The design and selection of refractory materials for the bottom and interior of non-ferrous metal smelting furnaces
author: XINTAI
2025-07-08
At present, refractory materials used in the non-ferrous metal smelting industry can be roughly divided into two categories: slightly acidic refractory materials and slightly alkaline refractory materials. Slightly acidic refractory materials are mainly trivalent oxides (Al₂O₃-SiO₂ series), mainly including high alumina bricks, mullite bricks, zirconia corundum bricks, etc. The slightly alkaline refractory materials are mainly divalent oxides (MgO-Al₂O₃, MgO-Cr₂O₃ series), including magnesia-chrome bricks, magnesia-alumina bricks, magnesia-alumina spinel bricks, etc.
Design of the furnace bottom
After years of practical production experience, for lead smelting, the metallurgical furnaces used include dozens of types for processing various lead materials. However, the refractory linings of the metallurgical furnaces mainly use magnesia-chrome bricks, high alumina bricks, and high alumina refractory ramming materials, etc.
1. Permanent layer area at the bottom of the furnace
In the design of the furnace lining, the selection of refractory materials varies accordingly at different positions within the furnace body. Taking the furnace body of a fixed horizontal metallurgical furnace as an example, the materials commonly used for the furnace bottom include magnesia-chrome bricks, high alumina bricks, aluminum-chrome spinel, high alumina ramming materials, magnesia ramming materials, etc. Some also use high-strength anti-seepage ramming materials, whose composition belongs to the Al₂O₃-SiO₂ series, with an Al₂O₃ content of more than 75%. The specific gravity of liquid lead reaches 10.6g/cm³, and it has extremely strong permeability. Therefore, the refractory material at the bottom of the furnace must not only have the function of heat dissipation but also possess a high ability to prevent lead seepage.
At present, the widely used practice is to first lay high alumina bricks on the steel plate at the bottom of the furnace. High alumina bricks have a relatively high compressive strength (compressive strength at room temperature of 40 to 60MPa), and it is more reasonable to use them as a cushion layer at the bottom of the furnace. A layer of refractory material with lead penetration resistance should be set on the upper part of the furnace bottom cushion layer. Currently, magnesia ramming material or high-strength anti-seepage ramming material (high alumina) is used, and both can serve as a separator layer. The ratio of magnesia ramming material is: magnesia sand: magnesia powder = 7:3, mixed with brine. The particle size of magnesia sand is: 0.2-0.5mm70%, 1.5-3.0mm 30%. The composition of high-strength anti-seepage ramming material is made up of various sizes of aggregates and bone powder of high alumina. After high-temperature baking, the aggregates of various sizes expand and combine closely, achieving the ideal anti-seepage purpose of lead.
It must be noted that after the ramming of magnesia and magnesia-chromium ramming materials is completed, they need to be subjected to low-temperature baking. After baking out the free water, the expansion joints should be filled with fine magnesium powder to ensure the strength and density of the ramming layer. The thickness of the ramming material is recommended to be 150 to 300mm, which not only facilitates the completion of ramming in one go but also enables a relatively uniform baking process, forming an integral layer with better anti-seepage effect.
2. Working layer area at the bottom of the furnace
Magnesia-chrome bricks are widely used in the selection of refractory materials for the safety layer and working layer at the bottom of the furnace. Among them, the safety layer can use directly bonded magnesia-chrome bricks, while the working layer can use semi-rebonded magnesia-chrome bricks. With the fluctuation of the lead liquid level, the temperature at the bottom of the furnace fluctuates significantly. Therefore, semi-rebonded magnesia-chrome bricks with good thermal shock resistance should be selected. The safety layer and working layer at the bottom of the furnace also use high alumina bricks. Generally, this type of furnace has a bottom lead layer about 400mm high, so the furnace bottom will not be eroded by slag. High alumina bricks with an Al₂O₃ content of no less than 75% can be selected as the lining bricks for the safety layer and working layer at the bottom of the furnace.
1. Permanent layer area at the bottom of the furnace
In the design of the furnace lining, the selection of refractory materials varies accordingly at different positions within the furnace body. Taking the furnace body of a fixed horizontal metallurgical furnace as an example, the materials commonly used for the furnace bottom include magnesia-chrome bricks, high alumina bricks, aluminum-chrome spinel, high alumina ramming materials, magnesia ramming materials, etc. Some also use high-strength anti-seepage ramming materials, whose composition belongs to the Al₂O₃-SiO₂ series, with an Al₂O₃ content of more than 75%. The specific gravity of liquid lead reaches 10.6g/cm³, and it has extremely strong permeability. Therefore, the refractory material at the bottom of the furnace must not only have the function of heat dissipation but also possess a high ability to prevent lead seepage.
At present, the widely used practice is to first lay high alumina bricks on the steel plate at the bottom of the furnace. High alumina bricks have a relatively high compressive strength (compressive strength at room temperature of 40 to 60MPa), and it is more reasonable to use them as a cushion layer at the bottom of the furnace. A layer of refractory material with lead penetration resistance should be set on the upper part of the furnace bottom cushion layer. Currently, magnesia ramming material or high-strength anti-seepage ramming material (high alumina) is used, and both can serve as a separator layer. The ratio of magnesia ramming material is: magnesia sand: magnesia powder = 7:3, mixed with brine. The particle size of magnesia sand is: 0.2-0.5mm70%, 1.5-3.0mm 30%. The composition of high-strength anti-seepage ramming material is made up of various sizes of aggregates and bone powder of high alumina. After high-temperature baking, the aggregates of various sizes expand and combine closely, achieving the ideal anti-seepage purpose of lead.
