Simultaneous immobilization of Pb, Cd and As in soil by hybrid iron-, sulfate- and phosphate-based bio-nanocomposite: Effectiveness, long-term stability and bioavailablity/bioaccessibility evaluation.

Here, the bio-nanocomposite (n-HFP + n-HFS)@An was developed to simultaneously immobilize Pb, Cd and As in the severely contaminated soil. The immobilization rates of diethylenetriaminepentaacetic acid (DTPA)/decarbonate-extracted bioavailable Pb, Cd and As were 59.87%, 31.28% and 62.30%, and the immobilization rates of their water-soluble forms were 63.12%, 60.02% and 89.39%, respectively. Moreover, the ten-year acid rain simulated leaching assay showed that the maximum cumulative release contents of Pb, Cd and As in the treated soil samples were decreased by 2.94, 2.46 and 40.60 times, comparing to the un-treated ones. Additionally, the results of SBRC (Solubility Bioaccessibility Research Consortium) revealed that the bioaccessible rates of the three metals in intestinal phase were lower than in gastric phase, and both of them decreased with increasing the immobilization time. The gastric bioaccessibility of Pb, Cd and As had a higher correlation with the contents of water-soluble forms, while the intestinal bioaccessibility was more strongly positively associated with the bioavailable forms.

Simultaneous adsorption of As(III), Cd(II) and Pb(II) by hybrid bio-nanocomposites of nano hydroxy ferric phosphate and hydroxy ferric sulfate particles coating on Aspergillus niger.

To develop an efficient, convenient and cost-effective method to simultaneously remove pollution of As(III), Cd(II) and Pb(II) in wastewater, a strategy to fabricate hybrid bio-nanocomposites ((n-HFP + n-HFS)@An) of nano hydroxy ferric phosphate (n-HFP) and hydroxy ferric sulfate (n-HFS) particles coating on Aspergillus niger was applied. The scanning electron microscope and energy dispersive spectrum analyses showed that (n-HFP + n-HFS)@An composites had been successfully developed which well solved the self-agglomeration problem of the nano particles. Comparing to the bulk nanoparticles, the adsorption rates of the (n-HFP + n-HFS)@An composites for the three metals were promoted 145.34, 28.98 and 25.18% and reached 76.84, 73.62 and 94.31%, respectively. Similarly, the adsorption capacities for As(III), Cd(II), and Pb(II) were 162.00, 205.83 and 730.79 mg/g, respectively. Moreover, the pseudo-second-order kinetic model was more relevant to the adsorption on the three metals by (n-HFP + n-HFS)@An, and adsorbing As(III) was fitted to the Freundlich isotherm model, while the adsorption on Cd(II) or Pb(II) was related to the Langmuir isotherm model. In addition, the adsorption of Cd(II) and Pb(II) was associated with transformation of hydroxyl groups and precipitation with phosphate. As(III) was adsorbed through exchange between AsO2- and SO42- in the (n-HFP + n-HFS)@An composites.