pH和有机酸对氟溶出砖红壤中铝离子的影响

Effect of pH and Organic Acids on Mobilization of Aluminum Ions from Latosol by Fluoride Dissolution

研究砖红壤对F-的吸附反应尤其是随后Al3+的释放过程,有助于增进对土壤酸化过程及其环境影响的理解.在初步揭示出F-吸附反应以及Al3+释放反应的动力学特征基础上,重点考察了pH和有机酸对上述反应的影响.结果表明:土壤对F-的吸附反应十分迅速,2 min内吸附量即可达到24 h内总吸附量95%,而土壤中不同含铝矿物的溶解度差异使Al3+的释放过程在前15 min十分迅速,释放量可达24 h内总释放量的80%,随后则逐渐减缓.降低反应体系pH可促进Al3+释放,但会使F-吸附量减少,这是因为伴随Al3+的释放,部分F-又可以AlF络合物的形态重新进入溶液,尽管在低pH条件下,土壤表面以带正电荷为主而有利于F-吸附.草酸和抗坏血酸对土壤吸附F-均有抑制作用,但对F-溶出土壤Al3+有促进作用.此外,草酸对土壤铁氧化物的选择性溶解作用,可使更多F-吸附在土壤铝氧化物位点,并导致Al3+释放量增加.

Investigating the sorption reaction of fluoride on Latosol,especially the subsequent release process of aluminum ions,would be helpful to enhance our understanding of the process of soil acidification and its effect on related environments.In this paper,the kinetic characteristics of the fluoride adsorption onto the soil and the subsequent release of aluminum were presented,and the influences of pH and organic acids on the processes were investigated.As the results show,adsorption of fluoride proceeded very fast,with the percentage of F-adsorbed within 2 min accounting for 95% of the total amount within 24 h.However,due to the difference in solubility of Al-containing minerals,the release of aluminum ions was characterized by an initial fast phase followed by a slow phase,with the percentage of Al3 ＋ release within 15 min accounting for 80% of the total amount within 24 h.Positive charge is dominant on soil surfaces at low pH conditions,which is favorable for F-adsorption.Aluminum release was promoted at low pH conditions,which was unfavorable for F-adsorption.The result was mainly explained that adsorbed F-could be returned to solution as the species of Al-F complex when aluminum was released from the soil.The presence of oxalic acid or ascorbic acid would inhibit the F-adsorption and promote Al3 ＋ release.Moreover,increase in Al3 ＋ release resulted because more F-occupied the sites on the Al-containing minerals,which were exposed after the oxalic acid selectively extracted amorphous Fe-oxides.