FR2888514A1 - Decontaminating fluid containing metalloids and suspended solids, e.g. to remove arsenic from water, involves recirculating the fluid up through a bed of activated alumina so that the bed expands to prevent clogging - Google Patents

Abstract

A method for the decontamination of fluid containing metalloids and suspended solids by adsorption of the metalloids on activated alumina (AA) in a rising-flow reactor, in which the fluid is fed into the lower part of the reactor containing a bed of AA, and recirculated from top to bottom after passing through the bed so as to cause expansion of the AA and maintain a level of expansion sufficient to prevent clogging of the bed, and the decontaminated fluid is recovered. An independent claim is included for an installation for use in the above method, comprising a means (2) of injecting contaminated fluid into the lower part of the reactor, a bed of AA (3) above the fluid injection point, a recirculation loop (4) from the top of the reactor to the bottom and a system (5) for recovering decontaminated fluid from the top of the reactor, fitted above the loop (4).

Description

2888514 1

  The present invention relates to the general technical field of fluid treatment, such as an aqueous solution, containing metalloids as well as suspended solids, in particular water for drinking or water of urban origin to be recycled or reject in the environmental environment.

  In particular, the present invention relates to a process for the removal of fluid containing metalloids as well as suspended solids by adsorption on a fluidized bed of activated alumina in a treatment reactor. The invention also relates to a fluid depollution installation containing metalloids and suspended solids, suitable for carrying out said method.

  Metalloids, such as arsenic, selenium, antimony, and fluorine, represent a particularly important source of pollution, both in terms of quantity and in terms of environmental risks, especially when it comes to of water to drink.

  In order to reduce the concentrations of metalloids in solution under the standards in force, various processes have been developed. In order to eliminate, for example, arsenic from effluents, physicochemical methods, such as chemical precipitation or co-precipitation by lime softening, ionic exchange processes on polymeric resins, or processes are conventionally used. coagulation-flocculation on direct filter, especially using iron salts and aluminum.

  Nevertheless, these processes generally require many reactors and structures to perform the various stages of treatment, such as coagulation, flocculation, and settling. These processes thus require heavy investments, both in GC and equipment.

  Furthermore, the treatments of the prior art to purify effluents containing metalloids, such as arsenic, by filtration through a fixed bed of adsorbent reagent are very inefficient because of the rapid clogging of the filter, when the Effluents to be treated contain colloidal substances or suspended solids.

  Therefore, there was a need to develop a process and an installation for the treatment of fluids, such as water or effluents, containing metalloids as well as suspended solids, not having the disadvantages of the processes. and devices of the prior art, making it possible in particular to perform effective depollution and separation of the fluid within a single treatment structure, by dispensing with a separate decantation work, and also to avoid clogging of the depollution device.

  The present invention fills this need. The Applicant has thus discovered a new process and an installation making it possible to efficiently treat and remove concentrated metalloid fluids, such as urban effluents or surface waters with a view to making them drinkable, in an upflow treatment reactor. compact, very simple operation and implementation, and in which is effectively carried out the adsorption of the metalloids to be eliminated, as well as the separation of the fluids to be treated.

  The method which is the subject of the present invention thus makes it possible to degrade a large fraction of metalloids in solution with a metalloid retention efficiency of up to 90 to 99%, generally around 95%, for a wide range of metalloids in question. varying concentrations.

  The method according to the present invention makes it possible in particular to carry out an efficient fluid depollution, such as an aqueous solution, by adsorption on a moving bed of activated alumina, as well as a gravitational separation of the treated fluid from the alumina suspension at within a single treatment structure, without significant loss of adsorbent, not requiring the addition of coagulation additives or flocculation, without the need to equip the structure with a mechanical mixing device, and allowing avoid rapid clogging of the bed and avoid the use of frequent filter washes.

  The method according to the present invention thus makes it possible to treat various types of water, such as water of urban or industrial origin, and makes it possible to get rid of a substantial part of the toxic pollutions, while avoiding clogging of the bed.

