Method for recovering high-quality blue iron ore from low-concentration phosphorus-containing sewage and application

Abstract

The invention discloses a method for selectively recycling phosphorus pollutants in low-concentration phosphorus-containing sewage and preparing high-quality blue iron ore and application, and belongs to the technical field of water treatment and recycling thereof. According to the method, the low-concentration phosphorus-containing sewage is adsorbed by a phosphorus specific nano adsorption material HFO-201, and then the material is desorbed by adopting sodium hydroxide and sodium chloride with specific concentrations. The desorbed filtering material and the filtered material can be repeatedly used for adsorbing phosphorus in low-concentration sewage. After the pH value of the filtered desorption solution is adjusted to a certain concentration, FeCl2 with a certain concentration is added, and high-quality blue iron ore (Fe3 (PO4) 2.8 H2O) can be generated by keeping the pH value through sodium hydroxide under an anaerobic condition. The phosphorus product recovered by the process can be used for preparing a high-value phosphate fertilizer and a high-energy-density energy storage material, namely lithium iron phosphate (LiFePO4). The HFO-201 used in the invention can realize low-concentration phosphorus adsorption through an ammonium group combined with a D-201 matrix and loaded HFO nanoparticles. And moreover, after alkali desorption, the damage to the material is very low, and the material can be repeatedly used. And finally, the process of producing the high-quality blue iron ore through phosphorus recovery of the desorption solution is simple and easy to operate. Through XRD, ICP and other detection, it is found that the phosphorus recovery product is determined to be the blue iron ore, and the purity is very high. Through economic analysis and life cycle evaluation, it can be found that the method has remarkable economical efficiency, and the influence on the environment in the production process is small.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment and resource utilization, and specifically relates to a recovery method for removing phosphorus from water by adsorbing a novel nano-adsorbent material and converting it into a high-value phosphate product. Background Art

[0002] Unlike non-renewable resources such as coal and oil that can be replaced by clean energy, phosphorus resources cannot be replaced. It is estimated that if global fertilizer consumption maintains an annual growth rate of 3%, the exploitable phosphorus resources will be exhausted in the next 50 years. In addition, eutrophication of water bodies is also a serious global environmental problem. Reducing exogenous phosphorus input is regarded as an important means to curb the eutrophication of lake water. Therefore, while controlling water eutrophication, recovering phosphorus resources is an important direction in the future water treatment and resource utilization. Methods for removing exogenous phosphorus from water bodies include coagulation and sedimentation, adsorption, and biological treatment. Among them, the adsorption method has attracted widespread attention due to its simple operation, low cost, high selectivity, and easy recovery. The idea of ​​phosphate adsorbent has been continuously studied. Iron is a metal element widely present in nature. It is used in specific adsorption research because of its low price and strong specific adsorption effect on phosphate. In "Development of polymer-based nanosized hydrated ferric oxides (HFOs) for enhanced phosphate removal from waste effluents" in "Water Research" Volume 43, 2009, a phosphate adsorption material HFO-201 obtained by combining a strong alkaline anion resin with iron was introduced. Since its development, it has been successfully commercialized and used in the fixed column adsorption stage of deep phosphorus removal from tail water of sewage treatment plants and has achieved good results.

[0003] HFO-201 is a small particle iron-loaded resin with uniform size. CN 200510095177.5 introduces its main synthesis method: prepare FeCl3, HCl and NaCl solution with a concentration ratio of 1:20:10, and make it pass through the strong alkaline anion D-201 resin placed in the adsorption column at a flow rate of 2-5BV / h; centrifuge and dehydrate the D-201 resin penetrated by Fe3+; then quickly add the D-201 resin after centrifugation and dehydration to a mixed solution of NaOH and NaCl with a mass ratio of 8% and 3% respectively, and react at 40-80℃ for 12-24h to obtain a resin-based phosphorus removal adsorbent. The product contains about 10% iron and has a phosphorus removal capacity of about 20mg P / g. Since it fully utilizes the synergistic advantages of iron and resin in phosphorus recovery, and the synthesis principle and operation are relatively simple, it is easy to realize industrialization, so it is widely used in fixed column adsorption fillers. Although this material has achieved good phosphorus removal results, there are few studies on the subsequent recycling of its desorption solution. However, with the reduction of phosphorus, a non-renewable and irreplaceable resource, various phosphorus recovery methods need to be paid attention to. Therefore, it is of great significance to explore the recovery of high-value phosphorus products in the HFO-201 phosphorus treatment process.

