METHOD AND DEVICE FOR PROCESSING IRON SILICATE ROCK

Abstract

A method is used to process iron silicate rock. At least one component is at least partially removed from the iron silicate rock. At least one component that is different from iron is thus removed from the iron silicate rock. The processed iron silicate rock is used for the production of pig iron or steel. The device for utilizing the processed silicate rock is designed as a device for producing pig iron or steel.

Description

The invention relates to a process for treating iron silicate rock in which at least one constituent is at least partly removed from the iron silicate rock.

The invention also relates to an apparatus for processing treated iron silicate rock.

Iron silicate rock is at present virtually exclusively mechanically utilized. The iron silicate rock is formed as slag in the smelting of copper ores.

The iron silicate rock is at present poured, for example, into molds and the moldings obtained are used for water frontage stabilization. Granulation of the iron silicate rock is likewise already known. Coarse granulated material is used, for example, as gravel for railroad embankments. Finer granulated material is used in sandblasting.

In terms of its proportions by weight, iron silicate rock consists essentially of iron, silicon and oxygen. Apart from the iron content, the iron silicate rock also contains secondary elements, for example copper, lead, arsenic, nickel and/or zinc.

In the smelting of copper ores (predominantly chalcopyrite), large amounts of slag are formed. Based on the amount of starting material containing metal of value, the copper industry produces 600 kg of slag/t of ore concentrate, which is about three times the amount of slag compared to the iron and steel industry.

Slag purification is already carried out worldwide with the main goal of increasing/maximizing the copper yield. There are ultimately two process approaches:

a) Pyrometallurgical—in an electric furnace or in an oil-/gas-fired Teniente furnace. Here, the molten slag is treated by phase gravimetric separation of the slag/copper matte mixture. A covering of coke (reducing agent) has the main task of avoiding contact of the melt with oxygen.

b) Hydrometallurgical—slag flotation. After solidification of the slag, a milling process is carried out, followed by flotation of the sulfidic copper particles. A concentrate is formed and this can be recirculated to the primary process.

The residual copper contents in these processes are about 0.4-0.8% and both processes are not designed for the metallurgical removal of further impurities. The slag product formed (regardless of whether from a pyrometallurgical or hydrometallurgical process) has a problem: there is virtually no economical use and the available uses have little added value. The greatest part of the copper slag produced worldwide (about 15 million t/a) is therefore dumped.

It is an object of the present invention to improve a process of the type mentioned at the outset in such a way that improved economics are provided.

This object is achieved according to the invention by at least one constituent other than iron being at least partly removed and by the treated iron silicate rock being used for the production of steel or pig iron.

A further object of the present invention is to construct an apparatus of the type mentioned at the outset in such a way that improved economics are achieved.

This object is achieved according to the invention by the apparatus being configured as a facility for producing pig iron or steel.

The metal content of copper slags has hitherto not been utilized (neither the nonferrous metals nor the iron content). At an amount of slag of 700 kt/a, this corresponds to an iron content of 280 kt/a. The slag is already liquid and comparatively little additional energy therefore has to be employed in order to carry out the process. The present invention is therefore based on the approach of removing the nonferrous metals from the slag product and using the remaining slag product (contains slag formers Si, Ca, Mg, Al and Fe as oxides) and raw material for producing pig iron or steel.

This downstream process allows the preceding process steps more flexibility in the processing of the copper raw materials. The complexity of these raw materials in respect of their composition will increase further in future, due to the available copper ore deposits becoming poorer. Apart from impurities of economic interest (processing smelters receive a reimbursement from the mines for the processing of concentrates having increased contents), e.g. As, Pb, in the steel industry other important parameters are especially, for example, Zn and steel contaminants such as S and P. In addition, the copper yield is naturally critical. The newly developed process of the invention covers these challenges and pursues the objective of “zero-waste metallurgy”, i.e. all products formed in the production process are processed further.

A key-point-type description of the essential process steps for carrying out the treatment according to the invention of iron silicate rock is given below.

Process Description

Starting materials:

• • Iron silicate rock, fayalite—(Cu slag from primary copper production)
  • Reducing agent (solid—coke, coal; gaseous—CO, H₂, Fe)
  • Collector metals (Cu, Fe)
  • Electric energy
  • Natural gas or natural gas decomposition products
  • Air/oxygen
  • Circulation products from the copper and steel industry (i.e. dross, litharges, fly dusts, speise, metal phases) or slags

Process temperature:

• • 1300-1600° C. (optimal process temperature hitherto 1400° C.)

Plant:

• • Electric furnace (rectangular, treatment zone, calming zone, tapping points configured as overflow, input via channel system, gas introduction by means of bottom flushing)
  • Closed AOD converter with bottom flushing

Process operation:

• • Discontinuous
  • Continuous (preferred, but whether it is actually implementable depends on ongoing studies)
  • Multistage—necessary!

