Method for preparing delta-calcium chromite from chromium-containing sludge

Abstract

The invention relates to a method for preparing delta-calcium chromite from chromium-containing sludge, and the method comprises the following steps: mixing auxiliary materials and pretreated chromium-containing sludge, and carrying out heating treatment in a vacuum atmosphere or an inert gas atmosphere to obtain the delta-calcium chromite, the pretreatment method comprises sintering. According to the method, the chromium-containing sludge is activated through pretreatment, the activity of the chromium-containing sludge is improved, and the high-purity single delta-calcium chromite product is prepared through fused salt heating treatment and acid pickling impurity removal. In the preparation process, molten salt heating treatment is carried out in a vacuum atmosphere or an inert gas atmosphere, trivalent chromium ions are prevented from being oxidized into hexavalent chromium ions, and then a high-purity product is obtained. According to the method, harmlessness, high-efficiency recycling and productization of the chromium-containing sludge are realized, and the method has remarkable economic value and social benefit.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic materials, and relates to a method for preparing calcium chromite, and in particular to a method for preparing delta-calcium chromite from chromium-containing sludge. Background Art

[0002] In the process of treating chromium-containing wastewater in the electroplating and leather industries, high-chromium sludge is produced. This type of sludge is a hazardous waste and its treatment and storage are strictly regulated. If high-chromium sludge is not properly treated and disposed of, it will not only waste expensive chromium resources and occupy a large amount of land, but also contain heavy metals (especially Cr 6+ The release of chromium-containing waste residues causes great harm to human health and the ecological environment. Therefore, it is particularly urgent to propose harmless and resource-based technologies for chromium-containing waste residues.

[0003] The mainstream disposal method of chromium-containing sludge is to use solidification or stabilization pretreatment and then landfill it in a hazardous waste landfill. The disposal fee is much higher than the landfill fee of general waste. Therefore, if a method can be found to recover chromium in sludge and eliminate the hazardous waste attribute of chromium-containing sludge, it will have important practical value for the resource utilization of chromium-containing sludge and reduce the cost of sludge disposal.

[0004] At present, there are two main methods for the recovery of chromium resources in chromium-containing sludge: first, chromium is extracted by acid leaching or alkaline leaching. CN109402400A discloses a method for recovering chromium from chromium-containing sludge under alkaline conditions, by mixing chromium-containing sludge with sodium carbonate solution, introducing CO2, heating and pressurizing for leaching, and solid-liquid separation after leaching to obtain chromium-containing solution and leached residue. This method can improve the extraction rate of chromium element, but it will produce a large amount of chromium-containing wastewater, which is easy to cause secondary pollution to the environment, and the recycling of chromium element is not fully realized. Another method is to use high-temperature roasting to recover chromium salts. CN110683739A discloses a treatment process for chromium-containing waste residues, which can detoxify chromium-containing waste residues such as chromium-containing sludge and coarse slag process chromium slag in wastewater stations, so that the highly toxic hexavalent chromium in the waste residue is converted into trivalent chromium with low toxicity, thereby reducing the situation in which the hexavalent chromium in the chromium-containing waste residue causes serious pollution to the surrounding environment. This process has high roasting temperature and high energy consumption. The separation of impurities and purification of products also have certain technical difficulties, and the commercialization of chromium-containing sludge has not been fully realized.

[0005] As an important industrial raw material, delta-calcium chromite has unique structure and properties and can be widely used in magnetic materials, catalysts, pigments or environmental remediation. In the existing technology, it is difficult to efficiently recycle and commercialize chromium-containing sludge. Therefore, converting chromium-containing sludge into corresponding industrial products, especially converting it into delta-calcium chromite, and realizing the commercialization of chromium-containing sludge has become an urgent problem to be solved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing delta-calcium chromite from chromium-containing sludge, wherein the chromium-containing sludge is activated by pretreatment to improve the activity of the chromium-containing sludge, and then a high-purity single delta-calcium chromite product is prepared by molten salt heating treatment and pickling for impurity removal. During the preparation process, the molten salt is heated in a vacuum atmosphere or an inert gas atmosphere to prevent trivalent chromium ions from being oxidized to hexavalent chromium ions. The present invention realizes the harmlessness, efficient resource utilization and productization of chromium-containing sludge, and has significant economic value and social benefits. The present invention makes full use of the chromium and calcium contained in the sludge, directly converts the sludge into a product with higher added value, delta-calcium chromite, and is convenient to operate and environmentally friendly.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing delta-calcium chromite from chromium-containing sludge, the method comprising the following steps:

[0009] After the auxiliary materials and the pretreated chromium-containing sludge are mixed, they are heated in a vacuum atmosphere or an inert gas atmosphere to obtain the delta-calcium chromite; the pretreatment method includes sintering.

