A comparative study of different materials (drinking water treatment sludge, nanoclay, and modified nanoclay) for simultaneous removal of hexavalent chromium and lead

Abstract

Drinking water treatment sludge in large quantities was generated in the flocculation process of the treatment plant, all over the world. It considered the secondary raw material due to having valuable inorganic compounds such as iron. Herein, a novel green method was developed to recover iron from drinking water treatment sludge for synthesizing nanoscale iron supported on nanoclay by a lemon Beebrush polyphenol. The surface of nanoclay containing iron nanoparticles was modified with ethylenediamine for their applications as heavy metals adsorbent. The field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, thermogravimetric analysis, derivative thermogravimetry, and Fourier-transform infrared spectroscopy techniques were utilized to examine the adsorbents. Based on the results of energy-dispersive X-ray analysis, iron and nitrogen were successfully introduced into the structure of modified nanoclay. A batch adsorption system was used to investigate the simultaneous removal performance of hexavalent chromium and lead onto drinking water treatment sludge, nanoclay, and nanoclay-iron nanoparticle-ethylenediamine. The influence of factors, e.g., initial concentration, contact time, pH, adsorbent dosage, and temperature, were evaluated. The maximum uptake for chromium was 0.303, 0.352, and 0.984 mmol/g and for lead 0.03, 0.042, and 0.108 mmol/g at pH of 3 onto drinking water treatment sludge, nanoclay, and nanoclay-iron nanoparticle-ethylenediamine, respectively. The results show that the quantity of chromium and lead adsorbed onto modified nanoclay was more than 2.5-fold than that adsorbed onto unmodified nanoclay. The equilibrium adsorption data of hexavalent chromium and lead were fitted well with the Langmuir isotherm model (R2 > 0.97). Besides, the pseudo-second-order kinetic model demonstrated the kinetic adsorption of the metal ions. The thermodynamic constants suggested that the adsorption of lead by three adsorbents was exothermic and spontaneous while that of hexavalent chromium was endothermic. It leads to a finding that nanoclay-iron nanoparticle-ethylenediamine could be an effective adsorbent for heavy metals removal from water and wastewater.