ES2564566B2 - New filtration system based on the use of green manganese sand for the removal of water content radius - Google Patents

Abstract

New filtration system based on the use of green manganese sand for the removal of the water content radio. # The present invention relates to a filtration system for the removal of the water content radio based on a filter bed characterized in that it comprises ) an upper layer formed by silica sand, ii) an intermediate layer formed by green manganese sand, and iii) a lower layer formed by silica sand. It also contemplates a method for the elimination of the Ra content in water, based on the use of said filtration system, which in turn allows the desorption of the stopped radio after filtration and the regeneration and reuse of said filtering system.

Description

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DESCRIPTION

New filtration system based on the use of Green Manganese Sand for the elimination of the Radio content in Water.

Object of the invention

The present invention is directed to the treatment of water intended for human consumption. In particular, it is aimed at a filtration system to remove Ra from water, based on the use of green manganese sand. Likewise, it is directed to the method for the elimination of Ra from water, based on the use of said filtration system, as well as the procedure of desorption of the radius and regeneration and reuse of said filtering system.

Background of the invention

The use of specific substances for the elimination of Radio (Ra) present in solution in water has been frequently studied from different approaches. Thus, various types of specific resins and adsorbents have been developed which, by impregnating various materials, produce great adsorption power for the radius. Examples of these substances would be MnO2-coated acrylic fiber filters (US4087853), radio selective complexes (Dow Chemical Company: 1986, “Material safety data sheet: XFS 43230.00 Experimental Radium Complexer) or BaSO4 impregnated in alumina (Clifford, D. et al. “Evaluating various adsorbents and membranes for removing radium from groundwater” J. Am. Water Works Assoc. 80 (7), 94-104), as well as silica sands (CA2374861 and “Radon, Radium, and Uranium in drinking water. ”Chapter 16. Dennis A. Clifford" Removal of Radium from Drinking water ", edited by C. Richard Cothern and Paul A. Rebers Dennis). Silica sand is a material that is used as a filter bed to retain small-sized solids that are in the water (which is why it is usually used as a filter bed in water treatment plants). Its ability to adsorb radio depends on working conditions and has many limitations.

All the methods described require a treatment of the adsorbent material for the removal of the radius and in some cases the associated cost is high.

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Green manganese sand (greensand) is a natural manganese dioxide, commonly used in the removal of iron and manganese from water, through a filtration process. Soluble iron and manganese are oxidized and precipitated by contact with major manganese oxides in the green sand granules. This formed layer is restored after regeneration by potassium permanganate. Likewise, its use in radio removal is also known (Qureshi et al. "Radium removal by HMO and manganese greensand" Peer reviewed. Journal Awwa 95: 3. March 2003).

The authors of the present invention have developed a filtration system that uses natural substances, allowed by the Spanish legislation in the treatment of drinking water (Order SAS / 1915/2009, of July 8, on substances for the treatment of water intended for the production of water for human consumption BOE n ° 172 July 17, 2009).

Based on the properties of green manganese sand for the adsorption of pollutants, the system designed by the authors of the present invention uses a sandwich structure formed by silica sand and green manganese sand, being very effective for the removal of the radius. Water content. In addition, the authors of the invention have developed a process of desorption of the radius and regeneration of said sand so that, once its adsorption capacity has been significantly reduced, it can be reused for that purpose, even more effectively than initially.

The filtration system of the present invention has a high effectiveness in the elimination of the radius, it is easy to implement in a Station of Drinking Water Treatments or for domestic use, and it provides a treated water that is not affected in its physical conditions. chemical

The design of the filtration system provides important advantages in the elimination of the radius with respect to the different methods used in the state of the art. In particular, the use of the two layers of silica sand provides significant filtration advantages over using only green manganese sand, among which are to avoid clogging the filter due to the suspended particles of the waters to be treated; facilitate the desorption-regeneration processes for its new reuse and increase the effectiveness of the green manganese sand for the adsorption of the radius, also facilitating the low turbidity in the treated water.

