不同原料生物炭对氮、磷、钾的吸附和解吸特性

Adsorption and desorption characteristics of nitrogen, phosphorus and potassium by biochars from different raw materials

【目的】通过三种不同原料生物炭(玉米秆炭、稻壳炭、稻秆炭)对氮、磷、钾的吸附解吸试验,了解不同材料来源的生物炭对无机养分的吸附和解吸特征,为将其作为添加物来调节有机肥的性质提供参考。【方法】在pH 6.75±0.25、25℃下,采用Langmuir和Freundlich方程对三种不同原料生物炭(玉米秆炭、稻壳炭、稻秆炭)氮、磷、钾的等温吸附进行拟合。对吸附养分后的生物炭进行连续5次解吸,前4次采用水浸提,第5次浸提采用1 mol/L KCl浸提氮,0.5 mol/L的NaHCO3浸提磷,1 mol/L的CH3COONH4浸提钾。【结果】1) Langmuir和Freundlich方程均可用来拟合生物炭对氮、磷、钾的等温吸附,Langmuir方程对氮、磷的吸附拟合较好,Freundlich方程对钾的吸附拟合较好。对不同原材料而言,稻秆炭对氮、磷、钾的吸附性能均较好,其最大吸附量qm分别为(2.44±0.15) mg/g、(2.91±0.12) mg/g和(4.97±0.22) mg/g。2)不同原材料生物炭对氮、磷、钾的单次解吸率和总解吸率具有一定的差异。生物炭对阳离子(铵根离子和钾离子)的最大吸附量受阳离子交换量和酸性官能团的数量以及pHpzc影响,对磷酸根的最大吸附量主要与阳离子交换量和碱性官能团的数量有关。【结论】所试三种生物炭对氮、磷、钾的吸附存在单分子层吸附和多分子层吸附,在单次解吸率和总解吸率上不同原料生物炭存在一定的差异性。在生物炭对氮和钾吸附的总量上,物理性吸附的贡献高于化学吸附;对磷的吸附总量上,化学吸附的贡献高于物理吸附。三种生物炭对氮、磷、钾的固储和缓释能力具有一定的差异,稻秆炭的保肥供肥能力优于玉米秆炭和稻壳炭。

【Objectives】The adsorption and desorption of nitrogen, phosphorus and potassium by biochars derived from corn stalk, rice husk and rice stalk were studied. The solid storage and slow release capacity of nitrogen, phosphorus and potassium from the biochars will provide a reference for adjusting the properties of organic fertilizers using biochar as additives.【Methods】The Langmuir and Freundlich equations were used for fitting the isothermal adsorption characteristics of nitrogen, phosphorus and potassium under pH 6.75 ± 0.25 at25℃. Five extractions were made for the desorption of the absorbed N, P and K. The first four extractions were all by water. The fifth extraction agent for N was 1 mol/L KCl, for P was 0.5 mol/L NaHCO3, and for K was 1 mol/L CH3 COONH4.【Results】The isothermal adsorption of N, P and K could be fitted by both Langmuir and Freundlich equations. Langmuir equation fitted better in the adsorption of nitrogen and phosphorus, while the Freundlich equation did better in that of K. Among the three tested biochars, the one derived from rice stalk performed the best in adsorption of N, P and K, with the maximum adsorption amounts of(2.44±0.15) mg/g,(2.91±0.12) mg/g and(4.97±0.22) mg/g, respectively. 2) Biochar derived from different raw materials were different in both the single and total desorption rates of N, P and K. The maximum adsorption of biochar to cations(NH4+ and K+) was affected by the amount of cation exchange and the number of acidic functional groups and pHpzc, and the maximum adsorption of P was mainly related to the amount of cation exchange and the number of basic functional groups.【Conclusions】The adsorption of N, P and K by the three biochars occurs in both monolayer and multilayers, and the adsorption rates are varied among them. The physical adsorption by biochar contributes more than chemical ones on N and K, and chemical adsorption contributes higher on P. The solid storage and sustained release ability of NPK are different among the three biochars, rice stalk biochar is the best of them.