3,939,256 Sulfur recovery process

Patent Number/Link:

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

France 423/578

ABSTRACT

3-,939',256

SUMMARY OF THE INVENTION

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

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.

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.

0.25

2.0

Grams/Liter of Slurry

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

The test showed significant yield benefits of 2 and 4

over I and 3.

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

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

and the product separated on a 100 mesh U.S. Standard

screen.

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

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

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

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.

* * * * *