KR940000492B1 - Nickel-copper matte converters employing nitrogen enriched blast - Google Patents

Abstract

No content.

Description

Nickel-Copper Matte Converter Process Using Nitrogen-Enriched Blast

FIELD OF THE INVENTION The present invention relates to the hot metallurgical production of nickel-copper mats refined from common ore sulfides, and more particularly to a converter process using nitrogen, air, oxygen and mixtures thereof. The introduction of nitrogen or nitrogen / oxygen-containing gases helps to control and cool the oxidation of the mat to be produced. Reducing the weakening of mass production results in more efficient converter work.

Nickel-Bessemer mats are molten mats from the primary smelting furnace of Pierce Smith converter, which generally injects air or an air / oxygen mixture into the bath through tuyeres. Manufacture by converting (converting). Pierce Smith converter is the most common type of converter used for this application, with a hooded opening at the top and a horizontal cylinder rotatable on an arc of 180 °. Many of the blow holes are located under the normal working height of the molten mat under blowing conditions and the blow holes are above the bath for pouring or containment.

The feed to the converter usually consists of a pure mat containing Ni ₃ S, Cu ₂ S, FeS and small amounts of oxygen, precious metals and other components. Most of the rock and lacquer, originally in the gold base crop, are removed from the upstream furnace operation.

The purpose of the conversion process is to oxidize FeS in the mat to form iron oxides, to liberate sulfur dioxide, and to also contain nickel and copper sulfides together with small amounts of cobalt, precious metals and dissolved oxygen. To be. This is accomplished by blowing oxygen-containing gas (air, oxygen-rich air or oxygen) into the mat through the tuyeres. Oxygen combines with iron and sulfur to form iron oxides and sulfur dioxide. Sulfur dioxide is treated to prevent fugitive emissions by discharging it in gaseous form. The iron oxide combines with the added silica flux to form iron silicate slack, which is rich in nickel and copper and iron floats on top of the greatly reduced mat. The oxidation process is an exothermic process and the exothermic heat is sufficient to keep this work on its own.

Blowing and slacking off all iron is removed, the resulting mats are cooled, cast and processed for recovery of important components and precious metals. By cooling, copper and nickel in the mat form a metal containing copper sulfide (Cu ₂ S), nickel sulfide (N _i3 S ₂ ), and a small amount of dissolved sulfur.

The desired composition of the baser mat product is highly dependent on the requirements of the downstream treatment. Important variables are the final iron and sulfur content. These contents are generally controlled by the degree of blowing and the blowing temperature. Conversion of the Ni-Cu mat is usually a batch process and carried out in the next step.

a) "slag blows" work in which the molten mat is filled in the converter and the FeS is oxidized to iron oxide and SO ₂ gas. The oxide is slack by siliceous flux, which is removed by successive kicking off (the top of the mat is discarded). The iron content of the mat is maintained above 10% Fe. The temperature during this step is maintained at 1150 ° C to 1300 ° C.

b) A ″ finishing blow ″ operation in which the FeS is oxidized without adding more molten mat to produce a mat containing about 3% Fe.

c) Excessive flux and cold dope (usually hard crusts and loads from mat and slack conveying operations) until the majority of the remaining FeS has been oxidized and the iron content of the converter melt is 1% Fe. There is a ″ dry-up- blows ″ operation to cool the melt by adding dripping At the end of the blow, the temperature of the melt varies from 1100 ° C. to 1250 ° C. depending on the blowing temperature and the availability of the coolant and mat refining technique. Changes to ° C.

d) ″ Cooling ″ is the final process in the manufacture of the Bessemer mat. In this process, the remaining Fe is oxidized and the melt is cooled to 700 ° C. to 1100 ° C., depending on the composition of the mat and other treatment requirements by convection and radiation loss. At this stage a final product containing 1% or less of iron is produced. For this step, the melt is transferred to another similar converter equipped for this purpose.

In the dry blow-up process, a considerable amount of nickel and cobalt oxides, as well as magnetite (magenetite: Fe ₃ O ₄ ), are formed. The result is a very large slack that is difficult to remove from the converter. Excessive solvent injection and low temperature dope addition during this blow further exacerbate this situation. When the melt is withdrawn from the converter, a large amount of ″ mush ″, mainly composed of magnetite, nickel oxide (NiO), iron olivine slag (xFeO-ySiO ₂ ) and insoluble flux remains in the converter. This mush must be extinguished by the blast furnace mat at the beginning of the next converting cycle. This places a limit on the grade of mat that can be fabricated by the upstream initial refining unit.

The function of the cooling process is twofold; Cooling and / or a small blow of the melt removes most of the iron and also cools the converter melt to an appropriate temperature for the next treatment of the Bessemer mat. Cooling takes place by natural convection and radiation and lasts up to 4 hours.

