粒径和温度对玉米秸秆生物碳吸附锶的耦合影响

以玉米秸秆为原材料,在350℃下采用限氧裂解法制备了4种粒径的生物碳(BC-9.31、BC-20.26、BC-71.07、BC-101.90,数字代表样品的中值径,单位μm),对比研究了15℃、25℃、35℃、45℃下生物碳对锶的吸附行为,旨在阐明生物碳粒径和溶液温度对生物碳吸附锶的耦合影响。结果表明:生物碳粒径和溶液温度对等温吸附曲线的基本特征影响较小,Freundlich模型能较好地拟合吸附过程(R2=0.915~0.997,N=0.513~0.745);生物碳吸附锶是以熵驱动为主的物理吸附过程,熵变ΔS为75.66~99.43 J/(mol·K),焓变ΔH为18.18~25.84 k J/mol;生物碳对锶的吸附性能大体与溶液温度呈正相关,与颗粒粒径呈负相关,同时颗粒粒径与溶液温度存在耦合影响;生物碳粒径越小,锶吸附过程受温度影响越小;温度越高,锶吸附受粒径影响越小。

Effects of the particle size and temperature on the adsorption of strontium by the biochar derived from maize straw

The present paper is aimed at investigating and determining the mutual effects of the biochar particle size and the solution temperature on the adsorption of strontium through a comparative study of the adsorption behaviors of the following 4 biochar samples at the temperatures of 15 ℃,25 ℃,35 ℃,45 ℃.In the experiment,we have pyrolyzed 4 kinds of biochar samples in different particle sizes of maize straw powder,that is,BC-9.31,BC-20.26,BC-71.07 and BC-101.90,with the unit of μm representing their respective particle sizes,at the temperature of 350 ℃ in the oxygen-confined condition.The testing results show that neither the particle size of the maize straw derived biochar nor the temperature of the aqueous solution have made much effect on the characteristic features of the adsorption isotherm.Rather,the Freundlich model proves well fit for the nonlinear isotherm of strontium(L-type) by the 4 kinds of maize straw derived biochar samples at the different temperatures (R2,0.915-0.997;N,O.513-0.745).For instance,the Freundlich Nvalues of BC-71.07 and BC-101.90 prove to be gradually decreased,which reveals that the non-linearity of the adsorption isotherm tends to gradually increase with the increase of the aqueous solution temperature.As we know,when the entropy change ΔS of the adsorption process is 75.66-99.43 J/(mol · K),the enthalpy change ΔH is equal to 18.18-25.84 kJ/mol.Thus,the adsorption feature of strontium for the maize straw derived biochar is by nature a kind of physical adsorption process mainly driven by the entropy change,in which the adsorption capacity of strontium tends to increase with the increase of the solution temperature but decrease with the biochar particle size.What is more,the testing also proves that the temperature of the aqueous solution has had little effect of the particle size of strontium,if the particles were small.Therefore,it can be said that the effect of temperature may become less important on the adsorption when the particle size is decreased just as the decease of the impact of particle size with the increase of solution temperature.The aforementioned observations we have done in the current paper can thus be expected to provide a suggestion for the particle size selection of the adsorbent for sewage treatment in different temperature conditions.Detailedly speaking,low cost coarse particle adsorbent can be efficiently adopted when the sewage treatment is done at high temperatures(such as the hot sewage left over after the workshop business),but fine particle adsorbents are needed for the treatment at variable temperatures.