US3905807A - Recovery of tin from slags - Google Patents

Abstract

A method of producing tin from a low grade tin concentrate comprising the following steps: 1. Melting and partial reduction of the mixture of concentrate and flux, to form a liquid concentrate slag (i) having a high tin content; 2. Mixing and reacting the liquid concentrate slag (i) with a liquid tin-iron alloy (hard-head) (ii)) having a high iron content to yield a liquid crude tin metal product (iii) of low iron content and a liquid intermediate slag (iv) of high tin content. 3. Reduction of the tin in the liquid intermediate slag (iv) resulting from step (2) to produce liquid tin-iron alloy (ii) for recycle to step (2) and a liquid discard slag (v) of low tin content. The process may be operated either continuously or batchwise.

Description

[451 Sept. 16, 1975 1 1 RECOVERY OF TIN FROM SLAGS John Millice Floyd, Glen Waverley, Australia [75] lnventor:

' [73] Assignee: Commonwealth Scientific and Industrial Research Organization, Campbell, Australia [22] Filed: Aug. 22, 1974 [21] Appl. No.: 499,644

Related U.S. Application Data [63] Continuation-impart of Ser. No. 276,052, July 28,

1972, abandoned.

[30] Foreign Application Priority Data July 30, 1971 Australia 5733/71 [52] U.S. Cl. 75/85; 75/89; 75/93 [51] Int. Cl. C22B 25/00 [58] Field of Search 75/85, 89, 91, 93, 72, 75/12; 266/34 C [56] References Cited UNITED STATES PATENTS 2,663,631 12/1953 Tschop et a1. .1 75/91 2,673,797 3/1954 Whitehouse et a1. 75/91 2,815,267 12/1957 Platteeuw et a1. l 75/85 2,849,860 9/1958 Lowe 266/34 C 3,201,104 8/1965 Berry 266/34 C 3,575,706 4/1971 Ummel 266/34 C 3,634,069 1/1972 Worner 75/85 3,674,463 7/ 1972 Yannopoulos 75/72 FOREIGN PATENTS OR APPLICATIONS 17,002 7/ 1906 United Kingdom 75/85 401,372 5/1969 Australia 75/12 Primary Examiner-Walter R. Satterfield Attorney, Agent, or F irm-Cushman, Darby & Cushman 5 7 ABSTRACT A method of producing tin from a low grade tin concentrate comprising the following steps:

1. Melting and partial reduction of the mixture of concentrate and flux, to form a liquid concentrate slag (i) The process may be operated either continuously or batchwise.

10 Claims, No Drawings RECOVERY OF TIN FROM SLAGS This invention is a continuation in part of U5. Ser. No. 276,052 filed July 28, 1972 and now abandoned.

This invention relates to the smelting of tin concentrates using a process involving the gaseous reduction of liquid slags containing tin. The invention has particular relevance to the smelting of low grade tin concentrates.

Conventional methods of tin extraction are concerned with the treatment of high grade tin concentrates. The mineral beneficiation of alluvial tin deposits to tin rich concentrates with greater than 60% tin is comparatively simple, and does not result in a great loss of tin in tailings. Hard rock tin deposits, on the other hand, can usually only be concentrated to these levels with the loss of over half of tin content of the ore. The production of lower grade concentrates from hard rock deposits results in lower tin losses, so that if this material can be smelted economically, then a considerable saving in tin can result.

Tin mining has traditionally been concerned with alluvial deposits, but production from these deposits has been unable to produce enough tin for rising world consumption, and an increasing proportion of the total tin output is produced from hard rock deposits.

In the conventional process for tin smelting tin concentrates containing greater than 60 percent tin, mixed with a solid reductant, such as coal, and a flux, such as limestone to produce a fluid slag, are smelted in a reverberatory furnace at a temperature of about I200C.

' A crude tin is produced for refining, and a slag with a in a reverberatory furnace. In the slag smelt the temperature is raised to about 1400". A tin metal of high iron content (hard-head) is produced, and is charged with concentrate to the first smelting stage. The resulting slag contains 1.5 to 3 percent tin and is discarded. This process cannot be economically used for smelting low grade concentrates because of the necessity of cooling and reheating large quantities of slag. Reduction of tin from the slag requires intimate contact between reductant and slag, and with a solid carbonaceous reductant this can only be achieved by cooling,

mixing with reductant and reheating to much higher temperatures than used in the method described in this invention.

