Primary Examiner-G. O. Peters
Attorney, Agent, or Firm--Shetidan, Ross & Fields
1 Claim, No Drawings
A method for the separation and recovery of elemental
sulfur from mixtures of foreign material and sulfur
which comprises washing the foreign material and sulfur
mixture to remove impurities which are deleterious
to coalescence of the sulfur particles followed by adding
as a cleansing and coalescence agent an alkali
metal hydroxide or carbonate, heating the mixture to
a temperature above the melting point of sulfur for
one hour to coalesce the sulfur particles, and separating
the coalesced sulfur from the foreign material.
United States Patent [19]
Kazel
[54] SULFUR RECOVERY PROCESS
[75] Inventor: William G. Kazel, Arvada, Colo.
[73] Assignee: Cyprus Metallurgical Processes
Corporation, Los Angeles, Calif.
[22] Filed: Mar. 9, 1972
[21] App\. No.: 233,352
[52] U.S. CI 423/578 A
[51] Int. CJ.2 COIB 17/14
[58] Field of Search 423/567, 578, 571;
23/308 S, 312 S, 313
[56] References Cited
UNITED STATES PATENTS
1,798,912 3/1931 Sperr 423/571
1,990,602 2/1935 Guernsey 23/312 S X
2,459,764 1/l949 Yeiser. 23/308 S
2,838,391 6/l958 Kaufman et al. 23/308 X
3,371,999 3/l968 Skrzec 423/478
FOREIGN PATENTS OR APPLICATIONS
1,00 I,486 8/l965 United Kingdom 423/578
346,835
350,573
1,023,248
[57]
4/l931
6/l931
3/l953
[II] 3,939,256
[45] Feb. 17, 1976
United Kingdom 423/578
United Kingdom 423/578
France 423/578
ABSTRACT
3-,939',256
SUMMARY OF THE INVENTION
1
SULFUR RECOVERY PROCESS
The present invention relates to the recovery of sulfur
from an input feed containing elemental sulfur and
mineral impurities which has been ground sufficiently
fine to permit slurrying. The invention contemplates a
pretreatment which consists of an acid or water wash to
remove heavy metal and alkaline earth metal impurities
which may be acid soluble or water soluble. This pretreatment
process is followed by a thermal or heat
treatment above the melting point of sulfur and in the
range of about 120° - 140°C, in the presence of an
alkaline treating agent selected from alkali metal hydroxides
and carbonates in the amount of at least five
pounds perton of dry feed or 0.30 grams per 100 grams
feed.
BACKGROUND OF THE INVENTION AND PRIOR
ART
2
moval of.'certain deleterious acid soluble metal ions
associated with elemental sulfur produced from metallic
sulfides. Thus, the elemental sulfur wets the mineral
impurity surfaces and cannot be separated. Further, in
5 the McGauley patent there is no provision for a prolonged
heating time since the patent gives a maximum
of 5 minutes and, finally, no provision for basic additives
during that treatment.
10 Additionally, the process of U.S. Pat. No. 3,371,999,
Skrzec, is of interest. In separating iron and sulfur chlorides
contained in molten sulfur, the patentee passes
the molten sulfur by-product countercurrent to a dilute
basic aqueous solution to extract the chlorides and
IS collect the elemental sulfur in a pool.
While peripherally relevant, substantial differences
exist between the process of Skrzec and the present
invention. In the patent there is no suggestion of a
pre-wash to remove acid or water soluble, deleterious
Elemental sulfur frequently occurs in nature inti- 20 ions. Further, there is no coale,scence from mineral
mately admixed with various mineral impurities. Where impurities and the amounts and ,nature of the alkaline
such deposits occur at or near the surface, the tradi- treating agents or additives are different. Finally, the
tional "Frasch" recovery method cannot be used. As a patent shows uniformly a short treating time while in
result, such deposits cannot be economically exploited. the present process, optimum coalescence with respect
Elemental sulfur may also be produced by certain 25 to yield occurs after about I hour and optimally 2 hours
chemical reactions, and in particular by the oxidation (120 minutes).
of the sulfide sulfur in metallic sulfides. Specific examples
of such oxidation are the electrolytic oxidation of
nickel sulfides as taught in U.S. Pat. No. 2,839,461, arid It has been found that in the separation of elemental
the ferric chloride oxidation of copper sulfide as taught 30 sulfur from mineral impurities by the method ofheating
in U.S. Bureau of Mines Report of Investigation R.I. an aqueous slurry oithe elemental sulfur and mineral
7474.
