Method for complexing, extracting and separating strontium and calcium ions based on acidic extractant

Abstract

The invention discloses a method for complexing, extracting and separating strontium and calcium ions based on an acidic extractant, which comprises the following steps: dissolving a to-be-separated substance containing strontium and calcium ions in water, and adding a complexing agent to obtain a water phase; and taking a diluent of an acidic extractant as an organic phase, mixing the organic phase with the water phase, and extracting to obtain an organic phase containing calcium ions and a water phase containing strontium ions, so as to realize separation of the strontium ions and the calcium ions. Through the complexing effect of the complexing agent and the strontium ions, the extraction efficiency of the calcium ions is remarkably improved, and the performance of the acid extraction agent in the aspect of separating the strontium ions and the calcium ions is further enhanced. In addition, the acidic complexing extraction system does not need saponification treatment, and can still keep a relatively high strontium and calcium ion extraction separation effect under the condition that the pH value of a water phase does not need to be adjusted. Compared with a traditional method, the system has the advantages that the investment cost and the production cost are lower, and meanwhile, a saponification treatment step is avoided, so that the negative influence on the environment is further reduced.

Description

Technical Field

[0001] The invention relates to the technical field of mineral waste post-treatment, and in particular to a method for separating strontium and calcium ions by complex extraction based on an acidic extractant. Background Art

[0002] Among the many processes for preparing strontium carbonate from celestite, the carbon reduction method stands out for its maturity and large-scale production capacity, and has been widely used in industry. The annual output of strontium carbonate produced by this method nationwide has exceeded 200,000 tons. This process will produce waste slag rich in strontium for each ton of strontium carbonate produced. In order to effectively recycle these waste slag resources, a hydrochloric acid leaching process is used to obtain a mixed solution containing strontium chloride and calcium chloride. Due to the specific operation of the leaching process and the differences in the raw materials used, the ratio of strontium chloride to calcium chloride in the solution will be different, but under normal circumstances, the ratio of strontium chloride is dominant, and its ratio generally exceeds that of calcium chloride, reaching more than 1:2. Therefore, in order to obtain a high-purity strontium chloride product, it is necessary to further implement the separation and purification steps of calcium ions.

[0003] At present, the calcium impurity removal processes in the preparation of strontium chloride include solvent extraction, oxalic acid precipitation, caustic soda pH adjustment precipitation, etc. Compared with the precipitation method, solvent extraction is more operable at room temperature, and with its significant advantages such as high efficiency and high selectivity, it is regarded as a better technical choice for removing calcium impurities from strontium solution.

[0004] In the market, acidic organophosphorus extractants are widely used as the most common type of extractants. For example, in CN115627354A, a mixed solution of TODGA, TBP and kerosene is used as the extractant to obtain a first preset volume of the extractant; a second preset volume of a high-radiation solution containing strontium ions and calcium ions is obtained; the acidity of the high-radiation solution is adjusted to a preset value to obtain a first solution; the extractant and the first solution are both placed in an extraction device, and the first solution is extracted by the extractant to obtain a target solution, thereby achieving separation of strontium ions and calcium ions in the high-radiation solution.

[0005] CN 112680594A discloses a method for recovering strontium from bastnaesite to prepare strontium carbonate, comprising the following steps: (1) hydrochloric acid pickling; (2) adding sodium carbonate to precipitate calcium, strontium and barium; (3) using P-507 fractional extraction to separate calcium; (4) adding SO4 2- Separation of barium; (5) adding ammonium bicarbonate to produce strontium carbonate, which effectively solves the problem of difficulty in recovering strontium carbonate when purifying rare earths in fluorocarbon cerium ore.

