A method for extracting chromium by oxidizing and roasting chromium-containing materials

Abstract

The present invention provides a method for extracting chromium by oxidative roasting of chromium-containing materials. The method comprises the following steps: grinding and mixing the chromium-containing material, an alkali, and an additive, followed by oxidative roasting to obtain a roasted clinker; the additive comprises the following elements: Cr, Fe, Si, and C; and leaching the roasted clinker to obtain a leachate and a leached residue. The present invention utilizes a specific additive mixed with the chromium-containing material and the alkali to effectively enhance the oxidative roasting process of the chromium-containing material, achieving efficient extraction of chromium from the chromium-containing material and resource utilization of the chromium in the additive. The method also reduces the oxidative roasting temperature, achieving low-temperature, energy-saving roasting of chromite ore. Subsequently, after leaching and solid-liquid separation of the roasted clinker, the chromium content in the leached residue is significantly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic salt production and relates to a method for extracting chromium by oxidizing and roasting chromium-containing materials. Background Art

[0002] Currently, the primary method for industrially producing chromium salts is the calcium-free roasting method. The main technical route involves using an alkali such as sodium carbonate to decompose and oxidize chromite under oxidative roasting conditions, converting the insoluble trivalent chromium compounds in the chromite into water-soluble sodium chromate. The chromium in the ore is then separated through water leaching. The resulting sodium chromate solution is then acidified, evaporated, and crystallized to produce sodium dichromate. The sodium dichromate is then used in a sulfuric acid process to produce chromic anhydride, or reduced to produce chromium salts such as chrome green.

[0003] However, in the traditional chromite oxidation roasting process, the roasting temperature is as high as 1100-1200°C. Sodium chromate has a low melting point and easily forms low-melting-point eutectics with by-products such as sodium ferrite and sodium aluminate in the charge. This leads to problems such as reduced chromium oxidation reaction rate and oxidation conversion rate, and kiln ring formation, which greatly affects production. To eliminate the adverse effects of the liquid phase on the production process, it is necessary to add slag or limestone / dolomite as fillers, which is 2-3 times the amount of ore, to the roasting charge to reduce the proportion of liquid phase in the charge. Despite this, the oxidation conversion rate of chromium in chromite is still less than 85%. At the same time, the chromium grade in the slag is relatively low. The addition of large amounts of slag is equivalent to lowering the overall grade of the ore, reducing the effective contact area between the alkali and chromium, thereby reducing the chromium oxidation rate and resulting in a low leaching rate.

[0004] CN116590545A discloses a method for intensifying the chromium extraction process by calcium-free roasting of chromite. The method comprises the following steps: adding a sulfuric acid solution to a chromium slag to carry out a leaching reaction to obtain an acid leaching residue; using the acid leaching residue as a modified filler and mixing it with chromite and sodium carbonate to obtain a mixed material; roasting the mixed material in an air atmosphere to obtain a roasted clinker; directly quenching the roasted clinker with water or cooling it and then soaking it in water, performing solid-liquid separation, and obtaining a sodium chromate solution and a chromium filter residue. While this method solves the problems of large chromium slag emissions and large chromium residues in existing chromite ore production processes, the chromium slag still contains residual impurities such as aluminum and magnesium during the acid leaching process, and the continuous circulation during the roasting process affects the chromium recovery rate and reduces production stability.

[0005] Currently, flow batteries are considered one of the leading technologies for large-scale energy storage due to their safety, long cycle life, recyclable electrolyte, and environmental friendliness. Iron-chromium flow batteries, the earliest proposed and applicable type of flow battery, offer significant advantages such as independent system energy and power, low material cost, ease of scalability, high safety, fast response, long cycle life, and high energy efficiency. They are a promising large-scale energy storage technology that has experienced rapid development in recent years.

[0006] CN116826127A discloses a method for preparing an electrolyte for an iron-chromium flow battery. The method comprises the following steps: mixing a ferrochromium raw material with hydrochloric acid to obtain a leachate; concentrating and cooling the resulting leachate to crystallize it, thereby obtaining mixed crystals and a mother liquor; and dissolving the resulting mixed crystals, followed by mixing with hydrochloric acid and a chloride salt, thereby obtaining an electrolyte for an iron-chromium flow battery. However, the method does not disclose a comprehensive utilization scheme or method for the ferrochromium alloy leachate residue.

