Method for separating and recovering calcium sulfide and calcium ferrite from gypsum reductive decomposition products

Abstract

The invention discloses a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reductive decomposition products, and belongs to the technical field of solid waste treatment. The method comprises the following steps: mixing pyrite and gypsum, and carrying out first ball milling; roasting the ball-milled material in an inert atmosphere; mixing the roasted product with a first part of water, and carrying out secondary ball milling to obtain slurry; adding a second part of water into the slurry, carrying out aeration under the conditions of stirring and introducing CO2, and recovering hydrogen sulfide gas generated in the aeration process; after the aeration is finished, carrying out solid-liquid separation to obtain a solid containing calcium ferrite and ferroferric oxide; and reacting the recovered hydrogen sulfide gas with calcium hydroxide to obtain calcium sulfide. The method is simple in process and environmentally friendly, the pyrite is used as a reducing agent, efficient decomposition of the gypsum at the low temperature is achieved, the roasted product is effectively separated, calcium ferrite and ferroferric oxide can further serve as slag formers of an iron and steel plant, and good economic value is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste treatment, and in particular to a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products. Background Art

[0002] In addition to naturally occurring gypsum resources, some also exist as industrial byproducts (primarily flue gas desulfurization gypsum, phosphogypsum, citric acid gypsum, fluorspar gypsum, titanium gypsum, nickel gypsum, and thenardite gypsum). Large-scale, open-air storage of gypsum as industrial solid waste not only consumes land resources but also contains acids and other harmful substances that can easily pollute the surrounding environment.

[0003] Gypsum, an industrial by-product, contains rich secondary resources of sulfur and calcium. If it is properly utilized, it can not only effectively control the pollution of the secondary environment, but also replace a large amount of primary mineral resources.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, so as to solve or improve the above technical problems.

[0006] The present invention can be achieved like this:

[0007] In a first aspect, the present invention provides a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, comprising the following steps:

[0008] The pyrite and gypsum are mixed and then ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product;

[0009] The calcined product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and hydrogen sulfide gas generated during the aeration process is recovered; after the aeration is completed, solid-liquid separation is performed to obtain a solid containing calcium ferrite and ferrosoferric oxide; the recovered hydrogen sulfide gas is reacted with calcium hydroxide to obtain calcium sulfide.

[0010] In an optional embodiment, the gypsum includes at least one of phosphogypsum, natural gypsum, titanium dioxide by-product gypsum, fluorgypsum and anhydrite.

[0011] In an alternative embodiment, the molar ratio of ferrous disulfide in pyrite to calcium sulfate in gypsum is 1:0.9 to 1:1.2.

[0012] In an optional embodiment, the ball-to-material ratio of the first ball milling is 5:1 to 10:1 by mass, and the rotation speed is 300 rpm to 500 rpm.

[0013] In an alternative embodiment, the inert atmosphere comprises a nitrogen atmosphere or an argon atmosphere.

[0014] In an optional embodiment, the calcination temperature is 900° C. to 1000° C., and the calcination time is 0.5 h to 1.5 h.

[0015] In an optional embodiment, the solid-liquid ratio of the total amount of the first portion of water and the second portion of water to the calcined product in the slurry is 50 mL:1 g to 150 mL:1 g, wherein the solid-liquid ratio of the first portion of water to the calcined product in the slurry is 10 mL:1 g to 15 mL:1 g.

[0016] In an optional embodiment, the ball-to-material ratio of the second ball milling is 5:1 to 10:1, and the rotation speed is 300 rpm to 500 rpm.

[0017] In an optional embodiment, the CO2 introduction rate is 10 mL / min to 30 mL / min.

[0018] In an optional embodiment, the aeration time is 0.5 h to 3 h.

[0019] The beneficial effects of the present invention include:

[0020] (1) By ball-milling pyrite and gypsum and then roasting, the reduction decomposition temperature can be significantly reduced;

[0021] (2) During the separation and recovery process, there is no need to add reducing agents such as coal, which can reduce carbon dioxide emissions and is environmentally friendly;

[0022] (3) By introducing CO2 into the slurry, the dissolution of calcium sulfide can be accelerated, thereby effectively separating the solids including calcium ferrite and ferroferric oxide from the calcium sulfide. The separated calcium ferrite and ferroferric oxide can be reused as slag-making agents for steelmaking;

[0023] (4) The separation and recovery process provided by the present invention is simple and is conducive to large-scale industrialization. DETAILED DESCRIPTION

[0024] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0025] The method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products provided by the present invention is described in detail below.