[0006] However, when acidic extractants are used to extract rare earth elements, they release hydrogen ions into the aqueous phase, which may cause the concentration of hydrogen ions in the aqueous phase to increase, thereby interfering with the smooth progress of the extraction reaction. To address this problem, the industry often uses a pretreatment method, namely saponification, to treat the acidic extractant, among which NaOH solution and ammonia water are the most commonly used saponifiers. However, the salt content in the wastewater generated during the saponification process is too high. If it is discharged directly, it will aggravate land salinization, cause serious environmental pollution problems, and lead to a significant increase in governance costs.

[0007] Therefore, the increase in saponification costs and wastewater treatment issues have become key factors restricting the application of extractants in the field of separation and impurity removal, greatly limiting their widespread industrial application. Summary of the invention

[0008] In view of the difficulty in separating strontium and calcium ions, the present invention provides a method for separating strontium and calcium ions by complex extraction based on an acidic extractant. The complexing effect of the complexing agent significantly enhances the efficiency of the acidic extractant in separating strontium and calcium ions, and efficient separation of strontium and calcium ions can be achieved without saponification treatment. This improvement not only reduces production costs, but also reduces the negative impact of the extraction process on the environment.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for separating strontium and calcium ions by complex extraction based on an acidic extractant comprises the following steps:

[0011] Step 1, dissolving the substance to be separated containing strontium and calcium ions in water, and adding a complexing agent to obtain an aqueous phase;

[0012] Step 2, mixing an acidic extractant and a diluent to obtain an organic phase;

[0013] Step 3, the aqueous phase and the organic phase are mixed for extraction to obtain an organic phase containing calcium ions and an aqueous phase containing strontium ions, thereby achieving separation of strontium and calcium ions.

[0014] The complex extraction system of the present invention is composed of an acidic extractant and a diluent to form an organic phase, and a complexing agent is added to a strontium chloride and calcium chloride solution to form a strontium calcium chloride-complex mixed solution as an aqueous phase for extraction and separation. No saponification treatment is required during extraction, and only when a complexing agent is added as a complexing agent, a good separation effect of strontium and calcium ions is exhibited. And a good calcium extraction ability and a separation effect of strontium and calcium ions are maintained at different pH values.

[0015] The complexing agent includes any one or more of EDTA, DTPA, lactic acid, citric acid, tartaric acid, and ammonium citrate. Preferably, the complexing agent is ammonium citrate.

[0016] The acidic extractant includes di(2-ethylhexyl) phosphate (P204), 2-ethylhexyl phosphate mono-2-ethylhexyl ester (P507) or di(2,4,4-trimethylpentyl) hypophosphorous acid (C272); preferably, the acidic extractant is P204 or P507, which have better extraction effects.

[0017] The diluent includes one or more of sulfonated kerosene, chloroform or toluene.

[0018] The concentration of the complexing agent in the aqueous phase of step 1 is 0.005-0.1 mol / L, preferably, the concentration of the complexing agent in the aqueous phase is 0.01-0.06 mol / L, and more preferably, the concentration of the complexing agent is 0.01-0.04 mol / L, which is just enough to effectively complex strontium ions, thereby making the separation and extraction effect more excellent.

[0019] The pH of the aqueous phase in step 1 is 1-6, preferably pH 3-6, and more preferably pH 4-6. The extraction and separation effect is better under a neutral environment.

[0020] In step 2, the volume ratio of the acidic extractant to the diluent is 1:1 to 9;

[0021] In step 3, the volume ratio of the organic phase to the aqueous phase is 1:1-9.

[0022] In step 3, the extraction temperature is 10-50° C., and the extraction time is 1-60 min. The extraction separation system of the present invention can achieve extraction separation equilibrium in a short time at room temperature.

[0023] The method further comprises step 4, adding a stripping agent to the organic phase for stripping to obtain a water phase containing calcium ions.

[0024] The stripping agent includes one or more of hydrochloric acid, nitric acid and sulfuric acid.

[0025] The molar concentration of the stripping agent in the organic phase is 0.01-5 mol / L. The extraction system of the present invention can achieve a high-efficiency stripping effect at a low concentration of the stripping agent.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The complex extractant of the present invention is low in price, has a simple preparation process, has good stability, good recycling performance, and is environmentally friendly.