Low grade tin concentrates in general possess a higher iron to tin ratio than high grade tin concentrates.

During the reduction of tin from the oxide to the metal wt. 71 Fe in slag wt 7: Sn in slag wt. 7! Sn in metal wt. 7; Fe in metal The value of is strongly dependent on the iron content of the metal. The distribution coefficient for the first stage of conventional smelting with metal containing less than 2 wt. Fe, has a value in the range to 400, while the second stage distribution coefficient, has a value in the range 20 to 50 for iron contents in the metal of 20 to 60 wt. Fe.

Low grade concentrates are at present smelted in a blast furnace where conditions are normally strongly reducing so that a large proportion of the iron in the charge reports in the metal. If metal with a low iron content is required from the blast furnace then a low iron content charge is selected and a light reduction is used to produce a' slag with high tin content for further treatment. For example if a metal with 2 percent iron is required assuming a 2 value of 200, the ratio of iron to tin in the slag cannot be greater than about 4. Normally a metal with high iron is produced, and this is then subjected to treatments for removal of iron which entail production of more tin-rich material for further treatment. The complete process sequence for blast furnace operation may be quite complicated.

In some recently developed processes the slag from the slag smelt is subjected to a fuming operation, similar to that used for zinc recovery from lead blast furnace slag. In the fuming process for tin, air, with entrained fine carbonaceous reductant such as crushed coal, and entrained sulphidising agent such as pyrites, is blown into the liquid slag. Volatile tin sulphide is formed, removed by the entraining gas, and reacts with oxygen above the slag bath to produce a fume of SnO The fume is filtered from the gas and charged to a reverberatory furnace smelt. The slag after fuming contains 0.1 to 0.5 percent tin.

A method of smelting low grade tin concentrates was proposed in Australian Patent Application 10581/66 and involved the use of a rotary furnace in a two stage countercurrent process. In the first stage concentrate, flux, iron-tin alloy, and possible solid carbonaceous reductants were smelted to produce a crude tin for refining, which was tapped fromthe furnace, and a slag with a high tin content. Solid carbonaceous reductant and flux were to be added to the molten slag and smelted in the second stage to produce a low tin content slag, which was to be tapped from the furnace, and an irontin metal which was to have remained in the furnace, for the first stage to be repeated. In the first stage the iron in the metal acts as a reducing agent for the tin in the concentrate but, if desired, additions of carbonaceous reductant could be made. the process was not exploited commercially because the second stage did not produce a significant quantity of hard-head or a slag of low enough tin content for discarding, in full scale trials.

There were two principal reasons why the process failed in the second stage. Firstly the addition of carbonaceous reductant to the liquid slag resulted in the reductant floating on the slag surface, so that good contact between reductant and slag was not achieved. Secondly commercial rotary furnaces cannot achieve temperatures above 1300C, and it has been found that temperatures greater than 1350C are required for effective reduction of tin slags by carbonaceous reductants.

We have now shown that both of these factors can be overcome by injecting a reducing gas into the slag due to the very different physical situation thereby produced. The bubbles of reductant provide a relatively large contact area, and in rising to the surface they mix the slag, thus improving rates of mass transfer so that the reduction is effective at lower temperatures.

The present invention involves a process for the smelting of low grade tin concentrates which in essence involves the following three steps:

1. Melting and partial reduction of the mixture of concentrate and flux, to form a liquid concentrate slag (i) having a high tin content 50% Sn);

2. Mixing and reacting the liquid concentrate slag (i) with a liquid tin-iron alloy (hard-head) (ii) having a high iron content l0 60% Fe) to yield a liquid crude tin metal product (iii) of low iron content (0.1 2% Fe) and a liquid intermediate slag (iv) of high tin content (lO 40% Sn). This reaction may be achieved by mixing of the liquid phases resulting from the injection of gases, or combustion mixtures of fuel and air such as will produce reducing gases, or by use of a rotary furnace. The metal product (iii) and the intermediate slag (iv) are then separated.

3. Reductionof the tin in the liquid intermediate slag ,(iv) resulting from step (2) to produce liquid tin-iron alloy (ii) for recycle to step (2), and a liquid discard slag (v) of low tin content (0.5 2% Sn). This reduction is carried out by injecting reducing gases (which may contain entrained solid carbonaceous reductants) or reducing mixtures of fuel and air and/or oxygen into the liquid slag.

The process may be operated in a batch-wise manner or continuously in a variety of equipment.

