Recycling of LCW produced form water plants for synthesizing of nano FeO(OH), Al(OH)3, and layered double hydroxide: Effect of heat-treatment

Abstract Liquid concentrate waste (LCW) is a high concentrated liquid produced as a by-product from water plants. It contains huge amounts of aluminum and iron residues. Its disposal causes many environmental problems, so it is significant to recycle this waste for production of interested nano materials such as FeO(OH) or Fe2O3·H2O, Al(OH)3 and layered double hydroxide (LDH) to be used for different applications. In the present work, these materials were chemically prepared using suitable chemicals and under appropriate conditions to get nano powders. The synthesized Al(OH)3 was utilized for preparation of Mg-Al-LDH in the presence of magnesium salt. The synthesized nano powders were investigated by X-ray diffraction (XRD), fourier transform infrared (FTIR), transmission electron microscope (TEM) and scanning electron microscope (SEM). The crystallite size was also calculated using XRD data by Scherrer equation. Effect of temperature up to 1000 °C on the phase composition and morphology of LDH was also studied. The results revealed that well crystalline Al(OH)3 and weak crystalline FeO(OH) nano powders were successfully synthesized by the suggested chemical method. Al(OH)3 exhibited ultrafine, fiber-like crystalline forms consisted of tiny hexagonal-like plates with size of about 30 nm, whileas FeO(OH) exhibited hexagonal prism particles with size of about 60 nm. Well crystalline hexagonal plate LDH having size of 80 nm was obtained after precipitation at 75 °C; its crystallinity was increased after hydrothermally treated at 140 and 180 °C. LDH having gel structure with very small particles was obtained at 180 °C. Heat treatment of LDH up to 1000 °C led to dissociation with the formation MgAl2O4 spinel. Grain growth was happened after heat treatment but the size was still in the nano range.