Novel magnetic nanoadsorbents for wastewater remediation

The tannery, petrochemical and dye manufacturing industries produce large quantities of liquid effluents with heavy metals, dangerous dyes, pigments and hazardous organic compounds. The unappropriated discharge of these... [ view full abstract ]

The tannery, petrochemical and dye manufacturing industries produce large quantities of liquid effluents with heavy metals, dangerous dyes, pigments and hazardous organic compounds. The unappropriated discharge of these wastewaters poses serious threats to the environment due to the adverse effects of their pollutants. The magnetically assisted chemical separation technology have proven to be a very promising tool to remove pollutants from industry effluents because it is efficient, economical, and fast [1]. This work work addresses the removal of Remazol Brilliant Blue R (RBBR), Direct Yellow 12 (DY12) and hexavalent chromium (Cr(VI)) from aqueous solutions using magnetic nanoadsorbents based on ferrite nanoparticles (NP) modified with cetyltrimethylammonium bromide (CTAB). The nanoadsorbents were synthesized using the hydrothermal coprecipitation method in alkaline medium followed by a surface treatment with Fe(NO₃)₃. Controlling the pH of the medium (NaOH or CH₃NH₂), samples composed by nanoparticles of two different mean sizes were produced (7.2 nm and 14.0 nm). The surface modification was carried out by mixing the NP and CTAB in aqueous solution at an appropriate pH with sonication for 15 min leading to CoFe₂O₄@ɣ-Fe₂O₃@CTAB nanoparticles. The influence of pH, contact time and initial pollutant concentration were evaluated from batch studies using 0.7 g/L of the nanoadsorbent. After adsorption, the NP were separated using a hand-held magnet and the final concentration of the pollutants in decanted solution (Fig.1) was determined. The results of the batch studies were analyzed in the framework of Langmuir and Freundlich models to evaluate the maximum adsorption capacity and the extent of affinity. The maximum adsorption of RBBR, DY12 and Cr(VI) occurred at pH 3.0, 5.0 and 2.5 respectively leading to almost 100% of pollutant removal. The pollutants adsorption onto the magnetic adsorbents well followed the pseudo-second-order rate indicating that the rate-limiting step involves electrostatic forces between pollutants and nanoadsorbents. It was evidenced that the maximum adsorption capacity was nearly 50% higher for the nanosorbents of the smaller mean size due to its higher surface area.