ES2283218A1 - Adsorbents for removing chlorides, bromides and iodides from water - Google Patents

Abstract

Adsorbents for removing chlorides, bromides and iodides from water, which are based on silver-cation-doped aerogels. The proposed system is geared principally to the removal of bromide and iodide anions from drinking water and also to obtaining water of high purity.

Description

Adsorbents for the removal of chlorides, bromides and iodides of the waters.

Use of organic aerogels doped with cations silver as adsorbents for the removal of chloride anions, bromide and iodide of the waters.

Technical sector

The proposed treatment system, based on the use of organic aerogels doped with silver, like new adsorbent materials, is focused mainly on the removal of bromide and iodide anions from drinking water as well as to obtaining high purity waters (water Milli-Q), very necessary in numerous industries chemical, pharmaceutical and in different types of laboratories.

Object of the invention

The treatment system based on the use of organic aerogels doped with silver, as new materials adsorbents, arises in order to reduce the ion concentration chlorides, bromides and iodides of the waters.

The concentrations in which bromide and iodide anions are present in water sources intended for human consumption are usually very low (0-1000 µg / L) (von Gunten U. Ozonation of drinking water: Part II. Disinfection and by-product formation in presence of bromide, iodide or chloride, Water Research, 37, 1469-1487 (2003)). However, the presence of these anions in them can be very harmful, since i) compounds of high toxicity to humans can be generated during the purification process, such as bromate anions, and ii) chemicals that significantly increase the organoleptic characteristics of water (iodine-methanes) (Rock JJ, Formation of haloforms during chlorination of natural waters . Journal of Water Treatment and Examination, 23, 234-243, 1974). For this reason, it is necessary to carry out the removal of these anions (bromides and iodides) from the waters before being subjected to the classic treatment of purification. On the other hand, although the presence of chloride ions in the waters destined for human consumption is not of great concern, the search for new systems that allow an efficient elimination of them is of special interest for obtaining high purity waters ( Milli-Q water), necessary in numerous chemical and pharmaceutical industries.

The object of the present invention is to take advantage of the presence of silver cations on the surface of the organic airgel, solid material characterized by presenting a high surface area and porosity, to produce precipitation  Anion chemistry chloride, bromide and iodide from the waters of a selective form on the surface of the material.

State of the art

Until now, the existing treatment systems for the removal of chloride, bromide and iodide anions from water are mainly based on the use of different types of ion exchange resins (Humbert H., Gallard H., Suty H. , Croué JP Performance of selected anion exchange resins for the treatment of a high DOC content surface water . Wat. Res., 39, 1699-1708, 2005). However, this treatment is not very efficient due to its high cost and the low selectivity of the exchange process. Currently, activated carbon with silver ions deposited on its surface are being prepared in order to selectively adsorb chloride, bromide and iodide anions present in waters intended for human consumption (Hoskins JS, Karanfil T. Removal and sequestration of iodide using silver -impregnated activated carbon, Environmental Science and Technology, 36, 784-789, 2002). The results obtained have shown that the adsorptive efficiency of these materials is not very high due, mainly, to the dissolution of surface silver species during the treatment process. These new activated carbons are still under development, so they have not yet been applied on an industrial scale.

Description of the invention

The present treatment system is intended use organic aerogels doped with silver as materials adsorbents for the removal of chloride, bromide and anions iodide of the waters. Due to the process of preparing these materials, it is possible to carry out the anchoring of the cations silver in its structure, preventing their dissolution during its application in water treatment. In addition, these Materials are characterized by presenting a high area superficial and porosity, so they will allow adsorbing at the same time, dissolved organic matter and organic microcontaminants present in the waters. One of the great advantages of this material resides in that, due to the procedure of its preparation, it can be obtained in a wide variety of solid forms, which It implies an increase in the technical possibilities of application. Thus, water treatment could be carried out i) through columns filled with this material in granular form, ii) by filtration with membranes developed from it, and even, iii) including a phase separation system appropriate at the end of the treatment process, the waters could be try simply by adding the silver aerogels in the form of dust to them.

