A method for recycling rare earth by-product phosphorus iron waste residue

Abstract

The application discloses a method for recycling rare earth by-product phosphorus-iron waste residue, and belongs to the technical field of comprehensive utilization of metallurgical solid waste resources. The method uses rare earth smelting by-product phosphorus-iron waste residue as raw material, and carries out acidification and decomposition through 50%-98% sulfuric acid to obtain calcium sulfate and acidolysis liquid through solid-liquid separation. The calcium sulfate is mixed with humic acid to prepare a saline-alkali soil modifier. After radioactive thorium is separated from the acidolysis liquid through extraction, rare earth is precipitated and recovered in an acidic environment. After impurities are removed, ammonia is introduced to ammoniate, and ferrous pyrophosphate precipitate and ammonium sulfate solution are separated. The ferrous pyrophosphate is polymerized at high temperature to prepare polymerized phosphate compound fertilizer, and the ammonium sulfate solution is concentrated and crystallized to prepare ammonium sulfate fertilizer. The method can separate and obtain the soil conditioner through sulfuric acid, and can recover and utilize the rare earth and ferrous pyrophosphate through ammoniation and fractional precipitation, so that the phosphorus-iron waste residue is recovered and utilized in stages. Finally, the polymerized phosphate compound fertilizer is obtained, and can be applied to the agricultural field.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of metallurgical solid waste resources, and in particular to a method for recycling and reusing rare earth by-product phosphorus iron slag. Background Technology

[0002] Rare earth elements are an indispensable strategic resource for national economic development, and the high-temperature sulfuric acid roasting method is currently the mainstream industrial process for smelting mixed rare earth ores. In this process, the rare earth concentrate is roasted with concentrated sulfuric acid, leached in water, and neutralized to remove impurities. The supernatant then enters the rare earth extraction and separation process. The precipitate produced during the neutralization and impurity removal stage is the rare earth smelting water leaching residue, also known as rare earth by-product phosphorus-iron waste residue. This type of waste residue is generated in enormous quantities annually, containing not only recoverable rare earth oxides, phosphorus, iron, calcium, and other valuable components, but also enriched with radioactive elements such as uranium and thorium introduced from the original ore. It has long been a core challenge for solid waste disposal and environmental risk management in the rare earth smelting industry.

[0003] Currently, existing technologies for the disposal and resource utilization of rare earth by-product phosphorus and iron waste generally suffer from insufficient resource utilization. Most technologies focus only on the single recovery of rare earth elements, neglecting the high-value utilization of the main components such as calcium, phosphorus, and iron, which account for the largest proportion of the waste. The remaining waste after dilution still needs to be stockpiled in large quantities, which not only occupies a lot of land resources but also poses an environmental risk of leakage and diffusion of radioactive elements. It is impossible to achieve full disposal and reduction of solid waste, and it is difficult to form a closed-loop resource utilization system.

[0004] Existing wet recovery processes suffer from inherent drawbacks, including low recovery rates of valuable elements. They commonly suffer from poorly designed element separation sequences, often employing a route of first neutralizing and precipitating phosphine and iron, followed by rare earth recovery. During the precipitation of phosphine and iron components, rare earth elements are easily co-precipitated and significantly lost, resulting in extremely low overall rare earth recovery rates. Furthermore, existing acid leaching processes exhibit poor parameter adaptability. Low-concentration acid systems result in unsatisfactory leaching of valuable components, while high-acid systems suffer from excessive acid consumption and poor economic viability for industrial operation, making it difficult to balance recovery efficiency with production costs.

[0005] Existing processes lack specificity for separating radioactive elements from waste residue. Conventional extraction systems have low separation efficiency for radioactive thorium, failing to achieve complete separation of radioactive elements from valuable components. This results in the recovered phosphorus-iron byproducts having excessive radioactivity, making them unsuitable for downstream applications and only suitable for storage and disposal as hazardous waste. This approach fails to achieve true harmlessness and resource recovery, and also restricts the large-scale application of the recovered products.

[0006] In addition, existing technologies suffer from low added value and poor industrial adaptability. The recovered ferrophosphate components are mostly primary industrial raw materials, which cannot meet product compliance requirements and are difficult to dispose of on a large scale. Furthermore, the large amount of calcium sulfate in the waste residue has not been effectively utilized, resulting in serious resource waste. Moreover, most existing processes are only at the laboratory pilot stage, with narrow process parameter ranges, poor adaptability to fluctuations in raw material composition, and high consumption of auxiliary materials such as extractants, acids, and alkalis. The recycling of these auxiliary materials is also difficult to achieve, making it difficult to guarantee the stability and economic viability of continuous industrial production, and thus failing to meet the actual needs of large-scale solid waste disposal in the rare earth smelting industry. Summary of the Invention

[0007] The purpose of this invention is to provide a method for recycling and reusing rare earth by-product phosphorus iron slag to solve the above-mentioned problems.

