生物炭对红壤团聚体吸附Cd的影响研究

Studies on the Influence of Biochar on the Adsorption of Cd onto Red Soil Aggregates

中国南方红壤区是Cd污染的集中地区,作为土壤修复材料的生物炭对Cd在土壤团聚体颗粒中的吸附行为具有重要的影响。为了研究生物炭对Cd在不同粒级团聚体中的吸附行为的影响规律,提高土壤修复过程中对不同粒径土壤团聚体改良的针对性,通过批量吸附实验,结合扫描电镜、FTIR红外等方法,探究了生物炭添加量(原土质量比例分别为0、1%、3%、5%、7%)、溶液初始pH值(2.0—6.5)等因素对不同粒径(>1 mm、1—0.25 mm、0.25—0.05 mm、<0.05 mm)红壤团聚体吸附Cd的影响。结果表明:生物炭添加能明显增加红壤中有机质、CEC以及游离氧化铁的含量;随生物炭添加比例的增加,Cd在土壤中的吸附量显著增加,生物炭添加量为原土比例的1%时,对Cd的单位吸附量增加最大,过高的生物炭投加量会降低生物炭的利用效率;Langmuir和Freundlich模型都能很好描述生物炭添加前后红壤团聚体中Cd的等温吸附特性(0.9730≤R2≤0.9961),生物炭添加对增加不同粒径团聚体吸附Cd能力的大小不同,总体上,土壤颗粒粒径越小对Cd的吸附能力越强,但是Cd在>1 mm团聚体中的吸附量相对增加量最大(42.9%);生物炭的添加能降低不同团聚体中Cd的解吸量,并随团聚体粒径的减小Cd的解吸量呈减小趋势,大粒径(>1 mm)团聚体中Cd的解吸量降低最为明显;同时,生物炭添加使团聚体Cd吸附量在较高pH情况下仍能有效增加,不同pH条件下,<0.05 mm的团聚体无论在生物炭添加前后均表现出最高的Cd吸附量,总体上,生物炭对于花岗岩发育的酸性红壤团聚体中的Cd具有较好的固定作用。

Cd pollution is concentrated in red soil in southern China.Biochar has an important influence on the adsorption behavior of Cd in soil aggregate particles.In order to study the influence of biochar on the adsorption behavior of Cd in aggregates with different particle sizes,and to improve soil aggregates particles in the process of soil remediation,based on batch adsorption experiments combined with scanning electron microscopy,FTIR infrared and other methods,the effects of biochar addition amount and(0%−7%),initial pH value(2.0−6.5)of the solution on the adsorption of Cd by red soil aggregates of various particle sizes(>1 mm,1−0.25 mm,0.25−0.05 mm,<0.05 mm)were explored.The results show that:the addition of biochar can effectively increase the content of organic matter,CEC and free iron oxide in red soil.with the increase of the biochar addition amount,the adsorption amounts of Cd increased significantly.When the biochar content was 1%of the original soil,the adsorption capacity of Cd per unit increased the most,too high biochar addition will reduce the utilization efficiency of biochar.Langmuir and Freundlich models could well describe the isotherm adsorption characteristics of Cd in red soil aggregates before and after the addition of biochar(0.9730≤R2≤0.9961),the addition of biochar has different effects on increasing the Cd adsorption capacity of aggregates of different particle sizes.In general,the smaller the particle size of the soil,the higher adsorption capacity of Cd.The relative increasing amount of Cd in the>1 mm aggregates was the largest(42.9%).The desorption amount of Cd in various aggregates could be reduced by the addition of biochar,the change of the desorption capacity for Cd decreases with the decrease of the size of the aggregates.and the reduction in the>1 mm aggregates was the most obvious.Meanwhile,the addition of biochar can effectively increase the Cd adsorption capacity of aggregates at higher pH conditions.Under different pH conditions,<0.05 mm aggregates show the highest Cd adsorption capacity before and after the addition of biochar.Biochar has a good fixation effect on Cd in acid red soil aggregates developed by granite.