METHOD FOR TREATING POLLUTED SOIL BY A HYDRAULIC BINDER WITH MAYENITE PHASE

Abstract

A method for treating polluted soils, includes mixing the soil with a hydraulic binder, wherein the hydraulic binder includes: as the only high-alumina clinker, a high-alumina clinker including more than 80 wt % of mayenite C12A7 phase or a mayenite isotope, the high-alumina clinker making up at least 70 wt % of the weight of the hydraulic binder; and 1 wt % to 30 wt %, relative to the total weight of the binder, of lime.

Claims

1. A method for treating polluted soils, comprising mixing said soil with a hydraulic binder, wherein the hydraulic binder comprises: as the sole aluminous clinker, an aluminous clinker comprising more than 80% by mass of mayenite C12A7 phase or a mayenite isotype, said aluminous clinker represents at least 70% by weight of the weight of the hydraulic binder; from 1 to 30% by weight, relative to the total weight of the binder, of lime.

2. The method according to claim 1, wherein the aluminous clinker comprises as the sole aluminate phase the mayenite C12A7 phase.

3. The method according to claim 1, wherein the lime is free lime, slaked lime, or a mixture of free lime and slaked lime.

4. The method according to claim 1, wherein the hydraulic binder comprises from 5 to 25% by weight, relative to the total weight of the binder, of quicklime or slaked lime.

5. The method according to claim 1, comprising mixing said soil with said hydraulic binder in soil/binder mass proportions comprised between 1 and 10 parts binder per 100 parts soil.

6. A method to stabilize soils in situ or before storage, comprising mixing said soil with a hydraulic binder, wherein the hydraulic binder comprises: as the sole aluminous clinker, an aluminous clinker comprising more than 80% by mass of mayenite C12A7 phase or a mayenite isotype, said aluminous clinker represents at least 70% by weight of the weight of the hydraulic binder; from 1 to 30% by weight, relative to the total weight of the binder, of lime.

7. The method according to claim 1, wherein said polluted soils are polluted by anions and/or heavy metals.

8. The method according to claim 7, wherein said anions are sulfate ions.

9. The method according to claim 3, wherein the lime is slaked lime.

10. The method according to claim 6, wherein said soils are polluted by anions and/or heavy metals.

11. The method according to claim 6, wherein the aluminous clinker comprises as the sole aluminate phase the mayenite C12A7 phase.

12. The method according to claim 6, wherein the hydraulic binder comprises from 5 to 25% by weight, relative to the total weight of the binder, of quicklime or slaked lime.

13. The method according to claim 6, comprising mixing said soil with said hydraulic binder in soil/binder mass proportions comprised between 1 and 10 parts binder per 100 parts soil.

Description

EXAMPLE 1

Treatment of Soils Contaminated by Different Sulfate Contents with Binders According to the Invention or Comparative Binders

[0078] The process for treating contaminated soils was carried out with binders of the invention and comparative binders.

[0079] Three materials to be treated were used: two supragypseous marls with two levels of pollution and a Roissy silt polluted by natural gypsum.

[0080] One supragypseous marl contained a sulfate SO.sub.4 content of 5220 mg/kg of dry matter, another supragypseous contained a sulfate SO.sub.4 content of 7000 mg/kg of dry matter and a silt having a sulfate content partly provided by a natural gypsum of 15060 mg/kg of dry matter.

[0081] The following binders were tested: [0082] C12A7-based binder: binders according to the invention [0083] CEM I binder: comparative binder based on Portland clinker [0084] CSA binder: comparative binder based on calcium sulfoaluminate (CSA) clinker

[0085] The compositions of these binders are described below.

[0086] 1. Preparation of Clinkers

[0087] 1.1 Clinkers According to the Invention

[0088] Aluminous clinker is obtained by melting, at a temperature between about 1250 and 1300 C., a mixture of white bauxite and limestone. The silica and iron content of the raw materials should be as low as possible to ensure an optimal level of C12A7.

[0089] After firing, the clinker is cooled in ambient air, then ground to a Blaine fineness of about 3500 cm.sup.2/g and a particle size of less than about 100 m. The mineralogical composition (% by mass) of the aluminous clinker according to the invention is presented in the following table.

