JP7370852B2 - Caking-inhibiting sulfate magnesium fertilizer and its manufacturing method - Google Patents

Description

The present invention relates to a sulfate magnesium fertilizer that has high hygroscopicity and exhibits an excellent caking inhibiting function.

In general, chemical fertilizers contain a large amount of hygroscopic and deliquescent components, so the fertilizer particles tend to stick together and form clumps. Concerns about quality deterioration have been pointed out as a result of fertilizer caking, but even if there is no quality problem, it can cause a decrease in the uniformity of fertilization, so fertilizers that are difficult to caking are needed. Particularly in today's world where fertilization by machinery is common, the permissible range for fertilizer caking has narrowed, and mechanical fertilization is likely to cause trouble even with a light degree of caking, so fertilizers that are difficult to clump and have good fluidity are needed. It is being

In particular, recently, bulk blend fertilizers (hereinafter referred to as BB fertilizers), which contain two or more types of granular fertilizer raw materials such as ammonium phosphorus, ammonium sulfate, ammonium chloride, urea, heavy superphosphate, potassium chloride, and potassium sulfate, have come into use. , BB fertilizers contain multiple fertilizer components and are prone to caking, so more effective caking prevention measures are required.

Consolidation of fertilizer is mainly caused by moisture (free water) present on the surface of fertilizer particles. This free water turns into a saturated solution with fertilizer components dissolved, forming liquid bridges between particles, and then temperature increases. When water evaporates and recrystallization occurs due to changes in fertilizer or humidity, liquid bridges change to solid bridges, and fertilizer particles adhere to each other, causing caking. Simple fertilizers and chemical fertilizers cause fertilizer caking through this mechanism, but BB fertilizers also cause caking due to the products generated by the reactions of multiple fertilizer components, so compared to single fertilizers, BB fertilizers have a higher rate of caking than single fertilizers. The problem is more serious.

For example, in a BB fertilizer containing ammonium sulfate and potassium chloride, ammonium chloride and potassium sulfate are produced by the reaction between ammonium sulfate and potassium chloride, as shown in the following equation [1-1], and the solubility of ammonium chloride and potassium sulfate is Since the solubility of the fertilizer particles is lower than that of ammonium sulfate and potassium chloride, it crystallizes and precipitates, resulting in caking.
(NH ₄ ) ₂ SO ₄ + 2KCl → 2NH ₄ Cl + K ₂ SO ₄ ...[1-1]

In addition, in BB fertilizers containing dianic phosphate and peroxide or peroxide, these react to liberate water of crystallization, as shown in the following formula [1-2], and this free water causes the surface of fertilizer particles to Caking occurs due to wetting.
(NH ₄ ) ₂ HPO ₄ + Ca(H ₂ PO ₄ ) ₂・H ₂ O → 2NH ₄ H ₂ PO ₄ + CaHPO ₄ + H ₂ O ・・・[1-2]

General measures to prevent caking of fertilizers include reducing the amount of water and adding anti-caking agents to suppress reactions between particles. As anti-caking agents, inorganic silica gel powder, talc powder, clay, silica fume, and organic surfactants are often used for urea, ammonium nitrate, and chemical fertilizers.

However, the anti-caking agents that can be used in BB fertilizers are regulated by law (Fertilizer Control Law) and are limited to silica gel powder, talcum powder, clay, silica powder, diatomaceous earth, silica fume, perlite, and lubricating oil. The amount added is limited to 6% or less for silica gel powder, 3% or less for other powders, and 0.3% or less for lubricating oil used in combination with talcum powder, clay, diatomaceous earth, or perlite. Therefore, these anti-caking effects are not sufficient. Furthermore, the addition of these anti-caking agents causes problems such as a relative decrease in the amount of active ingredients in the fertilizer, and powdered anti-caking agents that cause dust to scatter during fertilization. There is also the problem that using expensive silica gel powder increases fertilizer costs.

On the other hand, with regard to magnesium phosphate fertilizer, it has been disclosed that an excellent caking inhibiting effect can be obtained by containing hygroscopic components consisting of monomagnesium phosphate, monolime phosphate, and sodium dihydrogen phosphate. (Patent Document 1). However, with regard to sulfate magnesium fertilizers, no sufficient measures have been shown to replace anti-caking agents.

Japanese Patent Application Publication No. 2018-188314

The present invention solves the above-mentioned conventional problems regarding sulfate magnesium fertilizer, and provides a sulfate magnesium fertilizer that does not contain an anti-caking agent different from the fertilizer components and has an excellent caking inhibiting effect, and its production. provide a method.

