For industrial fluoride-bearing wastewater — polishing after precipitation, deep removal ahead of discharge limits, and adsorption units inside water-treatment projects. We supply material, data, screening and test support; engineering design and final discharge compliance stay with you or your local licensed partner.
We do not sell ordinary precipitated silica as a universal defluoridation agent. Silica-based fluoride adsorbents described in the published literature are typically iron-modified, aluminium-modified or composite systems: the fluoride activity comes from the functionalised surface and its active components, not from food-grade silica itself. Material identity is confirmed against the supplier TDS, an active-component statement and real water-sample data before any project discussion.
Scope is industrial fluoride-bearing wastewater only — not drinking water, municipal supply or household point-of-use treatment.
For high-concentration fluoride wastewater, precipitation and coagulation are normally used first to bring the fluoride load down. Adsorption and ion-exchange routes are better suited to the stage that follows — deeper removal and end-of-line polishing. This solution is positioned at that second stage, not as a replacement for front-end precipitation.
Vistasilica offers this track as VS-DA300, an alumina-modified functionalised silica fluoride adsorbent. It is neither a granular activated alumina nor a food-grade white carbon black: the active aluminium species is supported on a precipitated silica framework, which is the structural reason its capacity sits above conventional activated alumina on a per-gram basis.
| Component | Chemical form | Content | Function |
|---|---|---|---|
| Framework | Precipitated silica, SiO₂·nH₂O | ≥ 70% | High-surface-area support; disperses and anchors the active sites |
| Primary active component | Supported alumina / boehmite (Al₂O₃ / AlOOH) | 8–15% as Al₂O₃ | Surface hydroxyls exchange with F⁻ — the core adsorption site |
| Modifier | Alkali metal oxide (Na₂O) | ≤ 0.5% | Controls surface charge and pH buffering |
Removal mechanism. Ligand exchange (Al–OH + F⁻ → Al–F) accounts for over 80% of uptake, with electrostatic adsorption and anion exchange as secondary contributions.
| Property | Unit | VS-DA300 |
|---|---|---|
| SiO₂ content (dry basis) | % | ≥ 70 |
| Al₂O₃ content (active component, dry basis) | % | 8 – 15 |
| Na₂O content | % | ≤ 0.5 |
| BET specific surface area | m²/g | 250 – 350 |
| Particle size (granular) | mm | 0.5–1 / 1–3 (customisable; powder grade on request) |
| Bulk density (granular) | g/cm³ | 0.45 – 0.65 |
| Crush strength | N/particle | ≥ 25 (1–3 mm) |
| Attrition rate | % | ≤ 1.0 |
| Water absorption | % | ≥ 60 |
| pH (5% aq. suspension) | — | 6.0 – 8.0 |
| Loss on ignition (1000 °C) | % | ≤ 10 |
Test conditions: 25 ± 2 °C, dosage 2 g/L, 24 h contact to equilibrium, pH 6.5.
| Initial fluoride C₀ (mg/L) | Equilibrium capacity qe (mg F⁻/g) | Removal (%) |
|---|---|---|
| 5 | 2.6 | 95 |
| 10 | 5.0 | 90 |
| 20 | 9.4 | 84 |
| 50 | 18.5 | 74 |
| 100 | 22.0 | 55 |
Saturated static capacity (Langmuir Qmax) ≥ 20 mg F⁻/g; Langmuir monolayer model, R² ≥ 0.95. Dynamic capacity runs at roughly 70–80% of the static figure — size your column on the dynamic number, not this table.
| Condition | Behaviour |
|---|---|
| Optimal pH | 5 – 7 — matches typical industrial polishing-stage conditions |
| Usable pH range | 4 – 8.5, retaining ≥ 80% of capacity |
| Above pH 9 | Capacity drops markedly; front-end pH adjustment recommended |
| SO₄²⁻ / Cl⁻ / NO₃⁻ | Minor effect |
| HCO₃⁻ / CO₃²⁻ | Competitive inhibition; high-alkalinity water needs pH pre-adjustment or a higher dosage |
| PO₄³⁻ | Strong competition; phosphate-bearing streams should be segregated or dephosphorised first |
Regeneration cycle: soak in 4% NaOH for 2–4 h → rinse to neutral → activate in 5% HCl for 1–2 h → rinse to neutral pH.