TABLE-US-00001 TABLE 1 Mineralogical composition of C12A7 clinker with 98% purity (in mass percentage) C3S (cement notation) ND C2S (cement notation) ND C3A (cement notation) ND C4AF (cement notation) ND C4A3$ (cement notation) ND C12A7 (cement notation) 98 S (cement notation) ND MgO ND C2AS (cement notation) ND CaSO.sub.4 ND Iron perovskite ND Other minority phases 2

TABLE-US-00002 TABLE 2 Mineralogical composition of C12A7 clinker with 85% purity (in mass percentage) C3S (cement notation) ND C2S (cement notation) ND C3A (cement notation) ND C4AF (cement notation) ND C4A3$ (cement notation) ND C12A7 (cement notation) 85 S (cement notation) 13 MgO ND C2AS (cement notation) ND CaSO.sub.4 ND Iron perovskite ND Other minority phases 2

[0090] 1.2 Comparative Test Clinkers

[0091] 1.2.1 As a first comparative clinker, a commercial clinker, CEM I 52.5 N CE CP2 NF as produced by the Lafarge cement plant in Saint-Pierre-La-Cour, was used. This clinker is hereinafter referred to as CEM I.

[0092] CEM I 52.5 N CE CP2 NF clinker has a Blaine fineness of about 3900 cm.sup.2/g and a particle size of less than about 100 micrometers.

[0093] The mineralogical composition of CEM I clinker is presented in the following table.

TABLE-US-00003 TABLE 3 Chemical composition of CEM I clinker (in mass percentage) Component Mass percentage SiO.sub.2 20.07 Al.sub.2O.sub.3 4.95 Fe.sub.2O.sub.3 2.96 CaO 63.89 MgO 0.89 K.sub.2O 1.06 Na.sub.2O 0.25 SO.sub.3 3.41 TiO.sub.2 0.19 Mn.sub.2O.sub.3 0.14 P.sub.2O.sub.5 0.27 Cr.sub.2O.sub.3 <LD ZrO.sub.2 0.02 SrO 0.02 Loss on ignition 1.56 LD = limit of detection

[0094] 1.2.2 As a second comparative clinker, a sulfoaluminate clinker comprising about 60% by mass of ye'elimite phase was used. This clinker is hereinafter referred to as CSA.

[0095] The sulfoaluminate clinker is prepared in two steps: [0096] preparation of a raw mixture comprising a mixture of raw materials previously selected so that the chemical composition of the raw mixture corresponds to the chemical composition of the desired clinker; [0097] firing the raw mixture to obtain the clinker, in an optionally rotary kiln, at a temperature comprised between 1100 C. and 1300 C. to be adjusted according to the chemical composition of the raw mixture.

[0098] After firing, the clinker is cooled in ambient air, then ground to a Blaine fineness of about 5240 cm.sup.2/g and a particle size of less than about 300 micrometers.

[0099] The mineralogical composition of CSA clinker is presented in the following table.

TABLE-US-00004 TABLE 4 Mineralogical composition of CSA clinker (in mass percentage) Phase Mass percentage C3S (cement notation) ND C2S (cement notation) 22.7 C3A (cement notation) ND C4AF (cement notation) 1.9 C4A3$ (cement notation) 65.2 C12A7 (cement notation) 0 MgO 1.3 C2AS (cement notation) 1.3 CaSO.sub.4 0.8 Iron perovskite 6.3 Other minority phases 0.2

[0100] Three binders are then prepared by adding slaked lime (Fleur de Chaux HX80 Saint Hilaire) to each of these binders.

[0101] 2. Treatment Process

[0102] Samples of contaminated soil are treated by the process according to the invention with hydraulic binders prepared beforehand according to the following protocol: [0103] A quantity of wet soil equivalent to 600 g dry soil is introduced into a Perrier type mixer. [0104] Wet means the natural moisture content of the soil, which may be adjusted to optimize the hydration of the binder. The water content may be comprised between 5% and 40% of the weight of the soil, depending on its nature. [0105] The binder for the treatment is introduced on the surface and then the whole is mixed, at low speed, for at least 2 minutes until a mixture homogeneous in color and texture is obtained. [0106] The whole of the treated material is extracted from the bowl and stored for 1 hour in an airtight bag. [0107] After one hour, the whole was passed over a 4 mm sieve. Oversized material is broken by hand or with a tool so that all the treated material passes through a 4 mm sieve. [0108] The whole of the sieved material is placed back into the airtight bag to prevent the material from drying.

