Differences And Advantages of Zinc Oxide Produced by Different Processes

Zinc oxide (ZnO) is a versatile inorganic material widely used in rubber, ceramics, cosmetics, electronics, coatings, and pharmaceuticals. Its performance varies significantly with production routes. The three mainstream industrial processes—direct process (American process), indirect process (French process), and wet chemical process—differ sharply in raw materials, purity, particle size, activity, cost, and application scenarios. This article compares their characteristics and respective advantages to support material selection.

Direct Process (American Process)

The direct process uses zinc ores, zinc calcine, or zinc-containing waste as raw materials. These are mixed with coal or coke and heated to 1000–1300°C in a reduction furnace. Zinc oxide in the feed is reduced to zinc vapor, which is then oxidized by air and collected after cooling.

Key Characteristics

· Purity: 90%–95%, with relatively high impurities (Pb, Cd, Fe, S).

· Particle size: Coarse (0.5–10 μm), low specific surface area.

· Production efficiency: Simple flow, high output, low investment.

Core Advantages

The greatest strength of the direct process is low cost and wide raw material availability. It eliminates zinc refining and enables large-scale production from low-grade zinc resources, making it ideal for bulk industrial applications with low purity requirements.

Typical Applications

General rubber products, ceramics, low-grade coatings, glass, and non-premium animal feed.

Indirect Process (French Process)

The indirect process starts with high-purity zinc ingots (≥99.99%). Zinc is melted at 600–700°C, vaporized at 1250–1300°C, oxidized into fine ZnO particles, and collected by cooling and bag filtration.

Key Characteristics

· Purity: 99.5%–99.9%, extremely low heavy metals, high whiteness.

· Particle size: Fine and uniform (0.1–0.5 μm), good dispersibility.

· Crystal structure: Complete crystallinity, stable electrical properties.

Core Advantages

This process delivers high purity, consistent quality, controllable particle size, and broad compatibility. It balances performance and cost, serving as the most widely adopted route for mid-to-high-end zinc oxide.

Typical Applications

High-performance tires, pharmaceuticals, cosmetics, electronic ceramics, varistors, coatings, and zinc-based lubricants.

Wet Chemical Process (Wet Process / Precipitation Method)

The wet chemical process uses zinc salts (zinc sulfate, zinc chloride) as precursors. After dissolution and purification, a precipitant (soda ash, ammonia) is added to form basic zinc carbonate precipitate. The precipitate is washed, filtered, dried, and calcined at 500–800°C to obtain zinc oxide.

Key Characteristics

· Purity: Up to 99.7%–99.99%, deep impurity removal.

· Particle size: Ultrafine to nanoscale (1–100 nm), ultrahigh specific surface area (30–100 m²/g).

· Activity: High surface reactivity, excellent dispersibility.

Core Advantages

The wet process enables precise control of particle size and morphology, ultrahigh purity, and high chemical activity. It can produce functional nano-zinc oxide for high-value sectors.

Limitations

Longer process flow, higher production cost, and wastewater treatment requirements.

Typical Applications

Nano zinc oxide for sunscreens, antibacterial materials, photocatalysts, sensors, conductive coatings, high-grade rubber, electronic pastes, catalysts, and lithium battery materials.

Conclusion

Selection of zinc oxide production process should be based on application requirements:

· Choose the direct process for large-volume, cost-sensitive, low-purity demand.

· Choose the indirect process for high purity, stability, and general high-end applications (the industrial mainstream).

· Choose the wet chemical process for ultrafine/nano-scale, high-activity, and functional high-value products.

Reasonable matching between process characteristics and application scenarios maximizes performance, cost efficiency, and product competitiveness.