A composite phosphorus removal material and its preparation method and application

Abstract

The present invention relates to the technical field of water treatment agents, and specifically discloses a composite phosphorus removal material, a preparation method thereof, and an application thereof. Biomass, palygorskite, starch, and a first cross-linking agent are added to water, and a first reaction is carried out to obtain a first cross-linked body solution; the pH value of the first cross-linked body solution is adjusted to be weakly alkaline, chitosan, a second cross-linking agent, and an initiator are added, and a second reaction is carried out, and the obtained solid is freeze-dried to obtain a second cross-linked body; the second cross-linked body and a surfactant are added to a mixed solution containing rare metal salts and inorganic metal salts, and the mixture is stirred and impregnated to obtain a composite phosphorus removal material. The present invention uses biomass, palygorskite, and starch as the main materials of the adsorption carrier, grafts chitosan to improve the adsorption performance, and uses rare metal salts and inorganic metal salts as active components to improve the phosphorus removal effect; no pyrolysis process is required during the preparation process, and the reaction conditions are mild. It has the advantages of low carbon and environmental protection, low equipment requirements, and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment agents, and in particular to a composite phosphorus removal material, a preparation method thereof, and an application thereof. Background Art

[0002] Phosphate pollution has become a serious environmental problem in water bodies. As a common pollutant in wastewater, phosphate can lead to eutrophication, algal blooms, and deteriorating water quality. Wastewater phosphorus removal technologies are primarily divided into two categories: biological and physicochemical. Physicochemical methods can be further categorized into chemical precipitation, electrocoagulation, crystallization, and adsorption. Adsorption has been widely used for phosphorus removal due to its advantages, including large capacity, abundant adsorbent active sites, low energy consumption, minimal pollution, high efficiency, ease of operation, recyclability, and low cost. Adsorption utilizes porous or high-surface-area materials to remove phosphorus from wastewater through surface precipitation, ion exchange, or adsorption. However, my country's phosphate rock resources are limited due to the extensive use of phosphate fertilizers in agriculture. Therefore, effective measures are needed to control phosphorus in wastewater while also recovering and reusing it.

[0003] Currently, inorganic metal compounds are commonly used as phosphorus removal agents. For example, metal ions generated by calcium, iron, and aluminum salts react with phosphate to form insoluble phosphate precipitates to remove phosphorus from wastewater. Alternatively, metal oxides, hydroxides, and salts of metal elements such as iron, lanthanum, and zirconium can be used to adsorb and recover phosphorus through ligand exchange, hydrogen bonding, Lewis acid-base interactions, and surface precipitation. However, the adsorption capacity and efficiency of existing phosphorus removal adsorbents still need to be improved. Summary of the Invention

[0004] In response to the above problems, the present invention provides a composite phosphorus removal material, a preparation method and an application thereof. The present invention uses biomass, palygorskite and starch as the main materials of the adsorption carrier, and then grafts chitosan to improve the adsorption performance. Rare metal salts and inorganic metal salts are used as active components to enhance the interaction with phosphorus elements and further improve the phosphorus removal effect.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for preparing a composite phosphorus removal material, comprising the following steps:

[0007] S1, adding biomass, palygorskite, starch and a first cross-linking agent into water, and performing a first reaction at 65° C. to 85° C. to obtain a first cross-linked solution;

[0008] S2, adjusting the pH value of the first cross-linked body solution to be weakly alkaline, adding chitosan, a second cross-linking agent, and an initiator, conducting a second reaction at 70° C. to 90° C., and freeze-drying the obtained solid to obtain a second cross-linked body;

[0009] S3, adding the second cross-linked body and the surfactant into a mixed solution containing rare metal salts and inorganic metal salts, stirring and impregnating the solution to obtain a composite phosphorus removal material.