Where elemental sulfur is produced by chemical impurity above the melting point of sulfur (120°C) so
reaction, its separation from mineral gangue is required that the elemental sulfur coalesces, certain impurities
in order that it be of sufficient purity to be a marketable 35 frequently found in nature or in the production of such
by-product. sulfur by oxidation oimetallic sulfides are deleterious
Thus, whether the combination of sulfur and mineral and prevent the coalescence of the sulfur. Such deleteimpurity
occurs in nature or as a result of chemical rious ions may be removed through a preliminary washreactions,
the separation of the elemental sulfur and ing of the sulfur and mineral impurity prior to the cothe
mineral impurities has become important for eco- 40 alescence step.
nomic reasons. Furthermore, there is increasing public The term "foreign material" as used herein includes
concern over the large quantity of sulfur dioxide air mineral impurities with which elemental sulfur exists
contamination which results from the traditional smelt- uncombined in nature and may result from concentraing
of metallic sulfides. Processes for the conversion of tion of native sulfur ore or from concentrate used in the
sulfides by the chemical or electro-chemical means 45 recovery of metals from their sulfides in ores. The wash
cited above' which produce elemental sulfur are of medium of the slurry referred to herein may be water
public benefit. The low cost and efficient separation of or dilute mineral acid. Reference to "washing" the
the elemental sulfur produced is an important adjunct material includes washing with water or dilute mineral
to such processes. acid.
In the past, various techniques have been proposed 50 The so-called "deleterious metal ion" concentration
and used commercially to accomplish the separation of which is subject to acidic and/or water removal from
sulfur from mineral impurities. These have included elemental sulfur in the present process consists oione
melting and filtering, and sublimation. Neither process or more ions selected from the alkaline earth metals
has proven to be economical in the presence, of substantial
quantities of mineral impurities. More recently, 55 (Group 2a) and heavy metals ofthe top half of the
certain organic solvents have been proposed whereby Periodic Table of Elements (Handbook of Chemistry
the sulfur is dissolved and caused to reprecipitate in and Physics 49, Chemical Rubber Co., 1968-69). It has
pure form. Such processes have been shown to be ef- been further found that in a typical situation where the
fective in processing low grade sulfur feeds and in pro- raw material is chalcopyrite, zinc sulfide and the'like,
ducing pure products but are inherently expensive in 60 the principal deleterious or interfering ions subject to
capital and operating costs. acid wash removal are calcium, magnesium, ferric iron,
A process is taught in U.S. Pat. No. 2,537,842, ferrous iron, cupric copper, cuprous copper and zinc.
McGauley et aI., whereby an aqueous slurry of the Also; it has been found that as respects the following
sulfur is heated above the melting point of sulfur, and elements when present in a form capable of dissolving
then cooled below the melting point, resulting in the 65 in a mineral acid at an acid pH of 1.0 and above, and
formation of discrete sulfur particles which may be preferably in an acid pH range of about 1.0 to 4.0, the
separated by froth flotation from the mineral gangue. concentrations cited will prevent the coalescence of
However, in the patent there is no provision for re- the sulfur:
3,939,256
EXAMPLE I
Comparative Study - Pretreat Wash and Alkaline
Additive
Feed of 300 grams native sulfur concentrate of
50.2% grade was slurried in 1 liter of water. The agitated
slurry was held for 120 minutes at a temperature
above 120°C. The slurry was cooled and the product
screened off on a 100 mesh U.S. Standard screen.
Test I Test 2 Test 3 Test 4
Pretreatment None ·Washed None ·Washed
Additive None None 3.6 gm NaOH 3 gm Na.Coa
( 1.2 gm/! 00 gm (I gm/IOO gm
of feed) of feed)
Product 95.9% 94.9% 95.9% 97.4%
(o/c sulfur)
Yield 61.0% 75.0% 61.0% 92.0%
(per cent)
·The wash was accomplished by a 5-minutc wash with .1 N Hel and the pH of the
solution was 1.5.
4
solids for good sulfur-to-sulfur contact. A range of
slurry density of from 20 percent to 50 percent solids
by weight is preferred and a slurry density of 30-45
5 percent most preferred.
The temperature to which the slurry is raised is critical.
In order for the sulfur to coalesce, it is necessary to
raise the temperature above the melting point of sulfur
which is about 120°C. At higher temperatures, sulfur
becomes increasingly viscous so that temperatures
above 140°C are avoided. The preferred temperature
range is 1300 to 140°C.
To obtain these temperatures, a suitable pressure
device is required. Autoclaves with provision for agitation
are a preferred device but a pressure pipe with
mixing devices and other pressure devices may be used.
