Complete Analysis of Aluminum Dross Processing with Broyeur à cylindres vertical: Process Scheme, Equipment Selection, and Resource Utilization Value

Aluminum dross, especially secondary aluminum dross which is listed as hazardous waste, has long been regarded as a burden for the electrolytic aluminum and foundry industries. However, with advances in resource recycling technology and increasingly stringent environmental policies, this black‑gray powder is now being given a new lease of life. Vertical roller mill (VRM) processing technology, with its unique advantages of high efficiency, energy saving, and environmental protection, is becoming an ideal path for aluminum dross resource utilization. This article provides a comprehensive analysis of the process scheme, equipment selection, and resource utilization value of aluminum dross processing with VRM.

1. Why Is VRM Processing Needed for Aluminum Dross?

1.1 Composition of Aluminum Dross and Processing Challenges

Aluminum dross has a highly complex composition, typically containing 10%–30% metallic aluminum, 20%–40% alumina (Al₂O₃), as well as fluorides, nitrides (AlN), salts, and various other substances. China generates millions of tonnes of aluminum dross annually. Direct landfilling not only pollutes the environment but also represents a tremendous waste of resources.

The main challenges in aluminum dross treatment are threefold:

• Complex composition: It contains metallic aluminum, alumina, aluminum nitride, fluorides, and many other components. A single traditional process can hardly achieve comprehensive resource recovery.
• Hazardous waste classification: Secondary aluminum dross is listed in the national hazardous waste catalogue, requiring treatment processes that meet strict environmental standards.
• High reactivity requirements: Many high‑value utilization routes (such as refractories, ceramics, and cement raw materials) have strict requirements for raw material fineness, for example less than 5% residue on an 80‑μm sieve.

1.2 Unique Advantages of VRM Processing

After calcination and other harmless treatments, the main components of aluminum dross are alumina (Al₂O₃), silica (SiO₂), etc., which are relatively hard. The core functions of the VRM are:

• Grinding and modification: Through compression and grinding, the dross is turned into fine powder, greatly increasing its specific surface area and improving its chemical reactivity.
• Precise fineness control: The built‑in classifier in the VRM enables accurate particle size control, ensuring product consistency.
• Value addition: Powdered products have higher market value and a broader range of applications than raw dross.

2. Core Process Flow of Aluminum Dross Processing with VRM

The VRM system integrates “crushing – grinding – classification – calcination” in one flow, efficiently releasing valuable elements from aluminum dross. The entire process comprises four core stages:

Stage 1: Pretreatment and Crushing

Aluminum dross is first coarsely crushed by a concasseur à mâchoires to remove large impurities, and its moisture is adjusted before it is fed into the VRM system. The key at this stage is to ensure a uniform feed particle size to avoid equipment blockages and improve overall operational stability.

Stage 2: VRM Grinding and Preliminary Classification

This is the core of the whole process. After entering the VRM, the aluminum dross is driven by the high‑speed rotating grinding table and distributed uniformly over the grinding zone by centrifugal force. Under hydraulic system pressure, the grinding rollers apply compression and shear forces to the material, achieving efficient size reduction. Under hydraulic pressure, the combination of an arched grinding table and tapered rollers can grind aluminum dross down to 45–100 μm ultrafine powder.

During grinding, hot air is introduced simultaneously to dry the material, effectively preventing it from sticking to the mill. At the same time, the built‑in dynamic classifier separates fine and coarse particles in real time – coarse particles fall back for regrinding, while fine powder is carried out by the air stream, producing high‑fineness, high‑reactivity aluminum dross powder. Studies show that after mechanical grinding to 45 μm, aluminum dross can react rapidly with water at room temperature to release hydrogen, indicating significantly enhanced reactivity.

Stage 3: High‑Temperature Calcination and Resource Conversion

The ground aluminum dross powder is fed into a four rotatif for thermal treatment. At 1100–1300°C, the dross undergoes three simultaneous transformations:

• Metallic aluminum is oxidized to high‑purity alumina
• Aluminum nitride (AlN) is converted to alumina with nitrogen release
• Fluorides react with added calcium‑based fluorine‑fixing agents to form stable calcium fluoride, achieving simultaneous harmless treatment and resource recovery

Temperature gradient control is critical – the kiln head is maintained at 1250°C to promote calcium aluminate synthesis, while the kiln tail employs 850°C rapid cooling to effectively inhibit re‑formation of harmful substances such as dioxins.

