A method for desulfurization of iron phosphate

Abstract

The present invention provides a method for desulfurizing iron phosphate, the method comprising the following steps: (1) calcining and / or grinding the iron phosphate to be desulfurized to obtain treated iron phosphate; (2) aging the treated iron phosphate in water or an acidic solution to obtain desulfurized iron phosphate. The method is simple to operate, low in cost, and can obtain iron phosphate with a low sulfur content. No harmful substances are generated during the treatment process, and the method is a green and environmentally friendly treatment method.

Description

Technical Field

[0001] The invention relates to the technical field of iron phosphate purification, and in particular to a method for desulfurizing iron phosphate. Background Art

[0002] Lithium iron phosphate battery materials have been used in various electric vehicles and communication equipment due to their advantages such as large discharge capacity, long cycle life, high safety, and environmental friendliness. As an important precursor for the preparation of lithium iron phosphate, the quality of iron phosphate has a very important influence on the electrochemical performance of the battery. Ferrous sulfate, as one of the iron sources for the preparation of iron phosphate, has the advantages of being easy to obtain and low in cost, so it is widely used. However, the introduction of sulfate also increases the burden of subsequent washing processes, generating a large amount of salt-containing wastewater, which increases its treatment cost.

[0003] CN107902637A discloses a production method of high-purity ferric phosphate, which removes impurities and purifies the ferrous sulfate solution or the ferrous sulfate solution generated by the reaction of iron and sulfuric acid after the dissolution of the raw material ferrous sulfate heptahydrate crystals for producing ferric phosphate three times, utilizes the purified ferrous sulfate solution to generate ferric sulfate solution by oxidation reaction with hydrogen peroxide, and then drips phosphate solution under the condition of emulsifier to react and synthesize ferric phosphate precipitation, or adds phosphoric acid to the purified ferrous sulfate solution, stirs well and adds hydrogen peroxide for oxidation, adds emulsifier, synthesizes ferric phosphate precipitation, and then ages, rinses, filters, and dries the ferric phosphate precipitation to make water or anhydrous high-purity ferric phosphate. However, the method is cumbersome, and a large amount of reagents are added during the process to remove impurities, and the cost is relatively high.

[0004] CN108046229A discloses a method for comprehensive desulfurization of battery-grade anhydrous iron phosphate, which mainly controls desulfurization from three links in the production process of iron phosphate, specifically, in the production process of battery-grade anhydrous iron phosphate, a certain amount of emulsifier is added to form an emulsion under strong stirring, and a morphology control agent is added to control the crystal form and particle size to reduce the sulfur content; in the washing process, the sulfur content is reduced by three-stage washing, which is 0.05% citric acid solution washing, anhydrous ethanol washing, and 60°C hot water washing, which replace the traditional pure water washing method; before dehydration, the particles are pre-crushed to 1-5um, the particle size is refined, and the dehydration temperature is increased to 650°C, thereby reducing the sulfur content. However, this method has a long operation process, and more expensive citric acid is used in the process. After washing, the wastewater still needs to be harmlessly treated, and it has not yet been industrialized.

[0005] CN109179358A discloses a method for preparing battery-grade iron phosphate from waste lithium iron phosphate batteries. The method can prepare anhydrous battery-grade iron phosphate by disassembling and separating the battery, alkali leaching, acid leaching, oxidation, precipitation and calcination. First, by alkali leaching followed by acid leaching and precipitation, impurities such as aluminum in lithium iron phosphate can be removed to improve the purity of iron phosphate; the lithium-rich solution is repeatedly acidified and then new filter residues are leached to increase the concentration of lithium in the solution and the recovery rate of lithium, thereby reducing the cost of lithium recovery; and the low pH value at the precipitation end point (1.0-2.5) can reduce the tendency of iron hydroxide generation, and the aging process after the precipitation reaction ends can improve the purity of iron phosphate, and the obtained iron phosphate meets the industry standards. However, the process has many operating steps, a large amount of reagents are used in the process, and the cost is high.

[0006] CN11646447A discloses a method for recovering iron phosphate from iron-phosphorus slag after lithium extraction from lithium iron phosphate battery, wherein the iron-phosphorus slag after lithium extraction from lithium iron phosphate battery is first mixed with water for slurry preparation, reacted with acid, and solid-liquid separation is performed to obtain a leachate containing iron and phosphorus ions, and then copper is removed by adding iron replacement and aluminum is removed by resin to obtain a purified solution, and a phosphorus-iron ratio is adjusted by adding iron phosphate heptahydrate or phosphoric acid to obtain a synthetic stock solution with a certain P:Fe, and hydrogen peroxide and ammonia water are added to adjust the pH to obtain an iron phosphate precursor precipitation, and a battery-grade iron phosphate precursor product is obtained after post-treatment. However, the process still produces a large amount of ammonia nitrogen wastewater, which has a certain impact on the environment.