[0007] Therefore, a method for extracting chromium from chromite by calcium-free roasting using ferrochrome leaching residue as an additive is provided, so that the chromium in the ferrochrome leaching residue can be fully extracted, the conversion rate of chromium in the chromite roasting process can be improved, the amount of aluminum mud generated can be reduced, and low-temperature energy-saving roasting treatment of chromite can be achieved, which is of great value for promoting the development of the chromium salt production industry and the iron-chromium liquid flow battery industry. Summary of the Invention

[0008] The object of the present invention is to provide a method for extracting chromium by oxidative roasting of chromium-containing materials. The method adopts a specific additive to be mixed with the chromium-containing material and an alkali to effectively enhance the oxidative roasting process of the chromium-containing material, thereby achieving efficient extraction of chromium from the chromium-containing material and resource utilization of the chromium in the additive. At the same time, the temperature of the oxidative roasting is reduced, thereby achieving low-temperature and energy-saving roasting treatment of chromite.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] The present invention provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0011] (1) grinding and mixing the chromium-containing material, alkali and additives, and then oxidizing and roasting to obtain roasted clinker;

[0012] The additives include the following elements: Cr, Fe, Si, C;

[0013] (2) Leaching the roasted clinker in step (1) to obtain a leachate and a leach residue.

[0014] The method for extracting chromium by oxidizing and roasting chromium-containing materials provided by the present invention uses a specific additive to mix with the chromium-containing material and an alkali to effectively strengthen the oxidizing and roasting process of the chromium-containing material, thereby achieving efficient extraction of chromium from the chromium-containing material and resource utilization of the chromium in the additive. The oxidation reaction of chromium in the material is significantly accelerated, the oxidation rate is significantly improved, and the oxidizing and roasting temperature is reduced, the oxidizing and roasting time is shortened, and low-temperature energy-saving roasting treatment of chromite is achieved. Subsequently, after leaching the roasted clinker, the chromium content in the leached residue is significantly reduced.

[0015] It is worth noting that the additives used in the present invention have the following effects: first, when the additives are added during the oxidative roasting process, the iron element therein generates ferrate, which enhances the roasting and chromium extraction, thereby helping to increase the oxidation rate of chromium; second, during the oxidative roasting process, silicon combines with aluminum in the chromium-containing material to form aluminosilicates that are fixed in the slag phase, thereby reducing the generation of aluminum sludge in the subsequent neutralization process; third, carbon increases the calorific value during the roasting process, thereby reducing the roasting temperature and time, thereby having the advantages of energy conservation and emission reduction.

[0016] As a preferred technical solution of the present invention, the chromium-containing material in step (1) includes chromite and / or chromium slag.

[0017] In the present invention, the chromite and chromium slag both contain a certain content of Cr2O3.

[0018] As a preferred technical solution of the present invention, the base in step (1) includes any one of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide, or a combination of at least two of them, wherein the combination is typically but not limited to: a combination of sodium carbonate and potassium carbonate, a combination of potassium carbonate and sodium hydroxide, or a combination of sodium hydroxide and potassium hydroxide, etc.

[0019] Preferably, the mass ratio of the alkali to the chromium-containing material in step (1) is (0.5-2):1, for example, it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1 or 1.9:1, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] As a preferred technical solution of the present invention, the additive in step (1) includes the following elements in terms of mass content: Cr: 30wt.%~60wt.%, Fe: 10wt.%~30wt.%, Si: 1wt.%~20wt.%, C: 5wt.%~30wt.%, and the remainder is O and unavoidable impurities.

[0021] In the present invention, the Cr element in the additive mainly exists in the form of Cr single substance, the Fe element mainly exists in the form of Fe single substance, and the Si and C elements exist in the form of carbides and silicides.

[0022] In the present invention, the additive contains 30 wt.% to 60 wt.% of Cr element, for example, 32 wt.%, 35 wt.%, 38 wt.%, 40 wt.%, 42 wt.%, 45 wt.%, 48 wt.%, 50 wt.%, 52 wt.%, 55 wt.% or 58 wt.%, and the additive contains 10 wt.% to 30 wt.% of Fe element, for example, 12 wt.%, 15 wt.%, 18 wt.%, 20 wt.%, 22 wt.%, 25 wt.% or 28 wt.%, etc. The additive contains 1 wt.% to 20 wt.% of Si element, for example, it can be 2 wt.%, 5 wt.%, 8 wt.%, 10 wt.%, 12 wt.%, 15 wt.% or 18 wt.%, and the additive contains 5 wt.% to 30 wt.% of C element, for example, it can be 8 wt.%, 10 wt.%, 12 wt.%, 15 wt.%, 18 wt.%, 20 wt.%, 22 wt.%, 25 wt.% or 28 wt.%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the mass ratio of Fe to Cr in the additive in step (1) is (0.4-0.8):1, for example, it can be 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1 or 0.75:1, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] In the present invention, the mass ratio of Fe to Cr in the additive is controlled within a narrow range, thereby further improving the chromium oxidation rate and the purity of the subsequently leached chromium.