[0008] This invention provides a method for recycling and reusing rare earth by-product phosphorus iron slag, comprising the following steps: (1) Acidification and decomposition: using rare earth smelting by-product phosphate iron waste as raw material, it is mixed with sulfuric acid and then subjected to acidification and decomposition reaction to obtain acidification reaction slurry; (2) First-stage solid-liquid separation: The acidified reaction slurry obtained in step (1) is subjected to solid-liquid separation to obtain solid calcium sulfate and acid hydrolysate containing pyrophosphate and ferrous sulfate, respectively; (3) Soil conditioner preparation: The solid calcium sulfate obtained in step (2) is mixed evenly with the conditioner to prepare the soil conditioner; (4) Extraction to remove thorium: The acid hydrolysate obtained in step (2) is solvent extracted with an extractant to separate the thorium-loaded organic phase and the extraction decomposition liquid; the thorium-loaded organic phase is back-extracted with a back-extractant to recover thorium, and the blank extractant obtained after back-extraction is recycled to the extraction process. (5) Rare earth precipitation recovery: Add a precipitant to the extract decomposition liquid obtained in step (4) to carry out rare earth precipitation reaction. After the reaction is completed, solid-liquid separation is performed to obtain rare earth enrichment and precipitated liquid respectively. (6) Deep purification: Add a purification agent to the precipitate obtained in step (5) to remove heavy metal impurities from the system. After the reaction is completed, solid-liquid separation is performed to obtain a refined acid hydrolysate. (7) Ammoniation reaction and sedimentation separation: Gas ammonia is introduced into the refined acid hydrolysate obtained in step (6) to carry out ammoniation reaction. After the reaction is completed, the ammoniation slurry is separated by sedimentation to obtain ferrous pyrophosphate precipitate and ammonium sulfate solution respectively. (8) Fertilizer product preparation: The ammonium sulfate solution obtained in step (7) is concentrated and crystallized to prepare ammonium sulfate fertilizer; the ferrous pyrophosphate precipitate obtained in step (7) is subjected to high-temperature polymerization reaction to prepare polymerized phosphate compound fertilizer.

[0009] Preferably, the rare earth smelting by-product phosphorus iron slag is a water-leached residue produced after mixed rare earth ore has undergone high-temperature roasting with sulfuric acid, water leaching, neutralization and impurity removal processes. The core chemical components, by mass percentage, are: H2O: 40.90%, REO: 3.16%, P2O5: 15.00%, S: 9.29%, Ca: 16.16%, Fe: 11.13%, Th: 0.10%, with the remainder being trace impurities.

[0010] Preferably, in step (1), the sulfuric acid has a mass fraction of 50%-98%, the solid-liquid mass ratio of the rare earth smelting by-product phosphorus iron waste residue to sulfuric acid is (1-12):1, the temperature of the acidification decomposition reaction is 40℃-90℃, and the reaction time is 1h-4h.

[0011] Preferably, in step (3), the conditioning agent is humic acid, and the mass ratio of calcium sulfate to humic acid is 1:(0.1~0.5).

[0012] Preferably, in step (4), the extractant uses sulfonated kerosene as a diluent, and the volume fraction of the extractant in the organic phase is 10% to 30%.

[0013] Preferably, the stripping agent is a sulfuric acid solution with a concentration of 0.5 mol / L to 3 mol / L.

[0014] Preferably, in step (5), the precipitant is at least one of ammonium carbonate, ammonium bicarbonate, and oxalic acid, the pH of the precipitation reaction system is 4.0 to 6.0, the reaction temperature is 20℃ to 60℃, and the reaction time is 0.5h to 2h.

[0015] Preferably, in step (6), the impurity removal agent is at least one of ammonium thiocyanate and ammonium sulfide, the pH value of the impurity removal reaction system is controlled at 2.0 to 4.0, the reaction temperature is 20℃ to 50℃, and the reaction time is 0.5h to 1.5h.

[0016] Preferably, in step (7), the final pH value of the ammoniation reaction system is controlled to be 6.0 to 8.5, the reaction temperature is 30℃ to 70℃, and the reaction time is 1h to 3h.

[0017] Preferably, in step (8), the temperature of the high-temperature polymerization reaction is 180℃~300℃, and the reaction time is 1h~4h; the concentration and crystallization adopts the evaporation concentration-cooling crystallization process, the final solid content of the evaporation concentration is 40%~60%, and the cooling crystallization temperature is 20℃~40℃; when carrying out the high-temperature polymerization reaction, a portion of the ammonium sulfate solution obtained in step (7) is added to the ferrous pyrophosphate precipitate, mixed evenly, and then the high-temperature polymerization reaction is carried out, and the mass ratio of the ferrous pyrophosphate precipitate to the ammonium sulfate solution is 1:(0.2~1.0).

