Question

How would you obtain zinc from sphalerite (ZnS)?

Short answer

Extract zinc from sphalerite by concentrating the ore, roasting it to zinc oxide, reducing it with coke, and refining the zinc.

Step-by-step solution

Understanding the Ore

Sphalerite is a mineral composed primarily of zinc sulfide (ZnS). The main goal is to extract zinc from this mineral. The process for extracting zinc from sphalerite involves several key steps, focusing on removing sulfur and leaving behind pure zinc.

Concentration of the Ore

The zinc sulfide ore is concentrated first to remove gangue particles. This process typically uses froth flotation, where crushed ore is mixed with water and chemicals that allow zinc sulfide to float to the surface, separating it from other materials.

Roasting to Form Zinc Oxide

The concentrated zinc sulfide ore is then subjected to a roasting process. During roasting, zinc sulfide reacts with oxygen in the air to form zinc oxide (ZnO) and sulfur dioxide (SO₂). The reaction is as follows: \[ 2ZnS + 3O_2 ightarrow 2ZnO + 2SO_2 \]

Reduction of Zinc Oxide

To finally extract zinc, the zinc oxide is reduced to zinc metal by heating it with a reducing agent like carbon in the form of coke. The chemical reaction here is: \[ ZnO + C ightarrow Zn + CO \] This reaction occurs in a furnace at high temperatures, resulting in the production of pure zinc metal.

Refining the Zinc

The extracted zinc may still contain impurities. Therefore, it is refined, often through electrolysis, to produce high-purity zinc. Electric current is passed through a solution containing zinc ions, depositing pure zinc on the cathode.

Key concepts

Sphalerite

Sphalerite is a key mineral used for zinc extraction and is predominantly made up of zinc sulfide (ZnS). It serves as the most important source of zinc, which is a vital metal used in various industries. Found in several colors depending on the presence of impurities, its usual form is a brown, black, or even colorless crystal.
Sphalerite is often mined from deposits found underground or open pit. The primary component, zinc sulfide, makes it particularly valuable for zinc production. The mineral goes through concentration processes to separate it from less useful materials, paving the way for the extraction and purifying zinc.

Roasting Process

The roasting process is a critical step in extracting zinc from sphalerite. This stage involves heating the concentrated zinc sulfide ore with oxygen. During this thermal treatment, a chemical reaction occurs, where zinc sulfide is transformed into zinc oxide (ZnO) and sulfur dioxide (SO₂).
The reaction can be summarized as:

• 2ZnS + 3O₂ → 2ZnO + 2SO₂.

Roasting is carried out in a furnace under carefully controlled conditions to maximize efficiency. It's a crucial preparation step, turning the ore into a form that can be later processed to extract zinc. This conversion also makes it possible to capture sulfur dioxide, a component that can further be used to produce sulfuric acid in an environmentally friendly manner.

Froth Flotation

Froth flotation is an essential method used for concentrating zinc sulfide ores like sphalerite. It involves mixing the crushed ore with water and specific chemicals. These chemicals enable zinc sulfide particles to attach to air bubbles and rise to the surface. This forms a froth that can be skimmed off, separating zinc sulfide from other unwanted materials.
Froth flotation is advantageous because it efficiently boosts the concentration of zinc, making the ore purer for subsequent processing stages like roasting. This improved concentration reduces waste and allows for economic extraction of zinc from the ore. It's widely applied in mining operations due to its effectiveness and simplicity.

Zinc Refining

To achieve high-purity zinc, further refining is essential after its extraction. One common method is electrolytic refining. In this process, extracted zinc is dissolved in a solution of sulfuric acid, creating a zinc sulfate solution.
Electric current is passed through this solution to deposit pure zinc on the cathode, effectively removing impurities. This refinement process ensures that zinc meets necessary purity standards for industrial applications. Besides electrolysis, other methodologies like distillation can also be used based on specific requirements. Refining is a vital step to ensure that the zinc produced is of high quality, suitable for uses ranging from galvanization to alloy production.