Treatment method of solid waste residue containing calcium sulfate, magnesium element and rare earth element

Abstract

The invention provides a treatment method of solid waste residues containing calcium sulfate, magnesium elements and rare earth elements. According to the method, carbon dioxide gas is utilized, magnesium elements are separated from the solid waste residues through a carbonization method, and meanwhile part of calcium sulfate is converted into calcium carbonate to be directly recycled. Moreover, a carbonization additive is preferably added in the carbonization reaction, so that the reduction of the whiteness of the product is avoided while the carbonization reaction is ensured, and the subsequent reutilization of the product is not influenced. The method is low in cost, simple, convenient and feasible, and efficient in recovery, and has industrial application value.

Description

Technical Field

[0001] The invention belongs to the technical field of solid waste treatment, and specifically relates to a method for treating solid waste residue containing calcium sulfate, magnesium elements and rare earth elements. Background Art

[0002] The global warming problem caused by carbon dioxide gas emitted from fossil energy has become the focus of global attention. Carbon dioxide is a potential carbon resource, so it needs to be effectively utilized and turned into treasure. Carbon dioxide capture and storage technology (CCS) is a hot research topic in the academic community today. It aims to reduce greenhouse gas emissions by capturing and storing carbon dioxide produced by industry and energy industries. Among them, carbon capture is the first step of CCS technology, and its research focus is on the development of efficient and economical capture methods. Traditional carbon capture mostly uses alkaline solutions (including ammonia water) as absorbents. Currently, more research is done on alcohol amine solutions and porous solid adsorbent materials. However, CCS technology must consider both technical and economic factors. Therefore, the development of new low-cost carbon dioxide capture and storage technologies has important research significance and application prospects.

[0003] On the other hand, solid waste residues mainly containing calcium sulfate, magnesium and rare earth elements are a type of solid waste residue in industrial production treatment. For example, the process of neutralizing magnesium sulfate wastewater produced in the rare earth smelting process with lime is a solid waste with calcium sulfate as the main component, and also contains valuable elements such as magnesium and rare earth. At present, there has been no effective method for treating or recycling such solid waste residues. At present, only stockpiling treatment is done, which not only occupies land resources, but also causes waste of valuable elements and increases environmental pressure. If the valuable elements such as calcium sulfate, magnesium and rare earth contained in such solid waste residues can be recycled and reused, it can save resources and solve environmental problems. Summary of the invention

[0004] In view of the above technical status, the present invention aims to treat solid waste residue containing calcium sulfate, magnesium and rare earth elements, mainly to separate the magnesium element therein, and to turn the calcium sulfate therein into treasure.

[0005] In order to achieve the above technical objectives, the inventors adopt a carbonization method to comprehensively recover solid waste residues containing calcium sulfate, magnesium and rare earth elements, and use cheap and readily available carbon dioxide gas as a medium to separate magnesium from the solid waste residue through a carbonization method. At the same time, part of the calcium sulfate is converted into calcium carbonate. Since the application value of calcium carbonate in actual production and life is far greater than that of calcium sulfate, waste is turned into treasure. In addition, this method is also an effective method for capturing carbon dioxide gas.

[0006] The technical solution provided by the present invention is: a method for treating solid waste residue containing calcium sulfate, magnesium and rare earth elements, comprising the following steps:

[0007] (1) mixing the solid waste residue and water and slurrying;

[0008] (2) introducing carbon dioxide gas into the slurry obtained in step (1) to carry out a carbonization reaction;

[0009] (3) After the carbonization reaction in step (2) is completed, the liquid is subjected to solid-solid separation to obtain an upper slurry and a lower slurry;

[0010] The sizing material is subjected to solid-liquid separation, the obtained upper filter residue is mainly calcium carbonate, and the obtained upper filtrate is a magnesium-containing carbonized liquid;

[0011] The lower slurry is subjected to solid-liquid separation, the obtained lower filter residue is mainly calcium sulfate, and the obtained lower filtrate is a magnesium-containing carbonized liquid.

[0012] Preferably, the upper filtrate and the lower filtrate in step (3) are combined and subjected to a pyrolysis reaction, followed by solid-liquid separation to obtain basic magnesium carbonate solid; further preferably, the obtained pyrolysis liquid is returned to the pulping process of step (1).

