4,053,301 Process for the direct production of steel

Patent Number/Link:

United States Patent [19]

Stephens, Jr.

[11]

[45]

4,053,301

Oct. 11, 1977

[54] PROCESS FOR THE DIRECf PRODUCI10N

OF STEEL

[75] Inventor: Frank M. Stephens, Jr., Lakewood,

Colo.

[73] Assignee: Hazen Research, Inc., Golden, Colo.

[21] Appl. No.: 622,101

[22] Filed: Oct. 14, 1975

[51] Int. Cl.2 C21C 5/52; C22BlIlO

[52] U.S. Cl 75/11; 75/26;

423/148

[58] Field of Search 75/11, 26, 60, 32;

423/148

[56] References Cited

U.S. PATENT DOCUMENTS

228,329 1/1880 Edison 75/1

2,780,537 2/1957 Stelling 423/148

2,894,831 7/1959 Old 75/26

3,140,168 7/1964 Halley 75/26

3,364,009 1/1968 Kemmetmiiller 75/25

Primary Examiner-P. D. Rosenberg

[57] ABSTRACf

A process for the direct production of steel from partic-

. ulate iron oxides or concentrates including two major

steps in which in Step (1) the iron oxides are converted

to iron carbide and in Step (2) steel is produced directly

from the carbide in the basic oxygen furnace or the

electric furnace. In the production of the carbide the

oxides are reduced and carburized in a single operation

using a mixture of hydrogen as a reducing agent and

carbon bearing substances such as propane primarily as

carburizing agents. Iron carbide thus produced is introduced

as all or part of the charge into a basic oxygen

furnace to produce steel directly without the blast furnace

step. In order to make the steel making process

auto-thermal, heat is supplied either by using the hot

iron carbide from Step (1) or preheating the iron carbide

or by including sufficient fuel in the iron carbide to

supply the required heat by combustion.

53 Claims, 1 Drawing Figure

SCHEMATIC FLOWSHEET FOR DIRECT STEELMAKING PROCESS

IRON ORE

CONCENTRATE

FLUIDIZED

BED UNIT

HEAT

EXCHANGE

PREHEATER

SCRUBBER

'---H-=2+-_CO_+C0-=2+-_C.H.:.4..L MHA2K+ECUOP ..

SCRAP HOT

CO COOL AND

CLEAN

METAL FLUX

SLAG ------I MODIFIED

BDF

STEEL

u.s. Patent Oct. 11, 1977 4,053,301

SCHEMATIC FLOWSHEET FOR DIRECT STEELMAKING PROCESS

IRON ORE

CONCENTRATE

CO+C02+CH4+ H2 +HiJ HEAT

EXCHANGE

PREHEATER

SCRUBBER

H2+CO+C02+CH4 H2 +CO

L---=-__-=-----'-..L- MAKEUP •II

SCRAP HOT

CO COOL AND

CLEAN

METAL FLUX

SLAG __---I MODIFIED

BOF

STEEL

BRIEF DESCRIPTION OF THE DRAWING

The single drawing is a schematic flowsheet for the

direct steel making process of the invention.

DESCRIPTION OF PREFERRED

EMBODIMENTS

The invention will be described in detail in conjunction

with the accompanying drawing.

The basic oxygen and electric furnace processes referred

to herein for making steel are well known in the

prior art. The basic oxygen process or basic oxygen

furnace process differs chiefly from Bessemer converters

and open hearth furnaces in that the reactant used to

oxidize the carbon and certain impurities (sulfur, phosphorus,

etc.) in the charge is not air, but oxygen. The

oxygen is introduced by blowing it with a lance onto or

below the surface of the molten iron.

4,053,301

PROCESS FOR mE DIRECf PRODUCfION OF

STEEL

BACKGROUND OF THE INVENTION

ture range being about 900·-1200· F. The carburizing of

the reduced iron to carbide may be conducted so that

enough carbon is left in the iron carbide product to

supply sufficient heat upon combustion in the basic

5 oxygen furnace to make the process auto-thermal. The

1. Field of the Invention CO/C02 and hydrogen to water vapor ratios of the

The invention lies in the field of the pyrometallurgy gases in the reaction of Step (1) are maintained at a point

of ferrous metals. below which oxidation of iron carbide occurs.

2. Description of the Prior Art Off-gases from the steel making step, about 90 percent

The increasing necessity of using low grade iron ores 10 carbon monoxide, may be circulated for use as part of

for making steel because of the depletion of high grade the reducing gas for the reduction and carburizing step

ores, and economic factors, have created a demand for in the fluidized bed. Material balance calculations show

reduction of the costs in producing steel from iron ore. that the carbon content of the off-gas is sufficient to

Efforts to reduce costs have been directed to the elimi- supply all of the carbon necessary for the reduction and

nation of the use of the highly fuel-consuming blast 15 carburization step. Accordingly, when Steps 1 and 2 are

furnace. The present invention is directed to elimination performed in conjunction with each other as one conof

the use of the blast furnace by converting the iron tinuous operation, all ofthe carbon necessary for Step 1,

oxide to the carbide followed by producing steel di- subject to slight operating losses, may be provided by

rectly from the carbide in the basic oxygen furnace. The continuous cycling of the off-gas from Step 2 to Step 1.

conversion of iron oxides to carbides for various pur- 20 This eliminates the necessity for adding carbon to Step

poses has received some attention in the past but there 1 with the exception of small losses occurring in normal

has been no known activity toward producing steel operations. The result is that the carbon originally

directly from the carbide in a basic oxygen furnace. added to Step 1 to make iron carbide may be used over

U.S. Pat. No. 2,780,537, the closest prior art known, and over by recovering it in Step 2 in the off-gas as steel

discloses a process for converting iron oxides to car- 25 is produced and reusing it in Step 1 to make more carbides

in a fluidized bed process in which carbon monox- bide. When the steps are performed in conjunction with

ide is used as the chief reducing and carburizing gas. each other added heat is not required to make the pro-

The patent teaches that the reducing gas cannot contain cess auto-thermal, as the product going directly from

hydrogen in an amount more than 50 percent by volume Step 1to Step 2 is at a temperature which eliminates the

of the carbon monoxide content. It also refers to the 30 necessity for adding heat. When Steps 1 and 2 are perprior

art disclosing the use of hydrogen in a fluidized formed separately then the hot off-gas from Step 2 may

bed as a reducing gas for iron oxides having a low iron be used for preheating iron carbide or heat added by

content. The reference alludes to use of the iron carbide other means as necessary to make the steel making proproduct

for making "metallic iron" and in an "iron cess auto-thermal.

