A method for synthesizing a biogenic calcium oxalate mineral composite for selective immobilization of lead ions and applications thereof

Abstract

The application discloses a synthesis method of a biological source calcium oxalate mineral composite material for selective holding of lead ions and application thereof. The method inoculates a fungal spore suspension in a soluble calcium phosphate deficient stress liquid culture medium, and after the fungus fully releases insoluble phosphorus, a calcium oxalate mineral composite material is obtained by separation. The synthesized calcium oxalate mineral composite material has the characteristics of strong selectivity for lead ions, good adsorption effect and difficulty in desorption, and can selectively adsorb lead from mixed heavy metal waste liquid. The raw materials used in the application are easy to obtain and low in cost. The biological synthesis process is economic, environmental protection, simple in operation, the obtained mineral composite material is strong in acid resistance, storage and use are simple, and has a good application prospect for selective recovery of lead resources in composite heavy metal contaminated wastewater.

Description

Technical Field

[0001] This invention relates to materials for the selective recovery of heavy metal lead, and more particularly to a method for synthesizing a bio-derived calcium oxalate mineral composite material for the selective retention of lead ions and its application. Background Technology

[0002] Pollutant emissions from human production and daily life have led to a severe situation of heavy metal pollution in the environment, posing a significant threat to the normal life activities of organisms and human health. While heavy metals entering the environment are pollutants, they are also potential mineral resources. For example, lead is a crucial raw material for manufacturing batteries, cables, bullets, and ammunition; lead is also a major component of transparent shielding panels required in nuclear medicine, diagnostic radiology, and nuclear fuel processing, playing a vital role in reducing or eliminating the harmful effects of radiation sources on the human body. Therefore, the recovery of heavy metal resources such as lead from the environment can not only reduce heavy metal pollution but also has direct or indirect economic value. However, the recovery and utilization of heavy metal resources places higher demands on the implementation of engineered recovery processes, especially the selective recovery of heavy metals, which is more challenging.

[0003] Bio-derived or bio-modified mineral materials exhibit significantly higher adsorption performance for heavy metals than other biological and non-biological adsorbents due to their large specific surface area, organic-inorganic composite structure, and abundant mesoporous distribution. The research and development of bio-derived mineral materials has become a new hot topic in adsorption research. However, currently developed bio-derived or bio-modified mineral materials show some adsorption performance for multiple coexisting heavy metals. For example, Chinese Patent 202010050202.2 discloses a mineral bio-modification method for immobilizing lead ions under acidic conditions, as well as the modified mineral materials and their applications. In this method, serpentine and wollastonite, after modification with Aspergillus niger, achieved maximum Pb(II) removal capacities of 370.37 and 357.14 mg / g, respectively. However, these materials lack selectivity for specific heavy metals such as lead ions. Selective adsorption can achieve efficient separation of target heavy metals while effectively avoiding interference from coexisting heavy metals. However, there are no reports on the development of highly efficient selective bio-derived mineral materials and their selective recovery of specific heavy metal ions, necessitating further research and development. Summary of the Invention

[0004] Purpose of the invention: To address the problems existing in the prior art, this invention provides a method for synthesizing calcium oxalate composite materials for selective retention of lead ions. This invention is a method for preparing bio-derived mineral composite materials by transforming calcium phosphate or apatite using microorganisms. This invention can use calcium phosphate as a raw material and prepare lead ion selective adsorption composite materials with excellent adsorption effect by means of interaction between fungi and minerals.

[0005] This invention also provides a calcium oxalate composite material for selective retention of lead ions and its application. This invention synthesizes and prepares a safe, economical, and efficient bio-derived calcium oxalate composite material, which can be used for the efficient and selective separation of lead ions.

[0006] Technical solution: In order to achieve the above objectives, the present invention provides a method for synthesizing a bio-derived calcium oxalate composite material for selective retention of lead ions, comprising the following steps: inoculating a fungal spore suspension in a soluble phosphorus-deficient stress liquid culture medium with added calcium phosphate, and after the fungi have fully acquired the mineral phosphorus source, separating the calcium oxalate mineral composite material.

[0007] The calcium phosphate is either a powdered calcium phosphate chemical preparation or apatite mineral powder. Preferably, an analytical grade powdered calcium phosphate chemical preparation is used.

