Magnetite coated sand adsorbent for Cr(VI) removal from synthetic and pharmaceutical wastewater: adsorption isotherms and kinetics

Abstract

The present study analyzed the removal efficiency of Cr(VI) from synthetic and pharmaceutical wastewater streams using an adsorption technique by magnetite coated sand. In this context, batch experiments were performed using synthetic and pharmaceutical wastewater to analyze the influence of contact time and adsorbent dose on the removal efficiency of Cr(VI) in two different phases. Magnetite nanoparticles (Fe3O4) coated sand adsorbent was prepared by the coprecipitation method. The performances of the two batch reactors treating synthetic and pharmaceutical wastewater were compared to analyze the influence of contact time and adsorbent dose on Cr(VI) removal efficiency. In particular, different conditions of contact time and adsorbate concentration on the sorption process were studied. The adsorbent materials were further characterized by field emission scanning electron microscopy (FESEM), and the analysis of the Cr(VI) was analyzed using an inductively coupled plasma mass spectrometer (ICP-MS). Results obtained from the first phase of the study showed that for initial concentrations of 1 mg/L for both synthetic and pharmaceutical wastes, the remaining concentrations were determined to be 0.022 and 0.029 mg/L, respectively. The kinetic adsorption isotherms models have shown that the adsorbent follows the pseudo-second-order kinetic model. The isotherms were well fitted with Langmuir and Redlich–Peterson model, indicating monolayer adsorption of hexavalent Cr on the magnetite coated sand surface. However, the presence of other adsorbates in pharmaceutical wastewater influences the removal efficiency of Cr(VI) minutely. It can be inferred from the study that the adsorbent can be used for heavy metal treatment in a cost-effective manner since the magnetite is coated on the sand; it eliminates the problem of extraction of nanoparticles from treated wastewater and can be removed by a simple filtration process.