Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/01—Treating phosphate ores or other raw phosphate materials to obtain phosphorus or phosphorus compounds
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/16—Oxyacids of phosphorus; Salts thereof
  • C01B25/26—Phosphates
  • C01B25/37—Phosphates of heavy metals
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B5/00—Treatment of  metallurgical  slag ; Artificial stone from molten  metallurgical  slag 
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
  • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
  • C22B3/44—Treatment or purification of solutions, e.g. obtained by leaching by chemical processes
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
  • C22B7/04—Working-up slag

Definitions

• the present invention relates to a method for producing iron phosphate.
• phosphorus While phosphorus is used in a wide range of fields, including agriculture, food, medicine, and industry, it is a resource that is unevenly distributed around the world, and is only produced in China, the United States, Morocco, and other countries.
• the phosphorus resources circulating in Japan are phosphorus products such as yellow phosphorus and crude phosphoric acid, and the raw material for these, phosphate rock, and the entire amount is imported.
• the phosphorus concentration of molten pig iron tapped from a blast furnace is about 0.1% by mass, and the phosphorus concentration in steelmaking slag produced by subjecting this molten pig iron to conventional treatments (dephosphorization and decarburization refining) is as low as about 5% by mass at most, calculated as P2O5 .
• steelmaking slag has been used as a civil engineering material such as roadbed material, and the phosphorus in the steelmaking slag has not been recovered.
• the price of phosphorus resources has been rising sharply due to factors such as the depletion of phosphate rock and the monopolization of phosphate rock by China, the United States, and other countries.
• the phosphorus in steelmaking slag generated during steel smelting is being reconsidered as a valuable phosphorus resource.
• Patent Document 1 discloses a method for producing (recovering) phosphorus compounds using dephosphorized slag, a type of steelmaking slag, as a starting material.
• iron phosphate As a phosphorus compound produced (recovered) from a starting material such as steelmaking slag, for example, iron phosphate is desirable.
• the method described in Patent Document 1 involves many treatments such as cation exchange, and therefore requires a long time and is cumbersome to obtain the target phosphorus compound.
• the present invention was made in consideration of the above points, and aims to provide a method for producing iron phosphate that allows iron phosphate to be obtained easily.
• a method for producing iron phosphate comprising: a precipitation step of adding an alkali to a phosphorus-containing liquid to obtain a precipitate; a dissolution step of dissolving the precipitate with an acid to obtain a phosphoric acid liquid; and a re-precipitation step of adding an alkali to the phosphoric acid liquid to obtain a precipitate again, wherein in the re-precipitation step, the pH of the phosphoric acid liquid is adjusted to less than 4.0.
• the present invention provides a method for producing iron phosphate that allows iron phosphate to be obtained easily.
• 1 is a flowchart showing the flow of a method for producing iron phosphate according to the present embodiment.
• 1 is a graph showing the relationship between the pH of a phosphoric acid solution and the transfer rate of each element from the phosphoric acid solution to a precipitate.
• 1 is a graph showing the relationship between the pH of a phosphoric acid solution and the transfer rate of each element from the phosphoric acid solution to a precipitate.
• FIG. 1 is a flowchart showing the flow of the method for producing iron phosphate according to this embodiment.
• the method for producing iron phosphate according to the present embodiment is generally a method for recovering a phosphorus compound containing iron phosphate (a calcined product obtained by calcining a precipitate described below) from a phosphorus-containing liquid.
• the method for producing iron phosphate according to this embodiment includes a precipitation step (S1), a dissolution step (S2), and a re-precipitation step (S3) in this order.
• the method for producing iron phosphate according to the present embodiment may include a phosphorus-containing liquid preparation step (S0) prior to the precipitation step (S1).
• S0 phosphorus-containing liquid preparation step
• a phosphorus-containing liquid is prepared.
• components contained in the starting material are leached in acid to obtain an acidic phosphorus-containing solution.
