FR2962928A1 - STABILIZATION OF PORT SEDIMENTS POLLUTED BY MINERAL ADDITIVES - Google Patents

Abstract

The invention relates to the use of iron and / or iron oxides for the stabilization, in a basic medium, at a pH of between about 7 and about 8, of sediments polluted by both anionic pollutants and cationic pollutants. . It also relates to treatment compositions and a method for treating polluted or contaminated sediment, in particular a harbor sediment.

Description

STABILIZATION OF PORT SEDIMENTS POLLUTED BY MINERAL ADDITIVES

The present invention relates to the treatment and stabilization of polluted dredged sediments, including harbor sediments. It also relates to compositions for treating said polluted sediments and a method for treating said polluted sediments. Dredging is an important activity for port operations. In France, an average of 50 million m3 of sediment is dredged annually in ports and released into the marine environment. The uncontaminated or polluted sediments do not pose any particular problems with respect to their environmental effects and are in some cases used for wetland creation, beach fattening during erosion or road construction. On the other hand, the dredging and disposal of contaminated or polluted materials raises a number of questions concerning their effects on the physicochemical quality of water and the fate of toxic substances for living organisms. The management of sediments dredged in ports therefore raises the question of the risks of contamination of the environment. Recently, concentrations of metals and organic pollutants in marine sediments have been set (GEODE levels Nl and N2). Thus, when pollutant concentrations in marine sediments are too high (levels above GEODE N2 levels), they are considered as waste and must be treated ashore. Contamination of sediments imposes certain environmental considerations to guide the choice of location and disposal methods. In the past, few precautions were taken regarding the management of disposal sites, so that the issue of transfer of pollutants to neighboring ecosystems is now a topical issue. Disposal of contaminated dredged sludge on shore must be accompanied by treatment to limit the dispersion of pollutants into the environment. In fact, during the deposition of contaminated sediments in the open air, rainwater can percolate through the sediment, causing the soluble or particulate elements. These percolation solutions called leachate, are the vectors of pollutants to soils and aquifers that are close to the storage site. Several sediment treatment techniques have been developed in the past, such as physical and physico-chemical treatments (attrition, gravimetry, flotation, cycloning, etc.), biological treatments (bioleaching, phytoextraction, biodegradation, etc.). ), heat treatments (desorption, incineration, vitrification, etc.), chemical treatments (extraction by complexation, solvent, etc.) or phosphate treatments (calcium phosphates, apatitic phosphates, etc.). Among the above techniques, patent EP 0883585 describes in particular a method for treating sediments containing heavy metals and metallic aluminum with phosphoric acid and alkali metal phosphates. Patent EP 1341728 describes a process for treating sludges containing heavy metals and organic materials by adding phosphoric acid to the sludge before a calcination step. Treatment processes using phosphates are the most used to date. The NovosolTM process, developed by Solvay®, is used to stabilize polluted sediments. It consists in adding phosphoric acid to sediments to precipitate phosphates that will trap cationic pollutants. However, said Novosol® process does not allow the stabilization of anionic pollutants, such as in particular the arsenate anion AsO43-. On the contrary, it has recently been shown that this process facilitates the leaching of the anions. In addition, the addition of phosphoric acid and phosphates to the environment can also cause secondary pollution. There is therefore a need to economically stabilize large quantities of polluted sediments containing both anionic and cationic pollutants. It is this problem that the present invention proposes to solve with the aid of the compositions described below. Also, an objective that the present invention has set itself is to provide compositions that make it possible to stabilize the pollutants in anionic form and in cationic form contained in polluted sedimentation sediments. The invention therefore firstly relates to the use of iron and / or iron oxides, for the stabilization, in a basic medium, at a pH of between about 7 and about 8, of sediments polluted at the same time by pollutants. Anionic and cationic pollutants Alternatively, when the sediment to be stabilized has an acidic initial pH, calcite is additionally added to the sediment to buffer it at basic pH.

