Production Process Sharing of Flame Retardants: Antimony Trioxide Production Process

Production Process Sharing of Flame Retardants: Antimony Trioxide Production Process

Antimony metal is known as the "industrial monosodium glutamate" within the industry, widely used in industrial manufacturing and various additives. However, the extreme scarcity of antimony metal significantly impacts the production volume and cost for downstream additive manufacturers. In recent years, global antimony production has shown a declining trend, dropping from 167,000 tons in 2010 to 104,000 tons in 2024. This sustained decrease in production forces manufacturers of flame retardants to either purchase at higher prices or explore new avenues by developing alternative products.

Global antimony resources are primarily distributed in countries such as China, Russia, Bolivia, and Kyrgyzstan, with China holding 29.7% of the resources. Domestic antimony ore production in China is currently 60,000 tons, while foreign production is approximately 44,000 tons. Projected supplies for 2025-2027 are 60,700/61,400/62,300 tons domestically and 46,000/48,000/52,000 tons from foreign sources, indicating slow growth in supply.

The distribution structure of global antimony ore reserves in 2024 is shown in the chart below, where China has the largest reserves but still faces declining production issues. The primary strategies currently involve imports and the development of secondary recycling. As production decreases, secondary recycling technology is expected to gradually become the main reserve method for antimony metal.

For the flame retardant industry, antimony is difficult to replace, especially halogenated-brominated flame retardants, which are irreplaceable in plastics, rubber, textiles, chemical fibers, and other industries. The estimated consumption for 2025 is around 80,000 tons.

In the flame retardant industry, the antimony supply chain is distributed as shown in the figure below.

The trend chart of China's antimony ore production from 2011 to 2024 is shown below. As production gradually declines, many flame retardant R&D-oriented companies have begun production of substitutes and technological upgrades.

The preparation methods for antimony trioxide are mainly divided into dry methods and wet methods. Dry methods include the metallic antimony method and the stibnite method. Wet methods include the acid leaching method and the antimony salt decomposition method. Specific preparation details are as follows.

1. Metallic Antimony Method
Heat metallic antimony (containing sulfur) in a graphite furnace to 1200°C, introduce air at a rate of 0.3 m³/min for 5 minutes until the sulfur dioxide content in the exhaust gas is ≤5×10⁻⁶. Cool to 786°C, then blow air at a speed of 2 m³/min for 12 hours to obtain antimony trioxide with a yield of 92.1%.

2. Acid Leaching Method
Step 1: Add 1 kg of crude antimony ore (lead content 1.0%–2.0%) to 3 L of 1 mol/L hydrochloric acid for immersion. Then introduce chlorine gas (flow rate 300 L/h) into the solution, react at 70–90°C for 2–4 hours. After the reaction, filter and wash to obtain an antimony chloride mixture solution.
Step 2: Add 40 g of iron powder as a reducing agent to the antimony chloride mixture solution from Step 1, react at 70–90°C for 2–3 hours. After the reaction, filter and wash to obtain an antimony chloride solution.
Step 3: Slowly add the antimony chloride solution from Step 2 into a 4 mol/L sodium hydroxide solution under stirring until the precipitate in the solution no longer increases or begins to decrease, then stop adding. Adjust the solution pH to 8–9, continue stirring for 1–3 hours. After the reaction, filter and wash. Dry the filter residue, then calcine it at 600–800°C in an air atmosphere for 3–5 hours to produce antimony trioxide.
Step 4: Add the antimony trioxide from Step 3 into a smelting furnace, raise the temperature to 700–800°C until the solid completely melts. Then continuously introduce compressed air and a composite lead removal agent (added at 60 kg/m³ of antimony trioxide melt) into the molten liquid. Treat continuously for 60–90 minutes, remove the surface slag from the antimony liquid, then lower the furnace temperature to 400–550°C, discharge the waste liquid from the furnace to obtain antimony trioxide powder.
Step 5: Heat the antimony trioxide powder from Step 4 in a smelting furnace to 1600–1700°C, maintain for 1 hour for complete vaporization. The vaporized product enters a cooling and settling device while continuously introducing inert gas into the device for quenching, ultimately yielding high-purity antimony trioxide.

Conclusion
The scarcity of antimony and its "gentle slope" of supply have sounded an alarm for brominated flame retardant systems. On one side lies a still-growing rigid demand of 80,000 tons, on the other side, a mining sector facing both declining production and geopolitical risks, putting pressure on both price and delivery times. Accelerating the deployment of secondary recycling, developing low-antimony/antimony-free synergistic systems, and shifting from "relying on ore" to "relying on technology" are the true trump cards for the flame retardant industry to stabilize the supply chain and maintain cost lines in this era of "industrial monosodium glutamate" shortage.