[0010] The present invention activates chromium-containing sludge by pretreatment to improve the activity of chromium-containing sludge, and then prepares a high-purity single δ-calcium chromite product by molten salt heating treatment and pickling to remove impurities. In the preparation process, molten salt heating treatment is carried out under a vacuum atmosphere or an inert gas atmosphere to prevent trivalent chromium ions from being oxidized to hexavalent chromium ions to obtain a high-purity product. The present invention realizes the harmlessness, efficient resource utilization and productization of chromium-containing sludge, and has significant economic value and social benefits. The present invention makes full use of the chromium and calcium contained in the sludge, directly converts the sludge into a product with higher added value, δ-calcium chromite, and is convenient to operate and environmentally friendly.

[0011] Preferably, the pretreatment temperature is 400°C-600°C, for example, 400°C, 450°C, 500°C, 550°C or 600°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0012] Preferably, the pretreatment time is 2 h-8 h, for example, 2 h, 3 h, 4 h, 6 h or 8 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] The present invention can remove moisture and organic matter in chromium-containing sludge by pretreatment and reasonably regulating the temperature and time of pretreatment, and can activate the chromium-containing sludge, thereby improving the activity of the chromium-containing sludge, improving its reactivity and facilitating the synthesis of delta-calcium chromite, and can also further improve the yield and product purity of the chromium-containing sludge.

[0014] Preferably, the chromium-containing sludge comprises calcium oxide and chromium trioxide.

[0015] Preferably, the auxiliary material comprises calcium chloride.

[0016] Calcium chloride has a low melting point and forms a sub-molten salt state under high temperature. Calcium oxide has a high solubility in calcium chloride molten salt, which transforms the traditional solid-phase reaction into a liquid-phase reaction, which is beneficial to sufficient mass transfer between reactants, reduces the reaction activation energy, and is also beneficial to low-temperature and rapid reaction.

[0017] Preferably, the auxiliary material further comprises calcium oxide.

[0018] Preferably, the auxiliary material further includes carbon powder.

[0019] Preferably, the added amount of the carbon powder is 0.2wt%-0.8wt% of the chromium-containing sludge, for example, it can be 0.2wt%, 0.4wt%, 0.6wt%, 0.7wt% or 0.8wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, before the mixing, the auxiliary materials are dried.

[0021] Preferably, the drying temperature is 70°C-120°C, for example, 70°C, 80°C, 90°C, 100°C, 110°C or 120°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] Preferably, the drying time is 2h-4h, for example, 2h, 2.5h, 3h, 3.5h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] Preferably, the molar ratio of chromium trioxide in the chromium-containing sludge to calcium chloride in the auxiliary material is 1:(5-20), for example, it can be 1:5, 1:8, 1:10, 1:15, 1:18 or 1:20, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the molar amount of chromium trioxide in the chromium-containing sludge is M1, the molar amount of calcium oxide in the chromium-containing sludge is M2, and the molar amount of calcium oxide in the auxiliary material is M3, then the value of M1:(M2+M3) is 1:(1.5-3.5), for example, it can be 1:1.5, 1:2, 1:2.5, 1:3 or 1:3.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the mixing method comprises ball milling.

[0026] Preferably, the ball milling comprises dry ball milling.

[0027] Preferably, after the mixing and before the heating treatment, screening is also included.

[0028] Preferably, the mesh size of the sieving is 100-150 mesh, for example, it can be 100 mesh, 110 mesh, 120 mesh, 130 mesh, 140 mesh or 150 mesh, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] Preferably, the heating rate of the heat treatment is 4°C / min-8°C / min, for example, 4°C / min, 5°C / min, 6°C / min, 7°C / min or 8°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] Preferably, the atmosphere of the heat treatment includes a vacuum atmosphere or an inert gas atmosphere.

