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This is to certify that the
thesis entitled

AN ELKYL SUBSTITUTED TRIPHENYLVIETHANE
DYE AS A FLCTATION AGENT FOR STIBNITE

presented by
MYRON GILBERT BRCWN

has been accepted towards fulfillment
of the requirements for

m. 5.... _. degree mm‘ ENGINEERING

Major professor
Date W2 3" /750

AN ALKYL SUBSTITUTED TRIPHENYLMETHANE
DYE AS A FLOTATION AGENT FOR STIBNITE

by

MYRON GILBERT EROWN

A THESIS

Submitted to the Graduate School of Michigan
State College of Agriculture and Applied
Science in partial fulfillment of the
requirements for the degree of

MASTER OF SCIENCE

Department of Chemical Engineering

1950

ACKNOWLEDGEMENT

To Dr. Clyde C. DeWitt, acknowledgement is made for his
grasPing the feasibility of using an alkyl substituted dye as a
flotation agent for stibnite, and for his interest of and guidance
throughout the entire project. Prof. Malvern Obrecht furnished
helpful literature on flotation as well as demonstrated the use of
the laboratory test cell. The experiments were carried out in
the Chemical Engineering Research Room of Olds Hall, the In-

dustrial Laboratory, and the Highway Re search Laboratory.

244580

TABLE OF CONTENTS

ACKNO WLEDGENIENT

IN TRODUC TION

HISTORY

THEORY

PROCEDURE

DATA

GRAPHS AND DIAGRAM

DISCUSSION

BIBLIOGRAPHY

IS

17

19

22

INTRODUCTION

The most important ore of antimony is stibnite, szS3.

The best sources of stibnite are in Algeria and Hunan Province,
China. (1) There are some sources within the borders of the United
States such as in Los Angeles County, California. Most stibnite
deposits occur in narrow veins in siliceous rock, (quartz or granite),
and when crushed, yield an ore of low antimony concentration. It is
advantageous to concentrate these ores cheaply to reduce their bulk
before further refining. Froth flotation concentration has been used
with some success on various antimony ores. 2-5 and 2-6 xanthate
collectors have been shown. to yield fair recoveries. (11) There is a
tendency for the ground ore to slime. The association of stibnite
with dense arsenOpyrite makes a good separation extremely difficult.
(10)

The present work reports recovery data obtained by the use of a
normal-decyl substituted methyl violet dye as a collecting agent. The
use of CuSO4 and KCN as conditioning agents at various pH values is
studied. Previous work done in this laboratory by Ludt and De Witt on
the flotation of c0pper silicate indicated that one might hope to obtain a
concentration of antimony ore by means of a pr0per1y substituted
dye. (18) The use of antimony salts as mordants with methyl violet in-

dicates further the possibility of its employment as a collector. (6)

This substituted methyl violet dye was appr0priately synthesized. (4)
Flotation concentration tests with a California stibnite ore containing

12. 7% antimony are reported.

HISTORY

Froth flotation is a comparatively recent method of concentrating
ores, especially in the non-ferrous metals industry. Flotation is the
means by which a mineral is separated from a gangue by causing the
mineral particles to float on the surface of a pulp while the gangue
particles sink to the bottom. Flotation had its beginning in about 1860
when William Haynes discovered the difference in wettability of
various minerals. Bulk oil flotation was the first type to be employed
for mineral separations. This method was based on the fact that
minerals with a metallic luster are wet more by an oil than by water;
Bulk oil flotation was used as early as 1900. When finely ground
sulfide ores are gently placed on a water surface exposed to air the
gangue particles will sink but the sulfide particles have a tendency to
float. This type of concentration is known as skin flotation. This
type of flotation was used mainly about 1910.

Flotation using air as the buoyant medium had its introduction in
about 1902 when Froment used air bubbles for the levitation of oiled
sulfide particles. This combined use of a small quantity of oil with air
bubbles grew rapidly from 1912 to 1925, first in Australia and then in
the United States. During this period the flotation process consisted
of collecting all metallic ores in a gangue in one single concentrate.

The circuits during this period were of the acid type and used an oil

or fatty acid as the collector. This type of flotation is known as
"bulk flotation".

In the early 20's a need for a more selective type of flotation was
seen for the concentration of the various kinds of mixed sulfides.
There are about 5 classes of sulfides composed of mixtures of Cu,
Pb, Zn, Fe, and Ni. The separation of these sulfides was brought
about by three developments:

(1) use of the alkaline circuit

(2) use of specific organic collectors (xanthates)

(3) utilization of cyanides to depress sphale rite and pyrite.