[0018] Therefore, the present invention employs the above-described method for recycling and reusing rare earth by-product phosphorus iron slag, which has the following beneficial effects: (1) Through the integrated process of “acidification and calcium separation-graded extraction and precipitation-high value conversion of all components”, the graded recovery and high value conversion of all elements such as calcium, rare earth, thorium, phosphorus, iron and sulfur in the waste residue is realized. The separated calcium sulfate can be used to prepare soil conditioner, and the phosphorus, iron and sulfur components can be converted into agricultural fertilizer. The whole process does not generate any new secondary hazardous waste, and solves the land occupation and radioactive leakage risks caused by long-term storage of waste residue.

[0019] (2) The separation order of valuable elements was optimized, and the process route of preferential precipitation of rare earth in acidic environment was adopted to avoid the inherent defects of existing processes that pre-precipitate phosphorus and iron, resulting in a large amount of rare earth co-precipitation loss. At the same time, by precisely controlling the acidification and decomposition parameters, the leaching efficiency of rare earth was greatly improved. Combined with the subsequent efficient extraction and precipitation process, the overall recovery rate of rare earth was much higher than that of existing similar processes, realizing the efficient enrichment and recovery of low-content rare earth in waste residue.

[0020] (3) The extraction system is used to achieve efficient and deep separation of radioactive thorium, thus realizing the complete harmlessness of the product; at the same time, the extractant can be recycled after back-extraction, which effectively reduces the process operating cost while realizing closed-loop control of radioactive elements.

[0021] (4) Through deep impurity removal, precise ammoniation and high-temperature polymerization processes, the purified phosphorus and iron components are converted into polymeric phosphorus compound fertilizer, while ammonium sulfate fertilizer is produced as a by-product. The products can be directly applied to agricultural production, solving the problem of low added value and inability to be consumed on a large scale in existing processes.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of a method for recycling and reusing rare earth by-product phosphorus iron waste slag according to the present invention. Detailed Implementation

[0024] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0026] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0027] The rare earth smelting by-product phosphorus iron slag used in all embodiments and comparative examples is water leaching residue produced after mixed rare earth ore has undergone high-temperature roasting with sulfuric acid, water leaching, neutralization and impurity removal processes. The core chemical composition by mass percentage is: H2O: 40.90%, REO: 3.16%, P2O5: 15.00%, S: 9.29%, Ca: 16.16%, Fe: 11.13%, Th: 0.10%, with the remainder being trace impurities.

[0028] All embodiments, comparative test indicators, and calculation methods are as follows: Rare earth element leaching rate refers to the proportion of rare earth mass entering the acid hydrolysis solution during the acidification and decomposition process to the total mass of the raw rare earth. The formula is: ; In the formula: m is the mass, and w is the mass fraction of the corresponding component.

[0029] The total rare earth element recovery rate refers to the proportion of rare earth elements recovered in the entire process relative to the total mass of the raw material rare earth elements. It is determined by both the acid leaching rate and the recovery rate of the extraction-precipitation process. The formula is: ; The overall recovery rate of P2O5 refers to the proportion of the total mass of P2O5 in the final fertilizer product to the total mass of P2O5 in the raw material. The formula is: ; Radioactivity of polymeric phosphate compound fertilizer: The total α+β radioactivity of the sample was directly detected using a low-background α / β meter, with units of Bq / g. The detection method complies with the relevant specifications for the classification of radioactive solid waste.

[0030] The total solid waste resource utilization rate refers to the proportion of solid waste mass converted into usable products to the total mass of raw materials. The formula is: ; Acid consumption is evaluated for process economy using the formula: "mass of pure sulfuric acid consumed per unit mass of leaching v". .

[0031] Example 1 This embodiment provides a method for recycling and reusing rare earth by-product phosphorus iron slag, as detailed below: Acidification decomposition: Take 800g of the above-mentioned rare earth smelting by-product ferrophosphorus waste residue, mix it with 50% sulfuric acid aqueous solution at a liquid-solid mass ratio of 1:1, add it to the acidification reactor, control the reaction temperature at 60℃, stir the reaction for 2h, and obtain the acidification reaction slurry. First-stage solid-liquid separation: The obtained acidified reaction slurry is subjected to solid-liquid separation to obtain solid calcium sulfate and acid hydrolysate containing pyrophosphate and ferrous sulfate, respectively; Soil conditioner preparation: The obtained solid calcium sulfate and the conditioner humic acid were mixed evenly at a mass ratio of 1:0.3 to prepare a special soil conditioner for saline-alkali land. Thorium removal by extraction and extractant recycling: N1923 was used as the extractant and sulfonated kerosene as the diluent to prepare an organic phase with a N1923 volume fraction of 20%. The acid hydrolysate obtained after the first-stage solid-liquid separation was subjected to four-stage countercurrent extraction with the above organic phase at a ratio O / A = 1:1 to separate the thorium-loaded organic phase and the extraction decomposition solution. The thorium-loaded organic phase was subjected to two-stage countercurrent back-extraction using a 1.5 mol / L sulfuric acid solution as the back-extraction agent at a ratio O / A = 3:1. Thorium was recovered from the back-extraction solution, and the blank extractant obtained after back-extraction was recycled to the solvent extraction process. Rare earth precipitation recovery: Ammonium carbonate precipitant was added to the obtained extraction decomposition solution. The pH of the system was controlled at 5.0 under stirring conditions, the reaction temperature was 40℃, and the reaction was stirred for 1 hour. After the reaction was completed, solid-liquid separation was performed to obtain rare earth enrichment and precipitated solution, respectively. Deep purification: Add ammonium thiocyanate as a purification agent to the obtained precipitate, control the pH of the system to 3.0, the reaction temperature to 30℃, stir the reaction for 1 hour, filter after the reaction is completed to obtain the purified acid hydrolysate; Ammoniation reaction and sedimentation separation: Ammonia gas was introduced into the obtained purified acid hydrolysate. The final pH value of the system was controlled at 7.5 under stirring conditions, the reaction temperature was 50℃, and the reaction was stirred for 2 hours. After the reaction was completed, the ammoniation slurry was separated by sedimentation to obtain ferrous pyrophosphate precipitate and ammonium sulfate solution, respectively. Fertilizer product preparation: The obtained ferrous pyrophosphate precipitate and part of the ammonium sulfate solution were mixed evenly at a mass ratio of 1:0.5 and subjected to a high-temperature polymerization reaction. The reaction temperature was controlled at 250℃ and the reaction time was 2h to prepare a polymerized phosphate compound fertilizer. The remaining ammonium sulfate solution was evaporated and concentrated to a solid content of 50%, and then cooled to 30℃ to crystallize to prepare ammonium sulfate fertilizer.

