Method for chromium residue mineral phase deconstruction and metal cation synergistic sufficient chromium removal

Abstract

The application discloses a method for fully removing chromium from chromium residue by deconstructing mineral phase and extracting metal cations, which mainly utilizes phase conversion means to fully extract residual chromium elements in the chromium residue while selectively removing magnesium and aluminum. The steps are as follows: firstly, the chromium residue is crushed and sieved, an activating agent is added and roasting is performed, ultrasonic leaching is performed with a sulfuric acid solution, and then alkali-assisted hydrothermal deconstruction is performed on the activated residue to obtain chromium-iron residue and soluble aluminum and chromium solution; an oxidizing agent is added to the soluble aluminum and chromium solution, the pH value is adjusted after hydrothermal reaction, and aluminum hydroxide precipitate and soluble chromate solution are obtained; the chromium-iron residue is mixed with a carbonate and is ground, hot catalytic oxidation deconstruction is performed, ultrasonic leaching is performed with a sulfuric acid solution, and soluble chromate and magnetite are obtained. The chromium removal rate of the application can reach 96.49%, and the intermediate product ammonium sulfate can be recycled, realizing harmless treatment of the chromium residue.

Description

Technical Field

[0001] This invention relates to the field of chromium slag solid waste treatment technology, specifically to a method for the synergistic and thorough dechromium removal of chromium slag mineral phases by deconstructing metal cations. Background Technology

[0002] Chromium salts are crucial raw materials in chemical, electroplating, metallurgy, and pigment industries, playing a vital role in modern chemical production. With the booming development of the chemical and steel industries, the production and use of chromium salts have surged, inevitably generating chromium-containing waste—chromium slag. During transportation and open-air storage, chromium slag is subjected to prolonged weathering and rainwater immersion, leading to the slow loss and release of large amounts of hexavalent chromium ions into the environment. This pollutes groundwater, rivers, and lakes, severely impacting aquaculture, farmland, and various flora and fauna, posing a significant threat to human health and environmental safety. Furthermore, chromium slag is a potential source of the heavy metal chromium; approximately 10% of the total chromium resources in chromium slag are not fully extracted and utilized. Improper disposal of chromium slag not only damages the ecological environment and biosafety but also wastes usable resources. Therefore, the environmental safety and resource waste problems caused by chromium slag urgently need to be addressed.

[0003] Currently, commonly used methods for treating chromium slag include ferrous sulfate reduction, high-temperature roasting, hydrothermal extraction, and stabilization / immobilization. However, the chromium removed by the commonly used ferrous sulfate reduction and roasting methods cannot be recycled, and the reduced trivalent chromium will oxidize back to hexavalent chromium due to environmental changes, failing to completely detoxify it. In the industrial field, chromium slag is often converted into raw materials such as ceramics and microcrystalline glass at high temperatures, which can effectively utilize the chromium slag. However, in this process, the heavy metal chromium is not separated and extracted, resulting in a low chromium recovery rate.

[0004] Chromium in chromium slag exists in a complex and varied manner. Trivalent chromium mainly exists as chromite [(Fe,Mg)₂CrO₄] and calcite [Ca₂(Fe,Al)₂CrO₄], while hexavalent chromium mainly exists in chromium slag as adsorption / coating / encapsulation in solid interstices or as chromate solid solutions within the mineral lattice. Therefore, further treatment of the residue after leaching hexavalent chromium from chromium slag is a current research direction. Chinese patent "A Combined Treatment Method for Chromium-Containing Hazardous Waste by Leaching, Detoxification, and Mineralization Stabilization" (CN115006776A) uses oxidant to oxidize and roast chromium, converting it into soluble hexavalent chromium, and then uses an organic leaching agent to elute the hexavalent chromium, which relatively improves the removal of hexavalent chromium. However, the residue still contains unleashed chromium, which is subsequently recovered by adding a reducing agent and a precipitant. However, this method cannot completely detoxify the chromium slag, and the treated chromium slag still poses a serious environmental hazard. Chinese patent "A Comprehensive Utilization Method for Calcium-Iron-Chromium Sludge" (CN115626773A) involves mixing calcium-iron-chromium sludge, water, and soluble carbonates, then roasting them repeatedly to separate the calcium from the iron and chromium in the solution. This method requires a large amount of chemical reagents such as acids and precipitants, and the process is complex and costly. Summary of the Invention

