1.What are the characteristics and recycling methods of waste refractory materials?
Composition and Characteristics: Commonly used refractory bricks (such as high-alumina bricks and silica bricks) for annealing furnace linings, refractory castables, and refractory fiberboard. These materials are primarily composed of high-temperature resistant oxides such as Al₂O₃, SiO₂, and MgO. While inherently non-toxic, they may absorb small amounts of fuel residue or metal dust over time.
Recycling Methods:
Recycled Refractory Materials: After crushing, qualified particles are screened and mixed with new raw materials, re-pressed and sintered into low-grade refractory bricks (e.g., for use in furnace insulation rather than high-temperature working layers).
Building Materials: Used in the production of concrete aggregates, paving materials, and wall bricks, capitalizing on their high-temperature resistance and high strength.
Insulation Materials: Refractory fiber waste can be processed into lightweight insulation wool for low-temperature pipes or building insulation.
2.What are the characteristics and recycling methods of spent catalysts?
Composition and Characteristics: The catalysts used in the ammonia decomposition hydrogen production process are mostly nickel-based (Ni/Al₂O₃). After decomposition, the primary components are nickel (metal or oxide) and an alumina carrier, which may contain small amounts of carbon deposits or sulfur impurities.
Recycling Methods:
Metal Recovery: Nickel is extracted through acid dissolution, electrolysis, or pyrometallurgy. High-purity nickel can be used to regenerate nickel alloys or catalyst feedstock.
Carrier Recycling: After washing and calcining to remove impurities, the alumina carrier can be used as an adsorbent or low-activity catalyst support.
3.What is the composition of slag after fuel combustion and how is it recycled?
Composition and Characteristics: If clean fuels such as natural gas and low-sulfur coal gas are used, the amount of slag after combustion is minimal, consisting primarily of small amounts of unburned carbon particles or metal oxides (from steel strip abrasion).
Recycling Methods:
If the carbon content is high, it can be used as a fuel additive (e.g., mixed with pulverized coal);
If the metal oxides are enriched, it can be used as an auxiliary raw material for smelting (e.g., iron-containing slag is used in blast furnace ironmaking).
4.What are the wastes that are restricted for recycling or require special disposal?
Asbestos-Containing Refractory Waste
Hazards: Some older annealing furnaces use refractory products containing asbestos. Asbestos fibers are highly carcinogenic and can cause lung disease if inhaled.
Disposal Requirements: Recycling is strictly prohibited. Recyclable waste must be managed as hazardous waste and must be sealed, collected, incinerated, or safely landfilled by specialized agencies.
Waste Contaminated with Heavy Metals or Toxic Substances
Scenario: If the annealing furnace uses high-sulfur fuels such as heavy oil, the slag after combustion may contain heavy metals such as vanadium and nickel; or refractory materials may have absorbed pickling waste liquids remaining on the surface of the steel strip.
Disposal Requirements: Slag with excessive heavy metal content must be treated as hazardous waste and sent to a regulated hazardous waste disposal center for solidification/stabilization before landfill.
Refractory materials containing chlorine or fluorine are prohibited from use in construction materials or recycling due to the potential for toxic gases. They must be decontaminated at high temperatures before landfill. Waste Adsorbent
Ingredients and Characteristics: Activated carbon, molecular sieves, etc. used to purify protective gases. If they adsorb toxic substances such as VOCs and H₂S, they may become hazardous waste.
Disposal Requirements: If the adsorbed organic matter can be thermally decomposed, it can be incinerated in a rotary kiln.
If it contains non-degradable toxic substances, it must be landfilled as hazardous waste and cannot be directly recycled.
5.What are the key prerequisites for recycling?
Separate collection: During the production process, waste must be strictly separated by composition and contamination level to avoid mixing clean and hazardous waste, which reduces recycling value.
Environmental testing: Before recycling, waste must be tested for heavy metals and toxic organic matter to ensure it meets recycling standards.
Technical and economic feasibility: Low-value waste may be more suitable for harmless disposal rather than recycling if transportation and treatment costs are prohibitive.