Method for increasing the alkalinity of seawater using boron mud

Abstract

The present application belongs to the technical field of marine carbon sink, and relates to a method for improving seawater alkalinity by using boron mud. The steps include pretreatment of the boron mud, mixing the pretreated boron mud and seawater for reaction, then aerating the reactants to strengthen the reaction, regularly monitoring the temperature, pH value, dissolved oxygen concentration and other parameters of the reaction system to ensure the stability of the reaction conditions, and finally detecting the liquid indicators directly after the reaction without solid-liquid separation to ensure that the pH value is 8.0-8.5, and returning to the ocean directly after reaching the standard. The present application not only realizes the resource utilization of boron mud, but also significantly improves the seawater alkalinity and enhances the marine carbon sink capacity.

Description

Technical Field

[0001] This invention belongs to the field of marine carbon sequestration technology and relates to a method for increasing seawater alkalinity using boron mud. Specifically, it refers to a method for increasing seawater alkalinity using boron industrial solid waste (boron mud) to promote the absorption of atmospheric carbon dioxide by the ocean. Background Technology

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

[0003] Existing seawater alkalization technologies mainly include the following methods: (1) Mineral addition method: using calcite (CaCO3) or olivine (Mg2SiO4), the cost is as high as $500 / ton. (2) Electrochemical method: generating OH- through electrolysis of seawater, with energy consumption of 12-15kWh / m³. 3 (3) Bioengineering method: Cultivating highly calcified algae poses a risk of ecological invasion.

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

[0005] This invention provides a method for increasing seawater alkalinity using boron sludge, representing a low-cost and high-efficiency seawater alkalization method. This method enhances the ocean's carbon sequestration capacity while simultaneously solving the environmental pollution problem caused by boron sludge accumulation, achieving harmless treatment and high-value utilization of boron sludge, and reducing heavy metal pollution.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for increasing seawater alkalinity using boron mud includes the following steps:

[0008] (I) Pretreatment of Boron Sludge

[0009] Boron mud was selected, ensuring that the B2O3 content was ≤12%, the total CaO+MgO content was ≥30%, and the heavy metal content met the Class II standard of the "Marine Sediment Quality Standard" (GB 18668-2002). The particle size of the boron mud was limited to 100-500 mesh. Due to the high water content of the boron mud itself, no additional seawater was needed; it was directly subjected to wet milling. Wet milling resulted in a more uniform particle distribution, and the treated boron mud was ready for use.

[0010] (ii) Introducing borax mud and seawater into a mixed reaction

[0011] Pretreated boron mud and seawater are added at a mass ratio of 1:500-1:1000 and mixed for reaction. The reaction temperature is controlled at 10-40℃ using a temperature control device, and the pH of the reaction system is adjusted to 8.5-9.5 using the boron mud. Stirring ensures thorough mixing of the boron mud and seawater, guaranteeing a uniform reaction.

[0012] (III) Enhanced 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 of the air, ensuring it is ≥20%, and control the air temperature at 10-40℃ using a temperature regulator. Simultaneously, use a dissolved oxygen monitor to maintain the dissolved oxygen concentration in the reaction system at 5-8 mg / L. The reaction should continue for 2-4 hours, during which time the temperature, pH, and dissolved oxygen concentration of the reaction system should be monitored regularly to ensure stable reaction conditions.

[0014] (iv) Direct emissions

[0015] After the reaction is complete, there is no need for solid-liquid separation. The liquid index is directly tested to ensure that its pH value is 8.0-8.5. Once the standard is met, it is directly returned to the ocean to avoid secondary treatment.