[0005] Objective of the Invention: This invention aims to overcome the deficiencies of existing technologies and provide a method for the synergistic and thorough removal of chromium from chromium slag by deconstructing the ore phase and extracting metal cations. Based on the analysis of the composition and key elements of chromium slag, and the findings that Mg and Al play crucial roles in the Cr main phase, this invention introduces an activator during the removal process to remove Mg from the metal ore phase. 2+ Plasma is released from the mineral phase crystals, and after further solid-liquid separation, chromium remains in the mineral residue. The activated slag undergoes further dealuminization treatment, using an alkali-assisted hydrothermal-oxidant-assisted oxidation method to remove Al. 3+ The ions are released, followed by solid-liquid separation, and then the chromium is fully removed by a combination of carbonate roasting and acid leaching. This invention provides a feasible solution for the full extraction and resource utilization of residual chromium in chromium slag, and has reference value for the resource utilization of other chromium-containing solid wastes.

[0006] Technical solution: A method for the synergistic and complete dechromium removal of chromium from chromium slag phases through deconstruction, comprising the following steps:

[0007] 1) Weigh a certain amount of chromium slag, add an activator; mix and grind, then pyrolyze and oxidize under an inert atmosphere to obtain the calcined product;

[0008] 2) Add a certain amount of sulfuric acid solution to the roasted product obtained in step 1), perform ultrasonic leaching, and after solid-liquid separation, obtain the upper layer solution and the lower layer residue; wash the lower layer residue and then dry it to obtain the magnesium-removed residue.

[0009] 3) Add a certain amount of alkaline solution to the magnesium-removed residue obtained in step 2) and mix well. Place the mixture in a high-pressure reactor and carry out an alkaline-assisted hydrothermal reaction. After the reaction is completed, perform solid-liquid separation to obtain an upper solution and a lower residue. Wash the lower residue and then dry it to obtain the aluminum-removed residue.

[0010] 4) Add a certain amount of oxidant to the upper solution obtained in step 3), mix and stir at room temperature, and then put it into a high-pressure reactor for auxiliary oxidation hydrothermal reaction; after the reaction is completed, add hydrochloric acid dropwise until acidic, and after solid-liquid separation, aluminum hydroxide precipitate and soluble chromate solution are obtained.

[0011] 5) Mix and grind the dealuminized residue obtained in step 3) with a certain amount of carbonate, and perform thermal catalytic oxidation decomposition to obtain decomposition products; add sulfuric acid solution to the decomposition products and perform ultrasonic leaching to obtain soluble chromate solution and magnetite.

[0012] Further, in step 1), the chromium slag is a chromium slag with a residual chromium content of 5-10%, and the main mineral phases of the chromium slag are magnesium, aluminum spinel and diopside.

[0013] It should be noted that in step 2), the upper solution is a soluble magnesium solution; in step 3), the upper solution is a soluble aluminum and chromium solution (a dark green transparent solution containing aluminate and chromite), and the lower residue is ferrochrome slag (a black solid iron ore slag containing ferrochrome spinel phase).

[0014] Further, in step 1), the chromium slag is pretreated before adding the activator; the pretreatment includes drying, crushing and sieving the chromium slag. Drying and sieving the chromium slag reduces its moisture content, thereby further enhancing the reaction between the compounds within it.

[0015] Furthermore, the drying temperature is 70–80°C.

[0016] Furthermore, the sieve used for crushing and screening is 100-200 mesh. A 200-mesh sieve is preferred, as the chromium slag obtained by screening has a suitable particle size and is more likely to react with other additives.

[0017] Further, in step 1), the activator is ammonium sulfate, or a combination of sodium sulfate, potassium sulfate and ammonia, or a combination of sodium sulfate, potassium sulfate and ammonium chloride, hydroxylamine hydrochloride; the molar ratio of sulfate in the activator to magnesium and calcium elements (total) in the chromium slag is 1.2 to 3:1; the molar ratio of nitrogen in the activator to chromium in the chromium slag is 7 to 15:1.