[0026] The method provided by the present invention for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products comprises the following steps:

[0027] S1: pyrite and gypsum are mixed and ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product.

[0028] The active ingredient in the pyrite is ferrous disulfide, and the active ingredient in the dried gypsum is calcium sulfate.

[0029] The gypsum may illustratively include at least one of phosphogypsum, natural gypsum, titanium dioxide by-product gypsum, fluorgypsum and anhydrite.

[0030] In some optional embodiments, the molar ratio of ferrous disulfide in pyrite to calcium sulfate in gypsum can be 1:0.9 to 1:1.2, such as 1:0.9, 1:1, 1:1.1 or 1:1.2, or other values within the range of 1:0.9 to 1:1.2.

[0031] If the molar ratio of ferrous disulfide in pyrite to calcium sulfate in gypsum is lower than 1:0.9 (such as 1:0.5), it is not conducive to the formation of calcium ferrite; if the molar ratio of ferrous disulfide in pyrite to calcium sulfate in gypsum is higher than 1:1.2 (such as 1:1.5), unreacted calcium sulfate will exist in the reduction product.

[0032] In some optional embodiments, the ball-to-material ratio of the first ball milling can be 5:1 to 10:1, such as 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc., based on mass, or other values within the range of 5:1 to 10:1.

[0033] The rotation speed of the first ball milling can be 300 rpm to 500 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, or other values within the range of 300 rpm to 500 rpm.

[0034] In some optional embodiments, the inert atmosphere may illustratively include a nitrogen atmosphere or an argon atmosphere. By performing the calcination under an inert atmosphere, sufficient reduction can be ensured.

[0035] In some optional embodiments, the calcination temperature may be 900°C to 1000°C, such as 900°C, 950°C or 1000°C, or other values within the range of 900°C to 1000°C.

[0036] The calcination time may be 0.5 h to 1.5 h, such as 0.5 h, 1 h or 1.5 h, etc., or other values within the range of 0.5 h to 1.5 h.

[0037] If the calcination temperature is lower than 900℃ or the calcination time is shorter than 0.5h, it is not conducive to the formation of calcium ferrite; if the calcination temperature is higher than 1000℃ or the calcination time is longer than 1.5h, calcium ferrite will react further.

[0038] The calcined product finally obtained in the above S1 is a mixture containing calcium sulfide, calcium ferrite and ferrosoferric oxide.

[0039] S2: The calcined product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and the hydrogen sulfide gas generated during the aeration process is recovered; after the aeration is completed, solid-liquid separation is performed to obtain a solid containing calcium ferrite and ferrosoferric oxide; the recovered hydrogen sulfide gas is reacted with calcium hydroxide to obtain calcium sulfide.

[0040] In some optional embodiments, the solid-liquid ratio of the total amount of the first part of water and the second part of water to the calcined product in the slurry can be 50mL:1g to 150mL:1g, such as 50mL:1g, 80mL:1g, 100mL:1g, 120mL:1g or 150mL:1g, etc., or other values within the range of 50mL:1g to 150mL:1g.

[0041] If the total amount of water is too little, calcium sulfide will dissolve slowly; if the total amount of water is too much, acidification is required to release hydrogen sulfide.

[0042] Among them, the solid-liquid ratio of the first part of water to the roasted product in the slurry can be 10mL:1g to 15mL:1g, such as 10mL:1g, 11mL:1g, 12mL:1g, 13mL:1g, 14mL:1g or 15mL:1g, or other values within the range of 10mL:1g to 15mL:1g.

[0043] In some optional embodiments, the ball-to-material ratio of the second ball milling can be 5:1 to 10:1, such as 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc., based on mass, or other values within the range of 5:1 to 10:1.

[0044] The rotation speed of the second ball milling can be 300 rpm to 500 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, or other values within the range of 300 rpm to 500 rpm.

