红壤和潮土添加不同生物质炭后等温吸附磷酸盐的变化

Changes in isothermal phosphate adsorption in red soils and alluvial soils added with different biochars

为了解不同生物质炭对土壤等温吸附磷酸盐的影响,选取桃木、花生壳和玉米秸秆,在300和500℃下通过慢速热裂解制备生物质炭,按0%、0.5%、1%、3%和5%质量比加入到红壤和潮土中,经过4次干湿交替平衡后,加入系列磷酸盐溶液,测定其等温吸附特征。结果表明:1)所有土壤磷酸盐等温吸附行为均可用Langmuir方程进行拟合,添加活性炭均降低了红壤和潮土的等温吸附参数,而添加生物质炭显著地提高了红壤磷酸盐最大吸附量(qm),qm值平均提高了11%;但潮土的q_m值显著降低,平均降低了30%,而KL(Langmuir等温吸附常数)和最大缓冲容量(MBC)平均分别提高了179%和69%。这说明生物质炭对磷酸盐等温吸附的影响不仅取决于土壤属性,而且与生物质炭特性及其用量也存在一定的联系,qm值与K_L及MBC值之间的关系就反映出这种复杂性,相关的机理还有待进一步研究。

To understand the effects of different biochars on phosphate isotherm adsorption in soil,the biochars were prepared with peach wood,peanut hull and maize straw by slow pyrolysis at 300 and 500 ℃ respectively.The harvested biochars were then amended into red soil and alluvial soil at the rates of 0%,0.5%,1%,3% and 5%(M/M).Following four times of wetting and air-drying cycle,the isothermal adsorption characters for phosphate were determined by adding series of phosphate solution.The results showed that phosphate adsorption in all soil samples could be simulated by Langmuir equation.Adding activated carbon significantly reduced the isothermal adsorption parameters in both red and alluvial soils.However,biochar supplementation generally enhanced the maximum adsorption capacity(qm)of red soil by 11% on average,while decreased by 30% on average in alluvial soil.Furthermore,the values of KL and maximum buffer capacity(MBC)were respectively increased by 179% and 69%on average in the biochar-added alluvial soil.This study showed that the impacts of biochar amendment on isothermal adsorption of phosphate largely depended not only on soil,but also biochar and its addition rates.The relationships among qm,KL and MBC reflected such complexity.Further work is required to understand related mechanisms.