PM07 Pollutant Chemistry Transport, Cycling and Fate
Exhibit Hall
8:00 AM - Monday
(PM084) Effects of oxalate and humic acid on arsenate sorption by and desorption from red soil.
Zhang, Shuzhen1, Luo, Lei1, Shan, Xiaoquan 1, 1 Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China
ABSTRACT- Studies of arsenate sorption and desorption have been limited in individual soil minerals, the sorption and desorption reactions in real soils are poorly understood. In this study the sorption of arsenate by and desorption from Chinese red soil were studied in the presence of oxalate and humic acid (HA). Sorption of arsenate by soil was mainly through ligand exchange, and bidentate complexes were predominantly formed. The arsenate sorption maximum decreased to 20.4% and 25.0% in the presence of 200 mmol kg-1 oxalate and 100 g kg-1 HA, respectively, compared with that in the absence of oxalate and HA. The mechanisms relevant to the decrease in sorption of arsenate by oxalate and HA were different: oxalate competed the sorption sites with arsenate, while HA mainly blocked the sorption sites. Oxalate and HA can also enhance arsenate desorption from the soil. Both sorption and desorption kinetics were biphasic. Sorption kinetics, conducted on from 0.5-840 h, showed that arsenate sorption increased with increasing residence time. Sorption equilibrium was retarded and sorption maximum decreased in the presence of oxalate and HA. Desorption kinetics, conducted on the soils with the residence time of 24 h and 840 h, showed a significant residence time effect on the desorption of arsenate. The presence of oxalate or HA during the sorption process can conduce to more arsenate desorption from the soil. But due to the degradation of oxalate, soil treated with oxalate and with sorption residence time of 840 h had no significant difference in desorption kinetics from the soil.
Key words: sorption and desorption, arsenate, oxalate, humic acid