoOg1dissolved

: : : - - :- I;;: :50 :8.04 .8.3 :1.98 75.31 :i.6®

: ■: i : •2 : 50 :8.04 :6.6 :3.31 58.70 11.67

' : 1 - -:' ' : ■ I :3 :50 :8.04 :5.0 :4.77 40 #68 11.23

: : : •

In calculating the consumption of sodium sailphlde per gram of MoO3 dissolved it was assumed;that all of the sodium sulphide had reaeted. However, this was not the ease. Upon acidifying the filters tea frma Tests 1 arid 2 considerable hydrogen sulphide gas was evolved, Indicating that all of the sodium sulphide had not reacted with thewulfenlte. When the fliterate from Test 3 was acidified

■ ■■ - • '

there was only a slight odor of hydrogen sulphide which indicated that in Test 3 the sodium sulphide had been more depleted than in Tests 1 and 2; therefore, the

19-

value 1,23 grams of sodium sulphide eonsuaed per gram of MoOg dissolved Is probably nearer to the correct value than 1.66 or 1,67 as Indicated In Tests 1 and 2.

An explanation of this high consumption of sodium sulphide, 1.23 grams per gram of MoOg dissolved, as compared with 0,528 gram of sodium sulphide per gram of MoOg,dissolved from wulfenite , calculated from the equation, page 13, is based upon the following two facts:

First, inspection of the wulfenite concentrate revealed the presence of considerable lead carbonate. Lead carbonate-*-5

•^Paeon, Ira P., A Study of Certain Oxidized Lead and Zinc Minerals. Master of Science Thesis, University of Arizona,

• p - .■ . ' ■: . •. . ■ ■ . -reacts with sodium sulphide; the equation for tho reaction being -

PbGOg -h NagS - PbS*+ NagCogSecond, the reactions PbCog + NagS = PbS+-Nag Cog and

PbMo04-f NagS - PbS + NagMoO^ are examples of the heterogenous equilibrium -̂6 type of reaction in which one solid substance is

^6Millard, E. Be, Physical Chemistry fer Colleges, Third Edition, McGraw-Hill Co., II. Y« , p. 317______ ' ______ _________ _____

converted into another solid substance, in this case lead car­bonate and lead molybdate into lead sulphide. It is known that in reactions of this type althou^i the consumption of the converting reagent when the reaction has gone to completion will

—20—

be that as oaleuleted from the stole equation, the presence of an excess of the converting agent bringing about the conversion of one solid to another is necessary# Therefore, when the reaction between the sodium sulphide and the wulfe- nit® has reached equilibrium there will be some free sodium sulphide present, and this would increase the apparent consumption of sodium sulphide per gram of M0O3 dissolved from the wullbnite concentrate as calculated from this test#

Test 4. .

Effect of Size of Grinding on the Rate of Dissolution of Molybdenum from Wulfenite: The object of this test was to determine the effect of various degrees of grinding of the. wulfenite upon the rate of dissolution of the contained molybdenum when leached with an aqueous solution of sodium sulphide,

In studying the effect of grain size of the wulfenite upon the rate of dissolution a sample of the wulfenite concen­trate weighing 500 grams was placed upon a nest of screens arranged in the following order, 20- mesh, 35- mesh, 65- mesh, and 100- mesh* After screening, the material remaining upon

. i '

each sieve was weighed and Its M0O3 content determined, % e data of this sizing-assay test are given in Table 4a for reference.

21-

Table 4a— Sizing-Assay Test of Wulfenlte Concentrate

: Through : Through ; :20- mesh:35- mesh :on :on:35- mesh:65- mesh

[Birougti 65- mesh on100- mesh

Through100-mesh

Total

Grams of wulfenlte: :concentrate :123 :158

: :Per cent of total :24,60 :31,60

80 139 50016.00 27.80 100.00

Per cent of M0O3 :5,63 :7.89 7.33:

A 50-gram sample of each of the 35, 65, and 100 mesh sizes m s placed in a 350 oo. bottle with 60 oc. of a 10 per cent aqueous solution of sodium sulphide. The bottles were placed upon the reveling rolls and agitated for 60 minutes at a temperature of 45°C.