[0028] (2) Complexing agent complexing extraction has a good extraction and separation effect on calcium. In the extraction reaction of the two extractants, the single-stage extraction efficiency of calcium can reach more than 40%, and the loss rate of strontium is less than 5%.

[0029] (3) Compared with traditional solvent extraction, the extraction and separation method provided by the present invention has the advantages of not requiring saponification treatment, effectively reducing the discharge of saponification wastewater and reducing production costs.

[0030] (4) The extraction and separation method provided by the present invention does not require adjusting the pH in the aqueous phase, and a good calcium extraction effect can be achieved in the initial aqueous phase pH solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The effect of the presence or absence of a complexing agent in the P204-sulfonated kerosene system on the extraction and separation of strontium and calcium.

[0032] Figure 2 It is the stripping rate of P204-sulfonated kerosene-complexing agent system in different acid concentrations.

[0033] Figure 3 The effect of the presence or absence of a complexing agent on the extraction and separation of strontium and calcium in the P507-sulfonated kerosene system.

[0034] Figure 4 It is the stripping rate of P507-sulfonated kerosene-complexing agent system in different acid concentrations.

[0035] Figure 5 The effect of different aqueous phase pH in the P204-sulfonated kerosene-complexing agent system on the extraction and separation of strontium and calcium.

[0036] Figure 6 The effect of different aqueous phase pH in the P507-sulfonated kerosene-complexing agent system on the extraction and separation of strontium and calcium.

[0037] Figure 7 This paper studies the influence of different complexing agent concentrations on the extraction and separation of strontium and calcium in the P507-sulfonated kerosene-complexing agent system. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. 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. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0039] C used in the examples 16 H 35 O4P(P204)(98%,AR),C 16 H 35 O3P (P507) (95%, AR) was purchased from Shanghai MacLean Biochemical Technology Co., Ltd.; 260 #Sulfonated kerosene (AR) was purchased from Zhengzhou Hecheng New Material Technology Co., Ltd.; strontium chloride, anhydrous (99.99%, AR) and ammonium citrate (98.5%, AR) were purchased from Shanghai Titan Technology Co., Ltd.; calcium chloride, dihydrate (98%, AR) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; hydrochloric acid (36.0%-38.0%, AR) was purchased from Sinopharm Chemical Reagent Co., Ltd. All water used in the experiment was deionized water.

[0040] The distribution ratio D, extraction rate E and separation factor β involved in the experiment were calculated according to formulas (1), (2) and (3) respectively.

[0041]

[0042] Among them, C org represents the ion concentration in the organic phase after extraction equilibrium, C aq represents the remaining ion concentration in the aqueous phase, V org Represents the volume of the organic phase in the extraction test, V aq represents the volume of the aqueous phase, β a,b Represents the separation coefficient between a and b ions.

[0043] Example 1

[0044] A method for separating strontium and calcium ions by complex extraction based on a P204 acidic extractant comprises the following steps:

[0045] Step 1, weighing a certain amount of strontium chloride and calcium chloride solids and mixing them as the separated substance, dissolving them with deionized water to prepare a mixed solution containing strontium and calcium ions;

[0046] Step 2, adding 0.02 mol / L ammonium citrate (ATC) to the mixed solution obtained in step 1 to obtain a strontium calcium chloride-complexing agent mixed solution as an aqueous phase, without adjusting the pH of the aqueous phase, and the pH of the aqueous phase is about 6; and a control in which no ammonium citrate is added to the aqueous phase is used as a non-complexing control;

[0047] Step 3, diluting the P204 extractant with one of sulfonated kerosene, chloroform or toluene to prepare a P204 solution with a volume concentration of 20% as the organic phase;