[0032] Test results: The leaching rate of rare earth elements in a single acid hydrolysis was 48.53%, the total recovery rate of rare earth elements was 43.68%, the comprehensive recovery rate of P2O5 was 91.05%, the radioactivity of polymeric phosphate compound fertilizer was 0.48 Bq / g, and the resource utilization rate of solid waste throughout the entire process was 92.10%.

[0033] Example 2 In this embodiment, a 75% sulfuric acid aqueous solution with a liquid-to-solid mass ratio of 1:1 was used. The remaining process steps and parameters were completely consistent with those in Example 1.

[0034] Test results: The leaching rate of rare earth elements in a single acid hydrolysis was 48.47%, the total recovery rate of rare earth elements was 43.62%, the comprehensive recovery rate of P2O5 was 90.98%, the radioactivity of polymeric phosphate compound fertilizer was 0.48 Bq / g, and the resource utilization rate of solid waste throughout the entire process was 92.05%.

[0035] Example 3 In this embodiment, a 98% sulfuric acid aqueous solution with a liquid-to-solid mass ratio of 1:1 was used. The remaining process steps and parameters were completely consistent with those in Example 1.

[0036] Test results: The leaching rate of rare earth elements in a single acid hydrolysis was 48.62%, the total recovery rate of rare earth elements was 43.76%, the comprehensive recovery rate of P2O5 was 91.20%, the radioactivity of polymeric phosphate compound fertilizer was 0.48 Bq / g, and the resource utilization rate of solid waste throughout the entire process was 92.30%.

[0037] Example 4 In this embodiment, the acid hydrolysis raw material is the calcium sulfate filter residue produced by the first-stage solid-liquid separation in Example 3. A 75% sulfuric acid aqueous solution with a liquid-to-solid mass ratio of 2:1 is used for secondary acid decomposition. The remaining process steps and parameters are completely consistent with those in Example 1.

[0038] Test results: Secondary acid hydrolysis increased the rare earth leaching rate by 3.74%, the cumulative total rare earth leaching rate by 52.36%, the cumulative total rare earth recovery rate by 47.12%, the cumulative comprehensive recovery rate of P2O5 by 90.85%, the radioactivity of polymeric phosphate compound fertilizer by 0.48 Bq / g, and the resource utilization rate of solid waste throughout the process by 92.80%.

[0039] Example 5 The acid hydrolysis raw material in this embodiment is the filter residue obtained after secondary acid hydrolysis in Example 4. A 50% sulfuric acid aqueous solution with a liquid-to-solid mass ratio of 2:1 is used for three acid decomposition processes. The remaining process steps and parameters are completely consistent with those in Example 1.

[0040] Test results: The three acid hydrolysis processes increased the rare earth leaching rate by 2.82%, the cumulative total rare earth leaching rate by 55.18%, the cumulative total rare earth recovery rate by 49.66%, the cumulative comprehensive recovery rate of P2O5 by 90.78%, the radioactivity of polymeric phosphate compound fertilizer by 0.49 Bq / g, and the resource utilization rate of solid waste throughout the process by 93.20%.

[0041] Example 6 This embodiment uses a 50% sulfuric acid aqueous solution with a liquid-to-solid mass ratio of 12:1. The remaining process steps and parameters are completely consistent with those in Example 1.

[0042] Test results: The leaching rate of rare earth elements in a single acid hydrolysis was 87.97%, the total recovery rate of rare earth elements was 79.17%, the comprehensive recovery rate of P2O5 was 90.10%, the radioactivity of polymeric phosphate compound fertilizer was 0.49 Bq / g, and the resource utilization rate of solid waste throughout the entire process was 93.50%.