The pulps were filtered and the residues washed eight times using 150 oc. of wash water for each residue. The per cent of molybdenum dlssolved from each size is given in Table 4b.

Table 4b— Effect of (Spain Size on Rate of Dissolution of Molybdenum from Wulfenlte

Size of ;Wulfenlte grinding,:concentrate mesh :used

Volume of 10# sodium sulphide solution used cc.

Time,mins.

Temp.°0

**>63inresidue

% BoOg dissolved

:wt gms II

Through :20 on 35 :50 5.63 60 60 45° 0.45 92.03Through :35 on 65 :50 7.89 60 60 45° 0.28 96.44Through :65 on 100:50 7.33 60 60 45° 0.20 97.25

It may bei seen from Table 4b that the rate of dissolu­tion of the molybdenum, using 60 cc* of an aqueous solution of sodium sulphide as solvent, increases with the decreasing size of the mineral particle but not greatly as the per cent dissolved from the -20 + 35 mesh sizes was 92,03 and from the -65 i-100 mesh sizes was 97.25.

Test 5.

Leaching of Wulfenite by the Percolation Method: The objectof this test was to determine whether the wulfenlte concentrate could be leached to dissolve molybdenum with an aqueous sodium sulphide solution by the percolation method.

In studying the leaching of the wulfenlte concentrate by percolation a sample of the wulfenlte weighing 2000 grains, ground to -20 mesh, (see Table 4a, page 26 for sizing test) was placed in a 4 by 12 inch percolation jar; the resulting ore column being about 12 inches in depth. A volume (500 ee.) of a 10 per cent sodium sulphide solution was then added and allowed to percolate downwardly through the ere column until the concentrate had become comple tly wetted by the sodium sulphide solution. The aqueous sodium sulphide solution was allowed to remain in contact over night and then 300 co. of thesolution drained off. Three hundred cc. of a fresh 10 per cent aqueous solution w w t^en added and allowed to remain in

contact until the following morning. This procedure was repeated until a total of 2400 co. of a 10 per cent aqueous solution of sodium sulphide had baen added to and drained from the wulfenite. The leached residue was washed by down­ward percolation using two charges of 250 cc. of wash water. The washed residue was then discharged from the percolation jar.

An examination of the residue from this leaching test revealed that the aqueous sodium sulphide solution had not made thorough contact with the wulffenite. The wulfenite in the lower one-third of the percolator had packed into a hard lump. The leaching solution had passed around rather than through this portion of the material. The dissolution of MoOjj calculated as the difference in head and tailing assays was only 18.76 per cent. The results of this test indicate:: that wulfenite concentrate ground to 100 per cent minus 20- mesh and 31.6 per cent on 65 mesh is not adapted to the downward percolation method of leaching. Although upward percolation might insure more thorough contact between the concentrate and the leaching solution, resulting in an increase in the per cent molybdenum dissolved, the fact was not investigated by the writer.

—24—

CHAPTER IV. — EXPERIMENTAL WORK ON milUFACfURE OFSODimi SUTIPHIDE

Since the cost of the solvent sodium sulphide is the chief cost Involved in the leaching process described, this paper would be incomplete without some discussion of. the source and manufacture of sodium sulphide.

17Sodium sulphide is quoted at $0,035 per pound f.o.b.

^Chemical & Metallurgical Engineering, vol. 42, Ho. 4.April 1935, p.. 237

New York, April 12, 1935, for a product containing 62 per cent sodium sulphide. The price of this product per pound of sodium sulphide contained would be approximately $0,056 f.o.b. New York. It may be seen from the experimental work on leaching (tests) that between one and two powds of sodium sulphide are consumed per pound of Mo03 dissolved. Therefore, the cost of sodium sulphide will be a governing factor in considering the commercial feasibility of the sodium sulphide leach.

