Process for the treatment of sodium hypophosphite, a by-product of a phosphorane preparation process

Abstract

This invention provides a process for treating sodium hypophosphite, a byproduct in phosphine preparation, aiming to efficiently remove impurities and prepare high-purity hypophosphite. The process includes: taking a small-volume sample of the reaction mother liquor, introducing carbon dioxide gas, and plotting an acidification curve of pH versus conductivity; based on the plateau phase of the acidification curve, controlling the CO2 flow rate and pH value to achieve PO4+. 3‑ HPO4 2‑ Fe 3+ AsO4 3‑ S 2‑ Stepwise selective precipitation of impurities, avoiding the target component H2PO2 2‑ Loss; introduce calcium hydroxide suspension at the appropriate time to replenish Ca 2+ This promotes the efficient removal of phosphorus, arsenic, and sulfur impurities; subsequent cation exchange removes excess Na. + With Ca 2+ The product is then concentrated to obtain hypophosphoric acid with a purity of ≥99.5%. This invention features precise process control, thorough impurity removal, good repeatability and industrial adaptability, and significantly improves the resource utilization efficiency of by-products and the added value of the product.

Description

Technical Field

[0001] This invention relates to the field of hypophosphite preparation technology, specifically to a process for treating sodium hypophosphite, a byproduct of phosphine preparation. Background Technology

[0002] Hypophosphoric acid has a wide range of applications and excellent reducing properties. It is widely used in chemical electroplating, pharmaceuticals, resin coatings, inks, water treatment, and other fields. It can be used as a reducing agent, antioxidant, color-reducing agent, and UV-resistant additive. In addition, it can be used as an intermediate to prepare hypophosphite compounds, such as calcium hypophosphite, magnesium hypophosphite, aluminum hypophosphite, ammonium hypophosphite, and nickel hypophosphite. It has important value in agriculture, medicine, and electronics industries.

[0003] In the preparation of phosphine (PH3) from white phosphorus and a strong alkali, sodium hypophosphite (NaH3PO2) is often produced as a byproduct in the reaction system, and may also contain unreacted NaOH, sodium phosphite (Na2HPO3), sodium phosphate (Na3PO4), and metal ion impurities (such as Ca). 2+ Fe 3+ Sodium hypophosphite contains impurities such as sulfides and arsenates. In existing technologies, barium hypophosphite is typically added to the byproduct solution to remove sodium hypophosphite. However, this method does not consider impurities arising from other side reactions during the reaction process, raw material impurities, and environmental oxidation. This results in excessively low purity of the intermediate product, sodium hypophosphite, further limiting the low resource recovery rate of the byproduct.

[0004] Currently, there is a lack of quantitative and accurate removal methods for these impurities, resulting in limited purification and recycling of sodium hypophosphite, a byproduct of phosphine preparation. There is an urgent need to develop efficient processing techniques to improve resource utilization and product purity. Summary of the Invention

[0005] The purpose of this invention is to provide a process for treating sodium hypophosphite, a byproduct of phosphine preparation, in order to at least solve the problems of how to quantitatively, efficiently, and accurately remove impurities from sodium hypophosphite solution, a byproduct of phosphine preparation, while maximizing the retention of the target product sodium hypophosphite, thereby achieving resource utilization and ensuring product purity.

[0006] This invention provides a process for treating sodium hypophosphite, a byproduct of phosphine preparation, the process comprising the following steps: S100. Take the reaction mother liquor as a sample, introduce carbon dioxide gas into the sample, and plot the acidification curves of pH and conductivity. S200. Based on the acidification curve, formulate the acidification process, adjust the pH of the reaction mother liquor, and obtain a high-purity sodium hypophosphite solution; S300. The high-purity sodium hypophosphite solution is subjected to ion exchange in a resin tower to obtain a dilute hypophosphite solution; S400. Concentrate the dilute hypophosphoric acid to obtain hypophosphoric acid product; The reaction mother liquor is a by-product solution containing sodium hypophosphite and impurity components generated during the preparation of phosphine from elemental phosphorus and strong base.

[0007] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 1, with a pH value of 10.2-11.1 and an electrical conductivity value of 20.5-21.5 mS / cm; no obvious precipitation is formed during plateau phase 1.

[0008] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 2, with a pH value of 9.6-10.1 and an electrical conductivity value of 19.8-20.5 mS / cm; CaS and CaCO3 precipitates are formed during plateau phase 2.