[0007] Therefore, it is necessary to develop a method for desulfurization of iron phosphate that is efficient, economical, produces less waste after treatment, and has little impact on the environment. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for desulfurizing iron phosphate. The method can obtain iron phosphate with a low sulfur content by first calcining the iron phosphate to be desulfurized and then aging it in an acidic solution. The sulfur content in the iron phosphate after desulfurization is less than 100 ppm. The method is simple to operate and low in cost. No harmful substances are generated during the treatment process, and the method is a green and environmentally friendly treatment method.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for desulfurization of iron phosphate, which comprises the following steps:

[0011] (1) calcining and / or grinding the desulfurized iron phosphate to obtain treated iron phosphate;

[0012] (2) The treated iron phosphate is aged in water or an acidic solution to obtain desulfurized iron phosphate.

[0013] The present invention obtains anhydrous iron phosphate by calcining the iron phosphate to be desulfurized, and / or controls the particle size of the iron phosphate to be desulfurized within a specific range by means of abrasives and simultaneously realizes lattice distortion of the iron phosphate to be desulfurized, thereby exposing sulfur entrained in the lattice gaps of the crystal growth of the iron phosphate to be desulfurized, and then washes out the sulfur existing in the grain boundaries of the iron phosphate through liquid phase aging, and at the same time, the crystal structure of the iron phosphate is adjusted, thereby realizing separation of sulfur and iron phosphate to obtain desulfurized iron phosphate.

[0014] The method for desulfurization of iron phosphate of the present invention only uses calcination and / or grinding, and is combined with a water or acid solution aging step. The operation is simple, the acid solution used for aging can be recycled, no waste liquid is generated, the cost is low, and it is suitable for industrial large-scale production processes.

[0015] Preferably, the source of the ferric phosphate to be desulfurized in step (1) comprises any one of coprecipitation, crystallization, hydrothermal, sol-gel or template methods, or a combination of at least two of them, wherein typical but non-limiting combinations are a combination of coprecipitation and hydrothermal, a combination of hydrothermal and sol-gel, a combination of sol-gel and template, a combination of hydrothermal, sol-gel and template, a combination of crystallization, sol-gel and template, and the like.

[0016] As a preferred technical solution of the present invention, the sulfur content in the iron phosphate to be desulfurized is 0.01 to 8wt%, for example, it can be 0.01wt%, 0.1wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0017] Preferably, the sulfur in the ferrous phosphate to be desulfurized includes inorganic sulfur.

[0018] Preferably, the inorganic sulfur exists in the form of any one of sulfate, sulfide or elemental sulfur or a combination of at least two of them, wherein a typical but non-limiting combination is a combination of sulfate and sulfide, a combination of elemental sulfur and sulfide, etc.

[0019] Preferably, the calcination temperature in step (1) is 100°C to 900°C, for example, it can be 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C or 900°C, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0020] Preferably, the calcination time is 0.1 to 20 hours, for example, 10 minutes, 30 minutes, 60 minutes, 120 minutes, 180 minutes, 240 minutes, 720 minutes, 900 minutes or 1200 minutes, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0021] Preferably, the calcination in step (1) is carried out under a non-reducing atmosphere.

[0022] The present invention is further carried out under a non-reducing atmosphere, which can further prevent the iron phosphate from being reduced.

[0023] Preferably, the non-reducing atmosphere includes an oxidizing atmosphere and / or an inert atmosphere.

[0024] Preferably, the oxidizing atmosphere comprises oxygen and / or air.

[0025] Preferably, the inert atmosphere comprises any one of nitrogen, argon, helium or carbon dioxide, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of nitrogen and argon, a combination of helium and argon, a combination of nitrogen and helium, a combination of carbon dioxide and argon, and a combination of nitrogen and carbon dioxide.

[0026] Preferably, the grinding method in step (1) includes any one of stirred milling, ball milling, sand milling or air flow milling, or a combination of at least two of them, wherein a typical but non-limiting combination is a combination of stirred milling and ball milling, a combination of ball milling and sand milling, and a combination of sand milling and air flow milling.

[0027] Preferably, the stirred milling, ball milling or sand milling method includes dry milling or wet milling.