Molinari -̂5 describes a method of making sodium sulphide

l%olinari, E. B., General and Industrial Inorganic Chemistry, Second Edition, 1920. P. Blakiston’s Sons & Co. Philadel­phia, p. 538

by treating a mixture of coal and sodium sulphate to a high temperature (900°C). The equation for the reaction between

Table 6«— Production of Sodium Sulphide from Sodium Sodium Sulphate and Powdered Goal

TeetiWt.No.:NagSo4 .used,

: grams

: : ::Sodium :Theoret-:Fer cent :sulphide:leal s of theo-in cake,:yield, grams :grams

reticalyield

C-l-'Cake rolted some Ma®S ethm-ed to crucible and causing loss of NagS : :. ■ ' \ .. - ' -

From the data of Table 6 it may be seen that the ratio of coal to sodium sulphate in Test 2, namely 1:2 , is apparently the best ratio to completely convert NagSo^ to sodium sulphide.

In regard to the high yield of sodium sulphide in this test it was believed by the writer that tho method of analysis used to determine the sodium sulphide content of the fused cakes might be in error. Another test was made and the sodium sulphide content of the cakes determined by the gas evolution method of analysis (see pp.Q Chap. II).

27

In this test 750 grams of powdered sodium sulphate Wjert mixed with 300 grams of powdered coal. This mixture of eoal and sodium sulphate was divided into 10 eq,ual portions and each portion placed in a 50-gram crucible•The covered crucibles were then heated in the furnace to a temperature of approximately 850 to 900°C 30 minutes.The results of this test are given in Table 7.

Table 7— Production of Ha&S from Sodium Sulphate and Powdered Coal Contained

lit. of Wt. of Wt. of ilndioaied;Wt. of :Thooret- :PerNagS04used,gram

coalused,grams

sodsuloakdue

Ivm :per cent i sodium . sphlde :sodium :sulphide: e pro- :sulphide :oontein- ed,gme.:in cake :od in

, : ■ :eakeej: : grams

leal;yield of sodiul sulphide, grams

cent of theoret­ical yield

7^) 500 430: ; :::122.00 :524: :

412 127

From the data of Table 7 it m y be seen that the indicatedyield of sodium sulphide is greater by 27 per cent than the theoretical yield.

The only apparent explanation of this higi yield of• x

sodium sulphide is based on the assumption that at -compound was formed tha t yielded more sulphide, ion per unit weight than sodium sulphide; possibly (HH^JgS from (H%)gSo^ in coal or a pplysulphide suedi as KagSji*

-28-

In ooncluding tiio experimental work on "toe production of sodium sulphide from a fusion of sodium sulphate and odal it may he stated that the mthod used yielded a very satis­factory product from the. stand point of yield of sodium sulphide< -■ . ..... , . - r

The results of. a leaching test using the sodium sulphide produced; in this experimsnW. work are again given in Chapter VI.

CHAPTER V.— EmmiMSHTAL WORK CEt THE CALCIUM CHLORIM METHOD OP PRECIPITATING MOLYBDE1TOM DISSOLVED FROM WULFENITE Hf AQUEOUS SODIUM SULPHIDE

The experimental work on the precipitation of the molybdenum dissolved from the wulfenite concent rate by the •odium sulphide leech involved studies in (a) solubility of calcium molybdate in agueoum solution, (b) precipitation of dissolved molybdenum as calcium molybdate using calcium chloride as a neutralizing and precipitating reagent, and (c) precipitation of dissolved molybdenum using hydrochloric acid as a neutralizing agent and calcium chloride as a precipitating agent*

Test 1.

