Removal of BTEX and heavy metals from wastewater by modified smectite clays: ion exchange and adsorption mechanisms

This work reports the use of smectite clays (raw and modified samples) as adsorbents in the adsorption process for removing benzene, toluene, and metal ions present in wastewater generated in the petrochemical industries. Smectite clay was used in the adsorption of organic compounds and in the cation exchange process for the removal of heavy metal ions Cu(II) and Pb(II) as a post-treatment process for refinery effluents. From the chemical treatment of raw smectite clay with sodium carbonate (Na-modified smectite clay, Na-MSC) it has been achieved a good exchange of Ca(II) and Mg(II) ions for Na(I). Moreover, characterization analysis evidenced that the raw smectite and Na-MSC had mesoporous structure. The number of exchangeable ions increased from 81.34 to 89.39 meq 100 g(-1) after Na-addition. The adsorption and cation exchange experiments were conducted in batch mode using the sodium clays as adsorbents in the kinetic and equilibrium study. The isotherm of Langmuir-Freundlich was the most representative, and the adsorption capacity monolayer for benzene and toluene were 7.28 and 7.39 mg g(-1). The ionic exchange model was applied to represent the removal of Cu(II) and Pb(II), which indicated a capacity of 0.99 mg g(-1) and 1.10 mg g(-1) respectively. Kinetic constants obtained for benzene and toluene were 0.0016 L mg(-1) min(-1) and 0.019 L mg(-1) min(-1). Finally, Na-MSC obtained kinetic constants 0.049 L mg(-1) min(-1) and 0.063 L mg(-1) min(-1) for Cu(II) and Pb(II) respectively. The results acquired in batch experiments evidence the high efficiency of Na-MSC to remove BTEX and heavy metals from wastewater.