The present invention relates to a caking-inhibiting magnesium sulfate fertilizer having the following configuration and a method for producing the same.
[1] Containing 38% by mass or more of magnesium sulfate low hydrate represented by MgSO ₄ x H ₂ O (x is 1.32 to 2.30), at a relative humidity of 50% (equilibrium moisture/water-soluble magnesia) A caking-inhibiting sulfate magnesium fertilizer characterized by a ratio of 0.40 or more.
[2] The caking-inhibiting magnesium sulfate fertilizer according to the above [1], in which the content of hexahydrate or more of magnesium sulfate polyhydrate is less than 16% by mass.
[3] In X-ray diffraction, the peak intensity ratio _of MgSO ₄ . The caking-inhibiting magnesium sulfate fertilizer described in any of [1] to [2] above, which has a value of 2.13 or less when used as the main raw material, and 1.41 or less when periolite is used as the main raw material. .
[ ₄ ] Magnesium sulfate low hydrate represented by MgSO ₄ . A method for producing a caking-inhibited sulfate magnesium fertilizer, which comprises producing sulfate magnesium containing 38% by mass or more and having a (equilibrium moisture/water-soluble magnesium) ratio of 0.40 or more at a relative humidity of 50%.

The present invention will be explained in detail below.
[Sulfuric acid magnesium fertilizer]
The magnesium sulfate fertilizer of the present invention contains 38% by mass or more of magnesium sulfate low hydrate represented by MgSO ₄ xH ₂ O (x is 1.32 to 2.30), and has an equilibrium water content of 50% relative humidity. This is a caking-inhibiting sulfate magnesium fertilizer characterized by a ratio of 0.40 or more.

Magnesium sulfate anhydrous (MgSO ₄ ) is used as a desiccant by taking advantage of its property of absorbing water in the atmosphere and changing into a polyhydrate. Magnesium sulfate monohydrate (MgSO ₄ H ₂ O) It is also known to have hygroscopic properties. _Magnesium sulfate hypohydrate represented by MgSO ₄ .

In the present invention, it has been found that the hygroscopicity of magnesium sulfate hypohydrate (x is 1.32 to 2.30) is higher than that of magnesium sulfate monohydrate (MgSO ₄ .H ₂ O). As shown in FIGS. 1 and 2 of Example 3, at relative humidity of 50% to 60%, inventive samples No. 1 to 8 with x of 1.32 to 2.30 have x of 1.08 to 1. The ratio of equilibrium moisture to water-soluble magnesia (W-MgO) is much higher than that of comparative samples No. 9 to No. 13 of .20, and much higher than that of magnesium sulfate of 1.08 to 1.20 hydrate. It shows that it has high hygroscopicity.

The sulfated magnesium fertilizer of the present invention has an excellent caking inhibiting function by containing this magnesium sulfate low hydrate (x is 1.32 to 2.30) as a main component. The content of this magnesium sulfate low hydrate is preferably 38% by mass or more. If this content is less than 38% by mass, the hygroscopicity will not be sufficient and the caking suppressing function will deteriorate, which is not preferable. Further, when containing a hexahydrate or more of magnesium sulfate polyhydrate, the content is preferably less than 16% by mass. Magnesium sulfate in the form of hexahydrate or more has a water adsorption property close to the limit, so its hygroscopicity is low, and if this amount exceeds 16% by mass, the hygroscopicity of the magnesium sulfate fertilizer will not improve.

The sulfuric acid magnesium fertilizer of the present invention contains 38% by mass or more of magnesium sulfate low hydrate represented by MgSO ₄ xH ₂ O (x is 1.32 to 2.30), so that at a relative humidity of 50%, It has high hygroscopicity with a (equilibrium moisture/water-soluble magnesia) ratio of 0.40 or more. By having such a high hygroscopicity from a relative humidity of 50%, the magnesium sulfate hypohydrate preferentially absorbs moisture before other fertilizer particles absorb moisture, resulting in an excellent caking inhibiting effect. Moreover, since this magnesium sulfate low hydrate is a magnesium component of the fertilizer, the amount of active ingredients in the fertilizer does not decrease, and a magnesium fertilizer with high fertilizing effect can be obtained.

The fact that the sulfated magnesium fertilizer of the present invention contains magnesium sulfate low hydrate (MgSO ₄ x H ₂ O, x is 1.32 to 2.30) as a main component means that these peaks in X-ray diffraction This can be confirmed by being detected.

