Optimization arsenic immobilization in a sandy loam soil using iron-based amendments by response surface methodology

The survey of reports regarding high concentrations of arsenic in soils and groundwater around the world, which refers to increase of arsenic exposure to the living organisms, has been increased. In this research work arsenic immobilization process using three iron amendments (soluble Fe(II), zero-valent iron (ZVI), and Fe (II)-modified zeolite (Fe-Z)) was modeled and optimized in a spiked soil by response surface methodology (RSM). Three factors including initial concentration of As(III) (20 to 580 mg kg− 1 of soil), amount of added Fe (0.5 to 2.5 wt.% of soil for both Fe(II) and ZVI, 0.05 to 0.2 wt.% of soil for loaded Fe on zeolite) and shaking time (15 to 960 min) were selected as the independent factors on arsenic immobilization efficiency. The five-level central composite design (CCD) was used for experiment design and optimization model parameters. Variance analysis showed that CCD models were statistically significant for all amendments (p < 0.01) with high accuracy (R2 = 0.98 for Fe(II), R2 = 0.89 for ZVI and R2 = 0.92 for Fe-Z) in predicting As(III) immobilization. Optimization results showed that at 200 mg As kg− 1 soil and 600 minute shaking time, the immobilization of As(III) with Fe(II), ZVI and Fe-Z was 90.6%, 92% and 81.4%, respectively. However ZVI was most effective amendment, but with negligible difference in immobilization As(III), Fe(II) is more economical. In conclusion Fe(II) was more efficient and cost-effective than ZVI and Fe-Z in long-term immobilization.