Ferroalloy slag contains high-value metals such as chromium, manganese, molybdenum, nickel, and titanium. Therefore, it is preferable to recover valuable metals from it. For iron alloy slags that cannot be recycled at present, they can be used as building materials and agricultural fertilizers.

(1) Recycling metals

In order to recover the metal elements in the slag, a lot of research work has been done at home and abroad, and it is now possible to recover metals from various iron alloy slags.

Molybdenum iron slag contains 0.3%~0.8% molybdenum. Foreign magnetic separation method can be used to obtain 4%~6% molybdenum concentrate, which can be recycled.

In foreign countries, the method of wind sorting is used to separate the metal in the pulverized slag. Wind separation can separate the raw slag into slag blocks (>5mm), fine slag (<5mm) and slag powder (<1mm), and the metals contained in the slag accumulate in the slag. The refined ferrochrome slag contains about 5% of metal, and the metal can be recovered by sorting.

In a factory in China, the chromium-chromium alloy is washed with refined chrome-iron slag, which can reduce the chromium content in the slag from 4.7% to 0.48%, the chromium content in the silicon-chromium alloy increases by 1% to 3%, and the phosphorus decreases by 30% to 50%. Obvious economic effects. The electric furnace manganese metal and the medium-low carbon manganese iron furnace slag have higher manganese content, and most of them are used for smelting silicon-manganese alloy by various means. For example, some plants use the pulverized medium-manganese slag as a raw material for manganese ore sintering; some plants add a stabilizer to the medium-manganese slag to prevent slag from being pulverized for use in the furnace.

The ferrosilicon slag contains valence element silicon, silicon carbide and manganese, which is the main element of smelting silicon-manganese alloy and can be used as a charge for smelting silicon-manganese alloy. The use of ferrosilicon slag to smelt silicon-manganese alloy not only reduces the production of raw materials, silica, coke, but also saves electricity.

The tungsten iron slag contains 15% to 20% manganese and can be returned to the silicomanganese furnace for use.

(2) Used as cement admixture and slag brick

The blast furnace manganese iron slag (including the electric furnace manganese iron slag), the carbon manganese iron slag and the silicon manganese alloy slag can be water quenched into granular slag. The water quenching method can be variously used, and the slag can be directly slaged in front of the furnace, or the slag tank can be used to drag the slag to the slag pool, and the slag pool can be made into slag, and can also be dumped by the crane in the casting room. The slag tank is quenched by a nozzle under the launder. In China, iron alloy water quenching slag is the same as blast furnace water quenching slag, which is basically used as a blending material for cement plants. A ferroalloy plant in China sends the water-quenched silico-manganese slag to the cement plant for use as a blending material. When the clinker is 600, the amount of water slag is 30% to 50%, and the slag cement of No. 500 can still be obtained.

Ferroalloy water quenching slag can also be used as slag brick. The slag brick produced by a factory in China adopts the following ingredients: iron alloy water quenching slag 100%; gypsum 2%; lime 7%. The batch material can be put into use after being wheeled, mixed, shaped and cured.

(3) Production of cast stone products

Cast stone products can be produced by using molten silicon manganese slag, boron iron slag and molybdenum iron slag.

1. Silica-manganese slag cast stone

Silicomanganese slag is the waste residue produced when smelting silicomanganese. The hot-melt silico-manganese slag flowing out of the submerged arc furnace can directly cast the cast stone product. This product can be used for equipment and construction projects that require wear resistance. In addition, it is also possible to incorporate an additional material into the silicomanganese slag and heat and melt the cast acid-resistant cast stone product.

The production process of directly cast wear-resistant silicon-manganese slag cast stone includes the processes of hot slag receiving and casting, crystallization and annealing.

The hot slag is taken and cast by a crane to hoist the hot iron slag to the casting table and directly cast. No additional material is added to the hot slag. The hot slag is discharged at a temperature of 1450 to 1500 ° C, and the temperature of the cast cast stone is controlled at 1300 to 1350 ° C.

The crystal of the cast stone is carried out in a crystallization furnace, the crystallization temperature is controlled at 800 to 950 ° C, and the crystallization time is 30 to 50 min. The production process of acid-resistant silicon-manganese slag cast stone is as follows:

Undertake of molten slag - ingredients - electric furnace melting - casting - crystal annealing, the ratio of several acid-resistant silicon-manganese slag cast stone is shown in Table 1.

Table 1 Several acid-resistant silicomanganese slag cast stone ratio

The chemical composition (in %) of the acid-resistant silicomanganese slag cast stone is as follows:

SiO2 48~53 Al2O3 10-17

MnO 9~12 FO2O3+FeO 5~9

CaO 1~13 MgO 4~8 CrzO3 0.3~0.4

The casting temperature of the acid-resistant silico-manganese slag is generally 1250~1300°C. The crystallization temperature is 800~920°C, and the crystallization time is 45~60mm. Both the directly cast wear-resistant silico-manganese slag cast stone or the compounded acid-resistant silico-manganese slag cast stone need to be annealed in an annealing kiln or incubator, and the general annealing time is 3d.

The impact strength of the wear-resistant silicon-manganese slag cast stone is generally 10~24.6MPa, and the wear resistance coefficient is 0.26~0.40kgf/cm2. The chemical corrosion resistance of acid-resistant silicon-manganese slag cast stone is shown in Table 2.

