RU2847894C1 - Method for obtaining cast iron grinding rods - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of preparing raw materials for metallurgical processing, in particular charge for pellets for smelting cast iron for the manufacture of grinding media, and can be used for the disposal of non-ferrous metallurgy waste. To obtain cast iron grinding media, cast iron is smelted using pellets obtained from a charge containing sludge from the flotation of crystallised ground slag from copper production with a copper content of 0.7-2.4% by mass, granulated nickel production slag with a maximum grain size of 0.63 mm, and a carbonaceous reducing agent. The content of granulated slag in the charge for obtaining pellets is 35-70% by mass of the mixture of granulated slag and sludge from the flotation of crystallised ground slag. The pellets are dried and fired in a reducing atmosphere to obtain metallised pellets and are used when charging the charge into an electric arc furnace and melting it to obtain pig iron, which is poured into moulds to obtain grinding media.

EFFECT: expansion of the raw material base for ferrous metallurgy in the production of cast iron grinding media by involving copper and nickel production slags in the production process.

1 cl, 4 tbl

Description

The invention relates to the field of preparing raw materials for metallurgical processing, in particular a charge for pellets for smelting cast iron for the manufacture of grinding bodies, and can be used for the disposal of non-ferrous metallurgy waste.

A known charge composition for the preparation of metallized pellets for the production of grinding media is described in the "Method for Producing Cast Iron Grinding Media," presented in patent RU 2634535. It includes copper smelting slag with a copper content of 0.7 to 2.4% and a carbon reducing agent as starting materials. A disadvantage of this charge composition is the low quality of the pellets used to produce cast iron grinding media, which leads to disruption of the pellet roasting and cast iron smelting process, and reduced productivity.

The closest technical solution adopted as a prototype is the method described in patent RU 2818534 C1. This method for producing cast iron grinding media involves preparing the raw materials for a pellet charge, which contains a mixture of copper smelting slag containing 0.7 to 2.4% copper and a carbonaceous reducing agent. Pellets are produced from the resulting mixture, which is dried and fired in a reducing environment to produce metallized pellets, which are then remelted in an arc furnace to produce cast iron. According to the invention, the pellets consist of a mixture of two components: granulated slag with a maximum grain size of 1.25 mm and sludge from the flotation of crystallized ground slag, containing 40-70% by weight of granulated slag. The combination of two charge components: finely ground slag (sludge) and crushed granulated slag, which is essentially a coarsening additive, ensures high pellet strength.

The disadvantage of this method is the limited raw material base for granulated copper slag: only accessible waste from old production.

The problem is this.

Waste from copper and nickel production is a potential raw material source for the ferrous metallurgy industry. Copper production slag (copper slag) contains up to 40% iron by weight, while nickel production slag (nickel slag) contains up to 20% iron by weight.

The high sulfur content in copper and nickel slags (up to 1.5% and up to 0.8%, respectively) currently prevents the use of this raw material for iron smelting due to the complexity and high cost of the melt desulfurization process.

Copper slag is a sludge obtained from slag crystallized by slow cooling, which is then ground and subjected to froth flotation for additional copper recovery. Before the introduction of modern technology involving crystallization and milling, copper slag was granulated. Waste heaps fifty years old or older remain near some plants. Nickel slag is granulated and sent to waste heaps in this form.

One solution is to combine copper and nickel slags to produce cast iron, followed by the manufacture of grinding media. The increased sulfur content in cast iron made from copper slags does not reduce the performance characteristics of the grinding media, and the presence of copper (0.3-1%), a natural alloying additive, significantly improves its mechanical properties (Mikhailov, A.M., Bauman, B.V., Blagov, B.N., "Foundry Production," "Mashinostroenie," 1987).

A solution to this problem may be the use of granulated nickel slag as a coarsening additive. Granulated nickel slags contain a small amount of copper (up to 0.15%). However, when combined with sludge from the flotation of crystallized copper slag, which contains a sufficient amount of copper as a natural alloying additive, these slags can be used in the production of cast iron for grinding media.

Copper smelter waste dumps contain two types of slag with varying copper content: granulated slag, produced using outdated technology, and sludge, produced using a new technology from ground slag crystallized by slow cooling and subjected to froth flotation to further extract residual copper. Millions of tons of this waste are stored in dumps, occupying vast areas and creating environmental problems.

A similar situation exists with granulated slags from nickel production.

A distinctive feature of nickel slags is their high sulfur content, which hinders their use as a raw material for iron smelting for subsequent steel production: the high costs of melt desulfurization make the process economically unviable. One solution is to use these slags to produce iron and then cast grinding media.

