Removing zinc from water

Characteristics and risk control of zinc

Source characteristics:

Zinc content in galvanizing process wastewater: 50-200mg/L

Peak zinc concentration in metal processing wastewater: ≥500mg/L

Health threshold:

Drinking water zinc limit: ≤5.0mg/L (GB 5749-2022)

Acute toxicity concentration: >30mg/L causes gastroenteritis

Core treatment process

1. Ion exchange system

Operation mechanism:

Strong acid cationic resin (Na⁺ type) captures Zn²⁺ through ion exchange:

TEXT

2R-SO₃Na + Zn²⁺ → (R-SO₃)₂Zn + 2Na⁺

Technical points:

Penetration capacity: 40-60g Zn²⁺/L resin

Regeneration requirements: 8-10% NaCl solution, flow rate 4-6BV/h

Water quality adjustment:

The treated water needs to be mixed with the raw water at a ratio of 1:3 to maintain hardness >50mg CaCO₃/L

2. Reverse osmosis technology

Membrane separation performance:

Polyamide composite membrane Zn²⁺ retention rate: >98.5%

Operating pressure: 1.5-4.0MPa (adjusted according to TDS)

Application scenarios:

Electroplating rinse water reuse (water zinc <0.1mg/L)

Pharmaceutical ultrapure water preparation (supporting EDI fine treatment)

Engineering economic comparison

Data of a pilot project in an electroplating park

Process Investment cost Energy consumption per ton of water Zinc removal rate

Ion exchange ¥3.8 million 0.25kWh 99.8%

Reverse osmosis ¥6.2 million 1.8kWh 99.2%

Chemical precipitation ¥2.1 million 0.15kWh 97.5%

(Note: treatment scale 1000m³/d, inlet zinc concentration 85mg/L)

Key points of technical implementation

Ion exchange resin calcium penetration warning:

Set calcium online monitoring (response threshold>5mg/L)

Automatically trigger regeneration program to prevent zinc leakage

Reverse osmosis system anti-scaling measures:

Maintain LSI index <0.5 (antiscalant dosage 2-5ppm)

Regular citric acid cleaning (frequency ≤3 times/year)

All about water...