[0008] The soluble phosphorus-deficient stress liquid culture medium is a phosphorus-stress modified Czapek's medium.

[0009] In this study, 1-2 g of calcium phosphate was added to every 100 mL of phosphorus stress-modified Czapek's medium. The fungus used was *Aspergillus niger*, and the inoculation amount of its spore suspension was 1-2 mL per 100 mL of phosphorus stress-modified Czapek's medium, with a spore suspension concentration of 1-2 × 10⁻⁶. 7 cfu / mL.

[0010] As a preferred embodiment, the Aspergillus niger strain, with accession number 3.3928, is from the China General Microbiological Culture Collection Center (CGMCC).

[0011] The fungal spore suspension is inoculated into the culture medium and then cultured at 28-32℃ for more than 10 days.

[0012] As a preferred method, the culture temperature is 30℃ and the culture time is 10 days. After Aspergillus niger has grown sufficiently, the fungus fully releases insoluble phosphorus. The organic-inorganic mineral complex is collected, dried, and ground to below 60 mesh to obtain the bio-derived mineral composite material.

[0013] The calcium oxalate mineral composite material prepared by the method for synthesizing bio-derived calcium oxalate composite material for selective retention of lead ions described in this invention.

[0014] The present invention relates to the application of calcium oxalate mineral composite material in the selective recovery of lead ions or in the preparation of specific lead ion adsorbents.

[0015] The present invention discloses a selective adsorbent for recovering heavy metal lead ions, comprising the aforementioned calcium oxalate mineral composite material.

[0016] This invention involves inoculating a suspension of Aspergillus niger spores into a phosphorus-stressed liquid culture medium (containing calcium phosphate or apatite) and culturing it. After the fungus has grown, metabolized, and interacted with the minerals, a bio-based mineral composite material is obtained. The liquid culture medium is a modified Czapek's liquid medium for phosphorus stress. The culture medium of this invention utilizes a lack of available phosphorus, inducing Aspergillus niger to secrete oxalate-weathered phosphate minerals to obtain phosphorus. If the culture medium contains available phosphorus, Aspergillus niger will not secrete or will secrete only a small amount of oxalate, resulting in the absence or very low content of the prepared oxalate minerals. This significantly reduces the selective lead recovery efficiency of the prepared biomaterial.

[0017] The bio-derived calcium oxalate mineral composite material of this invention utilizes the large amount of organic acids (such as oxalic acid and citric acid) released by Aspergillus niger during its growth and metabolism to weather minerals. The alkaline ions released during mineral weathering can combine with the oxalic acid produced by Aspergillus niger metabolism to form calcium oxalate. This property allows calcium phosphate to be converted into an organic-inorganic mineral composite containing calcium oxalate crystals with a specific structure. The raw materials for this invention are derived from analytical grade calcium phosphate or apatite powder, and the strain used is Aspergillus niger, commonly used in industrial production. The composite material synthesized by this invention exhibits strong selectivity for lead ions, good adsorption effect, and is not easily desorbed, enabling selective adsorption of lead from mixed heavy metal wastewater. The raw materials used in this invention are readily available and inexpensive. The biosynthesis process is economical, environmentally friendly, and simple to operate. The resulting bio-derived mineral composite material has strong acid resistance, is easy to store and use, and has good application prospects for the selective recovery of lead resources from mixed heavy metal polluted wastewater.

[0018] This invention, based on the design principle of phosphate mineral regulation of Aspergillus niger metabolism under conditions of available phosphorus deficiency, successfully synthesized a novel organic-inorganic composite mineral material with highly efficient and selective retention of lead ions. This material can extract lead ions from complex heavy metal solutions. The material prepared by this invention can efficiently and selectively extract lead ions, while existing bio-derived mineral materials have poor selectivity and are difficult to function under strongly acidic conditions. Moreover, the unit retention capacity of the material prepared by this invention is far higher than that of most previously reported materials. Furthermore, the irregular morphology of the material, the different affinities of calcium oxalate composite materials for heavy metals, and the special organic-inorganic structure enable selective extraction of lead, achieving physicochemical adsorption. Existing materials show little difference in affinity for common heavy metals, and most are physically adsorbed.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] The method for synthesizing calcium oxalate mineral composite materials of the present invention utilizes Aspergillus niger, which is widely distributed in soil, to weather calcium phosphate minerals and couple them with secondary oxalate minerals. It is a mineral composite material containing unique crystalline calcium oxalate minerals, bacterial fragments and their metabolites. It is an organic-inorganic mineral composite material with efficient and selective lead retention characteristics developed based on the bioweathering and mineralization mechanism. It is a novel bio-derived mineral synthesis method for efficiently separating lead ions under conditions of complex heavy metal pollution.

