Sulfuric Acid H₂SO₄ in Aluminum Sulfate production — Process & ratios | Hóa Chất Lộc Thiên
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Sulfuric Acid H₂SO₄ in Aluminum Sulfate production — Process & ratios
TL;DR: Aluminum Sulfate (alum, Al₂(SO₄)₃) is produced from the reaction between Sulfuric Acid (H₂SO₄) and Aluminum Hydroxide (Al(OH)₃) at a 3:2 molar ratio. The product is used as a coagulant in potable water and wastewater treatment. Lộc Thiên supplies H₂SO₄ to Aluminum Sulfate production plants — same-day delivery to industrial parks, batch COA/MSDS included.
What is Aluminum Sulfate?
Aluminum Sulfate (alum) is the commercial name for aluminum sulfate — Al₂(SO₄)₃, CAS 10043-01-3 (anhydrous form) or 7784-31-8 (hydrated form). It is the most widely used coagulant chemical in potable water and industrial wastewater treatment, with over a century of global application.
Aluminum Sulfate exists in the following forms:
- Crystal form: Al₂(SO₄)₃·14H₂O (Al₂O₃ content ~17%)
- Powder/granular form: Anhydrous or partially hydrated Al₂(SO₄)₃
- Solution form: 47–50% w/w Al₂(SO₄)₃ (Al₂O₃ content ~8%)
Aluminum Sulfate is produced from Sulfuric Acid and Aluminum Hydroxide (Al(OH)₃) — an aluminum source refined from bauxite ore via the Bayer process.
Chemical reaction for Aluminum Sulfate production
The basic reaction between Sulfuric Acid and Aluminum Hydroxide:
2Al(OH)₃ + 3H₂SO₄ → Al₂(SO₄)₃ + 6H₂O
Reaction enthalpy: ΔfH = −156 kJ/mol (strongly exothermic)
For producing the 14-hydrate form (common commercial grade):
2Al(OH)₃ + 3H₂SO₄ + 8H₂O → Al₂(SO₄)₃·14H₂O
Raw material ratio calculation
| Raw material | Molecular weight (g/mol) | Theoretical ratio | Per 1 ton of 14H₂O alum |
|---|---|---|---|
| Al(OH)₃ | 78.00 | 2 mol = 156 g | ~289 kg |
| H₂SO₄ 100% | 98.08 | 3 mol = 294 g | ~545 kg |
| Reaction H₂O | 18.015 | 8 mol = 144 g | ~267 kg (excluding makeup water) |
| Al₂(SO₄)₃·14H₂O | 594.20 | 1 mol | 1,000 kg |
Converted to commercial H₂SO₄ 98%: approximately 556 kg of H₂SO₄ 98% is needed to produce 1 ton of 14-hydrate Aluminum Sulfate.
Aluminum Sulfate production process
Traditional batch method
Step 1 — Raw material preparation:
- Fine powder Al(OH)₃ (typically in 1-ton bags)
- H₂SO₄ 98% stored in acid-resistant tanks
- Process water supply
Step 2 — Reaction in stirred reactor:
- Add water and Al(OH)₃ into the reactor (acid- and heat-resistant vessel — acid-resistant brick-lined steel, FRP, or 316L stainless steel)
- Slowly add H₂SO₄ 98% to the continuously stirred mixture
- Reaction temperature maintained at 100–130°C
- Reaction time: 6–9 hours depending on scale
- Control final pH and concentration
Step 3 — Post-reaction treatment:
- The alum solution after reaction is diluted to the required concentration
- Filter through membrane or sedimentation tank to remove insoluble impurities
Step 4 — Final product formation:
- Liquid form: Dilute to 47–50%, pump into finished product tanks, ready for delivery by tanker truck
- Solid form: Pour into cooling molds, let solidify → crush → screen → pack in 25–50 kg bags
Improved method with catalyst
Recent technology uses HNO₃ or H₂O₂ as catalysts for the reaction at lower temperatures, reducing reaction time and relaxing the required concentration of incoming H₂SO₄. This method saves energy but incurs NOx treatment costs (if using HNO₃).
Applications of Aluminum Sulfate in water treatment
Aluminum Sulfate works through the coagulation mechanism: Al³⁺ ions hydrolyze in water forming positively charged hydroxide complexes, neutralizing the charge of negative colloidal particles (sludge, impurities), which then agglomerate and settle.