[0028] Preferably, the wet grinding medium comprises any one of methanol, ethanol, propanol, water, dilute hydrochloric acid, dilute sulfuric acid, dilute phosphoric acid, dilute nitric acid, dilute acetic acid or dilute citric acid, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of methanol and ethanol, a combination of ethanol and propanol, a combination of dilute hydrochloric acid and dilute sulfuric acid, a combination of dilute phosphoric acid and dilute nitric acid, and a combination of dilute citric acid and dilute nitric acid.

[0029] Preferably, the pH of the wet grinding medium is ≥ 1.0, for example, it can be 1.0, 1.2, 1.3, 1.5, 1.8, 2.0, 2.2, 2.3, 2.5, 3.0, 3.5, 5.0, 6.0 or 7.0, etc.

[0030] Preferably, the particle size D50 of the material after stirring and grinding is ≤15 μm, for example, it can be 15 μm, 14 μm, 13 μm, 12 μm, 10 μm, 8 μm or 7 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] Preferably, the particle size D50 of the material after ball milling is ≤15 μm, for example, it can be 15 μm, 14 μm, 13 μm, 12 μm, 10 μm, 8 μm or 7 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0032] Preferably, the particle size D50 of the material after sand grinding is ≤10 μm, for example, it can be 10 μm, 9 μm, 8 μm, 7 μm, 6 μm, 5 μm, 4 μm or 1 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0033] Preferably, D50 of the material after air flow milling is ≤15 μm, for example, it can be 15 μm, 14 μm, 13 μm, 12 μm, 10 μm, 8 μm or 7 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] The present invention has no special restrictions on the various process parameters of the abrasive, and any parameters that can be used for abrasives known to those skilled in the art can be used, and can also be adjusted according to the actual process.

[0035] Preferably, the wet-grinding slurry is directly aged after wet grinding, or the wet-grinding slurry is first subjected to solid-liquid separation to remove the wet grinding medium and then aged.

[0036] When the wet grinding medium contains any one of methanol, ethanol or propanol or a combination of at least two of them, it is preferred that the wet grinding slurry be subjected to solid-liquid separation to remove the medium (methanol, ethanol or propanol) before aging.

[0037] When the wet grinding medium includes any one of water, dilute hydrochloric acid, dilute sulfuric acid, dilute phosphoric acid, dilute nitric acid, dilute acetic acid or dilute citric acid, or a combination of at least two of them, the aging treatment can be performed directly, or the wet grinding medium can be removed by solid-liquid separation before aging.

[0038] Preferably, the iron phosphate to be desulfurized in step (1) is preferably calcined and ground in sequence, or preferably ground and calcined in sequence, to obtain treated iron phosphate.

[0039] The present invention further prefers to first perform calcination and then grinding, because the calcination process first converts dihydrate iron phosphate into anhydrous iron phosphate, and the particle size no longer decreases in the subsequent grinding process. The energy accumulation applied by the external force causes the lattice of the anhydrous iron phosphate to be further distorted, which is better than the subsequent aging treatment process. Transcrystalization can be carried out and the removal of intercrystalline sulfur can be achieved.

[0040] Preferably, the acidic solution in step (2) comprises any one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid or citric acid, or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of hydrochloric acid and phosphoric acid, a combination of phosphoric acid and nitric acid, a combination of phosphoric acid and acetic acid, a combination of nitric acid and citric acid, a combination of hydrochloric acid, phosphoric acid and citric acid, a combination of sulfuric acid and phosphoric acid, etc.

[0041] Preferably, the concentration of the solute in the acidic solution is 0.01 mol / L to 5 mol / L, for example, it can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L or 5 mol / L, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0042] Preferably, the liquid-to-solid ratio of the acidic solution or water to the treated ferric phosphate in step (2) is 0.5 to 100 ml: 1 g, for example, 0.5 ml: 1 g, 1 ml: 1 g, 10 ml: 1 g, 12 ml: 1 g, 15 ml: 1 g, 20 ml: 1 g, 30 ml: 1 g, 40 ml: 1 g, 50 ml: 1 g, 60 ml: 1 g, 70 ml: 1 g, 80 ml: 1 g or 100 ml: 1 g, etc., but is not limited to the listed values, and other values ​​not listed within the range are equally applicable.

