Method for improving seawater alkalinity by using boric sludge

Abstract

The invention belongs to the technical field of ocean carbon sink, and relates to a method for improving seawater alkalinity by using boric sludge. The method comprises the following steps: pretreating the boric sludge, and mixing the pretreated boric sludge with seawater for reaction; then carrying out aeration reinforcement on reactants, and regularly monitoring parameters such as temperature, pH value and dissolved oxygen concentration of a reaction system to ensure that reaction conditions are stable; and finally, after the reaction is finished, solid-liquid separation is not needed, liquid indexes are directly detected to ensure that the pH value is 8.0-8.5, and the liquid is directly returned to the ocean after reaching the standard. According to the method, resource utilization of the boron mud is achieved, the seawater alkalinity is remarkably improved, and the ocean carbon sequestration capacity is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine carbon sinks, and relates to a method for increasing the alkalinity of seawater by using boron mud, specifically a method for increasing the alkalinity of seawater by using industrial solid waste (boron mud) in the boron industry to promote the absorption of atmospheric carbon dioxide by the ocean. Background Art

[0002] Since the Industrial Revolution, the atmospheric CO2 concentration has increased from 280 ppm to 420 ppm, resulting in a 1.2 °C increase in the global average temperature (IPCC, 2023). The ocean is the largest carbon sink, absorbing approximately 30% of anthropogenic CO2 emissions annually. Seawater alkalinity (Total Alkalinity, TA) is a key parameter determining the ocean's carbon absorption capacity. For every 1% increase in TA, the CO2 absorption capacity can be increased by approximately 0.5%.

[0003] Existing seawater alkalization technologies mainly include the following methods: (1) Mineral addition method: Using calcite (CaCO3) or olivine (Mg2SiO4), with a cost as high as $500 / ton. (2) Electrochemical method: Generating OH- by electrolyzing seawater, with an energy consumption of 12 - 15 kWh / m 3 . (3) Bioengineering method: Cultivating highly calcified algae, which poses a risk of ecological invasion.

[0004] Boron mud is the waste residue generated during the production of products such as boric acid and borax. It is a grayish-white or yellowish-white powdery solid, alkaline, containing components such as boron oxide and magnesium oxide, commonly known as "boron mud". China annually produces approximately 2 million tons of boron mud, with the main components being MgO (20 - 30%), SiO2 (35 - 45%), B2O3 (3 - 5%) and a small amount of CaO (1 - 3%). Traditional treatment methods include open-air stacking or landfilling, which not only occupy a large amount of land but also cause soil alkalization near the storage yard and lead to the migration and transformation of boron, resulting in soil salinization and groundwater pollution, causing environmental pollution. For boron mud, the existing resource utilization is limited to building materials (such as brick making) and soil conditioners (such as neutralizing acidic soil), with low added value. Summary of the Invention

[0005] The present invention provides a method for increasing the alkalinity of seawater by using boron mud, which is a method for developing a seawater alkalization method with low cost and high efficiency. This method improves the ocean carbon sink capacity, simultaneously solves the environmental pollution problem caused by the accumulation of boron mud, realizes the harmless treatment and high-value utilization of boron mud, and reduces heavy metal pollution.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for increasing the alkalinity of seawater by using boron mud, comprising the following steps:

[0008] (I) Boron mud pretreatment

[0009] Select boron mud, ensuring that the B2O3 content in the boron mud is ≤ 12%, the total amount of CaO + MgO is ≥ 30%, and the heavy metal content complies with the second-class standard of the Marine Sediment Quality Standard (GB 18668-2002). The particle size of the boron mud is limited to 100-500 mesh. Since the boron mud itself has a relatively high water content, no additional seawater needs to be added to the boron mud material, and it can be directly subjected to wet grinding treatment. Through wet grinding, the particle distribution of the material becomes more uniform, and the treated boron mud can be put into use.

[0010] (II) Mix boron mud and seawater for reaction

[0011] Add the pretreated boron mud and seawater in a mass ratio of 1:500 - 1:1000 for mixing reaction. Use a temperature regulating device to control the reaction temperature at 10 - 40 °C, and adjust the pH of the reaction system to 8.5 - 9.5 with the boron mud. Stir to fully mix the boron mud and seawater to ensure uniform reaction.

[0012] (III) Enhance aeration

[0013] Connect the aeration equipment and introduce air into the reaction system at a gas-liquid ratio of 0.5 - 1.5 L / L·min. Use an oxygen sensor to monitor the oxygen content in the air to ensure it is ≥ 20%, and control the air temperature at 10 - 40 °C with a temperature regulating device. At the same time, use a dissolved oxygen monitor to maintain the dissolved oxygen concentration in the reaction system at 5 - 8 mg / L. The reaction lasts for 2 - 4 hours, and during this period, regularly monitor parameters such as the temperature, pH value, and dissolved oxygen concentration of the reaction system to ensure stable reaction conditions.