[0021] The bio-derived calcium oxalate mineral composite material of this invention achieves a maximum Pb(II) removal capacity of approximately 1073 mg / g, significantly higher than the corresponding values ​​of most current adsorption materials. In simulated aqueous solutions containing Pb(II), Cd(II), Cu(II), Zn(II), and Ni(II), this mineral composite material can efficiently and selectively adsorb Pb(II), while exhibiting weak adsorption of other heavy metals. Furthermore, it maintains a lead retention capacity of approximately 702 mg / g even in strongly acidic environments with a pH greater than or equal to 1. Simultaneously, the material prepared in this invention can rapidly remove Pb(II).

[0022] The biosynthesis method of this invention uses readily available and inexpensive raw materials. Its biosynthesis process is economical, environmentally friendly, easy to operate, and widely applicable. The resulting bio-based mineral composite material has strong acid resistance, good stability, and is convenient to store and use. It has good application prospects for the recovery and reuse of lead resources in wastewater polluted by complex heavy metals. Attached Figure Description

[0023] Figure 1 The crystals and organic functional groups of the bio-derived calcium oxalate mineral composite material in Example 1; Figure 1 A is the XRD pattern of biogenic calcium oxalate mineral; Figure 1 B is the FTIR spectrum of biogenic calcium oxalate minerals.

[0024] Figure 2 This is a diagram showing the morphology and elemental composition of the bio-derived calcium oxalate mineral composite material from Example 1. Figure 2 A is a biological SEM image; Figure 2 B, 2C, and 2D are diagrams showing the elemental composition of biogenic calcium oxalate.

[0025] Figure 3 This is a TG-DTA analysis of bio-derived calcium oxalate in Example 2.

[0026] Figure 4 Example 3 illustrates the selective adsorption characteristics of heavy metals by bio-derived calcium oxalate. Figure 4 A represents the adsorption in a single heavy metal solution; Figure 4 B represents the adsorption in the composite heavy metal solution.

[0027] Figure 5 Example 4 illustrates the effect of pH on the adsorption of lead by biogenic calcium oxalate.

[0028] Figure 6 Example 5 illustrates the effect of contact time on lead adsorption by bio-derived calcium oxalate mineral composite materials. Detailed Implementation

[0029] The present invention will be further explained below with reference to the embodiments and accompanying drawings.

[0030] Unless otherwise specified, all materials and reagents used in the embodiments are commercially available.

[0031] The calcium phosphate mineral powder was purchased from Shanghai Shisihewei Chemical Co., Ltd.

[0032] Aspergillus niger was purchased from the China General Microbiological Culture Collection Center, culture accession number: CGMCC 3.3928.

[0033] Improved Czapek's medium: containing 3% glucose, 0.3% KNO3, 0.05% KCl, 0.05% MgSO4·7H2O, and 0.01% FeSO4·4H2O by mass fraction.

[0034] Example 1

[0035] The preparation method of bio-derived calcium oxalate mineral composite material is as follows:

[0036] 1. Preparation of spore suspension: After incubating Aspergillus niger at 28℃ for 7 days until a large number of spores are produced, the spores are collected with sterile deionized water to prepare a spore suspension (approximately 1×10⁻⁶). 7 (cfu / mL).

[0037] 2. Scale-up culture and preparation of bio-derived calcium oxalate mineral composite material: 100 mL of modified Czapek's liquid medium was added to a clean 250 mL Erlenmeyer flask, followed by 1 g of calcium phosphate (analytical grade AR) as a poorly soluble phosphorus source. The flask was sterilized at 115 °C for 20 min. 2 mL of spore suspension was then inoculated and cultured at 30 °C with shaking at 180 rpm for 10 days to form the bio-derived calcium oxalate mineral composite material.