production furnace" operating below the melting point 35 The iron carbide produced in Step 1 is added directly

of iron or steel, however, there is no teaching of use of as the charge to the basic oxygen or electric furnace

the product for introduction into a fully molten steel along with fluxing agents, alloying material and other

system such as the basic oxygen furnace or electric conventional additives to produce steel directly with

furnace. Other somewhat remote prior art discloses elimination of the conventional blast furnace step. Heat

processes for converting metallic iron to iron carbide 40. is supplied to the charge when necessary in various

rather than conversion of iron oxide to the carbide. ways to make the process auto-thermal. These ways

Still other prior art discloses fluid bed processes for may include direct heating, addition of fuel such as

the direct reduction of iron oxides to metallic iron carbon, or producing sufficient free or combined carwhich

in turn could be further converted to carbide. bon in the carbide as it is produced, or others. Sensible

However, these other direct reduction processes have 45 heat from the off-gas of the BOF may be used and the

the disadvantages that the product may be pyrophoric off-gas may be partially burned to provide heat to the

in some cases requiring briquetting, and stickiness is not charge. If the latter is done the CO/C02 ratio in the

completely eliminated in some processes so that difficul- combustion gases must be maintained below that at

ties arise with the fluid bed process. which iron carbide will decompose at the required pre-

It is an object of this invention to provide a process 50 heat temperature.

for making steel from iron oxide without the use of a

blast furnace.

It is another object of this invention to provide a

successful process for making steel from iron oxide by

first converting the oxide to the carbide, followed by 55

introducing the carbide directly into the basic oxygen

furnace to produce steel.

SUMMARY OF THE INVENTION

A process for the direct production of steel from 60

particulate iron oxides or concentrates which comprises

(1) converting the oxides to iron carbide in a single step

in a fluidized bed at low temperatures with a mixture of

reducing and carburizing gases followed by (2) direct

conversion of the carbide to steel in a basic oxygen or 65

electric furnace.

The reducingand carburizing temperature of Step (1)

cannot exceed about 1300· F with a preferred tempera4,053,301

be used so long as they supply carbon to form iron

carbide.

By proper balancing of the ratios of the hydrogen and

carbon bearing materials, it is possible to restrict the

5 hydrogen to a reducing function and the carbon to a

carburizing function. This can readily be done by maintaining

quantities of hydrogen bearing gases which are

in excess of the quantities of the carbon bearing gases.

Because of the equilibrium conditions in.volved in

10 hydrogen-carbon-oxygen gas systems, the required hydrogen-

carbon ratios will automatically require that

methane be present in the gas system. The quantity of

methane present will be a function of carbon to hydrogen

ratios, as well as temperature and pressure condi15

tions.

Representative tests and results from an extensive test

program using the reduction and carburization procedure

described above in a fluid bed reactor are presented

in the following Table I.

TABLE I

The iron carbide produced by the process described

herein is a mixture of carbides having the molecular

formulas Fe2C and Fe3C with the Fe3C content being

predominant.

The fluidized bed reactor referred to herein is of the

conventional type in which finely divided feed material

on a grate or other perforate support is fluidized by

upwardly flowing gases which may include or entirely

comprise the reactant gases. Auxiliary equipment includes

heating and temperature control and monitoring

equipment, heat exchangers, scrubbers, cyclones, gas

cycling equipment, and other conventional equipment.

Some of this auxiliary equipment is shown schematically

in the flowsheet.

In this specification and the claims the reduction and

carburization step is referred to as Step 1 and the steel

making step as Step 2. The term "hydrogen bearing

gas" includes hydrogen gas alone and the term "carbon

containing material" includes carbon alone.

EXAMPLES OF Fe1C PRODUCTION

Gas Additions Off-gas Analysis· Pro-

Hz C3Hs N z Temp Hz N z CH4 CO COz duct

IImin IImin IImin • F % % % % % %C Remarks

Final red in

reactor 5.02% C

Good clean Fe3C

produced

Good Fe3C saturated

with excess C

Good Fe3C

5.02

8.96

4.94

4.67

4.77

4.69

5.42

77.0 0.5 6.3 8.9 2.0

72.0 5.2 13.2 2.9

72.1 6.5 7.8 3.4

72.6 6.4 10.6 4.0

69.3 7.9 12.2 4.4

62.5 6.7 16.1 6.7

67.5 6.0 11.6 3.9

58.3 6.1 21.4 6.8

1168 4.35

1170

1018

1081

1108

1112

1103

1130

2.5 1.0 0.5

Test Feed

No. Type Mesh Rate

FB- of Ore Size Ore g/min

30 Hematite -'-20+100 0

36 Hematite -20+100 0

37B Hematite -20+100 0

38B Hematite -20+100 0

39B Hematite -20+100 0

40 Hematite -20+100 2.7

41B Magnetite -20+100 0

41C Magnetite -325 3.8

·The balance of gas is water vapor.

The carbon content in the final product varies as the

percent iron oxide in the feed materials varies. Lower

grade ores with lower iron contents will automatically

yield products with lower carbon contents.

The volume of hydrogen in the hydrogen-carbon

monoxide reducing and carburizing mixture in the fluidized

unit should exceed the volume of carbon monoxide,

the preferred amount of hydrogen being over about

60 percent by volume of the carbon monoxide present.

The results show production by Step 1 of the process

of clean iron carbide which is highly suitable for use in

the basic oxygen or electric furnace. X-ray diffraction

analysis showed the carbon to be present as iron carbide

50 with no free carbon or metallic iron. The product was

found to be nonpyrophoric. Simulated weathering tests

showed that the product was stable in oxidizing atmospheres

containing water vapor up to a temperature of

2500 C.

The results also show that Step 1 of the process is

highly successful in producing iron carbide directly

from iron oxides when operated within temperature

ranges of about 10200 F - 11700 F using hydrogen to

water vapor ratios between 5 to 1 and 8 to 1 and CO/CO2ratios

between about 1 to 1 and 5 to 1. As stated

herein, Step 1 can be successfully operated within a

temperature range of about 9000 _13000 F, a hydrogen to

water vapor ratio of about 2.5 to 1 to about 8 to 1 and

a CO/C02 ratio of about 1 to 1, up to about 4 to 1.

Under these conditions, methane will be present in

quantities ranging from 1to 70 percent by volume of the

gas system containing the prescribed amounts of hydrogen,

water vapor, CO, and CO2. It was found that Step

Step 1 of the overall process is the conversion of the 35

oxides in the iron ore concentrate to iron carbide in the

fluidized bed unit shown in the flowsheet. The conversion

process must be carefully controlled to provide a

product suitable for use in the basic oxygen or electric

furnace. The iron carbide is desirable for use in these 40

processes because it is non-pyrophoric and resistant to

weathering which permits transport for long distances

and storage for reasonable periods.

