Due to the wide variety of refractory materials and the diverse raw materials used in their production, spent refractories come in many different types. When determining how to process spent refractories, different treatment methods should be considered based on factors such as the degree of erosion, the location of use, and the type of refractory material. Currently, domestic steel mills often store and dispose of spent refractories in a single, consolidated pile. This results in the mixing of different types and grades of refractories, making sorting and selection difficult and hindering the recycling of these materials. The treatment of spent refractories should be considered from the following perspectives.
1. Steel mills should sort and stack used refractory materials according to their application locations and types to facilitate sorting and prevent contamination or the introduction of harmful substances.
2. For sorted used refractory materials, separate processing should be conducted based on their degree of sintering and erosion. First, manual sorting should be performed to remove iron, steel, slag, and other contaminants from the surface of the refractory materials.
3. Different methods should be employed to process used refractory materials based on their specific erosion conditions and bond strength.
4. For functional components such as slide plates, those discarded due to minor damage may have the eroded sections removed and undergo composite processing to produce new products for reuse.
The following describes the different areas affected by erosion:
- Severely Eroded Working Layers and Transition Layers:
The working layers and transition layers are processed according to the procedure illustrated in the diagram below. The resulting recycled material is then utilized as a slag-forming agent or for lower-grade applications.
- Non-Working Surfaces (Original Brick Layers):
Different processing techniques are employed depending on the degree of sintering exhibited by the non-working surfaces.
The following section describes the specific approaches for magnesia-carbon bricks and refractory castables, respectively:
① Magnesia-Carbon Bricks: These materials primarily rely on the curing of resin to form a carbon network structure, which imparts strength to the finished product. However, the non-working surfaces of used magnesia-carbon bricks typically do not develop a ceramic bond; consequently, the bonding strength between the material particles remains relatively weak.
② Refractory Castables: Used castables first undergo coarse crushing. The crushed granular material is then immersed in an aqueous solution containing additives to reduce the bonding strength between the particles. Following this soaking process, the material undergoes fine crushing, iron removal, screening, flotation purification, and homogenization to produce qualified recycled material suitable for the manufacture of new refractory products.
③ Non-Working Layers with Established Ceramic Bonding: In cases where a ceramic bond has formed within the non-working layer—resulting in high bonding strength between the material particles—simple crushing alone is insufficient. Such treatment results in recycled material with a high content of “pseudo-particles” (agglomerates), low bulk density, and high internal porosity, thereby hindering its effective utilization. Consequently, the recycling of such refractory materials typically involves extending the duration of the fine-crushing process; through repeated grinding, the content of pseudo-particles is significantly reduced. This specific processing technique, however, generates a substantial quantity of fine powder, which tends to exhibit a relatively high impurity content.
In summary, to enhance the recycling rate of used refractory materials, researchers in the field should focus their efforts on developing advanced regeneration processing techniques and specialized production equipment tailored for these processes. By applying distinct processing methods to the non-working layers of various types of used refractory materials, it is possible to produce high-grade recycled raw materials for the refractory industry.
Methods and Technologies for the Recycling of Spent Refractory Materials
1. Optimal Utilization of Raw Materials
Processed particles from spent refractory materials should be prioritized for the remanufacture of primary refractory products, while fine powders should be considered for other applications, such as metallurgical additives or downgraded use.
Example: Spent magnesia-carbon bricks → Processing → Particles → Remanufactured magnesia-carbon bricks
or → Fine powder → Converter repair material
2. Regenerating the Original Product
e.g., Regenerating magnesium-aluminum bricks from used magnesium-aluminum bricks; regenerating magnesium-chromium bricks from used magnesium-chromium bricks.
3. Regenerating Other Products
e.g., Regenerating used slide plates for use as main channel material; regenerating used magnesium-chromium bricks for use as flow sand.
4. Downgraded Use
e.g., Regenerating used magnesium-aluminum castables from ladle working linings into permanent ladle lining castables; regenerating used main channel materials into iron channel materials.
5. False Particle Elimination Technology
① Using specialized processing equipment, e.g., custom crushing equipment for used magnesium-carbon bricks, to eliminate over 95% of false particles.
② Employing specialized processes, e.g., water immersion + mixing + temperature control.
6. Separation and Purification Technologies
Use air classification to separate fine powders, such as collecting graphite from used magnesium-carbon bricks via air classification. Employ mineral processing techniques to purify used refractory materials.
7. Regeneration Process Technologies
Based on the characteristics of the raw materials derived from used refractories, adopt corresponding processes to produce regenerated products. For example, adjustments must be made to particle size distribution, mixing time, binder type, binder dosage, and molding pressure.
Considerations for the Reuse of Spent Refractory Materials
1. Sources of spent refractory materials
It is essential to clearly identify the type of high-temperature vessel, the specific component, the material type, the chemical composition, and the phase composition of the spent refractory materials.
2. Homogenization of Material Composition
Since there are many grades of refractory products, the raw materials used also vary in grade. This results in certain deviations in the chemical composition of recycled materials prepared from the same spent refractory materials. Therefore, the recycled materials should undergo homogenization to minimize the impact of varying chemical compositions on the performance of the recycled products.
3. Removal of False Granules
False granules have high density and large porosity, and the material’s cohesion is looser compared to new material. When used to produce recycled products, they severely impair product performance. Production processes must be strictly controlled to reduce the content of false granules.
4. Selection of Binders During Recycled Material Production
Since the surface properties of recycled materials change, appropriate binders and their dosage must be selected based on the specific characteristics of the recycled material when remanufacturing recycled bricks.
5. Safe Reuse
Used refractory materials containing harmful substances must be rendered harmless before reuse. For example, used magnesia-chromite bricks containing Cr⁶⁺ can only be reused after converting Cr⁶⁺ to Cr³⁺.
6. The treatment of used refractory materials that have formed a ceramic bond is relatively difficult and requires special processing techniques.
7. Some steel mills store used refractory materials in mixed grades; due to their complex composition, these materials can only be downgraded for use.
8. The composition, mineral phases, and structure of used refractory materials inevitably undergo changes, which significantly affect the quality of recycled refractories. This must be given full consideration, and appropriate measures must be taken to ensure the quality stability of recycled products.
9. The cost of processing used refractory materials must be considered, and the methods and processes adopted must have practical application value.
10. The impact of recycled refractories on molten steel quality must be considered, and control over harmful components must be strengthened.