• the starting material is added to the acid, stirred, and then filtered. This yields a residue (I) and a leachate (A).
• the obtained leachate (A) is the phosphorus-containing solution.
• the acid used in the phosphorus-containing liquid preparation step (S0) is not particularly limited, but may be, for example, at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and citric acid, with nitric acid or hydrochloric acid being preferred, and nitric acid being more preferred.
• the concentration of the acid is not particularly limited, but is preferably 0.1 to 1.5M, more preferably 0.3 to 0.8M.
• the starting material is a phosphorus-containing compound (including a mixture of a phosphorus-containing compound and other compounds), and contains, for example, CaO, P 2 O 5 , Al 2 O 3 and Fe t O. However, considering that iron phosphate will ultimately be recovered, it is preferable that the starting material contains at least P 2 O 5 and Fe t O. Specific examples of such starting materials (phosphorus-containing compounds) include steelmaking slag such as dephosphorized slag and decarbonized slag; sewage sludge; and phosphoric acid-containing waste liquid. In addition, when the starting material is, for example, steelmaking slag, its particle size is not particularly limited.
• the pH of the acid used in the phosphorus-containing liquid preparation step (S0) is preferably 1.0 or less, more preferably 0.5 or less.
• the ratio of the starting material to the acid is not particularly limited as long as the pH of the acid used satisfies the above range. However, if the ratio of the starting material is high, the amount of Si eluted increases accordingly, and the resulting phosphorus-containing liquid may gel. Therefore, it is preferable to set this ratio by assessing the conditions of each step described below.
• the starting material is an acidic solution, it is not necessary to add the starting material to an acid, and the starting material may be used as it is as the phosphorus-containing liquid.
• the phosphorus-containing liquid prepared in the phosphorus-containing liquid preparation step (S0) preferably contains at least the elements phosphorus (P) and iron (Fe).
• the phosphorus-containing liquid may further contain elements such as calcium (Ca), aluminum (Al), silicon (Si), magnesium (Mg), and manganese (Mn).
• the phosphorus-containing liquid prepared in the phosphorus-containing liquid preparation step (S0) is acidic.
• the pH of the phosphorus-containing liquid is preferably less than 4.0, more preferably less than 3.0, and even more preferably less than 1.5.
• Precipitation Step (S1) an alkali is added to an acidic phosphorus-containing liquid to obtain a precipitate. Specifically, for example, an alkali is added to a phosphorus-containing liquid, followed by filtration, thereby obtaining a filtrate (B) and a precipitate (II). The precipitate (II) is a precipitate.
• the leachate (A) obtained in the phosphorus-containing liquid preparation step (S0) is used, but a liquid obtained in another step may also be used.
• the alkali used in the precipitation step (S1) is preferably aqueous ammonia (NH 4 OH) because it does not contain unnecessary cations.
• the concentration of the aqueous ammonia is not particularly limited, but is preferably 20 to 40% by mass, more preferably 25 to 35% by mass.
• the alkali is not limited to ammonia water; sodium hydroxide, potassium hydroxide, etc. can also be used.
• the pH of the phosphorus-containing liquid after the addition of alkali is not particularly limited as long as it is a pH at which a precipitate is formed, but it is preferably in the same range as the pH of the phosphoric acid liquid after the addition of alkali in the re-precipitation step (S3) described below (e.g., less than pH 4.0).
• the precipitate (II) obtained in the precipitation step (S1) is dissolved using an acid, thereby obtaining a phosphoric acid solution.
• the precipitate is added to an acid, stirred, and then filtered to obtain a filtrate (C) and a residue (III).
• the filtrate (C) is a phosphoric acid solution.
• the acid used in the dissolution step (S2) may be, for example, at least one selected from the group consisting of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and citric acid. Nitric acid or hydrochloric acid is preferred, and nitric acid is more preferred.
• the pH of the acid used in the dissolution step (S2) is preferably less than 4.0, more preferably less than 3.0, and even more preferably less than 1.5.