Treatment time and temperature will vary in accord
with the objective desired as the degree of coalescence
is time dependent. Times in excess of 60 minutes at
temperature are required to produce good grade particles
coarser than 100 mesh, U.S. Standard, upon cooling.
Utilizing somewhat longer times, as for example
1% to 2 hours, which is preferred, yields of+100 mesh
material are improved. At still longer times a pool of
sulfur can be obtained. Agitation at moderate speeds is
indicated in the process.
The separation of the elemental sulfur and the mineral
impurity may be accomplished by quenching the
slurry causing the coalesced sulfur to solidify in particles
coarser than the mineral feed. The coarse sulfur
may then be conveniently removed by screening. Alternately,
a liquid pool of coalesced sulfur may be obtained
in a pressure vessel maintained at a temperature
above the melting point of sulfur and slurry continuously
added and removed with periodic removal of the
sulfur pool providing continuous operation.
By this invention it is possible to separate sulfur from
mineral impurities and obtain a product quality of
85-95% purity and a yield of 65% or greater. The sulfur
is of sufficient purity so that it may be melted and filtered
to a product of above 99%,purity. The residual
mineral and sulfur trapped by filtration are readily
recycled to the original separation and. recovered.
This invention is further illustrated by the following
examples which were performed ata slurry pH of about
9-11 using feed passing 100 mesh screen.
65
0.25
0.25
2.0
2.0
2.0
Grams/Liter of Slurry
3
Calcium
Magnesium
Ferric Iron }
Ferrous Iron
Cupric Copper }
Cuprous Copper
Zinc
In a minority of situations, where such elements or 10
ions are present in the slurry but are so chemically
bound as to be insoluble at the acid pH utilized, or are
below effective concentrations, they are not deleterious
and an aqueous non-acid pretreatment may be
utilized. It is critical that the concentrate particles have IS
substantially all of the metal ions removed by washing
with water, acid or other agent which will dissolve in an
aqueous solution having a pH above about 1.0.
A preferred· acid-treating agent for the pretreatment
is selected from one or more strong mineral acids such 20
as hydrochloric and nitric, which are preferred. When
utilized in 0.1N solutions, hydrochloric and nitric acids
achieve a solution pH of about 1 which is optimum for
the process. Of the other commercial strong mineral
acids, sulfuric and ortho-phosphoric present some diffi- 25
culties in solubilizing the alkaline earth values present
and for this reason are not preferred.
It has been found that alkali metal hydroxides and
carbonates greatly promote the coalescence of sulfur
so that in the product elemental sulfur will collect on a 30
100-mesh screen, and it has been found that alkaline
earth hydroxides such as calcium hydroxide, Ca(OHh,
and ammonium hydroxide, NH40H, will not operate
successfully to coalesce sulfur.
The alkali metal utilized as the hydroxide and car- 35
bonate is defined as one or more of Group 1a of the
Periodic Table, Handbook of Chemistry and Physics 49,
ante, namely lithium, sodium, potassium, rubidium,
caesium and francium. Of this group, the commercially
feasible members are lithium, sodium and potassium, 40
and these latter are preferred. Using the strong base
sodium hydroxide as a standard, at least Sibs. must be
added per ton offeed to achieve the necessary basic pH
for the slurry and it is critical that this amount be used.
For sodium hydroxide, a preferred range is 10 lbs. - 30 45
lbs./ton, a most preferred range is 15 lbs. - 25 lbs./ton,
and an operable range is Sibs. to over 50 lbs./ton. The
less alkaline carbonates are generally utilized in larger
amounts, so that their utilization is near the upper end
of the Sibs. - 50 lbs./ton range. The process works 50
optimally from an economic standpoint at pH 9-11 and
above, and, e.g., IN Na OH imparts a pH of about 13
in a theoretical unbuffered solution.
The precise mechanism by which these additives
work is not known, but it is believed that in the pres- 55
ence of these basic alkalis the sulfur may dissolve in the
aqueous phase and then reprecipitate in pure form
promoting the coalescence.
It is further postulated that the alkali metal treating
agents dissolve some of the sulfur as sodium sulfide 60 --------------------which
precipitates out to serve as a nucleating agent for
crystallization. It is known that in the present process
after 1 hour a majority of the nucleated sulfur particles
are caught on a screen which would pass the original
feed.
The slurry density at which the separation is effected
is not critical within a broad range. It is only necessary
that there be sufficient aqueous phase present so that
the solids may move freely and that there be sufficient
J;939,256
5
The test showed significant yield benefits of 2 and 4
over I and 3.
6
EKample I. The slurry was cooled and the product separated
on a 100 mesh U.S. Standard screen.