The oxides are reduced to iron and the iron converted

to the carbide in a continuous process in the fluid bed 45

reactor in which the reducing the carburizing gases are

added together. In order to prevent any sticking caused

by the transient presence of metallic iron the temperature

is maintained below about 13000 F at all times and

preferably in the range of about 9000 _12000 F.

Hydrogen is preferably· used as the reducing gas although

carbon monoxide or hydrocarbon gases or mixtures

of hydrogen with CO and hydrocarbon gases may

be used. The flowsheet shows the use of hydrogen and

carbon monoxide with water being given off. Hydrogen 55

is preferred as the reducing gas because the oxidation

product of hydrogen, which is 'water, may be easily

removed from the furance off-gas thus permitting recycling

of the balance of the gas without the need for

extensive complicated and expensive chemical systems 60

for removing the oxidation products of carbon which

are carbon monoxide and carbon dioxide when carbon

containing reducing gases are used.

The preferred carburizing gas which is mixed with

the reducing gas is propane, although carbon monoxide 65

or other hydrocarbon gases, or solid carbon, may be

used with the lower alkyl hydrocarbon gases being

preferred. A wide range of carbonaceous materials may

4,053,301

I would not operate outside these ranges to successfully

produce iron carbide.

Step 2 of the overall process is the conversion of the

iron carbide to steel in the basic oxygen furnace. Because

of the nature of the basic oxygen furnace process, 5

special conditions apply to the processing of iron carbide

to steel by this process as compared to other steel

making processes in furnaces.

If Steps I and 2 are close-coupled so that the iron

carbide comes out of the fluid bed unit at an elevated 10

temperature ofabout 1100·-1300· F and at that temperature

is added directly to the basic oxygen furnace, then

the heat calculations show that no added heat is required

and the process is continuous and auto-thermal.

The modification shown in the flowsheet wherein the 15

off-gases are being sent directly to the fluidized bed unit

is used when Steps I and 2 are close-coupled in time. In

this modification of the process substantially all of the

carbon used in the fluidized bed unit to convert the

oxides to iron carbide is recovered as CO in the furnace 20

and recycled to the fluidized bed unit to be reused in

again making iron carbide.

If for purposes of transport or storage the Step I

product becomes or is cooled before Step 2, then heat

must be readded either in the form of reheating the 25

product or adding extra fuel to Step 2.

Heat balance calculations show that at ambient temperature

iron carbide does not contain sufficient fuel

value so that the reaction taking place in the basic oxygen

furnace is autothermal without adding heat to the 30

charge.

The additional heat required to make the reaction

self-sustaining may be supplied in a number of ways.

The off-gas from the basic oxygen furnace produced by

the processing of iron carbide contains about 90 percent 35

carbon monoxide in addition to substantial sensible heat.

The sensible heat may be used through heat exchangers

or otherwise to heat the incoming iron carbide. By

burning part of the off-gas, sufficient heat is achieved

for augmenting the sensible heat to effect the required 40

preheating of the incoming iron carbide charge to make

the process auto-thermal. Under some conditions the

sensible heat alone is sufficient. The heat for the preheating

can be obtained entirely from combustion of the

off-gas. The preferred preheat temperature range is 45

from about BOO· F to about 2000· F.

Tests conducted with iron carbide in a gaseous me·

dium simulating that of the combustion products from

partial combustion of the off-gas showed that the iron

carbide is not only stable under these conditions but 50

actually increased in carbon content from 5.9 to 7.1

percent due to the formation of the Fe2C carbide from

the normally predominant Fe3C, To achieve this result

the CO/C02 ratio in the combustion gas must be between

I to I and 2 to I when attaining preheat tempera- 55

tures of 900·-1300· F.

Added heat to make the process auto-thermal can be

supplied wholly or in part by direct heating of the Fe3C

charge with an external heat source. Sufficient carbon

may be added to the iron carbide to provide the re- 60

quired additional heat by combustion during the process.

The amount of carbon added varies from about 3

to 5 weight percent of the iron carbide charge. The

carbon may be added directly· to the iron carbide by

preheating the iron carbide in carbon bearing gases 65

having a CO/C02ratio greater than I to 1.

Heat may be supplied by reaction of the basic oxygen

furnace off-gas with incoming iron carbide. The neces-

sary carbon content of the iron carbide to furnish the

required heat upon combustion can be supplied during

Step I of the process described above by adjusting the

content of the carbonaceous material in the reacting gas

mixture of the fluidized bed to provide for the production

of suffiCient Fe2C in the Fe3C product. As shown in

the flowsheet, hot scrap metal may be added to the basic

oxygen furnace charge.

Step 2 of the process may also include the addition of

pig iron carbide charge in the basic oxygen and electric

furnaces. A significant advantage of this feature is that

iron carbide can then be added for cooling in an amount

three times that of scrap iron which can be added to

conventional basic oxygen furnace processes for cooling.

Iron carbide for this purpose can be added in' an

amount up to about 60 percent by weight of the iron

carbide-pig iron charge. One advantage of this is that

present pig iron furnaces can be continued in operation

in conjunction with the present process.

The invention includes all of the above procedures

alone or combined for providing the necessary heat for

the iron carbide charge to make the reaction in the basic

oxygen furnace auto-thermal.

If Step 2 is conducted in the electric furnace, any

extraneous heat required may be supplied by means of

the electrical evergy normally used in this type of furnace.

Step I of the process provides a convenient and effective

means for concentrating low grade non-magnetic

ores to separate the iron ore from the gangue. As the

iron carbide produced from non-magnetic ores is magnetic

it is only necessary to process non-magnetic ore,

such as, oxidized taconites, in accordance with Step I to

convert the iron oxide therein to iron carbide and subject

the treated ore to magnetic separation to separate

the magnetic iron carbide from the gangue. The iron

carbide recovered may then be used in Step 2 of the

process of the invention.

A number of advantages of the invention are apparent

from the above description. Its principal advantage is

that it eliminates the expensive intermediate blast furnace

step in converting iron ore to steel. When the two

steps are performed in conjunction no added heat is

necessary for the second step and carbon monoxide

from the second step provides the necessary carbon for

carbonization of reduced iron in the first step so that the

carbon can be reused continuously in both steps. Step I

includes the production of water as a by-product, thus

simplifying the recovery of by-product carbon containing

gases. This step can be performed to give a product

having a high enough ratio of Fe2C to Fe3C to provide

a high enough carbon content in the charge for the basic

oxygen furnace to make the steel making process autothermal.