• this is not a limitation when there are priorities over purity, such as reducing the amount of waste liquid, as described below.
• the pH of the phosphoric acid solution obtained in the dissolution step (S2) is also preferably within the above range (e.g., less than 4.0).
• the types of elements contained in the phosphoric acid solution obtained in the dissolution step (S2) are similar to the types of elements contained in the phosphorus-containing solution described above.
• ⁇ Reprecipitation generation step (S3)> In the re-precipitation step (S3), an alkali is added to the phosphoric acid solution to obtain a precipitate again. Specifically, for example, an alkali is added to the phosphoric acid solution, and then the solution is filtered. This yields a filtrate (D) and a precipitate (IV). The precipitate (IV) is the precipitate.
• the alkali used in the reprecipitation step (S3) is preferably the same as that used in the precipitation step (S1).
• the pH of the phosphoric acid solution is adjusted when alkali is added to the phosphoric acid solution.
• FIGS. 2 and 3 are graphs showing the relationship between the pH of the phosphoric acid solution and the transfer rate of each element from the phosphoric acid solution to the precipitate.
• the migration rate of element A is calculated to be 80% by mass.
• the migration rates shown in Figures 2 and 3 are normalized and therefore unitless.
• the element concentrations in the precipitates that are formed vary depending on the pH of the phosphoric acid solution at the time the precipitates are formed. For example, the lower the pH, the less Al and Si are transferred to precipitates. Furthermore, when the pH is high, the rate at which P migrates to the precipitate decreases.
• the pH of the phosphoric acid solution is adjusted to a low value. That is, even after adding alkali to the phosphoric acid solution, the pH of the phosphoric acid solution is prevented from rising too much (the pH of the phosphoric acid solution is maintained at a low value), thereby increasing the purity of iron phosphate in the precipitate (hereinafter simply referred to as "purity").
• the purity means the content of iron phosphate in the fired product (phosphorus compound) obtained by firing the precipitate.
• the pH of the phosphoric acid solution after the addition of alkali is less than 4.0, preferably 3.5 or less, more preferably 3.0 or less, and even more preferably 2.5 or less. In this case, it is preferable to adjust the pH of the phosphoric acid solution so that the purity is 90% by mass or more.
• the pH adjustment of the phosphoric acid solution to have a purity of 90% by mass or more is carried out, for example, by the following procedure.
• (1) Add alkali little by little to the phosphoric acid solution produced in the dissolution step (S2).
• the amount of alkali to be added may be determined by trial and error.
• equilibrium calculation software such as "PHREEQC” may be used to simulate the addition of alkali and perform an analysis to change the pH, thereby determining the amount of alkali to be added that will result in a pH range in which iron phosphate is produced.
• PPHREEQC equilibrium calculation software
• the production of iron phosphate is terminated due to the purity being unsatisfactory, and measures such as reducing the amount of alkali added (increasing the oxidation-reduction potential) are taken, and the production of iron phosphate is restarted from the beginning.
• the dissolution step (S2) and the reprecipitation step (S3) may be considered as one cycle, and multiple cycles may be repeated to increase the purity.
• the pH of the phosphoric acid solution obtained in the dissolving step (S2) described above (hereinafter referred to as “phosphoric acid solution (S2)" for convenience) is, for example, less than 4.0.
• the pH of the phosphoric acid solution after the addition of alkali in the reprecipitation step (S3) (for convenience, referred to as “phosphoric acid solution (S3)) is also less than 4.0.
• the two do not overlap. That is, even if the pH of the phosphoric acid solution (S2) and the pH of the phosphoric acid solution (S3) are both less than 4.0, the relationship pH of the phosphoric acid solution (S2) ⁇ pH of the phosphoric acid solution (S3) is satisfied.
• the phosphoric acid solution may contain insufficient Fe and P, making it impossible to obtain the desired purity.
• additional raw materials may be added in the reprecipitation step (S3).
