Case Study: Wastewater Treatment for Electroplating Using FeCl₂ — 95% Reduction in Cr⁶⁺, 31% Cost Savings

This article is a detailed case study for engineers operating electroplating wastewater treatment systems and industrial chemical buyers seeking cost-effective solutions for Cr6+ removal.

1. Background

The Bien Hoa Industrial Park (Dong Nai) is one of the major electroplating hubs in the Southeast region of Vietnam. Here, dozens of electroplating plants operate daily, discharging wastewater containing significant amounts of heavy metals—among which Cr⁶⁺ (hexavalent chromium) is the most serious pollutant. Cr⁶⁺ is an extremely toxic substance capable of causing cancer, genetic mutations, and liver and kidney damage even at very low concentrations. For this reason, QCVN 40:2011/BTNMT sets very strict limits: the concentration of Cr⁶⁺ in treated industrial wastewater must not exceed 0.1 mg/L (Column B) and 0.05 mg/L (Column A).

An electroplating plant in the Bien Hoa Industrial Park has a treatment capacity of 200 m³ of wastewater per day. The influent wastewater has a Cr⁶⁺ concentration ranging from 15 to 25 mg/L, far exceeding the permissible limit set by QCVN 40:2011/BTNMT (Column B: 0.1 mg/L) —which is 150–250 times the safety threshold. This plant specializes in decorative plating for automotive and motorcycle components; the chrome plating line accounts for 60% of its output, resulting in consistently high Cr⁶⁺ levels in the wastewater. Given this situation, the plant faces the risk of having its operations suspended if it cannot find an effective and stable long-term treatment solution.

2. The Problem

The traditional method the plant had previously used involved using NaHSO₃ (sodium bisulfite) to reduce Cr⁶⁺ to Cr³⁺, followed by adding NaOH to raise the pH to 8–9 to precipitate Cr(OH)₃. However, this approach has several limitations:

With chemical and sludge treatment costs reaching 4,200,000 VND/day, the plant needs a solution that ensures compliant effluent while optimizing operating costs.

3. Solution

After conducting a site survey and a two-week pilot test, the technical team at Lộc Thiên Chemicals proposed switching to FeCl₂ (Iron(II) Chloride) as a replacement for NaHSO₃. Reaction mechanism:

3Fe²⁺ + Cr⁶⁺ → 3Fe³⁺ + Cr³⁺

FeCl₂ reduces Cr⁶⁺ to Cr³⁺ in an acidic environment. Subsequently, 50% NaOH is added to raise the pH to 8.5, simultaneously precipitating Cr(OH)₃ and Fe(OH)₃.

The new process is established as follows:

1. Reaction Tank 1: Add FeCl₂ (38% solution) to the wastewater; maintain pH at 3–4; agitate for 15 minutes
2. Reaction Tank 2: Add 50% NaOH to raise the pH to 8.5, forming a precipitate; agitate for 10 minutes
3. Settling Tank: Anionic polymer aids sedimentation; retention time is 2 hours
4. Neutralization Tank: Adjust the pH to 6–8 before discharging the effluent

The key point is that Lộc Thiên Chemicals supplies FeCl₂ that meets industrial standards, with regular deliveries twice a week from the Đồng Nai warehouse, eliminating the need for the plant to stockpile large quantities of chemicals.

4. Results

After 3 months of stable operation with the new process, the results exceeded expectations:

• The outlet Cr⁶⁺ concentration decreased by 95%, stabilizing below 0.05 mg/L—significantly lower than the QCVN threshold (0.1 mg/L)
• Chemical costs decreased by 31%, equivalent to savings of ~39 million VND/month
• Sludge volume decreased by 25%, resulting in additional savings on sludge dewatering and transportation costs
• Reaction time was reduced by nearly half, increasing the system’s treatment capacity

5. Lessons Learned

1. FeCl₂ is the optimal choice for treating Cr⁶⁺ in electroplating wastewater — it is both technically effective and more cost-efficient than NaHSO₃. For the same amount of Cr⁶⁺ to be reduced, the amount of FeCl₂ required (in moles) is less than that of NaHSO₃, and the cost per kilogram is also significantly lower
2. pH control is a critical factor — FeCl₂ performs optimally at a pH of 3–4, requiring an automatic NaOH dosing system to precisely raise the pH after the reduction reaction. Investing in an automatic pH control system is a worthwhile expense, helping to prevent pH fluctuations that reduce precipitation efficiency.
3. A stable supply is key — High-quality chemicals and on-time delivery ensure continuous, uninterrupted plant operations. With six warehouses stretching from Bac Ninh to Can Tho, Loc Thien Chemicals guarantees delivery within 24 hours to all key regions
4. The combination of FeCl₂ and NaOH creates a complete solution — FeCl₂ reduces Cr⁶⁺ and NaOH precipitates Cr³⁺; they are an inseparable pair in electroplating wastewater treatment. Purchasing both chemicals from the same supplier helps optimize logistics and pricing

Get FeCl2 Solution Consulting for Electroplating Systems

Are you operating an electroplating wastewater treatment system and looking to optimize costs? Get advice from Lộc Thiên’s technical team.

Hotline: 0979 891 929 | Website: hoachatlocthien.com

Please have the following information ready: wastewater flow rate (m³/day) · inlet Cr⁶⁺ concentration · chemicals currently in use · desired budget.

Our Commitment: on-site survey within 48 hours · solution proposal with cost estimate · jar-test support · on-time delivery.

See also:

• FeCl₂ Comprehensive Guide: Properties, Applications & Trusted Suppliers
• FeCl₂ Ferrous Chloride 15-30% — B2B Price Quote

LOC THIEN INVESTMENT AND DEVELOPMENT CO., LTD.

• Address: 452/6B Provincial Road 10, Binh Tri Dong Ward, Binh Tan District, Ho Chi Minh City
• Phone: 028 6269 5669 - 028 6269 5662
• Hotline: 0979 891 929
• Website: hoachatlocthien.com