[0038] 3. Collection of bio-derived calcium oxalate mineral composite material: The culture medium was filtered to separate the solid composite material after culture. The composite material was placed in a 65°C oven, dried, ground, and passed through a 60-mesh sieve to obtain the bio-derived mineral material for later use.

[0039] The chemical composition and morphology of the solid powder obtained in step (3) were identified using XRD, FTIR, and SEM-EDS. XRD and FTIR results showed that the only crystalline mineral in the solid powder was calcium oxalate. Figure 1 A and Figure 1 B). SEM observation showed that the biogenic calcium oxalate minerals exhibited irregular morphologies. Figure 2 A). EDS results show that the mineral is composed of C, O, Ca, and other elements. Figure 2 B, 2C, and 2D). Based on the above analysis, the obtained bio-derived mineral material was identified as a bio-derived calcium oxalate organic-inorganic mineral complex. Figure 1 , Figure 2 The bio-derived calcium oxalate mineral composite material prepared in this embodiment has a sheet-like irregular aggregate structure with numerous pores on the surface, resulting in a large specific surface area that allows for sufficient contact with lead. However, when Aspergillus niger spores were cultured directly on modified Czapek's medium (without added calcium phosphate) using the above method, grayish-white spherical or ribbon-like mycelia were collected by filtration after ten days. The solution pH was around 7 (virtually no acid production), and XRD did not detect any crystalline minerals.

[0040] Example 2

[0041] Thermal stability analysis of bio-derived calcium oxalate mineral composites Figure 3 )

[0042] The bio-derived mineral materials obtained in Example 1 were subjected to stability analysis using a thermogravimetric-differential thermal analysis (TG-DTA, Perkin-Elmer, USA). The measurement parameters were 25-1000℃, N2 atmosphere, and 10℃ / min. Figure 3The TG results showed that the thermal weight loss of the bio-derived calcium oxalate mineral composite material went through seven stages. The first stage of thermal weight loss occurred between 25 and 98 °C, primarily due to the evaporation of free water. The second stage of thermal weight loss occurred between 98 and 187 °C, mainly caused by the evaporation of calcium oxalate's water of crystallization. The endothermic peak of the DTA curve at 155 °C was caused by the endothermic evaporation of the water of crystallization. The third stage of thermal weight loss occurred between 187 and 253 °C, mainly due to the thermal decomposition of organic acids such as oxalic acid on the mineral surface (accounting for 4.42% of the total weight). The fourth stage of thermal weight loss occurred between 253 and 406 °C, due to the combustion of a large amount of organic matter (accounting for 11.41% of the total weight). The fifth stage of thermal weight loss occurred between 406 and 579 °C, including the decomposition of calcium oxalate to form calcium carbonate, while releasing CO. The DTA curve showed an endothermic peak at 488 °C. The sixth stage of thermogravimetric analysis (TGA) occurs between 579 and 736℃, characterized by the decomposition of calcium carbonate accompanied by the formation of CaO and CO2. The DTA curve shows an endothermic peak at 714℃. The seventh stage of TGA occurs between 736 and 991℃, which may be related to the pyrophosphorylation of phosphates or a crystallization phase transition of the mineral. The DTA curve shows an endothermic peak at 930℃. Comprehensive analysis of the seven stages of TGA results indicates that the organic matter content in the bio-derived calcium oxalate mineral composite material is approximately 15.83%. Furthermore, the total weight loss in the first six stages is approximately 49.48%, which differs from the theoretical weight loss value of pure calcium oxalate monohydrate by 12.12%. The characteristics of the organic-inorganic composite structure prepared in this invention demonstrate that the material is a bio-derived organic-inorganic composite material with certain high-temperature resistance (room temperature - 253℃).