The technical objective and result of the invention is to expand the raw material base of metallurgical production and improve the quality of pellets by using a charge for pellets from a slag mixture of copper and nickel production waste in the method for producing cast iron grinding media.

A method for producing cast iron grinding bodies, according to the invention, includes preparing raw materials for a batch of pellets, which contains a mixture of copper smelting production slag in the form of sludge from the flotation of ground crystallized slag containing copper from 0.7 to 2.4%, and a carbonaceous reducing agent, pellets are made from the resulting mass, which are dried and fired in a reducing environment to obtain metallized pellets, which are used when loading the batch into an arc furnace and melting them to obtain cast iron, according to the invention, the batch additionally contains granulated slag from nickel production with a maximum grain size of 0.63 mm in an amount of 35-70% of the mixture of sludge from the flotation of crystallized ground slag and granulated slag.

To solve this technical problem, granulated nickel slag is used. It acts as a coarsening additive in the charge, combined with ground copper slag slurry (in the prototype technical solution, granulated copper slag serves as the coarsening additive). Granulated nickel slags contain up to 25% iron oxides by weight, but have not yet been used in metallurgical production due to their high sulfur content. However, when combined with slurry from the flotation of crystallized copper slag, which contains a sufficient amount of copper as a natural alloying additive, these slags can be used in the production of cast iron for grinding media.

Granulated slag from nickel production is coarse sand with a maximum grain size of 10 mm, predominantly (97% by weight) composed of glass. A characteristic of granulated nickel slag, similar to copper slag, is the brittleness of its grains. The slag glass is riddled with cracks, as confirmed by high-resolution electron microscopy. Compared to granulated copper slag, nickel slag has a more dense crack network. Even minor forces, heating, and cooling during drying lead to the destruction of large grains.

Avalanche-like failure, especially under impact and thermal loads, is typical for grains larger than 0.63 mm. Finer grains are highly durable and abrasive, and are difficult to grind.

The most efficient and cost-effective method is crushing to a grain size of 0.63 mm using impact and impact-attrition crushers. Further grinding to obtain a sufficient quantity of fine fractions to ensure pelletizing of the charge is energy-intensive and economically disadvantageous. Experiments have shown (during rotating drum testing) that dried pellets containing granulated slag that are not crushed to a grain size of 0.63 mm experience surface shedding due to the destruction of weak grains. This results in high losses (spillage) during handling and transportation and disruption of iron reduction and cast iron smelting processes.

The particle size distribution of the charge is of great importance in pellet production. As the specific surface area of the charge increases to a certain value, the quality parameters of the charge and pellets, including lumping, water content, green pellet strength, and dried pellet strength, improve. Further increases in specific surface area increase the water content, leading to reduced strength and increased energy consumption for drying.

Copper smelting slag has a relatively high specific surface area (approximately 1360 ^cm2 /g). Experiments have shown that, with such a high specific surface area, its use without a coarsening additive is ineffective. Due to its high moisture content, producing high-quality pellets requires high charge moisture, which leads to longer drying times, reduced productivity, and increased energy consumption. Insufficient charge moisture leads to reduced strength of both green and dried pellets.

The proposed combination of relatively large grains of granulated nickel slag, within the specified boundaries, creating the “framework” of the pellet, and a fine fraction – sludge, improving the cohesion of the particles, ensures the achievement of the required quality indicators: the strength of green pellets, the strength of dry pellets, and cost effectiveness.

The limits for the granulated slag content in the mixture are determined by the following. Exceeding the upper and decreasing the lower limits for granulated slag content in the charge degrades particle cohesion and the strength of green and dried pellets (Table 2). Using a mixture of two types of slag in the specified ratio in the charge expands the raw material base of the ferrous metallurgy industry by incorporating slags from existing copper and nickel smelters into production, improving pellet quality.

The claimed method is novel in comparison with the prototype due to the presence of such distinctive features as the use of granulated slag from nickel production in the charge with a quantitative content of components: 35-70% of granulated nickel slag from the mass of the mixture, the grain composition of the granulated nickel slag: fractions less than 0.63 mm, which together ensure the achievement of the specified result.

The proposed method for producing cast iron using a charge of the specified composition for pellets for smelting cast iron in the manufacture of grinding media can find wide application for the disposal of waste from copper and nickel smelters (in particular, in the Southern and Middle Urals, Taimyr, Kazakhstan and other regions).

The proposed method utilizes the claimed charge composition as follows. Sludge from the flotation of crystallized copper slag with a copper content of 0.7-2.4% and granulated nickel slag, previously crushed in a rotary or rod mill to a particle size of minus 0.63 mm, are mixed with a carbonaceous reducing agent (coal, coke), a binder (liquid glass, bentonite), and water. Pellets are produced in a drum or disc granulator and dried. Iron is reduced from the resulting pellets by roasting in a reducing atmosphere and then smelted, producing cast iron, which is then cast into molds to produce grinding media (balls).