[0043] Preferably, the aging temperature in step (2) is 20°C to 250°C, for example, it can be 20°C, 40°C, 60°C, 80°C, 100°C, 120°C, 130°C, 140°C, 150°C, 200°C or 250°C, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0044] Preferably, the aging time is 0.1 to 100 h, for example, 0.1 h, 0.5 h, 0.6 h, 0.8 h, 1 h, 5 h, 10 h, 15 h, 20 h, 30 h, 50 h, 60 h, 70 h, 80 h, 90 h or 100 h, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0045] Preferably, the aging in step (2) further includes calcination.

[0046] Preferably, the temperature of the calcination after aging is 100°C to 900°C, for example, it can be 100°C, 120°C, 130°C, 200°C, 250°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C or 900°C, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Preferably, the calcination time after aging is 0.1 to 20 h, for example, it can be 0.1 h, 1 h, 2 h, 4 h, 5 h, 8 h, 10 h, 12 h, 14 h, 15 h, 18 h or 20 h, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0048] Preferably, the calcination after aging in step (2) is carried out under a non-reducing atmosphere.

[0049] Preferably, the non-reducing atmosphere includes an oxidizing atmosphere and / or an inert atmosphere.

[0050] Preferably, the oxidizing atmosphere comprises oxygen and / or air.

[0051] Preferably, the inert atmosphere comprises any one of nitrogen, argon, helium or carbon dioxide or a combination of at least two thereof, wherein typical but non-limiting combinations are a combination of nitrogen and argon, a combination of argon and helium, and a combination of helium and carbon dioxide.

[0052] Preferably, washing and drying are carried out in sequence between the aging and calcining.

[0053] Preferably, the sulfur content in the desulfurized iron phosphate in step (2) is ≤100 ppm, for example, it can be 100 ppm, 95 ppm, 90 ppm, 80 ppm, 60 ppm, 50 ppm, 40 ppm, 30 ppm or 20 ppm, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0054] In the present invention, ppm is calculated based on mass.

[0055] Preferably, the desulfurized iron phosphate is iron phosphate for batteries.

[0056] The desulfurization method of iron phosphate provided by the present invention can make the sulfur content in the iron phosphate after desulfurization ≤0.01wt%, that is, below 100ppm, which can better meet the requirements of iron phosphate for batteries.

[0057] Preferably, the method comprises the following steps:

[0058] (1) The desulfurized iron phosphate with a sulfur content of 0.01 to 8 wt% is calcined at 100° C. to 900° C. for 0.1 to 20 h in a non-reducing atmosphere; or the desulfurized iron phosphate with a sulfur content of 0.01 to 8 wt% is ground to a material D50 ≤ 15 μm; or the desulfurized iron phosphate with a sulfur content of 0.01 to 8 wt% is first calcined at 100° C. to 900° C. for 0.1 to 20 h in a non-reducing atmosphere, and then ground to a material D50 ≤ 15 μm; or the desulfurized iron phosphate with a sulfur content of 0.01 to 8 wt% is first ground to a material D50 ≤ 15 μm, and then calcined at 100° C. to 900° C. for 0.1 to 20 h in a non-reducing atmosphere to obtain treated iron phosphate;

[0059] (2) The treated iron phosphate is aged in an acidic solution at 20°C to 250°C and with a solute concentration of 0.05 mol / L to 5 mol / L for 0.1 to 100 h, or in water for 0.1 to 100 h, wherein the liquid-to-solid ratio of the acidic solution or water to the treated iron phosphate is 0.5 to 100 ml:1 g. The aged solid phase is washed and dried, and then calcined at 100°C to 900°C in a non-reducing atmosphere for 0.1 to 20 h to obtain desulfurized iron phosphate.

[0060] The present invention has no special limitation on the washing in the above process. Any device and method known to those skilled in the art for washing may be used, and may also be adjusted according to the actual process, such as rinsing, immersion or ultrasonic washing, etc., or a combination of different methods.

[0061] The present invention has no particular limitation on the drying in the above process. Any drying device and method known to those skilled in the art can be used, and can also be adjusted according to the actual process, for example, it can be air drying, vacuum drying, oven drying or freeze drying, or a combination of different methods.