〔Production method〕
By reacting sulfuric acid with a concentration of 40 to 60 % to the raw material of magnesia, 38% by mass of magnesium sulfate low hydrate, represented by MgSO ₄ x H ₂ O (x is 1.32 to 2.30), is produced. Sulfuric acid magnesium containing the above can be produced.

Lightly calcined magnesia, heavy calcined magnesia, periolite, nickel slag, serpentine, etc. can be used as the magnesia raw material. It is preferable to react sulfuric acid at a concentration of 40 to 60 % with the magnesia raw material at a H ₂ SO ₄ /T-MgO molar ratio in the range of 0.70 to 1.20. Specifically, when light calcined magnesia is mainly used as the magnesia raw material, it is preferable to react the sulfuric acid at a concentration of 40 to 60% and the H ₂ SO ₄ /T-MgO at a molar ratio of 0.92 or more. When peridotite is mainly used as the raw material for magnesia, it is preferable to react the sulfuric acid at a concentration of 50 to 60% and the H ₂ SO ₄ /T-MgO molar ratio between 0.70 and 1.20.

If the concentration of sulfuric acid used exceeds 65%, the resulting magnesium sulfate hydrate will be less than 1.20, which is not preferable. On the other hand, if the sulfuric acid concentration is lower than 40%, the reaction will not proceed sufficiently.

The magnesium sulfate obtained by the production method of the present invention contains 38% by mass or more of magnesium sulfate low hydrate represented by MgSO ₄ xH ₂ O (x is 1.32 to 2.30), and contains hexahydrate. Since the content of the above magnesium sulfate polyhydrate is less than 16% by mass, the (equilibrium water/water soluble magnesium) ratio at 50% relative humidity is 0.40 or more, and it has an excellent caking prevention function. have

The sulfated magnesium fertilizer of the present invention has a (equilibrium moisture/water-soluble magnesium) ratio of 0.40 or more at a relative humidity of 50%, so it absorbs moisture in the atmosphere before other fertilizer particles start absorbing moisture. It exhibits an excellent caking prevention effect. Therefore, during long-term storage or transportation, the fertilizer is less likely to clump, and a uniform spreading effect can be obtained even with mechanical fertilizer application.

In addition, the magnesium sulfate fertilizer of the present invention has high hygroscopicity as a fertilizer component, magnesium sulfate low hydrate, and exhibits a caking inhibiting mechanism, and does not contain an anti-caking agent different from the fertilizer component. , it is possible to maintain a high fertilizer effect.

Equilibrium moisture curve graph (Samples No. 1 to 4, No. 9 to 11) Equilibrium moisture curve graph (Samples No. 5 to 8, No. 12, 13)

Examples of the present invention will be shown below along with comparative samples.
[Example 1: Production of sample]
A magnesium sulfate fertilizer was produced using the raw materials shown in Table 1 and according to the reaction conditions shown in Table 1. Samples Nos. 1 to 8 are samples of the present invention, and Samples Nos. 9 to 13 are comparative samples. The particle size of the manufactured fertilizer was set to be 1 mm or more and less than 4 mm, similar to general fertilizers. The initial temperature of sulfuric acid was set at 25°C or higher for samples whose main raw material was light calcined magnesia, and at least 70°C for samples whose main raw material was periolite, so that the maximum temperature during the reaction was 100°C or higher for all samples. I used one that had been kept warm.
Table 1 shows the components, heat loss, and ignition loss of the produced magnesium sulfate fertilizer. All values except heat loss are expressed as percentages per dry weight. Fertilizer components such as water-soluble magnesia (W-MgO) were analyzed based on the fertilizer analysis method. The loss on heating is the percentage loss (% by mass) when heated at 100° C. for 5 hours, and the loss on ignition (Ig.loss) is the percentage loss (% by mass) when heated at 500° C. for 1 hour. Calculation of loss on ignition and loss on heating assumes that magnesium sulfate contains only hexahydrate and x-hydrate, and when heated to 100°C, magnesium sulfate hexahydrate becomes x-hydrate, The x-hydrate was assumed to become anhydrous by heating.