This "differential flotation” became the basis for the concentration of

the base metal sulfide ores. (2)

THEORY

In the froth flotation concentration of ores there are several
terms used which ought to be defined, namely: (12)

1. frothers - generally organic compounds which are water
soluble and will form a stable froth with air.

2. collectors - generally organic compounds which induce a
mineral to float at air-water interface and form a stable

mineral froth.

3. activators - (conditioners) - generally inorganic compounds
which promote flotation with an otherwise inactive collector.

4. depressants or inhibitors - generally organic compounds
which prevent the collector frim functioning.

When a mineral is to be concentrated by froth flotation it
first must be liberated from its ore by proper grinding. Usually
the ore is ground wet to form a pulp which is ready to be introduced
into the flotation machines. The amount of grinding to be done
must be determined by the economy desired.

A method of producing air bubbles in the bottom of the cell
must be furnished by dire ct introduction of air along with agitation.
The right type of collector and modifying agents must be present to
form a water repellent coating on the mineral particles desired to
be concentrated. The particles are made hydr0phobic. The collector
used generally consists of a polar and a non-polar part. The polar

part reacts with the mineral surface and leaves the non-polar

hydrocarbon chain sticking out. This chain is water repellent and
will cause the mineral particles to adhere to the air bubbles and
cling to them as they rise to the surface of the cell. There must

be also present a frothing agent which will lower the surface tension
of the water so that the air bubbles coated with mineral particles will
be able to break the surface and remain to be collected.

Most of the frothers contain a solubilizing group and a hydrocarbon
radical of at least five carbon atoms. A froth is obtained from the
opposing tendencies of the polar and non-polar parts. The insolu-
bility of the frothing agent depends on the number of carbon atoms in
the non-polar group. Some of the more common frothers used are pine
oil, cresylic acid soaps and mixtures of aliphatic alcohols.

In general collectors fall within one of the three following classes:

1. Oils insoluble in water - oleic acid.

2. Organic compounds containing sulfur such as alkyl thio
acids and mercaptans.

3. Alkyl sulfuric and sulfonic acids, used in the form of
their alkali salts such as soaps and xanthates.

The collector must be.either adsorbed or react with the surface of
the mineral desired to float and must stick to it securely, There
must not be any reaction with the gangue to cause it to take on a

hydr0phobi c laye r .

In 1935, over 21 million tons of ore were concentrated using
1, 290 tons of synthetic reagents. (12)

The term, modifying agent, would include activators,
depressers, pH regulators, etc. Activators are adsorbed as
anions or cations or react with mineral surface to make it more
susceptible to the collector. NaZS is used to sulfidize the surface
of oxidized heavy metals. CuSO4 is used as an activator in the
concentrating of zinc blende and also in the flotation of stibnite
with xanthates. The lead ion is also an activating agent in conjunc-
tion with aerofloats or thiocarbonilid.

Depressants may change the nature of the mineral surface so
that differential flotation can take place. A gangue which may
have a tendency to float with a collector may be made, by the use of
the prOper depressant in the right pH range, to be hydr0philic. Both
NaCN and NaZS are used in alkaline solutions as depressants. The

NazS can be either an activator or depressant depending on the

minerals present in the pulp.

PROCEDURE

Preparation of the Antimony Ore.

 

About half of the 20 pounds of stibnite ore received from
California was crushed in a jaw crusher and then finally in a
roll mill so that it would all pass through a #100 sieve. The ore
was deslimed by several washings and decantations of the wash
water. No ore was used finer than a #325 sieve.

Operation of the Flotation Cell.

 

Each run was made in a laboratory flotation cell built of
lucite to aid observations. 200 ml. of distilled water was
added to the unit. This was followed by the addition of the con-
ditioning reagents, HCl or NaOH, and 100 gms. of deslimed ore.
The ore was allowed to circulate with the conditioning agents for
10 minutes before filling the cell to within 3/8" of the overflow.
The collecting agent (n-decyl methyl violet), tannic acid, and
pine oil were added in the order mentioned. The ore was allowed
to condition in the absence of air agitation. After the addition of
pine oil from a fine dip-wire, compressed air was turned into the
flotationcell. The stable foam which formed was swept off into a
Buechner funnel over a 5 minute period. The collected concentrate

was dewatered by vacuum, dried at 150°F, weighed, and then analyzed

according to the method of Treadwell and Hall. (8).

Analysis of the Concentrate.

 

A 0. 5 gm. sample of the dried concentrate was dissolved in
10 ml. of cold conc. HCl. After action had ceased 0. 3 gm. KCl
was added and the remaining HZS was driven off over a steam bath for
10 minutes. After the solution cooled to room temperature, 3 gms. of
tartaric acid in 5 ml. of water was added and then the solution was
agitated while adding 10 gm. of NazCO3 in 200 m1. of water. The
entire mixture was then titrated with 0. l N. iodine solution using 2 m1.
of a soluble starch solution as indicator. The 0. 1 N. iodine solution had been
standardized using arsenious trioxide, A5203. A pale blue-violet color
was obtained at the end point.

