鸡粪生物炭表征及其对水和土壤镉铅的修复效果

Characteristics of chicken manure biochars and its effect on Cd and Pb remediation in water and soil

采用缺氧控温法,在200、400、600和800℃条件下制备鸡粪生物炭(BC200、BC400、BC600和BC800),利用比表面积及孔径分析仪(BET accelerated surface area and porosimetry system)、扫描电镜(scanning electron microscopy)、透射电镜(transmission electron microscope)、傅里叶红外光谱仪(Fourier transform infrared spectroscopy)等对其理化性质和结构特征进行表征,并研究了鸡粪不同温度处理下生物炭对水体和土壤中Cd、Pb污染修复效果。结果表明,鸡粪生物炭灰分含量、pH值、BET比表面积及孔径随热解温度的升高而增加,表面出现大量无规则的孔隙结构,且以介孔为主,而生物炭产率则随温度升高而显著降低(P<0.05)。鸡粪生物炭对Cd2+、Pb2+的吸附分为快速吸附和慢吸附2个阶段,Elovich模型能更好地模拟Pb^2+、Cd^2+的动力学过程,平衡时最大吸附量分别达到52.02 mg/g (BC600)和242.59 mg/g (BC800)。添加鸡粪生物炭显著提高了土壤pH值(P<0.05),而TCLP提取态Pb、Cd含量降低,最大较对照分别降低16.5%和14.5%。与对照相比,鸡粪生物炭不同程度上降低了Pb、Cd弱酸提取态、可还原态以及可氧化态比例,其残渣态比例则分别增加了5.49%~15.14%和2.51%~6.30%。综上所述,鸡粪生物炭对重金属Pb、Cd具有较强的钝化效果。

Heavy metals in soils are one of the most hazardous pollutants in the environment owing to their universality, concealment and irreversibility. Some universally think harmful heavy metals to mankind and environment are lead, cadmium, copper, zinc, manganese and chromium. They can destroy the normal functioning of soil, cause fertility degradation, lead to crop losses, crop quality declined and cause teratogenic carcinogenesis to human. Biochar (BC) is a passivation material and has demonstrated potential as a highly efficient emerging low-cost adsorbent used in the removal of heavy metals from soil or sewage. Experts and scholars have recently extensively researched biochars in environmental and agricultural applications. The adsorption mechanisms of biochars toward heavy metals indicate that the characteristics of biochars are strongly affected by the raw materials, pyrolysis time, and especially the pyrolysis temperature. Therefore, research on the heavy metal adsorption effect of biochars produced at different pyrolysis temperatures is very important in developing methods for treating sewage. To promote the sustainable usage of agricultural wastes like chicken manures and control heavy metal pollution, in this study, chicken manure biochars (BC200, BC400, BC600 and BC800) were produced through pyrolysis under oxygen-limited condition at the preparation temperature of 200, 400, 600 and 800 ℃. The physicochemical and structure characteristics of chicken manure biochars were detected by BET accelerated surface area and porosimetry system (This indicator is usually referred to as BET), scanning electron microscopy (This indicator is usually referred to as SEM), transmission electron microscope (This indicator is usually referred to as TEM), Fourier transform infrared spectroscopy (This indicator is usually referred to as FTIR), then the remediation effects of different pyrolysis temperatures of chicken manure biochars on heavy metal Cd and Pb were studied. The results showed that ash content, pH values, BET surface area, and average pore diameter increased with the increases of pyrolysis temperature, and the surface of chicken manure biochars had lots of irregular pore structure, mainly being mesoporous, while the yields of chicken manure biochars was significantly reduced with the increasing temperature (P<0.05). The adsorption of heavy metal Cd^2+ and Pb^2+ on chicken manure biochars included an initial fast sorption phase and a second slow phase, and Elovich equation could better simulate the processes of kinetic adsorption. The maximum adsorption capacities of heavy metal Cd2+ and Pb2+ at equilibrium reached 242.59 mg/g (BC800) and 52.02 mg/g (BC600), respectively. The application of chicken manure biochars significantly increased soil pH values (P<0.05), while the contents of heavy metals TCLP-Cd and -Pb were decreased, with the maximum reduction of 16.5% and 14.5%, respectively, in contrast with the blank treatments. When compared with CK (treatment without adding chicken manure biochar), the ratios of weak-acid-extractable, reducible fraction and oxidizable heavy metals Cd and Pb were decreased to some extent, but the percentage of residue fraction was increased by 5.49%-15.14% and 2.51%-6.30%, respectively. In summary, chicken manure biochars has a strong passivation effect on heavy metals Pb and Cd.