High efficiency adsorption of uranium in solution with magnesium oxide embedded horse manure-derived biochar

In this study, three kinds of horse manure-derived biochars (HMBM-300, HMBM-500 and HMBM-700) were obtained by calcination of an active horse manure loaded with magnesium chloride in nitrogen at different temperatures (300, 500 and 700 °C). Compared with HMBM-300 and HMBM-700, the Mg 2+ in HMBM-500 was completely converted into MgO and no agglomeration of minerals onto HMBM-500 was observed, which led to the existence of abundant active adsorption sites on the surface of HMBM-500. Therefore, HMBM-500 possessed an excellent adsorption performance for uranium species in solution with a short equilibrium time (< 50 min), a fast adsorption rate (5.23 mg/(g·min)), a large adsorption capacity (625.8 mg/g) and a high removal efficiency (98.7%). In other words, the adsorption ability of the magnesium oxide embedded horse manure-derived biochar could be improved by selecting an appropriate calcination temperature. Besides, the adsorption characteristics of the HMBM-500 to uranium could be kept with environmentally interferences, such as coexisting ions and pH, which meant that the horse manure-derived biochar could be appropriate for treating the actual wastewater. Furthermore, the electrostatic interaction, surface complexation and precipitation were proven to play an important role in the adsorption behavior of uranium on HMBM-500 via multiple characterizations and it could be inferred that the high adsorption performance of HMBM-500 was attributed to the coordination and precipitation to uranium with surface active sites. This work showed that the surface modification of biochar was decisive for developing the adsorbents for uranium with high performance. • Horse manure was converted into biochar to improve its utilization. • Mg-composited biochar benefitted the removal of U 6 species from wastewater. • The maximum adsorption capacity of U 6 on HMBM-500 was 625.8 mg/g. • The interaction mechanism between U 6 and HMBM-500 was further explored.