[0043] Comparative Example 1 This comparative example uses a sulfuric acid aqueous solution with a mass fraction of 25%, and the remaining process steps and parameters are completely consistent with those in Example 3.

[0044] Test results: Rare earth element leaching rate was 48.21%, calcium sulfate separation effect was poor, filter residue carried a large number of valuable components, P2O5 comprehensive recovery rate was only 82.30%, the radioactivity of polymeric phosphate compound fertilizer was 0.51 Bq / g, the resource utilization rate of solid waste in the whole process was 85.20%, acid consumption in the whole process increased significantly, and the industrialization economy was poor.

[0045] Comparative Example 2 This comparative example uses a sulfuric acid aqueous solution with a mass fraction of 10% and a liquid-to-solid mass ratio of 2:1. The remaining process steps and parameters are completely consistent with those in Example 3.

[0046] Test results: The leaching rate of rare earth elements was only 12.35%, the total recovery rate of rare earth elements was 11.12%, the comprehensive recovery rate of P2O5 was only 32.60%, the radioactivity of polymeric phosphate compound fertilizer was 0.62 Bq / g, and the resource utilization rate of solid waste throughout the process was only 45.20%. This proves that the sulfuric acid concentration was low, resulting in extremely poor leaching effect and failure to achieve effective recovery.

[0047] Comparative Example 3 This comparative example uses the filter residue from the single acid hydrolysis of Comparative Example 2 as the acid hydrolysis raw material, and performs a second acid hydrolysis using a 10% sulfuric acid aqueous solution. The remaining process steps and parameters are completely consistent with those of Example 3.

[0048] Test results: The secondary acid hydrolysis resulted in a rare earth leaching rate of only 2.18%, a cumulative total rare earth leaching rate of 14.53%, a cumulative total rare earth recovery rate of 13.08%, a cumulative comprehensive recovery rate of P2O5 of only 35.72%, a radioactivity of 0.58 Bq / g in polymeric phosphate compound fertilizer, and a solid waste resource utilization rate of 47.10% for the entire process. Even with cyclic acid hydrolysis, the low sulfuric acid concentration still prevents effective recovery.

[0049] Comparative Example 4 The acid hydrolysis raw material used in this comparative example is the filter residue after the second acid hydrolysis of Comparative Example 3. A 10% sulfuric acid aqueous solution was used for the third acid hydrolysis. The remaining process steps and parameters are completely consistent with those in Example 3.

[0050] Test results: The newly added rare earth leaching rate after three acid hydrolysis cycles was only 1.07%, the cumulative total rare earth leaching rate was 15.60%, the cumulative total rare earth recovery rate was 14.04%, the cumulative comprehensive recovery rate of P2O5 was only 36.85%, the radioactivity of polymeric phosphate compound fertilizer was 0.55 Bq / g, and the resource utilization rate of solid waste throughout the process was 48.30%. Multiple cycles still could not make up for the low sulfuric acid concentration.

[0051] Comparative Example 5 In this comparative example, a 30% phosphoric acid aqueous solution was used instead of a sulfuric acid aqueous solution, and the remaining process steps and parameters were completely consistent with those in Example 3.

[0052] Test results: The leaching rate of rare earth elements was only 8.72%, the total recovery rate of rare earth elements was 7.85%, the comprehensive recovery rate of P2O5 was only 28.45%, the radioactivity of polymeric phosphate compound fertilizer was 0.50 Bq / g, the resource utilization rate of solid waste in the whole process was 42.30%, and the effective separation of calcium sulfate and phosphorus iron components could not be achieved.

[0053] Comparative Example 6 In this comparative example, N235 was used as the extractant instead of N1923, and the remaining process steps and parameters were completely consistent with those in Example 3.

[0054] Test results: rare earth element leaching rate was 56.10%, total rare earth recovery rate was 43.50%, P2O5 comprehensive recovery rate was 90.80%, the radioactivity of polymeric phosphate compound fertilizer was 42.28 Bq / g, far exceeding the radioactivity limit for agricultural products, the resource utilization rate of solid waste throughout the process was 91.50%, and the thorium separation efficiency was only 18.30%, making it impossible to achieve product harmlessness.

[0055] Comparative Example 7 This comparative example adjusts the process sequence, first performing ammoniation to precipitate ferrophosphorus after thorium extraction, and then recovering rare earth elements. The remaining process parameters are completely consistent with those in Example 3.

[0056] Test results: rare earth element leaching rate was 48.62%, total rare earth element recovery rate was only 2.15%, more than 95% of rare earth elements were lost through co-precipitation with ferrous pyrophosphate precipitation, P2O5 comprehensive recovery rate was 90.50%, radioactivity of polymeric phosphate compound fertilizer was 0.49 Bq / g, and the resource utilization rate of solid waste throughout the process was 91.80%.