[0062] Compared with the prior art, the present invention has at least the following beneficial effects:

[0063] (1) The method for desulfurization of iron phosphate provided by the present invention sequentially performs calcination and / or grinding of the iron phosphate to be desulfurized, and an impurity removal process of acid aging, without generating solid or liquid waste, having little impact on the environment, and without significant secondary processing costs, thereby saving resources;

[0064] (2) The method for desulfurization of iron phosphate provided by the present invention sequentially performs calcination and / or grinding on the iron phosphate to be desulfurized, and an impurity removal process of acid aging, so that the sulfur content in the iron phosphate after desulfurization is ≤100ppm, and can reach within 70ppm under preferred conditions, which can better meet the requirements of iron phosphate for batteries;

[0065] (3) The method for desulfurization of ferric phosphate provided by the present invention is easy to operate and has a fast desulfurization speed, and there is no need to wash the crude ferric phosphate product with water multiple times. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a process flow chart of iron phosphate desulfurization in a specific implementation manner of the present invention. DETAILED DESCRIPTION

[0067] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0068] The present invention is further described in detail below. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0069] like Figure 1 As shown, the present invention provides a specific implementation mode, specifically, the method comprises the following steps:

[0070] (1) The desulfurized iron phosphate is calcined under a non-reducing atmosphere; or the desulfurized iron phosphate is ground to a material D50≤15μm; or the desulfurized iron phosphate is first calcined under a non-reducing atmosphere to obtain calcined iron phosphate, and then ground to a material D50≤15μm; or the desulfurized iron phosphate is first ground to a material D50≤15μm to obtain ground iron phosphate, and then calcined under a non-reducing atmosphere to obtain treated iron phosphate;

[0071] (2) The treated iron phosphate is aged in an acidic solution at 20°C to 100°C and with a solute concentration of 0.1 mol / L to 5 mol / L for 0.1 to 30 h, with a liquid-to-solid ratio of the acidic solution to the treated iron phosphate of 1 to 100 ml:1 g. The aged solid phase is washed and dried, and then selectively calcined at 100°C to 900°C in a non-reducing atmosphere for 0.1 to 20 h (indicated by a dotted frame) to obtain desulfurized iron phosphate.

[0072] Example 1

[0073] This embodiment provides a method for desulfurization of iron phosphate, the method comprising the following steps:

[0074] (1) calcining the desulfurized iron phosphate with a sulfur content of 0.01 wt% at 200° C. for 0.1 h in an oxidizing atmosphere to obtain treated iron phosphate;

[0075] (2) The treated iron phosphate is aged for 0.5 h in an acidic solution of a mixture of hydrochloric acid and phosphoric acid at a concentration of 0.1 mol / L at 20° C., wherein the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 1 ml:1 g. The aged solid phase is washed and dried to obtain desulfurized iron phosphate.

[0076] Example 2

[0077] This embodiment provides a method for desulfurization of iron phosphate, the method comprising the following steps:

[0078] (1) calcining the desulfurized iron phosphate with a sulfur content of 8 wt % at 500° C. for 20 h in an argon atmosphere to obtain treated iron phosphate;

[0079] (2) The treated iron phosphate is aged for 30 hours in an acidic solution of a mixture of phosphoric acid and citric acid at a concentration of 5 mol / L at 100° C., wherein the liquid-solid ratio of the acidic solution to the treated iron phosphate is 100 ml:1 g. The aged solid phase is washed and dried to obtain desulfurized iron phosphate.

[0080] Example 3

[0081] This embodiment provides a method for desulfurization of iron phosphate, the method comprising the following steps:

[0082] (1) calcining the desulfurized iron phosphate with a sulfur content of 4 wt% at 800° C. for 5 h in a nitrogen atmosphere to obtain treated iron phosphate;

[0083] (2) The treated iron phosphate is aged in an acidic solution of a mixture of hydrochloric acid and acetic acid at a concentration of 2.5 mol / L at 80° C. for 10 hours, wherein the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 50 ml:1 g. The aged solid phase is washed and dried to obtain desulfurized iron phosphate.

[0084] Example 4

[0085] This embodiment provides a method for desulfurization of iron phosphate, the method comprising the following steps:

[0086] (1) calcining the desulfurized iron phosphate with a sulfur content of 6 wt % at 400° C. for 15 h in an oxidizing atmosphere to obtain treated iron phosphate;

[0087] (2) The treated iron phosphate is aged for 20 hours in an acidic solution of a mixture of nitric acid and acetic acid at a concentration of 4 mol / L at 60° C., wherein the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 20 ml:1 g. The aged solid phase is washed and dried to obtain desulfurized iron phosphate.

[0088] Example 5

[0089] This embodiment provides a method for desulfurization of iron phosphate, which differs from the method in Embodiment 1 only in that the calcination temperature is 1000°C.

[0090] Example 6

[0091] This embodiment provides a method for desulfurization of iron phosphate, which differs from that of Embodiment 1 only in that the concentration of the solute in the acidic solution is 7 mol / L.