[0010] Compared with the prior art, the preparation method of the composite phosphorus removal material provided by the present invention adopts a first cross-linking agent to cross-link biomass, palygorskite and starch at a specific temperature. In the first reaction process, the biomass, palygorskite and starch are continuously interlaced and cross-linked to form an adsorption carrier material similar to a three-dimensional network, with an increased specific surface area, forming an organic whole. In addition, in the first reaction process, starch (including starch in biomass) is gelatinized under the action of hot water, and absorbs a large amount of water, gradually expanding to form a large pore-forming filling body. Then, under the conditions of weak alkali and specific temperature, the biomass and starch on the first cross-linked body undergo a graft cross-linking reaction with chitosan, and the specific surface area is further increased. The rich amino functional groups provide adsorption sites for adsorbing phosphorus elements in water, and combined with cellulose The hydrogen bonding effect between the hydroxyl groups on the cross-linked body and the alcoholic hydroxyl groups on the starch further improves the binding ability and adsorption effect with the phosphorus element; while removing the moisture in the obtained solid by freeze-drying, the gelatinization effect of the starch disappears, its volume is greatly reduced, and a large number of narrow internal pores are formed, which improves the adsorption performance of the composite phosphorus removal material; finally, the second cross-linked body is immersed in a mixed solution containing active components (rare metal salts and inorganic metal salts). Under the action of the surfactant, the rare metal salts and inorganic metal salts are uniformly absorbed into the second cross-linked body. The rare metal salts and inorganic metal salts can adsorb and recover the phosphorus element in the wastewater through ligand exchange, hydrogen bonding, Lewis acid-base action and surface precipitation, further improving the adsorption efficiency of the composite phosphorus removal material and improving the phosphorus removal effect.

[0011] The present invention uses biomass, palygorskite, and starch as the main materials for the adsorption carrier, and then grafts chitosan to improve adsorption performance. Rare metal salts and inorganic metal salts are used as active components to enhance interaction with phosphorus, further improving the phosphorus removal effect. Biomass is a renewable and low-polluting resource with a diverse composition, mainly including organic polymers such as cellulose, lignin, hemicellulose, starch, oils, sugars, aldehydes, etc. It is renewable and biodegradable, and its products can re-enter the natural cycle, making it an important renewable resource. Palygorskite itself has a large specific surface area and adsorption capacity, and has certain rheological and catalytic properties. Starch can adsorb many organic and inorganic compounds and is also biodegradable. In addition, starch has the ability to gelatinize upon heating. The present invention uses starch as a pore-forming agent, and through thermal gelatinization and freeze-drying, the internal voids of the composite phosphorus removal material are expanded, further increasing the specific surface area and adsorption capacity. Chitosan is biodegradable, and the amino groups in its molecular structure are highly reactive, allowing for chemical modification reactions to increase the active sites of the adsorption carrier.

[0012] The preparation method of the composite phosphorus removal material provided by the present invention does not require a pyrolysis process during the preparation process, has mild reaction conditions, has the advantages of being low-carbon and environmentally friendly, having low equipment requirements and low cost, and has high market application value.

[0013] Preferably, in S1, the biomass is selected from plant straw, branches, waste wood or flowers and plants.

[0014] For example, in S1, the biomass needs to be acid-leached first to remove impurities such as ash and organic matter on the surface and inside of the biomass, thereby further improving the purity of the biomass. The present invention does not limit the specific conditions of the acid leaching, and conventional operations in the art can be used.

[0015] Preferably, in S1, the starch is selected from at least one of corn starch, tapioca starch or wheat starch.

[0016] The preferred starch of the present invention contains both amylose and amylopectin, which have different adsorption properties and can form crystalline complexes with phosphorus in wastewater to precipitate, thereby producing a certain adsorption and removal effect.

[0017] Preferably, in S1, the first cross-linking agent is N,N'-methylenebisacrylamide.

[0018] Preferably, in S1, the mass volume ratio of the biomass, the palygorskite, the starch, the first cross-linking agent and the water is (65~75)g:(10~15)g:(15~20)g:(18~25)g:(0.8~1.2)L.

[0019] By limiting the amount of each substance in S1, the present invention can better control the morphology of the resulting first cross-linked body and the subsequent second cross-linked body, maximizing the cross-linking effect and specific surface area. Using starch as a pore-forming agent, the present invention can achieve high porosity with relatively low starch addition levels, resulting in narrow internal voids and significantly increasing the specific surface area of ​​the composite phosphorus removal material.

[0020] Preferably, in S1, the time of the first reaction is 5h~6h.

