**2. Preparation of supported chelating agents**

These materials can be made in several ways depending upon the method of linkage that is chosen. The procedures can be placed in three categories. They are covalent linkage, ionic linkage, and London-forces linkages. As an example of the covalent linkage, it is interesting to compare (*vide infra)* two sources: the detail in the patent (Examples 1-4) [14] with a journal article by Gao and co- workers [13], as in the experiments section 2.3 (entitled "Preparing and characterizing of composite absorption particles of PEI/SiO2 ").
