The refining of antimony involves several stages to extract the metal from its ores and purify it for industrial use. Antimony is primarily obtained from stibnite ore (Sb₂S₃), though it can also be recovered as a byproduct of lead, copper, and silver smelting. The refining process typically includes ore preparation, reduction, and purification to achieve high-purity antimony.
Ore Preparation
The first step involves crushing and grinding the stibnite ore to liberate the antimony sulfide from gangue materials. The ore is then concentrated using froth flotation or gravity separation methods to increase the antimony content. This concentrate is further processed to remove impurities such as arsenic, iron, and sulfur before reduction.
Reduction Process
The concentrated antimony sulfide is reduced to metallic antimony through pyrometallurgical methods. One common approach is direct reduction in a reverberatory furnace, where the concentrate is heated with a reducing agent like coke or charcoal. The sulfur reacts with oxygen to form sulfur dioxide gas, leaving behind crude antimony. Alternatively, the sulfide can be roasted to form antimony oxide (Sb₂O₃), which is then reduced with carbon at high temperatures.
Purification
Crude antimony contains residual impurities that must be removed to meet industrial standards. Liquation is often employed, where the crude metal is heated slightly above its melting point (630°C) to separate higher-melting-point impurities. Electrolytic refining can also be used for higher purity, dissolving the crude antimony in an electrolyte solution and depositing pure metal on cathodes.
Final Processing
The refined antimony may be cast into ingots or further processed into alloys or compounds for specific applications. Antimony trioxide, a common derivative, is produced by oxidizing refined antimony and is widely used as a flame retardant.
Throughout the process, environmental controls are critical to manage emissions of sulfur dioxide and other pollutants. Modern refineries often incorporate gas scrubbing systems and waste treatment facilities to minimize environmental impact while ensuring efficient recovery of antimony.