[0009] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 3, with a pH value of 8.5-9.5 and an electrical conductivity value of 17.5-19.5 mS / cm; the main precipitates in plateau phase 3 are Ca3(PO4)2 and CaCO3.

[0010] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 4, with a pH value of 5.2-6.9 and an electrical conductivity value of 15.8-17.5 mS / cm; the main precipitate in plateau phase 4 is CaHPO3.

[0011] Preferably, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 5, with a pH value of 4.0-4.5 and an electrical conductivity value of 13.8-15.2 mS / cm; the main precipitate in plateau 5 is FeAsO4.

[0012] Preferably, a calcium hydroxide suspension is added to the reaction system.

[0013] Preferably, after the pH reaches a plateau of 5, the CO2 flow is stopped, and Ca(OH)2 suspension is added dropwise to the system until no precipitate is produced in the reaction system.

[0014] Preferably, the CO2 flow rate is 0.04-0.20 L / min.

[0015] Preferably, the resin tower is filled with macroporous strong acid cation exchange resin, the functional group of the resin is sulfonic acid group, the resin form is sodium form or hydrogen form, and the operating flow rate is controlled at 6-9 m / h.

[0016] Beneficial effects: This invention provides a process for treating sodium hypophosphite, a byproduct in phosphine preparation. Before large-volume treatment, a small-volume sample of the reaction mother liquor is taken and acidified by introducing CO2. The pH, conductivity, and precipitation are monitored in real time, and an acidification curve is plotted. The optimal control window is determined by combining the precipitation characteristics of each plateau phase. This provides a scientific basis and precise control parameters for the acidification treatment of large-volume reaction mother liquor, and significantly improves the selectivity and repeatability of impurity removal.

[0017] This invention introduces CO2 gas for acidification, which allows for precise control of the precipitation window of various impurity ions at different pH plateaus, selectively removing PO4 from the solution. 3- HPO3 2- Fe 3+ AsO4 3- S 2- Plasma impurities, while ensuring the target component H2PO2 - It remains stable throughout the process and does not participate in precipitation, oxidation, or decomposition reactions; when used in conjunction with calcium hydroxide suspension as a calcium source, it can provide calcium without significantly increasing the pH. 2+ This promotes the directional precipitation of phosphorus, arsenic, and sulfur impurities, and further removes excess Ca through cation exchange. 2+ and Na + Dilute hypophosphoric acid was prepared, and after a vacuum concentration step, the purity of the hypophosphoric acid product reached over 99.5%, which significantly improved the resource utilization efficiency of by-products and the added value of products, and has good prospects for industrial application. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The acidification curve for Example 1; Figure 2 The acidification curve for Example 2; Figure 3 The acidification curve for Example 3; Figure 4 This is a process flow diagram for the treatment of sodium hypophosphite, a byproduct of phosphine preparation. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the content.

[0022] This invention provides a process for treating sodium hypophosphite, a byproduct of phosphine preparation, comprising the following steps: S100. Take the mother liquor from the reaction and measure the initial pH and conductivity; S101. Carbon dioxide gas is introduced into the reaction mother liquor to adjust the pH of the solution, and the pH and conductivity of the solution are measured in real time; and an acidification curve is plotted based on the pH and conductivity. S200. Based on the acidification curve, formulate the acidification process, adjust the pH of the reaction mother liquor, and after filtration, obtain a high-purity sodium hypophosphite solution; S300. The high-purity sodium hypophosphite solution is subjected to ion exchange in a resin tower to obtain a dilute hypophosphite solution; S400. Concentrate the dilute hypophosphoric acid to obtain hypophosphoric acid product; The reaction mother liquor is a by-product solution containing sodium hypophosphite and impurity components generated during the preparation of phosphine from elemental phosphorus and strong base.

[0023] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 1, wherein the pH value of plateau phase 1 is 10.2-11.1 and the conductivity value is 20.5-21.5 mS / cm; no obvious precipitation is formed during plateau phase 1. The pH value of plateau phase 1 can be 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9, 11.0, or 11.1.

[0024] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 2, with a pH value of 9.6-10.1 and an electrical conductivity of 19.8-20.5 mS / cm; CaS and CaCO3 precipitates are formed during plateau phase 2. The pH value of plateau phase 2 can be 9.6, 9.7, 9.8, 9.9, 10.0, or 10.1.