[0057] Comparative Example 8 The endpoint pH value of the ammoniation reaction in this comparative example was controlled at 9.5 (strongly alkaline), and the remaining process steps and parameters were completely consistent with those in Example 3.

[0058] Test results: Rare earth element leaching rate was 48.62%, and the total rare earth recovery rate dropped to 35.60%. When the ammoniation pH was strongly alkaline, both product purity and rare earth recovery rate decreased significantly. The comprehensive recovery rate of P2O5 was 82.10%. The radioactivity of the polymeric phosphate compound fertilizer was 0.50 Bq / g. The resource utilization rate of solid waste throughout the process was 88.60%. The purity of the ferrous pyrophosphate precipitate was only 62.30%. The effective phosphorus content of the polymeric phosphate compound fertilizer did not meet the agricultural standards.

[0059] Table 1 below shows a comparison of experimental data from the acid hydrolysis of phosphorus-iron waste residue, a byproduct of rare earth smelting, in Examples 1-6 and Comparative Examples 1-8.

[0060] Table 1 Comparison of experimental data on acidolysis of phosphorus-iron waste residue from rare earth smelting.

[0061] The test results of Examples 1-6 and Comparative Examples 1-8 show that: Examples 1, 2, and 3 used 50%, 75%, and 98% sulfuric acid, respectively, for a single acid hydrolysis at a liquid-to-solid ratio of 1:1. The final rare earth leaching rate stabilized at 48.47%-48.62%, the total rare earth recovery rate stabilized at 43.62%-43.76%, and the comprehensive phosphorus pentoxide recovery rate stabilized at 90.98%-91.20%. Examples 4 and 5 used 75% and 50% sulfuric acid, respectively, for secondary and tertiary acid hydrolysis of the pre-acid hydrolysis filter residue. This further increased the cumulative rare earth leaching rate from 48.62% in a single cycle to 52.36% and 55.18%, respectively, meeting the cost reduction requirements of industrial closed-loop recycling. Example 6 used 50% sulfuric acid at a liquid-to-solid ratio of 12:1 for acid hydrolysis, achieving a final rare earth leaching rate of 87.97% and a total rare earth recovery rate of 79.17%, realizing the efficient enrichment and recovery of rare earths. In Comparative Example 1, using 25% sulfuric acid for acid hydrolysis, the final comprehensive recovery rate of phosphorus pentoxide was only 82.30%, resulting in a significant increase in acid consumption and extremely poor economic efficiency for industrial operation. Comparative Examples 2-4, using 10% sulfuric acid for three cycles of acid hydrolysis, achieved a cumulative rare earth leaching rate of only 15.60%, a total rare earth recovery rate of less than 15%, and a comprehensive phosphorus pentoxide recovery rate of less than 37%, completely failing to achieve effective recovery of valuable components. It is evident that Examples 1-6, utilizing 50%-98% sulfuric acid as the acid hydrolysis reagent, achieved efficient and stable leaching of valuable components such as rare earths and phosphorus from the waste residue. Cyclic acid hydrolysis can further improve the recovery rate, while using low-concentration sulfuric acid cannot achieve the same recovery effect.

[0062] Examples 1-6 all use sulfuric acid as an acidifying agent, achieving efficient separation of calcium sulfate solid phase from the acid hydrolysate containing phosphorus, iron, and rare earth elements. The separated calcium sulfate can be directly used to prepare soil conditioner, and the acid hydrolysate can simultaneously achieve graded recovery of subsequent valuable components. The overall solid waste resource utilization rate can reach over 90%, with no new secondary hazardous waste generated. Comparative Example 5 uses 30% phosphoric acid instead of sulfuric acid as the acidifying agent, resulting in a final rare earth leaching rate of only 8.72%, a total rare earth recovery rate of less than 8%, and a comprehensive phosphorus pentoxide recovery rate of less than 29%. It fails to achieve effective separation of calcium, phosphorus, and iron components, exhibiting extremely poor leaching performance and failing to achieve full-component resource utilization of the solid waste. It is evident that Examples 1-6, using sulfuric acid as the acidifying agent, achieve graded separation and resource utilization of all components of the waste residue, while using phosphoric acid as a substitute cannot achieve the same separation and recovery effect.

[0063] Examples 1-6 all used N1923 as the extractant, achieving deep separation of radioactive thorium from the acid hydrolysate. The radioactivity of the final phosphorus-iron compound fertilizer product was stably controlled at 0.48-0.50 Bq / g, fully meeting the radioactivity safety requirements for agricultural products and achieving complete harmlessness. Comparative Example 6 used N235 instead of N1923 as the extractant, resulting in a final product with a radioactivity activity as high as 42.28 Bq / g, far exceeding the safety limit for agricultural products. The thorium separation efficiency was less than 20%, failing to achieve harmless disposal of the product, and the recovered product could not be used in downstream applications. It is evident that Examples 1-6, using N1923 as the extractant, achieved efficient and deep separation of radioactive thorium, ensuring the safety of the final product. Using N235 as a substitute could not achieve the same separation and harmlessness effect.

