Gallium Recycling

Basic Properties

• Classification: A post-transition metal, belonging to Group 13 (boron group) and Period 4 of the periodic table.
• Atomic mass: ~69.72 u.
• Physical state: A soft, silvery-white metal. Notably, it has an extremely low melting point (~29.76 °C, just above room temperature), meaning it can melt in the palm of your hand. However, its boiling point is very high (~2403 °C), giving it one of the widest liquid ranges of any element.
• Density: ~5.91 g/cm³ (solid); ~6.09 g/cm³ (liquid).
• Other traits: Solid gallium is brittle and easily cut; liquid gallium is viscous and wets glass or ceramics.

Chemical Behavior

• Relatively stable in air at room temperature, forming a thin oxide layer (Ga₂O₃) that prevents further oxidation.
• Reacts slowly with dilute acids (e.g., hydrochloric acid, sulfuric acid) to release hydrogen gas.
• Does not react with concentrated nitric acid due to passivation (formation of a protective oxide layer).
• Exhibits amphoteric properties: reacts with strong bases (e.g., NaOH) to form gallates (e.g., NaGaO₂).

Occurrence & Extraction

• Gallium is a rare element, with an average abundance in Earth’s crust of ~15 parts per million. It rarely occurs in its free elemental form.
• Most commonly found as a trace impurity in minerals like bauxite (aluminum ore) and sphalerite (zinc ore).
• Extracted as a byproduct during the processing of aluminum or zinc ores, via solvent extraction or electrolysis.

Key Uses

• Semiconductors: Gallium-based compounds (e.g., gallium arsenide, GaAs; gallium nitride, GaN) are critical in electronics. GaAs is used in high-speed transistors, microwave devices, and solar cells (especially in space applications). GaN powers efficient LEDs, 5G technology, and electric vehicle chargers.
• Alloys: Added to low-melting-point alloys (e.g., with indium and tin) for applications like thermal fuses or moldable metals.
• Thermometry: Its wide liquid range makes it useful in high-temperature thermometers.
• Medicine: Radioactive gallium-67 is used in medical imaging to detect infections or tumors.

History

• Predicted in 1871 by Dmitri Mendeleev, who named it “eka-aluminum” based on gaps in his periodic table, describing its properties (e.g., low melting point) with remarkable accuracy.
• Discovered in 1875 by French chemist Paul-Émile Lecoq de Boisbaudran, who isolated it from zinc ore. He named it “gallium” after “Gallia,” the Latin name for France.