Common metals can be removed from wastewater by which process?

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Multiple Choice

Common metals can be removed from wastewater by which process?

Explanation:
Raising the pH to precipitate metal hydroxides is the practical, bulk method for removing common metals from wastewater. When you add base (like lime or NaOH), metal ions in solution react with hydroxide ions to form metal hydroxide solids: M^(n+) + n OH^- → M(OH)_n(s). These hydroxides are sparingly soluble at higher pH, so they precipitate out and can be separated by settling or filtration. This approach works well for a wide range of metals (iron, copper, zinc, lead, nickel, cadmium, etc.) because it relies on simple chemistry and inexpensive reagents, making it cost-effective for large volumes. Other methods serve different purposes or are less suited for bulk removal. Ion exchange can remove metals but requires resin beds and resin regeneration, which adds cost and complexity. Oxidation targets specific contaminants or redox-sensitive species, not general metal cations. Solvent extraction is a selective separation technique more typical in metal recovery processes and is less practical for disposing large volumes of wastewater.

Raising the pH to precipitate metal hydroxides is the practical, bulk method for removing common metals from wastewater. When you add base (like lime or NaOH), metal ions in solution react with hydroxide ions to form metal hydroxide solids: M^(n+) + n OH^- → M(OH)_n(s). These hydroxides are sparingly soluble at higher pH, so they precipitate out and can be separated by settling or filtration. This approach works well for a wide range of metals (iron, copper, zinc, lead, nickel, cadmium, etc.) because it relies on simple chemistry and inexpensive reagents, making it cost-effective for large volumes.

Other methods serve different purposes or are less suited for bulk removal. Ion exchange can remove metals but requires resin beds and resin regeneration, which adds cost and complexity. Oxidation targets specific contaminants or redox-sensitive species, not general metal cations. Solvent extraction is a selective separation technique more typical in metal recovery processes and is less practical for disposing large volumes of wastewater.

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