[0018] Further, in step 1), the pyrolysis oxidation-reduction calcination is a calcination with a programmed temperature increase to 700-800℃, and the temperature increase rate is 5℃ / min.

[0019] Further, in step 1), the mixture is ground in a mortar and the uniformly mixed solid is poured into a porcelain boat and placed in a tube furnace for calcination under an argon atmosphere; the grinding time is 20-60 min; the calcination time is 1-4 h.

[0020] Further, in step 2), the concentration of the sulfuric acid solution is 0.5–2 mol / L, the mass-to-volume ratio of the calcined product to the sulfuric acid solution is 1:10–20, and the ultrasonic leaching time is 0.5 h–1 h.

[0021] Further, in step 2), the solid-liquid separation is carried out by centrifugation, with a centrifugation speed of 6000-8000 rpm and a centrifugation time of 3-5 min; the drying is carried out in an oven at a temperature of 70-80℃, preferably 80℃; and the drying time is 8-12 h, preferably 10 h.

[0022] Further, under ultrasonic conditions, ammonia water is added dropwise to the upper layer solution (soluble magnesium solution) obtained in step 2), resulting in magnesium hydroxide precipitate and ammonium sulfate solution. The resulting ammonium sulfate solution can be used as an activator and recycled back to step 1).

[0023] Further, ammonia water is added dropwise to the upper solution obtained in step 2) until the pH of the solution is greater than 7.

[0024] Further, in step 3), the alkaline solution is sodium hydroxide or calcium hydroxide; the molar ratio of hydroxide ions in the alkaline solution to the total amount of aluminum and chromium elements in the chromium slag is 1 to 3:1; the temperature of the alkaline-assisted hydrothermal reaction is 160°C to 180°C, and the reaction time is 7 to 9 hours.

[0025] Further, in step 3), the volume of the reaction liquid in the alkali-assisted hydrothermal reaction is 60-70% of the volume of the polytetrafluoroethylene liner of the high-pressure reactor.

[0026] Further, in step 3), the solid-liquid separation is carried out by centrifugation, with a centrifugation speed of 6000-8000 rpm and a centrifugation time of 3-5 min; the drying is carried out in an oven at a temperature of 70-80℃, preferably 80℃; and the drying time is 8-12 h, preferably 10 h.

[0027] Further, in step 4), the oxidant is sodium hypochlorite or hydrogen peroxide; the molar ratio of sodium hypochlorite to chromium in the chromium slag is 0.8–1.2:1; the molar ratio of hydrogen peroxide to chromium in the chromium slag is 1.6–2.4:1; the temperature of the auxiliary oxidation hydrothermal reaction is 100–110°C, and the reaction time is 1–2 h.

[0028] Further, in step 4), hydrochloric acid is added dropwise to the solution after the auxiliary oxidation hydrothermal reaction is completed until the pH of the solution is 4 to 5, preferably 5; the concentration of the hydrochloric acid is 1 to 2 mol / L.

[0029] Further, in step 5), the carbonate is sodium carbonate or potassium carbonate, preferably sodium carbonate; the molar ratio of carbonate ions in the carbonate to chromium in the chromium slag is 10-15:1; the thermocatalytic oxidation decomposition is carried out under an argon atmosphere, with a heating rate of 5℃ / min to 500-700℃ and stable roasting for 2-3 hours.

[0030] Further, in step 5), the concentration of the sulfuric acid solution is 0.5–2 mol / L, and the mass-to-volume ratio of the deconstruction product to the sulfuric acid solution is 1:20–30.

[0031] Further, the soluble chromate solution obtained in steps 4) and 5) is acidified and concentrated to recover the dichromate product.