[0016] The method for increasing seawater alkalinity using boron sludge provided by this invention has advantages such as high efficiency, economy, and environmental friendliness. Through steps including pretreatment, mixing reaction, enhanced aeration, and solid-liquid separation of the boron sludge, not only is the resource utilization of boron sludge achieved, but seawater alkalinity is also significantly increased, enhancing the marine carbon sequestration capacity. Simultaneously, this method has minimal impact on the marine ecological environment, demonstrating good environmental benefits and sustainability. Detailed Implementation

[0017] Example 1: A method for increasing seawater alkalinity using boron mud

[0018] Boron mud meeting the Class II standard of the "Marine Sediment Quality Standard" (GB 18668-2002) was selected, with a B2O3 content of 5% and a total CaO+MgO content of 28%. The particle size of the boron mud was limited to 100-500 mesh. Due to the high water content of the boron mud itself, no additional seawater was needed; it was directly subjected to wet milling. Wet milling resulted in a more uniform particle distribution, and the treated boron mud was ready for use. The initial alkalinity, pH value, and carbon dioxide content of the seawater were measured. Nine sets of comparative experiments were set up, with the variables being the mass ratio of boron mud to seawater and the reaction temperature. Specific parameters are shown in the table below.

[0019] Experimental parameters of the reaction between boron mud and seawater

[0020] parameter Range of values Control method Boron mud to seawater mass ratio 1:500、1:750、1:1000 Electronic balance for precise weighing reaction temperature 20℃、25℃、30℃ Water bath heating device (accuracy ±0.5℃) initial pH value 8.5-9.5 Adjust with 1 mol / L NaOH solution Aeration gas-liquid ratio 1.0L / L·min Gas flow meter control air temperature 25-35℃ Air preheater regulation Dissolved oxygen concentration 5-8 mg / L Dissolved oxygen monitor provides real-time feedback on aeration rate reaction time 3 hours Timer control catalyst No addition ——

[0021] Pretreated boron mud and seawater were added to each experimental vessel according to the set mass ratio. The reaction temperature was adjusted to the set value using a temperature control device, and the initial pH was adjusted to 8.5-9.5 using a pH adjuster. Air with an oxygen content of 21% and a temperature of 28°C was introduced at a gas-liquid ratio of 1.0 L / L·min to maintain a dissolved oxygen concentration of 5-8 mg / L. The stirring device was turned on, and the reaction was carried out for 3 hours.

[0022] Seawater alkalinity was determined using acid-base titration, with pH values ​​monitored in real time using a pH meter. Non-dispersive infrared spectroscopy (NDIR) was used to detect carbon dioxide content in seawater, with measurements taken before and after the reaction. The results of the seawater alkalinity enhancement experiment are as follows:

[0023]

[0024] The data above show that all experimental groups achieved an increase in seawater alkalinity and carbon dioxide absorption. Experiment 2, with a boron mud to seawater ratio of 1:500 and a reaction temperature of 25℃, showed the best results, with an increase in seawater alkalinity of 0.18 mmol / L and a carbon dioxide absorption of 20.5 mg / L. Overall, a higher boron mud to seawater ratio and a suitable reaction temperature (around 25℃) are beneficial for increasing seawater alkalinity and promoting carbon absorption.

[0025] Example 2: Using boron mud to increase seawater alkalinity, thereby achieving carbon neutrality.

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

[0027] (1) Real-time monitoring of dissolved inorganic carbon (DIC) concentration changes

[0028] Non-dispersive infrared spectroscopy (NDIR) was used to monitor the concentration of dissolved inorganic carbon (DIC) in seawater before and after the reaction in real time. This method can accurately detect subtle changes in DIC concentration in seawater, providing crucial data for subsequent carbon sink calculations. Before the reaction began, seawater in the target area was sampled at multiple points, and the initial DIC concentration C was determined using NDIR equipment. DIC1 After the reaction was completed, seawater samples were collected again at the same sampling point to determine the final DIC concentration (C). DIC2 .

