| Resource & environmental sciences |
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| Preparation of biochars from coconut fiber and coconut shell and their adsorption for Pb2+ in solution |
| LAN Tian1,2, CHU Yingchao1, ZHANG Lingling1, ZHAO Wen1, PAN Yunzhou1,2, ZHANG Jiawei1, ZHU Zhiqiang1, WU Weidong1* |
| (1. Key Laboratory of Protection and Development Utilization of Tropical Crop Germplasm Resources, Ministry of Education, Hainan University, Haikou 570228, China; 2. Hainan Key Laboratory of Arable Land Conservation, Hainan Academy of Agricultural Sciences, Haikou 571100, China) |
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Abstract Heavy metal pollution has become more and more serious with the development of industry. Heavy metals can accumulate in plants, and enter into human body through the food chain. Lead (Pb) is one of the most common heavy metal contaminants in the environment, usually discharged with waste water and waste gas. Accumulation of lead in the body can cause physical function disorder, and it is even more harmful to children. Therefore, it is very urgent to control the lead pollution. As a new type of adsorbent for soil heavy metal, biochar has a great advantage compared with other traditional materials. Biomass-derived biochar combines an effective removal of water contaminants with low cost of remediation. Many researchers used waste biomass crops and other materials to make biochar by pyrolysis at high temperature to remove heavy metals. The water movement on the biochar pores is affected by metal adsorption, which is a novel and promising technique to identify the nature of biochar-metal bonds at the solid-liquid interface.
However, few researches were reported using common tropical biomass waste such as coconut shell and coconut fiber to prepare biochars. The coconut fiber become thick after matured, and the loose brown fibrous layers are soft and elastic, mainly are composed of hard stratum corneum. The coconut shell and coconut fiber are abundant, cheap and easy to collect in Hainan Province. Therefore, study on the adsorption of lead by biochars prepared from coconut shell and coconut fiber has a great significance to control heavy metal pollution. The objectives of this study were to: 1) characterize the biochars prepared from coconut shell and coconut fiber under different temperatures; 2) determine the adsorption characteristics and mechanisms of Pb2+ on biochars.
Biochars were prepared by pyrolyzing coconut fiber and coconut shell at the temperatures of 300, 500 and 700 ℃ respectively, and their physical and chemical properties were analyzed.
The results of Fourier transform infrared spectroscopy and element contents indicated that, the carbonation degree of the biochars increased with the pyrolysis temperature, while the amount of oxygen-containing functional groups decreased. In addition, the surface area, ash content, pH, cation exchange capacity (CEC) and basic functional group content enriched with the pyrolysis temperature. The adsorption of Pb2+ by biochars derived from coconut fiber and coconut shell was fitted better with Langmuir model. As the pyrolysis temperature increased from 300 to 700 ℃, the amount of Pb2+ adsorbed on the biochars gradually increased. Among the six kinds of biochars, the coconut fiber biochar prepared at 700 ℃ had the highest adsorption amount of 180.438 mg/g, which was better than many adsorption materials that reported previously. The CEC and ash content were important factors affecting the adsorption deduced from the fit curve. Under the condition of initial Pb2+ concentration with 200 mg/L, the saturated adsorption amounts of coconut fiber and coconut shell biochars were 44.89-96.08 mg/g and 15.82-61.77 mg/g, respectively. The saturated adsorption amount of coconut fiber biochars was higher than that of the coconut shell biochars. However, the stable adsorption amounts of coconut fiber and coconut shell biochars were 9.83-13.91 mg/g and 9.68-25.16 mg/g, respectively.
In conclusion, the different preparation temperatures can directly affect the physical and chemical properties of biochars. Different raw material sources and pyrolysis temperatures have a great influence on the adsorption capacity of Pb2+, and the largest amount of lead adsorption material is YA700 (180.438 mg/g). In addition, different raw material sources and pyrolysis temperatures have a great influence on the stable adsorption quantity of lead, and the adsorption of Pb2+ on the coconut shell biochar is more stable than coconut fiber biochar.
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Published: 20 July 2016
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椰衣和椰壳生物质炭的制备及其对溶液中Pb2+的吸附
以椰衣和椰壳作为原材料，在300、500和700 ℃条件下热解制备生物质炭，表征其物理化学性质；同时，研究所制备的生物质炭对溶液中Pb2+的吸附特征与机制。结果表明：随着热解温度升高，所制备的生物质炭的含氧官能团减少，灰分、pH值、阳离子交换量、比表面积和碱性官能团的含量随之升高。热解温度升高可促进生物质炭对Pb2+的吸附；Langmuir模型可较好地描述所制备的生物质炭对Pb2+的等温吸附；在供试的6种生物质炭中，吸附量最高的是在700 ℃条件下制备的椰衣生物质炭，且优于大多数已报道的用其他材料制备的生物质炭。拟合发现，所制备的生物质炭的阳离子交换量和灰分含量是影响其吸附Pb2+的重要因子，在初始Pb2+质量浓度为200 mg/L条件下，椰衣生物质炭对Pb2+的稳定吸附量为9.83~13.91 mg/g，椰壳生物质炭为9.68~25.16 mg/g。这表明椰壳生物质炭吸附态Pb2+比椰衣生物质炭吸附态Pb2+更稳定。
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