FeCl2 Wastewater Treatment: Dosage & Mixing Instructions | Loc Thien

In industrial wastewater treatment, FeCl2 for wastewater treatment Ferrous chloride is increasingly being mentioned as a supplementary option alongside aluminum sulfate and FeCl3. Ferrous chloride not only participates in coagulation but also removes sulfides—a clear advantage for electroplating wastewater and leachate. This article provides comprehensive information on... ferrous sulfate FeCl2: Mechanism, dosage, mixing instructions, operating procedures, technical specifications, and B2B purchasing notes.

What is FeCl2 and how is it used in wastewater treatment?

Definition of ferrous chloride / iron alum 2

FeCl2 — ferrous chloride, iron(II) chloride — has the formula FeCl₂, CAS number 7758-94-3. It is commercially available as a 25–30% liquid solution, pale blue to pale yellowish-green in color. Unlike FeCl3FeCl2, containing Fe²⁺, has stronger reducing properties — effective in sulfide removal and coagulation at neutral pH.

Coagulation – flocculation – sedimentation mechanism

When added to wastewater, Fe²⁺ ions react with OH⁻ to form positively charged colloidal iron hydroxide flocs. These flocs adsorb and bind to negatively charged suspended particles, color, and colloidal organic matter, causing them to clump together into larger flocs and settle. This is the fundamental coagulation-flocculation mechanism in wastewater treatment systems. wastewater treatment chemicals industrial.

When should FeCl2 be used instead of other coagulants?

FeCl2 is considered when simultaneous coagulation and sulfide removal (H₂S) treatment is required. Fe²⁺ ions react with S²⁻ to form precipitated FeS, reducing odor and sulfide load—an advantage that FeCl3 lacks. The final choice should be based on actual jar test results.

What types of wastewater is FeCl2 suitable for?

Electroplating wastewater and heavy metals

Electroplating wastewater contains Cr, Ni, Cu, Zn, Pb — ferric sulfate aids in the precipitation of heavy metal hydroxides and promotes good flocculation. Loc Thien also provides comprehensive consulting services. electroplating chemicals.

Textile dyeing and decolorization wastewater

High color intensity from reactive dyes, reducing agents, and pigments poses a significant challenge. Ferrous chloride, combined with alkaline pH adjustment (8–9), creates floc that effectively adsorbs color molecules. For wastewater with excessively high organic loads or dispersed dyes, the addition of activated carbon or Fenton reagents is necessary to meet discharge standards.

Leachate and desulfurization wastewater

Leachate contains high levels of H₂S, sulfides, and ammonia. Fe²⁺ reacts with S²⁻ to form precipitated FeS—deodorizing and reducing the sulfide load for subsequent treatment. This is a unique advantage of FeCl2 that FeCl3 lacks.

Industrial wastewater with high COD/color levels.

Wastewater from food processing, paper, leather tanning, and printing often has COD and color levels exceeding acceptable limits. Ferrous sulfate (Fe2+) is used as a pretreatment step to reduce the load on the subsequent biological treatment system. It is used in combination with... flocculant The polymer significantly improved the efficiency of floc separation and sedimentation.

What is the appropriate dosage of FeCl2 for wastewater treatment?

How to determine dosage using jar test

The jar test is a standard method for determining the optimal FeCl2 dosage. The procedure involves: taking a representative wastewater sample → preparing a series of 500–1000 mL jars with gradually increasing FeCl2 doses → stirring rapidly for 1–2 minutes → stirring slowly for 10–20 minutes → settling for 30 minutes → measuring color, TSS, and pH. The optimal dose yields the best results at the lowest cost. This method should be repeated when wastewater characteristics change seasonally or the production process changes.

Reference dosage range based on wastewater type

• Electroplating/heavy metal wastewater: 100–500 mg/L (depending on metal content and initial pH)
• Textile dyeing wastewater (decolorization): 150–400 mg/L, usually in combination with pH 8–9
• Leachate (sulfide-removed): Reference Fe:S ratio 3:1 to 5:1 mol — actual S²⁻ analysis is required.
• Industrial wastewater (high COD): 50–200 mg/L pretreatment, polymer combination 1–5 mg/L

Signs of underdosing and overdosing.

• Missed dose: Small floc size, cloudy water after sedimentation, TSS and color exceeding standards.
• Excess dose: Sludge increases significantly, effluent pH decreases; post-settlement water may turn yellow due to excess iron.

Note the optimal pH and coagulant.

Ferrous sulfate (Fe2+) works best at pH 7–9. Below pH 6, the ferrous hydroxide redissolves, reducing coagulation efficiency. After adding the chemical and adjusting the pH, further supplementation is recommended. coagulant chemicals Polymer (PAM) in the slow stirring stage helps the floc to form larger, faster, and firmer bonds, reducing sludge carryover to the settling tank.