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With respect to other types of filtration system by means of silica sand or activated carbon, this filtration system is also much more efficient than those, both because there is a greater elimination of the radius present in the water, and because it can be used for longer time, due to its slower saturation for this chemical element.

Description of the figures

Figure 1: Elimination efficiency of 226Ra (EF) by the silica sand filter bed against the volume of filtered double-distilled water.

Figure 2 .: Elimination efficiency of 226Ra (EF) by the silica sand filter bed against the volume of filtered natural water.

Figure 3 .: Diagram of the filtration system of the invention.

Description of the invention

In a main embodiment, the present invention relates to a new filtration system for the removal of the Radius (Ra) contained in water comprising a filter bed which in turn comprises a) a top layer formed of silica sand, b) an intermediate layer formed by green manganese sand, and c) a lower layer formed by silica sand, hereinafter "filtration system of the invention".

The preparation of the filter bed is carried out in such a way that the different layers of sand (c, b and a, in that order) are introduced sequentially through the top of a column until the system (I) is formed. Then, it is closed hermetically (II), washing with drinking water (tap) to eliminate possible impurities (III) and, the air that can contain the filtration system is purged, to avoid loss of efficiency (IV ).

Unlike other systems or methods used in the state of the art, the system of the invention allows optimum filtration of Ra, both in water in ideal conditions (double-distilled water + radius), and in real conditions (natural water, groundwater or surface waters). Natural water is defined as that which is found in nature and can be consumed by human beings, once it meets the physical, chemical, microbiological and radiological requirements specified by the legislation. In

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Spain these requirements are established in Royal Decree 140/2003, "Sanitary criteria of the quality of water for human consumption." The natural waters to which the present invention is applied are those that are intended for human consumption (ENAC 2007. Document NT -20 Rev. 2 July 2007) and that do not comply with the legislation in its radiological parameters, in particular waters that have high radio contents.

The Radium is adsorbed on the manganese dioxide (MnO2) of which the green manganese sand of the filtration system is composed.

On the other hand, the silica sand used in the sandwich structure of the filtration system of the invention has a double purpose: on the one hand it acts as a support for the green manganese sand and, on the other hand, it avoids the characteristic dark coloration of the treated water, when only green manganese sand is used. These two characteristics of the filtration system designed by the authors of the invention are due to the fact that silica sand retains the small particles of green manganese sand, which, when interspersed with silica sand, increases the effectiveness of the filter to eliminate radius. and prevents the coloration of treated water.

In particular, the top layer of silica sand protects the green manganese sand by preventing rapid clogging of the filter in the event of not being used, due to the suspended particles that the waters to be treated can normally possess. For its part, the lower layer of silica sand, larger in size than the upper one, increases the effectiveness of green manganese sand for adsorption of the radius, also facilitating low turbidity in the treated water.

Therefore, when comparing the filtration system of the invention with a filter containing only green manganese sand, differences are found, which not only affect the operation of the system, but also the turbidity of the resulting water. In this way, when green manganese sand is used alone, it clogs faster and increases the turbidity of the resulting water.

In a particular embodiment, the volume of layer c) of the filtration system is at least half the volume of layer b). Preferably, the ratio between the volumes of layers a), b) and c) is 1 -4-2.

The characteristics of the filtration system of the invention, in relation to the volume of

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The layers, diameter, height, etc., can be resized according to the flow needs of the water to be treated.

In another main embodiment of the invention a method is contemplated for the elimination of the Ra contained in water comprising i) the filtration of the water with Ra contents by passing it through the filter bed of the filtration system of the invention. Optionally, the elimination method comprises two additional steps that allow ii) desorption of the Ra adsorbed in the green manganese sand during step i) of filtration and iii) regeneration of the filtration system for subsequent reuse (see figure 3) .

The deadsorption of the Ra adsorbed in the green manganese sand (ii) is carried out by the use of dilute hydrochloric acid, preferably in a concentration between 1 and 1.5 M. Preferably, said acid is recirculated a minimum of three times, for a time of at least one hour per recirculation, in order to ensure that it is acting effectively in the system.