[0032] The principle of this invention is as follows: Cr in chromium slag exists in two valence states, Cr(III) and Cr(VI), with the main host phases being Mg- and Al-containing spinel and diopside. Based on the identification results of the host phases of Cr in chromium slag, various chemical activation systems are developed to deconstruct the chromium slag mineral phases and extract the metal cations (Mg... 2+ Al 3+ (etc.) is separated, and then combined with sodium carbonate roasting and acid leaching to convert the chromium in the chromium slag into hexavalent chromium for complete removal. Different activation systems are constructed, and chemical activators such as ammonium salts are introduced to selectively activate the Cr-bearing phase, thereby deconstructing and transforming the Cr-bearing phase in the chromium slag. The possible chemical reactions in the activation system are as follows:

[0033] (Taking (NH4)2SO4 roasting combined with H2SO4 leaching activation and deMg removal as an example)

[0034] (NH4)2SO4→NH4HSO4+NH3↑

[0035] (NH4)2SO4→H2SO4+NH3↑

[0036] Cr(VI)-MgCaSiO x+H2SO4→MgSO4+CaSO4+SiO2+Cr2O7 2-

[0037] Cr2O7 2- +NH3→CrO4 2- +Cr2O3+NO 2- +H2O

[0038] CrO4 2- +NH3→Cr2O3+NO - +H2O

[0039] Mg(Fe,Cr)2O4+H2SO4→MgSO4+(Fe,Cr)2(SO4)3+H2O

[0040] (Fe,Cr)2(SO4)3→(Fe,Cr)2O3+SO3

[0041] Because Al exhibits amphoteric properties, it dissolves in an alkaline environment. To selectively remove Al, an oxidizing agent can be added to the solution. The relevant reaction process is as follows:

[0042] AlFeO3+NaOH→Fe2O3+NaAlO2+H2O

[0043] Al3Fe5O 12 +NaOH→Fe₂O₃+NaAlO₂+H₂O

[0044] Cr 1.3 Fe 0.7 O3 + NaOH → Fe2O3 + NaCrO2 + H2O

[0045] Cr2O3 + NaOH → NaCrO2 + H2O

[0046] HCl+NaAlO2+H2O→NaCl+Al(OH)3↓

[0047] NaCrO2+NaClO+NaOH→Na2CrO4+NaCl+H2O

[0048] Chromium in ferrochrome spinel is difficult to remove by adding alkali. A basic process combining carbonate roasting and acid leaching is employed to construct different mineralization agent chromium extraction systems to fully remove chromium. The possible chemical reactions in the chromium extraction system are as follows:

[0049] (Taking Na2CO3 roasting combined with H2SO4 leaching for chromium extraction as an example)

[0050] Cr2O3+Na2CO3+O2→Na2CrO4+CO2↑

[0051] (Fe,Cr)2O3+Na2CO3+O2→Fe2O3+Na2CrO4+CO2↑

[0052] Na2CrO4+H2SO4→Na2Cr2O7+Na2SO4+H2O

[0053] Beneficial effects:

[0054] 1) Before chromium removal treatment, the present invention first performs magnesium removal and aluminum removal on chromium slag. Through the magnesium removal and aluminum removal steps, the chromium slag is deconstructed, and the magnesium and aluminum in magnesium, aluminum spinel and diopside (magnesium-aluminum and chromium coexisting phase) in the chromium slag are selectively removed. Hexavalent chromium is extracted from chromite using a carbonate-sulfuric acid leaching process, and the chromium slag is converted into easily extractable magnetite and chromates, thereby obtaining iron concentrate and high-purity dichromates, effectively extracting iron and chromium resources, and thus realizing the resource utilization of industrial solid waste chromium slag.

[0055] 2) Compared with the method of directly removing chromium from chromium slag by carbonate roasting and acid leaching, the present invention removes magnesium and aluminum from the chromium slag by deconstruction before carbonate roasting and acid leaching, which can extract chromium resources from the magnesium-aluminum-chromium coexisting phase and achieve full extraction of chromium; the present invention is still applicable to chromium slag with chromium content of less than 10%, and the chromium removal rate in chromium slag is as high as 96.49%, thereby further reducing the hazards of hazardous solid waste chromium slag;

[0056] 3) The ammonium sulfate solution obtained in the process of demagnesifying chromium slag can be used as an activator and added to the chromium slag for recycling, which saves more resources and helps reduce costs. Attached Figure Description

[0057] Figure 1 This is a technical roadmap of the method of the present invention;

[0058] Figure 2 The graph shows the effect of different amounts of ammonium sulfate added on the magnesium removal rate and residual amount in the magnesium residue after magnesium removal in Examples 1-2 and Comparative Examples 1-3.

