Method of depolluting soil polluted by hydrocarbons
OwnerPatrice Stengelinventor
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Abstract
The present invention relates to a depollution treatment method for soil constituted by materials based mainly on sand and/or earth that have been contaminated with hydrocarbons, wherein said hydrocarbon-contaminated material is mixed at ambient temperature with a hydrogen peroxide solution until gas is given off and said hydrocarbons are separated by flotation.
Claims15
1/ A method of depollution treatment for soil made up of materials based mainly on sand and/or earth that have been contaminated with hydrocarbons, wherein said hydrocarbon-contaminated material is mixed, preferably at ambient temperature, with a hydrogen peroxide solution so as to cause oxygen gases resulting from the disproportionation of the oxygenated water to be given off, causing said hydrocarbons to be separated by flotation.
2/ A method according to claim 1, wherein said hydrogen peroxide solution is an aqueous solution of hydrogen peroxide preferably containing 30% to 35% by volume of hydrogen peroxide.
3/ A method according to claim 1, wherein the following steps are performed in succession:
- 1) said hydrocarbon-contaminated material is mixed with a hydrogen peroxide solution;
- and
- 2) the mixture obtained in step 1) is poured into a receptacle containing an aqueous solution so as to separate hydrocarbons by flotation, said material in the clean state settling out into the bottom of the receptacle.
4/ A method according to claim 3, wherein, in step 1), said hydrocarbon-contaminated material is mixed with a hydrogen peroxide solution in a volume ratio of 5% to 25%, and preferably of 10% to 20%, of said hydrogen peroxide solution relative to the volume of said contaminated material.
5/ A method according to claim 3, wherein, in step 2), said mixture obtained in step 1) is allowed to settle in a receptacle containing an aqueous solution containing a small quantity of hydrogen peroxide, preferably 5% to 10% by volume of a hydrogen peroxide solution relative to the total volume of the solution, said hydrogen peroxide solution preferably containing 30% to 35% by volume of hydrogen peroxide.
6/ A method according to claim 1, wherein, prior to mixing step 1), a fluidizing step is performed in which said hydrocarbon-contaminated material is fluidized by crushing and/or mixing with a solvent, preferably in order to obtain a mixture presenting dynamic viscosity lying in the range approximately 300 cSt to 700 cSt and more preferably in the range 400 cSt to 500 cSt at 50° C.
7/ A method according to claim 6, wherein said step of fluidizing said hydrocarbon-contaminated material is performed by mixing with a hydrocarbon of viscosity that is lower than that of the polluting hydrocarbon contained in said contaminated material, preferably a light liquid hydrocarbon of the gasoil type.
8/ A method according to claim 7, wherein, in step 1) of mixing said contaminated material with a hydrogen peroxide solution, mixing takes place at ambient temperature in a medium that is neutral or basic, preferably having a pH greater than 9, and more preferably in the presence of a disproportionation catalyst such as iron.
9/ A method according to claim 1, wherein:
- 1a) said material contaminated with heavy hydrocarbons is fluidized, where necessary, by being mixed, preferably by being vigorously blended with a solvent, preferably a light liquid hydrocarbon;
- and
- 1b) said optionally fluidized contaminated material obtained in step 1) is mixed with a said hydrogen peroxide solution, and the mixture of said contaminated material and said hydrogen peroxide solution possibly together with said solvent is preferably subjected to vigorous blending so as to obtain a thoroughly homogenized mixture;
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- 2) the mixture obtained in step 2) is allowed to settle in a tank containing water with a small quantity of hydrogen peroxide;
- and
- 3) said material when cleaned and separated from said polluting heavy hydrocarbons is recovered from the bottom of the tank and said polluting hydrocarbons are recovered from the surface by skimming;
- and
- 4) the fine particles of sediment and the water still mixed with said polluting heavy hydrocarbons skimmed from the surface in step 3) are preferably separated.
10/ A method according to claim 1, wherein a transportable installation is used suitable for being set up on a polluted site or close thereto, the installation comprising from an upstream end to a downstream end:
- a) a mixer comprising an enclosure and blending means;
- b) a storage tank for storing a said hydrogen peroxide solution and feeding said first mixer;
- c) a separator/settling tank comprising an open vessel;
- and
- d) preferably a second storage tank for storing an aqueous solution containing a small quantity of hydrogen peroxide.
11/ A method according to claim 10, wherein said installation further comprises a storage tank for storing said solvent and preferably a metering pump enabling said first mixer to be fed with said solvent.
12/ A method according to claim 10, wherein said installation further comprises a 3-port settling tank for separating the polluting hydrocarbons, the water, and the residual fine particles of sediment skimmed from the surface of said separator/settling tank.
13/ A method according to claim 10, wherein the installation further comprises, at its upstream end, a crusher for crushing said contaminated material, preferably into the form of particles of size smaller than 5 mm.
14/ A method according to claim 10, wherein said installation further comprises conveyor means comprising an auger enabling said contaminated material to be conveyed into said first mixer, and second conveyor means comprising an auger enabling said contaminated material to be conveyed from the bottom of the separator/settling tank to an intermediate storage hopper for the depolluted material.
15/ A method according to claim 1, wherein said contaminated material is beach sand polluted with heavy hydrocarbons.