[0013] Preferably, the temperature of the pyrolysis reaction is 50°C-90°C.

[0014] The pyrolysis reaction can be carried out under normal pressure or under reduced pressure. In order to reduce operating costs and equipment requirements, the pyrolysis is preferably carried out under reduced pressure.

[0015] In the step (1), the mass ratio of the solid waste residue to water for pulping is 1:1-1:20. As a further preferred method, the solid waste residue is crushed and sieved before pulping, and the particle size of the solid waste residue is preferably below -100 mesh.

[0016] In the step (2), the requirement for the purity of carbon dioxide is not high, and the carbon dioxide mass content is preferably higher than 20%.

[0017] In the step (2), the termination pH of the carbonization reaction by passing carbon dioxide is preferably 6-9, and more preferably 6.5-7.5.

[0018] In the step (2), the reaction temperature of the carbonization reaction is preferably 0°C-40°C, and more preferably 5°C-30°C.

[0019] The solid-solid separation is a device for physically separating solid particles of different densities and particle sizes, and a hydrocyclone is preferred.

[0020] The solid-liquid separation is a device for physically separating solid particles from liquid phase, preferably a filter or a centrifuge.

[0021] The calcium carbonate slag separated in step (3) can be directly reused in the production process, or can be reused after drying. If the particle size and morphology of calcium carbonate need to be controlled, a crystal form regulator that does not significantly affect the process can be added to the carbonization process in step (2) to achieve this.

[0022] Compared with the solid waste residue (i.e., untreated solid waste residue) in step (1), the whiteness of the upper filter residue and the lower filter residue obtained in step (3) may be reduced. The reason is that the rare earth elements contain cerium, and the valence state of the cerium element changes during the carbonization reaction, causing the whiteness change. Considering that the upper filter residue and the lower filter residue obtained in step (3) have a higher whiteness, it is conducive to their reuse. For example, when the calcium sulfate residue has a whiteness greater than 80%, it can be used as a raw material for preparing calcium sulfate whiskers, or as calcium fertilizer or building material filler; the calcium carbonate residue has a higher whiteness and is conducive to a wider range of recycling. For this reason, after research and exploration, the inventor found that adding a carbonization additive to the carbonization reaction in step (2) can ensure the carbonization reaction while avoiding the reduction of the whiteness of the reaction product. The carbonization additive is selected from one or more of hydroxylamine compounds, hydrazine compounds, sulfur dioxide, sulfurous acid and their salts.

[0023] The hydroxylamine compound is not limited, for example, hydroxylamine sulfate is selected. The hydrazine compound is not limited, for example, one or two of hydrazine hydrate, hydrazine sulfate, etc. are selected.

[0024] Preferably, the ratio of the molar amount of the carbonization additive to the molar amount of cerium contained in the solid waste residue is not less than 0.5:1.

[0025] Preferably, water is added to the lower filter residue for pulping and the pH value is adjusted to acidic, so that one or more of carbonate ions, magnesium elements and rare earth elements can be dissolved therein.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The treatment method provided by the present invention can comprehensively recycle solid waste residues containing calcium sulfate, magnesium and rare earth at ambient temperature, thereby achieving the reduction of residue volume, harm reduction treatment and high-value conversion and reuse of industrial solid waste; the process used is simple and easy to operate, with high separation efficiency; the main raw material used is industrial by-product carbon dioxide, which is cheap and easy to obtain, has low processing cost and is easy to apply on a large scale. At the same time, the present invention is also an effective method for capturing carbon dioxide gas;

[0028] (2) The recovery rate of magnesium from solid waste residue in the present invention is higher than 80%;

[0029] (2) The water used in the present invention can be recycled, and the entire process is green and environmentally friendly;

[0030] (3) The calcium sulfate slag and calcium carbonate slag obtained by the preferred treatment method provided by the present invention have a high whiteness, which can be greater than 80%, and does not affect their subsequent treatment and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of the comprehensive recovery and treatment of solid waste residues containing calcium sulfate, magnesium and rare earth elements in Example 1 of the present invention.

[0032] Figure 2 The scanning electron microscope and energy scattering X-ray analysis spectra of the solid waste residue containing calcium sulfate, magnesium and rare earth elements in Example 1 of the present invention are shown in FIG. (a) is a scanning electron microscope image; FIG. (b) is an enlarged image of the circled area in FIG. (a); FIG. (c) is an energy scattering X-ray spectrum of calcium element; and FIG. (d) is an energy scattering X-ray spectrum of magnesium element.