[0059] Figure 3 The graph shows the effect of different calcination temperatures on the magnesium removal rate and residual amount in the magnesium residue after demagnesiation in Examples 2-4 and Comparative Examples 4-5.

[0060] Figure 4 The graph shows the elemental extraction rates of the residues after dealuminization in Examples 5-7 and Comparative Examples 6-8 with different amounts of NaOH added.

[0061] Figure 5 The image shows a comparison of the chromium removal results between Example 8 and Comparative Examples 9-10. Detailed Implementation

[0062] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0063] The chromium slag (COPR) used in the following examples is an industrial solid hazardous waste produced by steelmaking plants through a high-temperature alkaline roasting-acid leaching process to produce chromium salts. The main chemical composition of COPR is listed in Table 1.

[0064] Table 1. Main Chemical Composition of COPR

[0065]

[0066] The main metallic elements in the aforementioned chromium slag include Fe, Mg, Al, and Cr. The inventors discovered that these metallic elements primarily exist in the form of chromite [(Fe,Mg)₂CrO₄] and calcite [Ca₂(Fe,Al)₂CrO₄].

[0067] The present invention mainly consists of three parts for the dechromium removal treatment of chromium slag: the first part is selective demagnesiation by roasting with an activator; the second part is dealuminization assisted by adding an alkaline hydrothermal-oxidant; and the third part is chromium removal by roasting with sodium carbonate combined with acid leaching.

[0068] Example 1

[0069] (1) Dry the chromium slag at 80℃ for 12 hours, and sieve it through a 200-mesh sieve for later use. Weigh 5g of chromium slag and mix it thoroughly with 2.5g of ammonium sulfate (activator). After grinding for 30 minutes, pour the mixture into a ceramic boat and place it in a tube furnace. Heat it at 700℃ for 2 hours with argon gas through the furnace. The heating rate is 5℃ / min. This causes the chromium slag to undergo the first step of activation and deconstruction, resulting in the activated residue of the calcined product.

[0070] (2) The activated residue obtained above was ultrasonically soaked in 0.5 mol / L sulfuric acid for 30 min, and the volume was measured as 30 mL. It was centrifuged at 8000 rpm for 5 min to separate the solid and liquid; washed 5 times with deionized water; and the solid product was dried in an oven at 80℃ for 10 h to obtain the magnesium-removed residue.

[0071] Example 2

[0072] (1) Dry the chromium slag at 80℃ for 12 hours, and sieve it through a 200-mesh sieve for later use. Weigh 5g of chromium slag and mix it thoroughly with 3.75g of ammonium sulfate (activator). After grinding for 30 minutes, pour the mixture into a ceramic boat and place it in a tube furnace. Heat it at 700℃ for 2 hours with argon gas through the furnace. The heating rate is 5℃ / min. This causes the chromium slag to undergo the first step of activation and deconstruction, resulting in the activated residue of the calcined product.

[0073] (2) The activated residue obtained above was ultrasonically soaked in 0.5 mol / L sulfuric acid for 30 min, and the volume was measured as 30 mL. It was centrifuged at 8000 rpm for 5 min to separate the solid and liquid; washed 5 times with deionized water; and the solid product was dried in an oven at 80℃ for 10 h to obtain the magnesium-removed residue.

[0074] Example 3

[0075] The difference compared to Example 2 is that the calcination temperature is 750°C.

[0076] Example 4

[0077] The difference from Example 2 is that the calcination temperature is 800°C.

[0078] Example 5

[0079] (1) 5g of the magnesium-removed residue obtained in Example 4 and 0.8g of sodium hydroxide were added to 60mL of deionized water and mixed evenly at room temperature. Then the mixture was put into a high-pressure reactor and heated at 180°C for 8h.

[0080] (2) The suspension obtained after the reaction in the high-pressure reactor is completed is subjected to solid-liquid separation to obtain the upper layer containing AlO. 2- With CrO 2- The solution and the iron slag solid containing chromium oxide were then centrifuged and washed, and dried at 80°C for 10 hours to obtain the dealuminized residue.

