Environment Impact of Extraction of Zinc from Sphalerite

Environment Impact

The  extraction of zinc from sphalerite will produce large amount of sulfur dioxide as well as cadmium vapour.

Sulfur dioxide is poisonous.  Residues from the process such as smelter slag also contain a significant amount of heavy metals, which is damaging to the environment. This affects the atmosphere greatly.

Furthermore, the soils contaminated with excess zinc due to the extraction process will also interfere will the soil’s ability to be able to absorb essential nutrients such as manganese and iron. In order words it will affect the plant ecosystem whereby the plants are not able to grow well and greatly influence the whole food web.

Sources: (Both this post on environment impact and the Process of Extraction of Zinc-Last Post)

http://en.wikipedia.org/wiki/Zinc
http://www.eoearth.org/article/Flue_gas_desulfurization

Extraction of zinc from zinc blende

Question: Extraction of zinc from zinc blende – “even number” groups

• Explain how the metal is extracted from its ore and how the extraction method has an impact on the environment.

1)What is Zinc Blende/Sphalerite/Black-Jack

Sphalerite

It is a mineral that is a chief ore of zinc. It has a chemical formula of (Zn,Fe)S. It consists mainly of Zinc Sulfide in crystalline form but always almost contain variable amounts of Iron. The Iron content affects it's coulou and it is usually found in association with galena, pyrite, and other sulfides with calcite, dolomite and fluorite.

Zinc Blende has a crystal structure. In the structure, zinc and sulfur atoms are tetrahedrally coordinated. It's structure is closely related to diamond.

2)How zinc is extracted from zinc blende

Firstly, after the grinding of the ore,

zinc sulfide undergoes froth floatation, a process to separate materials based on whether it is hydrolilic or hydrophobic, to obtain an ore concentration. Note that at this point of time, only 50% of the ore concentration is zinc.

Next,
Roasting of the ore concentration will then convert the zinc sulfide into zinc oxide and sulfur dioxide. Based on the equation below:

2 ZnS + 3 O₂ → 2 ZnO + 2 SO₂

The sulphur dioxide is needed for the leaching process later on.

After this process, prometallurgy is by reducing the zinc oxide with carbon or carbon monoxide at a high temperature of 950 degrees Celcius.

From this reducing process, zinc vapour is distilled.

The equations for the reaction are as follows:

2 ZnO + C → 2 Zn + CO₂

ZnO + CO → Zn + CO₂                      

OR

After the  roasting of the ore, an electrowinning process will leach off zinc from its ore

ZnO + H₂SO₄ → ZnSO₄ + H₂O

And thereafter, electrolysis is used to produce zinc metal via this equation:

2 ZnSO₄ + 2 H₂O → 2 Zn + 2 H₂SO₄ + O₂

Note that the sulfuric acid is then recycled to be used in the leaching stage.

en.wikipedia.org/wiki/Sphalerite

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