Cadmium: Element Properties And Uses

Introduction to Cadmium

Cadmium (atomic number 48, abbreviation Cd) is a soft, bluish-white metal distinguished by its exceptional physical properties and thoroughly documented toxicity. Cadmium was first isolated during the 19th century and has since emerged as a key material in various industrial processes from batteries to pigments. It is primarily manufactured as a by-product of zinc smelting, with 2022 global output being around 23,000 metric tonnes, concentrated primarily in countries like China, South Korea, and Japan. Due to its toxicity, cadmium is highly regulated in most industries.

Chemical Properties of Cadmium

Cadmium tends to exhibit a +2 oxidation state (Cd²⁺), which covers most of its chemical behaviour. While very inert relative to other transition elements, cadmium will react with oxygen, sulphur, and halogens to give compounds such as cadmium oxide (CdO) and cadmium sulphide (CdS). Such compounds form the basis of electroplating, pigments, and semiconductors.

The principal chemical properties include:

• Resistance to reaction in air at room temperature, though it is slowly oxidised by the formation of a protective coating.

•      Acid solubility so that it can participate in electrochemistry.

•      Absorption capacity to form gleaming coloured compounds, particularly with sulphur and selenium, which previously made it valuable for pigments.

For more chemical detail, see Stanford Advanced Materials (SAM).

Key Industrial Applications with Examples and Statistics

1. Nickel-Cadmium (Ni-Cd) Batteries

• Ni-Cd batteries found widespread use in portable electronics, power tools, and aviation technology.
• A typical 1.2V Ni-Cd battery contains about 5–10% cadmium by weight.

Although stable and capable of withstanding hundreds of charge-discharge cycles, environmental concerns have led to decreased usage. For instance, the European Union restricted application of Ni-Cd batteries with the Battery Directive (2006/66/EC).

2. Plastic, Ceramic, and Glass Pigments

• CdS produces intensely coloured yellow pigments, while CdSe produces red-orange pigments.
• Case example: CdS pigments were applied to building plastics in the 1990s, providing colourfast goods lasting over 20 years without deteriorating.
• RTEs pigments are presently regulated, with cadmium content limited to less than 0.01% in consumer products in most countries.

3. Electroplating and Corrosion Resistance

Cadmium electroplating is used in aerospace and defence because of its high corrosion resistance, especially in marine environments.

Example: Cadmium-coated, military-grade fasteners resist salt spray corrosion for over 1,000 hours, while zinc-plated alternatives fail after 200–300 hours.

4. Semiconductors and Photovoltaics

• Cadmium telluride (CdTe) is used in thin-film solar cells, which are an efficient and cost-effective alternative to silicon.
• Case data: CdTe solar modules can achieve efficiencies of up to 22% in standard test conditions with lower production costs per watt than crystalline silicon.

Environmental and Health Concerns

Cadmium is highly poisonous to animals and humans. Prolonged exposure in small quantities leads to:

• Kidney impairment and decalcification of bones

• Respiratory illness and lung cancer (through the inhalation of cadmium dust or fumes)

• Bioaccumulation within the food web, particularly in leaf vegetables, cereals, and shellfish

Its hazards are exposed through environmental events:

• In Japan's Itai-Itai disease (1960s), cadmium-polluted rice caused important bone and kidney ailments in over 200 victims.

• Mining and smelting cadmium emissions are now tightly regulated; e.g., the EPA limits wastewater cadmium to 0.005 mg/L, demonstrating how tightly control must be applied to prevent ecological and human harm.

Because of these risks, industries are transitioning to cadmium-free alternatives, e.g., lithium-ion batteries for Ni-Cd replacement batteries and non-cadmium pigments for plastics and paints. Cadmium has no substitutes, however, in high-performance solar cells and specialty electroplating applications due to its unique characteristics.

Frequently Asked Questions

What is the atomic number of cadmium?

The atomic number of cadmium is 48, making it a series of transition metals.

How toxic is cadmium?

It is highly toxic; long-term exposure causes damage to kidneys, bones, and lungs. Regulative doses are drastic in a bid to restrict human and environmental risk.

What are the main industrial uses today?

Ni-Cd batteries, pigments, cadmium electroplating, and CdTe solar cells remain significant uses.

How is cadmium manufactured?

It is mainly manufactured as a by-product of zinc smelting, typically by roasting, distillation, and electrolytic processes.

Is there an alternative that is safer?

Yes. NiMH and lithium-ion substitute for Ni-Cd, while non-cadmium pigments reduce environmental exposure. Cadmium is nevertheless needed, however, in certain high-performance uses like aerospace coatings and CdTe photovoltaics.