Solubility of Calcium Molybdate in Aqueous Solutions: Theobject of this experiment was to determine the completeness of the precipitation of molybdenum as calcium molybdate from aqueous solutions of sodium molybdate containing different concentrations of molybdenum and using calcium chloride as the precipitating reagent*

In studying the completeness of the precipitation of molybdenum as calcium molybdate by calcium chloride from

50-

solutions of different molybdenum conoentrntion four 20 oe. pertims'Of a an aqueous solution of sodium molybdate (C,P,) wore diluted with water to different volumes so that the MoOg oonoentrationa of the diluted solutions were 4*26, 2*98, 2.15, and 1,29 p®r eent# re#eotively, in equal weight of Caolg, an amount that contained 20 per cent more calcium chloride than was theoretically required to completely precipitate the contained molybdenum, was added to each solution. The mixed aqueous solutions of calcium chloride end sodium molybdate were then heated to a tempera­ture of 92°C for ten minutes and filtered. The filterstes were analyzed for their molybdenum contents. The results of this test are given in Table 8.

Table 8— Precipitation of Molybdenum as Calcium. : • ■' • ' :Molybdate from Solutions Containing

Different Concentrations of Molybdenum

: : :Test :Volume of :Mo0g contentsiCalcium No. :sodium :of Ba^loO^ :chloride

molybdate:solutions perisdded,:solution,:cent sgrams

toOgprecipitated as calcium molyb­date , per cent

1 20.00 :4.26 :0.54 99.662 28.57

::2.98

S'' !:0.54 @9.903 40.00 :2.13

::0.54 99.444 60.66

i:1.29::0.54 99.38

: - :

-51-

Referring to Table 8 , the data Indieate that molybdenum as sodium molybdate in an agueous solution is about eompletely preeipitated by oaloium chloride as calcium molybdate and that the concentration of the molybdenum has little effect upon the completeness of precipitation since the per cents of molybdenum precipi­tated from solutions containing 4.26 per cent of MoOg Mid 1,29 per cent of MoOg respectively are over 99.

m a t 2.

Neutralization and Precipitation by Calcium Chloride: Theobject of teis experiment was to determine the completeness of the precipitation of molybdenum, dissolved from wulfenite by on aqueous solution of sodium sulphide, as oaloium molybdate using calcium chloride to neutralize the reagent solution and to precipitate the contained molybdenum.

In studying the completeness of the precipitation of the molybdenum contained in the pregnant solution using calcium chloride as a precipitant and neutralizing reagent 200 grams of wulfenite concentrate were leached with an aqueous solution of sodium sulphide for 30 minutes. The solids were then allowed to settle and the clear sodium sulfide pregnant solution decanted Into another beaker con­taining 200 grams of wulfenite concentrate. This pulp was agitated for 15 minutes and then set aside for three hours.

After three hours contact between the sodium saljhiae solution m d the milfenlte concentrate titration of a portion of the elear solution with a standard Iodine solution revealed very little sodium sulphide present. .The alkalinity of this solution was determined by titrating a portion with standard sulphuric acid solution. To 100 oe. of the dear solution enough calcium chloride was added to neutralize the solution and about SO per cent excess to precipitate the contained molybdenum. (Sonardl states that only a alight excess calcium chloride over that needed to neutralize the solution is necessary to precipi­tate the molybdenum).

The solution containing the soluble molybdenum salt and the calcium chloride was heated to boiling for 15 minutes and then filtered. The residue was washed three times and the combined fliterate and washings were analyzed for their molybdenum contents. The precipitate was dried at approximate ly 100°C m d its molybdenum and sulphur contents determined. The results of this experiment are given in Table 9.