The airgel used to carry out these experiences, was obtained by mixing the appropriate proportions of silver acetate, resorcinol, formaldehyde and water. Later this mixture was introduced in glass tubes of 25 cm in length and 0.5 cm in diameter and subjected to a healing process. Finally, the solid obtained was cut in the form of small pills and subjected to a supercritical drying process with carbon dioxide (sample A). This material is characterized by have a surface area value of 428 m2 / g, one volume of mesopores V2 = 0.35 cm3 / g, a volume of macropores V 3 = 0.84 cm 3 / g, a pH value of the zero point of charge pH_ {pzc} = 4.5 and a content of surface silver atoms, determined by X-ray spectrophotometry (XPS) of the 10%

From the silver airgel (A) a Ag activated airgel sample, sample we will call A-A This material was obtained by submitting the original airgel (A) to a carbonization process, in a N2 atmosphere at high temperature and subsequently at a physical activation process with carbon dioxide. The treatment applied considerably developed the surface area value (845 m2 / g) of the original airgel (A).

The experimental system used for the treatment of water contaminated with bromide and / or iodide ions consists of i) a peristaltic pump, ii) a column filled with silver doped airgel of the desired particle size, whereby contaminated water is filtered and iii) a sample collector located at the exit of the column.

The columns used have the following dimensions: 8 cm high by 1 cm wide. The granulometry of material used is between 0.5-0.8 mm The flow used is 1.5 mL / min.

In summary, a system for the removal of chloride anions, bromides and / or water iodides characterized by using organic aerogels doped with silver, both in granular form and in powder, as adsorbents or using membranes prepared from aerogels doped with silver.

Organic aerogels doped with silver can undergo a physical activation process with water vapor or with carbon dioxide, or to a chemical activation process with alkaline hydroxides or with phosphoric acid, increasing the adsorptive properties thereof.

This method has been used in a system that it comprises a peristaltic pump, a column filled with the airgel doped with silver of the desired particle size, whereby filters contaminated water and a sample collector located at the column output

Preferred Embodiment

The following is indicated by way of example illustrative but not limiting, a practical realization of procedure object of the present patent:

Example

Removal of bromide and iodide anions from water intended for human consumption through the use of silver aerogels as column adsorbents

The described system has been used previously to compare the ability of Ag aerogels with Sorbo® activated carbon in the removal of water bromides from the Lake of Zurich.

In order to determine the maximum capacity of adsorption of the silver aerogels, the determination of adsorption isotherms of chloride anions, bromide and iodide on this new material at a temperature of 25 ° C

The results are presented in Figure 1. The high adsorption capacity observed is due to the presence of Ag on its surface, which can lead to the formation of the corresponding Ag halides characterized by presenting very low solubility Thus, the values of the constants of the solubility products (K PS) for these compounds range between 10 -13 for the case of AgBr and 10 -17 for the case of the Agl. This makes the corresponding halide anions dissolved in water are retained on the surface of the coal through a chemisorption process.

The observed results (Figure 2) show that the airgel has an adsorption capacity far superior to the one observed for activated carbon Sorbo®. Activated carbon Sorbo® is a coal widely used in plants drinking water treatment, and that, as can be seen in the Figure 2 is not able to adsorb bromide and iodide anions from the waters

In Figure 3 they are represented, by way of For example, the results obtained for the adsorption process of bromides on the activated airgel sample. So, you can conclude that the activation process (sample A-A) increases the adsorption capacity of bromide and iodide ions of The aerogels considerably. This fact would be due mainly to i) an increase in the microporosity of the sample, which would cause a greater number of sites to exist of superficial silver accessible to bromide and iodide anions and, in addition ii) to an increase in its hydrophobicity, producing an increase in electrostatic interactions attractive between the surface of the sample, positively charged at working pH and the corresponding anion.

In order to determine the applicability of Silver aerogels in the halide anion removal process of the waters destined for human consumption, were carried out adsorption studies of bromide and iodide anions in regime dynamic by using the indicated columns previously.

In Figure 4, it is represented by way of example, column break curves for bromide anion during two adsorption / regeneration cycles, as well as the evolution of bromide concentration during the regeneration process applied. The regeneration process of the saturated columns is carried out by passing for 12 hours a solution of 0.02 M concentration ammonia through the column at a flow 1.5 mL / min Subsequently, and in order to eliminate NH_ {3} adsorbed on the surface of the airgel, the washing the column by passing water Milli-Q for 24 hours through it at a flow of 1.5 mL / min.