Advantages of Step 2 are that it provides sources of

heat for making this step auto-thermal without the use

of extra materials, i.e., sensible heat from the off-gases

can be used or the CO in the off-gases can be burned to

provide the necessary heat, or the CO can be reacted

with the iron carbide from Step I to raise the ratio of

Fe2C to Fe3C in the charge so that sufficient carbon will

be available for combustion to supply the augmenting

heat to make Step 2 auto-thermal. When pig iron is

added to the charge, large amounts of iron carbide can

be added for cooling. The overall process is practically

pollution-free and provides for maximum conservation

and reuse of non-product reactants. A further advantage

of the overall process is that it results in a saving in

4,053,301

7 8

transportation costs when the carbide is made near the 16. The process of claim 14 in which at least part of

mine before transport to the steel making furnace as iron the heat for the preheat step is derived from off-gases

carbide represents a higher percentage of usable mate- from step (b).

rial than the oxide. 17. The process of claim 14 in which at least some of

What is claimed is: 5 the heat for the preheat step is derived from sensible

1. A process for the direct production of steel from heat in the off-gases.

iron oxides which comprises: 18. The process of claim 14 in which at least some of

a. converting the iron in the oxides to iron carbide; the heat for the preheat step is derived from combustion

and of CO in the off-gases.

b. converting the iron in the iron carbide directly to 10 19. The process of claim 18 in which the' CO/C02

steel in the basic oxygen furnace. ratio in the gas combustion products is maintained from

2. The process of claim 1 in which in step (b) the about 1:1 to about 2:1 when attaining preheat temperaconversion

is accomplished by oxidizing the carbon in tures of 900·_BOO· F.

the iron carbide to carbon monoxide with the heat re- 20. The process of claim 14 in which the heat for the

leased thereby providing heat for operation of the basic 15 preheat step is provided by reacting at least part of the

oxygen furnace. off-gas to produce Fe2C in the iron carbide from step

3. A process for the direct production of steel from (a~l. The process of claim 20 in which the composition

iron oxides which comprises: of the reactive medium of step (a) is adjusted to provide

a. reducing the oxides and converting the iron to iron 20 the required amount of Fe2C in the iron carbide charge.

carbide in one step in a fluidized bed with a mixture 22. The process of claim 3 in which the iron carbide of

of hydrogen bearing gas and a carbon containing step (a) has lost heat before step (b) is performed and

material which provides carbon for the iron car- sufficient fuel is added to it to provide additional heat

bide, the hydrogen being present in an amount ex- upon combustion in the process to render the reactions

ceeding 50% of the CO present; and 25 occurring in the conversion of the iron carbide to steel

b. adding the iron carbide to a basic oxygen furnace in the basic oxygen furnace autothermal.

and processing it to steel by the basic oxygen fur- 23. The process of claim 22 in which the fuel is carnace

process without the addition of external heat. bon.

4. The process of claim 3 in which steps (a) and (b) are 24. The process of claim 23 in which the carbon is

performed in conjunction and the iron carbide of step 30 added in an amount from about 3 to 5 weight percent of

(a) is added directly to the basic oxygen furnace without the iron carbide charge.

substantial heat loss so that the process is auto-thermal. 25. The process of claim 23 in which the carbon is

5. The process of claim 4 in which the iron carbide is added directly to the iron carbide charge.

at a temperature between about 900· F to 1300· F when 26. The process of claim 3 in which molten pig iron is

it leaves step (a). 35 added to the iron carbide charge in step (b) and iron

6. The process of claim 4 in which off-gas is cycled carbide is used to control the temperature of the melt.

from step (b) to step (a). 27. The process of claim 26 in which the temperature

7. The process of claim 6 in which the off-gas pro- controlling iron carbide is added in an amount up to

vides substantially all of the carbon for step (a). about 60 weight percent of the iron carbide-pig iron

8. The process of claim 3 in which in step (a) the ratio 40 charge.

of hydrogen to formed water in the reaction medium of 28. A process for conversion of iron oxides to iron

the fluidized bed is maintained from about 2.5 to 1 to carbide which comprises reducing the oxides and conabout

8 to 1 and the CO/C02ratio is maintained from verting the iron to iron carbide in one step in a fluidized

about 1 to 1 to about 4 to 1, the prescribed CO/C02_ bed with a mixture of hydrogen and a carbon containing

hydrogenIH20 ratios being essentially in· equilibrium 45 material which provides carbon for the iron carbide, the

with methane. mixture containing hydrogen in an amount over 60

9. The process of claim 3 in which the volume of percent by volume of the carbon monoxide present.

hydrogen exceeds the volume of CO in said fluidized 29. The process of claim 28 in which the ratio of

hydrogen to formed water in the reaction medium of

bed. . 50 the fluidized bed is maintained from about 2.5 to 1 to

10•.The process of claim 3 in which the carbon con- about 8 to I and the ratio ofCO/C02is maintained from

taining material is solid carbon.

11. The process of claim 3 in which the carbon con- about I to I to about 4 to I, the prescribed CO/C02hydrogen/

H20 ratios being essentially in equilibrium

taining material is lower alkyl hydrocarbon gas. with methane.

12. The process of claim 11 in which the gas is pro- 55 30. The process of claim 28 in which the carbon conpane.

taining material is solid carbon.

13. The process of claim 8 in which the temperature 31. The process of claim 28 in which the carbon conof

the reaction gas mixture is between about 900· F and taining material is a lower alkyl hydrocarbon gas.

BOO· F. 32. The process of claim 31 in which the gas is pro-

14. The process ofclaim 3 in which the iron carbide of 60 pane.

step (a) has lost heat before step (b) is performed and 33. The process of claim 28 in which the temperature

sufficient heat in a preheat step is added to it for step (b) of the mixture is between about 1100· F and about BOO·

to render the reactions occurring in the conversion of F.

the iron carbide to steel in the basic oxygen furance 34. A process for converting iron carbide to steel in

auto-thermal. 65 the basic oxygen furnace by the basic oxygen furnace

15. The process of claim 14 in which the iron carbide process, said process comprising the step ofaugmenting

charge is preheated to a temperature between about the heat produced in the conversion process which is

BOO· F and about 2000· F. produced by oxidizing the carbon in the iron carbide,

4,053,301

with additional heat, to make the process in the basic

oxygen furnace autothermal.

35. The process of claim 34 in which the heat is added

in a preheat step.

36. The process of claim 35 in which the temperature 5

of the iron carbide charge is between about BOO· F and

about 2000· F before it is added to the basic oxygen

furnace.

37. The process of claim 35 in which the preheat step 10

is performed by directly heating the iron carbide

charge.

38. The process of claim 35 in which at least some of

the heat for the preheat step is derived from sensible

heat in the off-gases. 15

39. The process of claim 35 in which at least some of

the heat for the preheat step is derived from combustion

of CO in the off-gases.

40. The process of claim 39 in which the CO/C02

ratio in the gas combustion products is maintained from 20

about 1:1 to about 2:1 when attaining preheat temperatures

of 900·-1300· F.