Its second object is a composition for treating polluted harbor sediments comprising on the one hand iron and / or iron oxide, and on the other hand calcite. Its third object is a stabilized harbor sediment comprising a composition according to the invention, characterized in that it comprises between approximately 3 and approximately 20% of iron and / or iron oxide and between 1% and 25% of calcite by weight of the total weight of the sediment. Finally, its fourth object is a method for treating, in a basic medium, at a pH of between about 7 and about 8, a sediment polluted by both anionic pollutants and cationic pollutants comprising the steps of adding to the sediment. polluted with iron, iron oxides and / or calcite; and composting polluted sediment by watering and aeration. The invention will be better understood on reading the nonlimiting description which follows, written with reference to the appended drawings, in which: FIGS. 1 to 6 show curves comparing, for six different samples of sediments, the quantity of anionic arsenic , cationic cadmium, cationic copper, cationic nickel, anionic molybdenum and cationic zinc, dissolved in 16 weeks of leaching; FIG. 7 represents a comparison of the total pollutant flux in mg / m 3 / day for six different sediment samples. FIG. 8 shows the arsenic binding on an iron oxide as a function of the pH for six different samples of sediment - Figure 9 shows lead binding to iron oxide as a function of pH for six different sediment samples. Figure 10 shows a comparative electrical conductivity for six different sediment samples for 16 weeks; Figure 11 shows the pH values of six different sediment samples for 16 weeks.

The document entitled "Arsenic adsorption onto hematite and goethite", Rendus Chemistry Volume 12, issue 8 pages 876-881, August 2009, describes that retention of the arsenate anion is maximal in acidic medium and decreases with increasing pH. . Thus, this document suggests that the retention of anionic pollutants is low in a basic medium. This document neither describes nor suggests the use, in a basic medium, of a treatment composition comprising iron and / or iron oxides. Surprisingly, as illustrated in Example 1, the Applicant has been able to demonstrate that the treatment of polluted sedimentation sediments, in particular port sediments, by addition of iron and / or iron oxides in a basic medium is also effective. to decrease the amount of anions as the amount of cation passing in solution relative to the raw sediment. Thus, the total flow of pollutant can be very effectively reduced by the treatment according to the invention.

Also, the solution provided by the present invention is surprising, since it was absolutely not obvious to be able to stabilize acceptable anions in basic medium. Advantageously, in order to maintain the leaching water at a basic pH, preferably at a pH of 8, the treatment composition according to the invention comprises the presence of calcite. Preferably, the sediments polluted by both anionic pollutants and cationic pollutants are stabilized by the addition of at least about 3% by weight of iron and / or iron oxide, based on the total dry weight of polluted sediments to stabilize. Preferably, the anionic pollutants stabilized by the composition according to the invention are anions of arsenic, vanadium, chromium and / or molybdenum.

More preferably, the cationic pollutants stabilized by the composition according to the invention are cations of cadmium, chromium, copper, zinc and / or any other di- or trivalent cation.

The iron according to the invention is preferably in the form of zero-valent or trivalent iron. Among the iron oxides that may be present in the composition according to the invention, there may be mentioned in particular goethite, ferrihydrite and / or hematite. Preferably, the iron oxides used are hematite. According to a preferred embodiment of the invention, the polluted port sediment treatment composition comprises on the one hand iron and / or iron oxides, and on the other hand calcite. Preferably, the concentration of iron and / or iron oxide in the harbor sediment to be stabilized is between about 3 and about 20% by weight of the total weight of the sediment. The concentration of calcite in the harbor sediment to be stabilized is preferably between 1% and 25% by weight of the total weight of the sediment. According to a first embodiment of the invention, the polluted harbor sediment treatment composition comprises zero-valent iron at a concentration of between 80 and 100% by weight of the total weight of the composition, said concentration of the iron composition zero-valent in the harbor sediment to be stabilized being preferably between about 3 and about 20% by weight of the total weight of the sediment.

According to a second embodiment of the invention, the polluted harbor sediment treatment composition comprises goethite, ferrihydrite and / or hematite, taken alone or as a mixture, the concentration of the mixture of said compounds being between 80 and 100% by weight of the total weight of the composition. The concentration of said composition in the harbor sediment to be stabilized is preferably between about 3 and about 20% by weight of the total weight of the sediment.

