Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, India.
Environ Sci Pollut Res Int. 2018 Jun;25(18):18161-18178. doi: 10.1007/s11356-018-2025-z. Epub 2018 Apr 25.
Novel defluoridating adsorbent was synthesized by chemical treatment of carbonized bone meal using aluminum sulfate and calcium oxide. Precursor for chemical treatment was prepared by partial carbonization of raw bone meal at 550 °C for 4 h. Maximum fluoride removal capacity was 150 mg/g when carbonized bone meal (100 g/L) was treated with aluminum sulfate (500 g/L) and calcium oxide (15 g/L). Morphological analysis revealed formation of a coating layer consisting of aluminum compounds on the precursor surface. This was verified by stretching frequency of aluminum hydroxide (602 cm) in the infrared spectra. Presence of hydroxylapatite (2θ = 30° and 2θ = 24°) and aluminum mineral phases (2θ = 44°) in the adsorbent were identified from the X-ray diffractograms. Adsorption capacity decreased from 150 mg/g (30 °C) to 120 mg/g (50 °C) indicating exothermic adsorption. Adsorption experiments under batch kinetic mode were simulated using shrinking core model. Effective fluoride diffusivity in the adsorbent and the mass transfer coefficient were estimated as 5.8 × 10 m/s and 9 × 10 m/s, respectively. Desorption was maximum at basic pH and desorption efficiency was decreased by 31% after third cycle. Dynamic filtration with artificially fluoride-spiked solution showed that the empty bed contact time for a packed column with equal weight of carbonized and chemically treated adsorbent was 4.7 min and number of bed volumes treated (till WHO limit of 1.5 mg/L) was 340 for a column of 3-cm diameter and 18-cm length. The system was successfully tested using contaminated groundwater from an affected area. Fixed-bed column experiments were simulated from the first principles using convective pore diffusion-adsorption model for both synthetic solution and contaminated groundwater. Axial dispersion coefficient was found to be one order of magnitude less than the pore diffusivity indicating dominance of fluoride diffusion within porous network of adsorbent. The developed adsorbent exhibited antibacterial property as well.
新型脱氟吸附剂是通过硫酸铝和氧化钙对碳化骨粉进行化学处理合成的。化学处理的前体是通过将原始骨粉在 550°C 下部分碳化 4 小时制备的。当 100g/L 的碳化骨粉用 500g/L 的硫酸铝和 15g/L 的氧化钙处理时，最大氟去除容量为 150mg/g。形态分析表明，在先驱体表面形成了一层由铝化合物组成的涂层。这一点通过红外光谱中氢氧化铝的伸缩频率（602cm）得到了验证。从 X 射线衍射图中可以识别出吸附剂中存在羟基磷灰石（2θ=30°和 2θ=24°）和铝矿物相（2θ=44°）。吸附容量从 150mg/g（30°C）下降到 120mg/g（50°C），表明吸附是放热的。使用收缩核模型对批处理动力学模式下的吸附实验进行模拟。在吸附剂中的有效氟扩散系数和传质系数分别估计为 5.8×10m/s 和 9×10m/s。在碱性 pH 下解吸效果最大，第三次循环后解吸效率降低 31%。用人工含氟溶液进行动态过滤表明，装有等重量碳化和化学处理吸附剂的填充柱的空床接触时间为 4.7 分钟，用直径为 3 厘米、长 18 厘米的填充柱处理的床体积（直到达到世界卫生组织规定的 1.5mg/L 限值）为 340。该系统成功地应用于受影响地区的污染地下水进行了测试。使用对流孔扩散-吸附模型，根据合成溶液和污染地下水的实验数据，从第一性原理出发对固定床柱实验进行了模拟。发现轴向扩散系数比孔扩散系数小一个数量级，表明氟在吸附剂多孔网络内的扩散占主导地位。所开发的吸附剂还具有抗菌性能。
