FR3149221A1 - Process for extracting dense liquids in non-aqueous phase - Google Patents

Abstract

A method for extracting DNAPL from soil, comprising providing an injection well (23) positioned adjacent to a zone (21) comprising the DNAPL, and a recovery well (25) positioned such that a portion of the DNAPL is located between the injection well (23) and the recovery well (25). The method comprises the steps of: - injecting an aqueous solution of a shear-thinning polymer into the injection well (23) so as to release said solution into the zone (21) comprising the DNAPL to contact the DNAPL in the zone (21), and - extracting said polymer solution and the DNAPL from the recovery well (25). The aqueous polymer solution comprises a densifying agent so as to have a density substantially equal to the density of a liquid comprising the DNAPL. The densifying agent is soluble in the aqueous solution at said density. Figure for abstract: Figure 7

Description

Process for extracting dense liquids in non-aqueous phase

1 - Technical field of the invention

The invention relates to the field of decontamination of soils contaminated by Dense Non-Aqueous Phase Liquids (DNAPL), and in particular soils saturated with DNAPL. It relates more specifically to a method for extracting DNAPL from soils comprising. It also relates to an aqueous solution of a polymer for use in a method for extracting DNAPL. Finally, it relates to an installation for extracting DNAPL. DNAPL are liquids that are immiscible with water and have a density greater than water. They are mainly chlorinated organic pollutants.

2 - State of the art

DNAPL spills have caused serious pollution of soil and groundwater. DNAPL can penetrate through the soil and form insoluble lenses below the water table. Due to their high density and high interfacial tension, the removal of these compounds is difficult. Therefore, the use of conventional extraction technologies such as the pumping and treatment method is not effective. Indeed, pumping homogeneity is not possible in a heterogeneous medium: fingering occurs.

New and more advanced remediation methods including in situ thermal and chemical enhancement, biological remediation, and soil washing have been proposed. Injection of the invading chemical agents (including surfactant, foam, and polymer solutions) to displace DNAPL can result in higher recovery rates. Adding these agents during pumping to push DNAPL can prevent digitation and increase remediation rates.

In the case of polymer solutions as non-Newtonian fluids, they can displace the pollutant from contaminated areas. In other words, the viscous forces provided by the polymer solution enhance the recovery of contaminants from soils saturated with these contaminants. But these solutions have a density of the order of 1, which causes an upward movement when injected. In the case of DNAPLs, since they are denser than water, the forces of gravity actively oppose their movement when injecting the chemical agents. To mobilize the DNAPL ganglia trapped in the soil, the invading fluid must overcome gravity and capillary forces.

From the perspective of gravity forces, a density-driven mobilization approach using densified sodium iodide solution was proposed to displace DNAPLs from the contaminated area.

Although each of the proposed solutions (polymer solutions and increased density solution) can improve the recovery of DNAPL from soil in a closed system (like 1D columns), in case of an open system where the upper boundary between the DNAPL zone and water is open, they cannot provide high recovery rate.

Also, the inventors proposed a polymer suspension densified by barite particles (barium sulfate) to improve the displacement of DNAPLs (Alamooti et al., 2022). Indeed, when the polymer solution is densified, the upward movement caused by the polymer solution is limited and more horizontal, which further increases the purification efficiency. It has been shown that a polymer suspension densified by barite particles can increase the recovery rate compared to a pure polymer solution (not densified). However, the barite particles have the disadvantage of depositing in the porous medium, thereby leading to clogging problems, i.e. the pores are blocked.

Description of the invention

The invention aims in particular to propose a method for extracting DNAPL from soils using a polymer solution, allowing improved movement, while not having the above drawback.

For this purpose, the invention relates to a method for extracting a dense liquid in a non-aqueous phase from a soil which comprises the use of an injection well placed adjacent to a zone comprising the dense liquid in the non-aqueous phase, and a recovery well placed at a distance from the injection well, such that at least a portion of the dense liquid in the non-aqueous phase is located between the injection well and the recovery well. The method according to the invention comprises the following steps:
- injecting an aqueous solution of a shear-thinning polymer into the injection well so as to release said solution into the zone comprising the dense liquid in non-aqueous phase to come into contact with the dense liquid in non-aqueous phase in said zone so as to displace the dense liquid in non-aqueous phase towards the recovery well, and
- extraction of said polymer solution and the dense liquid in non-aqueous phase from the recovery well.
The aqueous polymer solution comprises a densifying agent so as to have a density substantially equal to the density of a liquid comprising the dense liquid in a non-aqueous phase to be extracted, and the densifying agent is soluble in the aqueous solution at said density.

