Aragaw Tadele Assefa, Angerasa Fikiru Temesgen
Faculty of Chemical and Food Engineering, Bahir Dar Institute of Technology, Bahir Dar University, Bahir Dar, Ethiopia.
Heliyon. 2020 Sep 19;6(9):e04975. doi: 10.1016/j.heliyon.2020.e04975. eCollection 2020 Sep.
In the present research, the kaolin adsorbents (beneficiated, raw powder, and calcined) were prepared from Ethiopian natural kaolin through mechanical, wet, and thermal processes. The geochemical and surface properties of kaolin adsorbent were characterized using FTIR, SEM/EDS, XRD, and XRF. In the batch experiment, basic operation parameters (initial dye concentrations, pH, temperature, contact time, and adsorbent dosage) were examined. Percentage removal efficiency basic yellow 28 (BY28) dye were recorded as 94.79%, 92.08%, and 87.08% onto beneficiated, raw, and calcined kaolin absorbents, respectively at an initial dye concentration of 20 mg/L, solution pH of 9, the temperature of 30 °C , and contact time of 60 min and adsorbent dosage of 1g/100L. The molar ratio of SiO/AlO was recorded as 2.911 Percent mass composition of Ethiopian kaolin which is higher than the expected pure kaolinite standard which allows us to classify the kaolin clay as a siliceous one. The calculated values of for beneficiated adsorbent are -1.243, 1.576, and 4.396 kJ/mol at 303.15, 323.15, and 343.15 K, respectively for 20 mg/L of dye concentration and solution pH of 9, suggests that the thermodynamic behavior at lowest temperature is more feasible and spontaneous as compared with the higher temperature one. A similar fashion was calculated for raw and calcined adsorbents. The negative values of ΔH and ΔS° suggest that the adsorption phenomenon is exothermic and the adsorbate molecules are organized on the solid phase in a more disordered fashion than the liquid phase. The pseudo-first-order and pseudo-second-order models have been used to describe the kinetics in the adsorption processes. The Pseudo-second-order model has been fitted for the BY 28 dye adsorption in the studied concentration range. The adsorption of BY 28 dye for raw and calcined adsorbents follows the Langmuir isotherm and the Freundlich isotherm fitted for the beneficiated adsorbent. The amount of BY28 dye taken up by beneficiated, raw, and calcined kaolin adsorbents was found as 1.896, 1.842, and 1.742 mg/g, respectively at a contact time of 1.0 h, the adsorbent dosage of 1.0 g, initial dye concentration = 20 mg/L and solution pH = 9 at 30 °C. The results found that these raw and prepared local kaolin adsorbents have a capacity as low-cost alternatives for the removal of dyes in industrial wastewater.
在本研究中，通过机械、湿法和热法工艺，以埃塞俄比亚天然高岭土制备了高岭土吸附剂（精选高岭土、高岭土原粉和煅烧高岭土）。利用傅里叶变换红外光谱（FTIR）、扫描电子显微镜/能谱仪（SEM/EDS）、X射线衍射仪（XRD）和X射线荧光光谱仪（XRF）对高岭土吸附剂的地球化学和表面性质进行了表征。在间歇实验中，考察了基本操作参数（初始染料浓度、pH值、温度、接触时间和吸附剂用量）。在初始染料浓度为20mg/L、溶液pH值为9、温度为30℃、接触时间为60min且吸附剂用量为1g/100L的条件下，精选高岭土、高岭土原粉和煅烧高岭土吸附剂对碱性黄28（BY28）染料的去除率分别为94.79%、92.08%和87.08%。埃塞俄比亚高岭土的SiO/AlO摩尔比为2.911，其质量组成百分比高于预期的纯高岭石标准，这使我们能够将高岭土归类为硅质高岭土。对于精选吸附剂，在303.15K、323.15K和343.15K时，染料浓度为20mg/L且溶液pH值为9的条件下，计算得到的 值分别为-1.243、1.576和4.396kJ/mol，这表明与较高温度相比，最低温度下的热力学行为更可行且自发。对高岭土原粉和煅烧吸附剂也进行了类似的计算。ΔH和ΔS°的负值表明吸附现象是放热的，且吸附质分子在固相中比在液相中以更无序的方式排列。采用伪一级和伪二级模型来描述吸附过程中的动力学。在所研究的浓度范围内，伪二级模型适用于BY 28染料的吸附。在接触时间为1.0h、吸附剂用量为1.0g、初始染料浓度 = 20mg/L、溶液pH = 9且温度为30℃的条件下，精选高岭土、高岭土原粉和煅烧高岭土吸附剂对BY28染料的吸附量分别为1.896mg/g、1.842mg/g和1.742mg/g。结果发现，这些天然和制备的当地高岭土吸附剂有能力作为低成本替代品用于去除工业废水中 的染料。
