A method for preparing materials suitable for controlling harmful algal blooms

Abstract

This invention belongs to the field of harmful algal bloom control, specifically a method for preparing materials suitable for controlling harmful algal blooms. Specifically, it uses aluminosilicate minerals as raw materials, treats them with an alkali activating agent, and then performs calcination, acid-base combined activation, and substrate curing, resulting in a material with significantly enhanced microalgae elimination capabilities suitable for controlling harmful algal blooms. Based on existing methods for preparing modified clay from activated clay minerals, this invention fully utilizes aluminosilicate mineral resources, significantly optimizes the processing conditions in existing methods, and further improves the algae-removing performance of the synthesized modified clay, providing an environmentally friendly and efficient optimized preparation method for controlling harmful algal blooms.

Description

Technical Field

[0001] This invention belongs to the field of harmful algal bloom control, specifically a method for preparing materials suitable for controlling harmful algal blooms. Background Technology

[0002] Harmful algal blooms (HABs) are an abnormal ecological phenomenon caused by the abnormal proliferation or aggregation of plankton in the aquatic environment, seriously endangering aquatic organisms and even human health. Harmful algal blooms caused by microorganisms in seawater are usually accompanied by a change in seawater color, with red being the most common, hence the name red tide.

[0003] The modified clay method, proposed by Chinese scientists to overcome the shortcomings of natural clay minerals in controlling harmful algal blooms, such as low flocculation capacity and large dosage, involves surface modification to enhance the efficiency of controlling harmful algal blooms. After more than 30 years of development, it has now become a widely recognized method both domestically and internationally, effectively removing common harmful algal blooms. This method is included in the national standard "Technical Guidelines for Red Tide Disaster Treatment".<GBT 30743-2014> It is recommended as a red tide emergency response method in the "Countermeasures for Monitoring and Management of Harmful Red Tides in Coastal Areas" jointly published by UNESCO and APEC; it is also a guiding method for the emergency response plan for red tide disasters in 13 coastal provinces and cities in my country, and has been successfully applied in more than 20 waters from north to south in my country.

[0004] Modified clay is a key supporting material for this method of controlling harmful algal blooms. How to improve the algae removal efficiency of modified clay and ensure its ecological safety is an important research hotspot in the development of this method. Among the published methods and technologies for preparing modified clay, the most commonly used method is to introduce some macromolecular flocculants, surfactants and other compounds with excellent flocculation efficiency into clay minerals to improve the flocculation and algae removal ability of clay. For example, Yu Zhiming et al. (1994) proposed to introduce macromolecular polyhydroxyaluminate into clay, which improved the algae removal efficiency of clay by nearly 20 times. However, the existing methods for synthesizing modified clay by introducing modifiers generally have problems such as low resource utilization, high energy consumption, and excessive waste and wastewater production. In addition, in the industrial production process of modified clay, the required mineral substrate and modifier are produced independently. Therefore, the traditional preparation method still has problems such as complicated overall process, difficult product quality control and low production efficiency.

[0005] Aluminosilicate clay minerals are widely distributed in nature, with their main chemical composition being Al2O3 and SiO2. Al and Si are also key components of common water treatment flocculants. Therefore, the inherent components of aluminosilicate minerals can be utilized to improve the surface properties of modified clay materials, fully leveraging their resource utilization. However, Al and Si in the mineral lattice have high stability and low activity. How to effectively activate these mineral lattice elements for clay surface modification is a research challenge for the efficient utilization of clay resources in the preparation of materials for controlling harmful algal blooms. To address this, our research team proposed a new method for directly activating clay minerals to prepare materials for controlling harmful algal blooms in patent CN201810365973.3. This method initiates research on modified clay preparation methods that explore the benefits of clay resources and reduce environmental impact and production costs. However, this method is still in its early stages of development and still faces challenges such as insufficient activation efficiency, demanding processing conditions, and the need for further improvement in the algae removal performance of the prepared products. In response to the new trends of increased scale, frequency, and significant destructive effects of harmful algal blooms, there is an urgent need to explore new methods for the efficient activation and modification of clay minerals, so as to promote the development of modified clay preparation processes and product performance towards a green and efficient optimization direction. Summary of the Invention

[0006] To address the shortcomings of existing methods for preparing modified clay from directly activated clay in terms of processing and algae removal efficiency, the present invention aims to provide a more efficient method for preparing modified clay.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a material suitable for controlling harmful algal blooms involves using aluminosilicate minerals as raw materials, treating them with an alkali activating agent, followed by calcination, acid-base composite activation, and substrate curing treatment to obtain a material suitable for controlling harmful algal blooms with significantly improved ability to eliminate microalgae.