The remaining tails and pulp water were drawn off at the bottom of
the cell and allowed to settle for about an hour. Upon settling the pH
was determined of the fluid by using a Beckman pH Meter. The cell was

cleaned out with distilled water between each run.

lO ,1

Preparation of the Substituted Methyl Violet

 

The n-decyl bromide was prepared from n-decyl alcohol, conc.
sulfuric acid, and 48% hydrobromic acid in a refluxing apparatus. (4)
It was purified by vacuum distillation at 35 mm. pressure. N-decyl bromide
was then refluxed with methyl violet B, ethyl alcohol and sodium hydroxide
for 6 hours. The solution was then neutralized with HCl, boiled with
water, and then filtered. The filtrate was then treated with sodium
chloride to salt out the decyl-methyl violet. (9) An alcoholic dye solution,
0. 2 gm. /100 m1. , (30% CZHSOH by vol.) was made up for use as a
collecting agent.

Re actions:

 

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stibnite particles.

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Collector concentration in all runs = . 08 #/ton ore.
Run %Sb. in
No. Reagents #/ton ore £11 Concentrate % Recovery
1 Not de slimed 21. 3 37. 4
2 31. 8 67. 8
4 7. 7 36. 8 75. 2
5 CuSO4 - 1. 0# 9. 0 44. 6 46. 6
9 CuSO4 - 1. 0 9. 3 44. 75 52. 1
10 CuSO4 - 1. 0 10. 85 35. 7 59. 5
11- K4Fe (CN)6 - 1. o 9. 4 44.25 66. 2
1 2 K4Fe (CN)6 - 1. 0 10. 1 37. 5 61. 6
1 3 CuSO4 - 1. 0 9. 32 33. 6 59. 7
14 KCN — 1.0 9.16 38.9 67.5
15 PbAcz - 1.0 10.25 36.4 68.0
16 CuSO4 - 1.0 4.7 50.6 59.8
17 KCN - 10 5.4 48.2 63. 5

1 8 CuSO4 - 1. 0 5. 5 47. 1 68. 9

l4

 

 

 

 

 

Collector Concentrate in all runs : .16 #/ton ore.
Run % Sb. in
No. Reagents #/ton ore 31:1— Concentrate % Recovery
3 32. 1 73. 6
6 CuSO4 - 0. 5 8. 4 35. 3 70. 6
7 CuSO4 - 0.5 7. 2 37.4 72. o
8 CuSO4 - 1. 0 10. 56 41. 9 53. 6
20 CuSO4 - 1. 0 5. 1 46. 4 67. 6

Collector Concentrate : . 24 #/ton ore.

 

19 CuSO4 - 2.0 4.4 42.2 49. 8

15

Data from two runs of antimony ores taken from Denver Equipment

Company bulletin No. T4-B7

. Description An Antimony ore containing
of stibnite, a small amount of
ore pyrite, and arsenic in a

siliceous gangue.

Assay of Ore. Antimony

Approximate Ar senic

Iron
Insoluble
Sulfur
Method or
Proce s s

Concentrates Unit cell conc.

and Recovery Flotation conc.

Reagents, PbN03
lbs. per ton Z-5 Xanthate

Pine Oil

Miscellaneous

Data pH, 6 . 5

6. 0%
0.1
2. 0

77. 0

3.0

Denver "Sub.
Denver "Sub.

An ore containing
stibnite and antimony
oxides in a siliceous

gangue.
26. 0%
1. l
59. 5
8. 7
- A" Unit Cell

- A" Flotation

 

 

”/0 ‘70 ”/0 ‘70
Antimony Recovery Antimony Recovery
67.0 69.0 65.5 29.0
69. 0 26. 0 54. 0 64. 0
2. 8 Soda Ash 2. 0

0. 3 PbN03 1. 8
0. 1 Z—6 Xanthate 0. 4
Pine Oil 0. 06
pH, 8. 0

16

Sieve analysis of the ground stibnite ore:

Fraction Percent

#100-140 17. 0
140-200 34. 9
200-270 30. 9
270-325 17. 2

100. 0

GRAPHS

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DISCUSSION

19

The writings of Freundlich and Neumann indicate that the
adsorption of certain basic dyes on mineral gels occurs with
quite a good deal of selectivity. (18) They contend that this
adsorption may be chemical in nature, involving the transferral
of cations between the dye and the mineral surface. All work at
this laboratory grew out of these references. The dyes cited by
Neumann and Freundlich actually act as depressants with some
minerals. Modification of the dye structure as indicated by Ludt, (18)
Thakkar (19) and this report gives strong evidence that when a long
aliphatic chain is substituted either in the benzene nucleus or, as in
the present report, in the amino side chain the substituted dyes act
as good flotation collectors for minerals upon which they adsorb.
Antimony salts have been used as mordants with methyl violet
dyes. (6) Upon the addition of an antimony compound to methyl violet
which has been partially precipitated with tannic acid an insoluble
lake is formed. When applying this fact to stibnite flotation it was
hoped that the insoluble lake would form an oriented coating over
the stibnite particles leaving the non-polar decyl chain to selectively

impart hydrophobic pr0perties to the ore particles. The data tends

to indicate that such a coating was formed.

The concentration of 0. 2 gm. /100 ml. was picked for the
collector solution so that one ml. would be equivalent to 0. 04 #/ ton
of ore. One ml. of the activators was equivalent to 0. 5 #/ton of ore.
The pine oil addition was equal to about 0. 1 #/ ton of ore .' The froth
formed after the usual induction period. Too long an induction period
indicated that too much pine oil was added.

The desliming of the ore was found to be quite essential. Several
runs made without desliming gave poor results. Reference to the
data reported indicates much better results with the deslimed ore.

The final concentration of 64% reported by the Denver Equipment
Company is for a multi—celled flotation procedure. (11) The maximum
recovery reported in this effort is about 73%. This figure of 73% represents
the efficiency of the decyl substituted methyl violet in a single flotation
separation that could be duplicated. This maximum recovery was found
to occur in a pH range of around 6 to 7 using CuSO4 as an activator
although the highest concentration of antimony in the concentrate was
obtained at a pH of 4 to 5.

For future work with this methyl violet type of collector it would be
advisable to make an ore mixtureof less than 12. 7% antimony by diluting
the California ore with pure ground Ottawa sand or some such siliceous
material. It would be interesting to note the effect of other salts as

activators, also.

 

21

It is hoped that results obtained in this thesis will be helpful

in future work with the beneficiation of stibnite ore.

BIBLIOGRAPHY

BOOKS

(1) Dana, E. S., "Textbook of Mineralogy", Ed. by Wm. Ford,
John Wiley and Sons, New York, 1949.

(2) "Flotation Fundamentals", Dow Chem. Co. , San Francisco, Cal. ,
2nd Ed. , 1947.

(3) Gaudin, A. M. , "Principles of Mineral Dressing", McGraw-Hill
Book Co. , New York, 1939. .

(4) Groggins, "Unit Processes in Organic Synthesis".

(5) Lewis, Squires, and Broughton, "Ind. Chem. of Colloidal and
Amorphous Materials", New York, The MacMillan Co. , 1948,
Pp. 267-270.

(6) Pratt, ”Chem. and Physics of Organic Pigments", p. 176.

(7) Taggart, A. F. , "Handbook of Mineral Dressing", New York
John Wiley and Sons, Sec. 12, 1945.

(8) Treadwell and Hall, "Analytical Chemistry" John Wiley and Sons,
New York, 1942.

(9) Rowe, F. M. , Editor, "Colour Index - Society of Dyers and
Colourists", 1924._

ARTICLES

 

(10) Denver Equipment Co. Bulletin No. FlO-BZZ
(11) Denver Equipment Co. Bulletin No. T4-B7

(12) DeWitt, C. C.. Ind. Eng. Chem., Vol. 32, page 652, 1940

 

(13) Hassialis, M. H. , "Surface Active Compounds in Flotation Ore
Dressing", N. Y. Academy of Sciences Annals, Vol. 46.

 

(14)

(15)

(16)

(17)

(18)

(19)

25

Mineral Trade Notes, U. S. Dept. of Interior - Bureau of Mines,
Vol. 30,#6, 1950.

Plante, Enid C. , American Institute of Mining and Metallurgical
Engineers, Tech. Pub. No. 2298, Mining Tech.,January1948.

 

Yamada G. and Yokoyama Y., Suiyokwai-Shi, Vol. 9, pp. 245-50
(1937).

 

Lenton, P. A. , "Froth Flotation Concentration of Azurite and
Malachite in Alkaline Earth Gangue Materials", M. S. C. ,
1943.

Ludt, R. W. , "The Flotation of Capper Silicate by Alkyl-Substituted
Triphenylmethane Dyes", M. S. C., 1947.

Thakkar, J. L. , "Alkyl Substituted Wurster's Salts as Flotation
Reagents", M. S. C., 1950.

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