It must be noted that after the ramming of magnesia and magnesia-chromium ramming materials is completed, they need to be subjected to low-temperature baking. After baking out the free water, the expansion joints should be filled with fine magnesium powder to ensure the strength and density of the ramming layer. The thickness of the ramming material is recommended to be 150 to 300mm, which not only facilitates the completion of ramming in one go but also enables a relatively uniform baking process, forming an integral layer with better anti-seepage effect.
2. Working layer area at the bottom of the furnace
Magnesia-chrome bricks are widely used in the selection of refractory materials for the safety layer and working layer at the bottom of the furnace. Among them, the safety layer can use directly bonded magnesia-chrome bricks, while the working layer can use semi-rebonded magnesia-chrome bricks. With the fluctuation of the lead liquid level, the temperature at the bottom of the furnace fluctuates significantly. Therefore, semi-rebonded magnesia-chrome bricks with good thermal shock resistance should be selected. The safety layer and working layer at the bottom of the furnace also use high alumina bricks. Generally, this type of furnace has a bottom lead layer about 400mm high, so the furnace bottom will not be eroded by slag. High alumina bricks with an Al₂O₃ content of no less than 75% can be selected as the lining bricks for the safety layer and working layer at the bottom of the furnace.
Working area inside the furnace
The selection of refractory materials in the working areas of the furnace (furnace wall and furnace top) is carried out in two zones. One part is the refractory bricks for the molten pool area (especially the slag line area), and the other part is the refractory bricks for the weather zone.
1. Molten pool area inside the furnace
The refractory bricks in the molten pool area (especially the slag line area) will be eroded and washed by the slag. The composition of the lead smelting slag is rather complex, and high alumina refractory materials will participate in the slag-forming reaction. Therefore, it is not appropriate to use high alumina refractory bricks. Magnesium-chromium refractory bricks should be selected instead. At the same time, considering the slag erosion resistance and erosion resistance of refractory bricks, magnesia-chrome bricks that are rebonded by electric melting should be selected.
The bricks of this material have better resistance to slag erosion than semi-rebonded magnesia-chrome bricks. An increase in the content of Cr₂O₃ can enhance the slag erosion resistance of bricks. Therefore, magnesia-chromium refractory bricks with a higher Cr₂O₃ content should be selected as much as possible.
2. Meteorological area inside the furnace
Refractory bricks in meteorological areas are not eroded by slag but are only subject to the splashing erosion of a small amount of slag and the scouring of dusty flue gas. Therefore, magnesia-chromium refractory bricks with a lower Cr₂O₃ content can be selected. In the lead reduction furnace of a certain domestic factory, the magnesia-chrome bricks used in the initial production stage were directly bonded magnesia-chrome bricks with a relatively high Cr₂O₃ content. As a result, phenomena such as no metal or slag coating on the surface of the magnesia-chrome bricks in the meteorological area, bricks breaking into two sections, and loose structure occurred. According to the analysis results, it was determined that a large amount of Fe³+ and Fe²+ in the refractory bricks were reduced to elemental Fe. This leads to a loose brick structure.
Therefore, during the maintenance, fused re-bonded magnesia-chrome bricks with a lower Cr₂O₃ content (12%) were used instead. The main reason for this improvement is that the apparent porosity of the fused re-bonded magnesia-chrome bricks is low, and at the same time, the content of Fe³+ and Fe²+ in the refractory bricks is reduced, which makes them more adaptable to the strong reducing atmosphere in the meteorological area and extends their service life. After switching to this type of electrically fused re-bonded magnesia-chrome brick, the service life was greatly extended and good results were achieved.
1. Molten pool area inside the furnace
The refractory bricks in the molten pool area (especially the slag line area) will be eroded and washed by the slag. The composition of the lead smelting slag is rather complex, and high alumina refractory materials will participate in the slag-forming reaction. Therefore, it is not appropriate to use high alumina refractory bricks. Magnesium-chromium refractory bricks should be selected instead. At the same time, considering the slag erosion resistance and erosion resistance of refractory bricks, magnesia-chrome bricks that are rebonded by electric melting should be selected.
The bricks of this material have better resistance to slag erosion than semi-rebonded magnesia-chrome bricks. An increase in the content of Cr₂O₃ can enhance the slag erosion resistance of bricks. Therefore, magnesia-chromium refractory bricks with a higher Cr₂O₃ content should be selected as much as possible.
2. Meteorological area inside the furnace
Refractory bricks in meteorological areas are not eroded by slag but are only subject to the splashing erosion of a small amount of slag and the scouring of dusty flue gas. Therefore, magnesia-chromium refractory bricks with a lower Cr₂O₃ content can be selected. In the lead reduction furnace of a certain domestic factory, the magnesia-chrome bricks used in the initial production stage were directly bonded magnesia-chrome bricks with a relatively high Cr₂O₃ content. As a result, phenomena such as no metal or slag coating on the surface of the magnesia-chrome bricks in the meteorological area, bricks breaking into two sections, and loose structure occurred. According to the analysis results, it was determined that a large amount of Fe³+ and Fe²+ in the refractory bricks were reduced to elemental Fe. This leads to a loose brick structure.
Therefore, during the maintenance, fused re-bonded magnesia-chrome bricks with a lower Cr₂O₃ content (12%) were used instead. The main reason for this improvement is that the apparent porosity of the fused re-bonded magnesia-chrome bricks is low, and at the same time, the content of Fe³+ and Fe²+ in the refractory bricks is reduced, which makes them more adaptable to the strong reducing atmosphere in the meteorological area and extends their service life. After switching to this type of electrically fused re-bonded magnesia-chrome brick, the service life was greatly extended and good results were achieved.
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