41. The process of claim 35 in which the heat for the

preheat step is provided by reacting at least part of the

off-gas with the iron carbide from step (a) to produce 25

Fe2C,

42. The process of claim 34 in which said heat is

augmented by adding a fuel to the iron carbide charge

for combustion during the conversion step.· 30

43. The process of claim 42 in which sufficient fuel is

added to the charge to provide additional heat upon

combustion in the process to raise the temperature of

the charge to at least about 1100· F.

44. The process of claim 42 in which the fuel is car- 35

bon.

45. The process of claim 44 in which the carbon is

added in an amount from about 3 to 5 weight percent of

the iron carbide charge.

46. A process of making steel from iron carbide in the 40

basic oxygen furnace which comprises adding pig iron

to the iron carbide charge and controlling the temperature

of the charge by the addition of iron carbide.

47. The process of claim 46 in which the pig iron is

added in an amount up to about 40 weight percent ofthe

charge and the temperature controlling iron carbide is

added in an·amount up to about 60 weight percent ofthe

iron carbide-pig iron charge. .

48. A process for concentrating non-magnetic low

grade iron ores ·which comprises converting the iron

oxide in the ores to iron carbide and separating the iron

carbide and gangue by subjecting the treated ores to

magnetic separation.

- 49. The process of claim 48 in which the iron oxides

are converted to iron carbide in one step in a fluidized

bed with a mixture of hydrogen bearing gas and a carbon

containing material which provides carbon for the

iron carbide.

50•. The process of claim 49 in which hydrogen is

present in an amount of over 60 percent by volume of

carbon monoxide in the fluidized bed.

51. A process for the direct production of steel from

iron oxides which comprises:

a. converting the iron in the oxides to iron carbide;

and

b. converting an iron in the iron carbide directly to

steel in an electric furnace.

52. A process for the direct production of steel from

iron oxides which comprises:

a. reducing the oxides and converting the iron to iron

carbide in one step in a fluidized bed with a mixture

of a hydrogen bearing gas and a carbon containing

material which provides carbon for the iron carbide,

the hydrogen being present in an amount exceeding

50% of the CO present; and

b. adding the iron carbide to the electric furnace and

processing it to steel in an electric furnace.

53. The process of claim 52 in which steps (a) and (b)

are performed in conjunction and the iron carbide produced

in step (a) is added directly to the electric furnace

without substantial heat loss.

* * * * '"

le='�b~p-i��font-family:"Times New Roman","serif";mso-fareast-font-family: HiddenHorzOCR'>stripping using alkaline-NaEDTA solution.

Palladium is stripped from the loaded organic using a 45

water soluble reducing agent in an acidified aqueos

solution. An important criteria in selecting a suitable

reductant reagent is that is should not contribute any

Product

Aqueous feed

Raffinate

Loaded Organic

Amount Assay, gil Grams

inml. Pt Pd Ir Rh Ru Fe Pt Pd

1050 0.40 3.30 1.10 3.80 4.10 0.002 0.42 3.5

1050 0.04 1.00 1.10 3.78 4.05 0.002 0.04 1.1

1575 0.24 1.58 0.02 0.003 0.05 0.004 0.38 2.5

foreign metals to the organic which might eventually

cause fouling or a reduction in loading capacity. Satisfactory

reductant stripping agents for use in the present

invention include acidified solutions of hydrazine salts,

hydroxylamine salts, and conventional organic reduc- 60

ing agents, i.e., thiourea. The reductant stripping solutions

are acidified to between 0.1 to about 3 N HCI and

are preferably employed as 0.5 N solutions. The preferred

reducing solution is 50 g/l hydrazine dihydrochloride

(N2lL.2HCI) acidified to 0.5 N HCI. AI- 65

though suggested concentrations of strippant solutions

have been described herein, those skilled in the art will

appreciate that these may be varied depending upon the

It will be seen from the above Table that platinum and

palladium were selectively extracted from an aqueous

hydrochloric acid solution containing iridium, rhodium,

ruthenium and iron by an organically substituted secondary

amine. The minute quantities of iridium, rhodium,

ruthenium andiron which are extracted along with

platinum and palladium are relatively insignificant.

EXAMPLE II

The tests in this Example illustrate that a variety of

alkaline reagents at different concentrations may be

EXAMPLE III

Test No.5. In all instances it was possible to obtain strip

solutions in which platinum was at a relatively high

concentration with respect to palladium as compared to

the original aqueous solutions from which they were

separated. .

4,041,126

used to selectively strip platinum from an organic extraction

solvent loaded with platinum and palladium.

A ten percent (%) by volume Amberlite-LA-I solution

in kerosene (AMSCO 175) containing 3% by volume

isodecanol (and conditioned to chloride form as in 5

Example I) was loaded with platinum and palladium by

contacting with an aqueous hydrochloric acid solution

assaying (in gil) gold 0.007, platinum 2.86, palladium The extraction and selective stripping tests in Exam-

8.40, iridium 0.031, rhodium 0.038 and ruthenium 1.13. pIe III were performed to illustrate that the sequence of

The loaded organic assayed in (gil) platinum 1.12 and 10 stripping platinum and palladium from a loaded seconpalladium

3.55. Predetermined quantities of the loaded dary amine organic is not important and either metal

organic were treated with solutions of NaZC03, NaH- may be stripped first through the process of the present

C03 and NaOH in separatory funnels at room tempera- invention.

ture (plus or minus 25° C) at an 01A ratio of 2 to 1. The To carry out Example III a 10% by volume solution

contact times and alkaline concentration of the stripping 15 of Amberlite LA-I in 3 volume percent (%) isodecanol

solution were varied as noted in Table II. Following and 87 volume percent (%) kerosene (AMSCO 175)

each contact period, the phases were separated, filtered was loaded with platinum and palladium in a single

and assayed for platinum distribution. Results of the contact with a hydrochloric acid solution assaying (in

respective assays are indicated in Tables II and IIA gil) gold 0.004, platinum 2.90, palladium 8.20, iridium

below. 20 0.024, ruthenium 1.13 and rhodium 0.036. Prior to the

TABLE II

Loaded organic: 1.12 gil Pt + 3.55 gil Pd

Stripping: 0/A = 211

Contact Assays 1/ % UK"

(concen-

Test Strip Volumes Taken, ml Time Temp Strip Org.,gll Strip Soln, g/I Stripped tration) Ratio Pt/Pd

O/A

No. Solution Organic Aqueous min °C Pd Pd Pt Pd Pt Pd Pt Pd in Strip

I 50 gil Na2C03 30 IS 5 ±25 0.03 . 3.30 2.19 0.49 97 7< I 7 4.5/1

2 50 gil NaOH 30 IS 5 ±25 0.03 2.80 2.06 0.91 97 21< I 3 2/1

3 11 gil Naif03 30 IS IS ±25 1.17 3.45 0.007 0.002< 1< I> 100> 100

4 50 gil Na C03 30 IS IS ±25 0.18 3.52 1.80 0.004 84< 1< 1> 100 450/1

5 50 gil NaHC03 50 25 15 ±40 0.25 3.52 1.80 0.038 78 1< 1 93 47/1

6 50 gil NaHC03 + 30 15 15 ±25 0.20 3.45 1.91 0.17 82 3< 1 20 11/1

5 gil NaEDTA2/

7 75 gil NaHCO; + 50 25 IS ±25 0.21 3.40 1.87 0.18 81 4< 19 10/1

5 gil EDTA3

50 gil NaHC03 + 50 25 15 ±25 0.28 3.44 1.76 0.17 75 3< 20 10/1

5 gil EDTA

IIAll assays were on filtered products and do not include losses, if any, in scum products.

