Effects of sulfate on speciation and bioavailability of rare earth elements in nutrient solution

Abstract

In this study, data of La3+, Gd3+ and Y3+were carefully selected from the published thermodynamic data base, and were then added to the thermodynamic database of the MINTEQA2 procedure. The species of rare earth elements (REEs, La, Gd, Y) in a nutrient solution were calculated out by MINTEQA2 procedure. The results showed that the precipitation of REEs would take place when the pH was greater than 7.5. Meanwhile, the species of light (La3+)_medium (Gd3+) and heavy (Y3+) REEs with SO42− were calculated using MINTEQA2. The effects of sulfate on the bioavailabilities of three REEs in wheat (Triticum) were investigated by experiments on culture. The results showed that bioaccumulation of La3+ and Gd3+ in roots was inhibited after adding SO42− to the nutrient solution containing 2.0 mg L−1 REE, but Y3+ was promoted. Only Gd3+ became increasingly bioaccumulated in tops (stem and leaves) after adding SO42− to three REE solutions. Kinetic experimental results indicated that bioaccumulation values of REEs in roots fit the linear growth equation (correlation coefficients were higher than 0.94) in nutrient solution containing 2.0mg L−1 REE + 0.01mol L−1 SO42−, and the high bioaccumulation values of REEs in the tops (stem and leaves) during the initial culture time were higher than those in the following few days. The species of REEs with sulfate and the bioavailabilities of REEs had no obvious correlation.