Assessment of the improved performance of magnetite-modified vermiculite in the reduction of BTEX and metals, as well as toxicity in petroleum-produced water

Abstract

Petroleum-produced water has raised considerable environmental concerns due to the large amount of contaminants-containing wastewater, generated during petrol and gas extraction. The present work proposes for the first time the use of vermiculite modified by magnetite (Fe3O4) nanoparticles (VMT-mag) as adsorbent for the extraction of metals and BTEX (benzene, toluene, ethylbenzene, and xylene) pollutants and toxicity reduction. Thermally-treated vermiculite was modified by Fe3O4 nanoparticles of 20 nm, which were strongly adhered to the surface, contributing to the magnetization of the material and adsorption of the metals. A 5 min exposure of wastewater to VMT-mag at 15 mg mL−1 led to the removal of 93 % of dissolved organic carbon, 85 % of BTEX compounds, and a reduction of 30–87% of metals (Ba, Al, Ag, Hg and Pb) at low concentration. An investigation was also conducted regarding the efficiency of VMT-mag in reducing toxicity via toxicity assays using the water flea Daphnia similis (ABTN NBR 12713 protocol); the results showed a reduction of Lethal Concentration at 50 % death (LC50) from 5.80 (v/v) to 13.3 % (v/v), respectively, for the samples before and after treatment. The findings show that the application of the proposed VMT-mag can lead to a significant reduction of toxicity and the removal of BTEX and metals in petroleum-produced water.