FR2784982A1 - Destruction of organochlorine pollutants in water comprises using non-zero valent reduced iron - Google Patents

Abstract

Process for destroying organochlorine pollutants in phreatic (pollutant-saturated) water layers comprises using one or more forms of non-zero valent reduced iron, intermediate between zero valent and trivalent, at ambient temperatures and pressures. An Independent claim is also included for an agent for treating phreatic water layers polluted with chlorine compounds, comprising non-zero valent iron.

Description

Process using non-zero-value iron as a barrier to
groundwater treatment, and new treatment agent
corresponding.

The technical sector of the invention
The present invention is intended for the degradation of chlorinated organic pollutants present in the water table, in which the pollutant molecules are degraded by iron. The present invention is particularly suitable for chlorinated compounds in groundwater which can be treated either in "above-ground" reactors or in situ.

Previous
The extraction of organic pollutants from the groundwater initially required technologies to transfer the components from one medium (water) to another (air, active carbon, etc.). Since these technologies do not make it possible to destroy the molecules of pollutants, such as chlorinated solvents (for example. Tetrachlorethylene, trichlorethylene, etc.), or chlorinated aromatics (for example. new, more recent technologies capable of destroying these molecules have been proposed. In 1987, the scientific community understood that halogenated solvents previously considered recalcitrant, could undergo a series of degradation reactions (Vogel et al. 1987, Environ. Sci Tech. 21: 722-736).

These reactions include the reductive dehalogenation of the halogenated components, in which the halogen is extracted from the molecule in the form of a free halogenated ion in aqueous solution and replaced on the molecule by a hydrogen ion. This reaction requires a source of electrons. As described in the article cited above, transition metals are often used for this reaction. Even biological degradation reactions of these compounds use cofactors with metal cores and enzymes. Scientists question the mechanism of dehalogenation and the source of electrons. Clearly, the reductive dehalogenation reaction requires a source of electrons, and often a metal site for the reaction. Since the first observations of these phenomena, several application patents have been filed, using different metals, different sources of electrons, and different supports for metals and for many applications for environmental protection and in particular for dechlorination. in the aqueous phase for the treatment of aquifers (e.g. USP 5,196,617; EPA 0563 669 A1; USP 5, 266, 213, WO 95/29 129).

However, the chemical reaction was naturally patented previously (1972 and 1983) among others by Sweeney. (USP 3,640, 821; USP 3,737,384; USP 4,219,419; USP 4,382,865). The difference between the first and most recent patents lies in a new approach to applications for environmental protection.

Zero-value iron technologies are relatively inexpensive in the in situ use of groundwater treatment. However, the availability of zero-value iron and the need for the water table to be anoxic, limit their application (USP 5,266,213).

Summary of the present invention:
The iron used here is different from that proposed in previous technologies, and a modification of the fundamental chemical mechanisms and operating conditions is carried out.

The foregoing methods described the use of zero-valent iron to treat an anoxic water table (without dissolved molecular oxygen) containing chlorine compounds. The reaction described then was the transformation of zero-valent iron into ferrous ion Fe2 + where the two liberated electrons were transferred (in one operation), to the chlorinated compound, which led to the extraction of chlorine in the form of chloride (CI- ).

 It has now surprisingly been discovered that ferric iron, in the system of the invention, is capable, by simple electron transfers, of also dechlorinating these pollutants, and moreover, that the use of iron under an already reduced form (Fe2 +) does not require that the water table be anoxic. The invention therefore has great practical and economic interest, since most of the water tables are not anoxic.

A real need therefore exists for this new and economical low-cost "iron" technology which does not limit the constraints of zero-value iron technology.

The present invention therefore results from the surprising discovery that non-zero-valent iron (particularly Fe2 + but also Fe 3+ and all the intermediate forms) is capable of carrying out the reductive dechlorination of chlorinated organic compounds in water in the presence or absence molecular oxygen.

The field of application of this technology is between approximately 5 gg and approximately 1 g of non-zero-valent iron / I of chlorinated compounds.

Detailed description of the invention
Metals: The iron used in this invention occurs in all intermediate forms (between zero-valent iron and Fe203). This feature allows the use of a varied range of ferrous materials, including among others: automobile residues, residues of equipment containing iron or steel. In addition, iron does not need to be isolated from the oxygen-containing water table.

Temperature: This invention is applicable for groundwater, the temperature of which normally varies from 4 to 35 C.

The ability of this invention to operate at these temperatures is fundamental to this application.

Pressure Similarly to temperature, the characteristic pressure range for natural aqueous media varies between 1 and 5 bars.

