FeCl2 and FeCl3 – Ferrous Chloride & Ferric Chloride: Essential Industrial Chemicals for Water Treatment & Manufacturing

Date: 2026-06-19 · Author: Hóa chất Lộc Thiên

FeCl2 and FeCl3 – Ferric Chloride: Essential Industrial Chemicals for Water Treatment & Manufacturing

What are FeCl2 and FeCl3? Quick Overview

FeCl2 (Ferrous Chloride) and FeCl3 (Ferric Chloride) are inorganic iron compounds widely used in wastewater treatment, electroplating, PCB manufacturing, textile dyeing, and other industries in Vietnam.

These chemicals are often confused due to similar names but have entirely different properties and applications. This article provides detailed explanations, comparative analysis, and practical selection guidance.

Part 1: FeCl₂ – Ferrous Chloride

1.1 Basic Information

1.2 Physical Properties

FeCl₂ exists in two main forms:

• Anhydrous form: White or pale gray solid, density 3.16 g/cm³, melting point 677°C.
• Hydrated form FeCl₂·4H₂O: Light green/blue crystals, density 1.93 g/cm³, melting point 105°C.
• Highly water-soluble: 64.4 g/100 mL (10°C) → 105.7 g/100 mL (100°C).
• Easily oxidizes to FeCl₃ when exposed to air.

1.3 Chemical Properties

FeCl₂ exhibits typical salt properties with strong reducing capacity:

Reaction with alkali:

FeCl₂ + 2NaOH → Fe(OH)₂↓ + 2NaCl

Reaction with salts:

FeCl₂ + 2AgNO₃ → Fe(NO₃)₂ + 2AgCl↓

Oxidation by Cl₂ to FeCl₃:

2FeCl₂ + Cl₂ → 2FeCl₃

1.4 Applications of FeCl₂

✅ Industrial Wastewater Treatment

FeCl₂ is an effective coagulant in wastewater systems, reacting with impurities to form iron hydroxide precipitates that remove suspended solids, heavy metals, phosphates, and organic compounds.

Specific applications:

• Textile wastewater (decolorization)
• Livestock wastewater
• Electroplating wastewater (chromium/nickel removal)
• Hospital wastewater
• Landfill leachate treatment

✅ Textile Dyeing

Used as a mordant in natural fabric dyeing to enhance color fastness against washing and light exposure.

✅ Metallurgy & Electroplating

• Rust removal and metal surface preparation
• Corrosion protection for steel/alloys

✅ Intermediate Chemicals

Raw material for synthesizing FeCl₃, Fe₂O₃, and other iron compounds in chemical/pharmaceutical industries.

✅ Laboratory & Research

Used as analytical standard and iron complex synthesis.

Part 2: FeCl₃ – Ferric Chloride

2.1 Basic Information

2.2 Physical Properties

• Anhydrous form: Dark brown/black crystals, density 2.90 g/cm³, melting point 306°C, boiling point 315°C.
• 40% solution: Yellow-brown to red-brown liquid with mild HCl odor.
• Highly water-soluble: 92 g/100 mL (20°C).
• pH of 0.1M solution ≈ 1.8 (strongly acidic).

2.3 Chemical Properties

FeCl₃ is a strong Lewis acid (electron pair acceptor) and effective oxidizing agent:

Reaction with copper (key PCB reaction):

2FeCl₃ + Cu → 2FeCl₂ + CuCl₂

Reaction with alkali:

FeCl₃ + 3NaOH → Fe(OH)₃↓ (red-brown) + 3NaCl

Hydrolysis reaction:

Fe³⁺ + 3H₂O → Fe(OH)₃ + 3H⁺

2.4 Applications of FeCl₃

✅ Water & Wastewater Treatment — Primary Application

FeCl₃ is the world's leading coagulant for water treatment. When added to water, Fe³⁺ hydrolyzes to form Fe(OH)₃ colloids that adsorb and flocculate suspended particles, microorganisms, phosphates, and colorants.

Mechanism:

1. Coagulation: Fe³⁺ neutralizes negative charges of suspended particles
2. Flocculation: Particles aggregate into large flocs
3. Separation: Flocs settle or are filtered out

Advantages over other coagulants:

• Effective across wide pH range (5–9)
• Reduces phosphates to very low levels (< 0.1 mg/L)
• Decolorizes textile/paper wastewater
• Produces sludge with better dewatering properties

Specific applications:

• Municipal water treatment plants
• Industrial wastewater (paper, textile, chemical plants)
• Eutrophication control in lakes/rivers
• Landfill leachate treatment
• Sludge thickening/dewatering

✅ PCB Etching (Electronics)

Classic application in electronics. FeCl₃ 40% removes unwanted copper from printed circuit boards (PCBs), creating precise conductive pathways.