Table 2 Chemical resistance of acid-resistant silicomanganese slag cast stone

2. Molybdenum iron slag cast stone

The molybdenum iron slag is a waste slag discharged when the ferromolybdenum alloy is smelted by an external furnace method. After the slag is added with some additional materials in a hot melt state, the cast stone product can be cast without heating and melting.

The purpose of adding the additive is to adjust the chemical composition of the slag and improve its crystallization property. The proportion of the ferromolybdenum slag cast stone: molybdenum iron slag 100; micro carbon chrome iron slag 15; iron scale 12; fluorite 10.

The chemical composition (in %) of ferromolybdenum slag is as follows:

SiO2 48~55 Al2O3 9.5~12 CaO 6~15 MgO 2~5

Fe2O3+FeO 14.5~19.8 R2O 2~2.5

The crystallization temperature of ferromolybdenum slag cast stone is 850~880°C, the crystallization time is 20~40min, and the annealing time is about 3d.

The main physical and chemical properties of ferromolybdenum slag cast stone are shown in Table 3.

Table 3 Main physical and chemical properties of ferromolybdenum slag cast stone

3. Boron iron slag cast stone

Boron iron slag is a waste residue produced when smelting boron-iron alloy by aluminum thermal method. Boron iron slag can be made into boron iron slag cast stone. The process is self-flow casting of molten slag into the sand mold. The method of using quartz stone insulation, natural crystallization and slow cooling is as follows:

Boron iron slag release → slag package → sand mold → vermiculite heat preservation → slow cooling → demoulding → boron iron slag cast stone brick

The chemical composition of the boron iron slag cast stone is as follows:

Al2O3 65.35% CaO 4.63% MgO 17.09% Fe2O3 0.24%

SiO2 1.13% B2O3 9.36%

Physical properties of boron iron slag:

Refractoriness>1770°C; softening point 1610°C; apparent porosity 2%; density 3.16g/cm3; normal temperature compressive strength 171MPa; density 3.32g/cm3.

Boron-iron slag cast stone has poor resistance to rapid cooling and rapid heat, but there is no crack or deformation when the temperature is changed above 500 °C. The alkali resistance is greater than 99.2%, but it is not resistant to acid. Boron-iron slag cast stone is mainly used as a refractory material, a large wear-resistant casting, and the like.

(4) Ferroalloy slag refractory

Metal chromium smelting slag can be used as advanced refractory concrete aggregate and has been promoted and used in China. The refractory concrete prepared with chromium slag aggregate and low calcium aluminate cement has a refractoriness of up to 1800 ° C and a load softening point of 1650 ° C. It still has a high compressive strength at high temperatures and is still 14.7 MPa at 1000 ° C. It is especially suitable for high temperature bearing parts with complex shapes.

In addition to metallic chromium, ferrotitanium and ferrochrome are also smelted by aluminothermic method, and the corresponding slag has high alumina (Al2O3), which can be used as refractory concrete aggregate.

(5) Iron alloy slag recycling chemical raw materials or agricultural fertilizer

Phosphorus sludge produced in the production of ferro-phosphorus alloy can recover industrial phosphoric acid and use phosphate residue to produce phosphate fertilizer. The principle is that the phosphorus sludge slag contains 5% to 50% of phosphorus, and combines with oxidation to form phosphorus oxide such as phosphorus pentoxide (P2O5). Phosphorus pentoxide (P2O5) is absorbed by water in the absorption tower to form phosphoric acid. The remaining residue contains 0.5% to 1% phosphorus and 1% to 2% phosphoric acid. Lime is added and stirred under heating. Produces heavy superphosphate, which is phosphate fertilizer.

The various slags of ferroalloys contain a variety of trace elements required for plant growth, which can increase the fertility of the soil. Refined ferrochrome slag can be used to improve acidic soils as calcium fertilizers. Manganese-containing, keyed iron alloy slag can also be used as agricultural fertilizer. Tests have shown that the application of silicomanganese slag in rice fields has the effect of promoting ripening and increasing yield, reducing rice blast; and helping to prevent lodging.

(6) Recycling of ferroalloy leaching slag

In addition to the pyrometallurgical slag, the ferroalloy industry produces some leaching slag. The metal chrome and vanadium iron leaching slag contains toxic Cr6+ and V5+. During the process of dumping, due to the infiltration of rainwater into the leaching residue, the V5+ wastewater will enter the groundwater system, causing groundwater pollution. In order to prevent the pollution of the water body by the waste residue yard, the method of treatment and storage is mainly adopted at present.

The research work on ferroalloy leaching slag has been carried out extensively, and its treatment and utilization are mainly in the following aspects.

Chromium leaching slag can be used in many applications, such as bricks made of chromium slag, iron making, cement, calcium magnesium phosphate, glass colorants, and the like.

The vanadium leaching residue contains a large amount of iron, which can be used as a raw material for iron making and cement. In order to make better use of this leaching slag, it is best to return to the vanadium-titanium magnetite smelter, but this will increase the transportation and management difficulties. At present, it is feasible to combine vanadium leaching slag with other iron ore to make sinter ore for iron making.

The electrolytic manganese leaching slag contains a considerable amount of ammonium sulfate, and the particles are very fine and difficult to dewater. Currently, they are transported to the countryside as a fertilizer for use as a fertilizer. This article is transferred from the Internet only for learning and communication, not for business, please notify us if there is any infringement.