The regeneration of the filtration system (iii) is carried out by using potassium permanganate preferably in a concentration between 0.1 and 0.2 M. In preferred embodiments, the recirculation of potassium permanganate is carried out therein. form the diluted hydrochloric acid from the previous step (ii), a minimum of three times, for a time of at least one hour per recirculation.

Finally, the filter bed is washed with drinking water (tap) to be used again.

As with any filtration system, turbidity causes the system to clog and therefore impairs the proper functioning of the filter, so that the filtration system of the invention works with greater operability the less turbidity (1-5 UNF) has in water. Therefore, any previous water treatment to reduce its turbidity, before passing it through the filtration system, will be beneficial for the optimum performance of said system.

In a particular embodiment, the method of elimination of Ra is carried out at pressures greater than 0.5 bar. In the method of eliminating the invention, the minimum pressure is essential since, although the method is still effective, below that pressure the

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Radio removal efficiency decreases.

Also, preferably, the removal method is carried out at room temperature. This supposes an important advantage, since it is the usual working temperature in the Drinking Water Treatment Stations or in its domestic use.

In step i) the spatial velocity of the water through the filtration system can be controlled and optimized based on the working flow of the water and the volume of the filter bed (Space velocity = Flow x Volume).

In the method of elimination of the present invention, the passage of water through the filtration system in i) is preferably carried out at a spatial speed of 75 h-1, which significantly favors the elimination of the radius.

The design of the structure of the filtration system of the invention facilitates the development of the desorption-regeneration processes for its new reuse.

Preferably, step ii) for desorption of Ra from the green sand by recirculation of HCl is carried out at pressures greater than 0.5 bar. This prevents the formation of air bubbles in the sand, which make the process more inefficient. The working temperature in this case would not be decisive, so, preferably, to facilitate working conditions, it is carried out at room temperature.

The filtration system of Ra contained in water of the present invention has important industrial applications, since the characteristics of its design can be resized for optimum use both in water treatment plants and in domestic consumption (tap).

EXAMPLES Example 1

Radio retention efficiency in the green manganese sand filter of the invention.

A green manganese sand filter with 140 mm diameter was manufactured, from a column in which its lower part was filled with silica sand, in its intermediate part the green manganese sand was placed and in the upper part, again sand was introduced from

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silica, the ratio between volumes of said sands being 1-4-2. Next, the column was closed hermetically, washing with potable water (tap) to eliminate possible impurities from the sands and, the air that could contain the filtration system was purged, to avoid loss of efficiency. Water was filtered through the sand, at room temperature. The natural water used (groundwater) had a concentration of radius 0.44 ± 0.03 Bq / L, manganese <0.01 mg / L, iron <0.05, calcium 80 mg / L and magnesium 58 mg / L, with a pH of 7.7. The space velocities used were based on those usually used in the Drinking Water Treatment Stations and were 75, 150 and 170 h-1 for a maximum operating time of 110 hours. From this time the elimination of the radius decreased enough that it would begin to be advisable to apply the regeneration of the system.

Successive alfcuotas were analyzed, in order to determine the content of the radius in the water after filtration. The activity of the radius was determined by radiochemical separation, to later be measured by alpha spectrometry.

The results obtained are summarized in Table 1. It shows the percentages of radius elimination (%), for different spatial speeds, with different treatment times.

Table 1 indicates that at a higher spatial working speed, the elimination of radius decreases and damages its adsorption by the green manganese sand. As can be seen in Table 1, the best results are obtained for the spatial velocity of 75 h-1.

TABLE 1

 Treatment time (h)

 1 5 10 15 20 25 40 45 55 70 80 85 90 110

 Speed

 75 h-1 99 98 95 90 91 90 78 78 84 72 80 83 86 71

 space

 150 h-1 95 88 85 85 86 67 71 56 - - - - - -

 170 h-1

 99 80 86 78 74 66

Example 2

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Desorption and regeneration of the green sand filter of manganese of the invention.

