Enhancement of the anionic dye adsorption capacity of clinoptilolite by Fe3+-grafting

- Iron-grafted clinoptilolite was found to have higher adsorption capacity than that of raw clinoptilolite.
- Iron-grafted clinoptilolite can be used as an efficient adsorbent for the removal of congo red at near-neutral pH.
- pH dependency of adsorption process is different for raw and modified clinoptilolites.