21NaEOTA = (Ethylenedinitrilo), tetra-acetic acid disodium salt.

'lEOTA = (Ethylenedinitrilo), tetra-acetic acid.

_=- TABLE IIA 40

Test

No.

extraction of emf of the aqueous solution was reduced

Physical Observations to _ 525 millivolts by the addition of hydroquinone.

Scum suspended thru aqueous. Poor phase The extraction organic was preconditioned to chloride

separation.

2 Scum suspended thru aqueous. Poor phase form by two contacts at an 01A ratio of 2 to 1 with 100

3 ~~:~al~~queous, poor phase separation. 45 grams per liter NaCI in IN HCI followed by washing

4 ( Scum suspended in aqueous, settles in with 20 grams per liter NaCI adjusted to pH 1.5 with

( aqueous, clear organic. Same problem, HCI. The extraction was carried out by allowing the

5 ( both tests.

6 Trace scum, no phase separation problem. aqueous solution to contact the organic for three min-

7 Clear organic + aqueous phases, no scums. utes at 24°C and at an 01A ratio of 2 to 1. Following

__8__C_l_e_ar_o_r_ga_n_ic_+_a...;q_ue_o_us_p_h_a_se_s,_n_o_s_cu_m_s_. 50 the contact period the phases were separated and the

loaded organic phase scrubbed by contacting with pH 1

HCL for three minutes at 24° C at an 01A ratio of 2 to

1. The phases were again separated and the scrubbed

platinum and palladium loaded organic was analyzed,

and assayed (in gil) platinum 1.06, palladium 3.52, iridium

0.002, ruthenium 0.002 and rhodium less than 0.001.

The loaded organic solution was then divided into three

approximately equal portions (labeled organic 1, 2 and

3) which were each contacted once with an aqueous

strip solution containing 50 gil NaHC03 for a period of

5 minutes at 25° C. After contacting the first loaded

organic portion, the phases were separated and sufficient

NaHC03 added to the aqueous phase to restore it

to 50 grams per liter NaHC03, and the restored solution

used to contact the second and third portions of loaded

organic in sequence. All contacts were carried out at an

01A ratio of 2 to 1 and the phases separated and analyzed

after each contact. The platinum pregnant aque-

The results of the tests illustrated in Table II indicate

that a variety of alkaline reagents can be used to selectively

strip platinum from an amine organic loaded with

platinum and palladium. The poor stripping action of 55

Test No.3 is attributable to use of a weak alkaline solution

(11 gil). The insoluble scums formed in Tests Nos.

1 through 5 resulted in poor phase separation. The

emulsion forming scum was solubilized by addition of a

chelating agent [NaEDTA (ethylene dinitrillo)tetraa- 60

cetic acid disodium salt] to the alkaline stripping solution

prior to contact with the loaded organic. As indicated

in the results of Tests Nos. 6 through 8, this entirely

eliminated the scum formation in most instances

or reduced it to trace levels and also alleviated the 65

physical problem of phase separation. A 50 gil solution

of NaHC03 provided optimum selective stripping of

platinum from palladium as illustrated in the results of

4,041,126

ous strip solution was then acidified to pH 1 with l2N TABLE IV-continued

HC!. Analyses of the scrubbed-loaded organic, each Amount Assay,gll

stripped organic portion and the acidified platinum .:.P.:'ro:::d~u::::ct~_...,---__...,---~m,;;-I O;-:/;;-A_-----;:;-:P:;rt~_,,-:Pdm_

pregnant strip solution were carried out and the results Ramnate 850 1.0 0.70 1.70

found to be as follows: 5 Loaded Organic 850 1.04 2.60

TABLE III

Amount Assay, gil Grams

Product ml O/A Au Pt Pd Ir Ru Rh Pt Pd

Scrubbed organic 1400 0.005 1.06 3.52 0.002 0.002 <0.001 1.48 4.9

Stripped organic I 440 2.0 0.05 3.52 0.02 1.5

Stripped organic 2 470 ! 0.06 3.52 0.03 1.6

Stripped organic 3 490 0.09 3.52 0.04 1.7

Pt pregnant strip 232 0.002 6.00 0.004< 0.001 0.001 <0.001 1.39< 0.001

(acidified) 1.48 4.8

Pt Pd

% stripped 94 0.03

Ratio Pt/Pd in pregnant strip = 1000/1

Amount Assay,gll Grams % Stripped

Product ml Pt Pd Pt Pd Pt Pd

Scrubbed

orlianic

stnpped 700 1.04 2.60 0.728 1.82

Combined

Pd/organic 700 1.00 0.56 0.700 0.39 <I 78

Pd pregnant

strip 200 0.10 6.90 0.020 1.38

0.720 1.77

The scrubbed loaded organic (assaying in gil) platinum

1.04 and palladium 2.60 was then subdivided into

two separate portions. The first portion was conJa~ted

with a 50 gil aqueous solution of N2lL.2 HCl.acldified

to 0.5N with HCL for 3 minutes at an 01A ratio of 2 to

1. Following phase separation the aqueous raffinate

phase was used to contact the second portion of scrubbed

organic (at an 01A ratio 1.5 to 1) for 3 minutes at

25°C. The palladium pregnant aqueous raffinate was

separated from the organic extract phase which was

then combined with the previously stripped first organic

portion. As in the initial ~est, th~ percentages and

amounts of platinum and palladIUm strIpped were determined

by analysis of the respective separated phases as

indicated in the following table:

TABLE IVA

Product

Aqueous

EXAMPLE IV

This test was conducted to illustrate that platinum The combined palladium stripped organic was then

and palladium may be stripped from a loaded secondary contacted with pH 1 HCl at an 01A ratio of 2 to 1 for

amine organic in the order (1) palladium, (2) platinum. 50 3 minutes at 25° C to scrub the organic phase. Follow-

