In chemical industry and industrial production, chelating agents are added to convert metal ions into chelates with completely different properties. This is the main method to reduce and control the concentration of metal ions.
Chelates are widely used in mineral flotation, hydrometallurgy, extraction and separation of metallic elements, catalytic synthesis, water softening, electroplating, pharmaceuticals, and dyeing processes.
They are also applied in bleaching with hydrogen peroxide and hypochlorite for pulp and paper, including deinking. Some chelating agents are used in medicine for treating poisoning caused by heavy metals such as lead and mercury.
Main Applications:
- Effectively inhibit catalytic decomposition of hydrogen peroxide and hypochlorite bleaching agents by metal ions, thus improving bleaching efficiency, saving chemicals, and reducing costs.
- Strong ability to capture Fe ions, preventing them from reacting with phenolic groups in pulp to form dark-colored complexes. This protects fibers, improves pulp brightness, and reduces yellowing.
- Prevent precipitation caused by Ca²⁺ and Mg²⁺ ions during bleaching, thus avoiding scaling in equipment and pipelines, while gradually removing existing scales.
- Provide dispersing ability to improve the dispersion of sodium silicate.
- Protect pulp fibers by preventing fiber damage caused by NaOH peeling reactions.
- Compared with traditional DTPA, they offer better cost performance.
- Applied in metal separation and purification, textile dyeing, and organic pigment manufacturing.
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Inorganic Chelating Agents
- Polyphosphates
- Sodium tripolyphosphate (STPP): Strong chelation ability for Ca²⁺ and Mg²⁺ ions. Widely used in detergents to soften hard water and improve cleaning efficiency.
- Sodium hexametaphosphate (SHMP): Chelates various metal ions, especially Fe³⁺. Used in the food industry to prevent discoloration and deterioration caused by metal ions (e.g., prolongs juice shelf life).
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Organic Chelating Agents
- Aminocarboxylic Acids
- Ethylenediaminetetraacetic acid (EDTA): The most common chelating agent. Chelates Ca, Mg, Fe, Cu, Zn, etc. Used in titration analysis, industrial water treatment, and as a detox agent for heavy metal poisoning.
- Nitrilotriacetic acid (NTA): Similar to EDTA, with better performance in some applications (e.g., metal surface cleaning, rust removal).
- Hydroxamic Acids
- Benzohydroxamic acid: Strong chelation with Fe, Cu, Pb. Used in mineral flotation (e.g., copper oxide ore beneficiation).
- Salicylhydroxamic acid: Used for extraction and separation of metal ions, particularly rare earths.
- Sulfur-containing Chelating Agents
- Dimercaprol (British anti-Lewisite, BAL): Strong chelator for Hg, As, Sb. Used as a medical antidote for mercury and arsenic poisoning.
- Penicillamine: Chelates Cu, Hg, Pb. Used for treating Wilson’s disease (copper metabolism disorder).
