Borax is chemically known as sodium tetraborate and is a compound naturally occurring in evaporate deposits. Smelting is the process of applying heat to ore to extract a metal, such as iron or gold, in a molten state for purification. Borax is consistently used in the high-temperature world of metal extraction and refinement. Its distinct chemical and physical properties make it important for improving the efficiency and quality of the final metal product. The addition of this compound is fundamental to separating the valuable metal from the unwanted materials in the ore or scrap.
Borax as a Fluxing Agent
The primary function of borax in smelting is to act as a flux, a material added to a molten substance to remove impurities. Ores and scrap metal contain non-metallic impurities, such as silica and metal oxides, which hinder the melting process. These contaminants increase the overall melting temperature of the mixture and decrease the fluidity of the molten metal. Borax accomplishes this by reacting with the impurities at high temperatures, forming a glassy waste product, and reducing the overall melting point of the smelting mixture.
How Borax Facilitates Impurity Removal
Borax’s effectiveness stems from its ability to chemically dissolve metal oxides and silica, which are the most common impurities in metal ores. When heated, borax melts into a highly fluid liquid that acts as a solvent for these contaminants. The borax chemically binds to the oxides and silica, creating a less dense, molten material known as slag. This newly formed slag is immiscible with the denser molten metal and naturally floats to the surface, allowing the impurities to be easily skimmed or poured off the top of the molten metal. Borax also provides a protective molten layer over the surface of the pure metal, which prevents further oxidation from the surrounding furnace atmosphere, protecting the metal’s integrity.
Practical Use and Safety Considerations
Borax is widely employed in the metallurgy of non-ferrous and precious metals, including gold, silver, copper, and brass. In small-scale operations, such as gold recovery by artisanal miners or in jewelry making, borax is mixed with the crushed ore or concentrate before heating in a crucible. For gold recovery, the borax method is recognized as a safer alternative to using toxic chemicals like mercury. The amount of borax used is adjusted based on the type of metal and the quantity of impurities present. When using borax in any high-temperature process, safety measures are important for personal protection. While borax is relatively non-toxic, smelting produces intense heat and potential fumes. Proper ventilation is necessary to safely disperse metal fumes or dust particles generated during the heating process. Handling of the molten metal and the hot slag requires insulated gloves, face shields, and other appropriate protective gear to prevent severe burns.