This improves the recovery efficiency of DNAPL. Indeed, the presence of polymer is associated with an increase in viscosity and good horizontal propagation of the solution. The polymer is shear-thinning, i.e. its viscosity decreases when the force applied to it increases. The shear-thinning behavior of a polymer refers to its ability to reduce its viscosity when subjected to an applied shear stress or strain rate. There are different methods for measuring the shear-thinning behavior of a polymer, and the most common technique is to perform a rheological analysis using a rotational rheometer. Common examples of shear-thinning polymers are: Polyethylene oxide (PEO), Polyacrylamide (PAM), Polyvinyl alcohol (PVA), Hydroxypropyl methylcellulose (HPMC), xanthan gum, Polyethylene glycol (PEG), Polyurethane (PU), Polyethylene terephthalate (PET), Polymethyl methacrylate (PMMA). The shear-thinning polymer makes it possible to obtain a shear-thinning solution. Thanks to this characteristic, we overcome the spatial anisotropy of the soil, which opposes decontamination, mainly due to the accumulation of contaminants in areas that are difficult to access and the preferential circulation of treatment fluids in the most permeable areas. This way, the viscosity of the solution is adapted to the viscosity of the DNAPL.
In addition, since the polymer solution has a density substantially equal to that of the DNAPLs to be extracted, it will be more effective in displacing the DNAPLs. Finally, since the densifying agent is soluble in the aqueous solution, the displacement of the DNAPLs is improved by limiting clogging problems.

A liquid comprising DNAPL comprises at least DNAPL. It may consist solely of DNAPL when the sol is saturated with DNAPL. It may comprise a mixture of DNAPL with one or more liquids. The density of the aqueous polymer solution is substantially equal to the density of a liquid comprising DNAPL, i.e. it is accepted that the density of the aqueous solution has a maximum difference of 5% with the density of the liquid comprising the DNAPL to be extracted.

According to the invention, a densifying agent soluble in the aqueous solution is soluble in demineralized water at 25°C, at the concentration required to obtain the desired density of the aqueous solution.

Preferably, multiple injection wells are used.

Typically, multiple recovery wells are required to achieve best results.

Advantageously, the densifying agent is sodium iodide.

Advantageously, the polymer is a biopolymer such as xanthan, guar gum, carboxymethyl cellulose or a mixture of these compounds. These polymers have an environmental advantage because they are derived from renewable resources and are potentially biodegradable.

Even more advantageously, the polymer is xanthan.

Preferably, the xanthan is present in the solution at a concentration ranging from 0.3 g/ml to 1.5 g/ml, preferably from 0.4 to 1.2 g/ml, even more preferably from 0.55 g/ml to 1 g/ml, and more preferably from 0.8 g/ml. Thus, the polymer solution has, in the presence of the densifying agent, a viscosity allowing a broad spectrum of DNAPL to be displaced.

The density of the aqueous polymer solution can range from 1.01 to 1.80 g/ml. Preferably it is 1.70 g/ml. These densities allow the recovery of a broad spectrum of DNAPL.

Advantageously, the water in the aqueous solution is demineralized; it is advantageously degassed.

The DNAPL(s) to be extracted may be single-component or multi-component. They may be a chlorinated organic pollutant such as hexachlorobutadiene, hexachloroethane, pentachlorobenzene, carbon tetrachloride, perchloroethylene or trichloroethylene, any other pure phase DNAPL (chlorinated solvents or Polycyclic Aromatic Hydrocarbons), or a mixture of at least two of these pollutants.

Optionally, DNAPL has the following composition:
- from 55.1 to 60.9% by mass of hexachlorobutadiene, preferably from 56.8 to 59.2%, and preferentially 58%,
- from 13.3 to 14.7% by mass of hexachloroethane, preferably from 13.7 to 14.3%, and preferentially 14%,
- from 3.3 to 3.7% by mass of pentachlorobenzene, preferably from 3.4 to 3.6%, and preferentially 3.5%,
- from 3.8 to 4.2% by mass of carbon tetrachloride, preferably from 3.9 to 4.1%, and preferentially 4%,
- from 7.6 to 8.4% by mass of perchloroethylene, preferably from 7.8 to 8.2%, and preferentially 8%, and
- from 1.8 to 2.2% by mass of trichloroethylene, preferably from 1.9 to 2.1%, and preferentially 2%.

