title: Effect of organic acids on adsorption and desorption of rare earth elements.
abstract: Effect of citric, malic, tartaric and acetic acids on adsorption of La, Ce, Pr and Nd by and desorption from four typical Chinese soils was studied. Generally, adsorption capacities of rare earth elements (REEs) were significantly correlated with the cation exchange capacity (CEC) of soils. In the presence of acetic acids adsorption of REEs was similar to that in the presence of Ca(NO3)2. However, in the presence of citric, malic and tartaric acids adsorption of REEs by Heilongjiang, Zhejiang and Guangdong soils decreased to varying extents if compared with that in the presence of nitrate and acetic acid. The significance of suppression followed the order of citric acid > malic acid > tartaric acid > acetic acid, which was consistent with the order of stability of complexes of REEs with these organic acids. However, the adsorption increased with increasing equilibrium solution pH. For Jiangxi soil with low soil pH, CEC and organic matter these organic acids exerted an even more serious suppression effect on the adsorption of REEs. Another feature of the relationship between the adsorption of REEs and equilibrium solution pH was that the adsorption of REEs decreased with increase of pH from 2 to 4.5 and then slightly increased with further increase of pH. Desorption of REEs varied with soils and with organic acids as well. REEs were released easily from Heilongjiang, Zhejiang and Guangdong soils in the presence of organic acid. Generally, desorption of REEs decreased with increasing equilibrium solution pH. Effect of organic acids on desorption of REEs from Jiangxi soil was more complicated. In the presence of citric and malic acids no decrement and/or slight increase in desorption of REEs were observed over the equilibrium solution pH from 3 to 6.5. The reasons for this were ascribed to the strong complexing capacity of citric and malic acids and low soil pH, CEC and organic matter of Jiangxi soil.
authors.affiliation: Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing. xiaoquan@mail.rcees.ac.cn
authors.forename: Xiao-Quan
authors.initials: XQ
authors.lastname: Shan
authors.forename: Jun
authors.initials: J
authors.lastname: Lian
authors.forename: Bei
authors.initials: B
authors.lastname: Wen
mesh_terms: D019342:Acetic Acid / Q000737:chemistry*; D000327:Adsorption; D019343:Citric Acid / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008293:Malates / Q000737:chemistry*; D008674:Metals, Rare Earth / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D013644:Tartrates / Q000737:chemistry*
chemical_list: D008293:Malates; D008674:Metals, Rare Earth; D012989:Soil Pollutants; D013644:Tartrates; D019343:Citric Acid; C030298:malic acid; D019342:Acetic Acid; C029768:tartaric acid