There are several drawbacks to the current fixation. A large amount of mush remaining in the converter after dry-up must be redissolved during the first blow of the subsequent converter cycle. This limits the mat rating. Sufficient FeS should be present in the mat to supply the heated fuel and to act as a reducing agent to promote dissolution. Second, the long cooling time in the cooling stage brings serious limitations in terms of the efficiency of use of equipment for converter work. Third, all material added as coolant must be partially dissolved in the mat and the mush must be dissolved again in the next charge.

Thus, the molten nickel-copper mat is finished to besomer product properties and cooled to a suitable casting temperature by blowing with a nitrogen and / or nitrogen-oxygen (air) mixture. The use of nitrogen can promote cooling and control the iron oxidation to be greater than the final iron content in the besomer mat.

The present invention utilizes working tonnes of nitrogen or nitrogen / oxygen (air) mixtures to control oxidation of Ni / Cu converter mats and improve cooling. In particular, the present invention controls the rate of oxidation approaching the end of the converter cycle of the Cu / Ni spacer polymer; Minimize mush formation; During the final stage of the conversion, the converter temperature and mat composition are adjusted; It is concerned with accelerating the cooling of the mat to a temperature reasonable to improve the kicking, casting and subsequent refining processes.

Cooling carried out by blowing in a nitrogen-rich gas stream shortens cycle times and improves converter productivity.

Nitrogen use also helps in the overall cost effectiveness of the entire nickel-copper refining operation, since sometimes pure oxygen for various purposes must be generated and stored on site. Rather than blowing up nitrogen, it is collected and used in this process.

Many of the problems listed can be minimized by blowing operations with nitrogen and / or nitrogen-oxygen (air) mixtures during the cooling cycle. By controlling the rate of blowing and the nitrogen content of the blast, the rate of oxidation and the final content of iron and sulfur in the mat can be controlled. Thus, there is no need to move the mat to the container or add coolant, which shortens the cycle time and increases the meltability and productivity.

The addition of nitrogen to air or oxygen blowing allows the sulfur content to be controlled in the baser mat. In a typical embodiment, the final sulfur content of the Bessemer mat is primarily controlled by the blowing temperature, i.e. increasing the temperature tends to decrease the sulfur content, lower the blowing temperature, and increase. Dilution of the blast with nitrogen removes sulfur from the bath, which plays an additional role in controlling the composition of the besememet.

Nitrogen addition to air or oxygen blasts is also useful for other converter processes. For example, nitrogen / air or nitrogen / oxygen mixtures are used to complete the mat and to control iron and sulfur content. Separately, nitrogen is primarily used to cool the mat. Iron and sulfur regulation are not major factors in this example.

Nitrogen addition and addition time are a function of the type, temperature and amount of mat.

For a typical dry-up finish blow, the mat generally contains 3% or less of iron. Nitrogen is mixed with air in a volume ratio of 0.5-2: 1 and the mixture is fed to the converter at a rate of 2.5-7.5 cubic meters / minute per tonne of mat. If nitrogen is added to oxygen, the volume ratio should be 6-14: 1 and the feed rate is 2.5-7.5 cubic meters / minute per tonne of mat. You can change these parameters to manually control the state.

In a representative cold blow, the finished mat generally contains 1-3% or less of iron and is at a temperature of 1100 ° C-1250 ° C. Nitrogen is mixed with air or oxygen in a volume ratio of 3-20: 1 or 20-100: 1 respectively. The feed rate is 2.5-7.5 cubic meters / minute per tonne of mat. The volume of gas supplied to the converter should be chosen to reduce the temperature by 50 ° C-200 ° C. These values may change depending on the situation.

Only nitrogen may be used to cool the mat. Nitrogen is added to cool the mat at a feed rate of 2-4 cubic meters / minute per tonne of mat.

Since it is generally easier to measure the amount of oxygen than to measure the amount of nitrogen, it is most useful to employ a small analyzer to test and measure the gas entering the converter. Knowing the oxygen content, the nitrogen content can be determined. Thus, when nitrogen-containing working gas enters the converter, the blast is 5-15% oxygen (or 23-70% air) for oxidation purposes and 1-5% oxygen (or 5-20%) for cooling purposes. Air). It is found that it is desirable to carry out nitrogen dilution immediately after the start of the final blowing with 10% Fe and also increase it gradually. In this way, it is possible to precisely control the mat composition and temperature throughout the finishing blowing process and thus obtain a firmer final product and temperature.

Three non-limiting examples illustrate the effect of the present invention.

Example A

Use of N ₂ -air during dry blow-up

120 tons of partially converter-treated mat at 2.6% Fe and 1230 ° C. are transported through the air hole to a Pierce-Smith converter designed to blow the N ₂ air mixture.