Test I Test 2 Test 3
Additive
Time at temperature
Product (% sulfur')
Yield (per cent)
2 gm NaOH
(2/3 gm/IOO gm of
feed)
135 min.
96.7
82.0
2 gm NaqH
(2/3 gm/lOO gm
of feed)
78 min.
96.6
71.0
1 gm Na2Co3
(1/3 gm/lOO gm
of feed)
240 min.
92.2
98
Increasing yield of coarse sulfur particles with in15
creasing time is clearly shown.
EXAMPLE IV
Effect of Added Measured Iron Impurity
About 270 grams of a concentrate produced by the
oxidation of chalcopyrite-containing sulfur 48%, chalcopyrite
12%, pyrite and other minerals 40%, was slurried
in I liter of water and held at 135°C ± 5° for 135
minutes. The' feed had been washed with acidified
water to remove acid-soluble impurities. Subsequently,
measured amounts of impurities shown below were
added with the following results. The slurry was cooled
<:Ind the product screened., off on a 100 mesh U.S. Standard
screen.' '
EXAMPLE II
Comparative Study Using Several Alkaline or Basic
Additives
300 grams of concentrate was produced by the oxida- 20
tion of chalcopyrite-containing sulfur 25.5%, chalcopyrite
26.6%, pyrite and other minerals 47%. The feed
was washed, to remove soluble ions utilizing an acid
wash-soak of O.IN HNOa for 20 minutes with a recorded
pH of 3.0. The feed was then slurried in one 25
liter of water and held at 135°C for 135 minutes. The
slurry was cooled and the product screened off on a
100 mesh U.S. Standard screen. ' ,
Test 1 Test 2 Test 3 Test 4 Test 5
Additive None I gm 2 gm KOH 3 gm 4 gm Li2Co3
NaOH NaHCo3
(1/3 gm/lOO (2/3 gm/ (I gm/IOO (1/3 gm/lOO
gm of feed) 100 gm gm of feed) gmof feed)
of feed)
Product 48.7% 91.7% 94.1% 88.4% 92.4%
(% sulfur)
Yield 50% 88% 68% 92% 80%
Test 1 Test 2 Test 3 Test 4 Test 5
Additive 2 gm 2 gm 2 gm 2 gm 2 gm
NaOH NaOH NaOH NaOH NaOH
(.74 gm/ (.74 gm/ (.74 gm/ (.7~ gm/ (.74 gm/
100 gm 100 gm 100 gm 100 gm 100 gm
of feed) of feed) of feed) of feed) of feed)
Impurity
added None I gm Fe+++ 2 gm Fe+++ 1 gm Fe++ 2 gm Fe++
Product
(% suI·
fur) . 86.7 89.7 85.7 86.3 85.7
Yield
(per'
cent) 59.0 39.7 25.0 52.0 27.0
The results showed substantial increase in yield for 45
each alkaline additive as against the standard in Test 1.
The deleterious effect of the heavy metal ion is
shown as against the reference standard (Test 1).
EXAMPLE III
Effect of Heating Time on Yields
300 grams of concentrate produced by the oxidation
of chalcopyrite-containing sulfur 49.2%; chalcopyrite
2.3%, pyrite and other minerals 47.7%, was slurried in
I liter of water and held at 135°C ± 5Hor the time
periods shown. The feed had been washed,to re)J1ove
soluble ions using the acid pretreatment as set out in
EXAMPLE V
60 Effect of Added Measured Metal Impurities
About 270 grams of concentrate produced by the
oxidation of chalcopyrite-containing sulfur 48%,chalcopyrite
12%, pyrite and other minerals 40%, was slurried
in I liter of water and held at 135°C ± 5° for 135
65 minutes. The, feed had been washed with acidified
water ,to remove acid soluble impurities in the manner
of Example II. The,amounts of impurities shown were
added with the following results. The slurry was cooled
3,939,256
7
and the product separated on a 100 mesh U.S. Standard
screen.
8
Test I Test 2 Test 3 Test 4 Tcst 5
Additivc 2 gm 2 gm 2 gm 2 gm 2 gm
NaOH NaOH NaOH NaOH NaOH
(.74 gml (.74gml (.74 gml (.74 gml (.74 gml
100 gm 100 gm 100 gm 100 gm 100 gm
of feed) of feed) of feed) of feed) of feed)
Impurity
added None I gm Cu++ 2 gm Cu++ 0.25 Ca++ 0.25 Mg++
Product
(% sulfur)
86.7 92.5 86.0 84.4 70.8
Yield (%) 59.0 60.0 21.8 8.3 1.0
EXAMPLE VIII
The deleterious effect of varied metal impurities on
yield was noted by comparison to the reference in Test
I.
