182
species mediated by pH in groundwater by sunflowers and peas. The results showed
that the phytoremediation efficiency of uranium by these two plants became the
highest at pH 3~5, and it exceeded 90%. Inorganic anions, such as carbonates, phosphates, natural organic acids, etc., tended to form complexes with uranium, which
affected the uptake of uranium by plants (Nakajima et al. 1979; Greene et al. 1986;
Srivastava et al. 2010; Laurette et al. 2012a; Li and Zhang 2012; Pratas et al. 2012,
2014; Nie et al. 2014; Pan et al. 2016). Greene et al. (1986) and Nakajima et al.
(1979) reported that with the increase of carbonate concentration, the amount of the
adsorbed uranium by single-cell algae (C. regularis and C. vulgaris) gradually
decreased. When phosphate was present in the solution, it reacted with uranium to
form a precipitate, and the bioaccumulation of uranium decreased (Mkandawire
et al. 2007; Misson et al. 2009).
Azolla-Anabaena is a kind of fern-algae symbiotic aquatic plant and has been
used as green manure in rice fields, due to its strong nitrogen fixation ability (Tang
et al. 2000). Arora et al. (2006) and Rai (2008) have found that Azolla-Anabaena
had strong accumulation ability for heavy metals in solutions. Other studies have
also showed that Azolla-Anabaena had a strong accumulation capability for uranium. Hu et al. (2012) have found that Azolla-Anabaena symbiotic system had
excellent performance for removal of uranium. Heavy metal and uranium accumulation by Azolla-Anabaena has been reported extensively; however, the accumulation behavior of different uranium species by Azolla-Anabaena has not been studied.
In this paper, the proportions of different species of uranium in solutions under
different conditions were calculated with MINTEQ 3.1 software, which is a chemical equilibrium computer program that has an extensive thermodynamic database
enabling users to calculate the speciation, solubility, and equilibrium of solid and
dissolved phases of minerals in an aqueous solution (Gustafsson 2006). Based on
the calculation results, five solutions containing UO 2
2+
, (UO 2 ) 3 (OH) 5
+
, UO 2 (OH) 3
−
,
UO 2 (CO 3 ) 3
4−
, and UO 2 PO 4
−
, respectively, were prepared. The effects of uranium
speciation on the bioaccumulation by and translocation in Azolla-Anabaena were
finally investigated through hydroponic experiments, and the new ideas and theoretical basis for further improving the removal efficiency of uranium by AzollaAnabaena from water were provided.
2 Material and Methods
2.1 Material
Azolla-Anabaena was taken from a field in the suburb of Hengyang city in South
China. After the Azolla-Anabaena was washed with tap water for 3–5 min, it was
put into the improved Hoagland nutrient solution and cultivated for 2 weeks for
experimentation (Hu et al. 2012).
N. Hu et al.
species mediated by pH in groundwater by sunflowers and peas. The results showed
that the phytoremediation efficiency of uranium by these two plants became the
highest at pH 3~5, and it exceeded 90%. Inorganic anions, such as carbonates, phosphates, natural organic acids, etc., tended to form complexes with uranium, which
affected the uptake of uranium by plants (Nakajima et al. 1979; Greene et al. 1986;
Srivastava et al. 2010; Laurette et al. 2012a; Li and Zhang 2012; Pratas et al. 2012,
2014; Nie et al. 2014; Pan et al. 2016). Greene et al. (1986) and Nakajima et al.
(1979) reported that with the increase of carbonate concentration, the amount of the
adsorbed uranium by single-cell algae (C. regularis and C. vulgaris) gradually
decreased. When phosphate was present in the solution, it reacted with uranium to
form a precipitate, and the bioaccumulation of uranium decreased (Mkandawire
et al. 2007; Misson et al. 2009).
Azolla-Anabaena is a kind of fern-algae symbiotic aquatic plant and has been
used as green manure in rice fields, due to its strong nitrogen fixation ability (Tang
et al. 2000). Arora et al. (2006) and Rai (2008) have found that Azolla-Anabaena
had strong accumulation ability for heavy metals in solutions. Other studies have
also showed that Azolla-Anabaena had a strong accumulation capability for uranium. Hu et al. (2012) have found that Azolla-Anabaena symbiotic system had
excellent performance for removal of uranium. Heavy metal and uranium accumulation by Azolla-Anabaena has been reported extensively; however, the accumulation behavior of different uranium species by Azolla-Anabaena has not been studied.
In this paper, the proportions of different species of uranium in solutions under
different conditions were calculated with MINTEQ 3.1 software, which is a chemical equilibrium computer program that has an extensive thermodynamic database
enabling users to calculate the speciation, solubility, and equilibrium of solid and
dissolved phases of minerals in an aqueous solution (Gustafsson 2006). Based on
the calculation results, five solutions containing UO 2
2+
, (UO 2 ) 3 (OH) 5
+
, UO 2 (OH) 3
−
,
UO 2 (CO 3 ) 3
4−
, and UO 2 PO 4
−
, respectively, were prepared. The effects of uranium
speciation on the bioaccumulation by and translocation in Azolla-Anabaena were
finally investigated through hydroponic experiments, and the new ideas and theoretical basis for further improving the removal efficiency of uranium by AzollaAnabaena from water were provided.
2 Material and Methods
2.1 Material
Azolla-Anabaena was taken from a field in the suburb of Hengyang city in South
China. After the Azolla-Anabaena was washed with tap water for 3–5 min, it was
put into the improved Hoagland nutrient solution and cultivated for 2 weeks for
experimentation (Hu et al. 2012).
N. Hu et al.