[0033] Figure 3 It is the scanning electron microscope and energy dispersive X-ray analysis spectrum of the carbonized slag in Example 1 of the present invention.

[0034] Among them, (a) is a scanning electron microscope image; (b) is an enlarged image of the circled area in (a); (c) is the energy scattering X-ray spectrum of calcium; (d) is the energy scattering X-ray spectrum of carbon; (e) is the energy scattering X-ray spectrum of sulfur; (f) is the energy scattering X-ray spectrum of oxygen.

[0035] Figure 4 1 is a curve showing the change of solution pH value with carbonization reaction time in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the embodiments and drawings. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0037] The words “include”, “including” and the like used in the present invention should be interpreted as including rather than being exclusive or exhaustive; that is, the meaning is “including but not limited to”.

[0038] Embodiment 1:

[0039] The morphology and composition analysis results of solid waste residue containing calcium sulfate, magnesium and rare earth provided by a certain enterprise are shown in Figure 2 and Table 1. Figure 2 It can be seen that calcium sulfate is in the form of large rods and long blocks, up to tens of microns long and about 5μm-10μm wide; the compounds formed by magnesium mainly exist in smaller particles, some of which are attached to calcium sulfate, and the content of rare earth elements is less and dispersed.

[0040] Table 1. Element contents of solid waste residues containing calcium sulfate, magnesium and rare earth determined by ICP

[0041]

[0042] like Figure 1 As shown, 1 kg of the solid waste residue after grinding and sieving at -100 mesh was taken and placed in a series carbonization tower. Water was added at a mass ratio of 1:10 for slurrying, and then 4 g of calcium bisulfite was added. Carbonization reaction was carried out at 20°C with carbon dioxide until the pH value reached 6.98. After the reaction was completed, samples were taken for testing. The morphology and composition of the solid obtained by sampling are shown in Figure 3 , it can be seen that the main components of the solid after the reaction are calcium carbonate and calcium sulfate. Compared with the two, most of the calcium sulfate crystals still maintain large rods and long blocks. Compared with before the reaction, it is found that their morphology and size have not changed much, and some have become smaller long rod-shaped particles; while the calcium carbonate crystals mainly generate smaller rice-like particles, about 1μm long and about 0.4μm in diameter, and calcium carbonate is mainly attached to the surface of the calcium sulfate crystals. After the reaction, the liquid is pumped into the hydrocyclone for solid-solid separation. The upper slurry flowing out of the top of the hydrocyclone is filtered under reduced pressure to obtain 165g of calcium carbonate solid slag and the first magnesium-containing carbonized liquid; the lower slurry flowing out of the bottom of the cyclone is separated by solid and liquid to obtain 216g of calcium sulfate solid slag and the second magnesium-containing carbonized liquid. The first magnesium-containing carbonized liquid and the second magnesium-containing carbonized liquid are combined and transferred to the pyrolysis reactor, pyrolyzed at 90℃ and normal pressure for 1 hour, and basic magnesium carbonate solid is obtained after filtration. The liquid phase obtained by pyrolysis returns to the pulping process of solid waste slag containing calcium sulfate, magnesium and rare earth.

[0043] Comparative Example 1:

[0044] The rest is the same as Example 1, except that the carbonization additive calcium bisulfite is not added after the solid waste residue containing calcium sulfate, magnesium and rare earth is slurried with water.

[0045] The pH change curves of the carbonization process of Example 1 and Comparative Example 1 are shown in Figure 4 It can be seen that the presence or absence of carbonization additives has no obvious effect on the pH change of the carbonization process. Subsequent analysis found that the carbonization additives have a positive effect on the whiteness of the calcium sulfate solid slag obtained by carbonization. The measured results are shown in Table 3.

[0046] Embodiment 2:

[0047] The rest is the same as Example 1, except that 4 g of hydroxylamine sulfate is added after the solid waste residue containing calcium sulfate, magnesium and rare earth is slurried with water.

[0048] The purity of calcium carbonate slag, the purity of calcium sulfate slag, the total calcium recovery rate and the magnesium recovery rate in Comparative Example 1 and Examples 1 and 2 are shown in Table 2 below.

