Novel Non-crystalline iron-phosphate nanoparticles for remediating toxic heavy metals and radionuclides

Abstract

Novel iron-phosphate nanoparticles have been synthesized here. These are less than 12 nanometers in dimension. They are deemed useful for remediation of heavy metals and radionuclides and can be applied to insitu remediation of contaminated soils and contaminated waters.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Partial federal funding was used to support product development

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The purported invention has to do with use of nanoparticles in remediation.

(2) Description of the Related Art

Soils at current or previously mined and smelter sites normally contain higher concentrations of heavy metals such as Pb, Cu, Cd, and Hg exceeding the current regulatory levels (Diawara et al., 2006).

Engineered nanoparticles have been found to offer great promise for remediation of contaminated soils and groundwater (Karn et al., 2009).

General mechanisms of remediation using engineered nanoparticles are induction of various sorption processes (e.g., adsorption to Fe₂O₃ nanoparticles), reductive immobilization (e.g., EZVI for reduction of chlorinated solvents), or surface precipitation of new contaminant phases with much reduced mobility.

Surface precipitation of new contaminant phases include Pb immobilization via addition of apatite resulting in precipitation of recalcitrant pyromorphite (Kumpiene et al., 2008; Knox et al., 2006).

Phosphate can effectively capture metal cations including those of heavy metal contaminants, and phosphate-metal precipitates are typically very stable over a wide range of environmental conditions (Knox et al., 2006).

Therefore, metal-phosphate nanoparticles hold promise for effective remediation of contaminated sites.

Metal-phosphate nanoparticles have not been investigated with the exception of recent nano-remediation work by researchers Liu and Zhao, (2007a and 2007b).

Their iron phosphate (vivianite) nanoparticles particles showed reduced Cu(II) leachability by 63-87% and its bioaccessibility in acid, alkaline, and neutral soils after amendment for 56 days (Liu and Zhao, 2007a).

Vivianite nanoparticles were similarly shown to be effective with Hg, and Pb remediation (Liu and Zhao, 2007b; U.S. Pat. No. 7,581,902).

The effect of vivianite nanoparticles was examined only one metal at a time. Soils are contaminated with multiple metals and metal interactive effects can alter remediation efficacy. For example, in As and Pb contaminated soils, Fe and PO₄ application affected the mobility of As and Pb in opposite ways (Cui et al., 2010).

BRIEF SUMMARY OF THE INVENTION

Here we have synthesized novel iron-phosphate nanoparticles. They are useful for remediating toxic heavy metals including but not limited to Pb(II), Cu(II), Cd(II), Hg(II), radionuclides, Cr(VI), and As(V).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Transmission electron micrographs of non-crystalline iron-phosphate nanoparticles

FIG. 2: Initial concentration of Pb, Cd, Cu, and Hg were 207 mg/L, 112 mg/L, 63 mg/L, and 200 mg/L, respectively. Concentration of dissolved metals (Pb, Cd, Cu, and Hg) in mg/L after addition of FePO₄ nanoparticles as a function of time at pH 4

FIG. 3: Initial concentration of Pb, Cd, Cu, and Hg were 207 mg/L, 112 mg/L, 63 mg/L, and 200 mg/L, respectively. Concentration of dissolved metals (Pb, Cd, Cu, and Hg) in mg/L after addition of FePO₄ nanoparticles as a function of time at pH 6

FIG. 4: Initial concentration of Pb, Cd, Cu, and Hg were 207 mg/L, 112 mg/L, 63 mg/L, and 200 mg/L, respectively. Concentration of dissolved metals (Pb, Cd, Cu, and Hg) in mg/L after addition of FePO₄ nanoparticles as a function of time at pH 8

DETAILED DESCRIPTION OF THE INVENTION

Here we have synthesized novel nanoparticles.

We have characterized them as iron-phosphate nanoparticles.

Our novel non-xl FePO₄ nanoparticles are smaller than Liu and Zhao's 8.4±2.9 nm size (2007a and 2007b) vivianite. We expect our nanoparticles to be more effective in remediation.

In lab tests we have shown them to be effective in remediation heavy metals.

Example 1: Synthesis of Novel Iron-Phosphate Nanoparticles

Prepare 250 ml of 0.5 M ferric-nitrate.9H₂O and 250 ml of 0.5 M KH₂PO₄ in PP volumetric flasks using millipore water. Combine the two solutions while stirring and immediately adjust pH to 3.2 with 4.5 M KOH and then 0.5 M KOH. The suspension is aged for 42 hrs at 99 degree C. in a dry air oven. After 42 hrs, aging, remove the suspension from the oven and wash three times with water to remove salts.

Example 2: TEM Micrographs of Iron-Phosphate Nanoparticles

The aggregated nano-particles measure roughly 10-12 nm in size with individual nanoparticles likely smaller than stabilized vivianite nanoparticles (see TEM micrograph, FIG. 1).

