施加生物炭对河流沿岸土吸附铜的影响机制

Effect of Biochar Application on Adsorption of Copper by Riverbank Soils

为探究生物炭施加对河流沿岸土吸附铜的影响机制,采集嘉陵江流域(川渝段)内苍溪(CX)、南部(NB)、嘉陵(JL)和合川(HC)沿岸土表层(S,0~20 cm)、亚表层(D,20~40 cm)共8种土样,分别将1%(质量比)生物炭(B)加入到8种土样中形成混合土样(CXSB、NBSB、JLSB和HCSB;CXDB、NBDB、JLDB和HCDB)。以原始土样作为对照,批处理法研究各供试土样在不同温度、pH和离子强度下的Cu2+吸附和热力学特征,并分析Cu的吸附形态。结果显示:(1)各供试土样对Cu2+的等温吸附都适用Langmuir模型描述,Cu2+的最大吸附量qm在62.20~363.64 mmol/kg之间,S层土样对Cu2+的吸附量均呈现JL>NB>CX>HC的趋势,而D层土样呈现JL>CX>NB>HC的趋势。施加生物炭有助于增强D层土壤对Cu2+的吸附。(2)20~40℃范围内,各供试土样对Cu2+的吸附量均随温度的升高而升高,表现为增温正效应。热力学参数结果表明各混合土样对Cu2+的吸附是一个自发、吸热和熵增的过程。(3)pH的升高有利于各供试土样对Cu2+的吸附。随着离子强度的增加,各混合土样(HCS和HCD除外)对Cu2+的吸附量均呈现先增后降的趋势,0.1 mol/L时最大。(4)土样中吸附的铜主要以碳酸盐结合态和铁锰氧化物结合态铜存在,生物炭的施加增加了土样中可交换态(HC除外)和有机结合态铜含量,而对碳酸盐结合态和铁锰氧化物结合态铜影响较小。供试土样对Cu2+的qm主要是由CEC和比表面积决定的。

In order to explore the effects of biochar addition on the adsorption mechanisms of copper by riverbank soils,the surface (S,0-20 cm) and subsurface (D,20-40 cm) layers in Cangxi (CX),Nanbu (NB),Jialing (JL) and Hechuan (HC) along the Jialing River (Sichuan-Chongqing section) were collected as the target soil samples. Biochar (B) was added into the soil samples with a mass ratio of 1% to form eight mixed samples (CXSB,NBSB,JLSB and HCSB;CXDB,NBDB,JLDB and HCDB),and the original soil samples were used as the controls. Cu2+ adsorption and thermodynamic characteristics of each tested sample under different temperature,pH value and ionic strength were studied using the batch method,and the adsorption morphology of Cu was analyzed. The results showed that: (1) The Langmuir model could describe the isothermal adsorptions of Cu2+ on all tested samples well. The maximum adsorption capacity qm of Cu2+ was between 62. 20-363. 64 mmol/kg,and the adsorption amount of Cu2+ presented a trend of JL > NB > CX > HC for S layer samples and a trend of JL > CX > NB > HC for D layer samples. The application of biochar enhanced the Cu2+ adsorption on the D layer soils. (2) In the temperature range of 20-40 ℃,the adsorption amount of Cu2+ increased as temperature increasing,showing the positive temperature effect. The results of thermodynamic parameters showed that the adsorption of Cu2+ by mixed samples was a spontaneous,endothermic and entropy-adding process. (3) Increasing pH was beneficial to the Cu2+ adsorption by all samples. With the increase of ionic strength,the adsorption amounts of Cu2+ in all mixed soil samples (except HCS and HCD) increased firstly and then decreased,and presented the largest at 0. 1 mol/L. (4) Adsorbed copper mainly existed in carbonate-bound and iron-manganese oxide-bound states in soil samples. The application of biochar improved the exchangeable state (except HC) and the organic bound copper contents but had little effect on the carbonate bound and iron-manganese oxide bound copper contents in soil samples. The maximum adsorption capacity of Cu2+ on soil samples correlated highly with CEC and specific surface area of soil samples.