The present invention relates to a method for cleaning polluted soil and the like, more particularly for removing not easily removable substances from the soil, such as hexachlorocyclohexane and polycyclic aromatic hydrocarbons, referred to hereafter as HCH and PAHs respectively. A problem arising with this kind of pollution is that it has a high boiling point and dissolves poorly in water.

Within the scope of the present invention, the term 'soil' should be understood in the broad sense. It covers, among other things, also sand-like residues such as construction waste, which often contain PAHs in particular.

The present invention provides a method for cleaning polluted soil, resulting in very thorough cleaning in an effective and relatively cheap way. According to the present invention the method includes at least two steps, i.e. a first step in which the soil is treated with an organic solvent and a subsequent step in which the same soil is treated with a heated medium. Treatment of the soil in this way enables the choice of a solvent for the treatment of the soil that effectively removes particular pollutants from the ground. However, the solvent itself constitutes a pollution of the soil that can only be removed from the soil through heating.

Preferably, the organic solvent used is an apolar organic solvent, such as hexane, pentane, or mixtures of alkanes (for example cleaning spirit) of which it is known that they are very effective for removing particular apolar pollutants such as mineral oil, HCH and PAHs from the soil.

The organic solvent can be introduced -into the soil in the form of a fluid. However, it is also possible and under certain circumstances preferable to introduce the solvent into the soil in the form of vapour (heated) .

According to the present invention, the heated medium can be water in the form of hot water and/or steam, and it is also possible to use hot air as the medium.

More particularly, the method according to the present invention is suitable for the removal of mineral oil, HCH and/or PAHs from polluted soil. In further accordance with the present invention, the method permits application at the polluted site, i.e. without the soil being dug off. In that case, a plurality of pipes is inserted into the soil which introduce both the organic solvent and the heated medium into the soil successively. This introduction can occur below or slightly above the groundwater table, and is itself a known technique and disclosed in GB-A-2 098 644 for example.

It is also possible to dig off the polluted soil and deposit it in special containers, which containers are suitable for treating the soil according to the present invention. The treatment according to the present invention can also occur in a purpose-built processing device to which the soil must be transported.

Further, the present invention relates to the device for applying the method for cleaning polluted soil, which device can be provided with a tubing system to be disposed in the non-dug off soil or with means for introducing an organic solvent and subsequently a heated medium into the dug-off soil.

The invention will now be explained in more detail, more particularly in relation to the cleaning of soil polluted

with HCH .

HCH was produced particularly in the 1948-1952 period, during which period much production waste was dumped, usually in the environs of the production site.

The substance HCH is associated with various problems. Firstly, it is a toxic substance which is a public health threat. Further, this substance causes stench. Yet another problem is that HCH is difficult to remove from the soil, which is caused by its poor solubility in water and in many other solvents and the relatively high boiling points of the various HCHs. Soil polluted with HCH will ultimately not only contain HCH but also, for example, chlorobenzene and other products created by the slow disintegration of HCH in the soil. This occurs particularly in calcareous soil .

.An effective way to remove HCH and, if necessary, other substances from polluted soil is treating the soil with an apolar organic solvent, such as hexane, which has a high dissolving power for HCH, is relatively non-toxic, is cheap, can be recycled and can be used in conventional steaming equipment, so that it can be passed through the soil at high temperatures in the form of steam. In practice, it appears that the HCH concentration in polluted soil can be reduced to a minimum by treating this soil with hexane.

After the hexane treatment a certain amount of hexane remains in the soil, which in itself constitutes a new pollution of the soil. However, because hexane has a low boiling point, far below 100 °C, it appears that the hexane is completely removable from the soil by treating the soil with water in the form of steam. Because of the difference between the boiling point of water and the boiling point of hexane the steam and hexane mixture can be easily

separated, so that the hexane is reusable. Because of the poor miscibility of hexane and water and because of the difference in densities, the two substances can be easily separated in the fluid phase also.

In practice, it appears that an eight-hour treatment with hexane and a subsequent eight-hour treatment with water in the form of steam produces excellent results, and reduces the pollution of the soil to a minimum.

The intensity of cleaning can be increased by carrying out the treatments of the soil under pressure, for example a pressure of 1.5 to 3 bar.

Essentially, the method disclosed herein first replaces the existing pollution in the polluted soil by another pollutant, after which the other pollutant is removed from the soil during subsequent treatment.