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BR-112021025106-B1 - METHOD FOR TREATING WATER TO REDUCE ITS DISSOLVED SILICA CONTENT

BR112021025106B1BR 112021025106 B1BR112021025106 B1BR 112021025106B1BR-112021025106-B1

Abstract

METHOD FOR TREATING WATER TO REDUCE ITS DISSOLVED SILICA CONTENT. This is a method for treating water to reduce its dissolved silica content, characterized by comprising at least one step for adsorbing dissolved silica, which consists of passing the water through a reactor housing a granular adsorbent material consisting of iron(III) hydroxide and/or iron(III) oxyhydroxide grains, and at least one step for regenerating the adsorption power of the granular material, which consists of contacting the granular material with a base and at least one chloride.

Inventors

  • Bastien RIVIERE
  • Vincent GEORGEAUD

Assignees

  • VEOLIA WATER SOLUTIONS & TECHNOLOGIES SUPPORT

Dates

Publication Date
20260310
Application Date
20200713
Priority Date
20190712

Claims (6)

  1. 1. A method for treating water in order to reduce the dissolved silica content thereof, characterized by comprising at least one step of adsorbing said dissolved silica, wherein the step consists of passing said water through a reactor housing a granular adsorbent material consisting of grains of iron(III) hydroxide and/or iron(III) oxyhydroxide, wherein at least 5% of said granular adsorbent material is in the form of akaganeite; wherein said grains of iron(III) hydroxide and/or iron(III) oxyhydroxide have a size between 0.2 mm and 5 mm, and at least one step of regenerating the adsorption power of said granular material, wherein the step consists of bringing said granular material into contact with a base and at least one chloride.
  2. 2. Method according to claim 1, characterized in that said regeneration step is performed with a regeneration solution containing said base and said chloride.
  3. 3. Method according to claim 1, characterized in that said regeneration step is performed with two regeneration solutions, one containing said base, the other containing said chloride.
  4. 4. Method, according to any one of claims 1 to 3, characterized in that said base is selected from the group consisting of NaOH, KOH, NH4OH, LiOH.
  5. 5. Method according to any one of claims 1 to 4 characterized in that said chloride is selected from the group consisting of NaCl, KCl, LiCl, NH4Cl, MgCl2, CaCl2, BaCl2, MnCl2.
  6. 6. A method, according to any one of claims 1 to 5, characterized in that said granular material is used in the form of a fixed bed and said adsorption step is carried out with a volume load of between 5 and 30 cubic meters of water passing per cubic meter of granular material per hour.

Description

FIELD OF THE INVENTION'S TECHNIQUE [001] The invention relates to a method for treating water to reduce the dissolved silica content thereof. [002] More specifically, the invention relates to such a method in which dissolved silica is adsorbed onto a regenerable adsorbent material. PREVIOUS TECHNIQUE [003] Silicon (Si) is present in many rocks and sediments. Through various chemical alteration processes, this element is found in many types of water (seawater, brackish water, river and lake water, etc.). Although the chemistry of silicon in water is complex and insufficiently understood, it is understood that silicic acid is found in soluble form (“dissolved silica”) in these waters in concentrations that vary depending, in particular, on the chemical species they contain and their temperature. However, this dissolved silica has a number of disadvantages when it is desirable to use such water for certain applications. [004] In fact, the dissolved silica can precipitate under certain conditions and thus cause malfunction of certain equipment when using the water in question. [005] For example, its presence is undesirable in water intended to supply boilers, in water intended to be treated in evapoconcentrators, in water intended to be treated by membrane filtration devices, in particular those incorporating reverse osmosis membranes, etc. In such installations, dissolved silica can precipitate and flake off or clog the equipment. [006] Dissolved silica can therefore also constitute a problematic species, not because it can precipitate, but because its presence will disrupt certain chemical or psychochemical reactions involved in the treatment of certain water. For example, the presence of silica generates colloidal impurities in certain liquid-liquid extraction methods that significantly disrupt phase separation. Another example is the interfering nature of dissolved silica in chelating resin methods that aim to remove other compounds. [007] There are several techniques in the prior art for reducing the amount of silica dissolved in water. [008] Thus, they can be coagulated or electrocoagulated and then clarified. However, these methods lead to the production of sludge, which must also be treated, and involve the use of large quantities of coagulating agent, which increases their costs. [009] Coprecipitation of dissolved silica in the presence of alkali metals is also known. Besides the fact that this technique also requires large quantities of chemical reagents, such as caustic soda or limestone, to cause the formation of insoluble alkali metal salts, it also implies the need, when the concentration of dissolved alkali metal in the water to be treated is low, to add large quantities of highly soluble alkali metal salts, such as magnesium chloride, to said water. This technique, therefore, is also relatively expensive to implement. [010] These different techniques also share the disadvantage of having to be implemented at high pH values, typically greater than 10. [011] There is therefore a need for an alternative solution to the aforementioned different methods of the prior art, allowing the reduction of the silica content dissolved in water without having to use large quantities of chemical reagents, and which can be used at lower pH values. [012] For this purpose, the use of ion exchange resins is not industrially feasible. In fact, since dissolved silica is mainly ionized only by pH values > 9.4, its elimination by said method would require a pH adjustment to an alkaline range which, for water containing a certain alkalinity and/or hardness, would cause the undesirable precipitation of carbonate salts. Furthermore, since such anionic resins are not strictly selective with respect to dissolved silica, a large portion of the exchange capacity of said resins would be mobilized by other anions (Cl-, Br-, SO42-, ...) present in the water to be treated. The said lack of selectivity of anion exchange resins makes said method industrially unsustainable for silica removal, due to the fact that this would require the use of very large quantities of resins. PRESENTATION OF THE INVENTION [013] The said need is satisfied thanks to the invention relating to a method for treating water in order to reduce the dissolved silica content thereof, characterized in that it comprises at least one adsorption step consisting of passing said water through a reactor housing a granular adsorbent material consisting of iron(III) hydroxide and/or iron(III) oxyhydroxide grains and at least one step for regenerating the adsorption power of said granular material consisting of placing said granular material in contact with a base and at least one chloride. [014] The invention therefore proposes the use of such material to adsorb dissolved silica and, when its adsorption power with respect to said chemical species is insufficient, to regenerate said adsorption power by placing it in contact with a basic solution and at least one chloride