-35-

Table 9— P%*olpit#$ian of MolyMem* from an Aqueous Solution of MelyMenum t r m

the Leaching of Wulfeni te with an Aqueous Solution of Soditsa Sulphide

: : : : • • :Volume of d M u j Cool? added,. :Weight of :Analyeie :MoO« in :MoO-soditm :eontent :_____m s , :calcium jof cal. :fllterate:recoveredmoljbiate :of soditm :For nett- :For ̂ pe-xmolyWate tmalybdate :«nd wash-:as calciumsolution rmolybdato itrelizer* jeipita- :precipitate:precipitate tings. :molybdate, teken, ee.:eolation itiom itlon :obtained, : per cent :grama :per cent

:taken.Ktaa.: : ______ :grama :KoQx :Sulphur:_____ : ..... _: i : : : : j s (1)100 :1.08 iS.15 :1.65 :9.85 :7.15 :0e4S :0.5m :81.iOv ':_______ :_________ : :___________ : : • ■ :..... • •

JtoOa-weeovezeA as ealcltm molybdate was calculated as the difference in the molybdenum content of the solution before and after the precipitation of the calcium molybdate,

Referring to Table 9, the data indicate that the recovery of molybdenum, as calcium molybdate from the pregnant solution obtained by leaching wulfenite concentrate with sodium sulphide using calcium chloride as a neutralizing and precipitating reagent was lower than would be expected from a solution containing molybdenum, supposedly as sodium molybdate. It may also be seen from Table 9 that the grade of calcium molybdate obtained by this method was lower in MoOg content than the wulfenite concentrate leached, the low HoOg content was attributed to contamination with calcium hydroxide or calcium carbonate resulting from the neutraliza­tion of the alkaline pregnant solution with calcium chloride.

In conclusion it may be stated that the calcium chloride method of neutralizing and precipitating molybdenum as calcium molybdate from the pregnant solution of the sodium sulphide leach of wulfenite concentrate is unsatisfactory because of the low recovery of the molybdenum, namely 81.5 per cent, and the low grade of Calcium molybdate obtained.

Test 5.

Neutralizing Pregnant Solution with Hydrochloric Acid and Precipitating Molybdenum with Calcium Chloride: The object of this tost was to attempt to obtain a higher grade of

calcium molybdate than that obtained in % a t Z; by neutralizing the alkaline pregnant solution,, obtained from leeching of wulfenite with aqueous sodium sulphide, with hydrochloric acid and precipitating, from this neutral solution, the molybdenum with calcium chloride.

In studying the hydrochloric acid and calcium chloride ; c. ' ■ ' ■ • . .. -

method of obtaining calcium molybdate a solution ofsodium sulphide was treated with wulfenite as described in Test B. The solution resulting from this leach was neutralized with hydrochloric acid and enough calcium chloride was then added to precipitate the molybdenum and SO per cent in excess • Upon heating the neutral solution of molybdenum and oalcium chloride to boiling the color of the solution turned to dark blue indicating that molybdenum was being reduced. Molybdenum in the lower valence state Is not precipitated by oalcium chloride. Potassium permanganate was added to the solution until the blue color disappeared. Upon heating this solution to boiling calcium molybdate was precipitated.

iHo quantitative determinations were made in this test

since it was evident that the hydrochloric acid and calcium chloride method of obtaining molybdenum from the pregnant solution was unsatisfactory because the molybdenum contained

-36-

in the neutralised solution was reduced upon boiling, and in the lower valence state molybdenum cannot be precipitated by calcium chloride.

Although unsatisfactory results have been indicated in the experimental work dealing with the precipitation of calcium molybdate, the writer believes tEat further experimental work would be needed to definitely decide the merits of the methods used.

