褐煤、热改性褐煤和钙/镁改性褐煤用于磷酸盐修复。
Lignite, thermally-modified and Ca/Mg-modified lignite for phosphate remediation.
机构信息
Department of Chemistry, Mississippi State University, Mississippi State, MS, USA.
Department of Engineering Management and Systems Engineering, The George Washington University, Washington, DC, USA.
出版信息
Sci Total Environ. 2021 Jun 15;773:145631. doi: 10.1016/j.scitotenv.2021.145631. Epub 2021 Feb 5.
Aqueous phosphate uptake is needed to reduce global eutrophication. Negatively charged adsorbent surfaces usually give poor phosphate sorption. Chemically- and thermally-modified lignite (CTL) was prepared by impregnating low-cost lignite (RL) with Ca and Mg cations, basified with KOH (pH ̴ 13.9), followed by a 1 h 600 °C pyrolysis under nitrogen. CTL has a positive surface (PZC = 13) due to basic surface Ca and Mg compounds, facilitating the aqueous phosphate uptake. CaCO, MgO, Ca(OH), and Mg(OH) surface phases with 0.22 μm particle sizes were verified by XRD, XPS, SEM, TEM, and EDX before and after phosphate uptake. Higher amounts of these mineral phases promoted more CTL phosphate uptake than raw lignite (RL) and thermally treated lignite (TL) without Ca/Mg modification. Phosphorous uptake by Ca/Mg occurs not by classic adsorption but by stochiometric precipitation of Mg(PO), MgHPO, Ca(PO), and CaHPO. This offers the potential of substantial uptake capacities. CTL's phosphate removal is pH-dependent; the optimum pH was 2.2. Water-washed CTL exhibited a maximum Langmuir phosphate uptake capacity of 15.5 mg/g at pH 7, 6 and 14 times higher than that of TL and RL, respectively (particle size <150 μm, adsorbent dose 50 mg, 25 mL of 25-1000 ppm phosphate concentration, 24 h, 25 °C). The unwashed CTL exhibited a maximum Langmuir phosphate removal capacity (80.6 mg/g), 5.2-times greater than the washed CTL (15.5 mg/g). Insoluble Ca and Mg phosphates/hydrophosphate particles dominated CTL's phosphate removal. Phosphates were recovered from both exhausted unwashed and washed CTL better in HCl than in NaOH. P-laden washed CTL exhibited a slow phosphate leaching rate under initial pH of 6.5-7.5 (52-57% over 20 days) after phosphate uptake, indicating it could serve as a slow-release fertilizer. Unwashed CTL retained more phosphates than washed CTL (cumulative q for 4 cycles = 391.8 mg/g vs 374.7 mg/g) and potentially improves soil fertility more.
为了减少全球富营养化，需要吸收水中的磷酸盐。带负电荷的吸附剂表面通常对磷酸盐的吸附效果不佳。通过用 Ca 和 Mg 阳离子浸渍低成本褐煤 (RL)、用 KOH 碱化 (pH~13.9)、然后在氮气下 600°C 热解 1 小时来制备化学和热改性褐煤 (CTL)。CTL 具有正表面 (PZC=13)，因为表面存在碱性的 Ca 和 Mg 化合物，有利于水相磷酸盐的吸收。通过 XRD、XPS、SEM、TEM 和 EDX 在吸收磷酸盐前后对 0.22μm 粒径的 CaCO、MgO、Ca(OH)和 Mg(OH)表面相进行了验证。与原始褐煤 (RL)和未经 Ca/Mg 改性的热处理褐煤 (TL)相比，这些矿物相的含量越高，CTL 对磷酸盐的吸收就越多。Ca/Mg 通过化学计量沉淀 Mg(PO)、MgHPO、Ca(PO)和 CaHPO 来吸收磷，而不是通过经典的吸附作用。这提供了大量吸收容量的潜力。CTL 的磷酸盐去除取决于 pH 值；最佳 pH 值为 2.2。水洗后的 CTL 在 pH 为 7 时对磷酸盐的最大 Langmuir 吸收容量为 15.5mg/g，分别比 TL 和 RL 高 6 倍和 14 倍（粒径<150μm，吸附剂剂量 50mg，25mL 浓度为 25-1000ppm 的磷酸盐，24h，25°C）。未水洗的 CTL 表现出最大的 Langmuir 磷酸盐去除容量（80.6mg/g），是水洗 CTL（15.5mg/g）的 5.2 倍。不溶性 Ca 和 Mg 磷酸盐/磷酸氢盐颗粒主导着 CTL 的磷酸盐去除。用过的未水洗和水洗的 CTL 在 HCl 中比在 NaOH 中更容易回收磷酸盐。在初始 pH 为 6.5-7.5 下，负载磷的水洗 CTL 表现出缓慢的磷酸盐浸出率（20 天内为 52-57%），表明它可用作缓释肥料。未水洗的 CTL 比水洗的 CTL 保留更多的磷酸盐（4 个循环的累积 q=391.8mg/g 与 374.7mg/g），并且更有可能提高土壤肥力。
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