Effect of humic acids on pentachlorophenol sorption to cetyltrimethylammonium-modified, Fe- and Al-pillared montmorillonites

Because natural organic matter is commonly present in surface water and might interfere with the removal of organic contaminants, we investigated the effect of humic acids (HA) on the adsorption of pentachlorophenol (PCP). The sorbents are synthetic clay compounds: surfactant-modified pillared montmorillonite (SMPM). First the cation exchange sites of an Algerian bentonite were blocked by intercalation of metallic polycations from either Fe(III) or Al(III); then cetyltrimethylammonium cations were adsorbed in order to obtain two hydrophobic and organophilic clay compounds. According to batch adsorption isotherms in single systems, both PCP and HA sorptions increased when pH decreased, especially for Fe-SMPM in comparison with inorganic pillared clays without cationic surfactant. The Fe-SMPM was more effective than the Al-SMPM for PCP sorption: at pH 6, the maximum PCP sorption capacities were 530 mg g− 1vs. 300 mg g− 1, respectively. From data treatment with an extended Freundlich model, in binary systems at pH 6 and at various PCP/HA ratio (ranging between 1/4 and 4/1 g g− 1), the competition affected both forms of SMPM quite strongly. In addition, the competition between PCP and HA was more important for the Fe-SMPM than the Al-SMPM, with respective maximum PCP sorption capacities of 133 vs. 53 mg g− 1. Due to their high thermal stability and efficiency towards organic compounds, SMPM may have environmental applications in treating surface water and wastewater for the removal of organic pollutants such as chlorinated phenols.

Research highlights
► The Fe-SMPM was more effective than the Al-SMPM for PCP sorption.
► In PCP/HA binary systems, the competition affected both forms of SMPM quite strongly.
► Competition between PCP and HA was more important for the Fe-SMPM than the Al-SMPM.