Method for treating wastewater from production of hydrated silica by carbonation

Abstract

The application discloses a treatment method of carbonation hydrated silica production wastewater. The method comprises the following steps: 1) adding calcium-magnesium carbonate as a desiliconizing agent in the carbonation hydrated silica production wastewater; 2) heating and wet decomposing sodium bicarbonate in the carbonation hydrated silica production wastewater, cooling the solution through heat exchange, then performing settlement and filtration to obtain a precipitate and a desiliconized filtrate; the precipitate contains a large amount of calcium-magnesium carbonate, which is returned to step 1) for desiliconization; carbon dioxide generated in the wet decomposition process is returned to a production system to participate in the synthesis of hydrated silica as an acid source; 3) after the desiliconized filtrate is precisely filtered, the desiliconized filtrate is concentrated through a membrane to obtain concentrated salt-containing wastewater and concentrated effluent, and the concentrated effluent is returned to a production line to be used as process water; 4) the concentrated salt-containing wastewater is transferred to an evaporation crystallization system to be concentrated and crystallized, to obtain sodium carbonate monohydrate crystals and condensed water, the condensed water is reused as production water, and the sodium carbonate monohydrate is sent to a drying system; 5) the sodium carbonate monohydrate sent to the drying system is calcined at high temperature to obtain sodium carbonate products, which are sent to a water glass production workshop through pipeline transportation and used as raw materials. The application solves the bottleneck of scaling in the treatment process of the carbonation hydrated silica production wastewater in the prior art, and solves the problems of high operation cost and large equipment investment of the wastewater treatment.

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment, and specifically relates to a method for treating wastewater produced by carbonization of hydrated silicon dioxide, that is, a method for treating wastewater containing silicon dioxide and carbonates generated during the carbonization production of hydrated silicon dioxide products such as white carbon black and silica gel. Background Art

[0002] Hydrated silica products such as white carbon black and silica gel are a general term for white powdery amorphous silicic acid and silicate products, with silicon dioxide as the main component.

[0003] Since the raw materials used in the production of hydrated silica are highly clean and the production process is completely inorganic with no side reactions, only silica and carbonates are produced during the production process. Therefore, the wastewater quality is good, with COD generally below 50 mg / L, and the main pollutant is total salt (carbonate).

[0004] Table 1 Main indicators of hydrated silicon dioxide production wastewater

[0005] Serial number Test items unit Water quality indicators 1 pH — 5～8 2 Conductivity at 25℃ μs / cm 15000～78000 3 <![CDATA[COD Cr ]]> mg / L ≤50 4 SS mg / L ≤150 5 Sodium bicarbonate ％ 1.5-6.5 6 sodium carbonate ％ 0.2-1.5 7 Chloride ions mg / L ≤200 8 Phosphate mg / L ≤2 9 Soluble silica mg / L ≤300 10 colloidal silicone mg / L ≤200

[0006] Table 1 shows the main indicators of hydrated silica production wastewater. From the above data, it can be seen that in addition to carbonates, the silicon content in this wastewater ranks first. Silicon exists in two forms in water, active silicon (monosilicon) and colloidal silicon (polysilicon). Colloidal silicon does not have ionic characteristics, but its scale is relatively large. Colloidal silicon can be intercepted by fine physical filtration processes, such as reverse osmosis; its content in water can also be reduced through coagulation technology, such as coagulation clarification tanks. However, the above schemes rely on separation technologies with ionic charge characteristics, such as ion exchange resins and continuous electrodeionization processes (C / EDI), which are very limited in effect on the removal of colloidal silicon.

[0007] Active silica is much smaller than colloidal silica, so most physical filtration techniques, such as coagulation and clarification, filtration, and flotation, are unable to remove it. Reverse osmosis, ion exchange, and continuous electrodeionization are the only processes that can effectively remove active silica. While ultrafiltration offers improved filtration during desiliconization and colloidal silica treatment, it cannot effectively resolve blockages. Disassembly and subsequent flushing are the only possible solutions, which can easily damage the ultrafiltration tubes and cause financial losses. To ensure effective filtration while reducing the number of disassembly and flushing cycles, automatic flushing and anti-clogging technology can be added to the filtration process to simplify disassembly and ensure continuous filtration. Patent CN202211713483.0 discloses a TMF ultrafiltration wastewater filtration and removal of colloidal silica anti-clogging device and its use method, which mainly makes structural improvements. However, for a wastewater treatment system with the purpose of recovering alkali liquor, this method does not solve the scaling problem in the later alkali liquor recovery process. At the same time, the waste liquor cannot be completely treated during the treatment of carbonized silica filtrate. The waste liquor after backwashing needs to be further treated before it can meet the discharge standards. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for treating wastewater from the production of hydrated silicon dioxide by carbonization in order to address the above-mentioned defects of the prior art.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A method for treating wastewater from the production of hydrated silicon dioxide by carbonization, comprising the following steps:

[0011] 1) In order to prevent scaling of silicon dioxide in the evaporation and evaporation crystallization process of carbonized hydrated silicon dioxide production wastewater, active calcium magnesium carbonate is added as a silicon removal agent to the carbonized hydrated silicon dioxide production wastewater containing trace silicates;

[0012] 2) heating the carbonization-process hydrated silicon dioxide production wastewater to which calcium and magnesium carbonates have been added to wet decompose sodium bicarbonate, cooling the solution by heat exchange, and then sedimenting and filtering to obtain a precipitate and a desiliconized filtrate; the precipitate contains a large amount of calcium and magnesium carbonates and can be returned to step 1) for silicon removal; at the same time, the gas produced by the wet decomposition process is mainly composed of carbon dioxide and water vapor, so that a small portion of the gas is used to produce calcium bicarbonate and then remove silicon, and the remaining gas can be directly introduced into the carbonization-process hydrated silicon dioxide reaction device as an acid source (instead of sulfuric acid and hydrochloric acid in traditional methods) to participate in the synthesis of hydrated silicon dioxide;

[0013] It should be noted that before silicon removal, the calcium magnesium carbonate suspension is introduced with carbon dioxide produced by wet decomposition to convert the calcium magnesium carbonate into calcium bicarbonate, thereby increasing its solubility in water. Calcium bicarbonate is easily soluble in water, so calcium ions will react with carbonate and silicate in the aqueous solution to generate calcium silicate and calcium magnesium carbonate precipitation, thereby achieving the purpose of silicon removal.

[0014] 3) After the desiliconization filtrate is finely filtered, it is concentrated through a membrane to obtain concentrated saline wastewater and concentrated effluent, which is returned to the production line for use as process water;

[0015] 4) The salinity of the concentrated saline wastewater is increased by 2-6 times, and the wastewater is sent to an evaporative crystallization system for concentration and crystallization to obtain sodium carbonate monohydrate crystals and condensed water. The condensed water is reused as production water, and the sodium carbonate monohydrate enters a drying system;

[0016] 5) The sodium carbonate monohydrate entering the drying system is calcined at high temperature to obtain a finished sodium carbonate product, which is then transported through pipelines to the water glass production workshop as raw material.

[0017] Furthermore, the composition of the carbonization method hydrated silicon dioxide production wastewater in step 1) is: 1.5-10% sodium bicarbonate, preferably 1.5-6.0%; 0.2-1.5% sodium carbonate, preferably 0.2-0.8% sodium carbonate; and 100-600 ppm soluble silicon dioxide.

[0018] Furthermore, the calcium magnesium carbonate in step 1 includes one or both of calcium carbonate and basic magnesium carbonate.

[0019] Furthermore, in step 2), the carbonization process hydrated silicon dioxide wastewater is heated to decompose sodium bicarbonate to convert the sodium bicarbonate into sodium carbonate, and the decomposition temperature is 60-150°C, preferably 80-100°C.

[0020] Furthermore, the membrane concentration described in step 3) is RO membrane concentration or nanofiltration membrane concentration. When RO membrane concentration is used, the water inlet pressure is 3.0-9.0 MPa and the water inlet temperature is ≤40°C; when nanofiltration membrane concentration is used, the water inlet pressure is 2.0-4.0 MPa and the water inlet temperature is ≤40°C; the conductivity of the concentrated water is controlled at ≤600 μS / cm, which can be used for production reuse; the concentrated saline wastewater is mainly sodium carbonate with a salt content of 10-30%, preferably a salt content of 10-18%.

[0021] Furthermore, in step 4), the concentrated salt-containing wastewater is sent to an evaporation crystallization system for a concentration and crystallization process, and the resulting condensed water conductivity is controlled at 20-80 μS / cm, preferably 40-60 μS / cm, which can be used as water for the production of hydrated silicon dioxide by carbonization. The evaporation crystallization system can adopt a negative pressure MVR evaporation system with an operating pressure of 0.05-0.09 MPa (absolute pressure), preferably 0.06-0.08 MPa. The salt content of the wastewater after membrane concentration is increased by 2-6 times, so whether the subsequent equipment uses waste heat for multi-effect evaporation or adopts negative pressure MVR evaporation crystallization, the subsequent evaporation crystallization equipment investment and operating costs are reduced by at least 50%.

[0022] Furthermore, in step 5), the high-temperature calcination temperature is 100-240° C., preferably 100-150° C., and the sodium carbonate monohydrate is completely decomposed into sodium carbonate and can be transported as a water glass raw material through a pipeline back to the water glass production unit.