An organic extraction solution was prepared and ing phase separation, the scrubbed organic phase was

preconditioned to chloride form as in Example III and analyzed and found to assay (in gil) platinum 1.00, and

used to contact an aqueous hydrochloric acid solution palladium 0.56. The scurbbed organic phase was .t~en

assaying (in gil) gold less than 0.001, platinum 1.70, contacted with a 50 gil solution of NaHC03contammg

pallaadium 4.59, iridium 0.025, ruthenium 1.10, and 55 5 gil EDTA which was prepared ~y adjusting an

rhodium 0.036. The emf of the aqueous solution was EDTA suspension in water to l?H 8 With NaOH s?lureduced

to - 525 millivolts by the addition of dry hy- tion to dissolve the EDTA, addmg NaHC03 and ddut.

droquinone prior to contacting the extraction o~ganic. ing with water to final volume. The organ~c was di-

A single organic/aqueous contact was then carned out vided into two equal aliquots. The first ahquot was

for three minutes at 25° C at an 01A ratio of 1/1. Fol- 60 contacted with the alkaline stripping solution for 10

lowing phase separation the organic extract phase was minutes at 25° C. Following phase separation, 5.1 grams

scrubbed by contacting pH 1 HCl for three minutes at of NaHC03 was dissolved in the aqueous phase to rean

organic to aqueous ratio of2 to 1. Analysis of each of store the alkaline solution.to 50 gil NaHC03

• The rethe

respective phases gave the following results. stored strippant solution was then used to contact the

TABLE IV 65 second aliquot for 10 minutes at 25° C. Both of the -------...,---A-m.:.o.:.u=nt=-=--:.---A-::s~Sa~y:-,g/::-;;--1 --- preceding contacts were carried out at an organic. to

ml O/A Pt Pd aqueous ratio of 2 to 1. No scum was observed dUrIng

850 1.70 4.59 the first contact and only trace scums were apparent at

Table III indicates that 94% of the platinum was Aqueous Scrub 412 2.0 0.009 0.02

stripped from the loaded organic while. less tha~ 0.03% 20 :::S::::cr~ub::::b::e=-d-=:O:.:.rg~a::n:::ic~_---.:8:..:2_5 1_.04 2_.6_O _

of the palladium was removed. The ratio of platmum to

palladium in the pregnant strip solution ~as gre~ter

than 1,000 to 1. Platinum stripped orgamc portions

(Nos. 1, 2 and 3) were combined and assayed (in. gil)

platinum 0.070 and palladium 3.48: The platmum 25

stripped organic was then scrubbed with IN HCl for 3

minutes at 25° C at an 01A ratio of 2 to 1. After phase

separation, the scrubbed organic phase was analy.zed

and found to assay (in gil) platinum 0.070 and palladIUm

3.50. The scrubbed organic was then contacted three 30

times in succession with a fresh solution of 50 gil

N2lL.2HCl in 0.5N HCl at an organic aqueous ratio of

2 to 1 for a period of 5 minutes, the phases being sep~.

rated after each contact. The separated aqueous strIp

solutions were combined and an analysis ofthe.aqueous 35

strip solution revealed that 75% of the palladIUm present

in the scrubbed organic and less than 2% of the

platinum had been stripped into the aqueous solution by

the acidic strip treatment.

The results of this test indicate. that an or~anicallr 40

substituted secondary amine orgamc loaded with platinum

and palladium may be selectively stripped from a

loaded secondary amine organic ina stripping sequence

in which platinum is first removed followed by pallailium.

4,041,126

separating said organic extract phase from said aqueous

raffinate phase,

contacting said organic extract phase with an acidified

aqueous solution of a. water soluble reducing

agent to form an aqueous phase loaded with palladium

and a platinum containing organic extract

phase,

separating said platinum containing organic phase

from said palladium containing aqueous phase,

contacting said platinum containing organic extract

phase with at least the stoichiometric quantity of an

aqueous alkaline stripping agent required for neutralization

of said extract phase, said contact resulting

in the formation of an queous phase loaded with

platinum and a stripped organic phase.

2. The process of claim 1 wherein R1 is a fatty alkyl

group.

3. The process of claim! wherein said aqueous acidic

medium is hydrochloric acid.

4. The process according to claim 3 wherein said

alkaline solution contains between about 5 and 100

grams per liter of an alkaline reagent.

5. The process of claim 4 wherein said alkaline reagent

is a water soluble member selected from the

group consisting of the carbonates, bicarbonates and

hydroxides of alkali and alkaline earth elements.

6. The process of claim 5 wherein a metal chelating

agent is added to said aqueous alkaline solution prior to

contacting said organic extract phase.

7. The process of claim 6 wherein said metal chelating

agent is an amino carboxylic acid compound:

8. The process of claim 1 wherein said reducing agent

is selected from the group consisting of acidified solutions

of hydrazine salts, hydroxylamine salts, and thiourea.

9. The process of claim 8 wherein said acidified reducing

agent is hydrazine dihydrochloride.

10. The process of claim 9 wherein said acidified

reducing solution is adjusted to between 0.1 and 3.0 N

HCI.

11. The process of claim 3 wherein said aqueous solution

is extracted in plurality of times by contacting the

aqueous raffinate phase and subsequent raffinates with

said organic extractant.

12. A continuous process for the selective separation

and recovery of platinum and palladium dissolved in an

aqueous chloride solution which comprises:

reducing said solution to an emf between about -425

mvand -650 mv,

contacting said aqueous chloride solution with a

mixed extraction reagent comprising a water immiscible

organic solvent having dissolved therein an

organically substituted secondary amine compound

of the general formula:

the interface of the second stripping contact. After

phase separation following the second stripping

contact, the stripped organic phases were combined and

the platinum pregnant strip solution was adjusted to pH

1 by addition of 12N HCI to stabilize the solution. As 5

in the preceding test, the percentage of platinum and

palladium stripped was determined by analysis of the

separated phases as indicated below:

Amount Assay, gil Grams % Stripped

Product ml Pt Pd Pt Pd Pt Pd

Pd stripped

organic

(scrubbed) 600 1.00 0.56 0.60 0.336

Pt stripped 15

organic 600 0.15 0.55 0.09 0.330 85 <2

Pt pregnant

strip 151 3.20 0.071 0.48 0.011

0.57 0.341

TABLEIVB

-----------::-----=,.------:c--::c-:--.,--10

The tabulated data indicate that the initial stripping 20

operation resulted in the strip of 78% of the palladium

and less than 1% of the platinum from the loaded organic.