[0021] Preferably, in S2, ammonia water is used to adjust the pH of the first cross-linked body solution to 8-9.

[0022] In the present invention, the second reaction is carried out under specific weakly alkaline conditions (pH=8-9), which is conducive to cross-linking of chitosan and the first cross-linker.

[0023] Preferably, in S2, the second cross-linking agent is a silane coupling agent, and the initiator is ammonium persulfate.

[0024] For example, in S2, the silane coupling agent is KH-550‌.

[0025] Preferably, in S2, the mass volume ratio of the first cross-linked solution, the chitosan, the second cross-linking agent and the initiator is (0.8~1.2)L:(30~40)g:(3~5)g:(2~4)g.

[0026] Preferably, in S2, the time of the second reaction is 1 h to 2 h.

[0027] For example, in S2, crushing is required after freeze-drying.

[0028] By limiting the conditions of the second reaction, the present invention can better graft a specific amount of chitosan onto the first cross-linked body. At the same time, since the first reaction time is relatively short, under specific temperature conditions, the biomass, palygorskite, starch, chitosan and cross-linking agent (including the first cross-linking agent and the second cross-linking agent that have not reacted completely) can continue to undergo the second reaction on the basis of the first cross-linked body, further optimizing the structural morphology of the obtained cross-linked body, which is beneficial to increasing the specific surface area and porosity of the second cross-linked body after subsequent freeze-drying, and increasing the number of active sites in the second cross-linked body, thereby further improving the adsorption capacity and phosphorus removal effect of the composite phosphorus removal material.

[0029] Preferably, in S3, the rare metal salt is selected from at least one of yttrium salt, lanthanum salt, cerium salt, neodymium salt, titanium salt, zirconium salt or vanadium salt.

[0030] Preferably, in S3, the inorganic metal salt is selected from at least one of aluminum salt, calcium salt or iron salt.

[0031] Further preferably, in S3, the aluminum salt is selected from at least one of aluminum sulfate, aluminum chloride, aluminum silicate or alum.

[0032] Further preferably, in S3, the calcium salt includes at least one of calcium chloride, calcium sulfate, calcium carbonate, calcium hydroxide or calcium oxalate.

[0033] Further preferably, in S3, the iron salt includes at least one of ferric chloride, ferric sulfate or ferric nitrate.

[0034] Preferably, in S3, the surfactant is stearic acid.

[0035] The preferred surfactant in the present invention can increase the surface tension of the system and optimize the distribution of rare metal salts and inorganic metal salts on the second cross-linked body, thereby improving the adsorption effect of the composite phosphorus removal material on phosphorus elements, and is also conducive to the subsequent application as a slow-release phosphate fertilizer.

[0036] Preferably, in S3, the mass volume ratio of the second cross-linked body, the surfactant and the mixed solution is 100g:(3-5)g:(1-1.2)L.

[0037] Preferably, in S3, the concentration of the rare metal salt in the mixed solution is 1.25 mol / L to 1.35 mol / L, and the concentration of the inorganic metal salt is 0.6 mol / L to 0.8 mol / L.

[0038] It should be noted that, in the present invention, the concentration of the rare metal salt refers to the concentration of the rare metal ions, and the concentration of the inorganic metal salt refers to the concentration of the inorganic metal ions.

[0039] Preferably, in S3, the temperature of the stirring and immersing is 10° C. to 40° C., and the time is 2 h to 3 h.

[0040] In step S3 of the present invention, high concentrations of rare metal ions and inorganic metal ions are incorporated into the second cross-linked body with a high specific surface area through stirring and impregnation, which is beneficial to improving the subsequent phosphorus removal effect.

[0041] In a second aspect, the present invention provides a composite phosphorus removal material prepared by the composite phosphorus removal material preparation method.

[0042] The composite phosphorus removal material provided by the present invention uses almost entirely pollution-free raw materials. The product after phosphorus removal can store phosphorus. Leveraging the biodegradable properties of cellulose, starch, and chitosan, it can be used as a slow-release phosphate fertilizer, fully utilizing phosphorus in wastewater. Furthermore, the composite phosphorus removal material also contains certain rare metal salts and inorganic metal salts. The rare metal salts can promote crop rooting and increase seedling emergence rates, while the inorganic metal salts can also serve as a base fertilizer for crops. Together, these two materials can promote nutrient absorption and improve crop quality.

