稻壳炭对铵态氮的吸附机理研究

Adsorption Mechanism of Ammonium Nitrogen onto Rice Husk Biochar

研究了500℃连续热解制备的稻壳炭对水溶液中NH+4-N的吸附特性和稻壳炭用量、颗粒粒径、NH+4-N初始质量浓度、p H值、振荡时间等因素对NH+4-N吸附特性的影响。结果表明,随着NH+4-N溶液初始质量浓度、p H值的不断升高,稻壳炭对NH+4-N的平衡吸附量不断增加,而随着振荡时间的推移,平衡时稻壳炭对NH+4-N的单位吸附量不断增加,60 min内吸附较快,在吸附90 min左右时保持不变,这说明稻壳炭对NH+4-N的吸附在1.5 h左右基本达到平衡,对于初始质量浓度为3 mg/L和5 mg/L的NH+4-N溶液,稻壳炭对NH+4-N的最大吸附量分别为31.26、81.14 mg/kg。稻壳炭的颗粒粒径越小,单位吸附量越高,0.25 mm以下的稻壳炭对NH+4-N的吸附容量较大。从热力学和动力学角度探究了吸附机理,结果表明,稻壳炭对NH+4-N的等温吸附过程符合Freundlich模型,表明稻壳炭对水溶液中的NH+4-N吸附为不均一的多分子层吸附;准二级吸附模型能较好地描述吸附的全过程,稻壳炭吸附NH+4-N主要包含液膜扩散、表面吸附、颗粒内部扩散过程,主要以物理吸附为主。

The adsorption mechanism of rice husk biochar to ammonium nitrogen was investigated. The influence of biochar amount,particle size,original concentration and p H value of ammonium nitrogen solution and shaking time on the adsorption characteristics were explored. The results showed that the unit adsorption quantities of ammonium nitrogen were increased with the increase of original concentration and p H value of ammonium nitrogen solution. The adsorption rate reached the highest point within 60 min and then kept unchanged within 90 min. The adsorption equilibrium of ammonium nitrogen was gained within 1. 5 h. The maximum adsorption for ammonium nitrogen solutions was 81. 14 mg / kg. Additionally,the effect of particle size on the adsorption process was significant. High adsorption quantities of ammonium nitrogen were got with small particle size and the adsorption capacity of rice husk biochar reached the maximum with particle size of 0. 25 mm. The adsorption mechanism was investigated using thermodynamic and kinetics analyses. The results indicated that the adsorption behavior of biochar for ammonium nitrogen was inhomogeneous and it belonged to one of polymolecular layer fitted by Freundlich model properly. Quasi-dynamic equations were matched well with adsorption process of biochar to ammonium nitrogen,which included the diffusion in the fluid film,shift inside the grains and surface adsorption process by physical adsorption.