USING ALUMINUM CHROMIUM SLAG TO PRODUCE CHROMIUM-ZIRCONIUM CORUNDUM BRICKS FOR NON-FERROUS METAL SMELTIN

Refractories for non-ferrous metal kilns work in harsh environments, such as fuming furnaces for smelting lead, zinc, and tin, and refractories for side blowing furnaces. These kilns require refractory materials with high room temperature compressive strength, erosion resistance, reduction resistance and thermal shock resistance. These are not available in the original magnesia-chromium refractories. Aluminum chrome brick has the advantages of good high temperature performance, strong erosion resistance, corrosion resistance, etc., and is mainly used in the slag line of the kiln in the non-ferrous metallurgical industry. However, the existing common chromium slag refractories have the problems of poor resistance to reduction reaction and thermal shock, which cannot meet the requirements of these kilns.
Aluminum chromium slag is a by-product produced when smelting metallic chromium. Its main phase is a solid solution of α-Al2O3 and Cr2O3. The total amount of Al2O3 and Cr2O3 in the chemical composition is generally ≥90% (w), which is a performance Excellent refractory material. Aluminum chromium slag can be made into chromium slag bricks and used in the working lining of non-ferrous kilns. However, the content of impurities Na2O, Fe2O3, Si O2 and metallic Cr in aluminum chromium slag is relatively high and unstable, which affects its use effect.
In this work, aluminum-chromium slag, alumina, and low-chromium ore were used as raw materials, and the aluminum-chromium material re-synthesis experiment was carried out by the electric melting method. Then, chromium-zirconium corundum bricks were prepared by blending fused aluminum and chromium materials with fused zirconium mullite, focusing on the influence of the amount of fused zirconium mullite on the thermal shock resistance of chromium-zirconium corundum bricks.
1 Synthesis test of fused aluminum chromium material
1.1 Raw materials
The raw materials are aluminum chromium slag, alumina powder and low chromium ore with a particle size of ≤ 1 mm. The main phases of aluminum chromium slag are chromium corundum, β-Al2O3 and metallic Cr. The chemical composition of aluminum chromium slag and low chromium ore varies slightly depending on the used 300 k VA shelling electric furnace and 6 300 k VA dumping electric furnace.
1.2 Test methods and results
1.2.1 Electric melting test of 300 k VA shelling electric furnace
Using aluminum chromium slag, alumina powder, and low chromium ore as raw materials, three test ratios were designed. Mix the ingredients according to the test ratio and mix evenly. Take about 1 000 kg of the mixture, put it into a 300k VA shelling electric furnace, and smelt at 1 900-2 100°C. In order to volatilize Na2O and other impurities during the smelting process, different smelting and refining times are designed. A total of 3 furnaces were tested, and they were cooled by natural cooling with the furnace. Observing the appearance of the frit, it is found that the upper and lower parts are dense, and the slag core is honeycomb-shaped. Each sample contains a small amount of metallic Cr. Considering the manufacturing cost and product performance comprehensively, it is determined that the raw material ratio in the mass test is 3#, the smelting time is 8 h, and the refining time is ≥40 min.
1.2.2 6 300 k VA dumping electric furnace electric melting test
Due to the limited smelting temperature of the small-scale experimental electric furnace, the small furnace body and short holding time, the honeycomb slag core material in the middle part of the electric melting material is more. Therefore, in a 6 300 k VA dumping electric furnace at 2 100 ~ 2 200 ℃, a large batch of raw materials electrofusion synthesis test was carried out. The aluminum chromium slag, alumina powder, and low chromium ore in Table 4 are used as raw materials, and the three are batched according to the mass ratio of 12:3:5, and the common material is 18 tons. The smelting time is 8 h, and the refining time is ≥40 min. Pour the electro-melted material into the receiving bag, and unpack it after natural cooling for 72 hours. When smashing and selecting, it was found that the material on the upper part, lower part and around the electrode is relatively dense, hard, and evenly fused; the material in the middle part has large pores, but the texture is hard; there is a small amount of carbon-containing ferrochrome deposit at the bottom.
The chemical analysis of the fused aluminum and chromium material is based on the chemical composition of the raw materials and the test ratio. To 0.28% (w), indicating that about 80% of the Na2O volatilized during the smelting process; the Fe2O3 content decreased from 6.3% (w) during the batching to 0.27% (w) after the smelting; the metal Cr content changed from the batching The 2.48%%(w) of smelting is reduced to 0.64%(w) after smelting. Except for part of the smaller metal Cr oxidized to Cr2O3, the rest forms ferrochrome with Fe2O3 and settle at the bottom of the receiving package. The content of metallic Cr is reduced, which can effectively avoid the expansion and structural looseness caused by the oxidation of metallic Cr during use of the composite material. It can be seen that the electrofusion synthesis can effectively remove the impurities Na2O, Fe2O3, and Cr in the aluminum chromium slag raw materials, and obtain the aluminum chromium composite material with lower Na2O and Fe2O3 content, thereby improving the high-temperature performance of the refractory prepared by it.
2 Test of preparing chromium-zirconium corundum bricks with fused aluminum-chromium materials
2.1 Raw materials and sample preparation
The test materials include fused aluminum and chromium particles (particle size of 5～3, 3～1, ≤1 mm) and fine powder (≤0.088mm) synthesized by the above dumping furnace test, and fused zirconium mullite particles (particle size of 3～ 1 mm), active α-Al2O3 powder and phosphoric acid.
Mix the ingredients according to the test ratio, and place them for more than 48 hours after mixing. A 630 t electric screw press was used to form bricks of 230 mm×114 mm×65 mm, dried at 80-100°C for 24 hours, and fired in a 45 m3 shuttle kiln at 1550°C for 22 hours.
2.2 Performance testing and results
Test the bulk density, apparent porosity, compressive strength at room temperature and the starting temperature of load softening (0.2 MPa load) of the sample according to conventional standards. The air-cooled method was used to test the thermal shock resistance. The sample size was 114 mm×40 mm×40 mm, and the thermal shock temperature was 950°C (heat preservation 30 min). Except for the load softening temperature, each item is tested twice in parallel. Each sample has very little difference in bulk density, apparent porosity, normal temperature compressive strength and load softening start temperature, but the thermal shock resistance is quite different: the test with fused zirconium mullite added at 10% (w) The number of thermal shocks of the sample CZA-1 is 56 and 51, and the number of thermal shocks of the sample CZA-2 with the addition of 5% (w) of fused zirconium mullite is 13 and 17, without the addition of fused zirconium mullite. The number of thermal shocks of the sample CZA-3 from Laishi is only 4 and 5. It can be seen that when the addition amount of fused zirconium mullite is 10% (w), the air-cooled thermal shock resistance is significantly better than that of fused zirconium mullite with 5% (w) and no addition.
3 Conclusion
(1) Using aluminum chromium slag, alumina powder, and low chromium ore as raw materials, mixing with a mass ratio of 12:3:5, smelting in a dumping furnace at 2 000-2 200 ℃ for 8 hours, the obtained fused aluminum chromium material The structure is compact, and the content of impurities Na2O, Fe2O3, Si O2 and metallic Cr is significantly reduced.
(2) Using fused aluminum chromium pellets and fine powder as the main raw materials, adding 10% fused zirconium mullite pellets (3 ~ 1 mm), the thermal shock resistance of the prepared chromium zirconium corundum bricks (950 ℃, air cooling) up to 56 times, good thermal shock resistance.