A method for preparing high-purity phosphorus iron by rough phosphorus iron microwave roasting-phosphorus-preserved impurity removal acid leaching

Abstract

The application discloses a method for preparing high-purity phosphorus iron by rough phosphorus iron microwave roasting-acid leaching phosphorus-removing impurities. After rough phosphorus iron is crushed and classified, the rough phosphorus iron is heated to 500-680 DEG C by 2.45GHz microwave in a fluidized atmosphere containing 0.5%-2.0% oxygen and 3%-8% water vapor and is kept for 4-15 min, so that impurities such as silicon, calcium and manganese are selectively oxidized in the enriched phase, and micro-cracks are formed at the interface between the enriched phase and the main phase of the phosphorus iron; after the roasted material is subjected to one-stage rapid leaching by acetic acid or citric acid and two-stage washing by a complexing agent, the roasted material is dried to a constant weight in an inert atmosphere or vacuum. The microwave power and the composition of the fluidized gas are adjusted by closed-loop regulation of the bed temperature and the oxygen content of tail gas, so that the phosphorus loss rate of the acid leaching is not higher than 5%.

Description

Technical Field

[0001] This invention relates to the fields of industrial solid waste resource utilization, phosphorus chemical industry, metallurgy and functional materials technology, and specifically to a method for preparing high-purity ferrophosphorus by microwave roasting of crude ferrophosphorus followed by acid leaching to retain phosphorus and remove impurities. Background Technology

[0002] Crude ferrophosphorus typically consists mainly of FeP and / or Fe2P, while also containing impurity phases such as Si, Ca, and Mn. The particle size, phosphorus content, and impurity content (Si, Ca, Mn, etc.) vary between different batches of crude ferrophosphorus due to variations in raw material source, smelting process, and cooling conditions, leading to inconsistent reaction conditions required for subsequent roasting and leaching. The goal of high-purity ferrophosphorus ore is to retain the main iron-phosphorus components while removing impurities, rather than performing dephosphorization and iron extraction as in the beneficiation of high-phosphorus iron ore.

[0003] Existing roasting or leaching methods typically control the process by setting the equipment temperature, rated power, or fixed acid leaching time, making it difficult to adjust in real time according to the dielectric response and oxidation degree of the material. Microwave heating has selective and volumetric heating characteristics, and the difference in dielectric loss between different phases can form thermal stress and microcracks at the interface; however, the iron-containing phase in crude ferrophosphorus may cause microwave reflection and local hot spots, and uneven temperature and oxygen potential distribution may also occur in the fluidized bed, thus resulting in insufficient selectivity of key reactions and poor batch stability of products.

[0004] When the oxygen potential in the roasting atmosphere is too low, the impurity phase is not sufficiently activated; when the oxygen potential or temperature is too high, FeP / Fe2P may oxidize, leading to phosphorus loss. Insufficient acid concentration and leaching time cannot adequately remove activated impurities, while excessive concentration will simultaneously dissolve Fe and P. Existing methods often lack comprehensive quantitative control over the entire process, including bed temperature, tail gas oxygen content, phosphorus loss rate, and the total Fe and P content of the product, making it difficult to balance impurity removal rate, phosphorus yield, and product quality.

[0005] Existing technologies such as CN109136540B mainly target dephosphorization of high-phosphorus iron ore. The raw material composition, technical objectives, and allowable phosphorus loss differ from those of crude ferrophosphorus refining. Existing technologies have not yet provided a method that can adapt to fluctuations in crude ferrophosphorus raw materials, form interfacial microcracks through microwave fluidized bed selective oxidation, and achieve stable phosphorus retention and impurity removal through closed-loop control and segmented leaching. Summary of the Invention