According to a third embodiment of the invention, the composition for treating polluted harbor sediments comprises a mixture of zero-valent iron on the one hand, and goethite, ferrihydrite and / or hematite on the other hand, with a concentration of between 80 and 100% by weight of the total weight of the composition. The concentration of said composition in the harbor sediment to be stabilized is preferably between about 3 and about 20% by weight of the total weight of the sediment.

According to a fourth embodiment of the invention, the composition for treating polluted harbor sediments comprises a mixture of zero-valent iron on the one hand, and calcite on the other hand, at a concentration of between 60 and 100% by weight. weight of the total weight of the composition. The concentration of said composition in the harbor sediment to be stabilized is preferably between about 3 and about 20% by weight of the total weight of the sediment. According to a fifth embodiment of the invention, the polluted harbor sediment treatment composition comprises a mixture of calcite on the one hand, and goethite, ferrihydrite and / or hematite on the other hand, at a concentration of between 60 and 100% by weight of the total weight of the composition. The concentration of said composition in the harbor sediment to be stabilized is preferably between about 3 and about 20% - by weight of the total weight of the sediment. According to a sixth embodiment of the invention, the polluted harbor sediment treatment composition comprises a mixture of zero valent iron and calcite on the one hand and goethite, ferrihydrite and / or hematite on the other hand. on the other hand, at a concentration of between 60 and 100% by weight of the total weight of the composition. The concentration of said composition in the harbor sediment to be stabilized is preferably between about 3 and about 20% by weight of the total weight of the sediment. The invention further relates to a method of treating anion and cation contaminated sediment comprising the steps of adding to the polluted sediment a composition comprising iron, iron oxides and / or calcite; and composting polluted sediment by watering and aeration. Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings and the person skilled in the art may be led, by means of routine operations, to make other embodiments not explicitly described. without departing from the scope and scope of the present invention. Example 1: In this example, the chemical stabilization of a Mediterranean harbor sediment was carried out under land storage conditions. The pollutant concentrations of the sediment before treatment are given in Table 1 below, as well as the GEODE levels of Ni and N2 references: Table 1: Sediment sample Levels Mediterranean harbor GEODE Pollutants Coefficient concentration Ni N2 the sample of variation (mg / kg) (mg / kg) (mg / kg) (%) As 128 ± 3 2.1 25 50 Cd 1.64 ± 0.07 4.2 1.2 2.4 Cu 1582 ± 69 4 , 4 45 90 Mo 13.2 ± 0.09 0.7 - - Ni 34.75 ± 0.33 1.0 37 74 Zn 1 723 ± 48 2.8 276 552 The proposed treatment is a chemical stabilization of the sediment based on on the adsorption properties of iron oxides and sequestration of zeolite for heavy metals and metalloids. Sediment quality was assessed by total analyzes of organic and inorganic pollutants. Swath sediment was chemically stabilized using mineral additives (hematite, metallic iron and zeolites) and composted for 3 months by weekly humidification and aeration cycles to promote degradation of organic pollutants. The various treatment compositions to be tested that have been prepared are listed in Table 2 below: TABLE 2 Samples Mass Additives Composition (kg) used (%) Sample 6 - Sample 1 Sample 6 5% Hematite 99.5% Hematite 2 Sample 6 15% Hematite 99.5% Hematite 3 Sample 6 5% Iron Zero-99.9% Iron 4 Value Sample 6 5% Zeolite Clinoptilolite 84% Zeolite 5 Fine Cristobalite 8% Sample 6 5% Zeolite Feldspar 4% Zeolite 6 gross Illite 4% During this bio-remedi- ation, the percolation water was collected during each humidification phase in order to follow the evolution of inorganic pollutant levels (As, Cd, Cu, Mo, Ni and Zn). ), pH and conductivity. The results of the tests, expressed in gg / kg of sample, are shown in Table 3 below. Table 3: Pollutants Ech. Ech. Ech. Ech. Ech. Ech. control 1 hematite 2 hematite 3 Iron 4 Zeolite 5 Zeolite 6 As 70.22 36.77 54.72 48.59 80.65 47.01 Cd 22.68 8.87 16.12 8.15 34.64 17.34 Cu 304.82 146.23 177.52 174.02 293.29 204.75 MB 500.40 82.63 50.19 116.87 583.56 361.69 Ni 94.29 41.64 72.22 45 24 132.33 54.83 Zn 949.07 551.35 446.54 550.92 1116.00 971.43 These results show that the chemical stabilization of the sediment by iron-based additives significantly improves the quality of the sediments. percolation waters by reducing the mobility of many inorganic pollutants. This stabilization technique, easy to implement and inexpensive, would allow the development of a field management of contaminated sludge dredging. Example 2