[0043] Preferably, the porosity of the composite phosphorus removal material is 70% to 95%.

[0044] In a third aspect, the present invention provides a composite phosphorus removal material prepared by the method for preparing the composite phosphorus removal material, or the use of the composite phosphorus removal material in removing phosphorus and fluorine from wastewater or preparing crop fertilizers.

[0045] The phosphorus removal product formed after the composite phosphorus removal material of the present invention absorbs phosphorus can be used as a slow-release phosphorus fertilizer and can be directly put into farmland to achieve controlled slow release of phosphorus element. At the same time, it also has a certain repair effect on the soil and has resource recovery and utilization value. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0047] Example 1

[0048] This embodiment provides a method for preparing a composite phosphorus removal material, comprising the following steps:

[0049] Sa, adding the crushed plant straw into an acid solution with a pH of 2 to 4, soaking it at room temperature for 8 hours, filtering it, and washing the solid with water until it is neutral to obtain biomass.

[0050] Sb, 70 g of biomass, 13 g of palygorskite, 17 g of corn starch and 21 g of N,N'-methylenebisacrylamide were added to 1 L of water, and a first reaction was carried out at 75°C and kept warm for 5.5 h to obtain a first cross-linked solution.

[0051] Sc, use ammonia water to adjust the pH of the first cross-linked body solution to 8.5, add 35g chitosan, 4g KH-550 and 3g ammonium persulfate, carry out the second reaction at 80℃, keep warm for 1.5h, separate the solid and liquid, freeze-dry the obtained solid, and crush it to obtain the second cross-linked body.

[0052] Sd, take 100g of the second cross-linked body and 4g of stearic acid and add them into 1L of a mixed solution containing 0.7mol / L lanthanum trichloride, 0.6mol / L cerium chloride and 0.7mol / L aluminum chloride, stir and immerse for 2.5h at room temperature to obtain a composite phosphorus removal material.

[0053] According to tests, the porosity of the composite phosphorus removal material in this embodiment is 88%.

[0054] Example 2

[0055] This embodiment provides a method for preparing a composite phosphorus removal material, comprising the following steps:

[0056] Sa, add the crushed branches into an acid solution with a pH of 2 to 4, soak at room temperature for 8 hours, filter, and wash the solid with water until it is neutral to obtain biomass.

[0057] Sb, 72 g of biomass, 12 g of palygorskite, 18 g of corn starch and 22 g of N,N'-methylenebisacrylamide were added to 1.1 L of water, and a first reaction was carried out at 80°C and kept warm for 5 h to obtain a first cross-linked solution.

[0058] Sc, use ammonia water to adjust the pH of the first cross-linked body solution to 9, add 38g chitosan, 3.5g KH-550 and 2.5g ammonium persulfate, carry out the second reaction at 75℃, keep warm for 2h, separate the solid and liquid, freeze-dry the obtained solid, and crush it to obtain the second cross-linked body.

[0059] Sd, take 100g of the second cross-linked body and 4.5g of stearic acid and add them into 1.2L of a mixed solution containing 0.5mol / L titanium tetrachloride, 0.8mol / L cerium chloride, 0.3mol / L calcium chloride and 0.4mol / L aluminum chloride, stir and immerse for 2.5h at room temperature to obtain a composite phosphorus removal material.

[0060] According to tests, the porosity of the composite phosphorus removal material in this embodiment is 85%.

[0061] Example 3

[0062] This embodiment provides a method for preparing a composite phosphorus removal material, comprising the following steps:

[0063] Sa, add the crushed waste wood into an acid solution with a pH of 2 to 4, soak it at room temperature for 8 hours, filter it, and wash the solid with water until it is neutral to obtain biomass.

[0064] Sb, 75 g of biomass, 10 g of palygorskite, 20 g of cassava starch and 25 g of N,N'-methylenebisacrylamide were added to 1.2 L of water, and a first reaction was carried out at 85°C and kept warm for 5 h to obtain a first cross-linked solution.