[0031] Preferably, in the vacuum atmosphere, the temperature of the heating treatment is 780°C-950°C, for example, 780°C, 800°C, 850°C, 900°C or 950°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] Preferably, the heating treatment time under the vacuum atmosphere is 45 min-80 min, for example, 45 min, 50 min, 60 min, 70 min, 75 min or 80 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] The invention performs heating treatment under vacuum atmosphere to form a molten salt environment, and further improves the yield of calcium chromite and the purity of delta-calcium chromite by further controlling the heating treatment temperature and the heating treatment time.

[0034] Preferably, the temperature of the heating treatment under the inert gas atmosphere is 750°C-850°C, for example, it can be 750°C, 770°C, 790°C, 800°C, 820°C or 850°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the heating treatment time under the inert gas atmosphere is 55 min-90 min, for example, 55 min, 60 min, 70 min, 80 min or 90 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] The invention performs heating treatment under an inert gas atmosphere to form a molten salt environment, and further improves the yield of calcium chromite and the purity of delta-calcium chromite by further controlling the heating treatment temperature and the heating treatment time.

[0037] Preferably, the inert gas atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

[0038] Preferably, after the heating treatment, washing and drying are also performed in sequence.

[0039] Preferably, the washing comprises acid washing and water washing performed sequentially.

[0040] Preferably, the pickling detergent comprises hydrochloric acid.

[0041] Preferably, the concentration of the detergent is 0.01mol / L-0.1mol / L, for example, it can be 0.01mol / L, 0.02mol / L, 0.04mol / L, 0.06mol / L, 0.08mol / L or 0.1mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] Preferably, the drying temperature is 70°C-90°C, for example, 70°C, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the drying time is 20 min-40 min, for example, 20 min, 25 min, 30 min, 35 min or 40 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] As a preferred technical solution of the present invention, the method for preparing delta-calcium chromite from chromium-containing sludge comprises the following steps:

[0045] (1) Drying the auxiliary material at 70° C.-120° C. for 2 h-4 h to obtain the dried auxiliary material.

[0046] (2) Pretreating the chromium-containing sludge at 400° C.-600° C. for 2 h-8 h to obtain pretreated chromium-containing sludge.

[0047] (3) The dried auxiliary material and the pretreated chromium-containing sludge are ball-milled and then sieved to obtain undersize material, wherein the mesh number of the sieve is 100-150 mesh.

[0048] (4) The screened material is subjected to heat treatment in a vacuum atmosphere or an inert gas atmosphere to obtain a crude product of delta-calcium chromite.

[0049] In the vacuum atmosphere, the temperature of the heating treatment is 780° C.-950° C., and the time of the heating treatment is 45 min-80 min.

[0050] In the inert gas atmosphere, the temperature of the heating treatment is 750° C.-850° C., and the time of the heating treatment is 55 min-90 min.

[0051] (5) The crude product of delta-calcium chromite is respectively subjected to acid washing and water washing, and then dried at 70° C.-90° C. for 20 min-40 min to obtain the delta-calcium chromite, wherein the acid washing detergent comprises 0.01 mol / L-0.1 mol / L hydrochloric acid.

[0052] Compared with the prior art, the present invention has at least the following beneficial effects:

[0053] (1) The present invention activates the chromium-containing sludge by pretreatment to improve the activity of the chromium-containing sludge, and then performs molten salt heating treatment and acid washing to remove impurities to prepare a high-purity single delta-calcium chromite product.

[0054] (2) In the preparation process of the present invention, a molten salt heating treatment is performed in a vacuum atmosphere or an inert gas atmosphere to prevent trivalent chromium ions from being oxidized to hexavalent chromium ions to obtain a high-purity product.