[0025] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 3, with a pH value of 8.5-9.5 and an electrical conductivity of 17.5-19.5 mS / cm. The main precipitates during plateau phase 3 are Ca3(PO4)2 and CaCO3. The pH value during plateau phase 3 can be 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, or 9.5.

[0026] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau phase 4, with a pH value of 5.2-6.9 and an electrical conductivity of 15.8-17.5 mS / cm; the main precipitate during plateau phase 4 is CaHPO3. The pH value during plateau phase 4 can be 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, or 6.9.

[0027] In some preferred embodiments, carbon dioxide gas is continuously introduced into the sample until the pH reaches plateau 5, where the pH value of plateau 5 is 4.0-4.5 and the conductivity value is 13.8-15.2 mS / cm; the main precipitate of plateau 5 is FeAsO4. The pH value of plateau 5 can be 4.0, 4.1, 4.2, 4.3, 4.4, or 4.5.

[0028] In this invention, the reaction mother liquor originates from the reaction system for preparing phosphine using white phosphorus and a strong alkali as raw materials. It is a byproduct solution produced during the reaction process, primarily containing sodium hypophosphite and a certain amount of impurities, including unreacted NaOH, sodium phosphite (Na₂HPO₃), sodium phosphate (Na₃PO₄), and metal ion impurities (such as Ca²⁺). 2+ Fe 3+ The mother liquor contains impurities such as sulfides and arsenates. Treating the mother liquor involved in this invention can reduce wastewater discharge during phosphine preparation and significantly improve resource utilization. Furthermore, since the mother liquor is formed under phosphine reaction conditions, the components of the mixed solution are clearly defined, and the byproducts are controllable. Compared to conventional phosphate mixed solutions, the concentration of sodium hypophosphite is higher, the types of impurities are relatively fixed and exhibit a certain regularity, and there is no interference from other complex components, allowing for targeted removal. This is the fundamental condition for the sodium hypophosphite byproduct treatment process involved in this invention. Simultaneously, the chemical environment formed during the phosphine preparation reaction facilitates subsequent acidification, ion exchange, and concentration processes.

[0029] This invention achieves efficient separation and control of impurity ions in large-volume mother liquors by sampling and testing the reaction mother liquor, plotting pH-conductivity acidification curves, and then developing targeted acidification processes based on these curves. Unlike traditional methods that rely on empirically set fixed pH points or acid drop volumes for impurity removal, this invention uses the specific physicochemical properties of any batch of reaction mother liquor as a basis. By detecting the trends in pH and conductivity, it reflects the reaction processes and solubility changes of various components in the system, thereby obtaining the conditions for impurity precipitation. During acidification, as the pH gradually decreases, impurities precipitate within a specific pH range. The degree of impurity removal can be determined based on the changes in pH and conductivity. The processing technology employed in this invention reduces acid loss and processing load by specifically controlling the acidification path, and also avoids the waste of subsequent ion exchange resin adsorption capacity and the risk of poisoning. This invention is suitable for processing byproduct solutions with highly variable batches and complex compositions.

[0030] This invention significantly improves the chemical purity of raw materials by selectively removing impurities and phosphorus byproducts through acidification of the reaction mother liquor. The sodium hypophosphite solution after impurity removal has high purity, which can effectively reduce the probability of side reactions in subsequent reactions, thereby further improving the purity of hypophosphite.

[0031] In addition, the temperature is kept between 0-25℃ throughout the acidification process to ensure that the precipitate can be formed. At the same time, sodium hypophosphite can exist stably under low temperature conditions.

[0032] In this invention, an acidification process for large-volume mother liquor treatment is established based on the acidification curve obtained from acidification experiments. The high-purity sodium hypophosphite solution obtained after solid-liquid separation is further processed through a resin tower, and finally, hypophosphite product is obtained through vacuum concentration technology. The processing path provided by this invention is clear and has a high resource utilization rate, solving the technical problems of complex impurities and difficult processing of traditional by-product solutions. It transforms the originally complex by-product solution into a high-value-added raw material, realizing the recycling and utilization of sodium hypophosphite resources.

[0033] In some preferred embodiments, the treatment process for sodium hypophosphite, a byproduct of phosphine preparation, further includes a washing liquid recovery process, which specifically includes: S301. After ion exchange, the resin in the resin tower is cleaned sequentially using primary washing solution, secondary washing solution, and pure water. in: The primary washing solution is pumped to the resin tower to clean the resin, and the washing solution is collected in the recovery tank. The washing solution after secondary washing is returned to the primary washing solution tank for recycling. After rinsing with pure water until the pH of the effluent is neutral, the rinsing solution is returned to the secondary rinsing solution tank for use as a subsequent secondary rinsing solution.

