Humic substances are naturally occurring biogenic heterogeneous organic materials that complex strongly with heavy metals and organic compounds . In order to study the sorption characteristics, natural humic acid are isolated, purified, and use in laboratory studies . However, these studies are often thwarted by the fact that it is difficult to separate the humic acid from other moieties present in the solution. A way to avoid this complication is the immobilization of the humic substances on inorganic or water insoluble organic particles that can be separate from their suspension. Covalent grafting of HA on SiO2 provides a promising technique for the production of a stable zero-leaching hybrid material .
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