几种稻田土壤对铵的矿物固定的动力学与热力学研究

本文采用振荡平衡法研究了紫泥田、河沙泥、灰泥田及红黄泥4种稻田土壤对铵的矿物固定的动力学及热力学特性。结果表明,供试土壤对添加铵的矿物固定速度很快,随着固铵量增多,固铵速度下降,反应后24小时固定基本上达到平衡,不因土壤种类而异。数学拟合结果表明,以一级动力学方程和E lovich方程描述供试土壤对铵的矿物固定资料最优,抛物扩散方程也能较满意地描述实验结果,以零级方程的拟合效果最差。供试土壤对铵的矿物固定的热力学资料均能用一元Langmu ir吸附等温式、Freund lich吸附等温式和Temk in吸附等温式拟合,拟合结果均达极显著水平,但以一元Langmu ir吸附等温式的拟合结果最优,由一元Langmu ir吸附等温式可以求得土壤对铵的矿物固定的热力学平衡常数、最大固铵量以及固铵过程中的自由能变△G°。供试土壤固铵过程的自由能变△G°均为负值,说明供试土壤对铵的矿物固定为一自发过程,4种土壤固铵强度依次为紫泥田>河沙泥>灰泥田>红黄泥。

Study on Kinetics and Thermodynamic Properties of Fixed Ammonium in Several Paddy Soils

By the method of batch equilibrium,kinetics and thermodynamic properties of NH~ _4 fixation were studied in Purple clayey soil,Alluvial sandy soil,Grey clayey soil and Reddish yellow clayey soil.The results indicate that the fixing rate for added NH~ _4 in the tested soils was quick,but velocity of NH~ _4-fixation grew slowly with the increase of fixed ammonium,and the reaction reached euquilibrium after 24 hour.Both first order equation and Elovich equation were adaptable to descrbing the NH~ _4-fixation kinetics.The parabolic diffusion euqation was optimal to describing NH~ _4-fixation kinetics properties.The parabolic diffusion equatoion could also describe the experimental data satisfactorily.Zero-level equation was not adaptable to descrbing the NH~ _4-fixation kinetics properties.Thermodynamic properties of NH~ _4-fixation in the four tested soils under constant temperature could be described by Single-surface langmuir equation,Freundlich equation and Temkin equation.Among the three adsorption equations,the Single surface langmuir equation was the best because thermodynamic equilibrium was constant.The maximum fixation capacities and Free energy change conld be calculated by single-surface langmuir equation.The negative changes of free energy illustrated that NH~ _4-fixation in the tested soils was a spontaneous reaction.The order of fixation ammonium strength was Purple clayey soil>Alluvial sandy soil>Grey clayey soil > Reddish yellow clayey soil.