An example of the practical implementation of the claimed charge in the method for producing cast iron grinding media.

Raw materials: a mixture including sludge from the flotation tailings of the Karabash Copper Smelter with a copper content of 0.7 wt.% and granulated copper slag from the Ufaley Nickel Plant, pre-crushed in a rod mill to a fraction of minus 0.63 mm, a reducing agent: coal, crushed in a disk mill to a fraction of minus 1 mm, in an amount of 20 wt.% of the slag weight, a binder - ground bentonite, in an amount of 1 wt.% of the charge weight. Granulated slag, sludge and coal were dried to constant weight, mixed with a binder. The amount of binder in the mixture was 0.9 wt.% of the charge weight. The granulometric composition of the original and crushed nickel slag is given in Table 1, the chemical composition in Table 2.

The amount of granulated nickel slag in the mixture of the two types of slag ranged from 35 to 70 wt.%. Additionally, for comparison, batch compositions with a granulated slag content of 25, 30, 75, and 80 wt.% were prepared. The mixture of these raw materials was mixed with water to a moisture content of 10% for 10 min, loaded into a laboratory drum granulator with a diameter of 340 mm, and granulated. The strength properties of green pellets with a diameter of 14-16 mm were determined by dropping them onto a cast iron plate. The green pellets were dried in a drying oven at a temperature of 120 degrees. The crushing strength of the dried pellets was determined. As shown by the pellet test results (Table 3), high strength indicators are achieved with a slag content of 35-70% in the slag mixture. When the granulated slag content decreases below 35% and increases above 70%, the strength of green and dried pellets decreases. Dried pellets of optimal composition (with a granulated nickel slag content of 35-70% by weight) were metallized by firing in a reducing atmosphere, after which they were smelted into cast iron in a laboratory arc furnace. The resulting metal was melted in an induction furnace and cast into split-cast iron molds.

The chemical composition of the resulting cast iron is given in Table 4.

As a result, samples of cast iron balls with a diameter of 40 mm were obtained.

No chips or dents were detected on the balls after repeated drops from a height of 4 meters onto a cast iron plate. Hardness testing of cast iron samples obtained by casting the balls yielded a value of 53 on the Rockwell scale, corresponding to hardness group II according to Technical Requirements GOST 7524-89 "Steel Grinding Balls" and KR ST 2310-2013 "Cast Iron Grinding Balls."

Table 1. Granulometric composition of the original and crushed slag

Name of material Residue on a sieve with a hole diameter, mm 5 2.5 1.25 0.63 0.32 0.1 bottom Original slag 3.5 22.1 29.7 32.2 7.58 1.3 3.7 Crushed slag - - - - 57.4 37.5 5.1

Table 2. Chemical composition of slags

Type of slag MgO Al ₂ O ₃ SiO ₂ CaO FeO Fe ₃ O ₄ Cu S Copper sludge 1.7 3.5 30.0 3.3 29.0 32.0 0.7 0.9 Nickel granulated slag 8.0 7.0 40.0 12.0 25.0 0.0 0.1 0.4

Table 3. Dependence of pellet strength characteristics on the nickel slag content in the mixture

Content of granulated slag in the mixture, wt.% 25 30 35 40 50 60 70 75 80 Raw (number of safe drops) 6.9 7.2 13.4 13.9 14.7 14.3 12.9 6.9 5.0 Dry (kg/pellet) 11.6 12.4 27.9 46.8 56.3 53.3 32.0 14.4 12.6

Table 4. Composition of cast iron

C Si S Cu Fe 2.8 2.9 0.9 0.9 ost

Thus, the use of the proposed charge composition ensures the expansion of the raw material base for metallurgical production, the production of pellets of the required quality (Table 3) and the smelting of cast iron from them for grinding media that meet regulatory requirements.

Claims (1)

A method for producing cast iron grinding media, which includes smelting cast iron using pellets obtained from a charge containing sludge from the flotation of crystallized ground slag from copper production with a copper content of 0.7-2.4 wt.% and a carbonaceous reducing agent, which are dried and fired in a reducing environment until metallized pellets are obtained, which are used when loading the charge into an arc furnace and melting it to obtain cast iron, then the cast iron is poured into molds to obtain grinding media, characterized in that the charge for obtaining pellets additionally contains granulated slag from nickel production with a maximum grain size of 0.63 mm, wherein the content of granulated slag in said charge is 35-70 wt.% of the mixture of granulated slag and sludge from the flotation of crystallized ground slag.