[0045] In some optional embodiments, the CO2 introduction rate can be 10mL / min to 30mL / min, such as 10mL / min, 15mL / min, 20mL / min, 25mL / min or 30mL / min, or other values within the range of 10mL / min to 30mL / min.

[0046] If the CO2 introduction speed is too slow, it is not conducive to the dissolution of calcium sulfide; if the CO2 introduction speed is too fast, it is not conducive to the capture of hydrogen sulfide gas.

[0047] In some optional embodiments, the aeration time may be 0.5 h to 3 h, such as 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h or 3 h, or other values within the range of 0.5 h to 3 h.

[0048] If the aeration time is too short, calcium sulfide will not dissolve completely and calcium carbonate precipitation will occur; if the aeration time is too long, calcium ferrite will dissolve.

[0049] The chemical reaction equations involved in S2 above include:

[0050] CaS(s)+CO2(g)+H2O→CaCO3(s)↓+H2S(g)↑;

[0051] CaCO3(s)+CO2(g)+H2O→Ca 2+ (aq)+2HCO 3- (aq);

[0052] Ca(OH)(aq)+HS(g)→CaS(s)+2HO(l).

[0053] In other words, the aeration process is primarily used to dissolve calcium sulfide, while calcium ferrite and ferroferric oxide do not participate in the reaction. Therefore, calcium ferrite and ferroferric oxide can be separated through subsequent solid-liquid separation. The separated calcium ferrite and ferroferric oxide can be further used as slag-forming agents in steel mills. The liquid after solid-liquid separation can be recycled.

[0054] In some optional embodiments, a gas absorption device may be used to recover the hydrogen sulfide gas generated during the aeration process; and the recovered hydrogen sulfide gas may be absorbed by calcium hydroxide to recover calcium sulfide.

[0055] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0056] Example 1

[0057] This embodiment provides a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, comprising the following steps:

[0058] S1: pyrite and gypsum are mixed and ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product.

[0059] The gypsum is natural gypsum; the molar ratio of ferrous disulfide, an effective component in pyrite, to calcium sulfate, an effective component in dried gypsum, is 1:1; the ball-to-material ratio of the first ball milling is 8:1, and the rotation speed is 400 rpm; the inert atmosphere is nitrogen atmosphere; the roasting temperature is 900° C., and the roasting time is 1.5 h.

[0060] S2: The calcined product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and the hydrogen sulfide gas generated during the aeration process is recovered by a gas absorption device; after the aeration is completed, solid-liquid separation is performed to obtain a solid containing calcium ferrite and ferrosoferric oxide, and the liquid is recycled; the hydrogen sulfide gas is absorbed by calcium hydroxide to obtain calcium sulfide.

[0061] The solid-to-liquid ratio of the total amount of the first and second water portions to the calcined product in the slurry was 50 mL:1 g, and the solid-to-liquid ratio of the first water portion to the calcined product in the slurry was 10 mL:1 g. The second ball milling had a ball-to-material ratio of 8:1, a rotation speed of 400 rpm, a CO2 injection rate of 20 mL / min, and an aeration time of 1 hour.

[0062] Example 2

[0063] This embodiment provides a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, comprising the following steps:

[0064] S1: pyrite and gypsum are mixed and ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product.

[0065] The gypsum is natural gypsum; the molar ratio of ferrous disulfide, an effective component in pyrite, to calcium sulfate, an effective component in dried gypsum, is 1:1.1; the ball-to-material ratio of the first ball milling is 8:1, and the rotation speed is 400 rpm; the inert atmosphere is nitrogen atmosphere; the roasting temperature is 900° C., and the roasting time is 1 hour.

[0066] S2: The calcined product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and the hydrogen sulfide gas generated during the aeration process is recovered by a gas absorption device; after the aeration is completed, solid-liquid separation is performed to obtain a solid containing calcium ferrite and ferrosoferric oxide, and the liquid is recycled; the hydrogen sulfide gas is absorbed by calcium hydroxide to obtain calcium sulfide.