| After | Capacity retained |
|---|---|
| 20 regeneration cycles | ≥ 85% |
| 50 regeneration cycles | ≥ 75% |
| Typical replacement interval | 1–2 years, depending on water chemistry and throughput |
20 / 25 kg paper sacks with PE liner, or 500 / 1000 kg bulk bags. Store sealed and dry at 5–30 °C, relative humidity ≤ 70%.
HG/T 3927 (general adsorbents), GB/T 22627-2014, GB 5749-2022 (effluent limit reference), REACH (EINECS 231-545-4, silicic acid).
Typical values. Figures above are representative of the grade. Performance on your effluent must be confirmed by jar test and dynamic column trial — a grade-specific specification sheet and COA are available on request.
Competition in fluoride removal is not mainly another silica-based adsorbent. The realistic alternatives are activated alumina, front-end calcium precipitation, anion-exchange resin and membranes. Functionalised silica-based fluoride media have not converged on globally standardised commercial grades the way oral-care silica has, so verifiable products and process routes are listed separately below rather than invented as like-for-like model numbers.
| Route | Verifiable representative products | Where customers use it | What to compare |
|---|---|---|---|
| Activated alumina | DI-tech / Weco Filters AAL-1CUFT; Tramfloc Activated Alumina; Actas® / Bee Chems Activated Alumina | Granular adsorbent media for fluoride and arsenic reduction; fixed bed, fluidised bed or cartridge formats | Dynamic breakthrough capacity, pH tolerance, competing-ion effect, media consumption and total project cost — not price per tonne alone |
| Calcium precipitation + coagulation | Lime / calcium hydroxide, calcium chloride — project-specific dosing, no single global grade | Front-end load reduction on high-fluoride streams, forming calcium fluoride sludge for solid-liquid separation | Not a route to displace. Functionalised silica adsorbent sits after it, for deep removal and polishing |
| Anion-exchange resin | Strong-base anion resin routes; grade depends on the customer's current brand, feed salinity and regeneration system | Low-concentration deep treatment, or where effluent limits are tight | Selectivity, regenerant consumption, competing-ion interference, spent regenerant handling and total operating cost |
| Reverse osmosis / membranes | Industrial RO / NF systems — benchmarked at system and element level, not as a single adsorbent grade | Projects removing multiple dissolved salts where the customer can handle the concentrate | Where membrane cost is high or concentrate disposal is difficult, adsorption can be the deep-treatment or hybrid option |
| Test dimension | What to watch | What it tells you |
|---|---|---|
| Fluoride removal | Effluent fluoride and removal rate across inlet concentrations | Whether the target discharge limit is within reach |
| pH tolerance | Stability of performance across your operating pH window | Whether additional pH adjustment is needed |
| Competing ions | Effect of bicarbonate, sulphate, chloride, phosphate and organics | Whether it holds up in the real effluent, not just synthetic water |
| Dynamic breakthrough capacity | Throughput before breakthrough, per unit mass of media | Replacement frequency and project economics |
| Pressure drop & particle strength | Whether the media powders, blinds or builds pressure too quickly | Whether it is operable at plant scale |
| Material safety & disposal | Active-component leaching, spent-media classification and disposal route | EHS and compliance cost |
| Cost per m³ treated | Media, pre-treatment, regeneration or replacement, sludge and disposal | Economics against alumina, resin, membrane and precipitation routes |
“This solution is not about replacing every fluoride-removal process with ordinary silica. For high-fluoride wastewater the load is normally cut by a front-end process first; what we bring is a functionalised silica-based adsorbent for deep removal after precipitation and for steady end-of-line control. We look at the water chemistry, the existing process and the target effluent first, then confirm fit through jar tests and dynamic column trials.”
More questions on grades, test methods and compliance: Technical FAQ