Zinc Production by Hydrometallurgical Process and Smelting Operation

Zinc Production by Hydrometallurgical Process: An Overview

Zinc is an essential metal in modern society, used in various applications such as galvanizing, alloys, and chemicals. The hydrometallurgical process is a widely used method for zinc production, offering several advantages over traditional pyrometallurgical methods. In this article, we'll delve into the chemical process and metallurgical technology involved in zinc production by hydrometallurgical process.

Zinc Minerals:

Sphalerite, marmalite and to a lesser extent calamine are the only commercially significant minerals. These ores contain about 12% Zinc.

Minerals ores chemical formula

1. Zinc blend (or) Sphelerite ZnS

2. Marmalite (ZnFe)S

3. Calamine (or) Smithesonite ZnCO3

4. Heminorphite 4ZnO.ZnSiO2.3H2O

5. Hydrozincite 4ZnO.2CO2.3H2O

6. Willemite 2ZnO.SiO2

Zinc is extracted pyrometallurgically as well as hydrometallurgically. Various pyrometallurgical techniques for the extraction of Zinc are

1. Distillation in horizontal retorts

2. Distillation in vertical retorts

3. Distillation in the electric furnace.

4. Zinc distillation in Blast Furnace (Imperial Smelting)

Introduction to Hydrometallurgy

Hydrometallurgy is a branch of extractive metallurgy that involves the use of aqueous solutions to extract and purify metals. The process typically involves leaching, purification, and precipitation stages. In the case of zinc production, the hydrometallurgical process offers a more efficient and environmentally friendly alternative to traditional smelting and refining methods.

The blast furnace and hydrometallurgy processes are widely in practice. Out of these two, hydrometallurgy processes have some benefits

• Hydrometallurgical methods are ideally suited for lean and complex ores
• Its operations ensure greater control than other conventional methods over energy step in the processing of ores, resulting in the recovery of valuable by-products.
• Besides meeting the mounting demands for both the quantity and quality of metals, hydro-metallurgy can produce metals in a variety of physical forms such as powders, nodules and coherent surface deposits.
• Leaching operations are generally carried out at room temperature or at slightly elevated temperatures.
• The water liquor from the final recovery step can be recycled to the initial leaching operation.

The hydrometallurgical route of Roaster-Leach Electro winning process is adopted for the extraction of electrolytic grade Zinc.

The Hydrometallurgical Process for Zinc Production

The hydrometallurgical process for zinc production involves the following stages:

1. Leaching: The zinc ore is leached with a sulfuric acid solution to extract the zinc. The resulting solution contains zinc sulfate and other impurities.
2. Purification: The zinc sulfate solution is then purified through a series of steps, including precipitation, filtration, and solvent extraction. This stage removes impurities such as iron, copper, and cadmium.
3. Electrowinning: The purified zinc sulfate solution is then subjected to electrowinning, where zinc is deposited at the cathode (negative electrode).
4. Melting and Casting: The deposited zinc is then melted and cast into ingots or other shapes.

The overall reaction :

2ZnSO4 + 2H2O à 2Zn + 2H2SO4 + O2

The hydrometallurgical process for zinc production involves several key chemical reactions:

Major steps in Hydro-metallurgical extraction:

     1. Roasting:

                   ZnS + O₂ à ZnO + SO₂

                   ZnO + Fe₂O₃ à ZnO.Fe₂O₃ + SO₂

      2. Leaching:

                    ZnO + H₂SO4 à ZnSO₄ + H₂O

      3. Electro Winding:

                    ZnSO₄ + H₂O à Zn + H₂SO₄  

      4 .Zinc Oxide Process:

                    ZnO.Fe₂O₃ à ZnO + Fe₃O₄     

Metallurgical Technology

The hydrometallurgical process for zinc production employs various metallurgical technologies, including:

• Leaching reactors: Designed to optimize the leaching process and minimize energy consumption.
• Solvent extraction: Used to separate zinc from other metals and impurities.
• Electrowinning cells: Designed to maximize zinc deposition and minimize energy consumption.

The hydrometallurgical process for zinc production offers an efficient, environmentally friendly, and cost-effective alternative to traditional pyrometallurgical methods. By understanding the chemical process and metallurgical technology involved, we can appreciate the complexity and sophistication of this process. As the demand for zinc continues to grow, the hydrometallurgical process will play an increasingly important role in meeting this demand.

References

- International Zinc Association. (n.d.). Zinc Production.

- National Institute for Occupational Safety and Health. (n.d.). Zinc Processing.

- Outotec. (n.d.). Zinc Hydrometallurgy.

Block diagram of Hydrometallurgical Process