几种稻田土壤对铵的矿物固定的动力学与热力学研究

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

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。

By the method of batch equilibrium, kinetics and thermodynamic properties of NH4^＋ 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 NH4^＋ in the tested soils was quick, but velocity of NH4^＋ - 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 NH4^＋ - fixation kinetics. The parabolic diffusion euqation was optimal to describing NH4^＋ - fixation kinetics properties . The parabolic diffusion equatoion could also describe the experimental data satisfactorily. Zero - level equation was not adaptable to descrbing the NH4^＋ - fixation kinetics properties. Thermodynamic properties of NH4^＋ -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 langrnuir equation. The negative changes of free energy illustrated that NH4^＋ - 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.