The converter was rotated to the blown position and air 311.5 m 3 / m (11,000 scfm) and nitrogen 215.2 m 3 / m (7600 scfm) were blown through 42 wind holes for 21 minutes. The oxygen analyzer indicated that the blast contained 11.6% by volume O ₂ .

After the blow was complete the iron content of the mat was analyzed to 1.3% and was at 1150 ° C. The 5261 kg (5.26 tonne) Mush remained in the converter in the form of a rigid 203 mm (8 in) finish. The mat was transported for subsequent processing and a Mush sample was obtained. Mush analysis showed 43% matte, 25% flux and 31% nonmetal oxide.

Example B

Use N ₂ air to cool the filling of the Bessemer mat

Using the same equipment as in Example A, 120 tonnes of finished mat with analytical value of 0.89% Fe and 1160 ° C was blown into a nitrogen-air mixture and cooled to casting temperature.

The blast mixture consisted of 31.1 m 3 / m (1100 scfm) of air and 229.3 m 3 / m (8100 scfm) of N ₂ and was blown for 22 minutes through 25 air holes. The oxygen analyzer indicated that the blast contained 3.1% by volume O ₂ . After the blow was complete, the mat contained 0.29% Fe and cooled to 1000 ° C. The mat was cast. Only a small amount of Mush remained in the converter. Analysis shows that this mush contains 59% Bessemer mat, 22% flux and 19% nonmetal oxide.

Example C

Use of N ₂ -air for cooling after dry-up

The same equipment used in Examples A and B was used. 120 tons of mat analyzed at 1150 ° C and 1.3% Fe is blown with 15.7 m 3 / m (555 scfm) air and 224 m 3 / m (7930 scfm) nitrogen (2.7 vol% O ₂ ) injected through 25 wind holes. Blowing was maintained for a total of 68 minutes during which 3629 kg (3.63 tons) of flux was added. After blowing, the mat temperature was 1000 ° C and the iron content was 0.34%. Bessemer mats were cast, leaving 5-8 tonnes of hard finishing dregs. This Mush sample consisted of 53% Bessemer Mat, 28% Emulsion and 10% Nonmetallic Oxide.

The prior art teaches the use of nitrogen in pyrometallurgy. However, there was no perception that the introduction of nitrogen-rich blasts into nickel-copper converters affected oxidation control, increased cooling and reduced mush formation. For example, U.S. Patent 3,671,197 discloses the use of an inert gas such as nitrogen to liberate sulfur from pyrite to form roasted pyrrot ite. Removes sulfur from the gas. Iron oxide production is the final goal. Canadian Patent No. 973,720 (assigned to the applicant) discloses the use of pur ge gas containing nitrogen to refine carburized copper containing impurities. The scrubbing gas causes the impurities in the bath, which have been pretreated to slack iron in the copper bath.

In comparison with the prior art and the conventional embodiment, the following advantages are obtained in this process.

1) The amount of mush remaining from the dry-up and cooling cycles is reduced and therefore the amount of material to be digested again in the next cycle.

2) The mat cooling speed is increased, the cycle time is shortened and productivity is increased.

3) There is no need to transfer to the cooling container, so there is no scrap, and the applicability and productivity are increased.

4) Nitrogen cooling allows the treatment of high quality initial mats.

5) This process may use nitrogen, a by-product of tonnage oxygen production, common in many non-ferrous smelters.

6) Nitrogen or N ₂ / air or oxygen mixtures may be blown through normal air holes.

For convenience of description, specific embodiments of the present invention have been described herein. Those skilled in the art will understand that there may be variations of the form of the invention protected by the claims, and that certain phenomena of the invention may take advantage without the corresponding use of other phenomena.

Claims (4)

In order to treat the sulfided molten nickel-copper mat from the ore, a) the molten nickel-copper mat is placed in a pyrometallurgical vessel and b) nitrogen is added at a nitrogen to oxygen ratio of 20 to 100: 1. A working gas containing 5-15% oxygen, supplied at a rate of 2.5 to 7.5 m ² / min per tonne of mat, c) oxidizing the mat with this gas and cooling the mat with nitrogen at this rate Converter process characterized in that (Converter process). The mat of claim 1 wherein the mat comprises iron sulfide and also metal sulfides and oxidizes a portion of the iron sulfide contained in the mat in the presence of the working gas before removing the mat from the container and forms iron-containing slag on the surface of the mat. And separating the slack from the mat. The process according to claim 1, wherein the oxygen content of the working gas is 1-5%. The process according to claim 1, wherein a working gas with a nitrogen-oxygen ratio of 6 to 14 is supplied into the vessel at a feed rate of 2.5-7.5 m ² / min per tonne of mat.