[0055] (3) The present invention realizes the harmlessness, efficient resource utilization and productization of chromium-containing sludge, and has significant economic value and social benefits. The present invention makes full use of the chromium and calcium contained in the sludge, directly converts the sludge into a product with higher added value, delta-calcium chromite, and is easy to operate and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 is a SEM image of delta-calcium chromite prepared in Example 1 of the present invention;

[0057] Figure 2 This is the XRD diagram of the delta-calcium chromite prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0059] Example 1

[0060] This embodiment provides a method for preparing delta-calcium chromite from chromium-containing sludge, the method comprising the following steps:

[0061] (1) drying the auxiliary materials CaO and CaCl2 at 80° C. for 3 h to obtain the dried auxiliary materials;

[0062] (2) pretreating the chromium-containing sludge at 500° C. for 4 h, wherein the composition of the chromium-containing sludge is as shown in Table 1, to obtain pretreated chromium-containing sludge;

[0063] (3) ball-milling the dried auxiliary material and the pretreated chromium-containing sludge, and then sieving to obtain undersize material;

[0064] The molar ratio of chromium trioxide in the chromium-containing sludge to calcium chloride in the auxiliary material is 1:15, and the molar ratio of chromium trioxide in the chromium-containing sludge to the sum of calcium oxide in the chromium-containing sludge and calcium oxide in the auxiliary material is 1:1.5; the mesh number of the sieving is 120 meshes;

[0065] (4) heating the undersize material in a vacuum atmosphere to obtain a crude product of delta-calcium chromite;

[0066] In the vacuum atmosphere, the heating temperature is 900°C, the heating time is 50 min, and the heating rate is 6°C / min.

[0067] (5) washing the crude product of delta-calcium chromite with acid and water respectively, and then drying at 80° C. for 30 min to obtain the delta-calcium chromite; the washing agent for the acid washing comprises 0.1 mol / L hydrochloric acid;

[0068] Figure 1 : This is a SEM image of the delta-calcium chromite prepared in Example 1 of the present invention. It can be seen from the image that the prepared delta-calcium chromite is a micron-sized flake with uniform size;

[0069] Figure 2 3 is the XRD diagram of the delta-calcium chromite prepared in Example 1 of the present invention. It can be seen from the figure that the calcium chromite prepared in this example is a delta phase.

[0070] Example 2

[0071] This embodiment provides a method for preparing delta-calcium chromite from chromium-containing sludge, the method comprising the following steps:

[0072] (1) drying the auxiliary materials CaO and CaCl2 at 70° C. for 4 h to obtain the dried auxiliary materials;

[0073] (2) pretreating the chromium-containing sludge at 600° C. for 2 h, wherein the composition of the chromium-containing sludge is as shown in Table 1, to obtain pretreated chromium-containing sludge;

[0074] (3) ball-milling the dried auxiliary material and the pretreated chromium-containing sludge, and then sieving to obtain undersize material;

[0075] The molar ratio of chromium trioxide to calcium chloride in the chromium-containing sludge is 1:5, and the molar ratio of chromium trioxide in the chromium-containing sludge to the sum of calcium oxide in the chromium-containing sludge and calcium oxide in the auxiliary material is 1:3.5; the mesh number of the sieving is 100 mesh;

[0076] (4) heating the undersize material in a nitrogen atmosphere to obtain a crude product of delta-calcium chromite;

[0077] In the nitrogen gas atmosphere, the heating temperature is 800° C., the heating time is 60 min, and the heating rate is 8° C. / min.

[0078] (5) The crude product of delta-calcium chromite is respectively subjected to acid washing and water washing, and then dried at 70° C. for 40 min to obtain the delta-calcium chromite; the acid washing detergent comprises 0.05 mol / L hydrochloric acid.

[0079] Example 3

[0080] This embodiment provides a method for preparing delta-calcium chromite from chromium-containing sludge, the method comprising the following steps:

[0081] (1) drying the auxiliary materials CaO, CaCl2 and carbon powder at 120° C. for 2 h to obtain the dried auxiliary materials;

[0082] (2) pretreating the chromium-containing sludge at 400° C. for 8 h, wherein the composition of the chromium-containing sludge is as shown in Table 1, to obtain pretreated chromium-containing sludge;

[0083] (3) ball-milling the dried auxiliary material and the pretreated chromium-containing sludge, and then sieving to obtain undersize material;

[0084] The molar ratio of chromium trioxide to calcium chloride in the chromium-containing sludge is 1:20, and the molar ratio of chromium trioxide in the chromium-containing sludge to the sum of calcium oxide in the chromium-containing sludge and calcium oxide in the auxiliary material is 1:2; the amount of carbon powder added is 0.6wt% of the chromium-containing sludge; the mesh number of the sieve is 150 mesh;

[0085] (4) heating the undersize material in a vacuum atmosphere to obtain a crude product of delta-calcium chromite;

[0086] In the vacuum atmosphere, the heating temperature is 780°C, the heating time is 80 min, and the heating rate is 4°C / min.