[0064] Examples 1-6 employ a process sequence of first preferentially precipitating and recovering rare earth elements under acidic conditions, followed by ammoniation to separate ferric phosphate. This avoids co-precipitation losses of rare earth and ferric phosphate components, resulting in a stable total rare earth recovery rate of over 43%, reaching a maximum of 79.17%. Simultaneously, the purity of the ferrous pyrophosphate precipitate is ensured, and the final fertilizer product meets all agricultural standards. Comparative Example 7 uses a reverse process sequence of first precipitating ferric phosphate and then recovering rare earth elements. Over 95% of the rare earth elements are lost through co-precipitation along with the ferric phosphate, resulting in a final total rare earth recovery rate of only 2.15%, which is completely ineffective. Examples 1-6 utilize a process sequence of "first precipitating rare earth elements, then extracting ferric phosphate," avoiding co-precipitation losses and achieving highly efficient rare earth recovery, whereas the reverse process cannot achieve effective rare earth recovery.

[0065] Examples 1-6 controlled the pH value at the endpoint of the ammoniation reaction within a near-neutral range of 6.0-8.5, achieving selective precipitation of ferrous pyrophosphate with high purity and no co-precipitation of ferric hydroxide. The effective phosphorus content of the prepared compound fertilizer fully met agricultural standards, while there was no additional rare earth co-precipitation loss. In contrast, Comparative Example 8 adjusted the pH value at the endpoint of the ammoniation reaction to a strongly alkaline range of 9.5. The final ferrous pyrophosphate precipitation purity was only 62.30%, resulting in insufficient effective phosphorus content in the compound fertilizer. Furthermore, rare earth elements were lost due to co-precipitation under the strongly alkaline environment, reducing the total rare earth recovery rate to 35.60%. Both product quality and rare earth recovery rate showed a significant decline. Examples 1-6, by controlling the pH value at the endpoint of ammoniation within a near-neutral range of 6.0-8.5, ensured both the purity of the ferric phosphate product and the recovery rate of rare earth elements, while neutralization to a strongly alkaline environment significantly deteriorated the effect.

[0066] Examples 4-5 use 50%-75% sulfuric acid to perform secondary and tertiary acidolysis on the pre-acidification filter residue, which can increase the cumulative rare earth leaching rate from 48.62% in a single acidolysis to 52.36% and 55.18%, respectively. While reducing acid consumption, this further improves the recovery rate of valuable components, perfectly meeting the cost reduction requirements of continuous industrial production. Comparative Examples 3-4 use 10% sulfuric acid for three-cycle acidolysis, resulting in a final cumulative rare earth leaching rate of only 15.60%, with no significant improvement compared to a single acidolysis. This shows that the recycling process cannot improve the recovery effect and is unsuitable for industrial production needs. Examples 4-5 utilize a 50%-75% sulfuric acid system, which is suitable for cyclic acidolysis processes to achieve cost reduction and efficiency improvement, while using low-concentration sulfuric acid cannot compensate for the leaching effect deficiencies through recycling.

[0067] In summary, Examples 1-6, through optimized acid hydrolysis concentration, acidifying agent selection, extractant selection, separation sequence of valuable components, and control of ammoniation pH, can stably achieve efficient rare earth recovery, deep harmless treatment of radioactive elements, and high-value utilization of all components of phosphorus, iron, and calcium from rare earth by-product phosphorus iron waste residue. The entire process generates no new secondary pollution and has both excellent environmental benefits and industrial adaptability. Comparative examples that deviate from the core parameters and routes of this process cannot achieve the same technical effect.

[0068] This invention utilizes an integrated process of "acidification-calcification-graded extraction and precipitation-high-value conversion of all components" to achieve graded recovery and high-value conversion of calcium, rare earth elements, thorium, phosphorus, iron, and sulfur from waste residue. The separated calcium sulfate can be used to prepare soil conditioners, and the phosphorus, iron, and sulfur components can be converted into agricultural fertilizers. The entire process generates no new secondary hazardous waste and solves the risks of land occupation and radioactive leakage caused by long-term waste residue storage. The separation sequence of valuable elements is optimized by adopting a process route that prioritizes the precipitation of rare earth elements in an acidic environment, avoiding the inherent defect of existing processes that first precipitate phosphorus and iron, resulting in a large loss of rare earth elements due to co-precipitation. At the same time, by precisely controlling the acidification and decomposition parameters, the leaching efficiency of rare earth elements is significantly improved. Combined with the subsequent efficient extraction and precipitation process, the overall recovery rate of rare earth elements is much higher than that of existing similar processes, achieving efficient enrichment and recovery of low-content rare earth elements from waste residue.

[0069] An extraction system is employed to achieve efficient and deep separation of radioactive thorium, ensuring complete product neutralization. Simultaneously, the extractant can be recycled after back-extraction, effectively reducing process operating costs while maintaining closed-loop control of radioactive elements. Through deep impurity removal, precise ammoniation, and high-temperature polymerization processes, the purified phosphorus and iron components are converted into polymeric phosphorus compound fertilizer, with ammonium sulfate fertilizer as a byproduct. The products can be directly applied to agricultural production, solving the problems of low added value and inability to scale up production using existing processes.

