In situ immobilization of Cu(II) in soils using a new class of iron phosphate nanoparticles

This study tested the feasibility of using a new class of iron phosphate (vivianite) nanoparticles synthesized using sodium carboxymethyl cellulose (NaCMC) as a stabilizer for in situ immobilization of Cu(II) in soils. Transmission electron microscopy measurements demonstrated that the particle size was about 8.4 ± 2.9 nm. Batch tests showed that nano-sized vivianite particles can effectively reduce the leachability and in vitro bioaccessibility of Cu(II) in three representative soils (calcareous, neutral, and acidic) at the low doses of 0.61 and 3.01 mg PO4 g−1 soil. The Cu leachability was evaluated by the toxicity characteristic leaching procedure and in vitro bioaccessibility was evaluated by the physiological based extraction test. In the case of soil amendment with nanoparticles in 3.01 mg PO4 g−1 soil, Cu leachability reduced 63–87% and Cu concentrations in TCLP extract decreased from 1.74–13.33 mg l−1 to 0.23–2.55 mg l−1 after those soils were amended for 56 d. Meanwhile, the bioaccessibility of Cu was reduced by 54–69%. Sequential extraction procedures showed the significant decrease of water soluble/exchangeable Cu(II) and carbonate bound fractions and concomitant increase of Cu residual fraction after the soils were amended with the nanoparticles, suggesting that the formation of copper phosphate minerals through precipitation and adsorption was probably responsible for the decrease of Cu availability in soils. Visual MINTEQ modeling further revealed that Cu3(PO4)2 and Cu5(PO4)3OH were formed in the vivianite–solid Cu(II) system, resulting in the decreased solubility of the Cu(II) in the acidic pH range.