[0009] The aluminosilicate minerals are minerals whose main chemical components are Al2O3 and SiO2, wherein the Al2O3 content is ≥20% and the SiO2 content is ≤40%.

[0010] The aluminosilicate minerals mentioned above are a class of minerals whose main chemical components are silicon dioxide and aluminum oxide. Common examples include kaolinite, montmorillonite, italite, hydromica, and their mixtures; those with an Al2O3 content ≥20% and a SiO2 content ≤40% are preferred.

[0011] The alkali activating agent is one or more of the hydroxides, oxides or salts of alkali metals or alkaline earth metals.

[0012] The alkaline activating agent treatment involves grinding and mixing the raw materials and alkaline activating agent at a mass ratio of 100:(1-20), preferably (10-40):1.

[0013] The calcination treatment involves heating and calcining the ground and mixed powder at 600–900°C for 0.5–4 hours, then adding acid and reacting at ≥70°C for 0.5–2 hours; subsequently adjusting the pH of the system to 2–4; and then adding the original soil substrate for maturation treatment to obtain a harmful algal bloom control material with significantly enhanced elimination ability against typical red tide microalgae.

[0014] The added raw material base after adjusting the pH value of the system is added to the above-mentioned acid-base activated mixture at a mass ratio of (1-6):1 (preferably (1-3):1) to the calcining material for aging treatment.

[0015] The curing treatment involves a continuous reaction at 50-90℃ for 2-24 hours. After curing, a material suitable for controlling harmful algal blooms with significantly enhanced ability to eliminate microalgae is obtained.

[0016] The advantages and positive effects of this invention are as follows:

[0017] This invention uses natural clay minerals as a base material and aims to fully activate clay mineral resources for surface modification. It innovatively proposes a new method for activating clay by adding an alkali additive for pre-activation before calcination, followed by calcination, acid-base composite activation, and substrate aging. The pre-activation method with the addition of alkali additives effectively stimulates the silica-alumina resources of the clay, further enhancing surface modification and yielding a modified clay material that can efficiently remove harmful algal blooms. By matching appropriate clay ratios with specific alkali additives, the optimized modified clay can achieve a removal efficiency of 80%-95% for typical red tide algae species along my country's coast. Simultaneously, this invention solves the problems of low production efficiency and harsh composite processing conditions in the direct activation of clay to prepare modified clay. The method, both in its processing and final product, meets the requirements of green and environmentally friendly development, representing a more efficient and effective method for preparing modified clay materials with broad prospects for industrial application. Attached Figure Description

[0018] Figure 1 This study compares the removal efficiency of modified clay prepared using different types of alkali activating agents (sodium hydroxide, sodium carbonate) provided in Examples 1 and 2 of this invention, and the modified clay provided in Comparative Examples 1, 2 and 3, on *Prorocentrum donghaiense*.

[0019] Figure 2 A comparison of the removal efficiency of modified clay prepared with different proportions of sodium carbonate (sodium carbonate: clay (g:g) = 1:2-100) provided in Example 3 of the present invention on Prorocentrum donghaiense.

[0020] Figure 3 This invention optimizes the removal effect of modified clay prepared in this invention and the modified clay provided in Comparative Examples 1, 2 and 3 on typical red tide organisms along the coast of my country.

[0021] Figure 4 The surface structure scanning electron microscope images of the modified clay prepared for the present invention and the modified clay provided in Comparative Examples 1 and 3 are shown in the figures. a is the unmodified clay, b is the SSSM-MC synthesized without alkali pre-activation, and c is the material obtained in Example 3 with the optimal ratio (mass ratio of alkali activating agent to clay is 1:40). Detailed Implementation

[0022] The following examples illustrate in more detail the preparation method of a material suitable for controlling harmful algal blooms according to the present invention, but do not imply limitation of the present invention.

[0023] Example 1

[0024] The activation raw material used in the method of this invention is commercially available washed kaolin from Indonesia. The activation treatment includes the following steps:

[0025] Step 1: Weigh 50g of kaolin and place it in a mortar. Weigh a certain amount of sodium carbonate according to the ratio of alkali activator to clay (g:g) of 1:10 and place it in the mortar. Mix and grind the kaolin thoroughly.

[0026] Step 2: Place the evenly ground powder in the mortar into a muffle furnace and heat it continuously at 700℃ for 2 hours.