The DNAPLs to be extracted can have a viscosity ranging from 0.1 to 10 mPa.s.

The method can be used in soils with permeability ranging from 10 to 1000 Darcy, and hydraulic conductivity ranging from 5 x 10 ^-2 to 5 x 10 ^-6 ms ^-1 .

The method can be used in soils with porosity ranging from 0.29 to 0.50. Soil porosity is determined on the basis of Darcy's law.

The injection rate can be adjusted between 1ml/min and 3 ml/min to approximate the groundwater velocity, especially 2 ml/min.

The injection rate of the aqueous polymer solution can range from 0.5 to 3 m/d depending on the hydrogeological context.

Advantageously, the method is used to extract DNAPL from DNAPL-saturated soils. This means that the empty spaces within the soil, called pore spaces, are mainly occupied by DNAPL. In an alternative embodiment, it can be used to extract DNAPL from DNAPL-contaminated soils as a dissolved phase in water. Indeed, DNAPLs are slightly soluble in water, meaning that they can be dissolved in water in small quantities, which is still harmful to the environment. For example, trichloroethylene is a well-known DNAPL that has a water solubility of between 999 and 1,472 mg/l at 25 °C (average 1,118 mg/l).

The invention also relates to an aqueous solution of a polymer for use in a DNAPL extraction process, in particular a process as described above.

The invention also relates to an installation for extracting DNAPL from soils comprising and using the solution described above.

Brief description of the figures

The invention will be better understood from reading the following description, given solely by way of example and with reference to the appended drawings in which:

shows the evolution of the viscosity of polymer solutions as a function of the shear rate, as well as the Carreau model fitted to the experimental data;

shows the evolution of DNAPL recovery efficiency as a function of pore volume and solution injected into a 1D column;

is a schematic front view of a 2D tank used for two-dimensional laboratory testing;

shows the propagation, at the end of injection, of three tested solutions (a), (b) and (c) in the 2D tank through a zone contaminated by DNAPL;

shows the evolution of DNAPL recovery efficiency as a function of time and solution injected into a 2D tank;

shows the dynamics of DNAPL displacement by solutions injected into the 2D tank through a DNAPL-contaminated area;

is a schematic representation of a field installation for implementing the method according to the invention.

Examples

Tested solutions

Three solutions were tested in laboratory scale demonstration trials. These solutions are:
- a pure NaI brine solution,
- a solution of pure xanthan, and
- a solution comprising a mixture of NaI and xanthan.
In these solutions, the solvent is demineralized and degassed water. The brine solution is composed of sodium iodide (NaI) with a density of 1.7 g/mL, the pure xanthan solution comprises 0.8 g/mL of xanthan. The mixture of xanthan and NaI has a density of 1.7 g/mL at a xanthan concentration of 0.8 g/mL.

The rheological behavior of the solutions was analyzed in the range of 0.1 to 100 1/s shear rate using the Haake Mars 60 rheometer.

The viscosity of NaI solution is around 4.26 mPa.s.
There shows the evolution of viscosity (Pa.s) as a function of shear (1/s) of the xanthan solution and of the mixture of xanthan and NaI brine as well as the Carreau model fitted to the experimental data (Carreau, 1972).

The square points correspond to the measured values for the pure xanthan solution, and the round points correspond to the measured values for the mixture of xanthan and NaI. The solid curve corresponds to the Carreau model fitted to experimental data for the pure xanthan solution. The dashed curve corresponds to the Carreau model fitted to experimental data for the mixture of xanthan and NaI.

The Tile pattern can be expressed as:

where, μ ₀ and μ _inf are the viscosities (Pa.s) at zero and infinite shear rates, χ is the relaxation time (s), and l is the power index.

The parameters of the Carreau model and R-squared are given in Table 1 for pure xanthan and the mixture of xanthan and NaI.

Solution μ_inf (Not) μ₀ (Not) Χ (s) L R ² Xanthan solution 0.0087 4,310 36,755 0.1237 0.988 Mixture of xanthan and NaI 0.0072 3,214 67,330 0.0515 0.988

Although similar shear thinning behavior could be observed in both solutions, the presence of NaI in the polymer solution reduced the viscosity.