[0014] (IV) Direct discharge

[0015] After the reaction ends, there is no need for solid-liquid separation. Directly detect the liquid index to ensure that its pH value is 8.0 - 8.5, and after reaching the standard, directly return it to the ocean to avoid secondary treatment.

[0016] The method for increasing the alkalinity of seawater using boron mud provided by the present invention has the advantages of high efficiency, economy, environmental protection, etc. Through steps such as pretreatment of boron mud, mixing reaction, aeration enhancement, and solid-liquid separation, not only the resource utilization of boron mud is realized, but also the alkalinity of seawater is significantly increased, enhancing the ocean carbon sink capacity. At the same time, this method has less impact on the marine ecological environment and has good environmental benefits and sustainability. Specific implementation method

[0017] Example 1: Method for increasing the alkalinity of seawater using boron mud

[0018] Select boron mud that meets the second-class standard of the Marine Sediment Quality Standard (GB 18668-2002), with a B2O3 content of 5% and a total CaO+MgO content of 28%. The particle size of the boron mud is limited to 100-500 mesh. Since the boron mud itself has a relatively high water content, no additional seawater needs to be added to the material, and it can be directly wet-ground. Through wet-grinding, the particle distribution of the material becomes more uniform, and the treated boron mud can be put into use. Measure the initial alkalinity, pH value, and carbon dioxide content of the seawater. Set up nine groups of comparative experiments, with the variables being the mass ratio of boron mud to seawater and the reaction temperature. The specific parameters are shown in the following table:

[0019] Experimental Parameter Table for the Reaction of Boron Mud with Seawater

[0020] Parameter Value range Control method Mass ratio of boron mud to seawater 1:500、1:750、1:1000 Precisely weighed with an electronic balance Reaction temperature 20℃、25℃、30℃ Water bath heating device (accuracy ±0.5 °C) Initial pH value 8.5-9.5 Adjusted with 1mol / L NaOH solution Aeration gas-liquid ratio 1.0L / L·min Controlled by a gas flow meter Air temperature 25-35℃ Adjusted with an air preheater Dissolved oxygen concentration 5 - 8mg / L The dissolved oxygen monitor provides real-time feedback on the aeration rate Reaction time 3 hours Controlled by a timer Catalyst Not added ——

[0021] In each experimental container, add the pretreated boron mud and seawater according to the set mass ratio. Use a temperature control device to adjust the reaction temperature to the set value, and use a pH regulator to adjust the initial pH to 8.5-9.5. Pass air with an oxygen content of 21% and a temperature of 28°C into the solution at a gas-liquid ratio of 1.0L / L·min to maintain the dissolved oxygen concentration at 5-8mg / L. Turn on the stirring device, and the reaction lasts for 3 hours.

[0022] Use acid-base titration to measure the seawater alkalinity, use a pH meter to monitor the pH value in real time, and use non-dispersive infrared spectroscopy (NDIR) to detect the carbon dioxide content in the seawater. Measurements are taken before and after the reaction starts. The results of the seawater alkalinity improvement experiment data are as follows:

[0023]

[0024] As can be seen from the above data, the seawater alkalinity has been increased and carbon dioxide has been absorbed in each experimental group. Among them, in Experiment 2, when the mass ratio of boron mud to seawater is 1:500 and the reaction temperature is 25°C, the increase in seawater alkalinity reaches 0.18 mmol / L, and the carbon dioxide absorption is 20.5 mg / L, with the best effect. Overall, a higher mass ratio of boron mud to seawater and an appropriate reaction temperature (around 25°C) are beneficial for increasing seawater alkalinity and promoting carbon absorption.

[0025] Example 2: Using Boron Mud to Increase Seawater Alkalinity

[0026] When measuring the carbon sink volume, a multi-parameter real-time monitoring and comprehensive calculation method is adopted to ensure the accuracy and reliability of the results. The measurement process is as follows:

[0027] (1) Real-time monitor the change in the concentration of dissolved inorganic carbon (DIC)

[0028] The concentration of dissolved inorganic carbon (DIC) in seawater before and after the reaction is monitored in real time by non-dispersive infrared spectroscopy (NDIR). This method can detect subtle changes in the DIC concentration in seawater with high precision, providing key data for subsequent calculation of the carbon sink amount. Before the reaction starts, seawater samples are collected at multiple points in the target sea area, and the initial DIC concentration C is measured using the NDIR device DIC1 . After the reaction ends, seawater samples are collected again at the same sampling points to measure the final DIC concentration C DIC2 .