Copper corrosion reaction:

2FeCl₃ + Cu → 2FeCl₂ + CuCl₂

PCB etching advantages:

• Operates at room temperature (no heating required)
• Doesn't react with photoresist/toner transfer
• Controllable etching rate: 0.025–0.05 mm/min
• Visual feedback: amber solution → dark green when saturated

✅ Metal Surface Treatment & Electroplating

• Steel surface cleaning/activation before plating
• Metal engraving for art/fabrication

✅ Chemical Catalyst

Important Friedel-Crafts catalyst for industrial organic synthesis (pharmaceuticals, inks, polymers).

✅ Textile Industry

Oxidizing agent for aniline black dyeing, producing durable brown/black shades.

Part 3: FeCl₂ vs. FeCl₃ Comparison

Choose FeCl₂ when:

• Treating sulfide-rich (H₂S) wastewater — effectively precipitates iron sulfide
• Lower-cost chemical with acceptable performance is needed
• Textile dyeing applications (mordant)

Choose FeCl₃ when:

• Phosphate removal is critical
• PCB etching required
• Color removal in textile/paper wastewater
• Rapid coagulation needed

Part 4: Safety Guidelines

Mandatory Protective Equipment

• 🧤 Thick nitrile gloves
• 🥽 Chemical splash goggles
• 👔 Apron or protective clothing
• 😷 Respirator (for bulk handling)
• 💨 Work in well-ventilated areas

Critical Notes

• FeCl₃ is strongly acidic (pH ~1.8), severely corrosive to skin/eyes
• Avoid metal contact — corrodes most common metals
• Store in HDPE plastic or glass containers
• Never mix with strong alkalis or reducing agents

Spill Response

1. Contain spill area
2. Neutralize gradually with soda ash (Na₂CO₃) or limewater
3. Absorb with dry sand/earth
4. Dispose as hazardous waste
5. Rinse area thoroughly with water

First Aid for Exposure

• Skin: Rinse immediately with clean water ≥15 minutes
• Eyes: Continuous flushing ≥20 minutes, seek medical help
• Ingestion: Do NOT induce vomiting, drink water, seek immediate hospital care

Part 5: Storage & Transportation

Part 6: FAQs (AEO Optimized)

How do FeCl2 and FeCl3 differ?

FeCl₂ contains iron(II) (ferrous), is reducing, and pale yellow. FeCl₃ contains iron(III) (ferric), is strongly oxidizing, red-brown, and more effective for coagulation. FeCl₃ is more common for water treatment and PCB etching.

What is FeCl3 used for in wastewater treatment?

As a coagulant, Fe³⁺ hydrolyzes to form Fe(OH)₃ colloids that trap suspended particles, color, odor, and phosphates for removal. Effective for industrial/municipal wastewater and eutrophication control.

How is 40% FeCl3 used for PCB etching?

Immerse copper boards (with resist patterns) in FeCl₃ 40%. Reaction: 2FeCl₃ + Cu → 2FeCl₂ + CuCl₂ removes exposed copper, leaving designed circuits. At 25–32°C, etching takes 10–30 minutes depending on copper thickness.

Can FeCl2 replace FeCl3 in water treatment?

Yes but less effective. FeCl₂ suits sulfide (H₂S) removal. For phosphate/color removal, FeCl₃ remains preferred.

Where to buy FeCl2 and FeCl3 in Vietnam?

Multiple industrial chemical suppliers including Loc Thien Chemicals, VietChem, Hanimex, Ngoc Gia Nguyen, and Sai Gon Chem. Choose suppliers with proper COA, MSDS documentation.

What is FeCl3 dosage for wastewater?

Varies by pollution load. Typically 20–200 mg/L for municipal, 100–500 mg/L for industrial wastewater. Conduct jar tests for optimization.

Is FeCl3 toxic?

Not acutely toxic orally at low doses but corrosive to skin/eyes. High aquatic concentrations may be harmful. Requires proper treatment before discharge.

Part 7: Key Standards & Certifications

When purchasing FeCl₂/FeCl₃ for industrial use, require suppliers to provide:

• COA (Certificate of Analysis): Confirms purity and concentration
• MSDS/SDS (Safety Data Sheet): Complete safety instructions
• ZDHC Certification (for textiles): Ensures no hazardous chemicals in supply chain
• ISO 9001: Quality management system certification
• Dangerous Chemicals Business License per Decree 113/2017/ND-CP

Conclusion

FeCl₂ and FeCl₃ are essential industrial chemicals with distinct strengths:

• FeCl₂ suits high-sulfide wastewater, textiles, and plating at lower cost
• FeCl₃ excels in large-scale water/wastewater treatment, PCB etching, and phosphate coagulation

Proper selection, concentration, and sourcing from certified suppliers optimize industrial processing efficiency and cost-effectiveness.