  The subject of the present invention is thus a process for the depollution of fluid containing metalloids as well as suspended solids by adsorption of metalloids on activated alumina in an upflow treatment reactor, comprising feeding the fluid to be treated. in the lower part of the reactor containing an activated alumina bed, the recirculation of the fluid having passed through the bed, from the upper part of the reactor to the lower part of the reactor, so as to create an expansion of the activated alumina and to maintain an expansion rate sufficient to prevent clogging of the bed, and recovery of the cleaned up fluid.

  In a particular embodiment of the present invention, the fluid to be treated is an aqueous solution, advantageously water to be watered, especially groundwater or surface water, such as river water , dam water, or alluvial water, or water of industrial origin.

  Advantageously according to the present invention, the pH of the fluid to be treated at the inlet of the reactor is between 6 and 7.5.

  According to a particular feature of the present invention, the metalloids are selected from the group consisting of arsenic, selenium, antimony, fluorine, and mixtures thereof.

  Advantageously according to the present invention, the expansion rate of the bed is maintained between 15 and 40%, advantageously between 20 and 35%, still more advantageously between 25 and 35%, in particular between 25 and 30%.

  In a particular embodiment of the present invention, in order to maintain the expansion ratio, the sum of the feed rate and the recirculation flow rate must be greater than the minimum fluidization flow rate of the activated alumina bed.

  In a particular embodiment of the present invention, the recovery of the cleaned fluid is carried out by overflow or by pumping the decanted and cleaned up fluid located in the upper part of the reactor overlying the activated alumina bed.

  The present invention also relates to a fluid pollution control installation containing metalloids and suspended solids comprising at least one treatment reactor (1) containing: - injection means (2) of the fluid to be partially treated lower reactor, - an activated alumina bed (3) surmounting said fluid injection means (2), 2888514 4 - a recirculation loop (4) from the upper part of the reactor to the lower part of the reactor, and - A recovery device (5) of the fluid removed in the upper part of the reactor, arranged above said recirculation loop (4).

  This installation is suitable for carrying out the process according to the present invention.

  The plant according to the present invention may contain a single treatment reactor or several associated processing reactors in parallel (flow sharing) or in series, especially in industrial applications. If the plant according to the present invention contains several treatment reactors, it is possible to selectively dimension each of the structures constituting the die by selecting the composition of the alumina bed (origin, grain size and quantity) and by adjusting the hydraulic operating parameters. (ascending velocity and useful height of material in particular) and adsorbent dosage.

  Typically, the installation can comprise two treatment reactors within each of which are carried out a depollution of the fluid, as well as a separation between the particles of activated alumina and the fluid. The first treatment reactor can then be a roughing work where the majority of the pollution is clipped, and the second treatment reactor can be a refining work to remove the remaining metalloids.

  Various objects and advantages of the present invention will become apparent to those skilled in the art by way of reference to the following illustrative drawing: FIG. 1 is a schematic sectional view of a fluid treatment reactor (1) in operation; which comprises a fluid injection manifold (2) to be treated, an activated alumina bed (3) expanded, a recirculation loop (4) from the upper part of the reactor to the lower part of the reactor, and a device for recovery (5) of the clear fluid decanted in the upper part of the reactor (1), arranged above said recirculation loop (4).

  As shown in FIG. 1, the fluid to be treated can be previously stored in a storage tank (6) or a feed tank, before being transferred, for example by means of pumps, to the treatment reactor. (1). The fluid 2888514 5 to be treated can undergo pretreatment, for example to promote the solubilization of metalloids. The treated fluid can be transferred to an extraction or storage tank (7), before being discharged for example into a treatment plant.

  The process according to the present invention can effectively treat various types of fluids, such as urban or industrial raw waters or effluents, concentrated in toxic metalloids, such as arsenic. The process according to the present invention is advantageously used to treat urban effluents or water to be treated, particularly turbid waters. The fluids that can be treated in the context of the present invention can be more or less loaded with MES, and can have MES contents of the order of a few hundred mg / L, for example of the order of 200 to 300 mg / L.