The Palladium containing aqueous strip solution

had a palladium/platinum ratio of 69/1. The platinum 25

stripped organic contained 0.15 gil platinum and 0.55

gil platinum (85% and less than 2% stripped, respectively)

and the aqueous platinum containing strip solution

had a platinum/palladium ratio of 46/1. Compared

to the starting feed liquor of the process, the Pd/Pt ratio 30

was increased from 2.7/1 to 6911 and the Pt/Pd ratio

was increased from 0.4/1 to 46/1. Overall recovery

from the loaded organic was 85% for platinum and 79%

for palladium.

The platinum and palladium values may be won from 35

the respective aqueous stripping solutions using techniques

well known in the art (e.g., precipitation of ammonium

chloroplatinate with NILCI to recover platinum,

or precipitation of dichlorodiaminopalladium by

sequential addition of ammonium hydroxide and hydro- 40

chloric acid solutions to recover palladium).

What is claimed is:

1. A process for the separation and selective recovery

of platinum and palladium values from an aqueous

acidic medium which comprises: 45

contacting the medium with a mixed organic extraction

reagent comprising a water immiscible solvent

having dissolved therein an organically substituted

secondary amine compound of the general formula:

wherein R1 and Rz are hydrocarbon groups and R1 +

Rzcontain between 18 and 35 carbon atoms, said com-

65 pound having a solubility of at least 1% in said solvent

and being capable of forming complexes of platinum

and palladium that are preferentially soluble in the organic

solvent and whereby the contacting results in the

wherein R1 and Rz are hydrocarbon groups and R1 +

Rzcontain between 18 and 35 carbon atoms, said compound

being sufficiently soluble in said solvent to make 60

a 1% solution and capable of forming complexes with

platinum and palladium that are preferentially soluble in

said solvent and whereby said contacting results in the

formation of an organic extract phase and an aqueous

raffinate phase,

maintaining said medium at an emf of between about

-425 and -650 millivolts during said contacting

operation,

4,041,126

creation of an organic extract phase and an aqueous

raffinate phase,

separating said organic extract phase from said aqueous

raffinate phase,

contacting said organic extract phase with an aqueous 5

solution containing at least the stoichiometric quantity

of sodium bicarbonate required for neutralization

of said organic phase and the disodium salt of

ethylenediaminetetraacetic acid to form a stripped 10

organic extract phase and an aqueous platinum

containing strip solution,

contacting said stripped organic extract phase with an

aqueous solution containing from about 5 to about

100 grams per liter of hydrazine dihydrochloride to 15

remove palladium from said stripped organic extract

phase, and

contacting a fresh platinum and palladium containing

aqueous chloride solution with said platinum and

palladium stripped organic extract phase. 20

13. A continuous process for the separation and selective

recovery of platinum dissolved in aqueous chloride

solutions with palladium which comprises:

reducing said aqeuous chloride solution to an emf

between about -425 mv and -650 mv, 25

contacting said aqueous chloride solution for a predetermined

time period with an organic solvent containing

at least 1% by weight of an organically

substituted secondary amine compound of the general

formula 30

wherein R1 and Rz are hydrocarbon groups and R1 +

Rzcontain between 18 and 35 carbon atoms, said compound

having a solubility of at least 1% in said solvent 40

and being capable of forming complexes of platinum

and palladium that are preferentially soluble in the organic

solvent and whereby the contacting results in the

creation of an organic extract phase and an aqueous 45

raffinate phase,

isolating said extract phase from said raffinate phase,

contacting said extract phase with at least the stoichiometric

quantity of an aqueous alkaline solution

required to neutralize the chloride form of said

amine to selectively separate said platinum values

from said palladium values in said organic extract

phase. and form a platinum stripped organic extract

phase and an aqueous platinum containing strip

solution, and

isolating said aqueous solution from said platinum

extract phase.

14. A continuous process for the separation and selective

recovery of palladium dissolved in aqueous chloride

solutions with platinum which comprises:

reducing said solution to an emf between about -425

mvand -650 mv,

contacting said aqueous chloride solution for a predetermined

time period with an organic solvent containing

at least 1% by weight of an organically

substituted secondary amine compound of the general

formula:

wherein R1 and Rz are hydrocarbon groups and R1 +

Rzcontain between 18 and 35 carbon atoms, said compound

capable of forming complexes of platinum and

palladium that are preferentially soluble in the organic

xolvent and whereby said contacting results in the creation

of an organic extract phase and an aqueous raffinate

phase, •

separating said organic extract phase from said aqueous

raffinate phase,

contacting said organic extract phase with an aqueous

solution containing a reducing agent acidified to

between about 0.1 to about 3.0 N-HCl to strip

palladium values from said organic extract phase,

said contact resulting in the formation of a palladium

loaded aqueous phase and a stripped organic

phase containing said platinum,

separating said loaded aqeuous phase and said

stripped organic phase, and recovering palladium

from said loaded aqueous phase.

* * * * *

no<ĩet0�(D�e:none'>point of elemental sulfur.

* * * * *

ture between about 500 C and the melting point of

sulfur to convert substantially all of the sulfide

sulfur to elemental sulfur in solid form and to effect

conversion of the metal compounds to metal chlorides,

and recovering metal from the chlorides.

22. The process of claim 21 in which chlorination is

performed at a temperature between about 800 C and

the melting point of sulfur.

23. The process of claim 2] in which the minerals

10 contain silver.

24. The process of claim 23 in which the silver containing

mineral is tetrahedrite.

25. The process of claim 21 in which sulfur chlorides

formed during dry chlorination are reacted with the

15 metal sulfides to form metal chlorides and elemental

sulfur.

26. The process of claim 25 in which the process is

performed by introducing the metal sulfides and dry

chlorine gas countercurrently into the reaction zone

20 and an inert sweep gas is introduced into the reaction

zone to bring sulfur chlorides formed during the dry

chlorination into contact with metal sulfides entering

the reaction zone.

4,011,146

lead, silver recovered from the leach solution by cementation,

the leach solution after removal of lead and

silver therefrom recycled to the sodium chloride leaching

step, the improvement comprising preventing the

build-up of zinc in the leach solution in the leaching 5

step by removing a bleed stream from the lead and

silver depleted leach solution, removing zinc from the

bleed stream and recycling the bleed stream to the

leaching solution in the leaching step.

19. The process of claim 18 including subjecting the

bleed stream to electrolysis after removal of zinc therefrom

to produce chlorine gas and recycling the chlorine

gas to the dry chlorination step.

20. The process of claim 19 in which the zinc is removed

by precipitating it as zinc carbonate by the addition

of sodium carbonate, the sodium hydroxide produced

in the electrolyis is carbonated to sodium carbonate

and the sodium carbonate recycled to the zinc

precipitation step.

21. The process of recovering metal values from

minerals of the polymorphic series of complex metal

sulfides tetrahedrite-tennantite comprising:

a. subjecting the minerals to dry chlorination with

chlorine gas in the absence of oxygen at a tempera-