[0092] Example 7

[0093] This embodiment provides a method for desulfurization of iron phosphate, which differs from the method in Embodiment 1 only in that the acidic solution is a 0.1 mol / L hydrochloric acid solution.

[0094] Example 8

[0095] This embodiment provides a method for desulfurization of iron phosphate, which differs from the method in Embodiment 1 only in that the acidic solution is a 0.1 mol / L phosphoric acid solution.

[0096] Example 9

[0097] This embodiment provides a method for desulfurization of iron phosphate, which differs from that of embodiment 1 only in that:

[0098] The calcination in step (1) is replaced by abrasives, specifically, the desulfurized iron phosphate with a sulfur content of 0.01wt% is ball-milled, the ball-to-material mass ratio is 15:1, the time is 120min, the rotation speed is 500rpm, and the particle size D50 of the material after ball milling is 3μm.

[0099] Example 10

[0100] This embodiment provides a method for desulfurization of iron phosphate, which differs from that of embodiment 1 only in that:

[0101] After the calcination in step (1), abrasive is added. Specifically, the desulfurized iron phosphate with a sulfur content of 0.01 wt% is calcined at 200° C. for 0.1 h in an oxidizing atmosphere to obtain calcined iron phosphate, which is then jet milled. The grinding gas volume of the jet mill is 120 m 3 / min, the classification power is 20kw, the time is 60min, and the treated iron phosphate with a material particle size D50 of 1μm is obtained.

[0102] Embodiment 11

[0103] This embodiment provides a method for desulfurization of iron phosphate, which differs from that of embodiment 1 only in that:

[0104] Before the calcination in step (1), abrasives are added, specifically, the desulfurized iron phosphate with a sulfur content of 0.01 wt% is subjected to a jet mill, and the grinding gas volume of the jet mill is 120 m 3 / min, the classification power is 20kw, the time is 60min, and the ground iron phosphate with a material particle size D50 of 1μm is obtained, which is then calcined at 200℃ for 0.1h in an oxidizing atmosphere to obtain the treated iron phosphate.

[0105] Example 12

[0106] This embodiment provides a method for desulfurization of iron phosphate, which differs from that of embodiment 10 only in that:

[0107] A calcination step is added after aging, washing and drying in step (2), and step (2) is specifically as follows:

[0108] The treated iron phosphate is aged for 0.5 h in an acidic solution of a mixture of hydrochloric acid and phosphoric acid at a concentration of 0.1 mol / L at 20° C., the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 1 ml:1 g, the aged solid phase is washed and dried, and then the solid phase is calcined at 500° C. for 20 h in a non-reducing atmosphere to obtain the desulfurized iron phosphate.

[0109] Embodiment 13

[0110] This embodiment provides a method for desulfurization of iron phosphate, which differs from that of embodiment 11 only in that:

[0111] A calcination step is added after aging, washing and drying in step (2), and step (2) is specifically as follows:

[0112] The treated iron phosphate is aged for 0.5 h in an acidic solution of a mixture of hydrochloric acid and phosphoric acid at a concentration of 0.1 mol / L at 20° C., the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 1 ml:1 g, the aged solid phase is washed and dried, and then the solid phase is calcined at 500° C. for 20 h in a non-reducing atmosphere to obtain the desulfurized iron phosphate.

[0113] Embodiment 14

[0114] This embodiment provides a method for desulfurization of iron phosphate, the method comprising the following steps:

[0115] (1) The desulfurized iron phosphate with a sulfur content of 0.01 wt% is calcined at 200° C. for 0.1 h in an oxidizing atmosphere to obtain calcined iron phosphate, and then sand-milled, with a ball-to-material mass ratio of 10:1, a time of 240 min, a rotation speed of 3000 rpm, and wet milling. The wet milling medium is a combination of methanol and ethanol in a ratio of 1:1. The wet milled slurry is filtered to obtain treated iron phosphate with a particle size D50 of 2 μm;

[0116] (2) The treated iron phosphate is aged in water at 35°C for 1 hour, and the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 2 ml:1 g. The aged solid phase is washed and dried, and then the solid phase is calcined at 100°C for 20 hours in a non-reducing atmosphere to obtain desulfurized iron phosphate.