[Example 2: Composition of sulfate magnesium]
We analyzed the composition of magnesium sulfate hydrate contained in the produced magnesium sulfate fertilizer. The composition of magnesium sulfate hydrate is divided into two types: x-hydrate and hexahydrate, and the composition ratio (mass%) is calculated by the following formula [2-1], formula [2-2], and formula [2- 3], calculated using formula [2-4]. The results are shown in Table 2.
In the following formula, W6 is the proportion of hexahydrate (mass %), Wx is the proportion of x hydrate (mass %), and Mx is the formula weight of x hydrate (g/mol). Formula weight of magnesium sulfate hexahydrate (g/mol) = 228.46, water molecular weight (g/mol) = 18.02, formula weight of MgO (g/mol) = 40.30, formula of anhydrate The amount (g/mol) was set to 120.37.

Heating loss (%) = (W6/228.46) × 18.02 × (6-x) ・・・[2-1]
Ignition loss (%) = (Wx/Mx)×x×18.02 + (W6/228.46)× x×18.02 ・・・[2-2]
W-MgO(%)＝ (Wx/Mx)×40.30 + W6/228.46)×40.30 ・・・[2-3]

The following equation [2-4] is obtained from equations [2-2] and [2-3]. The constants included in this formula [2-4] are the molecular weights and formula weights of H ₂ O and MgO, so rearranging this gives the following formula [2-5]. As shown in this formula [2-5], x of the hydrate is represented by the molar ratio of crystal water volatilized by ignition loss (500° C. ignition) and water-soluble magnesium. x can be determined from the value of loss on ignition and the value of water-soluble magnesia (W-MgO) shown in Table 1. From this x, Mx is determined by the following equation [2-6]. Furthermore, the ratio W6 (%) of hexahydrate is determined from the above formula [2-1] using the heating loss in Table 1 and the above x. Furthermore, using this W6 and the above x, the proportion Wx (%) of the x hydrate is determined from the above formula [2-2]. The results are shown in Table 2.

x = (Ignition loss (mass%)/18.02)/(W-MgO (mass%)/40.30) ・・・[2-4]
x = Loss on ignition (mol) / W-MgO (mol) ...[2-5]
Mx (g/mol) = 120.37 + 18.02×x ・・・[2-6]

As shown in Table 2, the magnesium sulfate samples Nos. 1 to 8 have hydrate x in the range of 1.32 to 2.30 and are samples of the present invention. The content of magnesium sulfate low hydrate (x is 1.32 to 2.30) in sample Nos. 1 to 8 is all 38% by mass or more, and the content of magnesium sulfate hexahydrate is 16% by mass. On the other hand, samples Nos. 9 to 13 of magnesium sulfate each have hydrate x outside the range of the present invention and are comparative samples.

[Example 3: Peak intensity of magnesium sulfate]
Qualitative X-ray diffraction analysis and peak intensity ratios were determined for the components of magnesium sulfate in samples Nos. 1 to 13.
Using α-alumina as an internal standard substance, α-alumina was mixed with the sulfuric acid magnesium fertilizers of sample Nos. 1 to 13 at a ratio of (9 sulfuric acid magnesium sulfate: 1 α-alumina), thoroughly pulverized, and then 2θ X-ray diffraction (XRD) measurement was performed (using Mini Flex manufactured by Rigaku Corporation). Cu was used for the XRD anticathode, and the material was identified by comparison with the ICDD database. As α-alumina, aluminum oxide α type (product of Kanto Kagaku Co., Ltd.) was used.
In this qualitative analysis, those with relative intensities of 20 or more were identified based on the relative intensities of the main peak and sub-peak positions of each magnesium sulfate hydrate shown in Table 3 with respect to all peaks.
Table 4 shows the relative intensity of the X-ray diffraction peak (2θ) of each sample, and also shows the XRD qualitative analysis results of magnesium sulfate hydrate of each sample determined based on this and the peak intensity ratio to α-alumina. 5.
The peak intensity ratio for α-alumina is the ratio of the relative intensities of the peaks of magnesium sulfate hydrate and the internal standard substance (α-alumina) in each sample (peak intensity of magnesium sulfate hydrate/peak intensity of α-alumina). ).
The (1-2) hydrates in Table 5 are a general term for monohydrates and dihydrates identified by the maximum peak appearing in the range of 2θ = 26° to 27° in X-ray diffraction. includes MgSO ₄ .H ₂ O, MgSO ₄ .1.32 H ₂ O, MgSO ₄ .2H ₂ O. In addition, when there were multiple peaks of magnesium sulfate hydrate between 2θ=26° and 27°, the intensity ratio of the stronger peak was adopted.

