Main Methods for Phosphoric Acid Reuse (Purification and Recovery of Phosphoric Acid Solutions)

Phosphoric acid reuse refers to the process of purifying, concentrating, and reusing phosphoric acid solutions containing impurities through physical, chemical, and membrane separation technologies.
The typical treatment process is:
Pretreatment → Separation/Concentration → Refining/Recovery → Final Disposal or Recycling.

Depending on the impurity type (suspended solids, Fe/Al ions, heavy metals, dissolved organics, fluoride ions, etc.), multiple unit operations can be flexibly combined. Common combinations include:

1. Mechanical/Chemical Pretreatment (settling, filtration, neutralization, coagulation)
2. Selective Membrane Separation (acid-resistant nanofiltration, reverse osmosis, ultrafiltration, ion-selective membranes)
3. Solvent Extraction or Ion Exchange (metal removal or phosphoric acid purification)
4. Evaporation/Crystallization and Electrochemical Refining (concentration, metal recovery, or electrodialysis desalination)
5. Polishing Treatment (activated carbon adsorption, microfiltration, electrochemical polishing)
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(1) Mechanical and Chemical Pretreatment

Principle: Removes suspended solids, oil, and insoluble precipitates, creating favorable conditions for subsequent treatment steps.
Common Techniques: Sedimentation, sand filtration, fine filtration, coagulation, and pH adjustment.
Applications: Phosphoric acid solutions containing suspended or oil-phase impurities.
Advantages: Low cost, effectively reduces the load on downstream membranes and resins, prolongs equipment life.
Notes: Coagulant selection must be compatible with subsequent membrane processes to prevent introducing poorly degradable organics.

(2) Acid-Resistant Membrane Separation (Nanofiltration / Special RO / Ultrafiltration)

Principle: Achieves separation or concentration of multivalent ions, organics, and suspended solids via pore size and chemical selectivity.
Applications: Removal of Fe, Al, Ca, and organic impurities while retaining and concentrating phosphoric acid.
Advantages: Energy-efficient, continuous operation, high selectivity; can enrich metal ions for subsequent recovery.
Disadvantages: Requires specialized acid-resistant membranes; sensitive to pH and temperature; prone to scaling and fouling.
Process Recommendations:

Perform ultrafiltration after pretreatment to remove suspended solids before membrane concentration.

Control temperature and pH; apply online monitoring and periodic cleaning.

For metal recovery purposes, use multi-stage membrane concentration followed by chemical or electrochemical recovery.

(3) Solvent Extraction

Principle: Uses selective organic solvents to extract impurities or metal components from phosphoric acid, followed by stripping to separate components.
Applications: Recovery of Fe, Al, U, rare, or precious metals; preparation of high-purity phosphoric acid.
Advantages: High selectivity, suitable for low-concentration metal recovery, mature process.
Disadvantages: High solvent loss, complex operation, stringent safety and environmental requirements.
Recommendations: Combine with membrane processes-conduct membrane concentration first, then extraction-to balance efficiency and cost.

(4) Ion Exchange / Adsorption and Evaporation–Crystallization

Principle: Selectively removes metal ions, fluoride, and other impurities through ion-exchange resins or adsorbents, while evaporation and crystallization remove water, increase acid concentration, or precipitate crystallizable impurities for solid–liquid separation and refining.
Applications: High-purity phosphoric acid production, specific metal recovery, or acid concentration enhancement.
Advantages: High selectivity and regenerability for ion exchange; mature evaporation–crystallization technology can significantly increase acid concentration.
Disadvantages: Resin regeneration produces secondary waste liquid; evaporation is energy-intensive and requires acid- and corrosion-resistant equipment.
Recommendations: Combine membrane separation and ion exchange, followed by evaporation–crystallization for deep purification. For energy control, apply multi-effect evaporation or MVR (Mechanical Vapor Recompression) after membrane pre-concentration to minimize overall energy consumption.

(5) Electrochemical and Electrodialysis Methods

Principle: Uses an electric field to drive ion migration or metal deposition for desalination, impurity removal, or metal recovery.
Applications: Recovery of Cu, Ag, and other electro-reducible metals or adjustment of ion composition in solutions.
Advantages: Clean and controllable, low chemical consumption, can directly obtain metallic products.
Disadvantages: High requirements for electrodes and membrane materials; relatively high system cost.
Recommendations: Suitable for metal recovery or as a polishing unit after membrane separation; combining with membrane systems yields better results

Impure Phosphoric Acid Treatment:
Inclined-plate sedimentation / fine filtration → ultrafiltration (suspended solids removal) → acid-resistant nanofiltration (metal removal, concentration) → ion exchange and evaporation–crystallization (refining) → reuse or product-level concentration.

Precious Metal Recovery Process:
Filtration → acid-resistant membrane enrichment → electrochemical reduction → metal recovery → permeate recycling.

High-Purity Phosphoric Acid Production:
Membrane separation for impurity removal → solvent extraction for trace metal removal → ion exchange and evaporation–crystallization for combined purification → production of high-purity phosphate.

Acid-Resistant Materials:
For high-concentration phosphoric acid, use 316L stainless steel, Hastelloy, or special plastic-lined materials; PVC and FRP are unsuitable for high-temperature strong acids.

Operational Control:
Temperature and pH must be strictly controlled to prevent corrosion and membrane degradation.

System Maintenance:
Establish backwashing and chemical cleaning protocols (acid, alkali, organic solvents); prevent unprocessed feed from entering the membrane system.

Environmental & Safety Measures:
Regeneration liquids, extraction residues, and evaporation waste must be properly treated; acid mist should be contained with exhaust and neutralization systems where necessary.

System design should comprehensively assess membrane cost and lifespan, cleaning frequency and reagent consumption, energy use in evaporation and electrochemical stages, recovery value (phosphoric acid and metals), and environmental and safety compliance-ensuring the process remains economically viable and sustainable.

To meet diverse phosphoric acid recovery needs, YIXUAN Environmental Technology Co., Ltd. has launched a special acid-resistant membrane series designed for phosphoric acid purification and recovery.
These membranes feature excellent acid resistance, selectivity, and operational stability. Specifications and operating parameters can be customized according to feed composition and target application.

The company provides full technical support, including water analysis, laboratory and pilot testing, membrane flux and rejection evaluation, cleaning strategy design, and complete system solutions (pretreatment, membrane system, post-treatment, and material selection) with engineering cost evaluation.

With extensive project experience and mature technology, YIXUAN has successfully helped multiple clients achieve efficient phosphoric acid reuse and simultaneous precious metal recovery, delivering significant results in energy conservation and resource sustainability.