For a batch-wise process, step (1) is achieved most efficiently in a shaft furnace, but can also be performed in a reverberatory, or rotary furnace using conventional techniques or in a vessel such as that described belowfor step (3). Step (2) requires mixing of the liquid slag thus produced with liquid tin-iron alloy. This can be achieved by injecting gases into a bath containing the liquid slag and hardhead, thereby using the stirring induced by this procedure, or in a conventional rotary furnace. Step (3) requires the removal of tin from liquid slags to low levels, and therefore requires anew approach, since this cannot be achieved using existing techniques. Experiments have shown that gaseous reductants (which may contain entrained solid reductants) or reducing mixtures of fuel and air and/or oxygen when injected into such slags can produce hardhead and a slag for discard having a very low tin content. This is preferably carried out in a vessel with a deep slag bath, and may, or may not, incorporate partial-combustion of the reductant to provide the heat required by reactions and heat losses in the system. Thus the batch-wise operation is achievable in a number of ways according to the method of producing concentrate slag, and reacting this slag with hardhead. The

gaseous reduction operation, step (3), can take place in a rotary, or reverberatory furnace, but a vessel having a deep slag bath is-preferable in order to achieve high efficiency of the reductant used.

Additions of solid carbonaceous reductant to the ini tial charge will generally be required in order to produce a non-viscous slag. The slag thus produced is reacted with hardhead and, before tapping the crude metal product containing less than 2 percent iron, it may or may not be advantageous to reduce further by injection of reducing gases depending on the iron to tin ratio in the concentrate. The quantity of reductant required in this stage varies from more than that necessary to reduce all of the iron and tin in the concentrate to the ferrous and stannous states for concentrates with low iron to tin ratios, to less than that quantity for concentrates with high iron to tin ratios. For example a concentrate containing 20 wt. percent. tin and 15 wt. percent iron only required about two-thirds of the quantity of reductant needed to reduce to the stannous and ferrous states, while a concentrate containing 45 wt. percent tin and 12 wt. percent iron requires about one and one-quarter times the quantity of reductant needed to reduce to the stannous and ferrous states.

For continuous operation, the process is desirably carried out in a vessel comprising suitable regions or zones for achieving the three process steps. For example, in a typical system, melting steps take place in a bath situated at the end of a reactor. Here combustible gases (or pulverised coal, or fuel oil) are burnt beneath the slag surface with co-injected oxygen containing gases to provide heat for melting. The concentrate and flux may be introduced by dropping them on to the surface of a pre-existing slag pool or entraining them in the combustion gases.

High tin intermediate slag (iv) flows from the end of the smelting chamber into a separate region where the gaseous reductant (which may contain solid carbonaceous material) is injected through a series of lances or tuyeres to produce the tin-iron alloy (ii) and low tin discard slag (v) which is tapped off and discarded. The alloy (ii) flows beneath the slag layer under gravity towards the concentrate smelting end of the reactor, where iron is removed by reaction with the tin-rich concentrate slag (i) to produce the tin metal product (iii) which is tapped from this region, and the intermediate slag (iv) which flows back to the reducing region.

The operation of a continuous tin smelting operation using different principles has been described by Worner (US. Pat. No. 3,634,069, 1972 The use of submerged reduction and combination in the present process eliminates the need for a blast furnace to produce hardhead, and leads to better control of one of the major operating parameters, namely the tin content of discard slag. If a shaft furnace were used in the present invention for concentrate smelting, only partial reduction to a low iron metal would be used and a high tin content slag would be produced.

The feasibility of the process has been investigated in small scale experiments in crucibles and also by submerged combustion techniques in a larger reactor. Step (1) may be carried out using conventional equipment and procedures or by injecting concentrates with fuel and air into a liquid slag. Step (2) is known to be effective when operated in a rotary furnace. In order to investigate the alternative of using gaseous injection to achieve the necessary mixing, small scale tests were performed. For example, hardhead containing 50% iron was reacted with a 20% tin concentrate by heating" to produce both phases in the liquid state and injecting nitrogen. The metal produced contained less than 1% iron. Step (3) was investigated at length using various slags and gaseous reductants and fuels. It was found that slags containing less than 2 percent tin were produced in reducing to hardhead at temperatures below l300C. The reduction proceeded at a very fast rate under the conditions studied. Hydrogen, methane and natural gas were found to be effective. Carbon monoxide injection alone did not result in hardhead production, but with entrained brown coal char, hardhead was produced at a similar rate to that for reduction with hydrogen, methane, and natural gas. The entrainment of a solid carbonaceous reductant with hydrogencontaining or hydrogen-producing gases ensures a high efficiency of gas utilization when a deep slag bath is used, by maintaining a high partial pressure of reductant in the gas according to the reactions:

and

co, c 2co 3. Rapid reactions ensure that discard slags are produced with an optimum tin content, depending on the tin-to-iron ratio of the concentrate.

