施用原始及铁改性生物质炭对土壤吸附砷(Ⅴ)的影响

Effect of raw and iron-modified biochar on the sorption of As(Ⅴ) by soils

【目的】考察生物质炭及铁改性生物质炭对土壤吸附砷[As(Ⅴ)]的影响。【方法】以法国梧桐Platanus orientalis修剪枝为原料在650℃限氧条件下热解制备生物质炭,并通过氯化铁(FeCl3)溶液浸渍、热解,将其进一步制备成铁改性生物质炭,对比考察改性后生物质炭理化性质和表面官能团的变化;并通过批量吸附试验探究不同As(Ⅴ)初始质量浓度、吸附时间对施炭土壤吸附As(Ⅴ)效果和规律的影响,通过分析吸附等温线特征和吸附动力学特征,探明吸附机制。【结果】铁改性生物质炭较原始生物质炭pH、比表面积及官能团数量降低,但灰分质量分数和电导率有所增加;Langmuir模型能较好拟合施炭土壤对As(Ⅴ)的吸附过程,表明吸附以单分子层为主。当As(Ⅴ)溶液初始质量浓度大于25 mg·L^(-1)后,铁改性生物质炭对As(Ⅴ)的吸附量大于原始生物质炭,且最大吸附量为0.36 mg·g^(-1)。原始生物质炭和铁改性生物质炭对As(Ⅴ)的动力学吸附符合准二级动力学方程,吸附过程在4 h前后分别为快速吸附和慢速吸附2个阶段,在24 h左右趋于平衡,且铁改性生物质炭处理下土壤的饱和吸附量比原始生物质炭处理高11%。【结论】施用2种生物质炭均能提高土壤对As(Ⅴ)的吸附效果,且铁改性生物质炭的吸附效果优于原始生物质炭。因此,施用铁改性生物质炭可以加强土壤对As(Ⅴ)的吸附作用从而降低As生物有效性。

[Objective]This study is aimed to investigate the effect of raw biochar and Fe-modified biochar on the soil adsorption of As(Ⅴ).[Method]First,the raw biochar was produced from the branches of Platanus orientalis by means of pyrolysis at 650℃in an oxygen-limited condition,while its Fe-modified biochar(weight ratio of Fe∶biochar=1∶20)was obtained from the impregnation with FeCl3 solutions and re-pyrolysis beofe the physiochemical properties and surface functional groups of two biochars were examined for changes.Then with the employment of a batch equilibration method,an investigation was conducted of the impacts of initial As(Ⅴ)concentration and sorption time on As(Ⅴ)sorption by soils treated with raw and Fe-modified biochars.At last,The characteristics of the sorption isotherms and kinetics were analyzed.[Result](a)The Fe-modified biochar had higher ash content and electrical conductivity,but lower pH,specific surface area and abundance of surface functional groups than those of the raw biochar;(b)Langmuir isothermal models could well describe the sorption process of As(Ⅴ)by biochar-amended soils,indicating that the monolayer sorption was the predominant process:with an initial As(Ⅴ)concentration higher than 25 mg·L^(-1) in the solution,the sorption capacity of the Fe-modified biochar to As(Ⅴ)(up to 0.36 mg·g^(-1))was greater than that of the raw biochar;(c)The kinetic sorption of As(Ⅴ)could be described by the pseudo-second-order kinetics and the sorption process could be divided into two stages from the critical point of reaction at 4 t h hour,i.e.,rapid sorption and slow sorption,respectively;(d)The sorption equilibrium was achieved around 24 hours of reaction,and the maximum sorption capacity of the Fe-modified biochar treatment was 11%higher than that of the raw biochar treatment.[Conclusion]Both biochars could enhance the As(Ⅴ)sorption capacity of the soil,and the addition of the Fe-modified biochar was more effective than that of the raw biochar.Therefore,the Fe-modified biochar is recommended in the reduction of the bioavailability of As(Ⅴ)in contaminated soils by enhancing its adsorption capacity.