[0048] Step 4, the aqueous phase and organic phase solutions obtained in step 2 and step 3 were mixed in a ratio of 1:1, 2 mL of the aqueous phase and 2 mL of the organic phase were respectively placed in 5 mL centrifuge tubes, and placed in a constant temperature oscillator at 300 rpm and 25°C for 30 minutes to ensure that the reaction reached equilibrium;

[0049] Step 5, after reaching the extraction equilibrium, the 5 mL centrifuge tube was placed in a centrifuge at 5000 rpm, centrifuged at high speed for 1 minute, and then taken out. The clear liquid was diluted and tested for the strontium and calcium content by ICP-OES, and the extraction rate was calculated. The extraction results are shown in Table 1 and Figure 1 shown.

[0050] Table 1 Extraction rate of strontium and calcium in different extraction systems of P204

[0051] Extraction system Calcium extraction rate (%) Strontium extraction rate (%) Strontium calcium separation factor P204 53.2 3.4 31.9 P204+ATC 78.5 4.7 75.0

[0052] Figure 1 The figure is the extraction and separation effect diagram of the P204-sulfonated kerosene system in the present invention with or without the presence of a complexing agent. It can be seen that under different extraction systems, the extraction efficiency of the extractant for calcium is 53.2% (without complexing) and 78.5% (with complexing). The separation factor β (Ca / Sr) of strontium and calcium is 31.9 (without complexing) and 75.0 (with complexing). In the process of extracting and separating strontium and calcium ions in this embodiment, when a complexing agent is added as a complexing agent, the extraction efficiency of P204 for calcium is significantly improved, indicating that the complexing agent has a certain promoting effect on the extraction of calcium.

[0053] Step 6, stripping the organic phase after extraction: add hydrochloric acid to the upper organic phase obtained in step 5 at 25°C and mix in a 5mL centrifuge tube to make the molar concentration of hydrochloric acid 0.1mol / L, 0.3mol / L, 0.5mol / L, 0.7mol / L and 1.0mol / L, and place the mixed solution in a 300rpm constant temperature oscillator for 30 minutes to ensure that the stripping process reaches equilibrium. Afterwards, dilute the lower clear liquid after stripping and test the calcium content therein by ICP-OES, and calculate the stripping rate. In the above stripping process, the stripping rate of calcium at different stripping agent concentrations is shown in Tables 2 and Figure 2 shown.

[0054] Table 2 Calcium stripping rate of P204 complex extraction system at different stripping agent concentrations

[0055]

[0056] Figure 2 is the stripping rate of P204-sulfonated kerosene-complexing agent system at different stripping agent concentrations, given by Figure 2 It can be seen that the system can achieve good stripping. Only when the stripping agent concentration is 0.1 mol / L, all calcium can be stripped out.

[0057] Example 2

[0058] A method for separating strontium and calcium ions by complex extraction based on P507 acidic extractant comprises the following steps:

[0059] Step 1, weighing a certain amount of strontium chloride and calcium chloride solids and mixing them as the separated substance, dissolving them with deionized water to prepare a mixed solution containing strontium and calcium ions;

[0060] Step 2, adding 0.02 mol / L ammonium citrate (ATC) to the mixed solution obtained in step 1 to obtain a strontium calcium chloride-complexing agent mixed solution as an aqueous phase, without adjusting the pH of the aqueous phase, and the pH of the aqueous phase is about 6; and a control in which no ammonium citrate is added to the aqueous phase is used as a non-complexing control;

[0061] Step 3, diluting the P507 extractant with one of sulfonated kerosene, chloroform or toluene to prepare a P507 solution with a volume concentration of 20% as the organic phase;

[0062] Step 4, the aqueous phase and organic phase solutions obtained in step 2 and step 3 were mixed in a ratio of 1:1, 2 mL of the aqueous phase and 2 mL of the organic phase were respectively placed in 5 mL centrifuge tubes, and placed in a constant temperature oscillator at 300 rpm and 25°C for 30 minutes to ensure that the reaction reached equilibrium;

[0063] Step 5, the 5 mL centrifuge tube after reaching the extraction equilibrium is placed in a centrifuge at 5000 rpm, centrifuged at high speed for 1 minute, and then taken out. The clear liquid is diluted and tested for the strontium and calcium content using ICP-OES, and the extraction rate is calculated. The extraction results are shown in Table 3 and Figure 3 shown.