EXAMPLE VI
Comparison of Effect ofZn++and Fe++on Yield
2I5 grams of concentrate produced by the oxidation
of zinc sulfide-containing sulfur 34.5%, ZnS 34%, minerai
impurity 3I.5% \vas slurried in I liter of water and
held at 135°C ± 5° for 135 minutes. The feed had been
washed with acidified water to remove acid-soluble
zinc ions using the acid pretreatment as set out in Example
I. The slurry was cooled and the product separated
on a 100 mesh U.S. Standard screen.
Pilot Plant Procedure
The feed for the autoclave was received as a filter
cake from the leaching operation. The material was
20 approximately 100% of -200 mesh size and ranged
from 10 to 20 percent water. This feed was then
charged into a repulp tank where it was slurried with
water to approximately 20% solids. The slurry was fed
to a filter where water was removed and fresh water as
25 a displacement 'Nash was added to the top.
The wash water removed in the filt~ring operation
was tested to determine the amount of metal ions, such
as iron, calcium and other detrimental ones. If the
analysis indicated a high level, the feed may be taken
back to the slurry tank where it was slurried with O. IN
Test 1 Test 2 Test 3
Additive 2 gm NaOH 2 gm NaOH 2 gm NaOH
(.93 gm/lOO gm of (.93 gm/lOO gm of (.93 gm/lOO gmof
feed) feed) feed)
Impurity
added Nonc 2 gm Fe++ 2 gm Zn++
Product
(% sulfur) 77.7 56.6 82.7
Yield (per
cent) 48.0 6.8 25.0
HCI solution and repulped and refiltered. This operation
was continued until the wash water checked below
45 acceptable levels of detrimental metals.
The solids were then repulped to 30 to 40 percent
solids, utilizing about 20 Ibs. of NaOH per ton of dry
feed to give a pH slurry reading of I I or 30 Ibs./ton for
a pH of 13 and charged into the autoclave. The autoclave
was sealed, the agitator started, and steam was
injected into the jacket for the heating cycle. The speed
of the agitator is that at which the particles are kept in
suspension and a homogeneous slurry is maintained. At
This example shows the process is effective for zinc
concentrates and shows the deleterious effect of zinc
and iron ions on yield.
EXAMPLE VII (See Example III)
About 270 grams of a concentrate produced by the
oxidation of chalcopyrite-containing sulfur 48%,chalcopyrite
12%, pyrite and other minerals 40%, was 50
washed, slurried in I liter of water and held at 135°C ±
5° for the times shown. The slurry was cooled and
screened on a 100 mesh U.S. Standard screen.
Test I Test 2 Test 3
Additive 2 gm NaOH 2 gm NaOH 2 gm NaOH
(.74 gm/lOO gm of (.74 gm/lOO gm of (.74 gm/lOO gm
feed) feed) of feed)
Time 30 min. 60 min. 235 min.
Product
(o/c sulfur) 88.5 90.9 86.7
Yield (%) 23.0 19.0 59.0
This example shows that while a ,small amount of 65
coalescence occurs very quickly that times in excess of
I hour are necessary to obtain a high degree of coale~cence.
the end of the heating cycle, steam was shut off, cooling
water was admitted to the jacket, the autoclave cooled
down, and when the temperature dropped below 80°C
the' agitator was slowed down, the bottom valve opened
and the autoclave 'dischargedtoa screen. The sulfur
3,939,256
9
product was removed as the oversize + 65 .mesh, and
the fine materials or the tailings proceeded on to a
thickener. The sulfur product averaged around 96%
elemental sulfur with a recovery of over 85%. The
particles were greenish-yellow in color and irregularly 5
shaped.
What is claimed is:
l. A process for the recovery of elemental sulfur
from mixtures in which it is present with soluble calcium
compound impurities which comprises: 10
a. contacting the mixture with water to solubilize
calcium ions;
b. separating the solids content of the treated mixture
from the liquid content and washing the solids
15
20
25
30
35
40
45
50
55
60
65
10
content to remove said solubilized calcium ions
from the solids content;
c. forming a water slurry of said solids content;
d. adding to the slurry a surface modifying additive
selected from the group consisting of alkali metal
hydroxides, alkali metal carbonates, and mixtures
thereof to produce an alkaline slurry pH of at least
about 9;
e. heating the slurry to at least the melting point of
sulfur for a period sufficient to coalesce substantially
all of the sulfur particles, and
f. recovering the coalesced sulfur from the slurry.
* * * * *