[0087] (5) The crude product of delta-calcium chromite is respectively subjected to acid washing and water washing, and then dried at 90° C. for 20 min to obtain the delta-calcium chromite; the acid washing detergent comprises 0.01 mol / L hydrochloric acid.

[0088] Example 4

[0089] The only difference between this embodiment and embodiment 1 is that, except that the pretreatment temperature in step (2) is 350° C., the rest is the same as embodiment 1.

[0090] Example 5

[0091] The only difference between this embodiment and embodiment 1 is that, except that the pretreatment temperature in step (2) is 650° C., the rest is the same as embodiment 1.

[0092] Example 6

[0093] The only difference between this embodiment and embodiment 1 is that, except that the pretreatment time in step (2) is 1.5 h, the rest is the same as embodiment 1.

[0094] Example 7

[0095] The only difference between this embodiment and embodiment 1 is that, except that the pretreatment time in step (2) is 8.5 h, the rest is the same as embodiment 1.

[0096] Example 8

[0097] The only difference between this embodiment and embodiment 1 is that, except for the temperature of the heating treatment in step (4) being 770° C., the rest is the same as embodiment 1.

[0098] Example 9

[0099] The only difference between this embodiment and embodiment 1 is that, except for the temperature of the heating treatment in step (4) being 960° C., the rest is the same as embodiment 1.

[0100] Example 10

[0101] The only difference between this embodiment and embodiment 2 is that, except for the temperature of the heating treatment in step (4) being 740° C., the rest is the same as embodiment 2.

[0102] Embodiment 11

[0103] The only difference between this embodiment and embodiment 2 is that, except for the temperature of the heating treatment in step (4) being 860° C., the rest is the same as embodiment 2.

[0104] Comparative Example 1

[0105] The difference between this comparative example and Example 1 is that, except that the pretreatment in step (2) is not performed, the rest is the same as Example 1.

[0106] Comparative Example 2

[0107] This comparative example provides a method for preparing calcium chromite from chromium-containing sludge, the method comprising the following steps:

[0108] (1) weighing raw materials according to a molar ratio of chromium trioxide to calcium chloride of 1:5 and a molar ratio of chromium trioxide to calcium oxide of 1:3.5, and successively ball milling and sieving to obtain a sieve-cut material; the mesh number of the sieve is 100 mesh;

[0109] (2) heating the undersize material in a nitrogen atmosphere to obtain a crude calcium chromite product;

[0110] In the nitrogen gas atmosphere, the heating temperature is 980°C, the heating time is 60 minutes, and the heating rate is 8°C / min.

[0111] (5) The crude calcium chromite product is respectively subjected to acid washing and water washing, and then dried at 80° C. for 30 min to obtain the calcium chromite; the acid washing detergent comprises 0.05 mol / L hydrochloric acid, and the prepared calcium chromite is mainly α-calcium chromite.

[0112] Test Method

[0113] The calcium chromite obtained in Examples 1-11 and Comparative Examples 1-2 was collected and subjected to XRD test, and the yield of calcium chromite and the purity of delta-calcium chromite therein were calculated and recorded in Table 2.

[0114] Table 1

[0115] Actual ingredients <![CDATA[Cr2O3]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Na2O]]> Proportion 73.22％ 19.36％ 2.79％ 1.34％ 0.8634％ 0.7985％

[0116] Table 2

[0117]

[0118]

[0119] The test results show that:

[0120] (1) It can be seen from Examples 1-11 and Comparative Examples 1-2 that the present invention activates chromium-containing sludge by pre-treatment to improve the activity of chromium-containing sludge, and then prepares a high-purity single δ-calcium chromite product by molten salt heating treatment and pickling to remove impurities. During the preparation process, molten salt heating treatment is carried out under a vacuum atmosphere or an inert gas atmosphere to prevent trivalent chromium ions from being oxidized to hexavalent chromium ions to obtain a high-purity product. The present invention achieves the harmlessness, efficient resource utilization and productization of chromium-containing sludge, and has significant economic value and social benefits. The present invention makes full use of the chromium and calcium contained in the sludge, directly converts the sludge into a product with higher added value, δ-calcium chromite, and is easy to operate and environmentally friendly.