[0070] 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue, characterized in that, Includes the following steps: (1) Acidification and decomposition: using rare earth smelting by-product phosphate iron waste as raw material, it is mixed with sulfuric acid and then subjected to acidification and decomposition reaction to obtain acidification reaction slurry; (2) First-stage solid-liquid separation: The acidified reaction slurry obtained in step (1) is subjected to solid-liquid separation to obtain solid calcium sulfate and acid hydrolysate containing pyrophosphate and ferrous sulfate, respectively; (3) Soil conditioner preparation: The solid calcium sulfate obtained in step (2) is mixed evenly with the conditioner to prepare the soil conditioner; (4) Extraction to remove thorium: The acid hydrolysate obtained in step (2) is solvent extracted with an extractant to separate the thorium-loaded organic phase and the extraction decomposition liquid; the thorium-loaded organic phase is back-extracted with a back-extractant to recover thorium, and the blank extractant obtained after back-extraction is recycled to the extraction process. (5) Rare earth precipitation recovery: Add a precipitant to the extract decomposition liquid obtained in step (4) to carry out rare earth precipitation reaction. After the reaction is completed, solid-liquid separation is performed to obtain rare earth enrichment and precipitated liquid respectively. (6) Deep purification: Add a purification agent to the precipitate obtained in step (5) to remove heavy metal impurities from the system. After the reaction is completed, solid-liquid separation is performed to obtain a refined acid hydrolysate. (7) Ammoniation reaction and sedimentation separation: Gas ammonia is introduced into the refined acid hydrolysate obtained in step (6) to carry out ammoniation reaction. After the reaction is completed, the ammoniation slurry is separated by sedimentation to obtain ferrous pyrophosphate precipitate and ammonium sulfate solution respectively. (8) Fertilizer product preparation: The ammonium sulfate solution obtained in step (7) is concentrated and crystallized to prepare ammonium sulfate fertilizer; the ferrous pyrophosphate precipitate obtained in step (7) is subjected to high-temperature polymerization reaction to prepare polymerized phosphate compound fertilizer.

2. The method for recycling and reusing rare earth by-product phosphorus iron slag according to claim 1, characterized in that, The rare earth smelting by-product phosphorus iron slag is a water-leached residue produced after mixed rare earth ore undergoes high-temperature roasting with sulfuric acid, water leaching, neutralization, and impurity removal processes. The core chemical components, by mass percentage, are: H2O: 40.90%, REO: 3.16%, P2O5: 15.00%, S: 9.29%, Ca: 16.16%, Fe: 11.13%, Th: 0.10%, with the remainder being trace impurities.

3. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (1), the sulfuric acid has a mass fraction of 50%-98%, the solid-liquid mass ratio of the rare earth smelting by-product phosphorus iron waste residue to sulfuric acid is (1-12):1, the temperature of the acidification decomposition reaction is 40℃-90℃, and the reaction time is 1h-4h.

4. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (3), the conditioning agent is humic acid, and the mass ratio of calcium sulfate to humic acid is 1:(0.1-0.5).

5. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (4), the extractant uses sulfonated kerosene as a diluent.

6. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (4), the stripping agent is a sulfuric acid solution with a concentration of 0.5 mol / L to 3 mol / L.

7. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (5), the precipitant is at least one of ammonium carbonate, ammonium bicarbonate, and oxalic acid. The pH value of the precipitation reaction system is 4.0 to 6.0, the reaction temperature is 20℃ to 60℃, and the reaction time is 0.5h to 2h.

8. A method for recycling and reusing rare earth by-product phosphorus iron slag according to claim 1, characterized in that, In step (6), the impurity removal agent is at least one of ammonium thiocyanate and ammonium sulfide, the pH value of the impurity removal reaction system is 2.0 to 4.0, the reaction temperature is 20℃ to 50℃, and the reaction time is 0.5h to 1.5h.

9. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (7), the final pH value of the ammoniation reaction system is controlled to be 6.0 to 8.5, the reaction temperature is 30℃ to 70℃, and the reaction time is 1h to 3h.

10. A method for recycling and reusing rare earth by-product phosphorus-iron waste residue according to claim 1, characterized in that, In step (8), the temperature of the high-temperature polymerization reaction is 180℃~300℃ and the reaction time is 1h~4h; the concentration and crystallization adopts the evaporation concentration-cooling crystallization process, the final solid content of the evaporation concentration is 40%~60%, and the temperature of the cooling crystallization is 20℃~40℃; when carrying out the high-temperature polymerization reaction, a portion of the ammonium sulfate solution obtained in step (7) is added to the ferrous pyrophosphate precipitate, mixed evenly, and then the high-temperature polymerization reaction is carried out. The mass ratio of the ferrous pyrophosphate precipitate to the ammonium sulfate solution is 1:(0.2~1.0).

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