[0065] Sc, use ammonia water to adjust the pH of the first cross-linked body solution to 9, add 40g chitosan, 5g KH-550 and 4g ammonium persulfate, carry out the second reaction at 90℃, keep warm for 1.5h, separate the solid and liquid, freeze-dry the obtained solid, and crush it to obtain the second cross-linked body.

[0066] Sd, take 100g of the second cross-linked body and 5g of stearic acid and add them into 1.2L of a mixed solution containing 0.65mol / L lanthanum trichloride, 0.7mol / L cerium chloride, 0.2mol / L aluminum sulfate and 0.2mol / L ferric sulfate, stir and immerse for 3h at room temperature to obtain a composite phosphorus removal material.

[0067] According to tests, the porosity of the composite phosphorus removal material in this embodiment is 78%.

[0068] Example 4

[0069] This embodiment provides a method for preparing a composite phosphorus removal material, comprising the following steps:

[0070] Sa, adding crushed plant straws and flowers with a mass ratio of 2:1 into an acid solution with a pH of 2-4, soaking for 8 hours at room temperature, filtering, and washing the solid with water until neutral to obtain biomass.

[0071] Sb, 65 g of biomass, 15 g of palygorskite, 15 g of wheat starch and 18 g of N,N'-methylenebisacrylamide were added to 0.8 L of water, and a first reaction was carried out at 65°C and kept warm for 6 h to obtain a first cross-linked solution.

[0072] Sc, use ammonia water to adjust the pH of the first cross-linked body solution to 8, add 30g chitosan, 3g KH-550 and 2g ammonium persulfate, carry out the second reaction at 70℃, keep warm for 1h, separate the solid and liquid, freeze-dry the obtained solid, and crush it to obtain the second cross-linked body.

[0073] Sd, take 100g of the second cross-linked body and 3g of stearic acid and add them into 1L of a mixed solution containing 1.25mol / L zirconium nitrate, 0.3mol / L ferric nitrate and 0.3mol / L calcium carbonate, stir and immerse for 2h at room temperature to obtain a composite phosphorus removal material.

[0074] According to tests, the porosity of the composite phosphorus removal material in this embodiment is 73%.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing a composite phosphorus removal material. This method is similar to that of Example 1, differing only in that the palygorskite in Sb is replaced with an equivalent mass of biomass (plant straw). All other conditions are the same as those of Example 1 and are not further described. The resulting composite phosphorus removal material has a porosity of 69%.

[0077] Comparative Example 2

[0078] This comparative example provides a method for preparing a composite phosphorus removal material. This method is similar to that of Example 1, differing only in that the starch in Sb is replaced with an equivalent mass of biomass (plant straw). All other conditions are the same as those of Example 1 and are not further described. The resulting composite phosphorus removal material has a porosity of 47%.

[0079] Comparative Example 3

[0080] This comparative example provides a method for preparing a composite phosphorus removal material, similar to Example 1, except that the temperature for the first reaction in Sb is 50°C, and the temperature for the second reaction in Sc is 50°C. The remaining conditions are the same as in Example 1 and are not further described. The resulting composite phosphorus removal material has a porosity of 54%.

[0081] Comparative Example 4

[0082] This comparative example provides a method for preparing a composite phosphorus removal material, similar to that of Example 1, except that hydrochloric acid was used to adjust the pH of the first cross-linked solution in Sc to 6.5. All other conditions were the same as in Example 1 and are not further described. The resulting composite phosphorus removal material had a porosity of 62%.

[0083] Comparative Example 5

[0084] This comparative example provides a method for preparing a composite phosphorus removal material, similar to that of Example 1, except that chitosan and ammonium persulfate were omitted from Sc. All other conditions were the same as those of Example 1 and are not further described. The resulting composite phosphorus removal material had a porosity of 60%.

[0085] Comparative Example 6

[0086] This comparative example provides a method for preparing a composite phosphorus removal material. This method is similar to that of Example 1, except that KH-550 in Sc is replaced with chitosan of equal mass. All other conditions are the same as those of Example 1 and are not further described. The resulting composite phosphorus removal material has a porosity of 65%.

