Indium

Indium (In)

1. Basic Information

2. Physical and Chemical Properties

Indium is a soft, ductile and lustrous metal with a silvery white color. It has a low melting point (156°C) and a high boiling point (2000°C). It is stable in air and water at room temperature, but soluble in acids. It can form various ionic and covalent compounds. Indium has the unique ability to wet glass.

3. Presence in Water and Health Effects

Indium is rarely found in natural water in significant concentrations. However, it can be present in wastewater from the electronics and mining industries. Chronic exposure to indium can cause lung, liver, and kidney problems. Indium compounds are considered toxic and should be handled with care.

4. Water Treatment Applications and Removal Methods

Although rarely a primary target in water treatment, indium can be removed by several methods:

• Ion exchange: Using specialized cation or anion exchange resins, depending on the chemical form of indium.

• Chemical precipitation: Precipitates indium as hydroxide at high pH.

• Adsorption: Using activated carbon or special adsorbents.

• Membrane filtration: Reverse osmosis or nanofiltration can be effective for removing indium ions.

5. Industrial Use in Water Treatment

Indium itself is rarely used in water treatment. However, some indium compounds have been investigated for specialized applications such as photocatalysis for degradation of organic pollutants in water.

6. Case Studies and Real World Applications

A Japanese study examined the removal of indium from semiconductor industry wastewater using adsorption on modified zeolites. Results showed a removal efficiency of up to 99% at optimal conditions. In China, a rare metal recycling plant developed a multi-stage wastewater treatment system to remove indium and other valuable metals, combining precipitation, ion exchange, and membrane technologies.

7. Regulatory Guidelines and Standards

Currently, there are no specific standards for indium in drinking water in most countries. However, some countries have set occupational exposure limits for indium in occupational air. For example, NIOSH in the US recommends an exposure limit of 0.1 mg/m³ for indium compounds.

8. Environmental Impacts and Sustainability Considerations

Releases of indium to the environment mainly come from the mining and electronics industries. Although its effects on ecosystems have not been extensively studied, there are concerns about potential bioaccumulation in the food chain. Recycling indium from used electronic equipment is becoming increasingly important for resource sustainability.

9. Future Trends and Research

Research is ongoing to:

• Develop more efficient and selective methods of indium removal from wastewater.

• Study the potential use of indium nanoparticles in photocatalytic water treatment.

• Investigate indium recovery techniques from wastewater to support a circular economy.

• Assess the long-term impact of indium on aquatic ecosystems.

10. Interesting Facts Related to Water Treatment

• Conductive transparent indium oxide (ITO) is used in solar panels and touch screens, which can end up in wastewater during manufacturing or disposal processes.
• Some researchers propose using indium-based sensors to detect certain contaminants in water.
• The ability of indium to wet glass has been utilized in the manufacture of high-quality mirrors, which can also be applied in optical water treatment technologies.