Nanofiltration Membrane for Divalent Ion Removal

1. Product Introduction

Nanofiltration membrane for divalent ion removal is a modified composite nanofiltration membrane, which is a functional separation membrane between ultrafiltration and reverse osmosis membranes, specially optimized for the selective removal of divalent ions. It is mainly made of modified polyamide through advanced interface polymerization technology, with a membrane pore size of 1-2nm and a molecular weight cut-off of 200-800 Da. The biggest feature is its high surface negative charge density, which enhances the electrostatic repulsion effect on divalent cations and anions, and its dense but flexible membrane structure ensures efficient interception of divalent ions while maintaining appropriate flux. The common configurations are spiral wound and hollow fiber, among which spiral wound is more widely used in large-scale water treatment due to its high packing density and stable operation. It is the core component of divalent ion removal systems, suitable for both industrial large-scale treatment and small-scale water purification, and can be customized according to the type and content of divalent ions in raw water.

2. Application Scenarios

Thanks to its excellent divalent ion removal performance, this membrane has a wide range of application scenarios. In municipal water softening, it is used to remove Ca²⁺ and Mg²⁺ in tap water, solving the problem of scale formation in pipes and household appliances, and improving water quality and taste. In industrial wastewater treatment, it is widely applied to printing and dyeing, chemical industry, electroplating and mining fields, intercepting divalent heavy metal ions and sulfate ions, realizing wastewater recycling and reducing environmental pollution. In brackish water desalination, it is used as a pretreatment component to remove divalent ions, reducing the load of subsequent reverse osmosis membranes and extending their service life. In 盐湖卤水提锂, it efficiently separates Mg²⁺ (divalent) and Li⁺ (monovalent), solving the core problem of magnesium-lithium separation and providing a green and efficient technical path for lithium extraction. In drinking water purification, it removes harmful divalent heavy metal ions and fluoride ions, ensuring drinking water safety.

3. Technical Parameters

The core technical parameters of nanofiltration membrane for divalent ion removal are focused on divalent ion interception and operational stability: membrane material is modified polyamide; standard diameters are 2.5", 4" and 8"; operating pressure is 0.5-1.5MPa, which is lower than reverse osmosis membranes and energy-saving; operating temperature is 5℃-45℃ (maximum 50℃ for short-term operation); pH adaptation range is 2.5-11.0 (ambient temperature), 2.0-11.5 (cleaning); rejection rate for divalent ions: Ca²⁺ ≥96%, Mg²⁺ ≥97%, SO₄²⁻ ≥98%, heavy metal divalent ions (Pb²⁺, Cd²⁺) ≥99%; rejection rate for monovalent ions is 10%-30%, ensuring the retention of beneficial monovalent ions; membrane flux is 40-80 L/(m²·h) under standard conditions (25℃, 1.0MPa); service life is 2-4 years under normal maintenance; maximum inlet SDI15 ≤5.0, maximum inlet turbidity ≤1.0NTU; chlorine tolerance is 300-500ppm·hours; surface negative charge density is -20 to -35 mC·m⁻², enhancing electrostatic repulsion to divalent ions.

4. Product Advantages

Compared with traditional divalent ion removal technologies (such as ion exchange, chemical precipitation) and ordinary nanofiltration membranes, this special membrane has obvious core advantages. First, high selectivity and interception rate: it can efficiently intercept various divalent ions with a rejection rate of more than 96%, while allowing beneficial monovalent ions to pass through, avoiding "over-purification" and resource waste. Second, environmental protection and no secondary pollution: it adopts physical separation, no need to add chemical agents, avoiding the generation of chemical sludge and secondary pollution, which is in line with green development trends. Third, stable operation and long service life: the modified polyamide material has excellent chemical stability and anti-fouling performance, and the high surface negative charge reduces the adsorption of pollutants, reducing cleaning frequency and extending service life. Fourth, energy saving and low cost: the operating pressure is lower than reverse osmosis membranes, saving energy consumption by 30%-50%, and the modular design reduces operation and maintenance costs. Fifth, wide adaptability: it can adapt to different raw water with varying divalent ion contents, and operate stably under complex water quality conditions.

5. Application Procedures

The application procedure of nanofiltration membrane for divalent ion removal is standardized, which directly affects the divalent ion removal effect and membrane service life, divided into six key steps. First, raw water pretreatment: through coagulation, flocculation, sedimentation and ultrafiltration, remove large particles, colloids and suspended solids in raw water, ensure inlet water meets the membrane operation requirements (SDI15 ≤5.0, turbidity ≤1.0NTU), and avoid membrane fouling caused by impurities. Second, membrane installation: install the membrane element in the pressure vessel according to the design direction, ensure tight connection and no leakage, and ensure the smooth flow of feed water and permeate. Third, trial operation: start the system, adjust the operating pressure to 0.3-0.5MPa, flush the new membrane for 2-3 hours, and discharge the produced water to remove the protective fluid on the membrane surface. Fourth, formal operation: adjust the operating parameters to the standard range, monitor the divalent ion rejection rate, flux and pressure drop in real time, and adjust parameters in time according to raw water quality changes. Fifth, regular cleaning: when the membrane flux decreases by more than 15% or the divalent ion rejection rate decreases by more than 5%, clean the membrane with acid-base cleaning agents to restore membrane performance. Sixth, regular maintenance: shut down regularly to inspect the membrane, replace aging or damaged elements in time, and store the membrane with special protective fluid when shutting down for a long time.