[0067] The solid-liquid ratio of the total amount of the first and second water portions to the calcined product in the slurry was 100 mL:1 g, and the solid-liquid ratio of the first water portion to the calcined product in the slurry was 10 mL:1 g. The second ball milling was performed with a ball-to-material ratio of 8:1, a rotation speed of 400 rpm, a CO2 injection rate of 20 mL / min, and an aeration time of 1 hour.

[0068] Example 3

[0069] This embodiment provides a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, comprising the following steps:

[0070] S1: pyrite and gypsum are mixed and ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product.

[0071] The gypsum is natural gypsum; the molar ratio of ferrous disulfide, an effective component in pyrite, to calcium sulfate, an effective component in dried gypsum, is 1:1.2; the ball-to-material ratio of the first ball milling is 8:1, and the rotation speed is 400 rpm; the inert atmosphere is nitrogen atmosphere; the roasting temperature is 1000° C., and the roasting time is 0.5 h.

[0072] S2: The roasted product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and the hydrogen sulfide gas generated during the aeration process is recovered by a gas absorption device; after the aeration is completed, the solid and liquid are separated to obtain a solid containing calcium ferrite and ferrosoferric oxide, and the liquid is recycled; the hydrogen sulfide gas is absorbed by calcium hydroxide to obtain calcium sulfide.

[0073] The solid-to-liquid ratio of the total amount of the first and second water portions to the calcined product in the slurry was 100 mL:1 g, and the solid-to-liquid ratio of the first water portion to the calcined product in the slurry was 10 mL:1 g. The second ball milling process had a ball-to-material ratio of 8:1, a rotation speed of 400 rpm, a CO2 injection rate of 20 mL / min, and an aeration time of 2 h.

[0074] Example 4

[0075] This embodiment provides a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, comprising the following steps:

[0076] S1: pyrite and gypsum are mixed and ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product.

[0077] The gypsum is natural gypsum; the molar ratio of ferrous disulfide, an effective component in pyrite, to calcium sulfate, an effective component in dried gypsum, is 1:1.2; the ball-to-material ratio of the first ball milling is 8:1, and the rotation speed is 400 rpm; the inert atmosphere is argon atmosphere; the roasting temperature is 900° C., and the roasting time is 1 hour.

[0078] S2: The roasted product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and the hydrogen sulfide gas generated during the aeration process is recovered by a gas absorption device; after the aeration is completed, the solid and liquid are separated to obtain a solid containing calcium ferrite and ferrosoferric oxide, and the liquid is recycled; the hydrogen sulfide gas is absorbed by calcium hydroxide to obtain calcium sulfide.

[0079] The solid-to-liquid ratio of the total amount of the first and second water portions to the calcined product in the slurry was 150 mL:1 g, and the solid-to-liquid ratio of the first water portion to the calcined product in the slurry was 10 mL:1 g. The second ball milling had a ball-to-material ratio of 8:1, a rotation speed of 400 rpm, a CO2 injection rate of 20 mL / min, and an aeration time of 3 hours.

[0080] Example 5

[0081] This embodiment provides a method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, comprising the following steps:

[0082] S1: pyrite and gypsum are mixed and ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product.

[0083] Among them, the gypsum is gypsum produced as a by-product of titanium dioxide; the molar ratio of ferrous disulfide, an effective ingredient in pyrite, to calcium sulfate, an effective ingredient in dried gypsum, is 1:1.2; the ball-to-material ratio of the first ball milling is 10:1, and the rotation speed is 500 rpm; the inert atmosphere is argon atmosphere; the roasting temperature is 1000°C, and the roasting time is 0.5 h.

[0084] S2: The roasted product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry and aerated under stirring and CO2 introduction conditions, and the hydrogen sulfide gas generated during the aeration process is recovered by a gas absorption device; after the aeration is completed, the solid and liquid are separated to obtain a solid containing calcium ferrite and ferrosoferric oxide, and the liquid is recycled; the hydrogen sulfide gas is absorbed by calcium hydroxide to obtain calcium sulfide.

[0085] The solid-to-liquid ratio of the total amount of the first and second water portions to the calcined product in the slurry was 120 mL:1 g, and the solid-to-liquid ratio of the first water portion to the calcined product in the slurry was 15 mL:1 g. The second ball milling had a ball-to-material ratio of 10:1, a rotation speed of 500 rpm, a CO2 injection rate of 30 mL / min, and an aeration time of 0.5 h.