[Example 4: Equilibrium moisture]
For the sulfate magnesium fertilizers (Samples No. 1 to 13), the equilibrium moisture content, which is related to the moisture absorption capacity, was measured. 2.0 g of each measurement sample was accurately weighed, placed in a constant temperature and humidity chamber set at 30° C. and 30% relative humidity (30% RH), allowed to stand until a constant weight was reached, and then weighed. Thereafter, the temperature was set to 40% RH, 50% RH, 60% RH, and 70% RH at 30° C., and the moisture content was calculated from the weight increase to determine the equilibrium moisture content. The results are shown in Table 6. Furthermore, the amount of moisture absorbed by the magnesium sulfate fertilizer depends on the amount of magnesium sulfate it contains. The hygroscopic properties of magnesium sulfate itself are related to the ratio of equilibrium moisture to water-soluble magnesia (W-MgO) (equilibrium moisture/water-soluble magnesium), so changes in the equilibrium moisture ratio at each relative humidity (equilibrium moisture curve) are shown in Figures 1 and 2. Figure 1 shows Samples No. 1 to 4 (samples of the present invention), Samples No. 9 to 11 (comparative samples), and Figure 2 shows Samples No. 5 to 8 (samples of the present invention), Samples No. 12 and 13 (comparative samples) ).

As shown in the equilibrium moisture curves in Figures 1 and 2, at a relative humidity of 70% RH, all samples have a high amount of moisture absorption, but at a relative humidity of 50%, the samples of the present invention (Nos. 1 to 8) are the comparative samples. The amount of moisture absorbed was larger than that of (No. 9 to 13), indicating high hygroscopicity. The fact that the hygroscopicity is high from the low humidity side means that the samples of the present invention (Nos. 1 to 8) preferentially absorb moisture before other fertilizer particles absorb moisture and function as an anti-caking agent. Therefore, the magnesium sulfate fertilizer of the present invention acts as an anti-caking agent when blended into BB fertilizer, and exhibits an excellent caking-inhibiting effect.

[Sample evaluation]
As shown in Tables 1 and 2, samples Nos. 1 to 4 of the present invention used sulfuric acid with a concentration of 40 to 60% by mass relative to lightly calcined magnesium, and the H ₂ SO ₄ /T-MgO molar ratio was 0. Samples Nos. 5 to 8 of the present invention use sulfuric acid with a concentration of 60% by mass based on periolinite, and the H ₂ SO ₄ /T-MgO molar ratio is 0.92 to 0.97. It is produced in the range of 70 to 1.20. Therefore, all of the present invention samples No. 1 to 8 are magnesium sulfate ( 1.32 to 2.30) hydrates, and this magnesium sulfate ( 1.32 to 2.30) hydrate is % or more, and the content of magnesium sulfate hexahydrate is less than 16% by mass. Furthermore, as shown in Table 5, 1.32 hydrate was detected in all of the present invention samples No. 1 to 8 regarding magnesium sulfate, and as shown in FIGS. % (equilibrium moisture/water-soluble magnesia) ratio is 0.40 or more, indicating high hygroscopicity.

On the other hand, in Comparative Samples Nos. 9 to 13, the sulfuric acid concentration at the time of production was 65% by mass or more, which is higher than that of the samples of the present invention. Therefore, as shown in Table 2, the magnesium sulfates of comparative samples 9, 10, 12, and 13 are low hydrates with x of 1.20 or less, and as shown in FIGS. The humidity ratio of 50% to 60% (equilibrium moisture/water-soluble magnesia) is significantly low, resulting in poor hygroscopicity. Comparative sample No. 11 has x of 1.35, but since it contains 33.54% hexahydrate, the weight ratio of magnesium sulfate x hydrate to magnesium sulfate hexahydrate (x hydrate (hexahydrate) is as low as 1.98, and as shown in Figure 1, the hygroscopicity is low. From this, the x-hydrate/hexahydrate ratio is preferably 2.0 or more.

Furthermore, in comparative samples No. 9, No. 10, and No. 13, 1.25 hydrate was not detected, and the hygroscopicity was significantly low. Although 1.25 hydrate was detected in comparative samples No. 11 and No. 12, as shown in FIGS. 1 and 2, the hygroscopicity was low. This is because comparative sample No. 11 has a very large amount of magnesium sulfate hexahydrate at 33.5%, significantly exceeding 16% by mass, and comparative sample No. 12 has magnesium sulfate x hydrate. However, as shown in Table 2, the value of x is as low as 1.20, and as shown in Table 5, the peak intensity ratio of MgSO ₄ · (1-2)H ₂ O is Since it is as high as 1.56, the hygroscopicity is considered to be low. In addition, comparative samples No. 9, No. 10, No. 12, and No. 13 all have a sulfuric acid concentration of 65% by mass or more at the time of synthesis, so they are magnesium sulfate (1.25 to 2.30) hydrate. This seems to be a manufacturing factor due to a decrease in the amount of .