[0064] Table 3 Extraction rate of strontium and calcium in different extraction systems of P507

[0065] Extraction system Calcium extraction rate (%) Strontium extraction rate (%) Strontium calcium separation factor P507 8.7 0.4 23.6 P507+ATC 44.3 0.5 154.0

[0066] Figure 3 The present invention shows a comparison of the extraction and separation effects of the P507-sulfonated kerosene system in the presence or absence of a complexing agent. It can be seen that under different extraction systems, the extraction efficiency of the extractant for calcium is 8.7% (without complexing) and 44.3% (with complexing). The separation factors β (Ca / Sr) of strontium and calcium are 23.6 (without complexing) and 154 (with complexing). When a complexing agent is introduced as a complexing agent into the process of extracting and separating strontium and calcium ions, it is observed that the extraction efficiency of P507 for calcium is significantly improved, while its extraction efficiency for strontium remains relatively stable. This result directly promotes the improvement of the separation effect of strontium and calcium ions, indicating that in the P507 extraction system, the complexing agent has a positive promoting effect on the extraction of calcium.

[0067] Step 6, stripping the organic phase after extraction: at 25°C, add hydrochloric acid to the upper organic phase obtained in step 5 and mix in a 5mL centrifuge tube to make the molar concentration of hydrochloric acid 0.1mol / L, 0.3mol / L, 0.5mol / L, 0.7mol / L and 1.0mol / L, and place the mixed solution in a 300rpm constant temperature oscillator for 30 minutes to ensure that the stripping process reaches equilibrium. Afterwards, dilute the lower clear liquid after stripping and test the calcium content therein by ICP-OES, and calculate the stripping rate. In the above stripping process, the stripping rate of calcium at different stripping agent concentrations is shown in Tables 4 and Figure 4 shown.

[0068] Table 4 Calcium stripping rate of P507 complex extraction system at different stripping agent concentrations

[0069]

[0070] Figure 4 It is the stripping rate of P507-sulfonated kerosene-complexing agent system at different stripping agent concentrations. It can be seen that the system can achieve good stripping. All calcium can be stripped out only when the stripping agent concentration is 0.1 mol / L.

[0071] Example 3

[0072] According to the process of Example 1, the pH of the aqueous phase in step 2 was adjusted to 1, 2, 3, 4, and 5 respectively using hydrochloric acid. The subsequent extraction and separation steps were consistent. The strontium and calcium contents were tested using ICP-OES, and the extraction rate was calculated. The extraction effect under the 20% P204+0.02MATC system was analyzed. The results are shown in Tables 5 and Figure 5 shown.

[0073] Table 5 Extraction rate of strontium and calcium in P204 aqueous phase systems with different pH values

[0074]

[0075]

[0076] Figure 5 The extraction rate and separation factor of strontium and calcium in water phase with different pH values ​​are shown in Figure 2. It can be seen that the separation effect is better under a neutral pH environment. Since the initial pH of the water phase solution is about 6, the reaction system can achieve a good extraction and separation effect without adjusting the pH value.

[0077] Example 4

[0078] According to the process of Example 2, the pH of the aqueous phase in step 2 was adjusted to 1, 2, 3, 4, 5 and no adjustment (pH about 6) by hydrochloric acid, and the subsequent extraction and separation steps were consistent. The strontium and calcium contents were tested by ICP-OES, and the extraction rate was calculated. The extraction effect under the 20% P507+0.02M ATC system was analyzed. The results are shown in Tables 6 and Figure 6 shown.