[0006] This invention provides a method for preparing high-purity ferrophosphorus by microwave roasting and acid leaching to retain phosphorus and remove impurities from crude ferrophosphorus, which can be verified by pilot-scale testing, achieves material balance, and takes into account safety and environmental constraints.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing high-purity ferrophosphorus by microwave roasting and acid leaching for phosphorus retention and impurity removal of crude ferrophosphorus includes the following steps: classifying crude ferrophosphorus containing FeP or Fe2P main phase into 0.1~3mm particles; heating the crude ferrophosphorus to 500~680℃ and holding it at that temperature for 4~15min in a fluidized atmosphere containing 0.5%~2.0% oxygen and 3%~8% water vapor using microwaves, so as to selectively oxidize the impurity-enriched phase and form microcracks at the interface between the impurity-enriched phase and the ferrophosphorus main phase; performing a first-stage rapid leaching with 0.2~0.6mol / L acetic acid or citric acid, followed by a second-stage washing with a complexing agent; controlling the phosphorus loss rate during acid leaching to be no higher than 5% throughout the entire process.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the microwave power and fluidizing gas composition are adjusted in a closed loop based on the bed temperature and the oxygen content of the exhaust gas. When the positive deviation of the bed temperature from the set roasting temperature is greater than 10°C or the oxygen content of the exhaust gas is higher than 2.0%, the microwave power and / or oxygen supply are reduced. When the absolute value of the negative deviation of the bed temperature from the set roasting temperature is greater than 10°C or the oxygen content of the exhaust gas is lower than 0.5%, the microwave power and / or oxygen supply are increased to maintain the bed temperature within ±10°C of the set value and to maintain the oxygen content of the exhaust gas between 0.5% and 2.0%.

[0010] Furthermore, the liquid-to-solid ratio of the first stage of acid leaching is 4~8 mL / g, the temperature is 50~70℃, and the time is 8~15 min.

[0011] Furthermore, the complexing agent is a citrate, EDTA salt, or aminocarboxylate, used to remove calcium, magnesium, manganese, or copper impurities from the iron surface.

[0012] Further, after the two-stage washing, solid-liquid separation is performed, and the filter residue is washed with deionized water until the washing liquid is neutral. Then, it is dried at 60~180℃ to constant weight under an inert atmosphere or vacuum.

[0013] Furthermore, the crude ferrophosphorus contains 15%~28% P, 1%~8% Si, and 0.2%~5% Ca, with a particle size of 0.2~2 mm.

[0014] Furthermore, the microwave frequency is 2.45 GHz and the power density is 0.8~4.0 kW / kg. Furthermore, the total Fe and P content in the ferrophosphorus produced by the method of this invention is not less than 95%, and the phosphorus loss rate from acid leaching is not higher than 5%.

[0015] Compared with the prior art, the present invention has the following beneficial technical effects: (1) The present invention aims to "retain the main phosphorus iron phases such as FeP and Fe2P while selectively removing impurities". By limiting the oxygen content to 0.5%~2.0% and the water vapor content to 3%~8%, and controlling the microwave roasting at 500~680℃ for 4~15min, the impurity phases such as silicon-rich, calcium-rich and manganese-containing phases are preferentially oxidized and activated, while inhibiting the deep oxidation of the main phosphorus iron phase and the conversion of phosphorus to soluble phosphate. This selective oxidation boundary is different from the high-phosphorus iron ore oxidation roasting-leaching process for the purpose of dephosphorization, and also different from the route of long-term air roasting for phosphorus iron treatment. It takes into account both the leachingability of impurities and the retention of phosphorus resources from the source.

[0016] (2) The difference in dielectric response of different phases in crude ferrophosphorus can create selective volumetric heating and interfacial temperature difference. Combined with the particle dispersion and heat and mass transfer of the fluidized bed, thermal stress and microcracks are generated at the interface between the impurity phase and the FeP / Fe2P bulk phase, making it easier for the acid to enter the impurity enrichment zone. Therefore, the reaction channel for subsequent leaching can be obtained without roasting all materials at high temperature for a long time, which is beneficial to shorten the roasting time, reduce thermal inertia and energy consumption per unit product, and reduce phosphorus oxidation loss caused by local overheating in the fixed bed.

[0017] (3) This invention uses bed temperature and tail gas oxygen content as feedback quantities to adjust microwave power and fluidizing gas composition in a closed loop, so that the bed temperature is maintained within ±10℃ of the set value and the tail gas oxygen content is maintained at 0.5%~2.0%. This control method can compensate for the fluctuations in particle size, phosphorus content and impurity content such as Si, Ca, and Mn in crude ferrophosphorus from different sources, reduce the risk of excessive local oxygen potential, bed temperature runaway and main phase oxidation, and improve the stability of continuous operation, batch consistency and scale-up feasibility.

[0018] (4) After selective oxidation and the formation of microcracks at the interface between the impurity-enriched phase and the phosphorus-iron main phase, a rapid leaching process of 0.2~0.6 mol / L acetic acid or citric acid for 8~15 min is used to preferentially dissolve and remove the calcium, silicon, manganese and other impurity phases exposed after oxidation, while reducing the co-dissolution of iron and phosphorus in the acid solution. Compared with conventional enhancement methods that increase acid concentration and extend leaching time, this invention is beneficial to reducing acid consumption, equipment corrosion and the amount of saline wastewater generated, and controlling phosphorus loss to within 5%.