Example 3: Remediation of Cu(II), Pb(II), Cd(II), and Hg(II) Contaminated Water Using Iron-Phosphate Nanoparticles in the Presence and Absence of Common Soil Ligands

Nitrate salts of heavy metals were added to pH adjusted (4.0-8.0) fixed suspension volumes (30 ml) containing 1.5 g/L non-xl FePO₄ nanoparticles in 10 mM KCl while stirring at moderate speeds. At pH 6, commonly available ligands, citrate (1 mM), and siderophores (0.25 mM desferrioxaine B) were also added. Total sample volume was 30 ml to allow for sufficient volumes of supernatant for ICP analyses. Controls comprised nanoparticles alone in the absence of heavy metals. Representative samples were withdrawn at 24, and 336 hrs and centrifuged and concentration of dissolved heavy metal contaminants was measured in supernatants to assess reduction in leachability from the soil solution phase. The ligand concentrations are based on the concentrations commonly found in soils.

The addition of FePO₄ nanoparticles was successful in reducing the concentration of all dissolved metals irrespective of pH (FIGS. 2, 3, and 4). However, remediation efficacy of FePO₄ nanoparticles was metal and pH dependent (FIGS. 2, 3, and 4). FePO₄ was most effective in remediating Pb, and Cu reducing their respective concentration to zero (FIGS. 2, 3, and 4). In addition, FePO₄ nanoparticles were most effective in remediating heavy metals at alkaline pH (FIG. 4). In the presence of ligands, citrate and DFO-B at near neutral pH of 6, FePO₄ nanoparticles were completely successful in remediating all the metals reducing their concentration to zero at 24 hr, and maintaining it to 336 hr.

Based on the above, we expect FePO4 nanoparticles to be similarly effective in remediating radionuclides.

REFERENCES

• Cui Y. S., Du X, Weng LP, et al., 2010. Assessment of In Situ Immobilization of Lead (Pb) and Arsenic (As) in Contaminated Soils with Phosphate and Iron: Solubility and Bioaccessibility. Water Air and Soil Pollution, 213: 95-104.
• Diawara, M. B., Litt, J. S., Unis, D., Alfonso, N., Martinez, L., Crock, J. G., Smith, D. B., and Carsella, J., 2006. Arsenic, Cadmium, Lead, and Mercury in surface soils, Pueblo, Colo.: implications for population health risk. Environmental Geochemistry and Health, 28:297315.
• Kumpiene J, Lagerkvist A, Maurice C, 2008. Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments-A review. Waste Management, 28:215-225.
• Karn B, Kuiken T, Otto M, 2009. Nanotechnology and in Situ Remediation: A Review of the Benefits and Potential Risks. Environmental Health Perspectives, 117:1823-1831.
• Knox A. S., Paller M. H., Nelson E. A., Specht W. L., Halverson N. V., Gladden J. B., 2006. Metal distribution and stability in constructed wetland sediment. Journal of Environmental Quality, 35:1948-1959.
• Liu, R., and Zhao, D., 2007a. Insitu immobilization of Cu(II) in soils using a new class of iron phosphate nanoparticles. Chemosphere, 68:1867-1876.
• Liu, R., and Zhao, D., 2007b. Reducing leachability and bioaccessibility of lead in soils using a new class of stabilized iron phosphate nanoparticles. Water Research, 41:2491-2502.

Claims

1. The novelty of the nanoparticles

2. The nanoparticles of claim 1 that contain iron and phosphate in the ratio of 1:1

3. The nanoparticles of claims 1 and 2 that have an aggregated particle size of ˜12 nm and individual particle size less than 10 nm.

4. The efficacy of nanoparticles of claims 1-3 in remediating Pb(II) in contaminated water and soil in the presence and absence of common soil ligands such as citrate and siderophores.

5. The efficacy of nanoparticles of claims 1-3 in remediating Cd(II) in contaminated water and soil in the presence and absence of ligands such as citrate and siderophores.

6. The efficacy of nanoparticles of claims 1-3 in remediating Cu(II) in contaminated water and soil in the presence and absence of ligands such as citrate and siderophores.

7. The efficacy of nanoparticles of claims 1-3 in remediating Hg(II) in contaminated water and soil in the presence and absence of ligands such as citrate and siderophores.

8. The efficacy of nanoparticles of claims 1-3 in remediating a mixture of heavy metals in contaminated water and soil in the presence and absence of ligands such as citrate and siderophores.

9. The coating of nanoparticles of claims 1-3 with various polymers like carboxymethyl cellulose to keep them naturally dispersed.

10. The efficacy of the nanoparticles of claims 1-3, and 9 in insitu remediation of contaminated soils or water with single heavy metals, or a combination of them in the presence or absence of common soil ligands such as citrate and siderophores.