The manganese green sand used for the removal of the radius in the water was subsequently subjected to a specific treatment in order to be able to use it again. To perform the desadsorption of the radius of the sand, it was treated with 1M hydrochloric acid, which was recirculated by the system three times, for 1 hour. In this way, 63% of the adsorbed radius in the sand was recovered, using 1 M HCl. Next, the green manganese sand was subjected to a regeneration process by using 0.1 M potassium permanganate; which was recirculated by the system three times, for 1 hour. Finally, said sand was reused for the removal of radio present in solution in the water. The experimental conditions were the same as in example 1, using the spatial velocity of 75 h-1. The results of the reuse of the filter bed are shown in Table 2. It shows the percentages of radius elimination (%), for the optimized space velocity, with different treatment times. These indicate, when compared with those obtained in example 1, that a better radio elimination occurs at higher treatment times, so that the desorption and regeneration processes carried out in the filter bed have as a consequence even an improvement in the characteristics that it has as a natural adsorbent of the radius.

TABLE 2

 Treatment time (h)

 Speed

 75 h-1 5 15 40 45 55 70 85 90 110

 space

   99 98 98 95 95 97 93 92 86

Example 3

To demonstrate the greater effectiveness and the advantages derived from the filtration system of the invention with respect to other systems employed in the state of the art, the authors of the present invention carried out comparative studies with filters formed exclusively of silica sand.

The test was carried out with natural water, with the same characteristics as the water used in the previous examples, and with double distilled water.

In the case of double-distilled water, which logically has a low saline content, and with pH 5.5, it was observed that the elimination was practically total for the radius content (Figure 1). However, as can be seen in Figure 2, for a natural water with a higher saline content and with two different pHs, the natural pH, 7.7, and a pH similar to double-distilled water (pH 6), rapidity occurred Loss in radio removal efficiency.

Therefore, the results obtained showed that, although these systems can adsorb radio under ideal conditions (double-distilled water + radio), under real conditions (groundwater or surface water), such as the water used in the previous examples, the radio adsorption in silica sand it descends rapidly, by filtering only 10 L 10 of said water.

Claims (13)

5 10 fifteen twenty 25 30 1. Filtration system for the elimination of the Radio content in water comprising a filter bed characterized in that it in turn comprises: i. An upper layer formed by silica sand, ii. An intermediate layer formed by green manganese sand, and iii. A bottom layer formed by silica sand. 2. System, according to the previous revindication characterized in that the volume of layer c is at least half the thickness of layer b. 3. System, according to revindication 2, characterized by the relationship between volumes of layers a, b and c is 1-4-2. 4. Method for elimination of water content Ra characterized in that it comprises i. water filtration with Ra contents by passing it through the filter bed of the filtering system of revindication 1. 5. Method, according to revindication 4, characterized in that it additionally comprises: ii. deadsorption of Ra stopped after step i) in the filter bed of the filtration system by using diluted hydrochloric acid, and iii. regeneration of the filtration system through the use of potassium permanganate. 6. Method according to revindication 4 or 5, characterized in that the elimination is carried out at pressures greater than 0.5 bar. 5 10 fifteen twenty 25 30 7. Method according to any of claims 4-6 characterized in that the elimination is carried out at room temperature. 8. Method according to any one of claims 4-7, characterized in that in step i) water filtration is carried out at a spatial velocity of 75 h-1. 9. Method according to any of claims 5-8, characterized in that in step ii) dilute hydrochloric acid in a concentration between 1-1.5 M is used. 10. Method according to any of claims 5-9 characterized in that in step ii) the hydrochloric acid is recirculated by the system a minimum of three times, for at least 1 hour. 11. Method according to any of claims 5-10, characterized in that in step iii) potassium permanganate is used in a concentration between 0.1 and 0.2 M. 12. Method according to any of claims 5-11, characterized in that in step iii) the potassium permanganate is recirculated by the system a minimum of three times, for at least 1 hour. 13. Method for manufacturing a filtration system, according to claims 1-3, comprising: I. Enter sequentially the 3 layers of sand c), b) and a), in that order, in a column until the filtration system is formed, II. Hermetically close the system obtained in I), III. Wash the closed system in II) with potable water, and IV. Purge the air that may be contained in the filtration system obtained in III).