6. Quality Standards

The production and detection of nanofiltration membrane for divalent ion removal strictly follow international standards (ISO/DIS 25175) and national standards (GB/T39808-2021, HJ 579-2010), as well as food-grade and pharmaceutical-grade standards for drinking water and pharmaceutical fields. High-quality modified polyamide materials are selected to ensure chemical stability, mechanical strength and high divalent ion interception performance. Production is carried out in a 100-level clean workshop, with strict control over each link such as membrane casting, cutting, winding and sealing. Each membrane element undergoes strict factory testing before leaving the factory, including divalent ion rejection rate, flux, anti-fouling performance and sealing performance tests, ensuring that all indicators meet the standard requirements. In addition, it complies with relevant industry standards for water softening and heavy metal treatment, ensuring the reliability and safety of application.

7. Working Principle

The working principle of nanofiltration membrane for divalent ion removal is based on pressure-driven membrane separation, combined with electrostatic repulsion (Donnan effect) and steric hindrance, which is the core of its high selective separation performance. Under the action of operating pressure (0.5-1.5MPa), pretreated raw water flows along the membrane surface. The membrane has a nanoscale pore size (1-2nm), which can intercept divalent ions through steric hindrance due to the larger hydrated radius of divalent ions compared with monovalent ions. At the same time, the membrane surface has high negative charge density, which produces strong electrostatic repulsion to divalent cations (such as Ca²⁺, Mg²⁺) and divalent anions (such as SO₄²⁻), further enhancing the interception effect. Water molecules and small monovalent ions with small hydrated radius and low charge pass through the membrane pores to form product water, while divalent ions are retained in the raw water and discharged as concentrated water, thus realizing efficient separation of divalent ions.

8. Future Prospects

With the increasing demand for water quality improvement, industrial wastewater recycling and new energy development (such as lithium extraction), the market demand for nanofiltration membrane for divalent ion removal is growing day by day. In the future, it will develop in the direction of higher selectivity, higher flux, longer service life and intelligence. On the one hand, membrane material modification technology will be optimized, such as using nanomaterial modification to further improve the negative charge density and anti-fouling performance, enhancing the interception effect on low-concentration divalent ions. On the other hand, it will be integrated with intelligent technology, combining IoT and big data to realize real-time monitoring of divalent ion rejection rate and membrane operation status, automatic fault early warning and intelligent cleaning. In addition, application scenarios will be further expanded to new energy (such as lithium extraction from salt lakes), environmental remediation and other fields, and the combination with other membrane technologies will form a more efficient separation system, promoting the sustainable development of related industries.

9. Conclusion

Nanofiltration membrane for divalent ion removal, as a high-performance functional separation membrane, has the core advantages of high divalent ion rejection rate, strong selectivity, environmental protection, energy saving and stable operation. It effectively solves the pain points of traditional divalent ion removal technologies, and plays an irreplaceable role in water softening, industrial wastewater treatment, 盐湖卤水提锂 and drinking water purification. Its standardized application procedures and strict quality control ensure stable and reliable operation, and its modular design is suitable for large-scale promotion and application. With the continuous progress of membrane material technology and intelligent upgrading, this membrane will be further optimized, with broader application prospects, making greater contributions to water resource protection, environmental pollution control and new energy development, and promoting the realization of circular economy.

10. Frequently Asked Questions (FAQs)

Q1: What is the core function of nanofiltration membrane for divalent ion removal? 

A1: Its core function is to efficiently intercept divalent ions (Ca²⁺, Mg²⁺, SO₄²⁻, heavy metal divalent ions) through electrostatic repulsion and steric hindrance, while allowing water molecules and beneficial monovalent ions to pass through, realizing efficient and environmentally friendly divalent ion removal. 

Q2: What is the rejection rate of this membrane for divalent ions? 

A2: The rejection rate is as high as 96%-99%, among which Mg²⁺ rejection rate ≥97%, SO₄²⁻ rejection rate ≥98%, and heavy metal divalent ions rejection rate ≥99%. 

Q3: Why is raw water pretreatment important for this membrane? 

A3: Pretreatment can remove large particles, colloids and suspended solids, avoid membrane fouling and damage, ensure stable divalent ion rejection rate and flux, and extend membrane service life. 

Q4: What is the difference between this membrane and ordinary nanofiltration membrane? 

A4: This membrane has higher surface negative charge density, stronger selectivity for divalent ions, higher rejection rate of divalent ions, and is specially optimized for divalent ion removal, while ordinary nanofiltration membrane focuses on general separation of macromolecules and ions. Q5: Can it be used for lithium extraction from salt lakes? 

A5: Yes, it can efficiently separate divalent Mg²⁺ and monovalent Li⁺, solving the core problem of magnesium-lithium separation, which is a green and efficient technology for lithium extraction from salt lakes.