[0027] Step 3: After cooling the calcined powder, place it in a round-bottom distillation flask under constant temperature magnetic stirring. Add 20% hydrochloric acid at a solid-liquid ratio of 1:3 (g:ml), and heat and stir for 40 minutes at 93℃ and 400 r / min. After acid heating treatment, adjust the pH of the mixed solution to approximately 3.7 using 5M NaOH.

[0028] Step 4: Weigh 1.3 times the mass of the kaolin from Step 1 and add it to the mixture from Step 3. Then, conduct a controlled-temperature ripening reaction at 70℃ for 3 hours.

[0029] Step 5: After the curing reaction is complete, the sample is dried and ground to obtain the final powdered modified clay. This is designated as Modified Clay of the Present Invention-I.

[0030] Example 2

[0031] The procedure was carried out under the same steps and conditions as in Example 1, except that the sodium carbonate in step 1 was replaced with an equal mass ratio of sodium hydroxide. The specific preparation method is as follows:

[0032] Step 1: Weigh 50g of kaolin and place it in a mortar. Weigh sodium hydroxide according to the ratio of alkali activator to clay (g:g) 1:10 and place it in the mortar. Mix the kaolin thoroughly and grind until well combined.

[0033] Step 2: Place the well-mixed powder in the mortar into a muffle furnace and heat it continuously at 700℃ for 2 hours.

[0034] Step 3: After cooling the calcined powder, place it in a round-bottom distillation flask under constant temperature magnetic stirring. Add 20% hydrochloric acid at a solid-liquid ratio of 1:3 (g:ml), and heat and stir for 40 minutes at 93℃ and 400 r / min. After acid heating treatment, adjust the pH of the mixed solution to approximately 3.7 using 5M NaOH.

[0035] Step 4: Weigh 1.3 times the mass of the kaolin from Step 1 and add it to the mixture from Step 3. Then, conduct a controlled-temperature ripening reaction at 70℃ for 3 hours.

[0036] Step 5: After the aging reaction is completed, the sample is dried and ground to obtain the final powdered modified clay, which is designated as Modified Clay-II of this invention.

[0037] Example 3

[0038] The preparation was carried out under the same steps and conditions as in Example 1, except that the mass ratio of sodium carbonate to clay in step 1 was changed. The specific preparation method is as follows:

[0039] Step 1: Weigh 10 portions of 50g kaolin and place them in a mortar. Then, according to the sodium carbonate: clay (g:g) ratios of 1:2, 1:3, 1:5, 1:10, 1:20, 1:30, 1:40, 1:60, 1:80, and 1:100, weigh a fixed amount of sodium carbonate and place it in each mortar. Mix it thoroughly with the kaolin and grind until well combined.

[0040] Step 2: Place the well-mixed powder in the mortar into a muffle furnace and heat it continuously at 700℃ for 2 hours.

[0041] Step 3: After cooling the calcined powder, place it in a round-bottom distillation flask under constant temperature magnetic stirring, add 20% hydrochloric acid at a solid-liquid ratio of 1:3 (g:ml), and heat and stir for 40 minutes at a temperature of 93℃ and a speed of 400r / min.

[0042] Step 4: After acid heating treatment, adjust the pH of the mixed solution to about 3.7 using 5M NaOH.

[0043] Step 5: Weigh 1.3 times the mass of the kaolin from Step 1 and add it to the mixture from Step 4. Then, conduct a controlled-temperature ripening reaction at 70℃ for 3 hours.

[0044] Step 6: After the reaction is complete, dry and grind the sample to obtain the final powdered modified clay.

[0045] Comparative Example 1

[0046] Unmodified clay, i.e., commercially available washed kaolin from Indonesia (from the same batch as in Example 1) (see...) Figure 4 a).

[0047] Comparative Example 2

[0048] Weigh 0.5g of kaolin and 0.1g of finished polyaluminum chloride powder to make the mass ratio of polyaluminum chloride to clay 1.2:6. Mix them evenly and set aside as MCI.

[0049] Comparative Example 3

[0050] The preparation method is based on CN201810365973.3. The main difference between this method and Example 1 is the absence of pre-activation treatment with alkali additives during the calcination stage. The specific preparation method for Comparative Example 3 is as follows:

[0051] Step 1: Weigh 200g of kaolin and calcine it in a muffle furnace at 700℃ for 2.5h.

[0052] Step 2: Divide the obtained calcined powder into two portions. Set aside one portion and place the other portion in a high-pressure reactor. Add 300 mL of 25% hydrochloric acid at a solid-liquid ratio of 1:3 (g:ml). Control the temperature of the reactor to 130℃ and react under pressure for 4 hours. After the reactor cools down, add the reserved calcined powder to the reactor and heat it back to 130℃ for another 2 hours under high pressure.