[0049] Table 2. Purity and recovery of calcium carbonate slag and calcium sulfate slag obtained

[0050]

[0051] The whiteness of the solid waste residue before treatment and the whiteness of the calcium sulfate obtained after treatment in Comparative Example 1, Example 1, and Example 2 are shown in Table 3 below.

[0052] Table 3. Whiteness test results of raw material slag and obtained calcium sulfate slag (%)

[0053]

[0054] Embodiment 3:

[0055] Take 50 g of the solid calcium sulfate residue obtained in Example 1, add 50 mL of water to slurry, adjust the pH value to 1-2 with 2 mol / L sulfuric acid, stir for 5 hours, filter, and measure the magnesium and lanthanum content of the residue by ICP to be 92 ppm, 10.8 ppm, and 45.1 ppm.

[0056] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating solid waste residue containing calcium sulfate, magnesium and rare earth elements, characterized in that: The steps include: (1) mixing the solid waste residue and water and slurrying; (2) introducing carbon dioxide gas into the slurry obtained in step (1) to carry out a carbonization reaction; (3) After the carbonization reaction in step (2) is completed, the liquid is subjected to solid-solid separation to obtain an upper slurry and a lower slurry; The sizing material is subjected to solid-liquid separation, the obtained upper filter residue is mainly calcium carbonate, and the obtained upper filtrate is a magnesium-containing carbonized liquid; The lower slurry is subjected to solid-liquid separation, the obtained lower filter residue is mainly calcium sulfate, and the obtained lower filtrate is a magnesium-containing carbonized liquid.

2. The processing method according to claim 1, characterized in that: In the step (1), the mass ratio of the solid waste residue and water mixed and slurried is 1:1-1:20; Preferably, the solid waste residue is crushed and sieved before pulping, and the particle size of the solid waste residue is preferably below -100 mesh.

3. The processing method according to claim 1, characterized in that: In the step (2), the mass content of carbon dioxide is higher than 20%; Preferably, in step (2), the termination pH of the carbonization reaction by passing carbon dioxide is 6-9, more preferably 6.5-7.5; Preferably, in step (2), the carbonization reaction temperature is 0°C-40°C, more preferably 5°C-30°C.

4. The processing method according to claim 1, characterized in that: The solid-solid separation equipment is a hydrocyclone; Preferably, the solid-liquid separation equipment is a filter or a centrifuge.

5. The processing method according to claim 1, characterized in that: The calcium carbonate slag separated in step (3) is directly reused in the production process, or can be reused after drying; Preferably, the calcium sulfate slag separated in step (3) is used as a raw material for preparing calcium sulfate whiskers, or as a calcium fertilizer.

6. The processing method according to claim 1, characterized in that: The upper filtrate and the lower filtrate in step (3) are combined and then subjected to a pyrolysis reaction, followed by solid-liquid separation to obtain a basic magnesium carbonate solid; Preferably, the pyrolysis liquid obtained by solid-liquid separation is returned to the pulping process of step (1); Preferably, the temperature of the pyrolysis reaction is 50°C-90°C; Preferably, the pyrolysis reaction is carried out at room temperature or under reduced pressure.

7. The processing method according to claim 1, characterized in that: In the step (2), a carbonization additive is added to the slurry; The carbonization additive is selected from one or more of hydroxylamine compounds, hydrazine compounds, sulfur dioxide, sulfurous acid and salts thereof; Preferably, the hydroxylamine compound is hydroxylamine sulfate; Preferably, the hydrazine compound is selected from one or both of hydrazine hydrate and hydrazine sulfate; Preferably, the ratio of the molar amount of the carbonization additive to the molar amount of cerium contained in the solid waste residue is not less than 0.5:

1.

8. The processing method according to claim 7, characterized in that: The whiteness of the upper filter residue in step (3) is greater than 80%, and the whiteness of the lower filter residue is greater than 80%.

9. The processing method according to claim 1, characterized in that: In the step (3), the magnesium recovery rate is greater than 80%.

10. The processing method according to any one of claims 1 to 9, characterized in that: After adding water to the lower filter residue for pulping, the pH value is adjusted to acidic to dissolve one or more of the carbonate ions, magnesium elements and rare earth elements therein.

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