• Fe when Fe is insufficient, iron nitrate or the like may be added as an additional raw material.
• the method for producing iron phosphate according to the present embodiment preferably further includes a firing step (S4) after the re-precipitation step (S3).
• the precipitate obtained in the reprecipitation step (S3) is a precursor of the final product (a phosphorus compound containing iron phosphate).
• the firing temperature is preferably 500° C. or higher, more preferably 570° C. or higher, and even more preferably 650° C. or higher, from the viewpoint of crystallizing the resulting fired product (phosphorus compound).
• the firing temperature is preferably 900°C or lower, more preferably 830°C or lower, and even more preferably 750°C or lower.
• the method for producing iron phosphate according to the present embodiment may further include a determination step (S5) after the re-precipitation step (S3).
• the determination step (S5) it is determined whether the purity of iron phosphate in the precipitate obtained in the re-precipitation step (S3) is equal to or greater than a threshold value.
• the precipitate obtained in the reprecipitation forming step (S3) is calcined to obtain a calcined product (phosphorus compound) (see the calcination step (S4)).
• an X-ray diffraction (XRD) pattern of the obtained fired product (phosphorus compound) is obtained, and the type of phosphorus compound contained in the fired product is identified, thereby determining whether or not the fired product contains iron phosphate. If the fired product is determined to contain iron phosphate, the fired product is then subjected to XRF (X-ray fluorescence) analysis to detect and quantify various elements (including Fe and P). Note that oxygen is not usually detected in XRF analysis. The ratio (unit: mass %) of the total mass of Fe and P to the total mass of all elements detected by XRF analysis is calculated as the content (i.e., purity) of iron phosphate in the fired product (phosphorus compound).
• a threshold value for example, 90% by mass.
• the subject making the determination may be an operator who operates the various measurement devices described above, or may be a device such as a personal computer (PC) to which the various devices are connected. If the purity is equal to or greater than the threshold, the above series of steps is terminated. On the other hand, if the purity is below the threshold, the above-mentioned dissolution step (S2) and re-precipitate generation step (S3) may be considered as one cycle, and multiple cycles may be repeated until the purity reaches or exceeds the threshold.
• S2 dissolution step
• S3 re-precipitate generation step
• the purity threshold is preferably 80% by mass or more, and more preferably 85% by mass or more.
• the threshold purity of iron phosphate is preferably 99.8% by mass or less, and more preferably 95% by mass or less.
• a specific example of the threshold value of the purity of iron phosphate is 90 mass %, but this can be changed as appropriate from the above-mentioned viewpoint.
• a calcined product (phosphorus compound) having a high content of iron phosphate is obtained.
• no treatment such as cation exchange is required, so iron phosphate can be obtained easily.
• the method for producing iron phosphate according to the present embodiment may further include a preliminary determination step (S6) after the phosphorus-containing liquid preparation step (S0) and before the precipitation step (S1).
• a preliminary determination step (S6) before the precipitation step (S1), it is determined whether the contents of phosphorus (P) and iron (Fe) in the phosphorus-containing liquid are equal to or greater than threshold values.
• the preliminary determination step (S6) first, the content of each element in the phosphorus-containing liquid is measured using an ICP optical emission spectrometer, and then it is determined whether the content (total content) of P and Fe in the phosphorus-containing liquid is equal to or greater than a threshold value (e.g., 15% by mass).
• a threshold value e.g. 15% by mass.
• the subject making the determination may be an operator who operates the various measurement devices described above, or may be a device such as a personal computer (PC) to which the various devices are connected.
• the purity of the iron phosphate in the precipitate obtained through the subsequent precipitation step (S1), dissolution step (S2) and reprecipitation step (S3) is expected to be low. Therefore, when the P and Fe contents in the phosphorus-containing liquid are less than the threshold values, the dissolving step (S2) and the re-precipitation generating step (S3) are considered as one cycle, and this cycle is repeated at least twice. The number of repetitions is appropriately set depending on the P and Fe contents in the phosphorus-containing liquid. If the P and Fe contents in the phosphorus-containing liquid are less than the threshold values, there is no need to perform the determination step (S5) after the first re-precipitation generating step (S3).