[0053] Step 3: After acid heating treatment, adjust the pH of the mixed solution to 4.2 using 5M NaOH.

[0054] Step 4: Add 100g of unmodified clay to the mixture obtained in step 3, mix well, and then mature at 70℃ for 24h.

[0055] Step 5: After the reaction is complete, dry and grind the sample to obtain the final powdered modified clay sample, denoted as SSSM-MC (see [link to sample 5]). Figure 4 b).

[0056] Application examples

[0057] The experimental organisms used were *Prorocentrum donghaiense* and *Heterosigma akashiwo*, both common harmful algal blooms in my country's coastal waters, sourced from the Key Laboratory of Marine Ecology and Environmental Science, Institute of Oceanology, Chinese Academy of Sciences. The culture medium used was L1 type, and the organisms were cultured at (20±1)℃ with a light-dark ratio of L:D = 12h:12h. The light intensity was set to 65 μmol photons / (m²). 2 ·s). The seawater used for algal culture was taken from the coastal waters of Qingdao, China. The collected seawater was filtered through a 0.45μm mixed fiber membrane and sterilized by high-temperature steam in an autoclave before use. For algal cell removal experiments, *Prorocentrum donghaiense* and *Heterosigma akashioense*, which were in the mid-to-late stages of exponential growth, were used as the target algal solutions.

[0058] The specific preparation method of L1 type culture medium is as follows: Add 1 ml of 75 g / L NaNO3, 1 ml of 5 g / L NaH2PO4·H2O, 1 mL of 30 g / L Na2SiO3·9H2O, 1 mL of trace element solution, and 0.5 mL of f / 2 vitamin solution to 950 ml of filtered and sterilized seawater.

[0059] 1) Weigh 0.25g each of the modified clays -I and -II prepared from different types of alkali activating agents (sodium hydroxide and sodium carbonate) provided in Examples 1 and 2, as well as the unmodified clay provided in Comparative Example 1, MCI provided in Comparative Example 2, and SSSM-MC provided in Comparative Example 3. Add 10ml of seawater to prepare a 25g / L modified clay suspension. Then, transfer a quantitative amount of the suspension to a colorimetric tube containing 50mL of *Prorocentrum donghaiense*, making the final concentration of the sample material 0.2g / L. After mixing by inverting the colorimetric tube, let it stand for 3 hours and measure the algal cell removal rate. The results show that the algal removal efficiency of modified clays -I and -II of the present invention both reached over 80%. Among them, the modified clay-I prepared by this invention has the highest algae removal efficiency. Compared with the unmodified clay provided by Comparative Example 1, its algae removal efficiency is improved by about 86%. Compared with the MCI prepared by Comparative Example 2, its algae removal efficiency is improved by about 33%. Compared with the SSSM-MC prepared by Comparative Example 3, its algae removal efficiency is improved by about 20%. Figure 1 Therefore, by adding a certain amount of alkali activating agent during calcination, followed by acid-base activation and substrate aging treatment, the algae removal efficiency of the obtained modified clay is significantly improved. Compared with sodium hydroxide, the algae removal efficiency of the modified clay synthesized after adding an equal mass of sodium carbonate is significantly improved. Therefore, sodium carbonate is selected as the optimal alkali activating agent in this invention.

[0060] 2) Modified clay was prepared using different sodium carbonate addition ratios as described in Example 3, and experiments were conducted according to the algae removal method described in step 1) above. Figure 2 As shown in the figure, the algae removal efficiency of the synthesized modified clay initially increases and then decreases with increasing proportion of alkali activator. Modified clay with excellent algae removal performance, achieving efficiencies exceeding 90%, can be obtained when the alkali activator is controlled at an addition ratio of 1:5 to 1:80. Considering the effective utilization rate of the alkali activator and investment costs, activating the modified clay with the minimum amount of alkali activator to obtain the highest algae removal efficiency is the optimal choice. As shown in the figure, when the mass ratio of alkali activator to clay is 1:40, the synthesized modified clay achieves a high algae removal efficiency of over 90%. Therefore, this method is used to optimize the preparation of modified clay (see Figure 1). Figure 4 c).