CHAPTER VI, — EXPERIMENTAL WCRK CH THE PRECIPITATIdi OFDISSOLVED MOUBDEHUM AS MbOg

Doeznep^7 Aesoribea a process for precipitating

„ ----------- :--------------------------------------------------------------------------------------------------- --------------------------*Doarner j H* A*, Recovery of Molybdite from the Ore.Technical Paper 399* United States Bureau of Mines, 1926, p . 7 ______ ;________ -

molybdenum from the pregnant solution of a sulphuric acid leach of a molybdite ore, "*«> the warm solution (40°G) is agitated about 16 hours with a large excess of scrap iron

until the molybdenum is completely reduced to the quadriva­lent or lower condition and the free acid is entirely

.neutralized* Under these conditions the molybdenum is quantitatively precipitated* probably as a hydrate MoOg«This precipitate xdien filtered, washed, and dried contains over 80 per cent molybdenum, a small but variable amount'.of iron, and traces of other impurities, including any phosphor­ous originally present. This procedure should not be confused with the well known method of precipitating an iron molybdate from an oxidized solution. The lower oxides of molybdenum are basic and do not react with iron or other bases. The iron found in the precipitate is partly insoluble salts, such as phosphate, and partly ferrous sulphate which has not been

completely removed by washing. In one test the roasted product contained 85.8 per cent M0O3 and 13.9 per cent tegOg. - ' • " • ; ' .. .

The possibility of using this product for direct addition to steel is worth consideration. The molybdenum is present as a lower oxidei which is not volatile at the temperature maintained in a steel furnacei If calcium molybdate is found to be preferable, it may be produeed by mixing the roasted precipitate with freshly slaked lime.”

Test 1.

Sulphuric Aoid-Scrat) Iron Method of Precipitating Molybdenum: (1 ) % e purposes of the experimental work described in this chapter ware to determine the results of employing sodium sulphide, manufactured in the laboratory (see Table 7, p.afl ), to dissolve molybdenum frcan wulfenite; (2) To determine the completeness of the precipitation of molybdenum as MoOg resulting from the treatment of the aqueous solution of molybdenum with scrap iron and sulphuric acid.

In studying the effectiveness of the manufactured sodium sulphide as a solvent and the completeness of the scrap iron- sulphuric acid method of precipitating molybdenum a sample of wulfenite concentrate weighing 1000 grams, ground to 100

■ . ' - ' -59-'99488

per sent minus 20- mesh and 51~per cent plus 65- mesh, was plaeed In a liter bottle along with 204 grama of the manufactured sodium sulphide. The ratio of sodium sulphide to molybdenum contained in the wulfenite concentrate used, namely 1.5 to 1, was determined from the result of test 5 described on page : . The bottle containing the dry mixture of sodium sulphide and wulfenite concentrate was placed on the revolving rolls and agitated for five minutes.A volume of top water amounting to 500 co. was poured into the bottle and the mixture agitated. It was noticed that considerable heat was evolved by the mixing of sodium sulphide wulfenite concentrate, and water. The highest temperature recorded by a thermometer thrust into the mixture was 70°C•The bottle was then stoppered and placed upon the revolving rolls for 90 minutes. The bottle was removed and its contents poured upon a suction filter. Washes used to remove contents from the bottle were also poured onto the filter. The residue was washed with 1000 co. of top water; washings’ and filterate being caught in one two-liter beaker* The alkalinity of the ooriblned filterate and washes was determined by titrating a 5 cc. portion with standard sulphuric acid. Sulphuric acid (95 per cent) was used to neutralise the alkaline solution and 56 cc. in excess were added to the solution. A weighed quantity of scrap iron, 100 grams, was added to the beaker containing the acidified solution. The beaker containing the

scrap iron and acidified molybdenum solution was then set aside at room te%#erature for six days. On the sixth day the solution was heated to. 60°C for two hours and filtered. The residue was a.blaek gelatinous precipitate of MoOg. The filterate was dark blue in color, indicating that all of the molybdenum had not been reduced to the quadrivalent state. To this filterate in a two-liter beaker was added 25 oo« of 95 per cent sulphuric acid, the scrap iron remaining from first precipitation, 15 grams of fresh scrap iron, and the mixture heated to TO°C for three hours. After standing over night th© solution was filtered and the resulting fliterate analyzed for its UoOg contents. The HoOg resulting from the two precipitation# were combined and washed three times with water by decanta­tion. The precipitate was then dried at temperatures of 150 to 200°C plus and the MoOg, FegOj^ond sulphur contents determined. The results of this test are given in Tables 10, 11, and 12.

