Separate, concentrate or purify phosphoric acid from a solution containing phosphoric acid (usually wet-process phosphoric acid or a leachate containing phosphoric acid), remove impurities (such as metal ions Mg²⁺, Fe³⁺, Al³⁺, Ca²⁺, SO₄²⁻, F⁻, etc.), and produce high-purity phosphoric acid or phosphate products.
Extraction and purification principle
The difference in solubility (different distribution coefficients) of phosphoric acid or its target impurities between the organic solvent (extractant) and the aqueous phase (liquid phase) is utilized. Through the mixing and separation process, the target substance (usually phosphoric acid) is selectively transferred to the organic phase, and the impurities remain in the aqueous phase (or vice versa), thereby achieving separation and purification. A stripping step is required to recover the target substance from the organic phase.
Process Flow of Phosphoric Acid Wet Extraction And Purification
1.Liquid preparation
Wet-process phosphoric acid or phosphoric acid-containing leaching solution is pretreated (such as defluorination, desulfurization, cooling, filtration to remove suspended solids, etc.).
2.Extraction section (multi-stage countercurrent)
Feed: The pretreated feed liquid (aqueous phase) and fresh or regenerated organic extractant (organic phase) enter the first stage centrifugal extractor separately.
Mixing: In the mixing chamber of the CWL-M centrifugal extractor, the two phases are mixed vigorously under the shear of the high-speed rotating impeller, and phosphoric acid (H₃PO₄) is selectively transferred from the aqueous phase to the organic phase.
Separation: The mixed liquid enters the high-speed rotating drum. Under the strong centrifugal force, the density difference is amplified, and the two phases are separated quickly and thoroughly. The purified water phase (raffinate, containing most impurities) is discharged from the heavy phase outlet and may be used for wastewater treatment or recovery of other valuable components. The organic phase loaded with phosphoric acid (loaded organic phase) is discharged from the light phase outlet.
Countercurrent flow: The loaded organic phase enters the next stage, and contacts with the fresh feed liquid from the previous stage to further improve the extraction rate. Finally, the nearly saturated loaded organic phase leaves the last stage of the extraction section.
3.Stripping section (multi-stage countercurrent)
Feed: The loaded organic phase and the stripping agent enter the first stage centrifugal extractor of the stripping section separately.
Mixing and separation: In CWL-M centrifugal extractor, the loaded organic phase is mixed with the stripping agent, and phosphoric acid is stripped from the organic phase into the aqueous phase. After separation, a pure phosphoric acid solution (stripping solution) is obtained, and the regenerated organic phase (lean organic phase) is discharged from the light phase outlet.
Countercurrent flow: The regenerated lean organic phase flows to the upper stage and contacts with the newly loaded organic phase from the next stage to fully recover the residual phosphoric acid. Finally, the purified and concentrated phosphoric acid solution (stripping solution) is discharged from the last stage and enters the subsequent refining or concentration process (such as evaporation and crystallization). The regenerated lean organic phase returns to the extraction section for recycling.
4.Solvent recovery
There may be a small amount of solvent dissolution or entrainment loss, and a solvent recovery device (such as a stripping tower, activated carbon adsorption, etc.) needs to be set up.
5.Wastewater/residue treatment
The raffinate and washing water need to be treated in an environmentally friendly manner.
Advantages of Centrifugal Extractor
- High separation efficiency and low entrainment
- Large processing capacity of a single equipment and compact structure
- Small liquid holding volume and less solvent retention
- Strong anti-emulsification ability
- Flexible operation and easy control
- High-grade corrosion-resistant materials to ensure long-life operation of the equipment
- High degree of automation
CWL-M centrifugal extractor has become the preferred core equipment in the phosphoric acid wet extraction and purification process due to its significant advantages such as high efficiency separation, low entrainment, strong anti-emulsification, excellent corrosion resistance, etc. It can effectively overcome many shortcomings of traditional mixer settler (large floor space, large liquid holding capacity, low stage efficiency, easy emulsification, high solvent loss, etc.), significantly improve the process economy, product quality and environmental protection, and is widely used in the fields of wet phosphoric acid purification, rare earth phosphate extraction, phosphoric acid recovery in nickel-cobalt hydrometallurgy, etc.
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