[0117] Embodiment 15

[0118] This embodiment provides a method for desulfurization of iron phosphate, the method comprising the following steps:

[0119] (1) The desulfurized iron phosphate with a sulfur content of 0.01 wt% was first subjected to a stirred mill with a ball-to-material mass ratio of 25:1, a time of 240 min, a rotation speed of 45 rpm, and a wet milling process. The wet milling medium was dilute phosphoric acid with a pH of 4.5 to obtain a milled iron phosphate with a particle size D50 of 4 μm. The milled iron phosphate was then calcined at 350° C. for 8 h in an oxidizing atmosphere to obtain a wet-milled slurry containing the treated iron phosphate.

[0120] (2) The wet grinding slurry containing the treated iron phosphate is aged for 1.2 h in an acidic solution of a mixture of hydrochloric acid and phosphoric acid at a concentration of 0.2 mol / L at 40°C, wherein the liquid-to-solid ratio of the acidic solution to the treated iron phosphate is 1.5 ml:1 g. The aged solid phase is washed and dried, and then the solid phase is calcined at 700°C for 3 h in a non-reducing atmosphere to obtain desulfurized iron phosphate.

[0121] Comparative Example 1

[0122] This comparative example provides a method for desulfurizing iron phosphate, which differs from Example 1 only in that the iron phosphate to be desulfurized is directly aged in an acid solution without calcination, and the process parameters are the same as those in Example 1.

[0123] Comparative Example 2

[0124] This comparative example provides a method for desulfurization of iron phosphate, which differs from Example 1 only in that only calcination is performed and the aging step in step (2) is not performed.

[0125] Test method: The sulfur content in the desulfurized iron phosphate was tested using a carbon-sulfur analyzer. The results are shown in Table 1.

[0126] Table 1

[0127]

[0128]

[0129] From Table 1, we can see the following points:

[0130] (1) It can be seen from Examples 1 to 15 that the method for desulfurization of iron phosphate provided by the present invention can further remove trace sulfur in iron phosphate by a simple method, wherein the sulfur content of iron phosphate can be removed to less than 100 ppm;

[0131] (2) From Example 1 and Example 5, it can be seen that the higher the calcination temperature is, the better the desulfurization effect is. The present invention significantly improves the desulfurization effect by controlling the desulfurization temperature within a specific temperature range.

[0132] (3) Combining Example 1 and Example 6, it can be seen that the concentration of the solute in the acidic solution of Example 1 is a mixed acidic solution of hydrochloric acid and phosphoric acid of 0.1 mol / L. Compared with the mixed solution with a high concentration of 7 mol / L in Example 6, the sulfur content in the iron phosphate after desulfurization in Example 1 is only 90 ppm, and although the sulfur content in Example 6 is only 88 ppm, the recovery rate of the iron phosphate after high concentration acid treatment in Example 6 is significantly reduced, which shows that the present invention can simultaneously ensure the desulfurization effect and the recovery rate by optimizing the concentration of the acidic solution;

[0133] (4) Combining Example 1 and Examples 10-11, it can be seen that Example 1 only adopts the step of aging after calcination. Compared with Example 10 adopting calcination first and then grinding, and Example 11 adopting grinding first and then calcination, under the same process parameters, the sulfur content in the ferric phosphate product of Example 10 is only 60ppm, and that of Example 11 is only 80ppm, while that of Example 1 is as high as 90ppm. This shows that the preferred pretreatment method of the present invention combining calcination and grinding can reduce the sulfur content in the product, and the further preferred method of calcination first and then grinding can better reduce the sulfur content in the ferric phosphate product;

[0134] (5) Based on Examples 10-11 and Examples 12-13, it can be seen that the present invention further adds a calcination step after aging, which can further desulfurize, and the sulfur content in the iron phosphate after desulfurization is only within 70 ppm;

[0135] (6) It can be seen from Example 1 and Comparative Examples 1-2 that the pretreatment and aging steps in the present invention are indispensable, and the interaction between the two can achieve a better desulfurization effect.

[0136] The present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the components selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for desulfurization of iron phosphate, characterized in that: The method comprises the following steps: (1) the iron phosphate to be desulfurized is subjected to calcination and grinding or grinding and calcination in sequence to achieve lattice distortion of the iron phosphate to be desulfurized, thereby obtaining treated iron phosphate; (2) aging the treated ferric phosphate in water or an acidic solution to obtain desulfurized ferric phosphate; The aging in step (2) further includes calcination.

2. The method according to claim 1, characterized in that The source of the ferric phosphate to be desulfurized in step (1) includes any one of coprecipitation method, crystallization method, hydrothermal method, sol-gel method or template method, or a combination of at least two thereof.

3. The method according to claim 1, characterized in that The sulfur content in the iron phosphate to be desulfurized is 0.01-8wt%.