[0034] Specifically, the primary and secondary washing solutions are sodium hypophosphite solutions. After the resin tower completes ion exchange, the primary washing solution is recycled and reused in a staged washing and diversion process to achieve recycling and resource utilization of the eluent. In detail, after the ion exchange in the resin tower, the resin is washed sequentially with primary washing solution, secondary washing solution, and pure water. After the washing solution recovery process, residual sodium hypophosphite and impurities in the resin can be effectively removed. The primary washing solution, with a high concentration of sodium hypophosphite, is used for preliminary resin cleaning, and the resulting washing solution is collected in a sodium hypophosphite recovery tank for preparing the sodium hypophosphite solution. The secondary washing solution is mainly used for further elution of residual components. The washing solution is returned to the primary washing solution storage tank for the next round of primary washing solution recycling, maximizing the recovery of residual target components. Pure water washing serves as the final rinsing step, washing until the pH of the effluent is close to neutral. The resulting washing solution is then returned to the secondary washing solution tank for use as secondary washing solution in subsequent processes.

[0035] The washing liquid recovery process adopted in this invention effectively improves the cleaning efficiency of resin, and realizes the recycling of sodium hypophosphite through the graded recycling of washing liquid. Compared with the traditional single cleaning or direct disposal of washing liquid, the washing liquid recovery process of this invention reduces the consumption of fresh sodium hypophosphite solution and pure water, and reduces waste liquid discharge.

[0036] In some preferred embodiments, in the processing technology involved in the present invention, the resin tower is filled with macroporous strong acid cation exchange resin, the functional group of the resin is sulfonic acid group, the resin form is sodium form or hydrogen form, and the operating flow rate is controlled at 6-9 m / h.

[0037] Specifically, macroporous resins possess advantages such as large specific surface area and good permeability, providing excellent mass transfer rates and ion exchange efficiency in treating high-concentration, complex ion systems. Sulfonic acid groups are strong acid cation exchange groups with strong affinity and stability, allowing for stable operation over a wide pH range. They effectively adsorb sodium ions in the solution, ensuring excellent effluent quality. Operating at a flow rate of 6-9 m / h ensures sufficient contact and reaction time between the resin and the solution, enabling thorough ion exchange. Simultaneously, a moderate flow rate helps maintain the uniformity and stability of the resin bed, preventing resin loss, compaction, or bed disturbance due to excessive flow, thus extending equipment operating cycles and reducing maintenance frequency. If the flow rate is too low, the throughput per unit time will decrease, affecting output; if the flow rate is too high, the contact time between ions and the resin will be reduced, leading to poor resin exchange efficiency and resource waste. Therefore, a flow rate of 6-9 m / h is the optimal choice.

[0038] Example 1 A process for treating sodium hypophosphite, a byproduct of phosphine preparation, includes the following steps: S100. Take 500 mL of the reaction mother liquor sample, measure the initial pH as 11.8, and the initial conductivity as 21.0 mS / cm; S101. Carbon dioxide gas is introduced into the reaction mother liquor at a flow rate of 0.05-0.12 L / min while stirring, and the changes in pH and conductivity are monitored in real time. At the same time, it is observed whether any precipitate is formed. Key data points during the acidification process:

[0039] Plateau phase 1 corresponds to the initial acidification stage. At this time, the pH of the mother liquor is high due to the presence of excess NaOH and other strongly alkaline components, creating an alkaline environment. The initial pH is typically between 10.2 and 11.9, and the solution contains OH-. - with Na + The ions and conductivity remained at a high level (21.0 mS / cm). During this stage, CO2 gas was continuously introduced at a low flow rate (0.05 L / min). The CO2 first reacted with water to form H2CO3, which then partially ionized to produce H+. + It also undergoes a neutralization reaction with the OH⁻ present in the solution, producing water and HCO₃⁻. - This gradually weakens the alkalinity and lowers the pH. Although H... + The addition of [a substance] caused the pH to drop slightly to approximately 10.9, but due to the HCO3 generated during the reaction... - And the original Na + The continued presence of HCO3- in the system actually increased the total ion concentration of the solution, leading to a slight increase in conductivity from 21.0 mS / cm to 21.5 mS / cm. With continued CO2 introduction, a system gradually formed in the solution with HCO3- as its constituent elements. - A weak acid buffer system, primarily composed of HCO3-. - The / CO2 buffer pair effectively suppressed large pH fluctuations. At this time, HCO3... - / CO3 2- The ratio is still significantly biased towards HCO3. - CO3 2- The concentration did not reach the solubility product threshold for CaCO3 precipitation (Ksp ≈ 2.8 × 10⁻⁶). -9 Even if trace amounts of Ca exist in the system 2+ No obvious calcium salt precipitation will form, so the system remains clear with no obvious precipitation.