[0025] Preferably, the additive in step (1) comprises any one of ferrochrome, ferrochrome acid leaching residue or ferrochrome chlorination decomposition residue, or a combination of at least two of them, wherein the combinations are typically but not limited to: a combination of ferrochrome and ferrochrome acid leaching residue, a combination of ferrochrome acid leaching residue and ferrochrome chlorination decomposition residue, or a combination of ferrochrome, ferrochrome acid leaching residue and ferrochrome chlorination decomposition residue, etc.

[0026] In the present invention, ferrochrome, ferrochrome acid leaching residue or ferrochrome chlorination decomposition residue is selected as an additive, so that chromium in the ferrochrome or its leaching residue can be fully extracted, the conversion rate of chromium in the chromite / chromium slag roasting process is improved, the amount of aluminum mud generated is reduced, and low-temperature energy-saving roasting treatment of chromite is achieved.

[0027] As a preferred technical solution of the present invention, the mass ratio of the additive to the chromium-containing material in step (1) is (0.1-2):1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1 or 1.9:1, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably (0.2-1.5):1.

[0028] Preferably, after grinding and mixing in step (1), the average particle size of the mixed material is ≤74 μm, for example, it can be 72 μm, 70 μm, 68 μm, 65 μm, 60 μm, 55 μm, 50 μm or 40 μm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] As a preferred technical solution of the present invention, the temperature of the oxidative roasting in step (1) is 300-1200°C, for example, it can be 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C or 1150°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, preferably 600-1000°C.

[0030] Preferably, the oxidative roasting time in step (1) is 10 to 400 min, for example, it can be 30 min, 50 min, 80 min, 100 min, 120 min, 150 min, 180 min, 200 min, 220 min, 250 min, 280 min, 300 min, 320 min, 350 min or 380 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] In the present invention, the equipment used for the oxidation roasting includes any one of a muffle furnace, a microwave heating furnace or an atmosphere furnace, or a combination of at least two of them.

[0032] Preferably, the oxidative roasting in step (1) is carried out in air and / or oxygen-rich gas.

[0033] In the present invention, the oxygen-rich gas is an atmosphere in which the volume percentage of oxygen is greater than 20%.

[0034] As a preferred technical solution of the present invention, step (1) further includes a second grinding after the oxidative roasting.

[0035] Preferably, after the second grinding, the average particle size of the calcined clinker is ≤74 μm, for example, it can be 72 μm, 70 μm, 68 μm, 65 μm, 60 μm, 55 μm, 50 μm or 40 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] As a preferred technical solution of the present invention, the leaching method in step (2) includes water immersion.

[0037] Preferably, the liquid-to-solid ratio of the leached liquid to the roasted clinker in step (2) is (2-10):1 mL / g, for example, it can be 3:1 mL / g, 4:1 mL / g, 5:1 mL / g, 6:1 mL / g, 7:1 mL / g, 8:1 mL / g or 9:1 mL / g, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] Preferably, the leaching temperature in step (2) is 50-100°C, for example, it can be 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the leaching time in step (2) is 1 to 5 hours, for example, it can be 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours or 4.5 hours, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, step (2) further includes solid-liquid separation after the leaching.

[0041] As a preferred technical solution of the present invention, the chromium content (calculated as Cr2O3) in the leaching residue in step (2) is less than 2 wt.%, for example, it can be 1.9 wt.%, 1.8 wt.%, 1.5 wt.%, 1.4 wt.%, 1.2 wt.%, 1 wt.%, 0.8 wt.% or 0.5 wt.%, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0042] As a preferred technical solution of the present invention, the method comprises the following steps:

[0043] (1) grinding and mixing the chromium-containing material, alkali, and additives to obtain a mixture with an average particle size of ≤74 μm, then oxidizing and roasting the mixture at a temperature of 300 to 1200° C. for 10 to 400 minutes, and then performing a second grinding to obtain a roasted clinker with an average particle size of ≤74 μm;

