去除氧化铁对Al在土壤中吸附-解吸的影响

Effects of ferric oxide removal on adsorption and desorption of aluminum in soils

用连二亚硫酸钠-柠檬酸钠-碳酸氢钠(DCB)法研究了去除土壤中的氧化铁后Al的吸附-解吸特征的变化情况.结果表明,在pH值<4.5条件下,去除氧化铁可使土壤对Al的吸附量有所增加,这种变化在赤红壤中尤为明显;而此后随pH值的升高,原土和去铁土对Al的吸附量基本相等.造成该现象的原因可归纳为去除氧化铁能降低土壤的电荷零点(ZPC)和增加土壤表面负电荷的数量,从而增强了土壤表面与离子之间的静电引力.另一方面,去除氧化铁后Al的解吸量也增加.其原因是与原土相比,去铁土吸附Al的机理中包含有部分静电吸附,这从离子强度对去铁土吸附Al的影响实验能得到较好的验证,因为在pH值<4.5时,提高离子强度将降低Al的吸附量,用高岭石做参考材料时也发现了类似的现象.

The adsorption and desorption of aluminum in two acidic soils was investigated. Under using technique of dithionite-citrate-bicarbonate (DCB), the change situation of Al adsorption-desorption characteristics after removal of Fe oxide in soil was studied. Results show that under the condition of pH<4.5, removal of Fe oxide soil could increase the amount of aluminum adsorption by the soils. This change is more pronounced in the lateritic red soil, but the adsorption amount of Al in the latosol before and after removal of Fe is same basically. This effect was attributed to the reduction of zero point of charge (ZPC) of soil and increase in the amount of soil surface negative charge which in turn enhanced the electrostatic attraction between ions and soil surface. On the other hand, the amount of aluminum desorped also increased. Compared with those in untreated soils, the cause may be partial electrostatic adsorption in the mechanism of Al adsorption in the Fe removed soils, which could be evidenced rather well by the test of the influence of ionic strength on the Al adsorption in the Fe removed soils, because at pH<4.5 the amount of Al adsorption would be decreased after ionic strength. The similar phenomenon also appears with kaonilite used as referential material.