[0109] The treated soil is allowed to mature over a period of 2 hours, 1 day, 7 days or 2 months at room temperature.

[0110] 3. Results of the Leaching Tests

[0111] The results are reported in the following tables in which the percentages are expressed by weight of each of the components of the binder relative to the weight of material to be treated. The tests were carried out on the three types of materials described above.

TABLE-US-00005 TABLE 5 Sulfate content in low-sulfate marl treated with a binder according to the invention and compared with CSA binder + 1% Ca(OH).sub.2 Sulfate content (mg/kg DM) Duration of treatment 2 hours 1 day 7 days 2 months Control (untreated) Supragypseous 5220 5220 5220 5220 Marl Comparative: 4.5% CEM I + 2790 3060 3180 2990 1% Ca(OH).sub.2 Comparative: 4.5% CSA + 480 570 650 610 1% Ca(OH).sub.2 Invention: 3.5% C12A7 (with 64.7 62 51 97 98% purity) + 0.6% Ca(OH).sub.2

[0112] Leaching tests carried out on a supragypseous marl with 7000 mg/kg SO.sub.4 with different binder compositions corresponding to the invention.

TABLE-US-00006 TABLE 6 Sulfate content in high-sulfate marl treated with different binders according to the invention Sulfate content (mg/kg DM) 2 7 Duration of treatment hours 1 day days Control (untreated) Supragypseous marl 7000 7000 7000 0.98% C12A7 (with 85% purity) + 0.12% Ca(OH).sub.2 5980 6143 5390 2.65% C12A7 (with 85% purity) + 0.33% Ca(OH).sub.2 660 860 830 2.6% C12A7 (with 98% purity) + 0.4% Ca(OH).sub.2 290 610 770 4.8% C12A7 (with 98% purity) + 0.79% Ca(OH).sub.2 19 80 200 4.8% C12A7 (with 98% purity) + 0.6% Ca(OH).sub.2 20 70 160 4.8% C12A7 (with 98% purity) + 0.05% Ca(OH).sub.2 30 100 210 6.1% C12A7 (with 98% purity) + 0.92% Ca(OH).sub.2 30 40 100 8.8% C12A7 (with 98% purity) + 1.19% Ca(OH).sub.2 20 20 30 7% C12A7 (with 98% purity) + 3.4% Ca(OH).sub.2 20 20 20

TABLE-US-00007 TABLE 7 Sulfate content in high-sulfate silt treated with different binders according to the invention Sulfate content (mg/kg DM) Duration of treatment 2 hours 1 day 7 days 2 months Control (untreated) Silt with 15060 15060 15060 15060 gypsum added Comparative: 9610 9770 8060 6690 6% CEM I + 2.5% Ca(OH).sub.2 Comparative: 650 1040 1570 2180 6% CSA + 2.5% Ca(OH).sub.2 Invention: 67 99 237 300 6% C12A7 (with 98% purity) + 0.8% Ca(OH).sub.2

[0113] These results show the effectiveness of C12A7 binder +lime in the process according to the invention: it is able to remove nearly all sulfates present in the soil, whether contaminated with low or high levels. In addition, the amount of binder used to decontaminate soils is lower than that required with other conventional binders.

EXAMPLE 2

Influence of Lime Concentration

[0114] In this example, we used the C12A7 clinker described in Example 1 supplemented with different amounts of slaked lime (as described in Example 1). The hydraulic binders tested include only this C12A7 clinker and this slaked lime at the contents indicated in the following table.

[0115] The treatment process is identical to the process described in Example 1 and the material to be treated is the low-sulfate soil (5220 mg/kg of dry matter) described in Example 1. The results are reported in the following table in which the percentages are expressed by weight of each of the components of the binder relative to the weight of the material to be treated.