[0019] (5) This invention separates the first-stage acid leaching of large amounts of impurities from the second-stage complexing washing of trace impurities: the former rapidly removes easily soluble main impurities such as calcium and silicon, while the latter utilizes citrate, EDTA salt, or aminocarboxylate salts to perform fine purification through the complexation of residual Ca, Mg, Mn, and Cu ions. This staged impurity removal method avoids prolonging the strong acid contact time to remove small amounts of residual metals, and can increase the total Fe and P content in the product under conditions of phosphorus preservation and low iron loss, with the target product achieving a Fe+P content of over 95%. Detailed Implementation Example 1

[0020] In batches of 100 kg, a standard crude ferrophosphorus containing approximately 70.0% Fe, 22.0% P, 4.0% Si, 2.0% Ca, 1.0% Mn, and the remainder being unavoidable impurities, with a particle size of 0.3~1.0 mm, was placed in a 2.45 GHz microwave fluidized bed. The roasting was carried out at a set roasting temperature of 600℃ and an initial power density of 2.0 kW / kg in a fluidized atmosphere consisting of 1.0% O2, 5% water vapor, and 94% N2. During the roasting process, the bed temperature and the oxygen content of the exhaust gas were continuously monitored. When the positive deviation of the bed temperature from the set roasting temperature was greater than 10℃ or the oxygen content of the exhaust gas was higher than 2.0%, the microwave power and / or oxygen supply were reduced. When the absolute value of the negative deviation of the bed temperature from the set roasting temperature was greater than 10℃ or the oxygen content of the exhaust gas was lower than 0.5%, the microwave power and / or oxygen supply were increased to maintain the bed temperature at 590~610℃ and the oxygen content of the exhaust gas at 0.5%~2.0%, and the temperature was maintained for 8 minutes. After cooling, the calcined material was leached with 0.40 mol / L acetic acid at a liquid-to-solid ratio of 5 mL / g at 60℃ for 15 min, followed by washing with 0.05 mol / L sodium citrate solution for 5 min. After the two-stage washing, solid-liquid separation was performed, and the filter residue was washed with deionized water until the pH of the washing liquid reached 6-7. The residue was then dried to constant weight at 120℃ under N2 atmosphere. The removal rates of Si, Ca, and Mn were 65%, 85%, and 45%, respectively, with a Fe loss rate of 0.8% and a P loss rate of 2.5%. The dried product yielded approximately 93.9 kg, including approximately 69.44 kg of Fe, approximately 21.45 kg of P, and a combined Fe and P content of approximately 96.8%. The Si content was approximately 1.49%, the Ca content approximately 0.32%, and the Mn content approximately 0.59%. The net microwave power consumption was 160-220 kWh / t crude ferrophosphorus, and the product yield was 92%. Example 2

[0021] Except for the microwave temperature of 500℃, power density of 1.2kW / kg, and holding time of 15min, the other conditions were the same as in Example 1. The removal rates of Si, Ca, and Mn were 42%, 68%, and 30%, respectively, the Fe loss rate was 0.5%, and the P loss rate was 1.3%; the product weight was approximately 96.3kg, with a total Fe and P content of approximately 95.2%, Si content of approximately 2.4%, and Ca content of approximately 0.66%. Example 3

[0022] Microwave treatment at 680℃ and 3.5 kW / kg for 5 min was used in an atmosphere containing 2.0% O2 and 3% water vapor; leaching was then performed with 0.50 mol / L acetic acid at 65℃ for 12 min. The removal rates of Si, Ca, and Mn were 76%, 91%, and 58%, respectively, but the Fe loss rate increased to 1.2% and the P loss rate was 4.6%. The product weight was approximately 91.7 kg, with a total Fe+P content of approximately 97.0%, Si of approximately 1.05%, and Ca of approximately 0.20%. Example 4

[0023] The sample was leached at 550℃ for 12 min using a power density of 0.8 kW / kg under an atmosphere containing 0.5% O2 and 8% water vapor. It was then leached in two stages at 50℃ for 10 min each using 0.20 mol / L citric acid at a liquid-to-solid ratio of 8 mL / g, with P and Si measured at the end of each stage. The removal rates of Si, Ca, and Mn were 55%, 78%, and 50%, respectively, with a Fe loss rate of 0.7% and a P loss rate of 2.0%. The product weight was approximately 94.8 kg, with a total Fe+P removal rate of approximately 96.2%. The acid consumption was equivalent to approximately 24.74 kg / t of anhydrous citric acid in crude ferrophosphorus. Example 5

