Optimized preparation of hydroxyapatite-modified carbonized rice husk and its adsorption property for Cr(VI) ions

Rice husk (RH) is one of the widespread agricultural waste materials in the world. At present, most of the husks are either burned out or thrown away as waste, causing serious environmen-tal pollution. This study prepared the hydroxyapatite-modified carbonized rice husk (HAP@ CRH) nanocomposites from rice husk (RH) with modifications, aiming to explore the feasibility of preparing heavy metal ion sorbents. The preparation process affecting its adsorption proper-ties on Cr(VI) ions was systematically investigated, which was optimized by carbonizing RH at 600 degrees C for 2.0 h to produce CRH and then depositing hydroxyapatite particles on the surface of CRH with a Ca2+/CRH ratio of 0.2 g/g. The physiochemical properties of samples were char-acterized. After modifications to be HAP@CRH, the surface presented a honeycomb-like struc-ture as its porosity increased. The Brunauer-Emmett-Teller specific surface area increased from 1.06 m2/g (RH) to 193.64 m2/g (CRH) and 183.91 m2/g (HAP@CRH) respectively, the total pore vol-ume increased from almost zero to 0.089 and 0.202 cm3/g, respectively. The results demonstrated the effective adsorption property of HAP@CRH for Cr(VI) ions as the removal rate of 98.57% and the adsorption amount of 5.91 mg/g were achieved within 24.0 h with adsorbent dosages of 5.0 g/L for initial Cr(VI) concentration of 30 mg/L at 30 degrees C and pH 2.0. This study is expected to promote the utilization of wasted rice husk biomass and provide a new economic and feasible adsorption material for wastewater treatment so as to achieve the purpose of treating waste with waste.