• the P and Fe contents in the phosphorus-containing liquid are equal to or greater than the threshold (or if they are less than the threshold but the cycle of the dissolution step (S2) and the re-precipitation step (S3) has been repeated at least twice), it is preferable to carry out the determination step (S5) after the re-precipitation step (S3) to determine whether the purity of the iron phosphate in the precipitate is equal to or greater than the threshold.
• the threshold value for the total content of P and Fe in the phosphorus-containing liquid is, for example, 15 mass %, but may vary slightly depending on the other components in the phosphorus-containing liquid. Therefore, the production of iron phosphate may be repeated, and the threshold value may be adjusted as appropriate during the process based on the total content of P and Fe in the phosphorus-containing liquid and the determination result in the determination step (S5). That is, when iron phosphate is repeatedly produced after a certain threshold is set, if the purity is frequently determined to be less than the threshold in the first determination step (S5) in each production, the threshold may be raised. In this case, it is preferable that the higher the threshold, the closer the Fe/P ratio is to 1. Conversely, if the purity is frequently determined to be significantly in excess of the threshold value in the first determination step (S5) in each production, the threshold value may be lowered.
• Examples 1 to 7 First, in the phosphorus-containing liquid preparation step (S0), steelmaking slag as a starting material was added to nitric acid (concentration: 0.5 M) and then stirred for 0.4 hours to obtain a phosphorus-containing liquid (pH: 0.5). The P and Fe contents in the obtained phosphorus-containing liquid were equal to or greater than the threshold value (15% by mass). Next, in the precipitation step (S1), ammonia water (concentration: 28% by mass) as an alkali was added to the phosphorus-containing liquid while stirring at 200 rpm. The pH of the phosphorus-containing liquid after the alkali addition is shown in Table 1 below. Thus, a precipitate was obtained.
• the precipitate was added to nitric acid (concentration: 0.5 M) and stirred for 0.5 hours to obtain a phosphoric acid solution.
• the pH of the obtained phosphoric acid solution is shown in Table 1 below.
• ammonia water concentration: 28% by mass
• the pH of the phosphoric acid solution after the alkali addition is shown in Table 1 below. This resulted in a precipitate.
• the precipitate obtained in the reprecipitation step (S3) was fired at 700°C to obtain a crystallized fired product.
• the XRD pattern of the obtained fired product (phosphorus compound) was obtained to identify the type of phosphorus compound contained in the fired product.
• “Product Phase” column of Table 1 below "A” is entered when iron phosphate was contained as the phosphorus compound, and "B” is entered when, in addition to iron phosphate, other phosphorus compounds or other phases including an amorphous halo peak were contained.
• the obtained fired product (phosphorus compound) was subjected to XRF analysis to determine the iron phosphate content (i.e., purity) in the fired product (phosphorus compound) according to the method described above.
• the results are shown in Table 1 below.
• Example 8 to 9 ⁇ Examples 8 to 9>
• the precipitation step (S1) was carried out, but the dissolution step (S2) and the reprecipitation step (S3) were not carried out (the corresponding columns in Table 1 below are marked with "-").
• the precipitate obtained in the precipitation step (S1) was evaluated in the same manner as in Examples 1 to 7. The results are shown in Table 1 below.
• Example 5 had the lowest iron phosphate content of 91 mass %, and when the dissolving step (S2) and the reprecipitation step (S3) were further repeated, a phosphorus compound with an iron phosphate content of 99 mass % was finally obtained. More specifically, the first cycle consisted of the initial dissolution step (S2) and re-precipitation step (S3), and the iron phosphate content gradually increased to 94% by mass after the second cycle, 97% by mass after the third cycle, and 99% by mass after the fourth cycle.

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