[0040] Plateau phase 2: During this phase, the pH gradually decreases from approximately 10.1 to 9.9, and calcium salt impurities gradually begin to precipitate from the system. With the continuous increase in CO2 flux, the ionization of the carbonate system in the system further deepens, and H2CO3 continuously ionizes to form HCO3-. - And further CO3 is generated under higher pH conditions. 2- When the pH drops to between 9.6 and 10.1, CO3... 2- The concentration reached the same level as Ca 2+ The minimum solubility product threshold for the formation of calcium carbonate precipitate, at which point the Ca in the system... 2+ Start with CO3 2- A reaction occurs, forming a flocculent precipitate of CaCO3. Simultaneously, within this pH range, soluble sulfides present in the system also begin to react with Ca... 2+ The reaction produces CaS precipitate. Because Ca... 2+ CO3 2- S 2- As conductive ions are continuously converted into precipitates, the concentration of free ions in the system gradually decreases, the ion mobility decreases, and the conductivity drops from 21.5 mS / cm to about 19.9 mS / cm.

[0041] Plateau phase 3 is a critical window for deep phosphate ionization and efficient precipitation removal. Within this pH range, the ionization equilibrium of phosphate shifts towards the higher charge form, especially at pH > 8.5, where PO4+... 3- It gradually became the dominant phosphorus ion in the system, while H2PO4 - and HPO4 2- The proportion of low-charge forms decreased rapidly. This change in ionization state greatly increased the affinity for Ca. 2+ The binding ability of Ca3(PO4)2 is reduced, thus promoting the formation of Ca3(PO4)2 precipitate. Ca3(PO4)2 has a low solubility product (Ksp ≈ 1×10⁻⁶). -28 In the alkaline to neutral region, precipitation is extremely strong. In this system, due to the presence of the carbonate buffer, the pH decreases relatively slowly, which is conducive to the crystal development and particle size increase of the precipitate particles, forming Ca3(PO4)2 crystals with a stable precipitate structure. To further enhance the precipitation efficiency of phosphate, the CO2 aeration rate is moderately increased to 0.08-0.12 L / min during the plateau phase 3. This accelerates the generation of H2CO3 and releases H+. + It promotes the ionization of phosphoric acid and further promotes the ionization of HPO4. 2- To PO4 3- On the other hand, it can accelerate the transformation of Ca. 2+ With PO4 3- The collisions between the particles increase the precipitation rate and achieve complete precipitation.

[0042] Furthermore, as CO2 is introduced and pH continues to decrease, the CO3 content in the system... 2- The concentration remained within the precipitation range, therefore, while Ca3(PO4)2 was being formed, Ca... 2+ Continue with CO3 2- The reaction forms CaCO3 precipitate. The large-scale formation of both types of precipitates increases the concentration of Ca in the solution. 2+ and PO4 3- CO3 2- The plasma concentration decreased significantly, which led to a significant decrease in conductivity, from approximately 19.9 mS / cm at the plateau phase 2 to 18.3 mS / cm at the end of the plateau phase 3.

[0043] During plateau phase 4, 50 mL of Ca(OH)₂ suspension was added to the reaction to introduce a slow-release Ca. 2+ This stage involves the reaction of phosphate and Ca. 2+ The key window for CaHPO3 precipitation is when carbon dioxide is continuously bubbled through the precipitate, causing the pH to gradually decrease, at which point HPO3... 2- The concentration increased significantly, and its pK a2 ≈6.7, with slow-released Ca 2+ CaHPO3 precipitate is formed. The reaction is relatively fast at this stage, the precipitate particles gradually become denser, and the conductivity decreases rapidly.