[0081] (3) Add AlO to the upper layer obtained above. 2- With CrO 2- Add 5 mmol of NaClO to the solution and mix. Place the mixed solution into a high-pressure reactor for hydrothermal heating at 100℃ for 1 hour. After the reaction is completed, cool to room temperature and add hydrochloric acid to adjust the pH of the solution to 5. Centrifuge to separate the solid and liquid phases to obtain Al(OH)3 solid precipitate and NaCrO4 solution.

[0082] Example 6

[0083] The difference compared to Example 5 is that the amount of sodium hydroxide added is 1.6g.

[0084] Example 7

[0085] The difference compared to Example 5 is that the amount of sodium hydroxide added is 2.4g.

[0086] Example 8

[0087] (1) Weigh 5g of the dealuminized residue (AR-HR) obtained in Example 7 and mix it with 3.25g of sodium carbonate for 30min. Then pour the mixture into a ceramic boat and calcine it in a tube furnace under an argon atmosphere at a calcine temperature of 600℃ for 2h with a heating rate of 5℃ / min.

[0088] (2) After the above roasting is completed, the sodium chromate is extracted by ultrasonication with 0.5 mol / L sulfuric acid for 30 min and soluble sodium chromate and the dechromated solid are collected.

[0089] Comparative Example 1

[0090] The difference compared to Example 1 is that the amount of ammonium sulfate added is 5.0g.

[0091] Comparative Example 2

[0092] The difference compared to Example 1 is that the amount of ammonium sulfate added is 6.25g.

[0093] Comparative Example 3

[0094] The difference compared to Example 1 is that the amount of ammonium sulfate added is 0g.

[0095] Comparative Example 4

[0096] The difference compared to Example 2 is that the calcination temperature is 850°C.

[0097] Comparative Example 5

[0098] The difference from Example 2 is that the calcination temperature is 900°C.

[0099] Comparative Example 6

[0100] The difference compared to Example 5 is that the amount of sodium hydroxide added is 3.2g.

[0101] Comparative Example 7

[0102] The difference compared to Example 5 is that the amount of sodium hydroxide added is 4.0g.

[0103] Comparative Example 8

[0104] The difference compared to Example 5 is that the amount of sodium hydroxide added is 0g.

[0105] Comparative Example 9

[0106] (1) Weigh 5g of original chromium slag (COPR) and mix and grind 3.25g of sodium carbonate for 30min. Then pour the mixture into a porcelain boat and calcine it in a tube furnace under an argon atmosphere at a temperature of 600℃ for 2h with a heating rate of 5℃ / min.

[0107] (2) After the above roasting is completed, the sample is leached with 0.5 mol / L sulfuric acid for 30 min by sonication, and the soluble chromate and the dechromated solid are collected.

[0108] Comparative Example 10

[0109] (1) Weigh 5g of the magnesium-removed residue (AR) obtained in Example 4 and mix and grind it with 3.25g of sodium carbonate for 30min. Then pour the mixture into a ceramic boat and calcine it in a tube furnace under an argon atmosphere at a calcine temperature of 600℃ for 2h with a heating rate of 5℃ / min.

[0110] (2) After the above roasting is completed, the sample is leached with 0.5 mol / L sulfuric acid for 30 min by sonication, and the soluble chromate and the dechromated solid are collected.

[0111] The upper soluble magnesium solutions and magnesium-removed residues obtained after calcination in Examples 1-2 and Comparative Examples 1-3 were analyzed. The amount of Mg leached from the leaching solution and its content in the solid matter were determined by ICP to calculate the removal rate. The residual Mg content in the magnesium-removed residues was determined, and the test results are shown in [Figure number missing]. Figure 2 and Figure 3 .

[0112] like Figure 2-3 As shown, Figure 2 The effects of different amounts of ammonium sulfate (2.5g, 3.75g, 5g, 6.25g, 0g) on ​​the magnesium removal rate and residual amount in the magnesium residue after demagnesification are shown in Examples 1-2 and Comparative Examples 1-3. It is found that 3.25g of ammonium sulfate is the optimal amount for 5g of chromium slag. Figure 3 The effects of different calcination temperatures (700℃, 750℃, 800℃, 850℃, 900℃) on the magnesium removal rate and residual amount in the magnesium residue after demagnesiation are shown in Examples 2-4 and Comparative Examples 4-5, revealing that 800℃ is the optimal temperature. Figure 2-3 It can be seen that the amount of ammonium sulfate added to 5g of chromium slag is 3.75g, the roasting temperature is 800℃, and the roasting time is 2h, which are the optimal conditions for the demagnesiation process in the method of the present invention.