[0023] The present invention adopts the above technical solution, uses calcium magnesium carbonate to carry out desiliconization reaction, and reacts with trace silicon dioxide in the filtrate through calcium magnesium carbonate. After the reaction is completed, it is filtered and separated, and the trace silicon dioxide is removed and then enters the evaporation crystallization unit to recover sodium carbonate in the filtrate.

[0024] The reaction mechanism is as follows:

[0025] CaCO3+2NaHCO3═Ca(HCO3)2+Na2CO3

[0026] Mg2(OH)2CO3+6NaHCO3═2Mg(HCO3)2+3Na2CO3+2H2O

[0027] Mg 2+ +Ca 2+ +2SiO3 2- ═CaSiO3+MgSiO3

[0028] The present invention has the following advantages:

[0029] Since the carbonization method of hydrated silica wastewater contains more than 70% sodium bicarbonate, the present invention adopts the calcium magnesium carbonate method to remove silicon. At the same time, the wastewater temperature is controlled to 60-130 ° C during the silicon removal process to wet decompose the sodium bicarbonate. The purpose is to convert all bicarbonate into carbonate, effectively reduce the solubility of calcium ions while achieving silicon removal, and provide support for subsequent membrane concentration. The excess calcium magnesium carbonate in the silicon removal process of the present invention can be recycled, which reduces the cost of silicon removal reagents and reduces the generation of solid waste. In addition, the main components of the hydrated silica wastewater after silicon removal under the wet decomposition conditions of the present invention are sodium carbonate and trace sodium chloride, so membrane concentration can be directly used to concentrate the salt content of the high-concentration salt-containing wastewater to 10-18%, greatly reducing the operating cost of subsequent sodium carbonate evaporation and crystallization and the investment cost of evaporation equipment.

[0030] The invention solves the bottleneck of scaling in the wastewater treatment process of carbonization-processed hydrated silicon dioxide production in the prior art, and simultaneously solves the problems of high operating cost and large equipment investment in the wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0032] Example 1

[0033] A method for treating wastewater from the production of hydrated silicon dioxide by carbonization, comprising the following steps:

[0034] 1) Carbonization hydrated silicon dioxide wastewater is transported to a stirred reactor. The wastewater composition is 3.2% sodium bicarbonate, 0.36% sodium carbonate, and 450 ppm soluble silicon dioxide. Calcium carbonate powder is added with stirring at a solid-liquid ratio of 1:20.

[0035] 2) The temperature was raised to 70°C, and the mixture was reacted for 1.5 hours, followed by filtration to obtain a precipitate and a desiliconization filtrate. The precipitate contained a large amount of unreacted calcium magnesium carbonate, which was returned to step 1) for further desiliconization. The steam generated during the heating and stirring process passed through the condenser reflux pipe, and the non-condensable gas contained 50% CO2. The non-condensable gas was directly introduced into a carbonization reactor filled with water glass for carbonization. The desiliconization filtrate had a composition of 2.6% sodium carbonate, 0.48% sodium bicarbonate, and 48 ppm soluble silicon.

[0036] 3) The desiliconized filtrate is pumped to the RO membrane concentration system at a pumping pressure of 4.0 MPa and an inlet water temperature of 37°C. The conductivity of the concentrated water after membrane concentration is 280 μS / cm, and it is returned to the production line for use as process water.

[0037] 4) The concentrated saline wastewater has a sodium carbonate concentration of 13.0% and a soluble silicon content of 96 ppm. The concentrated saline wastewater is pumped to a negative pressure MVR concentration and crystallization system, maintained at 85°C and an evaporation chamber pressure of 0.07 MPa, where it is concentrated to a sodium carbonate content of 38.0% and crystallized to obtain hydrated sodium carbonate crystals. The steam in the evaporation chamber is heat-exchanged to produce condensed water with a conductivity of 40 μS / cm. This condensed water enters a condensate tank and is reused as final washing water for silica.

[0038] 5) Sodium carbonate monohydrate is burned in a muffle furnace at 140°C to obtain anhydrous sodium carbonate, which is then transported to the water glass production workshop via a pipeline.

[0039] Example 2

[0040] A method for treating wastewater from the production of hydrated silicon dioxide by carbonization, comprising the following steps:

[0041] 1) The carbonization process hydrated silicon dioxide wastewater is transported to a stirred reactor. The wastewater composition is 2.8% sodium bicarbonate, 0.15% sodium carbonate, and 600 ppm soluble silicon dioxide. Basic magnesium carbonate powder is added with stirring at a solid-liquid ratio of 1:20.

