Method for preparing MgSO4•7H2O by using SO3 and SO2 waste liquid produced in the process of Na2S2O5 production

Abstract

The invention relates to the technical field of magnesium sulfate heptahydrate preparation, and discloses a method for preparing MgSO4·7H2O by using SO3 and SO2 waste liquid produced in the production process of Na2S2O5, comprising the following steps: step 1, physical impurity removal, filtering the dilute sulfuric acid solution of the pyrosulfate waste liquid through a polymer filter tank or an acid-resistant plate-frame filter press, fully contacting with oxygen to remove sulfurous acid to obtain an intermediate solution B; step 3, preparing magnesium sulfate, adding the intermediate solution B to a magnesium oxide mixed liquid container, adding concentrated sulfuric acid to the intermediate solution B, adding neutral polyacrylamide, stirring again and then standing to obtain a clarified mixed liquid C; step 4, recrystallization, filtering the clarified mixed liquid C to obtain crystallization tank crystals, and the crystallization tank crystals are recrystallized by a centrifuge to obtain high-purity magnesium sulfate heptahydrate. The invention is suitable for a method for preparing MgSO4·7H2O by using SO3 and SO2 waste liquid produced in the production process of Na2S2O5, magnesium sulfite is oxidized to magnesium sulfate by air, and high-purity magnesium sulfate is generated by crystallization and recrystallization, and the manufacturing cost is more economical.

Description

Technical Field

[0001] The invention relates to the technical field of magnesium sulfate heptahydrate preparation, in particular to a method for preparing MgSO4·7H2O by utilizing SO3 and SO2 waste liquid produced in the production process of Na2S2O5. Background Art

[0002] At present, the dilute sulfuric acid produced by pyrolysis falls into the category of environmental hazardous waste. The neutralization reaction of dilute sulfuric acid with alkali increases equipment investment, which is costly and affects the economic benefits of the enterprise. Summary of the invention

[0003] The present invention provides a method for preparing MgSO4·7H2O by utilizing SO3 and SO2 waste liquid produced in the production process of Na2S2O5, which solves the problems raised in the above-mentioned background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] The method for preparing MgSO4·7H2O by using SO3 and SO2 waste liquid produced in the production process of Na2S2O5 comprises the following steps:

[0006] Step 1: Physical impurity removal: filtering the dilute sulfuric acid solution of the pyrosulfate waste liquid through a polymer filter tank or an acid-resistant plate and frame filter press to obtain an intermediate solution A;

[0007] Step 2, oxidation reaction, the intermediate solution A is fully contacted with oxygen to remove sulfurous acid to obtain an intermediate solution B;

[0008] Step 3, preparing magnesium sulfate, adding intermediate solution B to the magnesium oxide mixed solution container, adding concentrated sulfuric acid to the intermediate solution B, stirring and mixing, controlling the pH value of the solution, adding neutral polyacrylamide, stirring again, and standing to obtain a clear mixed solution C;

[0009] Step 4, recrystallization, clarifying the mixed solution C and filtering to obtain crystals in a crystallization tank, and the crystals in the crystallization tank are recrystallized by a centrifuge to obtain high-purity magnesium sulfate heptahydrate.

[0010] As a preferred technical solution of the present invention, in step three, the component ratio of the intermediate solution B and the concentrated sulfuric acid is 65:35.

[0011] As a preferred technical solution of the present invention, in step three, the time for pouring the intermediate solution B into the container is 25-30 minutes, and the pH value of the intermediate solution is 8-9.

[0012] As a preferred technical solution of the present invention, in step three, the time for pouring concentrated sulfuric acid into the container is 20-35 minutes, and the pH value of the intermediate solution is 5-6.

[0013] As a preferred technical solution of the present invention, in step three, the clarified mixed liquor C is filtered through a filter press with a 280-mesh filter cloth and sent to a crystallization tank for crystallization.

[0014] As a preferred technical solution of the present invention, the pH value of the clarified mixed solution C is 5-5.5.

[0015] The present invention has the following benefits:

[0016] The invention is applicable to a method for preparing MgSO4·7H2O by utilizing SO3 and SO2 waste liquid produced in the production process of Na2S2O5. The method comprises neutralizing the MgSO4·7H2O with light-burned powder (90% magnesium oxide) in a reaction tank to generate magnesium sulfate and a small amount of magnesium sulfite. The magnesium sulfite is oxidized into magnesium sulfate by air, and high-purity magnesium sulfate is generated by crystallization and recrystallization. The manufacturing cost is more economical. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 The present invention is a flow chart of a method for preparing MgSO4·7H2O by utilizing SO3 and SO2 waste liquid produced in the process of Na2S2O5 production. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In one embodiment, see Figure 1 The method for preparing MgSO4·7H2O by using SO3 and SO2 waste liquid produced in the production process of Na2S2O5, SO3 and a small amount of SO2 produced by sulfur combustion in the front stage of sodium pyrosulfite, and the washed waste liquid, whose main components are sulfuric acid and a small amount of sulfurous acid, are collectively called dilute sulfuric acid, and includes the following steps:

[0021] Step 1: Physical impurity removal: filtering the dilute sulfuric acid solution of the pyrosulfuric acid waste liquid through a polymer filter tank or an acid-resistant plate-and-frame filter press to remove a very small amount of sulfur and other solid impurities in the dilute sulfuric acid to obtain a transparent and clear intermediate solution A, that is, a clear dilute sulfuric acid solution;

[0022] Step 2: Oxidation reaction: The intermediate solution A is fully exposed to oxygen to remove sulfurous acid, wherein sulfurous acid is converted into a very small amount of sulfuric acid. The reaction formula is:

[0023] 2SO2+O2=(catalyst)=2SO3

[0024] SO3+H2O=H2SO4

[0025] Obtaining intermediate solution B;

[0026] Step 3: Preparation of magnesium sulfate. The control of the process nodes in this reaction process is particularly critical. Dilute sulfuric acid alone does not react completely with magnesium oxide, which affects product quality and conversion rate. Therefore, the specific steps are as follows;

[0027] 1. Add intermediate solution B to the magnesium oxide mixed solution container according to the meter. Intermediate solution B accounts for 65% of the total amount. It takes about 25 to 30 minutes. The pH value of the solution is about 8 to 9.

[0028] 2. Add 35% of 98% concentrated sulfuric acid to the intermediate solution B according to the meter. The time is about 30 to 35 minutes. The pH value of the solution is controlled at 5 to 6, with a bias of 5;

[0029] 3. Stir for one hour, the pH value is stable at about 5.2, about 5.2, add food-grade 12 million macromolecular neutral polyacrylamide to the solution, the amount is 0.5%, stir for half an hour after adding, the pH value is about 5.2, and the flocculant is completely mixed;

[0030] 4. Let the solution stand for 3 hours to obtain a clear mixed solution C;

[0031] Step 4, recrystallization, the clarified mixed solution C is filtered through a filter press with a 280-mesh filter cloth to obtain crystals in a crystallization tank, the bottom residue liquid is filtered through another filter press to filter the solution into the mother liquor and returned to the reaction tank for re-production, and the crystals in the crystallization tank are recrystallized by a centrifuge to obtain high-purity magnesium sulfate heptahydrate, reaction formula:

[0032] Mgo+H2So4=MgSO4·7H2O

[0033] MgO+H2SO3=MgSO3+H2O.

[0034] The invention is applicable to a method for preparing MgSO4·7H2O by utilizing SO3 and SO2 waste liquid produced in the production process of Na2S2O5. The method comprises neutralizing the MgSO4·7H2O with light-burned powder (90% magnesium oxide) in a reaction tank to generate magnesium sulfate and a small amount of magnesium sulfite. The magnesium sulfite is oxidized into magnesium sulfate by air, and high-purity magnesium sulfate is generated by crystallization and recrystallization. The manufacturing cost is more economical.

[0035] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. A method for preparing MgSO4·7H2O using SO3 and SO2 waste liquid produced in the production process of Na2S2O5, characterized in that: The steps include: Step 1: Physical impurity removal: filtering the dilute sulfuric acid solution of the pyrosulfate waste liquid through a polymer filter tank or an acid-resistant plate and frame filter press to obtain an intermediate solution A; Step 2, oxidation reaction, the intermediate solution A is fully contacted with oxygen to remove sulfurous acid to obtain an intermediate solution B; Step 3, preparing magnesium sulfate, adding intermediate solution B to the magnesium oxide mixed solution container, the time for pouring intermediate solution B into the container is 25-30 minutes, and the pH value of the overall solution after adding intermediate solution B is 8-9, adding concentrated sulfuric acid to the intermediate solution B, the time for pouring concentrated sulfuric acid into the container is 20-35 minutes, and the pH value of the overall solution after pouring concentrated sulfuric acid is 5-6, stirring and mixing, controlling the pH value of the solution, adding neutral polyacrylamide, stirring again, and standing to obtain a clear mixed solution C, the pH value of the clear mixed solution C is 5-5.5; Step 4, recrystallization, clarifying the mixed solution C and filtering to obtain crystals in a crystallization tank, and the crystals in the crystallization tank are recrystallized by a centrifuge to obtain high-purity magnesium sulfate heptahydrate.

2. The method for preparing MgSO4·7H2O by using SO3 and SO2 waste liquid produced in the production process of Na2S2O5 according to claim 1, characterized in that: In step 3, the component ratio of the intermediate solution B and the concentrated sulfuric acid is 65:

35.

3. The method for preparing MgSO4·7H2O by utilizing SO3 and SO2 waste liquid produced in the production process of Na2S2O5 according to claim 1, characterized in that: In step 3, the clarified mixed liquor C is filtered through a filter press with a 280-mesh filter cloth and sent to a crystallization tank for crystallization.

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