[0079] Table 6 Extraction rate of strontium and calcium in P507 aqueous phase systems with different pH values

[0080] Water pH Calcium extraction rate (%) Strontium extraction rate (%) Strontium calcium separation factor 1 3.3 4.8 0.7 2 8.5 3.7 2.4 3 18.3 5.0 4.3 4 32.0 4.4 10.2 5 41.3 1.0 71.7 6 42.7 0.5 147.8

[0081] Figure 6 The extraction rate and separation factor of strontium and calcium under different pH of water phase are shown. It can be seen that the separation effect is better under neutral pH. Since the initial pH of the aqueous phase solution is about 6, the reaction system can achieve a good extraction and separation effect without adjusting the pH. The slight difference between the data and the data in Example 2 is the error in the repeated test process.

[0082] Example 5

[0083] According to the steps of Example 2, the concentrations of ammonium citrate in step 2 were adjusted to 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, and 0.06 mol / L, respectively. The subsequent extraction and separation steps were consistent. The strontium and calcium contents were tested by ICP-OES, and the extraction rate was calculated. The extraction effects at different complexing agent concentrations were analyzed. The results are shown in Tables 7 and Figure 7 shown.

[0084] Table 7 Extraction rate of strontium and calcium at different complexing agent concentrations of P507

[0085] TAC concentration (mol / L) Calcium extraction rate (%) Strontium extraction rate (%) Strontium calcium separation factor 0 11.2 4.3 2.8 0.01 17.1 0.2 107.9 0.02 41.7 0.5 157.8 0.03 56.8 1.0 129.5 0.04 71.0 3.7 63.6 0.05 80.2 6.7 56.3 0.06 83.4 9.5 48.2

[0086] Figure 7 The figure shows the strontium and calcium extraction and separation effects of 20% P507 at room temperature with different concentrations of ammonium citrate as the complexing agent. It can be seen that the concentration of the complexing agent is an important factor affecting the extraction and separation effects. After adding ammonium citrate as the complexing agent, the extraction rates of strontium and calcium increase with the increase of the complexing agent concentration, and the separation factor reaches the maximum value when the complexing agent concentration is 0.02 mol / L. The data are slightly different from the data in Example 2 due to the error in the repeated test process.

Claims

1. A method for separating strontium and calcium ions by complex extraction based on an acidic extractant, characterized in that: Includes steps: Step 1, dissolving the substance to be separated containing strontium and calcium ions in water, and adding a complexing agent to obtain an aqueous phase; Step 2, mixing an acidic extractant and a diluent to obtain an organic phase; Step 3, the aqueous phase and the organic phase are mixed for extraction to obtain an organic phase containing calcium ions and an aqueous phase containing strontium ions, thereby achieving separation of strontium and calcium ions.

2. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: The complexing agent includes any one or more of EDTA, DTPA, lactic acid, citric acid, tartaric acid, and ammonium citrate.

3. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: The acidic extractant includes P204, P507 or C272; The diluent includes one or more of sulfonated kerosene, chloroform or toluene.

4. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: The concentration of the complexing agent in the aqueous phase of step 1 is 0.005-0.1 mol / L.

5. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: The pH of the aqueous phase in step 1 is 1-6.

6. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: In step 2, the volume ratio of the acidic extractant to the diluent is 1:1 to 9; In step 3, the volume ratio of the organic phase to the aqueous phase is 1:1-9.

7. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: In step 3, the extraction temperature is 10-50° C., and the extraction time is 1-60 min.

8. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 1, characterized in that: The method further comprises step 4, adding a stripping agent to the organic phase for stripping to obtain a water phase containing calcium ions.

9. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 8, characterized in that: The stripping agent includes one or more of hydrochloric acid, nitric acid and sulfuric acid.

10. The method for separating strontium and calcium ions by complex extraction based on an acidic extractant according to claim 8, characterized in that: The molar concentration of the stripping agent in the organic phase is 0.01-5 mol / L.

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