Laboratory scale testing

The tests were carried out in soil containing DNAPL extracted from the polluted Tavaux site (Alamooti et al. 2022). This DNAPL is composed of heavy chlorinated organic pollutants (COCs) such as hexachlorobutadiene-HCBD (58%), hexachloroethane-HCA (14%) and pentachlorobenzene (3.5%), carbon tetrachloride (4%), and more conventional COCs such as perchloroethylene-PCE (8%) and trichloroethylene-TCE (2%). The other pollutants composing this DNAPL have not been identified. The density of this mass is 1.66 g/mL and its viscosity is 4.47 mPa.s. Thus, the NaI brine and the mixture of xanthan and NaI have a density approximately equal to that of the DNAPL used in the tests.

One-dimensional (1D) experiments were performed in a 1D column with an internal diameter of 4 cm and a length of 30 cm. The column was packed with sand with particle sizes ranging from 0.6 to 0.8 mm. It was first saturated with water and the permeability and porosity of sand were measured to be 206 Darcy and 40.7%, respectively. These experiments provide insight into the front displacement during two-phase flow of DNAPL-polymer/brine in a closed system.

The performance of the three tested solutions on the displacement of DNAPL in the closed 1D system was evaluated by injecting each of the solutions into the 1D column through a DNAPL-saturated soil with irreducible water saturation.

The recovery efficiency of DNAPLs during injection of these fluids is illustrated in which shows the evolution of the recovery efficiency of DNAPLs as a function of the porosity and the solution injected into a 1D column.

The square dots correspond to the recovery efficiency for the pure xanthan solution, the round dots correspond to the recovery efficiency for the mixture of xanthan and NaI, and the crosses correspond to the recovery efficiency for the NaI solution.

The recovery efficiencies for polymer solutions with and without NaI are almost the same, while they are lower for the NaI solution. This can be attributed to the higher viscosity of polymer solutions compared to pure NaI brine.

Two-dimensional (2D) experiments were performed in a 2D tank, shown in , which has been assigned the reference number 1. This tank 1 has a size of 50 cm length × 30 cm height × 2 cm depth. Tank 1 includes an injection point 3 located at the bottom, in a central position of the 2D system 1. The injection point 3 has an internal diameter of 1.6 mm. The tested solutions are injected from the injection point 3. Tank 1 also includes lateral cavities 5 allowing the fluids to flow. The lateral cavities 5 each measure 2 cm in the longitudinal direction of tank 1. Tank 2D does not include a cover. It therefore constitutes an open system which makes it possible to simulate the performances in a real polluted site. The vertical and lateral propagation of the invasive phase front is monitored. Tank 2D 1 also includes an unreferenced glass facade, making it possible to image the dynamics of the experiment. This produces images which are shown in particular on the . The 2D tank was filled to its full height with sand with a grain size between 0.6 and 0.8 mm. The sand was saturated with DNAPL to a height of 20 cm with irreducible water saturation. The contaminated zone 7 is represented by a dot filling. The rest of the sand 9, shown without filling, is saturated with water.

The three tested solutions were injected into the 2D tank 1 to estimate the effectiveness of using a viscous solution (pure xanthan solution), a densified solution (NaI solution), and a viscous and densified solution (mixture of xanthan and NaI) on the recovery rate and displacement of DNAPL in real conditions. To produce the same amount of DNAPL recovered from the soil, the level of DNAPL in the side cavities 5 was controlled and fixed at a constant height.

There illustrates the distribution of the tested solutions (a), (b) and (c), called “invading phases”, and the DNAPL at the end of the experiment. The experiment was stopped due to either the invading phase reaching the lateral limits of the 2D bin or the end of DNAPL production.

For the case of pure xanthan solution (c), the invading phase 11 moved mainly vertically and most of the DNAPL remained intact at the end of the experiment.

For the cases of pure NaI brine (b) or NaI-xanthan mixture (a), a larger area of the DNAPL zone is affected by the invading phase 11; however, the residual DNAPL saturation in the displaced zone for the case of pure brine (b) is lower than the NaI-xanthan mixture (a).

This is in agreement with the recovery efficiency curves presented on the obtained by mass balance during the injection of these fluids. The recovery efficiency is represented as a function of time expressed in minutes. These results show that the recovery efficiencies at the end of injection are equal to 0.47, 0.24, 0.09 for the mixture according to the invention of NaI and xanthan (curve (a)), the NaI brine (curve (b)) and the xanthan solution (curve (c)) respectively. The method according to the invention therefore makes it possible to increase the recovery rate of DNAPL from contaminated soil.

