Paper waste sludge derived-hydrochar modified by iron (III) chloride for effective removal of Cr(VI) from aqueous solution: Kinetic and isotherm studies

• DOI: 10.1016/j.jwpe.2020.101877
• Publication Date: 2020-12-25T10:37:22Z
• Authors: Lan Huong Nguyen; Huu Tap Van; Quang Trung Nguyen; Thu Huong Nguyen; Thi Bich Lien Nguyen; Van Quang Nguyen; Thu Uyen Bui; Hung Le Sy
• Keywords: 01 natural sciences; 6. Clean water; 0105 earth and related environmental sciences

Abstract This work investigated Cr(VI) adsorption onto pristine and iron modified hydrochar (PSH and PSH-Fe15, respectively) which were generated from paper waste sludge. The results indicate that the hydrothermal carbonization temperature of 200 °C was the most suitable for hydrochar production. The batch experiments and the adsorption isotherm and kinetic of Cr(VI) onto PSH and PSH-Fe15 were conducted and used to elucidate the adsorption mechanisms. The results demonstrate that the Cr(VI) adsorption capacity and efficiency onto both PSH and PSH-Fe15 reached equilibrium after 120 min at pH 3 and an initial Cr(VI) concentration of 60 mg/L. In this condition, the adsorption capacities were 5.94 mg/g and 8.67 mg/g and the removal efficiencies were 39.62 % and 57.80 % for PSH and PSH-Fe15, respectively. The adsorption processes were well described by the Sips and Redlich–Peterson isotherm models (with R2 of 0.9895, 0.9987 and 0.9947 and 0.9981 for PSH and PSH-Fe15, respectively) and pseudo-second-order kinetic model (with R2 of 0.98412 and 0.99681, respectively, for PSH and PSH-Fe15). The analysis of characteristics of PSH and PSH-Fe15 indicates the rough and heterogamous surface structures. Moreover, there was presence of iron ions on PSH-Fe15 based on EDS analysis and appearance of oxygen-containing surface functional groups recorded through FTIR results. Finally, it was observed that the reduction of Cr(VI) to Cr(III) caused by iron ions on PSM-Fe15’s surface and the presence of O H groups resulting in the precipitation of Cr(OH)3 on the hydrochar’s surface was the main mechanism of Cr(VI) adsorption onto PSH-Fe15.