[0043] Example 3

[0044] Selective retention of lead by bio-derived calcium oxalate mineral composites:

[0045] The bio-derived mineral material obtained in Example 1 was used for the adsorption of heavy metal lead: Single heavy metal adsorption solutions containing 356.51 mg / L Pb(II), 242.31 mg / L Cd(II), 245.01 mg / L Zn(II), 172.72 mg / L Cu(II), and 195.54 mg / L Ni(II) were prepared (each solution contained only one heavy metal ion, pH 5.0, and all subsequent solutions were set to pH 5.0). Then, 15 portions of the bio-derived calcium oxalate mineral composite material (0.01 g / portion) were weighed, with three replicates for each heavy metal. The weighed bio-derived calcium oxalate mineral composite material was added to 50 mL EP tubes containing 20 mL of the heavy metal solution, and then incubated in a shaker (25°C, 100 rpm) for 24 h. After incubation, the supernatant was collected after centrifugation (8500 rpm, 25℃, 10 min) and the concentration of heavy metal ions in the supernatant was determined using a flame atomic absorption spectrometer (AAS, AA-6300C, Shimadzu). Figure 4 A).

[0046] A composite heavy metal adsorption solution containing 183.07 mg / L Cd(II), 133.31 mg / L Zn(II), 107.76 mg / L Cu(II), 105.35 mg / L Ni(II), and Pb(II) (185.09 mg / L or 1026.07 mg / L) was prepared using double-distilled water (pH 5.0). Simultaneously, a single heavy metal adsorption solution containing 185.09 mg / L and 1026.07 mg / L Pb(II) was prepared (control group). Twelve 0.01 g samples of the bio-derived calcium oxalate mineral composite material were weighed and added to EP tubes containing 20 mL of either the composite or single heavy metal adsorption solution. Each adsorption system was repeated in triplicate. Finally, the EP tubes were incubated in a shaker (25°C, 100 rpm) for 24 h. After incubation, the supernatant was collected by centrifugation (8500 rpm, 25℃, 10 min) and the concentrations of various metal ions in the supernatant were determined using a flame atomic absorption spectrometer (AAS, AA-6300C, Shimadzu). The unit retention capacity of various heavy metals in the bio-derived calcium oxalate mineral composite material was calculated according to equation (1). Figure 4 B).

[0047]

[0048] C0 and C e The values ​​are: Pb(II) concentration (mg / L) in the initial solution and the supernatant after adsorption equilibrium, respectively; V is the volume of the solution in the adsorption system (L); and M is the mass of the adsorbent (g).

[0049] Figure 4 Results A showed that the bio-derived calcium oxalate mineral composite material exhibited weak adsorption of Zn(II), Cu(II), Cd(II), and Ni(II) in single-metal solutions, with unit adsorption capacities of 3.02±0.76 mg / g, 1.9±0.40 mg / g, 6.33±2.53 mg / g, and 7.25±1.06 mg / g, respectively. However, the unit adsorption capacity for Pb(II) was 734.95±9.21 mg / g. Therefore, the bio-derived calcium oxalate mineral composite material showed the highest unit adsorption capacity for Pb(II) in single-metal solutions. Figure 4 Results B show that the bio-derived calcium oxalate mineral composite material can still selectively adsorb Pb(II) in the composite heavy metal solution, with unit adsorption capacities of 278.28±0.15 mg / g and 525.07±7.62 mg / g, respectively. The unit adsorption capacities for other heavy metals are basically the same as those for single heavy metal adsorption solutions. These results indicate that the bio-derived calcium oxalate mineral composite material can selectively and efficiently separate and extract lead from composite heavy metal solutions. In contrast, the serpentine or wollastonite powder-modified mineral material prepared in Example 1 of Chinese Patent 202010050202.2, using the method described in this example, exhibits only moderate selectivity for Pb(II) in the composite heavy metal solution, with a unit adsorption capacity of only around 100 mg / g.

[0050] Example 4

[0051] The effect of pH value on lead adsorption of bio-derived calcium oxalate mineral composite materials Figure 5 ):

[0052] A 600.61 mg / L Pb(II) solution was prepared using double-distilled water. The pH of the solution was then adjusted using concentrated hydrochloric acid and dilute sodium hydroxide (pH values ​​were set to 1.01, 2.03, 3.01, 4.03, 5.00, 6.59, and 7.00, with three replicates for each pH). Twenty-one portions (0.01 g / portion) of the bio-derived calcium oxalate mineral composite material prepared in Example 1 were weighed (since Pb(II) precipitates at pH ≥ 6, the unit adsorption capacity was calculated only within the pH ≤ 5 range). The weighed bio-derived calcium oxalate mineral composite material samples were added to EP tubes containing 20 mL of Pb(II) solutions at different pH values ​​and incubated on a shaker (25°C, 100 rpm) for 24 h. The Pb(II) concentration in the supernatant was determined by centrifugation (8500 rpm, 25°C, 10 min). The unit retention capacity at different pH values ​​was calculated based on the experimental results and equation (1) in Example 3.