[0004] Vivianite is a phosphorus-containing compound that can be used as a raw material for the production of phosphate fertilizers and has high economic value. In the article "Phosphorus Competition in Bioinduced Vivianite Recovery from Wastewater" in Volume 52 of 2018 of "ENVIRONMENTAL SCIENCE & TECHNOLOGY", it was proposed that traditional phosphorus recovery products such as struvite have problems such as low recovery rate, so new options are needed to obtain storable, transferable and high-value phosphorus products, namely, vivianite. In the international market of phosphate ore, the unit mass phosphorus price of vivianite is relatively high, reaching 51 to 96 euros / kg. Vivianite with higher purity can also be used for the synthesis of high-energy density energy storage material-lithium iron phosphate (LiFePO4), which is one of the main synthetic raw materials for power lithium-ion batteries and has broad utilization prospects. Based on the above theory, we hope to recover high-value phosphorus products based on the process of removing phosphorus pollutants from wastewater by HFO-201, and develop a method and application for recovering high-quality vivianite from low-concentration phosphorus-containing wastewater. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the current demand for phosphorus resources is high and the treatment methods for low-concentration phosphorus-containing wastewater have low treatment efficiency, high energy consumption and difficulty in phosphorus recovery. The present invention discloses a method and application that can be applied to selectively recover high-value phosphorus products from phosphorus pollutants in low-concentration phosphorus-containing wastewater. The method uses phosphorus-specific nano-adsorption material HFO-201 to adsorb low-concentration phosphorus-containing wastewater, and then uses specific concentrations of sodium hydroxide and sodium chloride to desorb the material. After adjusting the pH of the filtered desorption liquid to a certain concentration, a certain concentration of Fe2+ is added, and the pH is maintained by sodium hydroxide under anaerobic conditions to generate high-quality blue iron ore (Fe3(PO4)2·8H2O) to supplement non-renewable phosphorus resources.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0007] A method and application for recovering high-quality blue iron ore from low-concentration phosphorus-containing wastewater, the steps of which are as follows:

[0008] 1) Take HFO-201 materials in corresponding proportion according to the amount of sewage;

[0009] 2) Control the sewage to pass through the HFO-201 material at a certain flow rate to remove phosphorus by adsorption, and the outflowing sewage can meet the sewage phosphorus discharge standard;

[0010] 3) taking out the material absorbed and penetrated in step 2), filtering and washing;

[0011] 4) placing the cleaned material in step 3) in an alkaline desorption solution of a certain concentration for a period of time;

[0012] 5) filtering the material desorbed in step 4) and reusing it in step 2);

[0013] 6) adjusting the pH value of the desorption solution obtained in step 4);

[0014] 7) adding a certain concentration of ferrous chloride to the desorption solution after the pH is adjusted in step 6), and stirring for a certain period of time, during which alkali needs to be added to maintain the pH of the solution;

[0015] 8) The solution obtained by the reaction in step 7) is centrifuged and freeze-dried to obtain high-quality blue iron ore;

[0016] The step 1) is applicable to municipal sewage, livestock and poultry sewage, and sewage that requires deep phosphorus removal after biological treatment; the ratio of material to sewage is about 2g / L, which needs to be adjusted according to the phosphorus concentration of the sewage.

[0017] Preferably, the alkaline desorption solution in step 4) is 0.5% sodium hydroxide + 2% sodium chloride, and the desorption time is 2-3 hours.

[0018] Preferably, the pH value in step 6) should be adjusted to 7.

[0019] Preferably, the mass of ferrous chloride in step 7) should be maintained at 1:6.10-1:6.20 to the mass of phosphorus in the desorption solution.

[0020] Preferably, the base in step 7) is 2.5 mol / L sodium hydroxide, the pH is maintained at 7, and the stirring time is 2-3 h.

[0021] The present invention also provides a high-quality cyanite product obtained by the preparation method. The cyanite is in the form of blue-green powder, and the purity of the cyanite product is 94.13%-98.00%.

[0022] Beneficial effects:

[0023] (1) This product can be recycled from a variety of wastewater scenarios, especially solving the problem of phosphorus recycling in low-concentration wastewater. It provides a new path for obtaining phosphorus resources, helping to resolve the contradiction between the large demand for phosphorus resources and the non-renewable and difficult-to-replace phosphorus resources. In addition, this product has a high recovery rate and high purity, and can be used to synthesize high-energy-density energy storage materials and produce high-value phosphate fertilizers.

[0024] (2) The recycling of this product has high market value and environmental friendliness. As the phosphorus-rich compound with the highest economic value, violet iron ore has an economic value and potential use far superior to MAP. Through LCA analysis, the violet iron ore produced by this process can effectively reduce carbon emissions and water eutrophication compared with other phosphorus recovery methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 : Schematic diagram of the process of phosphorus product recovery of the present invention

[0026] Figure 2 : SEM image of blue iron ore recovered by the present invention

[0027] Figure 3 : XRD image of the product of the present invention

[0028] Figure 4 : LCA analysis diagram of the present invention DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] Examples and Comparative Examples

[0031] Embodiment 1:

[0032] Prepare 200 ml of a phosphoric acid mixed solution with a phosphorus concentration of 500 mg / L and a pH of 7, add 5 g of HFO-201 material by mass ratio, and stir at 25°C;

[0033] The adsorption saturated material obtained in step 1) is filtered through a filter cloth and then washed;

[0034] The material obtained in step 2) was placed in a sodium hydroxide and sodium chloride solution and stirred for desorption for 3 hours, and filtered;

[0035] The filtrate obtained in step 3) was placed in a beaker, the pH was adjusted, and ferrous chloride was added under anaerobic conditions and stirred for reaction at 25°C for 3 hours;

[0036] The product obtained in step 4) is centrifuged, washed and freeze-dried to obtain the product blue iron ore;

[0037] After washing and drying, the filtered material obtained in step 3) can be reused in step 1);

[0038] The material prepared in this example is blue-green powder. After digestion, the iron content is about 33.75%, the phosphorus content is about 11.63%, and the iron-phosphorus ratio is about 1.58:1. The product purity is very high. The sample is tested and analyzed by XRD. The results are as follows: Figure 3 As shown, it has a distinct blue iron ore crystal structure.

