Pedosphere 25(3): 405--414, 2015
ISSN 1002-0160/CN 32-1315/P
©2015 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Adsorption of phosphate onto ferrihydrite and ferrihydrite-humic acid complexes
WANG Hui1, ZHU Jun1, FU Qing-Ling1, XIONG Jun-Wei1, HONG Can1, HU Hong-Qing1 and A. VIOLANTE2
1Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture, College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070 (China)
2Department of Soil, Plant, Environment and Animal Production Science, Faculty of Agriculture, University of Naples “Federico II”, Via University 100, 80055 Portici (Italy)
ABSTRACT
      The adsorption of phosphate onto ferrihydrite (FH) and two FH-humic acid (HA) complexes, obtained by co-precipitating FH with low (FH-HA1) and relatively high amounts of humic acid (FH-HA2), was studied through kinetics and isotherm experiments to determine the differences in phosphate adsorption between FH-HA complexes and FH and to reveal the mechanism of phosphate adsorption onto two soil compositions. The isoelectric point (IEP) and the specific surface area (SSA) of the mineral decreased as the particle porosity of the mineral increased, which corresponded to an increase in the amount of organic carbon. The adsorption capacity of phosphate was higher on FH than on FH-HA1 and FH-HA2 at the scale of micromoles per kilogram. The initial adsorption rate and adsorption affinity of phosphate decreased with an increase in the amount of HA in the mineral. The sensitivity of phosphate adsorption to the change in the pH was greater for FH than for FH-HA complexes. Ionic strength did not affect the adsorption of phosphate onto FH and FH-HA1 at a lower pH, and the increase in the ionic strength promoted phosphate adsorption at a higher pH. However, for the FH-HA2 complex, the increase in the ionic strength inhibited the adsorption of phosphate onto FH-HA2 at a lower pH and increased the adsorption at a higher pH.
Key Words:  adsorption isotherm, adsorption kinetics, co-precipitation, Fe oxides, ionic strength
Citation: Wang, H., Zhu, J., Fu, Q. L., Xiong, J. W., Hong, C., Hu, H. Q. and Violante, A. 2015. Adsorption of phosphate onto ferrihydrite and ferrihydrite-humic acid complexes. Pedosphere. 25(3): 405-414.
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