[0121] (2) It can be seen from Examples 1 and 4-7 that the present invention can remove moisture and organic matter in chromium-containing sludge by further regulating the temperature and time of pretreatment, and at the same time activate the chromium-containing sludge, thereby improving the activity of the chromium-containing sludge, improving its reactivity and facilitating the synthesis of δ-calcium chromite, and can also further improve the yield of calcium chromite.

[0122] (3) It can be seen from Examples 1-2 and Examples 8-11 that the present invention is beneficial to the synthesis of delta-calcium chromite and further improves the yield of calcium chromite by further regulating the temperature of the heating treatment.

[0123] (4) It can be seen from Examples 1-2 and Comparative Examples 1-2 that the present invention activates the chromium-containing sludge by pretreatment to improve the activity of the chromium-containing sludge, and then prepares metastable δ-calcium chromite by heat treatment; if the chromium-containing sludge is not pretreated or chromium trioxide is directly used as the raw material, the purity of the δ-phase calcium chromite in the product is relatively low.

[0124] In summary, the present invention activates chromium-containing sludge by pretreatment to improve the activity of chromium-containing sludge, and then prepares a high-purity single δ-calcium chromite product by molten salt heating treatment and pickling for impurity removal. During the preparation process, molten salt heating treatment is carried out under a vacuum atmosphere or an inert gas atmosphere to prevent trivalent chromium ions from being oxidized to hexavalent chromium ions to obtain a high-purity product. The present invention realizes the harmlessness, efficient resource utilization and productization of chromium-containing sludge, and has significant economic value and social benefits. The present invention makes full use of the chromium and calcium contained in the sludge, directly converts the sludge into a product with higher added value, δ-calcium chromite, and is easy to operate and environmentally friendly.

[0125] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing delta-calcium chromite from chromium-containing sludge, characterized in that: The method comprises the following steps: After mixing the auxiliary materials and the pretreated chromium-containing sludge, heating treatment is performed under a vacuum atmosphere or an inert gas atmosphere to obtain the delta-calcium chromite; The pretreatment method includes sintering.

2. The method according to claim 1, characterized in that: The pretreatment temperature is 400°C-600°C; Preferably, the pretreatment time is 2h-8h.

3. The method according to claim 1 or 2, characterized in that: The chromium-containing sludge includes calcium oxide and chromium trioxide; Preferably, the auxiliary material includes calcium chloride; Preferably, the auxiliary material further comprises calcium oxide.

4. The method according to claim 3, characterized in that The molar ratio of chromium trioxide in the chromium-containing sludge to calcium chloride in the auxiliary material is 1:(5-20); Preferably, the molar amount of chromium trioxide in the chromium-containing sludge is M1, the molar amount of calcium oxide in the chromium-containing sludge is M2, and the molar amount of calcium oxide in the auxiliary material is M3, then the value of M1:(M2+M3) is 1:(1.5-3.5).

5. The method according to any one of claims 1 to 4, characterized in that: The mixing method includes ball milling; Preferably, after the mixing and before the heating treatment, the step further includes screening; Preferably, the mesh size of the sieving is 100-150 mesh.

6. The method according to any one of claims 1 to 5, characterized in that: The heating rate of the heating treatment is 4°C / min-8°C / min; Preferably, the atmosphere of the heat treatment includes a vacuum atmosphere or an inert gas atmosphere.

7. The method according to claim 6, characterized in that In the vacuum atmosphere, the temperature of the heating treatment is 780°C-950°C; Preferably, the heating treatment time under the vacuum atmosphere is 45 min-80 min.

8. The method according to claim 6, characterized in that The temperature of the heating treatment under the inert gas atmosphere is 750°C-850°C; Preferably, the heating treatment time under the inert gas atmosphere is 55 min-90 min; Preferably, the inert gas atmosphere includes a nitrogen atmosphere and / or an argon atmosphere.

9. The method according to any one of claims 1 to 8, characterized in that: After the heating treatment, washing and drying are also performed in sequence; Preferably, the washing comprises acid washing and water washing performed sequentially; Preferably, the pickling detergent comprises hydrochloric acid.

10. The method according to claim 9, characterized in that The drying temperature is 70°C-90°C; Preferably, the drying time is 20 min-40 min.

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