Extraction of Zinc

Method of Extraction of Zinc from Its Ore, Zinc Blende

Concentration:

The zinc blende ore is concentrated using the froth floatation process, in which the ore is mixed with water and pine oil and some sodium ethyl xanthate in a tank. Air blows on this mixture. This results in particles “wetted by oil” (Sharma) rising to the surface in the form of froth, which can be skimmed off and collected. The impurities, on the other hand, are “wetted by water” (Sharma) and thus sink to the base of the tank. 

Roasting:

The concentrated zinc blende ore is roasted in the presence of air so that zinc sulphide will be converted to zinc oxide.

2 ZnS + 3 O₂ →2 ZnO + 2 SO₂

Reduction:

Mix the roasted ore with half its mass of powdered coal or coke (carbon) and placed “into a fireclay retort furnace” (Sharma).

ZnO + C →Zn + CO₂

At such a high temperature, zinc is gaseous. Thus, gaseous Zn could mix with the CO₂, so that when they are removed reoxidation of zinc could occur, giving us ZnO again.

To make the reoxidation minimal, smelters heat the ZnO with excess carbon so that the CO₂ formed is converted to CO.

CO₂ + C →2CO

As a result, the reduction of zinc oxide can be illustrated as follows:

ZnO + C →Zn + CO

Purification:

Using electrolysis, the zinc metal compound is broken apart to obtain pure zinc metal.

Effects of Extraction of Zinc from Its Ore, Zinc Blende

During the extraction process of Zinc form its ore, Carbon Monoxide and Sulphur dioxide is released into the atmosphere. This could lead to pollution of water sources or formation of acid rain.

Carbon monoxide is an industrial gas and may be collected from the extraction process to be used in other industrial processes, such as the purification of Nickel through the Mond Process.

Sulphur Dioxide similarly has several uses outside its toxicity. It may also be used as a reducing agent, or as a means of forming sulfite salts.

Instead of being released as waste gases, both products can be collected and reused for other industrial purposes. 

Reference:

Images:

“Froth floatation process” http://www.goiit.com/templates/default/images/chapters/gen_princp/fig.4.gif

Sharma, Neeraj, Prof. "Extraction of Zinc." Industrial Aspects of Inorganic Chemistry. 2007.

http://www.newton.dep.anl.gov/askasci/chem03/chem03435.htm

http://chem-guide.blogspot.sg/2010/04/occurrence-and-extraction-of-zinc-from.html

Short note on contributions:

Method of Extraction – Radhika

Effects of Extraction – Wei Liang

Solution to Problems –Elizabeth