There shows the dynamics of DNAPL displacement by solutions injected into the 2D tank through a DNAPL-contaminated area.
Profile (a), for the injection of a mixture according to the invention of xanthan and NaI, shows a completely displaced zone. Profile (b) also corresponds to the injection of a mixture according to the invention of xanthan and NaI; it shows a completely displaced and transition zone.
Profile (c), for injection of NaI brine solution, shows a displaced area.
Profile (d), for injection of xanthan solution, shows a displaced area.
In case of injection of a mixture according to the invention of xanthan and Nal (profiles (a) and (b)), two zones comprising totally displaced and transition regions are considered.
The injection of a mixture of xanthan and NaI allows to improve the radius of influence because it can propagate more horizontally in porous media.

There is a schematic representation of a field installation for implementing the method according to the invention. The installation 13 is set up in a soil 15 comprising a water-saturated zone 17 and a water-unsaturated zone 19. In this soil, a zone 21 contaminated by DNAPL is shown. The arrow 22 shows the direction of the groundwater flow.

The implementation of the extraction process will require the following facilities:
- at least one injection well 23 of the densified polymer, preferably several injection wells, placed adjacent to the DNAPL 21,

- at least one recovery well 25 of the densified polymer equipped with a pump 27, generally several recovery wells, preferably submersible, the recovery well 25 being placed at a distance from the injection well 23 such that at least part of the DNAPL are located between the injection well 23 and the recovery well 25,
- a unit 29 for preparing and mixing the densified polymer,
- a pump 31 for injecting the densified polymer mixture,
- storage units 33 of the densified polymer and DNAPL extracted by the recovery well 25.
In general, the injection pump 31 is equipped with a flow and pressure regulator; the flow rates and pressures can be calculated on the basis of laboratory experiments using samples from the site; if necessary, modeling will be carried out.
The installation 13 also preferably includes pressure sensors and flow meters, not shown.

For the implementation of the extraction method, the densified polymer solution is injected into the injection well 23 so as to release the densified polymer solution into the contaminated zone 21 to form a densified polymer solution comprising DNAPLs. The arrows 24 show the flow of densified polymer from the injection well 23. The densified polymer solution comprising DNAPLs then flows towards the recovery well 25, which is represented by the arrows 26. Under the action of the pump 27, the solution loaded with contaminants is sent to the surface to be stored in the storage unit 33. The solution loaded with contaminants may then be treated for removal of the DNAPLs, for example by incineration. The contaminated solution from the storage unit 33 may be subject to treatment to separate the densified polymer solution from the DNAPLs. Thus, the densified polymer solution freed from DNAPL can be recycled and sent to unit 29 for preparing and mixing the densified polymer, which is symbolized by arrow 34.

The method according to the invention makes it possible to increase the recovery rate of DNAPL from contaminated soil.
It allows to improve the radius of influence because it can propagate more horizontally in porous media.
The process can be applied in a real polluted site because its performance has been analyzed in an open system (2D tank without cover).
This method makes it possible to deliver chemical nanoparticles, in particular iron nanoparticles, into the residual DNAPL zones at the end of the displacement process at the end of the treatment. These nanoparticles react with the residual DNAPL. These nanoparticles, which are not soluble in water, are deposited in the porous media. The method according to the invention, which comprises a densifying agent soluble in the aqueous solution, does not cause the pores to clog. Consequently, the method according to the invention makes it possible to easily inject these end-of-treatment nanoparticles.
The process can be applied to a wide range of soil permeability because its injection pressure is much lower.
In the method according to the invention, the densified polymer solution can be mixed with a surface tension reducer such as a surfactant, which could further improve the recovery rate of DNAPL.
The xanthan and NaI solution does not cause too much injection pressure; therefore, it can be injected at different flow rates. In this method, the injection pressure is low because there is no problem of pore clogging. Therefore, the injection can be easily carried out in a low-permeability layer. In the exemplary embodiments, the maximum injection pressure was less than 3000 Pa for an injection flow rate of 2 ml/min.
Xanthan and NaI solution can be injected as a pre-rinse for secondary treatment such as alcohol injection. It can be injected as a post-rinse for primary treatment such as surfactant injection.
The method according to the invention can be used with different types of DNAPL, including single-component or multi-component and with different densities, ranging from 1.01 to 1.8 g/ml.
Since the xanthan-NaI solution exhibits non-Newtonian behavior, the method according to the invention can be used in multilayer systems.