TABLE-US-00008 TABLE 8 Sulfate content in low-sulfate marl treated with different binders according to the invention, as a function of lime content Sulfate content (mg/kg DM) Duration of treatment 2 hours 1 day 7 days 2 months Control (untreated) 5220 5220 5220 5220 Comparative: 3.5% C12A7 + 160 280 600 1240 0% Ca(OH).sub.2 Invention: 70 54 53 143 3.5% C12A7 (with 98% purity) + 0.43% Ca(OH).sub.2 Invention: 64.7 62 51 97 3.5% C12A7 (with 98% purity) + 0.6% Ca(OH).sub.2 Invention: 70 80 120 210 3.5% C12A7 (with 98% purity) + 1% Ca(OH).sub.2

[0116] These results show that the addition of lime significantly improves the efficiency of Cl2A7 clinker.

EXAMPLE 3

Impact of the treatment on the Presence of Heavy Metals in the Leachant

[0117] Conventionally, treatment with traditional binders may potentially provide very small quantities of leachable heavy metals such as hexavalent chromium (chromium VI). The present invention limits the supply of such compounds, including chromium VI. This is mainly due to the nature of the raw materials used in its manufacture and to the process used. The objective is therefore to limit the supply of this type of compound by the binder in order to meet the very low leaching thresholds for the disposal of treated waste or materials. For example, the acceptable threshold for considering a material inert under the regulation is 0.5 mg/kg of chromium VI relative to the dry material.

[0118] The tables below summarize the chromium VI contents found following leaching tests on all the treatments presented in the previous examples.

TABLE-US-00009 TABLE 9 Chromium VI content in supragypseous marl treated with a binder according to the invention (3.5% C12A7 with 98% purity + 0.6% Ca(OH).sub.2) and compared with a CEM I-based binder and a CSA-based binder Hexavalent chromium content (mg/kg DM) Duration of treatment 2 hours 1 day 7 days 2 months Control (untreated) ND ND ND ND Supragypseous Marl Comparative: 4.5% CEM I + 0.8 0.6 0.4 0.3 1% Ca(OH).sub.2 Comparative: 4.5% CSA + 1.8 2.0 2.2 2.0 1% Ca(OH).sub.2 Invention: ND ND ND ND 3.5% C12A7 (with 98% purity) + 0.6% Ca(OH).sub.2

TABLE-US-00010 TABLE 10 Chromium VI content in supragypseous marl treated with different binders according to the invention (3.5% C12A7 with 98% purity + 0.6% Ca(OH).sub.2) as a function of lime content in the binder Chromium VI content (mg/kg DM) Duration of treatment 2 hours 1 day 7 days Control (untreated) Supragypseous marl ND ND ND 0.98% C12A7 (with 85% purity) + 0.12% ND ND ND Ca(OH).sub.2 2.65% C12A7 (with 85% purity) + 0.33% 0.1 0.2 0.1 Ca(OH).sub.2 2.6% C12A7 (with 98% purity) + 0.4% 0.1 0.2 0.2 Ca(OH).sub.2 4.8% C12A7 (with 98% purity) + 0.79% ND ND 0.1 Ca(OH).sub.2 4.8% C12A7 (with 98% purity) + 0.6% ND ND 0.1 Ca(OH).sub.2 4.8% C12A7 (with 98% purity) + 0.05% ND 0.1 0.2 Ca(OH).sub.2 6.1% C12A7 (with 98% purity) + 0.92% ND ND ND Ca(OH).sub.2 8.8% C12A7 (with 98% purity) + 1.19% ND ND ND Ca(OH).sub.2 7% C12A7 (with 98% purity) + 3.4% Ca(OH).sub.2 ND ND ND

TABLE-US-00011 TABLE 11 Chromium VI content in silt treated with a binder according to the invention (3.5% C12A7 with 98% purity + 0.6% Ca(OH).sub.2) and compared with a CSA-based binder and a CEM I-based binder Chromium VI content (mg/kg DM) Duration of treatment 2 hours 1 day 7 days 2 months Control (untreated) Silt with ND ND ND ND gypsum added Comparative: 6% CEM I + 2.5% 0.8 0.8 0.7 0.7 Ca(OH).sub.2 Comparative: 6% CSA + 2.5% 1.2 1.7 2.0 2.7 Ca(OH).sub.2 Invention: 6% C12A7 (with 98% ND ND ND ND purity) + 0.8% Ca(OH).sub.2

[0119] All these results position the binder of the invention as an advantageous and effective solution to the problem of leaching of chromium VI supplied by traditional OPC or CSA binders.