Rubidium (Rb) is a rare alkali metal. With an electron configuration of 1s2 2s2 2p? 3s2 3p? 4s2 3d1? 4p? 5s1, it possesses exactly one valence electron in its outermost energy level. Due to properties such as excellent photoelectric performance (ease of ionization and ultra-high stability of atomic transition frequencies), high chemical reactivity, good electrical conductivity, and the radioactivity of its isotopes, Rb is widely used in fields including photocatalysis, photovoltaic materials, magnetohydrodynamic (MHD) power generation, rubidium atomic clocks, specialty glass, medicine, pyrotechnics, and quantum computing[1].

Resource Types

Rubidium resources generally fall into two categories: solid mineral resources and liquid mineral resources. Solid rubidium-bearing minerals primarily occur as associated components in minerals such as lepidolite, zinnwaldite, potassium feldspar, and tantalum-niobium ores. Liquid rubidium resources are mainly found in salt lakes, underground brines, and seawater. Notably, the concentration of rubidium in seawater is approximately 0.12 mg/L, which is significantly higher than that of most other metal elements.

Extraction Methods for Solid Rubidium Minerals

Extracting Rb from solid minerals typically requires converting the ore into a soluble form followed by leaching to obtain a rubidium-bearing solution. Major methods include acid leaching, roasting, and alkaline processing.

(1) Acid Method

Specific steps: Thermal activation of the ore (1300°C) followed by water quenching; sulfuric acid leaching (120 g/L H?SO? at 50°C); and solid-liquid separation to obtain an Rb?-containing solution.

Characteristics: This method offers high decomposition efficiency with sulfuric acid, achieving rubidium leaching rates exceeding 99.2%; however, it is highly corrosive and generates significant amounts of waste residue.

(2) Roasting Method

Specific steps: Mixing the ore with additives (such as CaO, Na?SO?, or CaCl?), roasting at high temperatures (500–1000°C), leaching with water or acid, and finally performing solid-liquid separation to obtain an Rb?-containing solution. Characteristics: Limestone roasting entails low costs but high energy consumption; chlorination roasting (e.g., using CaCl?) achieves a leaching rate of up to 98.7%; and sulfation roasting allows for the simultaneous leaching of Li, Rb, and Cs.

(3) Alkaline Process

Specific steps: Ore reacts with NaOH (320–600 g/L) at high temperature and pressure (230–250°C), followed by solid-liquid separation; subsequent solvent extraction can be used for further Rb purification.

Characteristics: This method is suitable for complex granite-type ores, achieving Rb leaching rates of 95–97.5%; however, it entails high alkali consumption and demanding equipment requirements.

Extraction Methods for Liquid-Phase Rubidium

Liquid rubidium resources (salt lake brines, groundwater, seawater) are characterized by low concentrations and high impurity ion content, necessitating selective separation technologies. Key methods include precipitation, fractional crystallization, ion exchange, solvent extraction, and electrochemical methods. Each method has its own advantages and disadvantages. Precipitation offers high efficiency for separating rubidium and cesium but requires complex precipitating agents and is suitable only for high-concentration solutions. Fractional crystallization is low-cost and pollution-free but involves long processing cycles and poor selectivity regarding chemically similar elements. Ion exchange is suitable for low-concentration, high-impurity solutions, offering high recovery rates and scalability, though it requires subsequent separation of K?/NH?? after desorption. Solvent extraction provides high extraction efficiency and automation potential but suffers from significant solvent loss and high costs, making it unsuitable for high-impurity solutions. Electrochemical methods are suitable for low-concentration, high-impurity solutions, are environmentally friendly, and allow for closed-loop operation, though the technology is not yet fully mature. Flowcharts for these two extraction methods are shown below:

Applications of Rubidium

Rubidium and its compounds are widely used in:

• Optoelectronic devices (e.g., perovskite solar cells, photomultiplier tubes)

• Timekeeping and navigation (rubidium atomic clocks, GPS)

• Quantum computing and simulation (neutral-atom qubits based on ??Rb)

• Magnetohydrodynamic (MHD) power generation (utilizing its low ionization potential to enhance efficiency)

• Specialty glass and optical instruments

• Medical applications (e.g., ?2Rb myocardial perfusion PET imaging)

• Catalysts, solid-state battery electrolytes, pyrotechnics, etc.

References

[1] ZHIFEI ZHANG . A review of rubidium: Resources, technologies, and applications[J]. Desalination, 2026, 620: Article 119612. DOI:10.1016/j.desal.2025.119612.