NF-1 DEFLUORIDATION FILTER MEDIA

Irregular hydroxyapatite granules for fluoride removal

Fluoride is removed by ion exchange between hydroxyl groups and fluoride ions as well as surface physical adsorption. Beneficial minerals in water are preserved. The media can be regenerated repeatedly with sodium hydroxide solution. With high mechanical strength, it hardly breaks during backwashing and lasts 2 to 5 years. It is suitable for groundwater, drinking water and low-concentration fluoride-containing industrial wastewater with low operation costs.

REFsorb FLUORIDE ADSORBENT

Spherical hydroxyapatite adsorbent for fluoride removal

Fluoride is removed by ion exchange between hydroxyl groups and fluoride ions combined with surface physical adsorption, and beneficial minerals in water are retained. The adsorbent can be regenerated repeatedly with sodium hydroxide for repeated use. Its spherical shape ensures uniform water distribution in the filter tank and prevents channel flow. It features large adsorption capacity and stable performance, suitable for high-fluoride groundwater, drinking water, as well as fluoride-containing wastewater from mining, photovoltaic and fluorochemical industries.

Both NF-1 irregular particles and spherical REFsorb adsorbent adopt hydroxyapatite as raw material with identical fluoride removal principle. The treatment mainly depends on lattice hydroxyl ion exchange, supplemented by physical adsorption, electrostatic adsorption, surface complexation and co-precipitation.

Core Mechanism

F⁻ (1.33 Å) and OH⁻ (1.37 Å) have similar ionic radii and conduct isomorphic substitution in the HAP lattice to spontaneously form thermodynamically stable fluorapatite. Competing anions Cl⁻, NO₃⁻, SO₄²⁻, HCO₃⁻ barely affect adsorption. The reaction releases OH⁻ via ion exchange, and F⁻ is directly embedded into the crystal framework. Hydroxyapatite has high substitution selectivity. NF-1 and REFsorb have large specific surface area and abundant surface hydroxyl groups, with higher exchange capacity than traditional defluoridation adsorbents.

Auxiliary Adsorption Mechanism

1. Electrostatic physical adsorption (rapid surface capture)
2. Surface complexation + dissolution-precipitation (remarkable at high fluoride concentration)

5～7

Weakly acidic to neutral

Combined mechanism of positive surface electrostatic adsorption and lattice hydroxyl exchange, delivering the maximum fluoride uptake capacity.

7 ~ 8.4

Neutral to weakly alkaline

Electrostatic attraction weakens, yet consistent treatment efficiency can still be maintained.

Suitable for long-term continuous operation.

＜ 5

Gradual dissolution of hydroxyapatite crystals causes media degradation, leading to elevated calcium and phosphorus concentrations in effluent.

Strongly acidic

Continuous inflow at high pH should be avoided.

＞ 8.5

Abundant free OH⁻ competes with F⁻ for lattice exchange sites. The negatively charged media surface repels fluoride ions, resulting in significantly deteriorated defluoridation performance.

Strongly alkaline

Continuous inflow at high pH should be avoided.

Effect of pH on Adsorption

Core Performance Advantages

Superior Fluoride Removal Efficiency

It enables deep removal of fluoride ions to achieve extremely low residual fluoride concentration in effluent, which can be undetectable under certain working conditions. For raw water with low fluoride content, mixing raw water with treated water is an option to cut long-term operating costs.

Broad Water Quality Adaptability

Stable performance is maintained within a wide pH range of 5–10. It retains steady fluoride uptake and removal efficiency in high-salinity water with strong tolerance to salinity interference.

Easy Regeneration & Reusability

Regeneration can be carried out using 2%–5% NaOH solution by mass via soaking, countercurrent flushing, heated circulating elution and other processes. Adsorbed fluoride ions can be thoroughly stripped. Suitable regeneration strategies can be selected flexibly according to on-site conditions for repeated cyclic application.

NF-1 and REFsorb are dedicated adsorbents for water defluoridation and possess prominent technical advantages based on hydroxyapatite substrate.

High Fluoride Uptake Capacity

NF-1 has a conventional fluoride uptake capacity of 1.0–1.5 mg/g, while REFsorb designed for wastewater treatment reaches 3–6 mg/g. Less media filling is required to achieve equivalent defluoridation effect, reducing equipment footprint and infrastructure investment.

Fast Adsorption Rate

A shorter contact time is required for fluoride ion capture. Lower media dosage can be adopted compared with conventional defluoridation media, enabling more compact filtering facilities.

Excellent Operational Safety

Manufactured from hydroxyapatite substrate, the media leaches no hazardous substances during operation or after saturation, ensuring reliable and safe effluent quality.

The media can adsorb iron and manganese without aeration with an uptake capacity of 5–10 g/kg. Nevertheless, iron and manganese adsorption is irreversible, which occupies exchange sites and impairs fluoride removal performance. Pre-treatment is recommended for raw water containing high concentrations of iron and manganese.

Test 1

Influent Source:

Influent Fluoride Concentration:

Treatment Requirement:

Adsorbents:

Adsorbent Dosage:

EBCT:

Groundwater

2 mg/L

Effluent fluoride concentration ＜ 1 mg/L (breakthrough threshold)

NF-1 hydroxyapatite defluoridation media, activated alumina, modified zeolite molecular sieve

1 kg for each material

9.5 min

Test 2

Influent Source:

Influent Fluoride Concentration:

Treatment Requirement:

Adsorbents:

Adsorbent Dosage:

EBCT:

Groundwater from high-fluoride areas

6 mg/L

Effluent fluoride concentration ＜ 1 mg/L (breakthrough threshold)

NF-1 hydroxyapatite defluoridation media, activated alumina, modified zeolite molecular sieve

1 kg for each material

12 min

With identical adsorbent dosage, the total treated water volume at breakthrough for NF-1 media is 10.9 times that of activated alumina and 20.8 times that of modified zeolite molecular sieve.

Test Result

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