How to mix FeCl2 and prepare the dosing solution.

Commonly used dilution concentrations

25–30% solutions are usually diluted to 5–15% before injection to ensure precise dose control and avoid local overdosing. Direct injection is possible if the system is designed to withstand sufficient corrosion.

Recommended mixing order and equipment

1. Prepare the formwork tank using HDPE, FRP, or 316L stainless steel — absolutely do not use carbon steel or unlined concrete.
2. Add clean water first (60–70% of the target volume).
3. Pour the concentrated solution slowly into the water while stirring gently — do not do the reverse.
4. Add water to the required volume, stir well; check the concentration with a hydrometer if necessary.
5. Label the containers completely before use.

Note on corrosion prevention and workplace safety.

Liquid ferric sulfate is highly corrosive to carbon steel, copper, and concrete. All piping, valves, and dosing pumps must be made of PVC, CPVC, PVDF, or 316L stainless steel. Operators must wear safety glasses, nitrile/rubber gloves, chemical-resistant aprons, and protective boots. The mixing area must be well-ventilated and have an emergency eyewash station nearby. Refer to the product's MSDS for hazard thresholds and specific handling procedures.

FeCl2 operating procedure in wastewater treatment systems

Chemical injection points and injection order

Ferrous chloride is added at the inlet of the rapid-mixing tank. Important: Add before Adjust the pH to ensure even dispersion of Fe²⁺. If alkali is added first, iron hydroxide will precipitate at the pump inlet, causing blockage. The settling agent polymer is added last in the slow-stirring tank.

Stir quickly and slowly

Rapid stirring (G ≈ 300–600 s⁻¹, 30–60 seconds) ensures even chemical dispersion. Slow stirring (G ≈ 20–80 s⁻¹, 15–30 minutes) allows the adhesive floc to bind into larger flocs without being broken by shear forces. These parameters are for reference only—adjustments are needed for each system.

Settling time, sludge discharge, and output control.

Settling time in vertical or inclined settling tanks (lamella) is typically 1–4 hours. Sludge is discharged periodically 2–4 times/day to prevent anaerobic fermentation that causes odor. The effluent water is tested for TSS, color, and pH before discharge. Based on Loc Thien's 10 years of experience, B2B clients achieve better results when combining ferrous sulfate with settling polymers and maintaining regular jar tests.

Technical specifications for FeCl2 25–30% (for reference)

Sensitive values ​​(% Fe²⁺ actual, density, pH) need to be confirmed via COA/MSDS for each batch.

Certificates of Origin/Quality, MSDS, and VAT invoices.

B2B customers require complete CO, CQ, MSDS/SDS and VAT invoices — Loc Thien provides a full set of documents for each shipment.

Safety precautions, storage, and transportation of FeCl2

Compatibility of container materials

Compatible materials: HDPE, PP, PVC, CPVC, PVDF, FRP, 316L stainless steel. Not suitable for: carbon steel, cast iron, copper, aluminum, unlined concrete. Gaskets and pump diaphragms should be Viton or PTFE. Using the wrong material will cause rapid corrosion, leaks, and chemical contamination.

Personal protective equipment (PPE)

• Full-face safety glasses or a full-face mask.
• Nitrile gloves (≥0,3mm) or chemical-resistant neoprene gloves
• Acid-resistant apron or clothing; plastic safety boots
• Confined spaces / high vapor concentrations: ABEK1 air filter mask

Workplaces require emergency eyewash and chemical showers. Eye or skin contact: rinse with clean water for ≥15 minutes and seek immediate medical attention.

Nationwide shipping in accordance with hazardous goods regulations.

Liquid ferric sulfate is a hazardous material (Decree 34/2024/ND-CP): vehicles must have proper signage, and drivers must be trained. Storage facilities must be well-ventilated, have spill collection systems, and be kept away from heat sources and oxidizing agents.

Frequently Asked Questions When Buying FeCl2 for Wastewater Treatment

Where to buy reliable FeCl2? Contact Loc Thien.

Choosing the right ferric sulfate supplier isn't just about price — it's also about consistent quality, complete documentation, and technical support. Here are 3 reasons why B2B businesses trust Loc Thien:

• Complete CO/CQ and MSDS documents are provided for each batch: Compliant with ISO certification, environmental audits, and hazardous chemical legal requirements.
• Nationwide delivery in accordance with regulations for transporting hazardous goods: Goods arrive safely, on time, and properly packaged — no worries about shipping problems.
• Technical support and consultation for jar testing and chemical combination: The technical team assisted in designing the jar test, combining FeCl2 + polymer + pH adjustment to optimize the system.

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