[0039] Application Example 1

[0040] An example of the effect of static adsorption of phosphate in water and recovery of blue iron ore by using HFO-201 as material to test the existence of competitive ions: a mixed solution containing PO43-, Cl- and SO42- is prepared, and its concentration is controlled to 500mg P·L-1, and the concentration of competitive anions is controlled to 2500mg·L-1. The initial pH is 7.0, the material dosage is 25g·L-1, and the adsorption is stirred at room temperature for 72h. The supernatant is taken to measure the PO43- concentration. The saturated material is desorbed and adsorbed with sodium hydroxide and sodium chloride solutions for 3h. A certain amount of ferrous chloride is added to the desorption solution, and an oxygen-free environment is ensured. After 3h of reaction, the product is obtained by centrifugation, washing and freeze-drying.

[0041] Under the condition of 2500mg·L-1 competitive anion, the competitive ions have a great influence on the adsorption effect of HFO-201. The adsorption amount is about 30% of the non-interfering ions, but the Cl- and SO42- adsorbed by the material have no great influence on the final synthesized blue iron ore product. The product recovery rate reaches 96.10%, the product purity changes little, and the iron-phosphorus ratio is about 1.51:1. The above results show that the process can still produce high-quality blue iron ore products in the presence of competitive anions.

[0042] In the presence of high concentrations of competing ions, the amount of product recovered from the process will be reduced, but the purity of the recovered product will not be affected.

[0043] Application Example 2

[0044] A column adsorption experiment was conducted using HFO-201 as the material to simulate the process under actual application conditions to adsorb phosphate in water and recover blue iron ore. Example: A solution containing 2 mg P·L-1 was prepared as the target water body, accompanied by 30 mg SO42-·L-1 as a competitive ion, and 5 ml of wet volume of material was used for adsorption, and the water flux was controlled to be 100 mL·h-1 (20 BV·h-1) for the adsorption process. After adsorption penetration, the material was taken out and desorbed with sodium hydroxide and sodium chloride solutions for 3 hours. A certain amount of ferrous chloride was added to the desorption solution, and an oxygen-free environment was ensured. After 3 hours of reaction, the product was obtained by centrifugation, washing and freeze-drying.

[0045] Under simulated actual application conditions, it is still possible to recover phosphorus from water and synthesize high-purity blue iron ore, indicating that the process is feasible for practical application.

Claims

1. A method for recovering high-quality blue iron ore from low-concentration phosphorus-containing wastewater, characterized in that: The steps include: 1) Take HFO-201 materials in corresponding proportion according to the amount of sewage; 2) Control the sewage to pass through the HFO-201 material at a certain flow rate to remove phosphorus by adsorption, and the outflowing sewage can meet the sewage phosphorus discharge standard; 3) taking out the material absorbed and penetrated in step 2), filtering and washing; 4) placing the cleaned material in step 3) in an alkaline desorption solution of a certain concentration for a period of time; 5) filtering the material desorbed in step 4) and reusing it in step 2); 6) adjusting the pH value of the desorption solution obtained in step 4); 7) adding a certain concentration of ferrous chloride to the desorption solution after the pH is adjusted in step 6), and stirring for a certain period of time, during which alkali needs to be added to maintain the pH of the solution; 8) The solution obtained by the reaction in step 7) is centrifuged and freeze-dried to obtain high-quality blue iron ore; The step 1) is applicable to municipal sewage, livestock and poultry sewage, and sewage that requires deep phosphorus removal after biological treatment; the ratio of material to sewage is about 2g / L, which needs to be adjusted according to the phosphorus concentration of the sewage.

2. The method according to claim 1, characterized in that: The alkaline desorption solution in step 4) is 0.5% sodium hydroxide + 2% sodium chloride, and the desorption time is 2-3 hours.

3. The method according to claim 1, characterized in that: The pH value in step 6) should be adjusted to 7.

4. The method according to claim 1, characterized in that: The mass of ferrous chloride in step 7) should be maintained at 1:6.10-1:6.20 with respect to the mass of phosphorus in the desorption solution.

5. The method according to claim 1, characterized in that: The base in step 7) is 2.5 mol / L sodium hydroxide, the pH is maintained at 7, and the stirring time is 2-3 h.

6. The blue iron ore prepared by the method according to any one of claims 1 to 5, characterized in that: The cyanite is in the form of blue-green powder, and the purity of the cyanite product is 94.13%-98.00%.

7. The recovery and application of blue iron ore according to claim 6, characterized in that: It can be used in a variety of sewage scenarios, especially to solve the problem of phosphorus recovery in low-concentration sewage.

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