4. The method according to claim 1, characterized in that: The sulfur in the iron phosphate to be desulfurized includes inorganic sulfur.

5. The method according to claim 1 or 2, characterized in that: The calcination temperature in step (1) is 100°C to 900°C.

6. The method according to claim 1, characterized in that The calcination time is 0.1 to 20 hours.

7. The method according to claim 1, characterized in that The calcination is performed under a non-reducing atmosphere.

8. The method according to claim 7, characterized in that The non-reducing atmosphere includes an oxidizing atmosphere and / or an inert atmosphere.

9. The method according to claim 8, characterized in that The oxidizing atmosphere includes oxygen and / or air.

10. The method according to claim 8, characterized in that The inert atmosphere includes any one of nitrogen, argon, helium or carbon dioxide, or a combination of at least two of them.

11. The method according to any one of claims 1 to 3, characterized in that: The grinding method in step (1) includes any one of stirred milling, ball milling, sand milling or air flow milling, or a combination of at least two of them.

12. The method according to claim 11, characterized in that The stirring milling, ball milling or sand milling method includes dry milling or wet milling.

13. The method according to claim 12, characterized in that The wet grinding medium includes any one of methanol, ethanol, propanol, water, dilute hydrochloric acid, dilute sulfuric acid, dilute phosphoric acid, dilute nitric acid, dilute acetic acid or dilute citric acid, or a combination of at least two thereof.

14. The method according to claim 12, characterized in that The pH of the wet milling medium is ≥ 1.

0.

15. The method according to claim 11, characterized in that The particle size D50 of the material after stirring milling is ≤15 μm.

16. The method according to claim 11, characterized in that The particle size D50 of the material after ball milling is ≤15 μm.

17. The method according to claim 11, characterized in that The particle size D50 of the material after sand grinding is ≤10 μm.

18. The method according to claim 11, characterized in that The D50 of the material after the jet mill is ≤15 μm.

19. The method according to claim 12, characterized in that The wet-grinding slurry is directly aged after wet grinding, or the wet-grinding slurry is first subjected to solid-liquid separation to remove the medium and then aged.

20. The method according to claim 1, characterized in that The acidic solution in step (2) includes any one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid or citric acid, or a combination of at least two thereof.

21. The method according to claim 1, characterized in that The concentration of the solute in the acidic solution is 0.01 mol / L to 5 mol / L.

22. The method according to claim 1, characterized in that The liquid-to-solid ratio of the acidic solution or water to the treated ferric phosphate is 0.5-100 ml:1 g.

23. The method according to claim 1, characterized in that The aging temperature in step (2) is 20°C to 250°C.

24. The method according to claim 1, characterized in that The aging time is 0.1 to 100 hours.

25. The method according to claim 1, characterized in that The temperature of the calcination after aging is 100°C to 900°C.

26. The method according to claim 1, characterized in that The calcination time after aging is 0.1 to 20 hours.

27. The method according to claim 1, characterized in that The calcination after aging in step (2) is carried out under a non-reducing atmosphere.

28. The method according to claim 27, characterized in that The non-reducing atmosphere includes an oxidizing atmosphere and / or an inert atmosphere.

29. The method according to claim 28, characterized in that The oxidizing atmosphere includes oxygen and / or air.

30. The method according to claim 28, characterized in that The inert atmosphere includes any one of nitrogen, argon, helium or carbon dioxide, or a combination of at least two of them.

31. The method according to claim 1, characterized in that The method comprises the following steps: (1) The desulfurized iron phosphate with a sulfur content of 0.01 to 8 wt% is first calcined at 100° C. to 900° C. for 0.1 to 20 h in a non-reducing atmosphere, and then ground to a material D50 ≤ 15 μm; or the desulfurized iron phosphate with a sulfur content of 0.01 to 8 wt% is first ground to a material D50 ≤ 15 μm, and then calcined at 100° C. to 900° C. for 0.1 to 20 h in a non-reducing atmosphere to obtain treated iron phosphate; (2) The treated iron phosphate is aged in an acidic solution at 20°C to 250°C and with a solute concentration of 0.05 mol / L to 5 mol / L for 0.1 to 100 h, or in water for 0.1 to 100 h, wherein the liquid-to-solid ratio of the acidic solution or water to the treated iron phosphate is 0.5 to 100 ml:1 g. The aged solid phase is washed and dried, and then calcined at 100°C to 900°C in a non-reducing atmosphere for 0.1 to 20 h to obtain desulfurized iron phosphate.

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