  Advantageously according to the present invention, the pH of the fluid to be treated is adjusted to between 6 and 7.5, before being injected into the treatment reactor (1), so that the activated alumina can effectively exert its adsorbent metalloid power.

  The metalloids that can be treated by the present invention are of various types, and may be in varying concentrations in the fluid to be treated.

  The treatment of fluids according to the present invention can be carried out continuously or discontinuously (batch type).

  The treatment reactor (1) according to the present invention is advantageously a cylindrical reactor of vertical axis, with a height generally of between 1 and 5 meters, typically about 2 to 4 meters.

  The introduction of fluid to be treated in the treatment reactor (1) can be performed by an injection manifold (2) equipped with orifices of adjusted diameter.

  The introduction of fluid can also be carried out using a screened floor, preferably provided with several strainers distributed over the section of the treatment reactor (1).

  In an exemplary embodiment of the present invention, a layer of sand or a similar material is placed in the treatment reactor (1) under the activated alumina bed (3), advantageously above the injection means. of the fluid to be treated, the type of floor screened. The sand can be coarse sand. The layer of sand or similar granular material used makes it possible to support and maintain the activated alumina bed (3) in the treatment reactor (1), and to improve the dispersion of the effluents in the bed.

  The treatment reactor (1) according to the present invention contains an activated alumina bed (3). The alumina bed can not be suspended by mechanical stirring, because of the friable nature of the material. The bed is advantageously put in fluidized form by injection of the fluid to be treated in the lower part of the upflow reactor (1), preferably at the base of the reactor, and by recirculation of the fluid in the treatment column (1) via the loop. recirculation (4). The recirculation flow rate makes it possible, in addition to the feed rate, to reach within the activated alumina bed the minimum fluidization speed, a speed beyond which the bed becomes expanded. Once the bed is expanded, suspended solids can pass through it, preventing clogging of the treatment reactor (1).

  The particle size of the activated alumina is advantageously selected so as to exert effective adsorption of the metalloids, while having an expandability, to create a mobile alumina bed by maintaining a dense suspension of expanded activated alumina. The activated alumina according to the present invention is typically with a particle size of between 0.1 and 2 mm, typically of the order of 0.3 to 0.8 mm.

  Within the activated alumina bed, no other treatment additive than alumina, such as coagulation or flocculation agents to remove the alumina particles, needs to be added in the process according to the present invention. invention. However, there may be an embodiment in which coagulation or flocculation agents are added to treat certain types of fluids.

  Advantageously according to the present invention, the height of the alumina bed, the speed and the flow rate of the fluid to be treated or recirculated, or the contact time of the fluid to be treated in the reactor, are chosen so as to exert effective adsorption metalloids, preferably of the order of 50 to 99%, in particular of 60 to 95%.

  Typically, the contact time in the treatment reactor (1) is of the order of a few minutes to a few hours, advantageously of the order of a few tens of minutes. The height of the alumina bed at rest can be determined as a function of the contact time and the flow rate of the fluid in the treatment reactor.

  By the term "minimum flow rate of fluidization" is meant in the sense of the present invention the minimum flow rate at which the alumina bed must be subjected to begin to expand. This minimum flow rate of fluidization Qmf is, for example, estimated by the Wen & Yu relation (AichE J, 12 (3), 610-612, 1966): (33.72 + 0.0408 dP3Pr (PP2 Pr) g -33.7 f in which Sr is the section of the treatment reactor (m2), is the viscosity of the fluid (Pa. $), Dp is the particle diameter (m), pf is the density of the fluid (kg / m3), pp is the particle density (kg / m3), and g is the acceleration of gravity.

  In the case of an adsorbent material with a particle size distribution, the minimum fluidization rate of the bed is preferably imposed by the larger diameter particles.

  Advantageously according to the present invention, the beginning of expansion of the bed takes place when the relation Qalim + Qrecirc> Qmf is verified.