Energy introduction:

• • Electric furnace→electric (very low oxygen potentials can be set)
  • AOD converter→gas-fired (substoichiometric combustion necessary (□<1; preferably 0.8-0.9; disadvantage—oxygen potential is increased compared to an electric furnace)

Residence time:

• • Not yet finally determined; about 2-6 h

Products:

• • Slag product(s)—fayalite product, magnetite product
  • Fly dust
  • Metal alloy

Illustrative embodiments of the invention are schematically depicted in the drawings. The drawings show:

FIG. 1: a schematic flow diagram of the process,

FIG. 2: a table showing the specification of the starting material,

FIG. 3: a table showing the specification for the slag product from the process.

FIG. 1 shows a schematic depiction for carrying out the individual process steps. In particular, the process sequence in the deep reduction of iron silicate rock to give a fayalite or magnetite product as raw material for use in the iron and steel industry is depicted.

The slag from the primary copper process is preferably introduced in liquid form into the deep reduction process. The liquid slag preferably has a temperature in the range from 1200° C. to 1350° C. A temperature value of about 1260° C. is typical.

As an alternative, working up slag heaps by the process of the invention is also envisaged. However, compared to processing of liquid slag, this involves a higher energy consumption since melting of the solid material is firstly required. A typical analysis of the starting material is shown in the table in FIG. 2.

The objective of the process is to separate the more noble metals of value present from the iron by selective reduction. The iron remains, bound to silicon and/or to oxygen as fayalite product (Fe₂SiO₄) or magnetite product (Fe₃O₄), for further use as starting material in the iron and steel industry. This product contains further oxides of Ca, Mg or Cr as impurities. The specification for the product is shown in the table in FIG. 3.

During heating to the preferred process temperature of 1400° C., the residual sulfur present has to be removed from the system by introduction of oxygen in order for the subsequent reduction period to be able to be carried out efficiently. The melt bath is covered and protected from further contact with oxygen by addition of not more than 7% of solid carbon, based on the amount of slag. The CO/CO₂ ratio of the process atmosphere should be set so that an oxygen potential of 10⁻¹² atm is not exceeded. In this phase, the volatile constituents of the slag vaporize and leave the process together with the offgas. In the course of the offgas treatment, these constituents are obtained in the form of their oxides as fly dust. The fly dust obtained has a composition of about 40-60% of Zn, 10-20% of Pb and <10% of As and can be used as raw material for zinc production, e.g. in the rolling process. In the example shown here with an annual tonnage of 700 000 t, an amount of fly dust of about 20 000 t is to be expected.

The copper content after this process step is still about 0.2-0.3% of Cu. To separate copper and iron selectively, carbon monoxide is introduced as reducing agent via flushing bricks arranged at the bottom. The advantage of bottom flushing is the significantly lower gas velocity required compared to flushing by means of a lance. This leads to intensive mixing between slag, metal and gas phase. The reduction takes place at the gas/slag phase interface according to the reaction equation Cu₂O+CO→2Cu+CO₂. The metal droplets formed are very fine (max. 20 μm) and have to be separated from the slag phase by density separation in a calming zone.

Depending on the further processing route, the mineralogy of the slag product can be matched to the respective use. If the product is, for example, to be used directly in a blast furnace, the fayalite phase obtained is satisfactory. For introduction via the blast furnace charger, pretreatment in the sintering plant is necessary. The melting range of fayalite (about 1180°) is too low for this and would lead to problems in processing. It is therefore necessary to set the magnetite content in the finished product. This ratio can be adjusted according to the requirements of the customer by addition of a defined amount of oxygen. The oxygen can be added not only in the form of oxygen gas but also in the form of intermediates which serve as oxygen donors, e.g. Fe₂O₃ dust from the steel industry.

Claims

1-11. (canceled)

12. A process for treating iron silicate rock, comprising the steps of: at least partly removing at least one constituent other than iron from the iron silicate rock; and using the treated iron silicate rock for producing pig iron or steel.

13. The process according to claim 12, wherein the iron silicate rock is treated in a liquid state.

14. The process according to claim 12, wherein the iron silicate rock is treated at a temperature of from about 1300° C. to 1600° C.

15. The process according to claim 12, including introducing a reducing agent.

16. The process according to claim 12, including carrying out the treatment in a plurality of stages.

17. The process according to claim 12, including introducing oxygen for at least part of the time during treatment.

18. The process according to claim 12, including carrying out the treatment within an electric furnace with bottom flushing.

19. An apparatus for treating iron silicate rock, comprising: a furnace that has a feed facility for a gas, the iron silicate rock being treated in the furnace.

20. An apparatus for processing treated iron silicate rock, wherein the apparatus is configured as a facility for producing pig iron or steel.

21. The apparatus according to claim 20, the facility is a blast furnace.