Fluoride adsorption and photoreduction of Cr(VI) using heterogeneous Al3+ modified mine-waste, an in-situ approach

Abstract

Herein, an in-situ ion-exchange mechanism of fluoride (F‒) uptake of the ore type present in Beldih (23°3'5"N 86°17'46"E, India) exhausted phosphate mines and fabrication of triclinic, pH-stable a cost-effective Al3+ modified nanocomposites using the phosphate mine-waste (MW) materials for F‒ adsorption and the photoreduction of Cr(VI) under Solar irradiation has been demonstrated. The materials were characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Furrier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), ξ-potential study, UV–vis diffuse reflectance spectra (UV–vis DRS), and Brunauer–Emmett–Teller (BET) surface area studies. The F‒ removal efficiency along with the photoreduction ability was highest for the MW2 (MW : Al3+ = 1:2, w/w %) with BET surface area 11.05 m2/g i.e. 80 % for 10 ppm F‒ solution and 81.89 % for 3 ppm Cr(VI) solution at pH 7 respectively. The F‒ removal occurred through chemisorption process revealed from the FTIR and BET isotherm studies. The photoreduction of Cr(VI) to Cr(III) followed the pseudo-1st-order kinetics and the mechanism established through the pH-controlled surface charge model.