The invention is not limited to the embodiments presented and other embodiments will be apparent to those skilled in the art. In particular, the water in the aqueous solution is not necessarily demineralized and degassed water. However, during the studies, demineralized water was used to avoid any effect of ions dissolved in the water, and degassed water was used to avoid possible trapping of air bubbles in the porous media.

List of references

Alamooti et al., 2022: A. Alamooti et al. Influence of the injection of densified polymer suspension on the efficiency of DNAPL displacement in contaminated saturated soils J. Hazardous Materials 440, 129702

Carreau, 1972 Carreau, PJ, 1972. Rheological equations from molecular network theories. Transactions of the Society of Rheology 16, 99–127.

Claims (8)

A method of extracting a dense non-aqueous phase liquid from a soil, which comprises providing an injection well (23) positioned adjacent to a zone (21) comprising the dense non-aqueous phase liquid, and a recovery well (25) positioned at a distance from the injection well (23), such that at least a portion of the dense non-aqueous phase liquid is located between the injection well (23) and the recovery well (25), the method comprising the steps of:
- injecting an aqueous solution of a shear-thinning polymer into the injection well (23) so as to release said solution into the zone (21) comprising the dense liquid in non-aqueous phase to come into contact with the dense liquid in non-aqueous phase in the zone (21) so as to move the dense liquid in non-aqueous phase towards the recovery well (25), and
- extraction of said polymer solution and the dense liquid in non-aqueous phase from the recovery well (25),
the aqueous polymer solution comprising a densifying agent so as to have a density substantially equal to the density of a liquid comprising the dense liquid in non-aqueous phase to be extracted, the densifying agent being soluble in the aqueous solution at said density. A method for extracting a dense liquid in a non-aqueous phase according to the preceding claim, in which the densifying agent is sodium iodide. A method for extracting a dense liquid in a non-aqueous phase according to any one of the preceding claims, wherein the polymer is a biopolymer such as xanthan, guar gum, carboxymethyl cellulose or a mixture of these compounds. Process for extracting a dense liquid in non-aqueous phase according to the preceding claim, in which the polymer is xanthan, preferably present in the solution at a concentration ranging from 0.3 g/ml to 1.5 g/ml, preferably from 0.4 to 1.2 g/ml, even more preferably from 0.55 g/ml to 1 g/ml, and more preferably from 0.8 g/ml. A method for extracting a dense liquid in a non-aqueous phase according to any one of the preceding claims, wherein the density of the aqueous polymer solution may range from 1.01 to 1.80 g/ml, and is preferably 1.70 g/ml. A method for extracting a dense liquid in a non-aqueous phase according to any one of the preceding claims, wherein the dense liquid in a non-aqueous phase to be extracted is a chlorinated organic pollutant such as hexachlorobutadiene, hexachloroethane, pentachlorobenzene, carbon tetrachloride, perchloroethylene or trichloroethylene, any other dense liquid in a non-aqueous phase in pure phase (chlorinated solvents or Polycyclic Aromatic Hydrocarbons), or a mixture of at least two of these pollutants. A method for extracting a dense liquid in a non-aqueous phase according to the preceding claim, wherein the dense liquid in a non-aqueous phase has the following composition:
- from 55.1 to 60.9% by mass of hexachlorobutadiene, preferably from 56.8 to 59.2%, and preferentially 58%,
- from 13.3 to 14.7% by mass of hexachloroethane, preferably from 13.7 to 14.3%, and preferentially 14%,
- from 3.3 to 3.7% by mass of pentachlorobenzene, preferably from 3.4 to 3.6%, and preferentially 3.5%,
- from 3.8 to 4.2% by mass of carbon tetrachloride, preferably from 3.9 to 4.1%, and preferentially 4%,
- from 7.6 to 8.4% by mass of perchloroethylene, preferably from 7.8 to 8.2%, and preferentially 8%, and
- from 1.8 to 2.2% by mass of trichloroethylene, preferably from 1.9 to 2.1%, and preferentially 2%. An aqueous solution of a shear-thinning polymer comprising a densifying agent, the solution having a density ranging from 1.01 to 1.80 g/ml, for use in a process for extracting dense liquid in a non-aqueous phase, the densifying agent being sodium iodide, and the polymer being a biopolymer such as xanthan, guar gum, carboxymethylcellulose or a mixture of these compounds.