What does zeolite bind to when it comes to compounds in the body, like heavy metals and ammonia?

Below is an extensively researched (though practically never 100% exhaustive) list of ions, metals, and molecular species that zeolites have been reported to bind or exchange. The exact binding capacity varies depending on the type of zeolite (e.g., clinoptilolite, mordenite, faujasite, zeolite A, ZSM-5), the pH of the environment, and other conditions. Different zeolites have different pore sizes, Si/Al ratios, and framework structures, all of which affect their affinity for specific ions or molecules. Nonetheless, this list reflects commonly documented species from peer-reviewed literature and standard references (e.g., Kulprathipanja, 2010; Weitkamp & Puppe, 1999; Auerbach et al., 2003).

Alkaline (Group 1) Metal Cations:

• Lithium (Li⁺)

• Sodium (Na⁺)

• Potassium (K⁺)

• Rubidium (Rb⁺)

• Cesium (Cs⁺)

Most zeolites naturally contain and readily exchange Na⁺ or K⁺, but they can also accommodate Li⁺, Rb⁺, and Cs⁺, particularly in ion-exchange applications for nuclear waste or industrial effluents.

Alkaline Earth (Group 2) Metal Cations:

• Magnesium (Mg²⁺)

• Calcium (Ca²⁺)

• Strontium (Sr²⁺)

• Barium (Ba²⁺)

Many natural zeolites (e.g., clinoptilolite) show high affinity for strontium (Sr²⁺) and barium (Ba²⁺), which makes them useful for remediation of radioactive 90Sr, and for softening water (removing Ca²⁺/Mg²⁺).

Transition & Post-Transition Metal Cations:

• Iron (Fe²⁺ and Fe³⁺)

• Copper (Cu⁺ and Cu²⁺)

• Zinc (Zn²⁺)

• Nickel (Ni²⁺)

• Cobalt (Co²⁺)

• Manganese (Mn²⁺)

• Chromium (Cr³⁺)

• Lead (Pb²⁺)

• Cadmium (Cd²⁺)

• Mercury (Hg²⁺)

• Silver (Ag⁺)

• Gold (Au³⁺) – less common but documented in certain ion-exchange studies

• Tin (Sn²⁺ or Sn⁴⁺) – less commonly reported

• Thallium (Tl⁺) – in some specialized research settings

Many of these transition and post-transition metal ions bind to zeolites via ion exchange or complexation in the zeolite framework. This property is exploited in water treatment processes for removing toxic and heavy metals (e.g., Pb²⁺, Cd²⁺, and Hg²⁺).

Ammonium & Other Polyatomic Cations:

• Ammonium (NH₄⁺) – widely recognized removal of ammonia/ammonium from wastewater

• Protonated amines (R–NH₃⁺) – in certain applications, organic cations can be exchanged into zeolite frameworks

Rare Earth & Lanthanide Series Cations:

• Lanthanum (La³⁺)

• Cerium (Ce³⁺ or Ce⁴⁺)

• Europium (Eu³⁺)

• Neodymium (Nd³⁺)

• Gadolinium (Gd³⁺)

• Samarium (Sm³⁺)

• Dysprosium (Dy³⁺)

Molecular & Neutral Species Adsorbed by Zeolites Although the question focuses on ions/metals, zeolites are also famous for adsorbing neutral molecules and gases due to their microporous structure. Notably:

• Water (H₂O) – zeolites are excellent desiccants

• Ammonia (NH₃)

• Hydrogen Sulfide (H₂S)

• Sulfur Dioxide (SO₂)

• Carbon Dioxide (CO₂)

• Nitrogen (N₂) and Oxygen (O₂) – relevant in gas separations

• Light Hydrocarbons (methane, ethane, propane, etc.)

• Volatile Organic Compounds (VOCs) – e.g., benzene, toluene, xylene (especially in hydrophobic high-silica zeolites)

Additional Notes and Caveats:

• Actual binding capacity or “affinity” depends on: – Zeolite structure (pore size, crystallographic channels)

– Si:Al ratio (affects cation exchange capacity)

– Presence of competing ions

– pH and temperature

– Pre-treatment or modification (e.g., acid-activated, metal-exchanged)

• While many metals and ions appear on this list, a single type of zeolite may not bind them all equally well; selectivity differs among zeolite varieties (clinoptilolite versus mordenite, etc.).

• Some of the more exotic or higher-valent ions require specialized conditions to be adsorbed or exchanged effectively.

References for Further Reading:

• Kulprathipanja, S. (Ed.). (2010). Zeolites in Industrial Separation and Catalysis. Wiley-VCH.

• Weitkamp, J., & Puppe, L. (Eds.). (1999). Catalysis and Zeolites: Fundamentals and Applications. Springer.

• Auerbach, S. M., Carrado, K. A., & Dutta, P. K. (Eds.). (2003). Handbook of Zeolite Science and Technology. CRC Press.

• Ming, D. W., & Mumpton, F. A. (Eds.). (1989). Natural Zeolites '89: Occurrence, Properties, Use. Pergamon.