From the breakage curves of the columns corresponding to the adsorption processes of bromide anions and iodide the values of the characteristics of the columns shown in Table 1. It shows that the amount adsorbed at the breaking point of the column (X 0.02) is higher for the bromide anion than for the anion I last. In addition, of the results presented in Table 1, it is interesting to note that regardless of the anion considered, the height of the mass transfer zone of the columns is very low (H_ {MTZ}), while fractional capacity (\ phi) In this area it is close to one. These results indicate a great effectiveness of the columns in the iodide removal process and water bromides, as evidenced by the degree of utility thereof, with values between 60% and 72%

The results obtained after applying the Airgel regeneration process described above indicate great effectiveness of it (Table 1), recovering, in agreement with the mass balance performed (Figure 4) 100% of the airborne adsorptive capacity. In fact, the characteristics of the column remain virtually constant after three adsorption / regeneration cycles (Table 1), both for the case of bromide anion as for iodide anion.

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TABLE 1 Characteristics of adsorption columns studied

one

V_ {0. 02}: Volume of treated water in the breaking point of the column X_ {0. 02}: Amount of halide adsorbed at the breaking point of the spine. H_ {MTZ}: Height of the mass transfer zone of the column. X_ {0. 95}: Percentage of halide adsorbed for the breaking value of 0.95. \ phi: Fractional capacity of the transfer zone of mass. G_ {u}: Degree of utility (X_ {0. 02} / X_ {0. 95}) x 100.

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A very important aspect, from the point of view of the applicability of this material in the treatments of waters, is the possible dissolution of the different precursors of the organic polymer created, as well as the possible reduction in surface silver concentration after several cycles of adsorption / regeneration. In order to elucidate these aspects, determined the concentration of dissolved organic carbon during the adsorption / regeneration process and analyzes of X-ray phototransmission (XPS) spectrometry of the samples airgel for the different adsorption / regeneration cycles. The results obtained showed that the carbon concentration organic at the exit of the column was zero, while the concentration of surface silver was 8% and 10% for the sample subjected to 3 adsorption / regeneration cycles and the sample original, respectively. These results would indicate that no produces the dissolution of the organic precursors of aerogels and that the concentration of surface silver is not modified significantly after 3 cycles of adsorption / regeneration.

Description of the figures

Figure 1. Water adsorption isotherms Milli-Q of halides on the organic airgel of silver (sample A). (\) indicates chlorides; (\ lozenge) indicates bromides and (\ triangle) indicates iodides.

Figure 2. Comparison of the capacity of Ag aerogels with commercial activated carbon in disposal of water bromides from Lake Zurich. (\ square) indicates airgel A y (zen) indicates Sorbo® activated carbon.

Figure 3. Anion adsorption isotherms bromide in Milli-Q water on samples of Ag airgel studied. (triangle) indicates sample A; (\ square) indicates sample A-A.

Figure 4. Breaking curves of the organic airgel doped with Ag in the adsorption of the bromide anion in water Milli-Q T 22 ° C, pH 7, [Br -] initial = 150 \ mug / L. (\ lozenge) represents the first cycle adsorption / regeneration, (\ triangle) the second cycle adsorption / regeneration and (\ blacksquare) indicates regeneration with NH 3 (0.02 M).

Claims (9)

1. System for the removal of chloride anions, bromides and / or water iodides characterized by using organic aerogels doped with silver as adsorbents. 2. System for the elimination of chloride, bromide and iodide anions in water according to the preceding claim, characterized in that the organic aerogels used as adsorbents are in granular form. 3. System for the elimination of chloride, bromide and / or iodide anions in water, according to claim 1, characterized in that the organic aerogels used as adsorbents are in powder form. 4. System for the elimination of chloride, bromide and / or iodide anions in water, characterized by using membranes prepared from aerogels doped with silver. 5. System for the elimination of chloride, bromide and / or iodide anions in water, according to any of the preceding claims, characterized by using organic aerogels doped with silver subjected to a physical activation process with water vapor. 6. System for the elimination of chloride, bromide and / or iodide anions in water, according to any one of claims 1 to 4, characterized by using organic aerogels doped with silver subjected to a physical activation process with carbon dioxide. 7. System for the elimination of chloride, bromide and / or iodide anions in water, according to any one of claims 1 to 4, characterized by using silver-doped organic aerogels subjected to a chemical activation process with alkaline hydroxides. 8. System for the elimination of chloride, bromide and / or iodide anions in water, according to any one of claims 1 to 4, subjected characterized by using silver-doped organic aerogels subjected to a chemical activation process with phosphoric acid. 9. Integrated system for the treatment of waters according to any of the preceding claims that understands:

to.

A paristaltic pump

b.

A silver-filled airgel column filled with silver the size of desired particle, through which water is filtered contaminated

C.

A phase separation system.

d.

A sample collector located at the exit of the column.