[0044] Prior to this stage, timely supplementation with calcium hydroxide suspension as a calcium source is to introduce slowly released Ca. 2+ This promotes the formation of insoluble precipitates from unreacted phosphate and phosphite anions. Calcium hydroxide suspension is chosen as the calcium source because of its low solubility, allowing for the slow release of Ca in an acidic environment. 2+ This avoids localized supersaturation or non-selective precipitation caused by instantaneous excessive release. Simultaneously, the continuous introduction of CO2 establishes a stable H2CO3 / HCO3 / H2CO3 ratio. - The buffer system has good pH adjustment capabilities. When alkaline calcium hydroxide is added, it releases OH-. - Although it can partially neutralize H + However, the system will compensate for the loss by releasing more CO2 to form new H2CO3. + This maintains buffer balance and prevents a sharp rise in pH. Utilizing the buffering effect of the carbonation system and the synergistic effect of selective calcium supplementation, phosphorus impurities can be efficiently removed while avoiding the formation of H2PO2. - Non-selective co-precipitation or oxidation occurs under low pH conditions, maximizing the retention of the target product.

[0045] Plateau phase 5, this plateau phase is mainly used for AsO4 3- Precipitation removal. At pH = 4.2, Fe 3+ With AsO43- The reaction produces FeAsO4 precipitate. At this point, the CO2 aeration rate is gradually reduced to 0.03-0.06 L / min, and the pH is controlled to decrease steadily to prevent excessive acidity from causing the decomposition or oxidation of the target product, hypophosphite. As AsO4 precipitates... 3- After the precipitation of ions, the conductivity of the system eventually stabilized at 14.5 mS / cm.

[0046] After the pH reaches plateau phase 5, stop the CO2 flow to prevent the pH from rising too quickly. Add Ca(OH)2 suspension dropwise until no precipitate forms. At this point, the residual CO3 in the system... 2- or unreacted HCO3 - Completely removed, the remaining carbonate ions in the system rapidly react with Ca... 2+ The two molecules combine to form the final CaCO3 precipitate.

[0047] In this invention, CO2 is chosen as the pH adjuster because the carbonate buffer system is controllable and mild, and CO2 gradually dissolves in the water to establish the following equilibrium system:

[0048] As CO2 is continuously introduced, the equilibrium gradually shifts to the right, and the generated H2CO3 slowly releases H+. + This process achieves a gentle acidification of the alkaline system. Compared to strong acids, this process does not cause a sudden pH change, protecting hypophosphatemoids in the system and preventing oxidation or co-precipitation under low pH conditions. With the increase of H... + After the release of the substance and the neutralization of alkaline components such as NaOH, the pH of the system gradually decreases, and it enters a suitable window for the selective precipitation of impurities such as phosphate, phosphite, and arsenate.

[0049] To achieve selective precipitation of impurities, the Ca content in the system must be controlled. 2+ With CO3 2- The concentration ratio must be carefully controlled to prevent the premature depletion of calcium source due to the excessive formation of CaCO3 precipitate after CO2 introduction. Therefore, the strategy of CO2 introduction and the dropwise addition of Ca(OH)2 suspension must be strictly coordinated. During CO2 introduction, the flow rate of CO2 is controlled to regulate the concentration ratio of H2CO3 and CO32-. 2- The generation rate of CO3 in the system 2- The concentration remained within a controllable range; simultaneously, Ca(OH)₂ was added as a low-solubility suspension, which slowly released Ca upon dissolution. 2+ To avoid Ca 2+ A sudden excess causes calcium carbonate to precipitate violently, thus achieving Ca... 2+ It is gradually released and selectively participates in subsequent precipitation reactions of phosphorus and arsenic.

[0050] Furthermore, the carbonic acid system itself possesses acid-base buffering properties; when a weakly basic Ca(OH)₂ is added, the released OH⁻ - It is first neutralized by H2CO3, generating HCO3-. - This maintains the pH within a slowly changing range; this prevents a significant increase in pH during calcium supplementation, thus avoiding premature co-precipitation of phosphate or H2PO2. - The reaction is disrupted. Through the carbonate buffer acidification and timely calcium source replenishment strategy of this application, a stable reaction environment can be maintained, and the Ca2+ reaction can be ensured. 2+ Mainly used with PO4 3- HPO3 2- AsO4 3- The impurities react to form insoluble precipitates such as FePO4, Ca3(PO4)2, FeAsO4, and CaHPO3.

[0051] The purified reaction mother liquor sample was filtered to obtain a high-purity sodium hypophosphite solution.