In Table 10 the per cent of MoOg dissolved from the wulfenite was calculated as the difference between the head and residue assays. Xn Table 11 the per cent of MoOg precipi­tated was calculated as the difference in the weight of MoOg dissolved from the wulfenite concentrate and the weight of MoOg in the barren solution.

-41-

Table 10— Results of leaching Wulfenite Concentrate withSodium Sulphide Manufactured in Laboratory

Wulfenite tsodium :Volume :Wt. of :Mo o3 :Mo03 di§-opnoentrate :sulphideused :in 500weight,:Por :cc. water grams :cent igrams♦TMO3:_________

1000 :8.04 :

804

of wash:residue10ontent :solved per water :from :of resi-:cent used,00:leach, :due, per:

:grams :eent :i ■ $ ■ -■ : _■___1100 i 930 0.30 96.53

Table 11— Results of Precipitating Molybdenum as MoO* Being Scrap Iron and Sulphuric Acid

S o l u t i o n :It.scrapcontainingmolybdenum

Iron eonBurned,gramsVolume 1 *

•'60.' J. .. : ■ :

M0O3con­tentsgrams

1740 77.61 90

Wt.sulphuric tVolume :Mo03 :MoOs tof icon- zpreclpi-:barren :tent :tation

trailze;cipitatesolut- :bf las grams :grams :ion :bar- jMoOg,- ■ • . : ' •• :from :^n

: :preci- :solu-:C©^2 :pitation:tion,:

_______ : toe. igratna:_______: . ' 2 , / . :79.3 : 147 2 1500 ;0.48 ; 99.382 • 2 : ' :

Table 18-?-Analyse# of Precipitate after Drying

Weight ofiMoOg iFegOs :S content,product, :content,:content,:per cent grams :per cent:per cent:

Total determined T*per cent

: .2 :72.00 : 83.24 ; 6.86 2 1.74: : 2

91.84

Referring to the data in Table 10 it may be seen that the sodium sulphide made by the writer by fusing a mixture of sodium sulphate and coal readily dissolved molybdenum from mlfenite.

Referring to the data in Table 11 it may be seen that the scrap iron-sulphuric acid method of recovering molybde­num from aqueous solution is efficient as far as completeness of precipitation is concerned.

Table 12 gives the results of analyzing the dried precipitate. It may be seen from the data in Table 12 that the sulphur content of the precipitate obtained is over the limit permissible in a molybdenum compound to be used for making molybdenum steel, A more thorough washing or a roast­ing of the precipitate may eliminate some of this sulphur.However, it may be said that the filtering and washing of■ ' ' - : - ' " :this precipitate offers difficulties.

43-

CHAPTER VII .— C01CLXJSI0HS AHD RECOMMKHBATIOIS

In oonolTullne, a brief anmm&ry of the results of the experimental work is given:

(1) Kolyb&enum is readily dissolved, from wulfenite by a ooaoontrated agneous solution of sodium sulphide• It is not necessary that the wulfenite be ground to an extremely fine degree ©r that heating of pulps be employed,

(2) Satisfactory sodium sulphide can be made by fusing a mixture of sodium sulphate and ooal.

(3) A brief Investigation of the precipitation of the molybdenum by calcium chloride from the pregnant solution of the sodium sulphide leach Indicated difficulties, immely,(1 ) a low recovery, (2) the production of a low grade product, and (3) a large consumption of calcium chloride,

(4) The molybdenum dissolved from wulfenite by sa aqueous sodium sulphide leaoh Can be almost completely precipitated as 3lo0g by the sulphuric-scrap Iron method of precipitation, but indications were obtained that it would be difficult to wash the precipitate sufficiently free of objectionable impurities.

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