[Example 5: Fertilizer deposition test]
A deposition test was conducted using magnesium sulfate fertilizers (samples A to C) having the components shown in Table 7, with the particle size of the fertilizer adjusted to 1 to 4 mm. Table 8 shows the blended raw materials and results of the deposition test.
In this deposition test, 225 g each of ammonium sulfate, DAP, and salt were mixed and allowed to absorb moisture under conditions of a temperature of 30° C. and a relative humidity of 75% RH until the weight increase was 3.5 g. 75 g of each of the dried samples A to C was mixed with the raw material, sealed in a fertilizer bag (200 x 150 mm), and deaerated to obtain a sample for measurement. In addition, as a control, a level was set in which no sample was mixed. Furthermore, apart from Samples A to C, fertilizer bags of the same size were filled with ammonium sulfate, DAP, and salt in the same proportions as above, and these were used as dummy bags. Prepare one bag of these fertilizer bag samples for each level, stack them, sandwich them between dummy bags, apply a load of 60 kg (200 g/cm ² ) on top of them, average temperature 22.5°C, average humidity 78°C. .9% room for 30 days.
After the deposition test was completed, the bag was opened, the consolidated portion was separated by hand, and the weight ratio (consolidation rate) was measured. In addition, for the consolidated portion, the hardness was measured at five locations using a Yamanaka soil hardness meter, and the average value was taken as the five-point average value of consolidation strength and is shown together with the maximum value.

As shown in Table 8, Samples A and B of the present invention had a consolidation ratio of 30% or less, and a maximum consolidation strength of 2.2 kg/cm ² or less. On the other hand, the consolidation ratio of the control sample was 57%, and the maximum consolidation strength was 24.8 kg/cm ² , and samples A and B of the present invention were both significantly lower than the control sample. In addition, Samples A and B of the present invention had clearly lower caking ratio and caking strength than Comparative Sample C, and showed a strong caking suppressing effect. Furthermore, as shown in the analysis value of W-MgO in Table 7, although the content of water-soluble magnesia in Comparative Sample C is 1.6 to 1.9 times that of Samples A and B of the present invention, First, the effect of suppressing caking is clearly higher in the present invention. As shown in Table 8, the equilibrium moisture content/W-MgO at 30°C and 50% relative humidity for each of Samples A, B, and C, which were measured in the same manner as the equilibrium moisture content in Example 4, was 0.401, They were 0.524 and 0.157. From the above, it can be seen that the magnesium sulfate fertilizer of the present invention has a remarkable caking inhibiting effect even in a small amount, since the amount of moisture absorbed per magnesium sulfate is extremely high especially at around 50% relative humidity.

Claims (4)

Contains 38% by mass or more of magnesium sulfate low hydrate represented by MgSO ₄ x H ₂ O (x is 1.32 to 2.30), and the (equilibrium moisture/water soluble magnesium) ratio at 50% relative humidity is 0. A caking-inhibiting sulfate magnesium fertilizer characterized by having a sulfuric acid magnesium of .40 or higher. The caking-inhibited magnesium sulfate fertilizer according to claim 1, wherein when containing a hexahydrate or more of magnesium sulfate polyhydrate, the content is less than 16% by mass. In X-ray diffraction, the peak intensity ratio of MgSO ₄・(1-2)H ₂ O when α-alumina was added as an internal standard substance to a content of 10% was determined by using light burnt magnesia as the main raw material as a magnesia source. The caking-inhibiting magnesium sulfate fertilizer according to any one of claims 1 to 2, which has a concentration of 2.13 or less when periolite is used as the main raw material, and 1.41 or less when periolite is used as the main raw material. By reacting sulfuric acid with a concentration of 40 to 60 % to the raw material of magnesia, 38% by mass of magnesium sulfate low hydrate, represented by MgSO ₄ x H ₂ O (x is 1.32 to 2.30), is produced. A method for producing a caking-inhibited sulfate magnesium fertilizer, which comprises producing sulfate magnesium containing the above and having a (equilibrium moisture/water-soluble magnesium) ratio of 0.40 or more at a relative humidity of 50%.

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