  The feed rate of the Qalim fluid is typically imposed by the necessary contact time between the fluid and the material to fix the metalloids. The Qrecirc fluid recirculation flow comes in addition to Qalim to ensure a flow rate greater than Qmf. Beyond Qmf, the material expands. The recirculation flow rate of the fluid Qrecirc is advantageously adjusted so as to reach the desired degree of expansion (for example up to 40%), this rate depending on the content of suspended solids, and thus on the potential for clogging of the bed. alumina. The more the fluid to be treated is loaded with solids in suspension, the higher the rate of expansion will be.

  Activated alumina makes it possible to adsorb the metalloids to be removed.

  The method according to the invention makes it possible to obtain a gravitational separation of the alumina particles from the depolluted fluid with the obtaining of a clear fluid decanted in the upper part of the reactor, with a very low residual activated alumina content. The effluent-free fluid is then advantageously recovered in the upper part of the reactor, for example by overflow, with the aid of a recovery device (5), such as a set of crenellated chutes, or by pumping.

  Typically, once the activated alumina is saturated with metalloids, which can be easily controlled when the de-polluted fluid has a metalloid leak (s) greater than a fixed limit, the alumina is discharged to a discharge, and the reactor is filled with new material.

  The following example is given as a non-limiting example and illustrates the present invention.

  Embodiment of the invention

Example 1

  An installation according to the present invention comprises a treatment reactor (1) with a diameter of the order of 150 mm, containing an activated alumina bed (3) with a height of 130 cm and a volume of material of 22.9 liters at rest. The activated alumina introduced has a particle size of 0.3 to 0.8 mm. The treatment reactor (1) also contains fluid injection means (2) to be treated, a recirculation loop (4) from the upper part of the reactor to the lower part of the reactor, and a recovery device ( 5) the fluid removed in the upper part of the reactor, arranged above said recirculation loop (4).

  Such an installation is used to purify a fluid that is injected at the base of the treatment reactor (1) with a feed rate of about 801 / h, and recirculated with a recirculation flow of about 130 1 / h. The expansion rate resulting from the bed is around 30%.

  The contact time is of the order of 15 minutes. The clear decanted fluid, located in the upper part of the reactor above the activated alumina bed (3), is recovered by pumping. The arsenic capture efficiency on the alumina bed is of the order of 97%.

Claims (1)

9 CLAIMS   1. A process for the depollution of fluid containing metalloids as well as suspended solids, by adsorption of metalloids on activated alumina in an upflow treatment reactor, comprising feeding the fluid to be treated in the lower part of the reactor containing a bed of activated alumina, the recirculation of the fluid having passed through the bed, from the upper part of the reactor to the lower part of the reactor, so as to create an expansion of the activated alumina and to maintain a sufficient expansion rate to avoid the clogging of the bed, and recovery of the fluid cleaned up.   2. Method according to claim 1, characterized in that the fluid to be treated is an aqueous solution, advantageously water to be treated, especially underground water or surface water, such as water. river, dam water, or alluvial water, or water of industrial origin.   3. Method according to claim 1 or 2, characterized in that the pH of the fluid to be treated at the reactor inlet is between 6 and 7.5.   4. Process according to any one of claims 1 to 3, characterized in that the metalloids are selected from the group consisting of arsenic, selenium, antimony, fluorine, and mixtures thereof.   5. Method according to any one of the preceding claims, characterized in that the expansion rate of the bed is maintained between 15 and 40%, preferably between 20 and 30%.   6. Method according to any one of the preceding claims, characterized in that for the maintenance of the expansion ratio, it is necessary that the sum of the feed rate and the recirculation flow rate is greater than the minimum flow rate of the fluid bed. activated alumina.   7. Method according to any one of the preceding claims, characterized in that the recovery of the cleaned fluid is carried out by overflow or by pumping the decanted and cleaned up fluid located in the upper part of the reactor overlying the activated alumina bed.   8. Installation for the removal of fluid containing metalloids and suspended solids comprising at least one treatment reactor (1) containing: injection means (2) for the fluid to be treated in the lower part of the reactor, a reactor bed; activated alumina (3) surmounting said fluid injection means (2), - a recirculation loop (4) from the upper part of the reactor to the lower part of the reactor, and a device for recovering (5) the cleaned fluid in the upper part of the reactor, arranged above said recirculation loop (4).