Formula-1 With HCl and H3PO4 to clean heavily rusted Mild Steel Components
Stock Chemical Formulation for Spray Derusting (Concentrate)
Used to remove rust (iron oxides) from ferrous surfaces prior to phosphating or coating. This stock concentrate is to be diluted on-site to make the working bath. Designed to make handling and dosing easier.
Target Dilution Ratio: 1:10 (v/v)
For every 100 L of stock, add to 900 L water to make 1000 L working bath.
Stock Concentrate Composition (for 100 L stock)
| Component | Qty (kg or L) | Purpose |
|---|---|---|
| Hydrochloric Acid (33%) | 45 L | Fast rust and scale removal |
| Phosphoric Acid (85%) | 25 L | Passivation, dissolves light rust |
| Non-ionic Surfactant (e.g., NP-9 or equivalent) | 1.0 kg | Wetting, penetration |
| Corrosion Inhibitor (e.g., thiourea-based) | 1.5 kg | Minimize flash rusting |
| NTA Trisodium Salt (40% solution) | 3.0 L | Chelating agent |
| Deionized/Soft Water | Balance to 100 L | Carrier |
Preparation Steps
- In a plastic drum, add ~50 L deionized water.
- Add phosphoric acid slowly with stirring.
- Add hydrochloric acid next, with care and continuous mixing.
- Add surfactant and corrosion inhibitor.
- Add NTA solution.
- Top up with water to 100 L.
- Mix thoroughly.
Usage:
Dilute 1 part stock with 9 parts water to prepare the working derusting bath.
NTA – Nitrilotriactic acid
NTA stands for Nitrilotriacetic Acid, a synthetic aminopolycarboxylic acid commonly used as a chelating agent in industrial formulations.
Chemical Details
- IUPAC Name: 2,2′,2”-Nitrilotriacetic acid
- Molecular Formula: C₆H₉NO₆
- Common Form Used: Trisodium NTA (NTA·3Na) – water-soluble and stable
- Appearance: White crystalline powder or clear solution (as 40% aqueous solution)
Structural Formula
Functions in Metal Treatment
- Chelation:
- Binds metal ions like Fe²⁺, Ca²⁺, Mg²⁺, Zn²⁺.
- Prevents scale and sludge formation in baths.
- Bath Stabilizer:
- Maintains solution clarity and stability over time.
- Improves Coating Quality:
- Ensures uniform surface condition for phosphating or derusting.
Comparison with EDTA
| Property | NTA | EDTA |
|---|---|---|
| Chelating Strength | High | Very High |
| Biodegradability | Good (readily) | Poor (persists) |
| Environmental Risk | Low | Moderate to high |
| Regulatory Status | More acceptable | Restricted in some regions |
Industrial Uses
- Iron phosphating
- Surface cleaning and derusting
- Detergents
- Boiler water treatment
- Textile and pulp industries
If you prefer a non-HCl version, or a version compatible with aluminum or mixed-metal cleaning make use of the following formulation.
Formula-2 Without HCl to clean moderately rusted Mild Steel Components
Non-HCl Spray-Type Derusting Stock Concentrate Formulation (100 L)
Designed for rust removal without hydrochloric acid—safer for handling, lower fumes, and suitable for mild steel surfaces. It is compatible with aluminum or mixed-metal cleaning.
Stock Concentrate Composition (for 1:10 dilution)
| Component | Qty (kg or L) | Purpose |
|---|---|---|
| Phosphoric Acid (85%) | 40 L | Rust removal, passivation |
| Organic Acid (Citric Acid, 50% soln) | 15 L | Mild rust remover, chelation |
| Surfactant (Non-ionic, e.g., NP-9) | 1.0 kg | Wetting, penetration |
| Corrosion Inhibitor (Amine/thiourea blend) | 1.5 kg | Prevents flash rusting |
| Chelating Agent (NTA·3Na, 40% soln) | 3.0 L | Sequesters Fe²⁺, Ca²⁺, etc. |
| Deionized/Soft Water | Balance to 100 L | Carrier |
Usage
- Dilution: 1 part stock + 9 parts water (e.g., 10 L stock → 100 L bath)
- Working pH: ~2.0–2.5
- Temperature: Ambient to 40°C
- Spray Time: 1–3 minutes
- Followed by: Rinse and phosphating or coating
Advantages
- No HCl fumes or corrosion risk to plant hardware
- Safer for operators and storage
- Moderate rust removal, suitable for light to medium rust