[0061] 3) The modified clay prepared according to the optimization of this invention (Example 3, the mass ratio of alkali activating agent to clay is 1:40), as well as the unmodified clay provided in Comparative Example 1, MCI provided in Comparative Example 2, and SSSM-MC provided in Comparative Example 3, were used to conduct experiments on typical red tide algae species (Dinoflagellate and Heterosigma auriculata) along the coast of my country, according to the algae removal method described in step 1) above. Figure 3 As shown, the modified clay prepared by the present invention has a good elimination effect on the typical red tide algae species *Prorocentrum donghaiense* and *Heterosigma honghaiense* along the coast of my country. The removal efficiency for the two red tide algae is increased by 85% and 77% respectively compared with Comparative Example 1, by 31% and 42% respectively compared with Comparative Example 2, and by 20% and 30% respectively compared with Comparative Example 3. Figure 3 Therefore, the modified clay prepared by this invention is a highly efficient material for removing harmful algal blooms.

[0062] 4) The surface morphology of the modified clay prepared according to the present invention (Example 3, the mass ratio of alkali activator to clay is 1:40) and the unmodified clay provided in Comparative Example 1 and the SSSM-MC provided in Comparative Example 3 were observed using an electron microscope scanner. Figure 4 As shown, the unmodified clay exhibits a layered structure with smooth and flat surfaces and edges, and clear angular interfaces. Figure 4 a) The edges of SSSM-MC sheets synthesized without pre-activation by alkali additives are irregular, with broken particles adhering between the sheets, and the clay surface becomes rough. Figure 4 b). The modified clay sheets prepared after pre-activation with the addition of an alkali additive are coated with a dense and uniform layer of nanoscale particles on their surface and edges, further enhancing surface roughness. Figure 4c) This indicates that adding alkali additives can fully activate the silicon and aluminum resources of clay minerals, causing significant changes in the surface structure of clay. These changes effectively increase the specific surface area of ​​modified clay, increase the contact area between modified clay particles and between modified clay particles and algal cells, and make it easier to form bridge-like aggregates during flocculation and algae removal, thereby enhancing the ability of modified clay to capture algal cells.

[0063] Furthermore, the optimized method for preparing modified clay described in this invention has significant advantages in terms of production efficiency and processing conditions. As shown in Table 1, in terms of production efficiency, the total time for preparing modified clay using the optimized method of this invention is approximately 6 hours, while the total time for preparing SSSM-MC as described in Comparative Example 3 is approximately 32.5 hours. The former represents an increase in production efficiency of approximately 80% compared to the latter. In terms of processing conditions, the optimized method for preparing modified clay using this invention employs milder conditions in the acid activation process, eliminating the need for stringent conditions such as high temperature and high pressure. Therefore, the novel activated clay method proposed in this invention, which involves pre-activation with an alkali additive before calcination, followed by calcination, acid-base composite activation, and substrate curing, not only provides a material with significantly enhanced microalgae elimination capabilities suitable for controlling harmful algal blooms, but also solves the problems of unsatisfactory production efficiency and stringent composite processing conditions associated with the direct activated clay method for preparing modified clay. Both the processing process and the final product meet the requirements of green and environmentally friendly development, and have broad prospects for industrial application.

[0064] Table 1 compares the processing flow of Comparative Example 3 with that of the optimized modified clay preparation method of the present invention.

[0065]

Claims

1. A method for preparing materials suitable for controlling harmful algal blooms, characterized in that: Using aluminosilicate minerals as raw materials, they are treated with an alkali activating agent, followed by calcination, acid-base composite activation, and substrate curing treatment to obtain a material with significantly improved ability to eliminate microalgae and suitable for the treatment of harmful algal blooms. The treatment with the alkali activating agent involves grinding and mixing the raw materials and the alkali activating agent at a mass ratio of 100:(1-20). The calcination treatment involves heating and calcining the ground and mixed powder at 600~900℃ for 0.5-4h, then adding acid and reacting at ≥70℃ for 0.5-2h; then adjusting the pH of the system to 2-4; and finally adding the original soil substrate for maturation treatment to obtain a material suitable for the control of harmful algal blooms with significantly improved ability to eliminate microalgae. The added raw material base after adjusting the pH value of the system is added to the acid-base activated mixture at a mass ratio of (1~6):1 with the calcining material for aging treatment. The curing treatment involves a continuous reaction at 50-90℃ for 2-24 hours. After curing, a material suitable for controlling harmful algal blooms with significantly enhanced ability to eliminate microalgae is obtained.

2. The preparation method of the material suitable for controlling harmful algal blooms according to claim 1, characterized in that: The aluminosilicate minerals are minerals whose main chemical components are silicon dioxide and aluminum oxide, wherein the Al2O3 content is ≥20% and the SiO2 content is ≤40%.

3. The preparation method of the material suitable for controlling harmful algal blooms according to claim 1 or 2, characterized in that: The alkali activating agent is one or more of the hydroxides, oxides or salts of alkali metals or alkaline earth metals.

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