[0053] Within the pH range of 1 ≤ pH ≤ 5, the adsorption capacity of the bio-derived calcium oxalate mineral composite material for Pb(II) initially showed an increasing trend (756.99–1073.17 mg / g), followed by a decreasing trend (1073.17–702.84 mg / g), but the adsorption capacity remained above 702.84 mg / g. This result indicates that the material can still efficiently separate lead in strongly acidic solutions, demonstrating greater potential for practical applications.

[0054] Example 5

[0055] The effect of contact time on lead adsorption by bio-derived calcium oxalate mineral composites Figure 6 ):

[0056] Take 27 50mL EP tubes and add 20mL of 600.61mg / L Pb(II) solution (pH approximately 5). Then weigh 27 portions (0.01g / each) of the bio-derived calcium oxalate mineral composite material samples prepared in Example 1. Add all samples to the above EP tubes respectively, and then the adsorption system is shaken and adsorbed in a shaker (25℃, 100rpm). At each time point, take 3 EP tubes (time point settings: 5, 10, 30, 60, 120, 240, 360, 480 and 720min) and centrifuge them respectively (8500r / min, 25℃, 10min) to obtain the supernatant. Further determine the Pb(II) concentration in the supernatant by atomic absorption spectrophotometry and calculate the unit adsorption capacity according to equation (1) in Example 3.

[0057] Figure 6 The results showed that the adsorption of Pb(II) by the bio-derived calcium oxalate composite material went through two stages: rapid adsorption and adsorption equilibrium. With an initial Pb(II) concentration of 600.61 mg / L, the rapid adsorption stage of Pb(II) by the bio-derived calcium oxalate composite material occurred within the 0-360 min range, with a unit adsorption capacity reaching 798.75 mg / g. Notably, within 5 min, the unit adsorption capacity of Pb(II) by the bio-derived calcium oxalate composite material reached 441.69 mg / g, demonstrating the rapid adsorption of Pb(II) by this material. The adsorption equilibrium stage of Pb(II) by the bio-derived calcium oxalate composite material occurred from 360 to 720 min, with the unit adsorption capacity remaining essentially constant. These results indicate that the adsorption of Pb(II) by the bio-derived calcium oxalate composite material is relatively rapid, and the adsorption time can be shortened accordingly based on practical applications.

Claims

1. The application of a bio-derived calcium oxalate mineral composite material in the selective recovery of lead ions or the preparation of a specific lead ion adsorbent, wherein the preparation of the bio-derived calcium oxalate mineral composite material includes inoculating a fungal spore suspension in a stress liquid culture medium lacking soluble phosphorus with added calcium phosphate, and after the fungi have fully released the insoluble phosphorus, the bio-derived calcium oxalate mineral composite material is separated. The soluble phosphorus-deficient stress liquid culture medium is phosphorus stress modified Czapek's medium; 1-2 g of calcium phosphate is added to every 100 mL of phosphorus stress modified Czapek's medium; the phosphorus stress modified Czapek's medium contains 3% glucose, 0.3% KNO3, 0.05% KCl, 0.05% MgSO4·7H2O, and 0.01% FeSO4·4H2O by mass fraction. The fungus is Aspergillus niger. Aspergillus niger The inoculation amount of the spore suspension is as follows: add 1-2 mL of spore suspension to every 100 mL of soluble phosphorus-deficient stress liquid medium supplemented with calcium phosphate, and the concentration of the spore suspension is 1×10⁻⁶. 7 -2×10 7 cfu / mL; Aspergillus niger Aspergillus niger The strain preservation number is CGMCC 3.3928; the application involves adding the bio-derived calcium oxalate mineral composite material sample to a Pb(II) solution and incubating it at 25°C and 100 rpm for 24 h with shaking, the pH of the Pb(II) solution being 2-3; the fungal spore suspension is inoculated into the culture medium and cultured at 28-32°C for more than 10 days.

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