4. The treatment of liquid hardhead to produce a crude tin product of low iron content avoids the necessity of coolingand remelting as in conventional practice.

These advantages are particularly important in treating low grade concentrates where a large amount of slag is produced for a given quantity of tin produced. They result in greater plant capacity, lower losses of tin in discard slag, less severe conditions for refractories, and lower fuel requirements. These advantages make the process attractive for the treatment of high grade as well as low grade tin concentrates.

The principles and practice of the present invention are further elucidated by the following examples.

EXAMPLE 1 (All parts and percentages are by weight.)

This example illustrates the first two steps of the invention and shows that the mixing of liquid hardhead with liquid concentrate slag by injecting a gas is effective in producing crude tin metal of low iron content.

A ceramic crucible containing a metal made up from 308g of tin and 30.8g of iron beneath 400 g of a low grade concentrate with 19 percent tin and 14% iron was heated to produce liquid phases at 1150C. Nitrogen was injected through an alumina tube of diameter 0.25 ins. at l000ml/min for 92 minutes, to provide agitation, while the temperature increased from 1 150C to 1330C. Samples of the slag obtained by dipping an Inconel rod into the slag and quenching the rod in water showed a rapid decrease in the tin content of slag due to reaction with iron in the hardhead. After 26 minutes the tin content of the slag remained constant, indicating that reaction with the metal had reached equilibrium. The temperature at this stage was 1260C. After cooling a metal button containing 0.8 percent iron was separated from the slag, which contained 8.8 percent tin. The difference between the weight of tin charged in the concentrate and alloy, and the weight of tin obtained in slag and metal indicated a loss of 34 percent of the input tin in fume. The large fume loss would be decreased by injecting nitrogen for the minimum time and restricting the temperature of operation.

EXAMPLE 2 This example shows the effectiveness of the gaseous reduction of liquid slag by injection of a hydrogen containing gas to produce hardhead and taken together with Example 1 demonstrates the operation of the overall process of the invention.

500g of a slag such as that produced in Example 1, containing 8.3 percent tin and 24 percent iron was heated in a ceramic crucible to 1250C. Natural gas was injected through an alumina tube into the liquid slag thus produced at 1000 ml/min with 0.6g/min of entrained powdered brown coal char. After 88 minutes of injection hardhead containing percent iron was produced leaving a slag of tin content 0.95 percent. Percentages of the input tin which reported in the metal, slag, and fume respectively were 76 percent, and 10 percent, and 14 percent.

EXAMPLE 3 This example shows that the reductants may be partially burnt within the liquid slag to generate heat without significantly lowering the rate of reduction in Step 3 of the process.

500g of a slag containing 6 percent tin and 14 percent iron was heated in a ceramic crucible to 1260C and a mixture of gases comprising methane at 600 ml/mins and oxygen at 500 ml/min entraining 0.6g/min of powdered brown coal char injected through an alumina tube. After 63 minutes metal containing 23 percent iron and slag containing 0.95 percent tin were produced. Percentages of input tin reporting in metal, slag, and fume were respectively 57 percent, 13 percent and 30 percent.

EXAMPLE 4 This example indicates that gaseous reduction of liquid slags is effective on a larger scale.

3270g ofa slag containing 6.6% tin and 14% iron was heated in a ceramic crucible to l3l0C and methane at 2,500 ml/min entraining lg/min brown coal char injected through an alumina tube. In the early stages of injection a considerable quantity of slag was lost due to splashing. After 92 minutes metal assaying 42 percent iron and slag containing 0.54 percent tin were pro duced. Percentage of input tin reporting in metal, slag, splashed slag and fume were respectively 46 percent, 5 percent, 28 percent and 21 percent.

EXAMPLE 5 The example further illustrates steps 1 and 2 of the process.

500 g of slag containing 20% Sn was prepared from a concentrate and fluxes and reacted with g of 50% Sn 50% Fe alloy by bubbling nitrogen at 1000 ml per minute through the liquid phases held at 1270C in a crucible. A crude tin metal phase containing 1.4% Fe and a slag phase containing 13.4% Sn were produced. Of the tin charged 35% reported in metal, 44.6% in slag and 20.4% in fume.

