Curbing toxic emissions from remediated substrate

Abstract

A process for curbing of emissions of toxic metals and chelating agent from remediated soils, sediments and other substrates contaminated with toxic metals, said process comprising: (a) remediation of contaminated soil, sediment and other substrate with washing solution, said washing solution comprising EDTA or other chelating agent from the group of aminopolycarboxylic acids and their salts and mixtures thereof; (b) addition of 0.05-5% (w/w, dry weight) of zero-valent Fe or Fe compounds from the group of Fe-oxides and Fe-oxide-hydroxides into the slurry phase of soil, sediment and other substrate; (c) mixing of Fe-amended slurry; (d) separation of solid phase of remediated and Fe-amended soil, sediment and other substrate; (e) ageing of remediated and Fe-amended soil, sediment and other substrate for 0.5-45 days.

Claims

1. A process for curbing of emissions of toxic metals and chelating agent from soils, sediments and other substrates contaminated with toxic metals, said process comprising: (a) remediation of contaminated soil, sediment and other substrate by washing with washing solution, said washing solution comprising EDTA or other chelating agent from the group of aminopolycarboxylic acids and their salts and mixtures thereof to form a slurry phase; (b) addition of 0.05-5% (w/w, dry weight) of zero-valent Fe or Fe compounds from the group of Fe-oxides and Fe-oxide-hydroxides into the slurry phase of soil, sediment and other substrate; (c) mixing of Fe-amended slurry; (d) separation of solid phase of remediated and Fe-amended soil, sediment and other substrate; and (e) ageing of remediated and Fe-amended soil, sediment and other substrate for 0.5-45 days.

2. The process of claim 1, wherein in step (b) the granulation of Fe and Fe compounds can vary from nanoparticles to grains with <2 mm in diameter.

3. The process of claim 1, wherein the Fe and Fe compounds can be in step (b) delivered into the slurry phase alone or in formulation with fertilizers, immobilizators of toxic elements and compounds, other conditioners and materials which enhance soil, sediment and other substrate quality.

4. The process of claim 1, wherein the said solid phase may be before and after addition of Fe and Fe-compounds in step (b) rinsed with clean solutions to remove the bulk of toxic metals and chelating agent.

5. The process of claim 1, wherein the remediated and Fe-amended soil, sediment and other substrate is in step (e) aged by short-term storage or by in situ maintaining a neutral water balance in remediated material.

6. The process of claim 2, wherein the Fe and Fe compounds can be in step (b) delivered into the slurry alone or in formulation with fertilizers, immobilizators of toxic elements and compounds, other conditioners and materials which enhance soil, sediment and other substrate quality.

7. The process of claim 2, wherein the said solid phase may be before and after addition of Fe and Fe-compounds in step (b) rinsed with clean solutions to remove the bulk of toxic metals and chelating agent.

8. The process of claim 3, wherein the said solid phase may be before and after addition of Fe and Fe-compounds in step (b) rinsed with clean solutions to remove the bulk of toxic metals and chelating agent.

9. The process of claim 2, wherein the remediated and Fe-amended soil, sediment and other substrate is in step (e) aged by short-term storage or by in situ maintaining a neutral water balance in remediated material.

10. The process of claim 3, wherein the remediated and Fe-amended soil, sediment and other substrate is in step (e) aged by short-term storage or by in situ maintaining a neutral water balance in remediated material.

11. The process of claim 4, wherein the remediated and Fe-amended soil, sediment and other substrate is in step (e) aged by short-term storage or by in situ maintaining a neutral water balance in remediated material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described with reference to the appended drawings, wherein:

(2) FIG. 1 shows potential Pb emissions (Pb concentration in extracts) from original (Org.), remediated but not Fe-amended (Rem.), and remediated and Fe-amended soil (Rem.+Fe). Data are given as means and standard deviations of three replicates.

(3) FIG. 2 shows potential Zn emissions (Zn concentration in extracts) from original (Org.), remediated but not Fe-amended (Rem.), and remediated and Fe-amended soil (Rem.+Fe). Data are given as means and standard deviations of three replicates.

(4) FIG. 3 shows potential Cd emissions (Cd concentration in extracts) from original (Org.), remediated but not Fe-amended (Rem.), and remediated and Fe-amended soil (Rem.+Fe). Data are given as means and standard deviations of three replicates.

(5) FIG. 4 shows potential Fe emissions (Fe concentration in extracts) from original (Org.), remediated but not Fe-amended (Rem.), and remediated and Fe-amended soil (Rem.+Fe). Data are given as means and standard deviations of three replicates.

(6) FIG. 5 shows potential EDTA emissions measured as a total chelating activity of EDTA and dissolved humic acids in extracts from remediated but not Fe-amended (Rem.) and remediated and Fe-amended soil (Rem.+Fe). Data are given as means and standard deviations of three replicates. The broken line denotes the limit of quantification (LOQ).

DESCRIPTION OF PREFERRED EMBODIMENT

(7) The acidic (pH=5.1) industrially contaminated soil (50 kg, dry weight) from Arnoldstein (Austria) with 860 mg kg.sup.1 Pb, 330 mg kg.sup.1 Zn and 3 mg kg.sup.1 Cd was washed in a mixing vessel with 60 mM EDTA kg.sup.1 solution (w:V ratio 1:1). According to the process described in the invention an addition of 1% (w/w) of zero-valent Fe (<0.5 mm granules) was applied into the soil slurry phase. The soil solid phase was then separated from slurry using a chamber filter press and in-press rinsed with 3 volumes of cleansed rinsing solution to remove the bulk of toxic chelates. The rinsing solution was cleansed and recycled as described in the patent application Soil and sediment remediation EP 3 153 246 A1.

(8) Soil washing with EDTA removed 78, 20 and 83% of the Pb, Zn and Cd, respectively. Lower levels of Zn extractability from soil is known to one skilled in art.

(9) The washed (remediated) soil contained 28% of moisture and was stored at room temperature for 8 weeks. Periodically, a 30 g sample was taken from the bulk of the soil and extracted on shaker with 50 mL of deionized water. The Pb, Zn, Cd and Fe concentration in extracts was determined using atomic absorption spectroscopy (AAS). The EDTA was assessed spectrophotometrically using modified method of Wang et al. (J. Wang, J. Yu, X. Z. Kong, L. Hou, Spectrophotometric determination of EDTA in aqueous solution through ferroin formation using sodium sulfite as the reducer, Chemosphere 91 (2003), pp. 351-357). EDTA was measured as a part of the total chelating activity in the extract comprising of concentrations of EDTA and of the humic acids dissolved from soil organic matter during soil-washing process.

(10) As apparent from FIGS. 1, 2 and 3 the Fe amendment significantly reduces extractability of toxic metals (Pb, Zn and Cd), Fe (FIG. 4) and EDTA (FIG. 5) from remediated soil. Furthermore, after 1-7 days of storage the potential emissions of metals from remediated and Fe-amended soil were equal or lower than from original, not-washed soil.