[0086] Comparative Example 1

[0087] The difference between this comparative example and Example 1 is that the molar ratio of ferrous disulfide in pyrite to calcium sulfate in gypsum is 1:0.5.

[0088] Comparative Example 2

[0089] The difference between this comparative example and Example 1 is that the calcination temperature is 600°C.

[0090] Comparative Example 3

[0091] The difference between this comparative example and Example 1 is that the solid-liquid ratio of the total amount of the first part of water and the second part of water to the roasted product in the slurry is 180 mL:1 g.

[0092] Comparative Example 4

[0093] The difference between this comparative example and Example 1 is that the aeration time is 0.2 h.

[0094] Test example

[0095] The recovery rates and purities of the calcium sulfide and calcium ferrite obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were compared, and the results are shown in Table 1.

[0096] Table 1 Measurement results

[0097]

[0098]

[0099] As can be seen from Table 1, the method provided by the present invention can effectively separate calcium sulfide and calcium ferrite from gypsum, and the separated calcium sulfide and calcium ferrite can be applied in other industrial fields to achieve the effect of turning waste into treasure.

[0100] In summary, the method provided by the present invention has at least the following advantages:

[0101] (1) By ball-milling pyrite and gypsum and then roasting, the reduction decomposition temperature can be significantly reduced;

[0102] (2) During the separation and recovery process, there is no need to add reducing agents such as coal, which can reduce carbon dioxide emissions and is environmentally friendly;

[0103] (3) By introducing CO2 into the slurry, the dissolution of calcium sulfide can be accelerated, thereby effectively separating the solids including calcium ferrite and ferroferric oxide from the calcium sulfide. The separated calcium ferrite and ferroferric oxide can be reused as slag-making agents for steelmaking;

[0104] (4) The separation and recovery process provided by the present invention is simple and is conducive to large-scale industrialization.

[0105] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for separating and recovering calcium sulfide and calcium ferrite from gypsum reduction decomposition products, characterized in that: The following steps are involved: The pyrite and gypsum are mixed and then ball-milled for the first time to obtain a ball-milled material; the ball-milled material is calcined under an inert atmosphere to obtain a calcined product; The calcined product is mixed with the first portion of water and then ball-milled for a second time to obtain a slurry; the second portion of water is added to the slurry, and aeration is performed under stirring and CO2 is introduced, and hydrogen sulfide gas generated during the aeration process is recovered; after the aeration is completed, solid-liquid separation is performed to obtain a solid containing calcium ferrite and ferrosoferric oxide; the recovered hydrogen sulfide gas is reacted with calcium hydroxide to obtain calcium sulfide.

2. The method according to claim 1, characterized in that The gypsum includes at least one of phosphogypsum, natural gypsum, titanium dioxide by-product gypsum, fluorspar and anhydrite.

3. The method according to claim 1, characterized in that The molar ratio of ferrous disulfide in the pyrite to calcium sulfate in the gypsum is 1:0.9 to 1:1.

2.

4. The method according to claim 1, wherein In terms of mass, the ball-to-material ratio of the first ball milling is 5:1 to 10:1, and the rotation speed is 300 rpm to 500 rpm.

5. The method according to claim 1, wherein The inert atmosphere includes a nitrogen atmosphere or an argon atmosphere.

6. The method according to claim 1, characterized in that The calcination temperature is 900°C to 1000°C, and the calcination time is 0.5h to 1.5h.

7. The method according to claim 1, characterized in that The solid-liquid ratio of the total amount of the first part of water and the second part of water to the roasted product in the slurry is 50mL:1g to 150mL:1g, wherein the solid-liquid ratio of the first part of water to the roasted product in the slurry is 10mL:1g to 15mL:1g.

8. The method according to claim 1, characterized in that: The ball-to-material ratio of the second ball milling is 5:1 to 10:1, and the rotation speed is 300 rpm to 500 rpm.

9. The method according to claim 1, characterized in that: The CO2 introduction rate is 10mL / min~30mL / min.

10. The method according to claim 1, characterized in that The aeration time is 0.5h~3h.

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