The rare earth wastewater (REW) contains nitrate-nitrogen (NO₃-N) and a large amount of metal ions. The commercial coconut shell biochar (CSHB), corn straw biochar (CSTB), and sawdust biochar (SDB) composites were fabricated by impregnating FeCl₃ solution, AlCl₃ solution, and FeCl₃ and AlCl₃ mixed solution, respectively. These composites were used as sorbents to remove NO₃-N from pretreated REW (PREW). The influence of adsorbent dosage, pH, contact time, and temperature on the NO₃-N removal was examined. Results revealed that Fe–Al impregnated CSHB (Fe–Al/CSHB) and Al-single impregnated CSTB (Al/CSTB) had good performance of NO₃-N at pH 1, with equilibrium adsorption capacity of 1.32 and 0.86 mg g⁻¹ at dosage of 5.3 and 8.0 g L⁻¹, respectively. The adsorption capacity of Fe-Al/CSHB decreased and that of Al/CSTB increased with increasing of temperature. Characterization analysis of the composites indicated that the preparation process induced a layer of FeOOH, Fe₂O₃, Fe²⁺, and Al₂O₃ mixture on the surface of Fe–Al/CSHB, and Al element existed on the surface of Al/CSTB in the form of Al₂O₃. The pseudo-second-order model depicted NO₃-N adsorption kinetics of Fe-Al/CSHB and Al/CSTB well. The electrostatic attraction may be the primary mechanism of NO₃-N adsorption by Fe-Al/CSHB on account of the preferential complexation of Ca²⁺ with –OH (or Fe–O) functional group. Al/CSTB removed NO₃-N by ligand exchange.

稀土废水(REW)含有硝酸盐-氮(NO ₃ -N)和大量金属离子。_{通过分别浸渍FeCl 3}溶液、AlCl ₃溶液以及FeCl ₃和AlCl ₃混合溶液制备商业椰子壳生物炭（CSHB）、玉米秸秆生物炭（CSTB）和锯末生物炭（SDB）复合材料。这些复合材料用作吸附剂以从预处理的 REW (PREW)中去除 NO _{3 -N。}考察了吸附剂用量、pH、接触时间和温度对NO ₃ -N 去除率的影响。结果表明，Fe-Al浸渍CSHB（Fe-Al/CSHB）和Al单浸渍CSTB（Al/CSTB）具有良好的NO _3性能。-N 在 pH 1 下，在 5.3 和 8.0 g L ^-1的剂量下平衡吸附容量分别为 1.32 和 0.86 mg g ^-1。随着温度的升高，Fe-Al/CSHB的吸附量下降，Al/CSTB的吸附量增加。复合材料的表征分析表明，制备过程在Fe-Al/CSHB表面形成了一层FeOOH、Fe ₂ O ₃、Fe ²⁺和Al ₂ O ₃混合物，Al元素存在于Al表面。 /CSTB 形式为 Al ₂ O ₃。伪二阶模型描绘了 NO ₃Fe-Al/CSHB和Al/CSTB的-N吸附动力学良好。^{由于Ca 2+}与-OH（或Fe-O）官能团的优先络合，静电吸引可能是Fe-Al/CSHB吸附NO _{3 -N的主要机制。}Al/CSTB通过配体交换去除NO _{3 -N。}