[0087] Comparative Example 7

[0088] This comparative example provides a method for preparing a composite phosphorus removal material. This method is similar to that of Example 1, except that stearic acid is omitted from the Sd mixture. All other conditions are the same as those of Example 1 and are not further described. The resulting composite phosphorus removal material has a porosity of 85%.

[0089] Comparative Example 8

[0090] This comparative example provides a method for preparing a composite phosphorus removal material, similar to Example 1, except that the Sd step is omitted, resulting in the composite phosphorus removal material being the second crosslinked product. All other conditions are the same as in Example 1 and are not further described. The resulting composite phosphorus removal material has a porosity of 86%.

[0091] Verification test

[0092] To verify the phosphorus removal effect of the composite phosphorus removal materials provided in Examples 1 to 4 and Comparative Examples 1 to 8 on wastewater, the following test was conducted: high-purity potassium dihydrogen phosphate was dried at 110°C for 2 hours and cooled in a desiccator. 13 portions of phosphorus-containing wastewater (measured in P) with a concentration of 100 mg / L were prepared, each 1 L, as simulated wastewater; 0.5 g of each composite phosphorus removal material of the Examples and Comparative Examples was added to 13 portions of simulated wastewater, respectively, and placed in an oscillator with the temperature set at 25°C and the speed set at 200 rpm. The oscillation was carried out for 8 hours, and then membrane filtration was performed. The phosphorus content in the filtrate was determined by the ammonium molybdate spectrophotometry method according to GB11893-89, and the adsorption capacity of the adsorbent was calculated. The specific results are shown in Table 1.

[0093] Table 1 Comparison of phosphorus removal effects of composite phosphorus removal materials on wastewater

[0094]

[0095] Adopt corn as research object, observe the application effect of the composite phosphorus removal material in the present invention as crop fertilizer by recording the germination growth situation of corn seeds.The composite phosphorus removal material provided in embodiment 1~4 is placed in industrial sewage containing excessive phosphorus element, and phosphorus removal treatment is carried out repeatedly until the phosphorus removal material reaches phosphorus absorption saturation state.Then the phosphorus removal product of phosphorus absorption saturation state is applied in the same soil as crop fertilizer respectively, and fertilizes on the same day after sowing. The blank control group is the soil without adding phosphorus removal product.Each group adopts 3 soil samples to carry out parallel experiment.When other growth conditions remain consistent, the germination situation of corn seeds and the average number of subsequent fully expanded leaves are recorded at the same time every day, as shown in Table 2 below.

[0096] Table 2 Seedling emergence and leaf expansion of corn seeds after fertilization

[0097]

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a composite phosphorus removal material, characterized in that: The following steps are involved: The crushed plant straw is added to an acid solution with a pH of 2 to 4, immersed at room temperature for 8 hours, filtered, and the solid is washed with water until it is neutral to obtain biomass; 70 g of the biomass, 13 g of palygorskite, 17 g of corn starch, and 21 g of N,N'-methylenebisacrylamide were added to 1 L of water, and a first reaction was carried out at 75° C. for 5.5 hours to obtain a first cross-linked solution; The pH of the first cross-linked product solution was adjusted to 8.5 with aqueous ammonia, 35 g of chitosan, 4 g of KH-550, and 3 g of ammonium persulfate were added, and a second reaction was carried out at 80° C. The temperature was kept for 1.5 hours, and the solid-liquid separation was performed. The obtained solid was freeze-dried and crushed to obtain a second cross-linked product; 100g of the second cross-linked body and 4g of stearic acid were added to 1L of a mixed solution containing 0.7mol / L lanthanum trichloride, 0.6mol / L cerium chloride and 0.7mol / L aluminum chloride, and stirred and immersed at room temperature for 2.5h to obtain a composite phosphorus removal material.

2. A composite phosphorus removal material, characterized in that: The composite phosphorus removal material is prepared by the preparation method of the composite phosphorus removal material according to claim 1.

3. Use of the composite phosphorus removal material prepared by the preparation method of the composite phosphorus removal material according to claim 1 or the composite phosphorus removal material according to claim 2 in removing phosphorus and fluorine from wastewater or preparing crop fertilizers.

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