Pollutants:: The invention applies to all chlorinated organic compounds represented by the main families of chlorinated solvents (for example: trichlorethylene) and chlorinated aromatics (for example: chlorobenzene).

Reactors: This invention can be extended to new methods of treating groundwater. The invention thus applies in "reactors in situ" where the material is placed freely in open trenches, either placed between elaborate sealed systems (of diaphragm walls type, walls, etc.), or combined with other techniques where ) the groundwater is treated by passing through a reactive module.

In general, those skilled in the art will understand that all systems for treating groundwater using above-ground reactors containing the principles of the reaction (non-zerovalent iron) are included in the invention.

Groundwater: Groundwater does not have to be anoxic.

Drawing:
Other advantages and modes of implementing the invention will be better understood on reading the description, and with reference to the appended drawing, in which: the single figure represents the chromatogram of the treatment of a water table by Fe2 + according to the invention, as described in the example below.

Examples:
A water table containing chloroform, tetrachloromethane and trichlorethylene was tested by a nonlimiting embodiment of the invention (ie Fell).

The characteristics of the sheet before and after treatment are collated in the table below.

10 g of iron (o) or 10 g of iron (II) were put in bottles containing 60 ml of ground water. The concentrations of chlorinated compounds present in the water table before the treatment are indicated in the table below.

The vials were gently shaken for 30 minutes, after which the GC analyzes (gas chromatography) were performed.

The results are also collated in the table below, with regard to iron (o) and iron (II).

In this example, iron oxide was tested to confirm the differences from zero valent iron (see single figure).

In the single figure attached,
DCE stands for dichloroethene
DCM stands for dichloromethane
TCM stands for trichloromethane (chloroform)
DCA means dichloroethane
CT stands for tetrachloromethane (carbon tetrachloride)
TCE stands for trichlorethylene or trichlorethylene
In addition, the groundwater simulation test was performed on water saturated with molecular oxygen, that is to say an absolutely non-anoxic groundwater.

It can be seen that the process according to the invention makes it possible, in a simple and inexpensive manner, to rapidly degrade certain chlorinated pollutants well known for their harmfulness.

The invention therefore relates to a process for destroying chlorinated organic molecules considered as pollutants of contaminated groundwater, of the type using iron, characterized in that it comprises the use of at least any one of the different forms of reduced iron, ie other than zero-value iron, at ambient pressures and temperatures.

The invention also relates to an agent for treating groundwater polluted by chlorinated compounds, characterized in that it comprises non-zero-valent iron.

BOARD
Groundwater treatment
TRIAL
BEFORE AFTER APR
Iron 11) (Iron 0)
Volatile chlorinated hydrocarbons microg microg microg (organochlorines) / liter / liter t liter
190 26 7.9 vinyl chloride
15 7.5 5.9 dichloromethane
5.4 <0.5 <0.5 trans dichlorethene
740 98 5.2 cis dichlorethene
15 1.3 <0.5 trichloromethane
100 6.5 0.9 1.1,1-trichloroethane
23 0.6 <0.5
Tetrachloromethane
400 15 1, 7
Trichloroethene
150 1.3 <0.5
Tetrachloroethene
1638 156 22
Sum of organochlorines
Note: AVT = state before treatment
APR = state after treatment with Fe (o) or Fe (II)

Claims (9)

 1.- Process for destroying chlorinated organic molecules considered as pollutants of contaminated groundwater, of the type using iron, characterized in that it comprises the use of at least any one of the different forms of iron reduced, ie other than zero-valent iron, including the intermediate forms between zero-valent iron and Fe203, at ambient pressures and temperatures.  2.-Method according to claim 1, characterized in that it uses a form of ferric iron Fe3 +, such as Fe203.  3.-Method according to claim 1, characterized in that it uses a form of ferrous iron Fe2 +.  4.-Method according to any one of claims 1 to 3, characterized in that the ambient pressure varies between 1 and 5 bars.  5.-Method according to any one of claims 1 to 4, characterized in that the ambient temperature varies between 4 and 35 C.  6.-Method according to any one of claims 1 to 5, characterized in that water is treated in the presence or in the absence of dissolved molecular oxygen.  7.- Method according to any one of claims 1 to 6, characterized in that one treats waters containing at least one of the chlorinated organic compounds represented by the large families of chlorinated solvents (trichlorethylene) and / or chlorinated aromatics (chlorobenzene).  8.-A method according to any one of claims 1 to 7, characterized in that the contaminated sheet is treated with a dose of non-zero-valent iron of between 5 p. g to 1 g / l of chlorinated compounds.  9.-Agent for treating groundwater polluted by chlorinated compounds, characterized in that it comprises non-zerovalent iron.