EXAMPLE 6 This example shows the operation of the overall process of the invention in a cyclical batchwise manner. Operation A (Steps 1 and 2) precedes Operation B (Step 3), from which the hard head product is recycled to Operation C (a further Step 1). The fume generated, consisting of almost pure SnO was treated elsewhere.

OPERATION A 500 g of a tin concentrate containing 49% Sn and 7% Fe were mixed with 89g of calcite and 355 of brown coal char, and heated to 1250C in a crucible. g of 50% Sn 50% Fe alloy was added to the melt and natural gas, at 200 ml/min and air at 1900 ml/min injected through two concentric alumina tubes for 40 minutes. 148g of crude tin product, containing 0.54% Fe and 253g of a slag containing 10.4% Sn for further treatment were produced.

OPERATION B The slag from Operation A was heated to 1250C and 500 ml/ min natural gas entraining 0.3 g/min brown coal char and 3,700 ml/min air were injected through two concentric alumina tubes into the melt for 60 minutes. A slag containing 0.8% Sn was produced for discard, together with 40g of tiniron alloy containing 49% Fe for recycle. I

OPERATION C The alloy from Operation B was again added to a melt produced from 500g of the same concentrate, 89g of calcite, and 35g of carbon. 200ml per minute natural gas and 1900 ml/minute air were injected into the bath at 1250C for 40 minutes. 150g of crude tin metal product containing 0.6% Fe was produced together with 240g of slag containing 1 1.4% Sn.

EXAMPLE 7 p This example illustrates smelting of concentrates by injection with a fuel/air/oxygen mixture into a bath of liquid slag to produce crude tin metal and subsequent reduction of the high tin slag thus produced to yield a low-tin slag for discard and a tin-iron alloy for recycle. Smelting A tin concentrate containing 50 percent tin and 7 percent iron was mixed with calcite flux and injected, with a reducing combustion mixture of natural gas, brown coal char, air and oxygen, into a bath of liquid slag contained in a refractory lined vessel. The vessel was of cylindrical shape, 0.3 m diameter and contained a slag bath about 0.2 m deep.

The fuel/air/oxygen mixture contained about 50% of the oxygen required for complete combustion, the injection rates being as follows:

natural gas 7.7 cfm brown coal char 140 g/min. air 6.5 cfm oxygen 11.3 cfm In 45 minutes, 26.3 kg of the concentrate and 1.8 kg of the flux were injected through the water-cooled steel lance after which a crude metal containing 1.1% iron was tapped.

Reduction Injection of the reducing fuel/air/oxygen mixture was continued for 53 minutes, without entrainment of concentrate and with the oxygen flow rate in the mixture lowered to 8.8 cfm thus reducing the oxygen content to about 40 percent of that required for total combustion. Finally, a slag containing 1.0 percent tin and a tin-iron alloy containing158% iron was tapped.

EXAMPLE 8 This example illustrates the reduction of a typical intermediate high-tin slag by injection of a reducing oil- /air/oxygen mixture on a 50 kg scale.

kg of a slag containing 18% tin and 26% iron was mixed with 5 kg of calcite and melted to form a liquid slag bath in the vessel of Example 7. A reducing combustion mixture of fuel oil, air and oxygen was injected into the liquid slag through a water-cooled lance for 59 minutes. The fuel/air/oxygen injection rates were as follows: 8n

No. 1 fuel oil 4 Imp. galL/hr.

(emulsified with water) Air 4.5 cfm Oxygen 6.9 cfm This mixture contains about 44 percent of the oxygen required for complete combustion. (The addition of a small amount of water to the oil significantly improves reduction rates. A few percent of water is sufficient; the above run used 75 ml; i.e., about 4 vol. percent).

The final products tapped from the vessel were a slag containing 1.5 percent tin and a metal containing 39 percent iron.

