Removal of lead from solution by using low cost adsorbents from Apiaceae family

Access to clean and safe drinking water is basic right of human. Water contamination by heavy metals such as lead, arsenic, mercury, aluminum, zinc, chromium and iron is a major environmental problem due to their acute toxicity and their accumulation in food chains. One of such toxic heavy metals is lead, which can occur naturally or manufacture from industries such as storage batteries, radiators and solder for joints. World Health Organization (WHO) suggests that the tolerance limit of lead concentration in drinking water is 0.01 mg/l and not over than 0.05 mg/l by Thailand Pollution Control Department (PCD) and the limit of discharge wastewater for lead in Thailand is 0.2 mg/l. Therefore, this research work has been carried out on the feasibility of three low cost adsorbents for the removal of lead from contaminated water. This thesis organized results of the laboratory based studies on lead removal in synthetic water. Plants from Apiaceae family namely parsley, coriander and culantro were selected as low cost adsorbents for the lead adsorptions experiments, and their efficiency was compared with the other studies. Physical and chemical characterization of selected adsorbents were carried out by Brunauer–Emmett–Teller (BET) in order to define the BET surface area, pore volume and average pore size, scanning electron microscope (SEM) for exploring the surface morphological and shape of external cell wall, Fourier Transform Infrared (FTIR) for surface functional groups analysis and Cation Exchange Capacity (CEC) for determine the number of exchangeable cations that adsorbents are capable of holding. The influence of various parameters like adsorbent dose, pH, agitation speed, contact time and initial lead concentration was investigated by a series of batch experiments at 25 ± 3 °C. The percentage removal of lead was found to increase with the increasing dose of adsorbents, agitation speed and time for 10 mg/l initial Pb (II) concentration, whereas the percentage removal of lead was found to decrease with the increase in pH value greater than 4 and lead concentration. Although, it seems that all of parameters affected to the adsorption process, the noticeable parameters are dosage, pH and initial lead concentration. Contact time and agitation speed did not influence much. The maximum lead uptake was found to be 96.61%, 95.95% and 96.55% by parsley, coriander and culantro, respectively. The equilibrium adsorption data after the experiments were designed with appropriate isotherms and kinetic models. The equilibrium data were well described for parsley and coriander by the Langmuir isotherm model, suggesting that the adsorption of Pb(II) onto these adsorbents is a mono-layer process and the adsorption behavior is homogeneous rather than heterogeneous for culantro data fitted well to Freundlich isotherm model indicating heterogeneous in the system. Kinetics data were best fitted by the pseudo second-order model for all of selected adsorbents, indicating that the adsorption process is chemisorption. Moreover, the tea bags were used in the final stage of the experiment. It was found that at neutral of pH and without centrifuge under various contact time with 1 mg/l lead initial concentrations, the lead removal efficiency was found greater than 85% for 12 hrs. contact time and at this suitable time, it found that concentration of lead remaining in synthetic wastewater reached Thailand’s wastewater quality standard. Therefore, three selected adsorbents from Apiaceae family can be used as low cost adsorbents with high efficiency for removing lead at low concentration from wastewater because it can prepare without chemical and physical treatments.获取清洁安全的饮用水是人类的一项基本权利。重金属如铅、砷、汞、铝、锌、铬与铁造成的水体污染是一类重大环境问题，因其具有急性毒性且可在食物链中富集。这类有毒重金属之一便是铅，其可自然存在，也可由蓄电池、散热器及接头焊料等工业生产活动产生。世界卫生组织（World Health Organization, WHO）建议饮用水中铅浓度的耐受限值为0.01 mg/l，而泰国污染控制部（Thailand Pollution Control Department, PCD）规定其限值不得超过0.05 mg/l，泰国对于含铅废水的排放限值则为0.2 mg/l。因此，本研究针对三种低成本吸附剂去除污染水体中铅的可行性展开了探究。本论文整理了合成水体中除铅实验的实验室研究成果。选取伞形科（Apiaceae）的欧芹（parsley）、芫荽（coriander）及刺芫荽（culantro）作为铅吸附实验的低成本吸附剂，并将其吸附效率与其他相关研究进行对比。对所选吸附剂开展了物理与化学表征：采用布鲁诺尔-埃梅特-特勒法（Brunauer–Emmett–Teller, BET）测定比表面积、孔体积与平均孔径；利用扫描电子显微镜（Scanning Electron Microscope, SEM）观测其表面形貌与外部细胞壁形态；通过傅里叶变换红外光谱（Fourier Transform Infrared, FTIR）分析表面官能团；借助阳离子交换容量（Cation Exchange Capacity, CEC）测定吸附剂可容纳的可交换阳离子数量。在25 ± 3 ℃条件下开展一系列批次实验，探究吸附剂投加量、pH值、搅拌速率、接触时间及初始铅浓度等多种参数对吸附过程的影响。在初始Pb(II)浓度为10 mg/L的条件下，铅去除率随吸附剂投加量、搅拌速率与接触时间的增加而提升；而当pH值大于4且初始铅浓度升高时，铅去除率则随之下降。尽管所有参数均对吸附过程存在影响，但影响较为显著的为投加量、pH值与初始铅浓度，接触时间与搅拌速率的影响相对有限。欧芹、芫荽及刺芫荽对铅的最大去除率分别可达96.61%、95.95%与96.55%。实验所得的平衡吸附数据通过合适的等温模型与动力学模型进行拟合。欧芹与芫荽的平衡吸附数据符合朗缪尔（Langmuir）等温线模型，表明这两种吸附剂对Pb(II)的吸附为单分子层过程，吸附行为均一；而刺芫荽的平衡数据则更契合弗雷德里希（Freundlich）等温线模型，说明其吸附体系呈现非均一性。所有所选吸附剂的动力学数据均更符合准二级动力学模型，表明该吸附过程为化学吸附。此外，实验最后阶段采用了茶袋吸附装置。结果显示，在中性pH条件下无需离心，当初始铅浓度为1 mg/L、接触时间达12小时时，铅去除率可达85%以上；且在该适宜接触时间下，合成废水中剩余铅浓度达到了泰国废水水质标准。因此，三种选自伞形科的吸附剂可作为低成本、高效率的吸附剂，用于去除废水中低浓度的铅，且其制备无需通过化学或物理处理。