Development status and research progress of wet phosphoric acid extraction technology

Abstract

Phosphoric acid, as a vital chemical raw material, holds an important position in the chemical industry. Its applications span across various sectors, determined largely by its purity. Low-purity phosphoric acid can be used in industrial and agricultural sectors, while high-purity phosphoric acid is essential for pharmaceuticals, food, electronics and other industries. The rising demand for batteries and semiconductors in recent years has led to increased requirements for phosphoric acid purity. There are two main methods for manufacturing phosphoric acid. The thermal method, while effective, is energy-intensive and environmentally unfriendly, conflicting with China’s green chemistry development goals. On the other hand, the phosphoric acid process, characterized by lower energy consumption, is more adept at handling China’s low-grade phosphate rock despite resulting in bulk and complex product impurities. Among various purification technologies, such as chemical precipitation, crystallization, electrodialysis, and ion exchange resin, the extraction method stands out. It offers environmental benefits, simple operation, and the capacity for large-scale production, marking it as a promising technique for phosphoric acid purification. This article summarizes in detail the research status of various extraction methods in recent years. It focuses on solvent extraction, aqueous two-phase extraction, reverse micelle extraction, ultrasonic-assisted extraction, and supercritical fluid extraction. It sorts out the solvent extraction method along with various extractants. The research on single extractants such as tri-n-butyl phosphate (TBP), methyl isobutyl ketone (MIBK), and n-octanol (NOA) has been primarily focused on identifying the optimal extraction conditions, including the O/A phase ratio, temperature, and air pressure. However, these single extractants typically target a single impurity, which limits their effectiveness in purifying phosphoric acid when multiple impurities are present. This limitation underscores the significant advantages of composite extractants in the purification process. Current research on composite extractants emphasizes determining the ideal proportion of extractants, often based on volume ratio, and establishing the optimal conditions for effective extraction. In addition to composite extractants, the development of new extractants offers promising solutions to the challenges posed by the low extraction efficiency of single extractants. Looking forward, the future of phosphoric acid extraction technology is poised for exciting developments: (1) The development of green composite extractants, alongside new extractants and materials combined with extractants, aims to achieve more efficient separation of impurities from phosphoric acid; (2) There is a growing interest in expanding research into the application of aqueous two-phase extraction and reverse micelle extraction for ion extraction, including the exploration of new aqueous phase systems; (3) The use of ultrasonic technology to accelerate the extraction process, coupled with studies on how supercritical fluids can improve the solubility and extraction efficiency of ions, represents another avenue for innovation. These advancements seek to reduce costs and explore specific application areas.

Keywords

• phosphoric acid
• wet phosphoric acid
• extraction
• extractant
• aqueous two-phase extraction
• reverse micelle extraction
• ultrasonic-assisted extraction
• supercritical fluid extraction