秸秆炭强化镁镧氧化物对沼液磷的回收效果

为回收沼液中的磷元素，前期研究采用了由镁镧金属离子调控合成的层状双金属氢氧化物（Mg/La0.1-LDO）材料，发现其具有丰富的层间离子和纳米粒子，在磷吸附方面体现了优异性能，但材料回收的分散性及原料成本高等因素降低了其应用价值。该研究利用农作物（水稻、玉米）秸秆固定强化Mg/La0.1-LDO，通过共热解法制备了不同温度（400、500和600 ℃）的秸秆炭镁镧双金属氧化物纳米复合材料（BC-LDO），考察不同条件下制备的BC-LDO对沼液磷的回收能力和机理。结果表明，高温（600 ℃）热解更有助于纳米粒子固定在秸秆炭上，秸秆炭强化镁镧氧化物复合材料（6YBC-LDO）含有丰富的介孔和微孔，更易与磷酸盐结合形成LaPO4沉淀和配体交换形成Mg3(PO4)2内球络合物，6YBC-LDO对磷酸盐具有高度选择吸附性并可多次重复利用，能在30 min内回收沼液中90%的磷，饱和吸附量达366.39 mg/g。将该材料应用于沼气工程沼液磷回收处理中，投加2 g/L吸附剂可去除沼液中90%以上的磷酸盐，表明采用6YBC-LDO处理沼液具有良好应用前景。

Enhanced phosphorus recovery from biogas slurry by biochar of straw with Mg/La oxide

Phosphorus has been widely used as the essential component in the fertilizer and feed of agriculture, but it is a non-renewable resource. Biogas slurry rich in phosphorus can serve as a recyclable agricultural waste resource. Phosphorus recovery from the biogas slurry can be widely expected to realize nutrient management and utilization, particularly for the green and sustainable development of circular agriculture. Therefore, it is necessary to recover the phosphate from the biogas slurry for sustainable agriculture. Alternatively, adsorption is one of the main technologies in nutrient recovery. Different types of adsorbents have been developed to capture phosphate, including biochar, metal-based materials, minerals, functionalized silica, and various modified wastes. Among them, the layered double oxides (LDO) can often be coupled with the biochar-based materials, which are taken as an adsorbent and as a host substance, due to the multiple parent materials. The introduction of biochar materials can improve the recovery rate of phosphorus in a cost-saving way. More importantly, the biochar-based materials with unique pores and abundant surface functional groups can greatly contribute to the pore structure and surface functional group density of composites, where the ions can be highly concentrated in recycled materials. Herein, a new composite adsorbent of biochar-LDO was proposed to recover the nutrient elements from the biogas slurry using adsorption, in order to effectively recover the phosphorus for better resource utilization. The synthesis temperature of composite material was also evaluated to improve the adsorption performance of phosphorus. It was found that the layered bimetallic oxide (Mg/La0.1-LDO) synthesized by the quantitative control of magnesium and lanthanum presented rich interlayer ions and nanoparticles in the early stage, indicating an excellent performance in the phosphorus adsorption. However, the dispersion of nanomaterials in the solution and the high cost of raw materials relatively reduced the value of material recycling and application. Therefore, the straw of crops (rice and corn) was added to fix and strengthen the Mg/La0.1-LDO, where the biochar-magnesium/lanthanum bimetal oxide nanocomposite (BC-LDO) was prepared for the phosphorus recovery from biogas slurry using the co-pyrolysis at different temperatures (400℃, 500℃ and 600℃). The resulting BC-LDO was then characterized to determine the recovery capacity by the SEM-EDX/TEM/FTIR/XRD techniques. The results showed that the pyrolysis at a high temperature (600 ℃) was more conducive to the fixation of nanoparticles on the straw biochar (6YBC-LDO), which was rich in meso- and micro-porous materials. The particle size of the nanocomposite decreased significantly (between 12 and 20 nm), with the increase in pyrolysis temperature. These nanocomposites were also easier to combine with the phosphate to form LaPO4 precipitation and Mg3(PO4)2 inner-sphere complexation. According to the Langmuir equation, the maximum phosphate uptake of 6YBC-LDO was estimated to be 366.39 mg/g, which was significantly higher than that of 5YBC-LDO and 4YBC-LDO. The kinetic investigation showed that the 6YBC-LDO effectively adsorbed the high phosphorus (69 mg/g) within 30 min, and strongly enriched the straw biochar, indicating an excellent phosphate adsorbent. The 6YBC-Mg/La0.1-LDO presented a high selective adsorption capacity for the phosphate, which was reused many times after desorption. The 6YBC-LDO rapidly removed more than 90% phosphate in the biogas slurry, where the phosphate concentration was reduced to less than 8.25 mg/L within 1 h. Consequently, the 6YBC-LDO has an excellent application prospect in the nutrient recovery from the biogas slurry.