I claim:

1. A method of producing tin from a low grade tin concentrate comprising:

a. melting and partially reducing a mixture of the concentrate and a flux to form a liquid concentrate slag (i) having a Sn content of from about 20 percent;

. mixing and reacting the liquid concentrate slag (i) with a liquid tin-iron alloy (ii) having an Fe content of about 10-60 percent to produce a liquid crude tin metal product (iii) of about 0.1 2 percent Fe content and a liquid intermediate slag (iv) of about 10 40% Sn content;

. separating the metal product (iii) and the intermediate slag (iv);

. injecting into the liquid intermediate slag (iv) a reducing material selected from the group consisting of hydrogen, hydrogen-containing gases, hydrogenproducing gases and solid carbonaceous and liquid hydrocarbon materials which on combustion produce such gases to reduce the slag (iv) and reform a molten tin-iron alloy (ii) and a liquid discard slag (v) having a Sn content of about 0.5 2 percent;

. separating the alloy (ii) and the discard slag (v);

and recycling the alloy (ii) to the mixing and reacting step.

2. A method as in claim 1, wherein the reducing material injected into the liquid intermediate slag (iv) is a gas containing an entrained solid carbonaceous reductant.

3. A method as in claim 2, wherein the solid carbonaceous reductant is brown coal char.

4. A method as in claim 1, wherein the reducing material is methane or natural gas.

5. A method as claimed in claim 1, wherein the reducing material is a fuel oil.

6. A method as claimed in claim 5, wherein the oil contains added water.

7. A method as in claim 1, wherein the reducing material is partially burned within the liquid slag.

8. A method as in claim 1, wherein the temperature of the liquid intermediate slag (iv) being reduced is below '1300C.

9. A method as in claim 1, wherein the mixing of the is carried out by injection of the concentrate and flux, liquid alloy (ii) and the liquid concentrate slag (i) is together with fuel and air and/or oxygen below the surcarried out by the injection of gases. face of a bath of concentrate slag with partial combus- 10. A method as in claim 1, wherein the melting and tion of the fuel. partial reduction of a mixture of concentrate and flux 5

Claims (10)

1. A METHOD OF PROUCING TIN FROM A LOW GRADE TIN CONCENTRATE COMPRISING: A. MELTING AND PARTIALLY REDUCING A MIXTURE OF THE CONCENTRATE AND A FLUX TO FORM A LIQUID CONCENTRATE SLAG (I) HAVING A SN CONTENT OF FROM ABOUT 2 - 50 PERCENT, B. MIXING AND REACTING THE LIQUID CONCENTRATE SLAG (I) WITH A LIQUID TIN-ION ALLOY (II) HAVING AN FE CONTENT OF ABOUT 10-60 PERCENT TO PRODUCE A LIQUID CRUDE TIN METAL PRODUCT (III) OF ABOUT 0.1I- PERCENT FE CONTENT AD A LIQUID INTERMEDIATE SLAG (IV) OF ABOUT 10 - 40% SN CONTENT, C. SEPARATING THE METAL PRODUCT (III) AND THE INTERMEDIATE SLAG (IV), D. INJECTING INTO THE LIQUID INTERMEDIATE SLAG (IV) A REDUCING MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, HYDROGEN-CONTAINING GASES, HYDROGEN-PRODUCING GASES AND SOLID CARBONACEOUS AND LIQUID HYDROCARBONN MATERIALS WHICH ON COMBUSTION PRODUCE SUCH GASES TO REDUCE THE SLAG (IV) AND REFORM A MOLTEN TIN-IRON ALLOY (III) AND A LIQUID DISCARD SLAG (V) HAVING A SN CONTENT OF ABOUT 0.52 PERCENT, E. SEPARATING THE ALLOY (II) AND THE DISCARD SLAG (V), AND F. RECYCLING THE ALLOY (II) TO THE MIXING AND REACTING STEP.

2. A method as iN claim 1, wherein the reducing material injected into the liquid intermediate slag (iv) is a gas containing an entrained solid carbonaceous reductant.

3. A method as in claim 2, wherein the solid carbonaceous reductant is brown coal char.

4. A method as in claim 1, wherein the reducing material is methane or natural gas.

5. A method as claimed in claim 1, wherein the reducing material is a fuel oil.

6. A method as claimed in claim 5, wherein the oil contains added water.

7. A method as in claim 1, wherein the reducing material is partially burned within the liquid slag.

8. A method as in claim 1, wherein the temperature of the liquid intermediate slag (iv) being reduced is below 1300*C.

9. A method as in claim 1, wherein the mixing of the liquid alloy (ii) and the liquid concentrate slag (i) is carried out by the injection of gases.

10. A method as in claim 1, wherein the melting and partial reduction of a mixture of concentrate and flux is carried out by injection of the concentrate and flux, together with fuel and air and/or oxygen below the surface of a bath of concentrate slag with partial combustion of the fuel.