[0024] The sample was rapidly heated at 630℃ with a power of 4.0 kW / kg and held for 4 min in an atmosphere containing 1.5% O2 and 5% water vapor. It was then leached with 0.60 mol / L acetic acid at a liquid-to-solid ratio of 4 mL / g at 70℃ for 8 min, followed by washing with 0.02 mol / L disodium EDTA for 3 min. The removal rates of Si, Ca, and Mn were 70%, 88%, and 62%, respectively, with a Fe loss rate of 1.0% and a P loss rate of 3.2%. The product weight was approximately 92.9 kg, with a total Fe+P removal rate of approximately 97.1%, and a Cu and surface Mn complexation removal rate of approximately 69.35%. Comparative Example 1

[0025] Microwave selective oxidation roasting was omitted, and the same batch of crude ferrophosphorus was directly leached according to the acetic acid concentration, liquid-solid ratio, temperature, and time specified in Example 1. The removal rates of Si, Ca, and Mn were 24%, 58%, and 18%, respectively, with a Fe loss rate of 0.4% and a P loss rate of 1.0%. The product had a total Fe+P content of approximately 93.7%~94.4%, while Si remained at approximately 3.1%. Comparative Example 2

[0026] The same 600℃, 8 min, and microwave power as in Example 1 were used, but the fluidizing gas was replaced with air, and the low oxygen potential was not controlled; the acid leaching conditions remained the same as in Example 1. The removal rates of Si, Ca, and Mn were 78%, 92%, and 65%, respectively, while the P loss rate increased to 9%~13% and the Fe loss rate was 1.5%~2.5%; the phosphorus recovery rate was only 87%, which did not meet the purpose of "retaining phosphorus and removing impurities".

Claims

1. A method for preparing high-purity ferrophosphorus by microwave roasting of crude ferrophosphorus followed by acid leaching for phosphorus retention and impurity removal, characterized in that, Includes the following steps: The crude ferrophosphorus containing FeP or Fe2P main phase is classified into 0.1-3 mm particles; in a fluidized atmosphere containing 0.5%-2.0% oxygen and 3%-8% water vapor, it is microwave-heated to 500-680℃ at 2.45 GHz and held for 4-15 min to selectively oxidize the impurity-enriched phase and form microcracks at the interface between the impurity-enriched phase and the ferrophosphorus main phase; a first-stage rapid leaching is performed using 0.2-0.6 mol / L acetic acid or citric acid, followed by a second-stage washing with a complexing agent; the phosphorus loss rate from acid leaching is controlled to be no higher than 5% throughout the entire process.

2. The method according to claim 1, characterized in that, The microwave power and fluidizing gas composition are adjusted in a closed loop based on the bed temperature and the oxygen content of the exhaust gas. When the positive deviation of the bed temperature from the set roasting temperature is greater than 10℃ or the oxygen content of the exhaust gas is higher than 2.0%, the microwave power and / or oxygen supply are reduced. When the absolute value of the negative deviation of the bed temperature from the set roasting temperature is greater than 10℃ or the oxygen content of the exhaust gas is lower than 0.5%, the microwave power and / or oxygen supply are increased to maintain the bed temperature within ±10℃ of the set value and maintain the oxygen content of the exhaust gas between 0.5% and 2.0%.

3. The method according to claim 1, characterized in that, The liquid-to-solid ratio of the first stage of acid leaching is 4~8 mL / g, the temperature is 50~70℃, and the time is 8~15 min.

4. The method according to claim 1, characterized in that, The complexing agent is a citrate, EDTA salt, or aminocarboxylate.

5. The method according to claim 1, characterized in that, After two stages of washing, solid-liquid separation is performed. The filter residue is then washed with deionized water until the washing liquid is neutral, and dried at 60-180°C under an inert atmosphere or vacuum until constant weight.

6. The method according to claim 1, characterized in that, The crude ferrophosphorus contains 15%~28% P, 1%~8% Si, and 0.2%~5% Ca, with a particle size of 0.2~2 mm.

7. The method according to claim 1, characterized in that, The microwave power density is 0.8~4.0kW / kg.

8. A phosphorus iron prepared by the method according to any one of claims 1 to 7, characterized in that, The total content of Fe and P in the phosphorus iron is not less than 95%.