Zinc ions (Zn²⁺) in water

Abstract: Zinc ions (Zn²⁺) in water
Sources:

Anthropogenic sources: Corrosion of galvanized pipes and fittings, industrial discharges (metal plating, mining, battery manufacturing).

Natural sources: Weathering of zinc-bearing minerals such as sphalerite (ZnS).

Chemical Properties and Appearance:

Solubility varies with pH: Highly soluble as Zn²⁺(aq) in acidic water; forms insoluble, turbid white zinc hydroxide (Zn(OH)₂) precipitate under alkaline conditions (pH > ~8).

In neutral water: May exist as soluble forms like Zn²⁺(aq) and ZnOH⁺(aq), but may precipitate or adsorb onto particle surfaces over time.

Health and Aesthetic Effects:

Health: An essential nutrient, but acute ingestion of water containing >5 mg/L zinc may cause gastrointestinal discomfort (nausea, cramps, vomiting).

Aesthetics: Produces a bitter metallic taste at concentrations exceeding 2-3 mg/L. Zinc hydroxide precipitation causes milky turbidity (cloudiness).

Regulatory Limits (Guidelines):

Primarily regulated as a secondary (sensory) contaminant.

WHO/EPA Secondary Standard: 5 mg/L (based on taste).

Stricter Guidelines: Some countries (e.g., China) set lower limits (e.g., drinking water standard of 1.0 mg/L).

Removal Methods:

Effective Methods: Ion exchange, reverse osmosis, distillation, and chemical precipitation/flocculation (common in industrial wastewater treatment).

Ineffective Methods: Boiling water does not remove zinc and may increase concentrations due to evaporation.

Environmental Impact:

Aquatic Toxicity: High concentrations of Zn²⁺ are toxic to fish, invertebrates, and algae, disrupting ecosystems. Zinc is a persistent bioaccumulative metal.

Key Additions/Clarifications Based on Original Text:
Pipe Corrosion Mechanism: Mentioning galvanized pipes is crucial. Soft water and acidic water accelerate corrosion by dissolving the protective zinc coating and releasing ions.

Lead Association: In older galvanized pipe residences, zinc corrosion may indicate potential lead contamination risks, as lead was widely used in solder and fittings.

Precipitation Explanation: Turbidity from Zn(OH)₂ often appears when water contacts air, as carbon dioxide release raises pH.

Treatment Considerations: Boiling does not remove zinc. However, if zinc exists as a solid precipitate (e.g., hydroxide), particulate matter can be filtered out using a 1-micron sediment filter cartridge.