[0042] 2) The temperature was raised to 80°C, and the mixture was reacted for 1.0 hour, followed by filtration to obtain a precipitate and a desiliconization filtrate. The precipitate contained a large amount of unreacted calcium magnesium carbonate, which was returned to step 1) for further desiliconization. The steam generated during the heating and stirring process passed through the condenser reflux pipe, and the non-condensable gas contained 42% CO2. The non-condensable gas was directly introduced into a carbonization reactor filled with water glass for carbonization. The desiliconization filtrate was composed of 2.2% sodium carbonate, 0.24% sodium bicarbonate, and 78 ppm soluble silicon.

[0043] 3) The desiliconized filtrate is pumped to the nanofiltration membrane concentration system at a pumping pressure of 3.0 MPa and an inlet water temperature of 37°C. The conductivity of the concentrated water after membrane concentration is 400 μS / cm, which is returned to the production line for use as process water.

[0044] 4) The concentrated saline wastewater has a sodium carbonate concentration of 11.5% and a soluble silicon content of 116 ppm. The concentrated saline wastewater is pumped to a negative pressure MVR concentration and crystallization system, maintained at 85°C and an evaporation chamber pressure of 0.07 MPa, where it is concentrated to a sodium carbonate content of 38.0% and crystallized to obtain monohydrated sodium carbonate crystals. The steam in the evaporation chamber is heat-exchanged to produce condensed water with a conductivity of 40 μS / cm. This condensed water enters a condensation tank and is reused as final washing water for silica.

[0045] 5) Sodium carbonate monohydrate crystals are calcined in a muffle furnace at 140°C to obtain anhydrous sodium carbonate, which is then transported to the water glass production workshop via a pipeline.

Claims

1. A method for treating wastewater from the production of hydrated silicon dioxide by carbonization, characterized in that: The following steps are involved: 1) Adding calcium magnesium carbonate as a silicon removal agent to the wastewater produced by carbonization hydrated silica; 2) The carbonization-processed hydrated silica production wastewater, to which calcium and magnesium carbonates have been added, is heated to wet decompose sodium bicarbonate. The solution is cooled by heat exchange and then sedimented and filtered to obtain a precipitate and a desiliconized filtrate. The precipitate contains a large amount of calcium and magnesium carbonates, which is returned to step 1) for silicon removal. Simultaneously, the carbon dioxide generated by the wet decomposition is returned to the production system to serve as an acid source for the synthesis of hydrated silica. 3) After precise filtration, the desiliconized filtrate is concentrated through a membrane to obtain concentrated saline wastewater and concentrated effluent, which is then returned to the production line for use as process water. 4) The concentrated saline wastewater is transferred to an evaporation crystallization system for concentration and crystallization to obtain sodium carbonate monohydrate crystals and condensed water. The condensed water is reused as production water, and the sodium carbonate monohydrate enters a drying system; 5) The sodium carbonate monohydrate entering the drying system is calcined at high temperature to obtain the finished sodium carbonate product, which is then transported to the water glass production workshop via pipelines as raw material.

2. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 1, wherein: The composition of the carbonization-processed hydrated silicon dioxide production wastewater in step 1) is as follows: 1.5-10% sodium bicarbonate, 0.2-1.5% sodium carbonate, and 100-600 ppm soluble silicon dioxide.

3. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 1, wherein: In step 1), the calcium magnesium carbonate comprises one or both of calcium carbonate and basic magnesium carbonate.

4. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 1, wherein: In step 2), the temperature for heating and decomposing the carbonization-processed hydrated silicon dioxide wastewater is 60-150°C.

5. The method for treating wastewater produced by carbonization-process hydrated silicon dioxide according to claim 1, wherein: The membrane concentration in step 3) is RO membrane concentration or nanofiltration membrane concentration, the conductivity of the concentrated water is controlled to be ≤600 μS / cm, and the salt content of the concentrated saline wastewater is 10-30%.

6. The method for treating wastewater produced by carbonization-process hydrated silicon dioxide according to claim 5, characterized in that: The water inlet pressure of the RO membrane concentration is 3.0-9.0 MPa, and the water inlet temperature is ≤40°C.

7. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 5, characterized in that: The water inlet pressure of the nanofiltration membrane concentration is 2.0-4.0 MPa, and the water inlet temperature is ≤40°C.

8. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 1, wherein: In step 4), the concentrated salt-containing wastewater is sent to the evaporation crystallization system for concentration and crystallization. The conductivity of the generated condensed water is controlled at 20-80 μS / cm, so that it can be used as water for the production of hydrated silica by carbonization.

9. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 1, wherein: In step 4), the evaporation crystallization system adopts a negative pressure MVR evaporation system with an operating pressure of 0.05-0.09 MPa.

10. The method for treating wastewater produced by carbonization-processed hydrated silicon dioxide according to claim 1, characterized in that: Step 5) The high-temperature calcination temperature is 100-240°C.

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