[0029] (2) Detection of CO2 partial pressure

[0030] The non-dispersive infrared spectroscopy (NDIR) is used to detect the CO2 partial pressure in seawater. The change in CO2 partial pressure reflects the dynamic process of CO2 exchange between seawater and the atmosphere, which is an important reference index for calculating the carbon sink amount. The CO2 partial pressure is recorded before and after the reaction and

[0031] (3) Measurement of calcium carbonate precipitation amount

[0032] The thermogravimetric analysis (TGA) is used to measure the amount of calcium carbonate precipitation generated during the reaction. The TGA method determines the calcium carbonate content by precisely measuring the mass change of the sample during heating. The solid precipitate is separated from the seawater mixed system after the reaction, and after pretreatment such as drying and grinding, it is analyzed using the TGA device to obtain the mass of calcium carbonate precipitation

[0033] (4) Calculation of boron mud consumption

[0034] Before the reaction starts, the mass m of the boron mud input into the reaction system is weighed 硼泥1 . After the reaction ends, the remaining boron mud is collected and weighed to obtain the remaining boron mud mass m 硼泥2 . Then the boron mud consumption Δm 硼泥 = m 硼泥1 - m 硼泥2 .

[0035] (5) Calculation of the total carbon sink amount

[0036] Based on the above monitoring and measurement data, the total carbon sink amount M is calculated using the following formula 碳汇 :[[]]END]]

[0037]

[0038] Where: ΔC DIC = C DIC2 - C DIC1 , representing the change in the DIC concentration in seawater before and after the reaction; V 海水is the volume of seawater participating in the reaction, with the unit of cubic meters (m 3 ).

[0039] △C DIC *V 海水 Calculate the amount of carbon fixed due to the change in the DIC concentration of seawater.

[0040] is the amount of carbon fixed by calcium carbonate precipitation. According to the chemical formula of calcium carbonate CaCO3, the mass fraction of carbon in calcium carbonate is 0.12, then

[0041] M 硼泥反应固定碳 is the amount of carbon fixed during the reaction between boron mud and seawater, which can be calculated based on the content of effective alkaline components (such as CaO, MgO, etc.) in the boron mud and their stoichiometric relationship with CO2. Assume the content of effective alkaline components in the boron mud is w (mass fraction), and the amount of carbon fixed per unit mass of effective alkaline component is calculated as k (kg / kg) according to the chemical reaction formula, then M 硼泥反应固定碳 =Δm 硼泥 *w*k.

[0042] Assume that the annual treatment amount of boron mud is 100,000 tons, the volume of seawater participating in the reaction is 1×106 m 3 , the change in the DIC concentration of seawater before and after the reaction ΔCDIC = 0.02 mol / m 3 , the amount of calcium carbonate precipitation mCaCO3 = 5000 tons, the content of effective alkaline components in the boron mud w = 40%, and the amount of carbon fixed per unit mass of effective alkaline component k = 0.3 kg / kg. Then the total carbon sink is 12840 tons / year.

Claims

1. A method for increasing the alkalinity of seawater by using boron mud, characterized by including The following steps: (1) Pretreatment of boron mud Select boron mud, ensuring that the B2O3 content in the boron mud is ≤ 12%, the total amount of CaO + MgO is ≥ 30%, and the heavy metal content complies with the second-class standard of the Marine Sediment Quality Standard (GB 18668-2002); (2) Mixing reaction of boron mud and seawater Add the pretreated boron mud and seawater in a mass ratio of 1:500 - 1:1000 for a mixing reaction; stir to fully mix the boron mud and seawater to ensure uniform reaction; (3) Aeration enhancement Connect the aeration equipment and introduce air into the reaction system at a gas-liquid ratio of 0.5 - 1.5 L / L·min; monitor the oxygen content of the air to ensure that the oxygen content is ≥ 20%, and control the air temperature at 10 - 40°C through the temperature regulating device; meanwhile, use a dissolved oxygen monitor to maintain the dissolved oxygen concentration in the reaction system at 5 - 8 mg / L; (4) Direct discharge After the reaction ends, there is no need for solid-liquid separation. Directly detect the pH value of the liquid to ensure that its pH value is 8.0 - 8.5, and then return the liquid to the ocean.

2. The method for increasing the alkalinity of seawater by using boron mud according to claim 1 is characterized by including The following steps: In step 1, the B2O3 content in the boron mud is 5%.

3. A method for increasing the alkalinity of seawater using boron mud according to claim 1 or 2, characterized by including The following steps: In step 1, the total amount of CaO + MgO is 28%.

4. A method for increasing the alkalinity of seawater by using boron mud according to claim 1 or 2 or 3, characterized by including The following steps: In step 1, the particle size of the boron mud is limited to 100 - 500 mesh. Since the boron mud itself has a high water content, there is no need to add additional seawater to the boron mud material. Directly carry out wet grinding treatment. Through wet grinding, the particle distribution of the material becomes more uniform, and the treated boron mud can be put into use.

5. A method for increasing the alkalinity of seawater by using boron mud according to claim 4, characterized by including The following steps: In step 2, use the temperature regulating device to control the reaction temperature at 10 - 40°C, and adjust the pH of the reaction system to 8.5 - 9.5 through the boron mud.

6. The method for increasing the alkalinity of seawater by using boron mud according to claim 4 is characterized by including The following steps: In step 3, the reaction lasts for 2 - 4 hours. During this period, regularly monitor the parameters of the reaction system to ensure stable reaction conditions.

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