Zinc mining and beneficiation refining process

Zinc Mining

The most common ore used to extract zinc is sphalerite, also known as zinc sulfide (ZnS). Historically, extracting zinc has been more difficult than extracting other metals because zinc is a gas at temperatures where metals such as iron typically begin to melt. Because of its very low boiling point, zinc escapes with the exhaust gas at these temperatures. The zinc content in sphalerite is not high, so it needs to be concentrated. The best concentration method for zinc ore is froth flotation.

Ore concentration: froth flotation process

The froth flotation process is mainly used to remove gangue from sulfide ores. The ore is ground into powder and formed into a suspension in water. The main components of foam flotation are collectors and foam stabilizers. Collecting agents (pine oil, fatty acids, etc.) can increase the wettability of the metal part of the ore and cause it to form foam, while foam stabilizers (cresol, aniline, etc.) can maintain the foam. Oil wets metal and water wets gangue. The paddles and air constantly stir the suspension to create foam. The metal foam is skimmed off the top and dried to recover the metal.

Concentrate metal

The next step in zinc extraction is roasting. The concentrate is ground into small pieces and suspended in an upward air current. Through this process, sulfur content can be significantly reduced. This also converts sphalerite into the more reactive zinc oxide.

The zinc oxide is then mixed with coke, ground into fine pieces, and heated to 1673 K in a refractory clay vessel, a process also known as the Belgian method. Here, zinc oxide is reduced to metallic zinc. The carbon in the coke acts as a reducing agent in this reaction.

Since the boiling point of zinc is well below 1180 K, the zinc formed immediately evaporates and distills, leaving behind non-volatile impurities such as cadmium, lead and iron. This gas containing zinc vapor is collected and cooled to obtain solid zinc. This crude metal is called argentite. It can be further purified by fractional distillation.

Alloys of zinc with many other metals: Nickel silver, bronze, brass and soft electrical solders all contain zinc. Mass-produced zinc is used to galvanize iron to prevent corrosion.