Adsorption of heavy metal ions on mesoporous silica-modified montmorillonite containing a grafted chelate ligand

The objective of this work is development of a new adsorbent on the base of an organoclay with a chelating ligand covalently attached to the clay mineral surface. The presence of a chelating ligand in the clay structure significantly improves its ability to immobilize heavy metal ions from contaminated sludge of wastewater. Montmorillonite and kaolinite were chosen as typical examples of expandable and non-expandable clay minerals. A two-step modification procedure comprised of sequential modification with oxides and grafting of a chelating agent to the modified clay minerals was used. Modifications with silica and ferric oxide were conducted by reacting the dispersed raw clay minerals with tetraethoxysilane and ferric nitrate solution. A chelating ligand, N-[3-(trimethoxysilyl)propyl]ethylenediamine triacetic acid trisodium salt, was introduced into interlayer space of raw and modified clay minerals in aqueous solutions. Laboratory tests of the organoclay efficiency for purification of wastewater were conducted with the most promising sample, i.e., organoclay with the highest specific loading of chelating agent. Experiments were conducted with model wastewater containing either individual or mixed heavy metal ions. The modified organoclay displayed high adsorption capacity for heavy metal cations even in acidic media. The method of modification presented in this work can be used for synthesis of efficient adsorbents for applications in contaminated areas.