[0113] The main metal contents in the dealuminized residues obtained in Examples 5-7 and Comparative Examples 6-8 were determined, and the test results are shown in [Figure number missing]. Figure 4 .

[0114] like Figure 4 As shown, Figure 4 The elemental extraction rates of the residues after dealumination in Examples 5-7 and Comparative Examples 6-8 with different NaOH addition amounts (0.8 g, 1.6 g, 2.4 g, 3.2 g, 4.0 g, 0 g) are shown. It can be seen that the proportion of Cr(III)-oxides increases after the addition of sodium hydroxide, and the main chromium-bearing phase is Cr2O3. Figure 4 It can be seen that adding 0.8-2.4g of sodium hydroxide to 5g of activated slag is a more favorable condition for the dealuminization process in the method of the present invention.

[0115] After digesting the chromium-removed samples obtained in Example 8 and Comparative Examples 9-10, their chromium content was determined by ICP using the formula: Removal rate (%) = (M Cr -M1)×100% / M1 (where M Cr M1 represents the mass fraction of chromium (mg / g) in the sample after chromium removal, and M2 represents the mass fraction of chromium (mg / g) in COPR. The chromium removal rate is calculated using this formula. The calculation results are shown below. Figure 5 .

[0116] like Figure 5 As shown, the chromium removal rate of Comparative Example 9 was 82.37%, the chromium removal rate of Comparative Example 10 was 94.16%, and the chromium removal rate of Example 8 was 96.49%. Figure 5 It is evident that the chromium removal rates of Comparative Example 10 and Example 8 are higher than those of Comparative Example 9, demonstrating that the activation and deconstruction treatment can release chromium from the chromium slag, which is an indispensable step in achieving thorough chromium removal. Although the chromium removal rate of Example 8 is only 2.33% higher than that of Comparative Example 10, this improvement is relatively small because smaller amounts of chromium remaining in the solid are more difficult to remove, but it is still higher than the chromium removal effect of other similar methods currently available. Figure 5 It can be seen that the method of removing magnesium and aluminum from chromium slag by deconstruction and then performing alkali roasting combined with acid leaching can achieve full extraction of chromium.

[0117] The above embodiments achieve the following beneficial effects compared to the prior art:

[0118] 1) Before chromium removal treatment, the present invention first performs magnesium removal and aluminum removal on chromium slag. Through the magnesium removal and aluminum removal steps, the chromium slag is deconstructed, and the magnesium and aluminum in magnesium, aluminum spinel and diopside (magnesium-aluminum and chromium coexisting phase) in the chromium slag are selectively removed. Hexavalent chromium is extracted from chromite using a carbonate-sulfuric acid leaching process, and the chromium slag is converted into easily extractable magnetite and chromates, thereby obtaining iron concentrate and high-purity dichromates, effectively extracting iron and chromium resources, and thus realizing the resource utilization of industrial solid waste chromium slag.

[0119] 2) Compared with the method of directly removing chromium from chromium slag by carbonate roasting and acid leaching, the present invention removes magnesium and aluminum from the chromium slag by deconstruction before carbonate roasting and acid leaching, which can extract chromium resources from the magnesium-aluminum-chromium coexisting phase and achieve full extraction of chromium; the present invention is still applicable to chromium slag with chromium content of less than 10%, and the chromium removal rate in chromium slag is as high as 96.49%, thereby further reducing the hazards of hazardous solid waste chromium slag;

[0120] 3) The ammonium sulfate solution obtained in the process of demagnesifying chromium slag can be used as an activator and added to the chromium slag for recycling, which saves more resources and helps reduce costs.

[0121] Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art should understand that various changes and modifications can be made to the present invention without departing from the scope defined by the claims.

