Conventional Waelz furnaces, which have been widely used in the mining industry for nearly a century, are generally designed as a single rotary kiln. Although effective, these systems are associated with several limitations, including high coal consumption, limited process controllability, low operational flexibility, and relatively high operating costs. Through a complete redesign of the conventional process, Sormak Mines Company developed the Three-Stage Waelz Furnace, an innovative technology that has been granted national patents and represents one of the Company's major research and development achievements.

Three-Stage Waelz Technology

The process is divided into three independent units comprising a Dryer Kiln, Calcination Kiln, and Reduction Kiln. Each unit operates with independently controlled temperature, rotational speed, and residence time, allowing precise optimization of processing conditions for different ore types and feed characteristics.

This modular configuration enables the drying, calcination, and reduction stages to be performed separately under optimized conditions, resulting in significantly improved process performance compared with conventional single-stage Waelz furnaces.

Technological Innovations

One of the key innovations of this technology is the conversion of the thermal system from a coal-fired process to a natural gas-fired process, taking advantage of Iran's abundant natural gas resources. This modification not only reduces operating costs but also provides more accurate temperature control and improves overall process efficiency.

Another major innovation is the separation of the calcination stage into an independent kiln. Carbon dioxide released from carbonate minerals, sulfur-bearing compounds, halogens, and other volatile components are removed before the reduction stage. These gases are subsequently treated through cyclones, scrubbers, and gas-cleaning systems to ensure compliance with environmental regulations.

The redesigned furnace has also reduced coal consumption from approximately 45% in conventional Waelz furnaces to about 12%, resulting in substantial reductions in operating costs while significantly improving process efficiency.

Process Description

The primary feed materials for the Three-Stage Waelz Furnace at the Ahangaran Mining & Industrial Complex consist of low-grade lead-zinc ores from the Takieh Mine, together with other suitable mineral feedstocks.

Following crushing and sizing, the feed enters the Dryer Kiln, where moisture is removed. The material is then transferred to the Calcination Kiln, where carbonate minerals, sulfur compounds, and other volatile constituents are eliminated under controlled oxidizing conditions.

The calcined material subsequently enters the Reduction Kiln, where zinc is reduced and vaporized. The zinc vapor is then re-oxidized to produce zinc oxide powder, which is recovered as the primary product. Process gases pass through a settling chamber, cyclones, cooling ducts, scrubbers, and dust collection systems before being released to the atmosphere in accordance with environmental standards.

Key Advantages

The Three-Stage Waelz Furnace developed by Sormak offers several technical and operational advantages over conventional Waelz technology, including:

• Proprietary technology designed and developed by Sormak Mines Company
• Patented modified Three-Stage Waelz Furnace technology
• Reduction of coal consumption from approximately 45% to about 12%
• Independent control of temperature, rotational speed, and residence time in each process stage
• Metal recovery efficiencies of approximately 90–95%
• Efficient processing of low-grade and complex lead-zinc ores
• Reduced processing costs and lower energy consumption
• Improved environmental performance through advanced gas treatment and emission control systems
• Capability to utilize natural gas as the primary energy source
• Suitable for processing both primary mineral ores and secondary zinc-bearing materials