Stage 4: Environmental Treatment and Product Finalization

Calcination exhaust gases are treated by multiple environmental protection facilities:

• SNCR denitrification system: NOx conversion efficiency exceeds 75%
• Bag filter: Collection efficiency up to 99.9%, with outlet particulate concentration stabilized at below 8 mg/Nm³, far stricter than the national standard limit of 20 mg/Nm³
• Alkali spray scrubber: Neutralizes acidic gases such as HF and HCl

The recovered products, including alumina and calcium aluminate, can be used as steelmaking deoxidizers, ceramic raw materials, or flame‑retardant materials, with significantly increased added value.

3. Key Points for VRM Equipment Selection

Processing aluminum dross places special demands on VRM equipment. The following factors should be emphasized during selection:

3.1 Precise Control of Grinding Fineness

Different downstream applications have different fineness requirements for aluminum dross powder:

• Matériaux réfractaires: Typically 80–200 mesh
• Adjuvants pour béton: Recommended 200–325 mesh
• High‑value applications: Need ultrafine powder of 45–100 μm

LM‑series VRMs can achieve flexible fineness control by adjusting the classifier speed. Equipment such as the LUM ultrafine vertical mill focuses on ultrafine grinding in the range of 400–3250 mesh, with adjustable and controllable fineness.

3.2 Drying Capacity

Aluminum dross often contains some moisture, so the VRM system must have concurrent drying capability. The LM broyeur à cylindres vertical integrates drying, grinding, classification, and conveying in one unit, making it particularly suitable for processing aluminum dross with higher moisture content. Its unique principe du broyage en lit interparticulaire ensures uniform grinding and avoids over‑grinding.

3.3 Automation Control

The VRM system uses a PLC system to adjust grinding roller pressure and air temperature, ensuring precise control of grinding fineness and drying efficiency. Aluminum recovery rates can reach over 85%, and the comprehensive utilization rate of spent pot lining and aluminum electrolyte exceeds 90%.

4. Environmental and Economic Benefit Analysis

4.1 Environmental Value

VRM‑based aluminum dross processing creates a closed‑loop cycle of “resources – products – recycled resources”. The entire line operates under fully enclosed negative pressure and is equipped with a three‑stage environmental protection system:

4.2 Economic Benefits

The economic value of VRM‑processed aluminum dross is considerable:

• Economies of scale: One enterprise using the VRM process achieved RMB 200 million in revenue by treating 50,000 tonnes of aluminum dross annually, with a return on investment as high as 50%.
• Improved aluminum recovery: Metallic aluminum recovery can be increased to over 92%.
• Downstream value: Aluminum‑dross‑based calcium aluminate shows 40% higher desulfurization efficiency than traditional bauxite. One steel mill trial reduced aluminium consumption per tonne of steel by 1.2 kg.
• Building material applications: Adding 15% treated aluminum dross to cement increased 3‑day compressive strength by 12% and reduced chloride diffusion coefficient by 50%.

5. Application Prospects and Development Trends

With increasingly strict national control over hazardous wastes such as aluminum dross, and the deepening of the “ double carbone ” strategy, the market for aluminum dross resource utilization is experiencing explosive growth. VRM processing technology, with its integrated advantages of combining crushing, drying, and classification, has become a preferred solution for green aluminum dross treatment.

In the future, aluminum dross processing with VRM will develop in the following directions:

• Broyage ultrafin: Product fineness will continue to break through to finer levels to meet high‑end application needs.
• Production à grande échelle: Single‑line capacity will keep increasing to accommodate centralized disposal needs of large aluminium smelters.
• Intelligentization: Deep integration of DCS distributed control and AI optimisation algorithms.
• Full resource recovery: Shifting from single‑product to multi‑product co‑production.

Aluminum dross processing with a broyeur à cylindres vertical is a comprehensive technical solution that integrates environmental treatment, resource recovery, and high‑value utilization. Through the integrated flow of “crushing – grinding – classification – calcination”, the VRM system not only achieves harmless disposal of aluminum dross but also converts hazardous waste into high‑added‑value products with significant economic benefits. Whether for new aluminum dross treatment projects or upgrading existing processes, VRM processing technology deserves serious attention and priority consideration.