Stabilized magnetite nanoparticles were synthesized with starch and sodium carboxymethyl cellulose (CMC) as a stabilizer, and tested for enhanced arsenate removal. Starch at ≥0.04 wt.% or CMC at ≥0.005 wt.% fully stabilized 0.1 g/L (as Fe) of the nanoparticles. While CMC-stabilized magnetite displays a highly negative ζ potential, starch-stabilized magnetite shows a nearly neutral surface. Increasing starch concentration from 0 to 0.04 wt.% doubles arsenate uptake capacity. Starch-stabilized magnetite offers much faster sorption rate and greater capacity than CMC-stabilized magnetite. The sorption kinetics can be modeled using an intraparticle-diffusion model. The sorption capacity increases with decreasing pH. Dissolved organic matter at 20 mg/L as TOC decreases arsenate uptake by 19%. When aged for &gt;1.5 years, the nanoparticles did not show any arsenate leaching or particle dissolution. Furthermore, we investigated effectiveness of starch-stabilized magnetite nanoparticles for in situ immobilization of arsenate in a model sandy loam soil. Batch tests showed that the nanoparticles offered an As(V) distribution coefficient of 10,000 L/g, which is &gt;3 orders of magnitude greater than that for the soil. Batch and column experimental results revealed that the nanoparticle treatment greatly reduced water-leachable As(V) and the leachability of As(V) remaining in the soil per TCLP (Toxicity Characteristic Leaching Procedure) analysis. While the nanoparticles are deliverable in the soil, the effective travel distance of the nanoparticles can be manipulated by controlling the injection flow rate. Under natural groundwater flow conditions (e.g., velocity ≤ 2.4x10-4 cm/s), the delivered nanoparticles are confined within a limited distance (&lt;6.1 cm). The stabilized nanoparticles are promising for in situ immobilization of arsenate in soil and groundwater.

Immobilization of arsenate in soil and groundwater using starch-stabilized magnetite nanoparticles

249th National Meeting (2015)

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