Leaching tests on fresh sediments containing various mineral additives were carried out for a period of 16 weeks, as illustrated in Figures 1 and 2. The curves of Figures 1 to 6 compare, for six samples, the amount of anionic arsenic, of cationic cadmium, cationic copper, cationic nickel, anionic molybdenum and cationic zinc, which go into solution after several weeks of leaching. The different compositions of the six samples tested are shown in Table 2 above: The different curves, measuring the amount of ions in gg / kg of sediment over 16 weeks, show that the treatment by addition of iron oxide (triangles white or black) or iron (white square) is effective both to decrease the quantity of anions and the amount of cation passing in solution, compared with the raw sediment (white diamonds) or sediments including zeolite ( round white or black). Thus, as illustrated in FIG. 7, the total pollutant flow can be very effectively reduced by iron oxide treatment or iron treatment. Figure 7 compares the total pollutant flux in mg / m3 / day of the different samples detailed in Table 2 above. Example 3 Figures 8 and 9 respectively illustrate the binding of arsenic to an iron oxide as a function of pH and the attachment of lead to an iron oxide as a function of pH. Thus, it appears that only a pH value between about 7 and about 8 allows simultaneous entrapment of the anions, fixed in acidic medium, and cations, fixed in basic medium, by the iron oxides. Thus, the additional presence of calcite in the compositions according to the invention makes it possible to buffer the pH of the leaching water around a value of approximately 8. EXAMPLE 4 FIGS. 10 and 11 study the evolution of the pH and conductivity in leachates for the six samples whose compositions are detailed in Table 2 above.

The decrease before stabilization of the conductivity after about 8 weeks, as illustrated in FIG. 10, shows that a solubilization and a rapid elimination of the soluble salts is obtained during the first weeks of humidification.

Figure 11 illustrates that the pH values are from about 7 to about 8 throughout the duration of the experiments. This basic pH value is achieved by dissolving the calcite buffering the pH to between about 7 and about 8.

Claims (10)

REVENDICATIONS1. Use of iron and / or iron oxides for the stabilization, in a basic medium, at a pH of between about 7 and about 8, of sediments polluted by both anionic pollutants and cationic pollutants. 2. Use according to claim 1, characterized in that the sediments polluted by both anionic pollutants and cationic pollutants are stabilized by the addition of at least 3% by weight of iron and / or iron, relative to the total dry weight of polluted sediments to be stabilized. 3. Use according to claims 1 or 2, characterized in that additionally calcite is added when the sediment to be stabilized at an acidic original pH, for buffering said sediment at basic pH. 4. Use according to one of claims 1 to 3, characterized in that the sediment to be stabilized is a harbor sediment. 5. Use according to one of claims 1 to 4, characterized in that the anionic pollutants to be stabilized are anions of arsenic, vanadium, chromium and / or molybdenum. 6. Use according to one of claims 1 to 5, characterized in that the cationic pollutants to be stabilized are cations of cadmium, chromium, copper or zinc and / or any di- or trivalent cation. 7. Use according to one of the preceding claims, characterized in that the iron is zero-valent iron and the iron oxides are goethite, ferrihydrite and / or hematite. 8. Composition for stabilization, in a basic medium, at a pH of between about 7 and about 8, of harbor sediments polluted by both anionic pollutants and cationic pollutants, said composition comprising on the one hand iron and / or iron oxide, and on the other hand calcite. 9. Stabilized harbor sediment comprising a composition according to claim 8, characterized in that it comprises between about 3 and about 20% of iron and / or iron oxide and between 1% and 25% of calcite, by weight of total weight of the sediment. 10. A method for treating in a basic medium, at a pH of between about 7 and about 8, a sediment polluted by both anionic pollutants and cationic pollutants comprising the steps of: adding to the polluted sediment of iron, iron oxides and / or calcite; and composting sediment polluted by watering and aeration.