Claims

1. A method for the synergistic and complete dechromium removal of chromium from chromium slag ore phases through the deconstruction of metal cations, characterized in that, Includes the following steps: 1) Weigh a certain mass of chromium slag, add an activator; mix and grind, then pyrolyze and oxidize under an inert atmosphere to obtain the calcined product; 2) Add a certain amount of sulfuric acid solution to the calcined product obtained in step 1), perform ultrasonic leaching, and after solid-liquid separation, obtain the upper solution and the lower residue. The lower layer residue is washed and then dried to obtain the magnesium-removed residue; 3) Add a certain amount of alkaline solution to the magnesium-removed residue obtained in step 2) and mix well. Place the mixture in a high-pressure reactor and carry out an alkaline-assisted hydrothermal reaction. After the reaction is completed, perform solid-liquid separation to obtain the upper solution and the lower residue. The lower layer of residue is washed and then dried to obtain the residue after aluminum removal; 4) Add a certain amount of oxidant to the upper solution obtained in step 3), mix and stir at room temperature, and then put it into a high-pressure reactor for auxiliary oxidation hydrothermal reaction; after the reaction is completed, add hydrochloric acid dropwise until acidic, and after solid-liquid separation, aluminum hydroxide precipitate and soluble chromate solution are obtained. 5) Mix and grind the dealuminated residue obtained in step 3) with a certain amount of carbonate, and perform thermal catalytic oxidation deconstruction to obtain the deconstruction product; Sulfuric acid solution was added to the deconstruction product, and ultrasonic leaching was performed to obtain a soluble chromate solution and magnetite. In step 1), the activator is ammonium sulfate, or a combination of sodium sulfate, potassium sulfate and ammonia, or a combination of sodium sulfate, potassium sulfate and ammonium chloride, hydroxylamine hydrochloride; the molar ratio of sulfate in the activator to magnesium and calcium in the chromium slag is 1.2~3:1; the molar ratio of nitrogen in the activator to chromium in the chromium slag is 7~15:

1.

2. The method according to claim 1, characterized in that, In step 1), the chromium slag is pretreated before the activator is added; the pretreatment includes drying the chromium slag, crushing and sieving; the drying temperature is 70~80℃, and the sieve used for crushing and sieving is 100~200 mesh.

3. The method according to claim 1, characterized in that, In step 1), the pyrolysis oxidation-reduction calcination is performed by programmed heating to 700~800℃, and the heating rate of the programmed heating is 5℃ / min.

4. The method according to claim 1, characterized in that, In step 2), the concentration of the sulfuric acid solution is 0.5~2 mol / L, the mass-to-volume ratio of the calcined product to the sulfuric acid solution is 1:10~20, and the ultrasonic leaching time is 0.5 h~1 h.

5. The method according to claim 1, characterized in that, In step 3), the alkaline solution is sodium hydroxide or calcium hydroxide; the molar ratio of hydroxide ions in the alkaline solution to aluminum and chromium elements in the chromium slag is 1~3:1; the temperature of the alkaline-assisted hydrothermal reaction is 160℃~180℃, and the reaction time is 7~9 hours.

6. The method according to claim 1, characterized in that, In step 4), the oxidant is sodium hypochlorite or hydrogen peroxide; the molar ratio of sodium hypochlorite to chromium in the chromium slag is 0.8~1.2:1; the molar ratio of hydrogen peroxide to chromium in the chromium slag is 1.6~2.4:1; the temperature of the auxiliary oxidation hydrothermal reaction is 100~110℃, and the reaction time is 1~2 h.

7. The method according to claim 1, characterized in that, In step 4), hydrochloric acid is added dropwise to the solution after the auxiliary oxidation hydrothermal reaction is completed until the pH of the solution is 4-5; the concentration of the hydrochloric acid is 1-2 mol / L.

8. The method according to claim 1, characterized in that, In step 5), the carbonate is sodium carbonate or potassium carbonate, and the molar ratio of carbonate ions in the carbonate to chromium in the chromium slag is 10~15:1; the thermocatalytic oxidation decomposition is carried out under an argon atmosphere, with the temperature increased to 500~700℃ at a heating rate of 5℃ / min and then stably roasted for 2~3 h.

9. The method according to claim 1, characterized in that, In step 5), the concentration of the sulfuric acid solution is 0.5~2 mol / L, and the mass-to-volume ratio of the deconstruction product to the sulfuric acid solution is 1:20~30.

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