[0029] (2) Detecting CO2 partial pressure

[0030] The partial pressure of CO2 in seawater was detected using non-dispersive infrared spectroscopy (NDIR). Changes in CO2 partial pressure reflect the dynamic process of CO2 exchange between seawater and the atmosphere and are an important reference indicator for calculating carbon sequestration. The CO2 partial pressure was recorded before and after the reaction. and

[0031] (3) Measure the amount of calcium carbonate precipitate

[0032] Thermogravimetric analysis (TGA) was used to measure the amount of calcium carbonate precipitate produced during the reaction. TGA determines the calcium carbonate content by accurately measuring the mass change of the sample during heating. Solid precipitates were separated from the post-reaction seawater mixture, and after pretreatment such as drying and grinding, they were analyzed using TGA equipment to obtain the mass of the calcium carbonate precipitate.

[0033] (4) Calculate the consumption of boron mud

[0034] Before the reaction begins, weigh the mass m of the boron mud to be added to the reaction system. 硼泥1 After the reaction is complete, the remaining boron mud is collected and weighed to obtain the mass m of the remaining boron mud. 硼泥2 The consumption of boron mud is Δm. 硼泥 =m 硼泥1 -m 硼泥2 .

[0035] (5) Calculate the total carbon sink

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

[0037]

[0038] Where: ΔC DIC =C DIC2 -C DIC1 V represents the change in DIC concentration in seawater before and after the reaction; 海水The volume of seawater involved in the reaction is expressed in cubic meters (m³). 3 ).

[0039] △C DIC *V 海水 The amount of carbon fixed due to changes in seawater DIC concentration was calculated.

[0040] The amount of carbon fixed by calcium carbonate precipitation, based on the chemical formula of calcium carbonate (CaCO3), indicates that the mass fraction of carbon in calcium carbonate is 0.12.

[0041] M 硼泥反应固定碳 The amount of carbon fixed during the reaction of boron mud with seawater 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. Assuming 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 components is calculated as k (kg / kg) based on the chemical reaction formula, then M... 硼泥反应固定碳 =Δm 硼泥 *w*k.

[0042] Assuming an annual boron sludge treatment volume of 100,000 tons and a seawater volume of 1*10⁶ m³ participating in the reaction. 3 The change in DIC concentration in seawater before and after the reaction, ΔCDIC, was 0.02 mol / m³. 3 With a calcium carbonate precipitation amount of mCaCO3 = 5000 tons, an effective alkaline component content of w = 40% in the boron mud, and a carbon fixation amount of k = 0.3 kg / kg per unit mass of effective alkaline component, the total carbon sink is 12840 tons / year, thus achieving effective carbon neutrality.

Claims

1. A method for increasing the alkalinity of seawater using boron mud, the method comprising The following steps are required: (a) Pretreatment of Boron Sludge Boron mud was selected, ensuring that the B2O3 content in the boron mud was ≤12%, the total CaO + MgO content was 28%, and the heavy metal content met the Class II standard of the "Marine Sediment Quality Standard" (GB 18668-2002); (ii) Mixing and reacting boron mud and seawater Add pretreated boron mud and seawater at a mass ratio of 1:500 - 1:1000 and mix them for reaction; stir to ensure that the boron mud and seawater are fully mixed and the reaction proceeds uniformly; use a temperature control device to control the reaction temperature at 10-40℃, and use the boron mud to adjust the pH of the reaction system to 8.5-9.5; (III) Enhanced Aeration Connect the aeration equipment and introduce air into the reaction system at a gas-liquid ratio of 0.5 - 1.5 L / (L·min), and control the air temperature at 10-40℃ using a temperature control 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. (iv) Direct emissions After the reaction is complete, there is no need for solid-liquid separation. The pH value of the liquid is directly measured to ensure that it is between 8.0 and 8.5, and then the liquid is returned to the ocean.

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

3. The method of claim 1, wherein the method comprises: In step (1), the particle size of the boron mud is limited to 100-500 mesh. The boron mud material does not require the addition of seawater and can be directly wet-milled. The treated boron mud can then be put into use.

4. The method for increasing seawater alkalinity using boron mud according to claim 3, characterized in that: In step (3), the reaction lasts for 2-4 hours, during which the reaction system parameters are monitored regularly to ensure stable reaction conditions.

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