[0052] Plotting based on pH and conductivity as follows Figure 1 Acidification curve; S200: Develop an acidification process, adjust the pH of the reaction mother liquor to selectively remove impurities, based on... Figure 1 Acidification curves were generated to determine the CO2 introduction rate and reaction control parameters corresponding to each critical pH plateau. Following this procedure, the pH of the bulk reaction mother liquor was adjusted, CO2 was introduced in stages, and Ca(OH)2 suspension was added at different pH points to supplement calcium and remove impurities.

[0053] After acidification, solid-liquid separation is performed, the precipitate is filtered out, and a clear and transparent high-purity sodium hypophosphite solution is obtained.

[0054] S300: The high-purity sodium hypophosphite solution in the sodium hypophosphite tank V101 is sent to the four-stage resin towers A, B, C, and D in series by the sodium hypophosphite feed pump P101. The hypophosphite solution after ion exchange is put into the dilute hypophosphite tank V102, and then sent to the concentration process by the dilute hypophosphite pump P102. After concentration, the finished hypophosphite product is obtained.

[0055] S400: Concentrate dilute hypophosphoric acid to obtain hypophosphoric acid product.

[0056] Example 2 The steps are the same as in Example 1, except that the acidification curve is different; The initial pH was measured to be 11.6, and the initial conductivity was 20.9 mS / cm. Key data points during the acidification process:

[0057] Plotting based on pH and conductivity as follows Figure 2Acidification curve; Example 3 The steps are the same as in Example 1, except that the acidification curve is different; The initial pH was measured to be 11.9, and the initial conductivity was 21.1 mS / cm. Key data points during the acidification process:

[0058] Plotting based on pH and conductivity as follows Figure 3 Acidification curve; In Examples 1-3, the analytical results of the filtrate after acidification were as follows: PO4 3- HPO3 2- Fe 3+ AsO4 3- S 2- The concentration of all ions was reduced to below the detection limit; total inorganic carbon: <10 mg / L, indicating that the impurity ions had been basically completely precipitated and removed; after ion exchange, the purity of hypophosphoric acid reached ≥99.5 wt%.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for treating sodium hypophosphite, a byproduct of phosphine preparation, characterized in that, The processing technology includes the following steps: S100. Take the reaction mother liquor as a sample, introduce carbon dioxide gas into the sample, and plot the acidification curves of pH and conductivity. Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau phase 1, with a pH value of 10.2-11.1 and an electrical conductivity value of 20.5-21.5 mS / cm; no obvious precipitation was formed during plateau phase 1. Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau phase 2, with a pH value of 9.6-10.1 and an electrical conductivity value of 19.8-20.5 mS / cm; CaS and CaCO3 precipitates were formed during plateau phase 2. Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau phase 3, with a pH value of 8.5-9.5 and an electrical conductivity value of 17.5-19.5 mS / cm; the main precipitates in plateau phase 3 were Ca3(PO4)2 and CaCO3. Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau phase 4, with a pH value of 5.2-6.9 and an electrical conductivity value of 15.8-17.5 mS / cm; the main precipitate during plateau phase 4 was CaHPO3. Carbon dioxide gas was continuously introduced into the sample until the pH reached plateau 5, with a pH value of 4.0-4.5 and an electrical conductivity value of 13.8-15.2 mS / cm; the main precipitate in plateau 5 was FeAsO4. S200. Based on the acidification curve, formulate an acidification process, adjust the pH of the reaction mother liquor, and obtain a high-purity sodium hypophosphite solution; S300. The high-purity sodium hypophosphite solution is subjected to ion exchange in a resin tower to obtain a dilute hypophosphite solution; S400. Concentrate the dilute hypophosphoric acid to obtain hypophosphoric acid product; The reaction mother liquor is a by-product solution containing sodium hypophosphite and impurity components generated during the preparation of phosphine from elemental phosphorus and a strong base.

2. The processing technology according to claim 1, characterized in that, After the pH reaches plateau 5, stop the CO2 flow and add Ca(OH)2 suspension dropwise to the system until no precipitate is produced in the reaction system.

3. The processing method according to any one of claims 1-2, characterized in that, The CO2 flow rate is 0.04-0.20 L / min.

4. The processing technology according to claim 1, characterized in that, The resin tower is filled with macroporous strong acid cation exchange resin, the functional group of which is sulfonic acid group, the resin form is hydrogen form, and the operating flow rate is controlled at 6-9 m / h.

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