Typical dosage
| Water type | Aluminum Sulfate dosage (g/m³) | Optimal pH |
|---|---|---|
| Potable water (low turbidity) | 10–30 | 6.0–7.5 |
| Potable water (high turbidity) | 30–60 | 5.5–7.0 |
| Light industrial wastewater | 50–150 | 5.5–7.5 |
| Textile wastewater | 100–400 | 6.0–7.0 |
| Paper mill wastewater | 150–300 | 5.5–6.5 |
Factors affecting coagulation efficiency
- pH: Best performance at pH 5.5–7.5. Outside this range, soluble aluminum increases, reducing coagulation efficiency
- Temperature: Cold water (<10°C) slows coagulation, requiring increased dosage or polymer aid
- Alkalinity: Low-alkalinity water requires lime or soda addition for pH stabilization
- Mixing intensity: Flash mixing (1–3 minutes, G > 300 s⁻¹) followed by slow flocculation (15–30 minutes, G = 20–70 s⁻¹)
Comparison with PAC
| Parameter | Aluminum Sulfate (alum) | PAC (polyaluminum chloride) |
|---|---|---|
| Typical dosage | 20–80 g/m³ | 10–40 g/m³ |
| Optimal pH | 5.5–7.5 | 5.5–8.5 |
| Sludge production | ~30% more | Less |
| Cost per active unit | Lower | Higher |
| Overall operating cost | Depends on dosage + sludge | Usually lower |
Aluminum Sulfate is cheaper than PAC per unit mass, but PAC requires lower dosage and produces less sludge — overall operating cost should be evaluated through jar testing.
H₂SO₄ quality requirements for Aluminum Sulfate production
H₂SO₄ used for producing Aluminum Sulfate for potable water treatment must meet the following specifications:
| Parameter | Requirement | Impact if exceeded |
|---|---|---|
| H₂SO₄ | ≥98% | Reduced reaction efficiency |
| Fe | ≤50 ppm | Iron contamination → yellow color, affects potable water |
| As | ≤1 ppm | Residual in alum → health risk |
| Pb | ≤5 ppm | Similar |
| Insolubles | ≤0.01% | Mechanical impurities |
For Aluminum Sulfate used in industrial wastewater treatment, the iron requirement can be relaxed, but heavy metal control must still be ensured.
Quality control of Aluminum Sulfate products
Aluminum Sulfate production plants test the following parameters before shipment:
| Parameter | Solid alum (14H₂O) | Liquid alum 47% | Method |
|---|---|---|---|
| Al₂O₃ | ≥17% | ≥8% | EDTA titration |
| 1% solution pH | 2.5–4.0 | 2.0–3.5 | pH meter |
| Fe | ≤0.05% (potable) | ≤0.05% | AAS/spectrophotometry |
| As | ≤2 ppm | ≤2 ppm | AAS |
| Insolubles | ≤0.1% | — | Gravimetric filtration |
| Basicity | 0–0.5% | — | Titration |
The plant’s QC department must retain samples from each batch for at least 6 months and issue COA with every delivery. Periodically send samples to independent laboratories for heavy metal and trace impurity testing.
Storage and transport
- H₂SO₄ 98% raw material: 316L stainless steel or PE/PP tanks, keep away from moisture and organic materials
- Solid Aluminum Sulfate product: 25–50 kg bags with PE liner, store in dry area to prevent moisture caking
- Liquid Aluminum Sulfate: Plastic or 316L stainless steel tanks, avoid excessive dilution causing crystallization
- Delivery: 5–30 ton tankers for liquid form, cargo trucks for solid form
Frequently asked questions
What is the H₂SO₄ : Al(OH)₃ ratio?
3:2 molar ratio (based on 2Al(OH)₃ + 3H₂SO₄). By mass: ~1.88 kg of H₂SO₄ 100% per 1 kg of Al(OH)₃.
Is Aluminum Sulfate soluble in water?
Yes, it is highly soluble — approximately 270 g/L at 20°C, increasing with temperature.
How much H₂SO₄ is needed to produce 1 ton of Aluminum Sulfate?
About 545 kg of pure H₂SO₄ (100%), equivalent to ~556 kg of H₂SO₄ 98%.
Is Aluminum Sulfate toxic?
At water treatment dosages (20–80 mg/L) it is safe. The crystal form is acidic and can cause skin and eye irritation upon direct contact.
Does using Aluminum Sulfate lower water pH?
Yes. Al³⁺ hydrolysis generates H⁺ which lowers pH. Water with low alkalinity (<50 mg/L CaCO₃) requires simultaneous alkalinity adjustment.
Between Aluminum Sulfate and PAC, which is better?
It depends on the water source. Aluminum Sulfate is cheaper per active unit; PAC has lower dosage, less sludge, and a wider pH range. A jar test comparison on actual water is needed.
Quote request / contact
🛒 Need H₂SO₄ for Aluminum Sulfate production in bulk? Request quote for Sulfuric Acid H₂SO₄ 98% — batch COA/MSDS, nationwide IP delivery. Hotline 0979 891 929.
Lộc Thiên supplies H₂SO₄ 98% and other concentrations for Aluminum Sulfate production plants — direct official import, batch COA/MSDS, delivered by tanker to industrial parks. 6 warehouses across 3 regions, same-day delivery in HCMC and neighboring provinces.
See also: Sulfuric Acid H₂SO₄ complete guide — properties, production, applications | PAC — complete guide to water treatment coagulant.
Quality control: QC Phan Cẩm Thủy inspects and Võ Thị Như Hòa approves each H₂SO₄ batch. Batch COA — transparent concentration and impurity data.