[0044] The chromium-containing material includes chromite and / or chromium slag; the alkali includes any one of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide, or a combination of at least two of them; the mass ratio of the alkali to the chromium-containing material is (0.5-2):1; the additive includes the following elements by mass content: Cr: 30wt.%-60wt.%, Fe: 10wt.%-30wt.%, Si: 1wt.%-20wt.%, C: 5wt.%-30wt.%, and the remainder is O and unavoidable impurities; the mass ratio of Fe to Cr in the additive is (0.4-0.8):1; the additive includes any one of ferrochrome, ferrochrome acid leaching residue or ferrochrome chlorination decomposition residue, or a combination of at least two of them; the mass ratio of the additive to the chromium-containing material is (0.1-2):1;

[0045] (2) leaching the roasted clinker in step (1) at a temperature of 50 to 100° C. for 1 to 5 hours, and obtaining a leachate and a leach residue after solid-liquid separation;

[0046] The liquid-to-solid ratio of the leached liquid to the roasted clinker is (2-10): 1 mL / g;

[0047] The chromium content in the leaching residue is less than 2 wt.%.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) The method for extracting chromium by oxidative roasting of chromium-containing materials provided by the present invention adopts a specific additive mixed with the chromium-containing material and an alkali to achieve enhanced calcium-free roasting and effectively enhance the oxidative roasting process of the chromium-containing material, thereby achieving efficient extraction of chromium from the chromium-containing material and resource utilization of chromium in the additive, and significantly accelerating the oxidation reaction of chromium in the material and significantly improving the oxidation rate. At the same time, the oxidative roasting temperature is reduced, the oxidative roasting time is shortened, and low-temperature energy-saving roasting treatment of chromite is achieved; subsequently, after leaching the roasted clinker, the chromium content (as Cr2O3) in the leached residue is less than 2wt.%;

[0050] (2) The present invention adopts a specific additive to realize resource recovery of chromium resources in the additive; the iron element in the additive generates ferrate to enhance roasting and chromium extraction, which helps to improve the oxidation rate of chromium; the silicon in the additive can combine with the aluminum in the chromium-containing material to form aluminosilicate and precipitate in the slag phase, reducing the amount of aluminum mud generated in the subsequent chromium salt production process; the carbon in the additive increases the calorific value during the roasting process, reduces the roasting temperature and time, and has the advantages of energy saving and emission reduction. DETAILED DESCRIPTION

[0051] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0052] In the following examples and comparative examples, the oxygen-rich gas is a gas having an oxygen volume percentage greater than 20%.

[0053] Example 1

[0054] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0055] (1) grinding and mixing chromite, sodium hydroxide, and ferrochrome acid leaching residue in a mass ratio of 1:0.6:1.5, wherein the average particle size of the mixture is ≤50 μm, and then oxidizing and roasting the mixture at a temperature of 800° C. for 120 min, followed by a second grinding to obtain a roasted clinker with an average particle size of ≤50 μm;

[0056] The content of Cr2O3 in the chromite is 43wt.%; the ferrochrome acid leaching residue comprises the following elements by mass: Cr: 45wt.%, Fe: 20wt.%, Si: 10wt.%, C: 10wt.%, and the balance is O and unavoidable impurities;

[0057] The oxidative roasting is carried out in air;

[0058] (2) soaking the roasted clinker in step (1) in water at 100° C. for 1 hour, and obtaining a leachate and a leach residue after solid-liquid separation;

[0059] The liquid-to-solid ratio of the water used in the water immersion to the roasted clinker is 6:1 mL / g.

[0060] Example 2

[0061] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0062] (1) chromite, sodium hydroxide, and ferrochrome are ground and mixed in a mass ratio of 1:0.9:0.2, wherein the average particle size of the mixture is ≤70 μm, and then oxidative roasting is performed at a temperature of 850° C. for 100 minutes, followed by a second grinding to obtain a roasted clinker with an average particle size of ≤70 μm;

[0063] The content of Cr2O3 in the chromite is 43wt.%; the ferrochrome comprises the following elements by mass: Cr: 52wt.%, Fe: 30wt.%, Si: 8wt.%, C: 5wt.%, and the balance is O and unavoidable impurities;

[0064] The oxidative roasting is carried out in air;

[0065] (2) soaking the roasted clinker in step (1) in water at 80° C. for 0.5 h, and obtaining a leachate and a leach residue after solid-liquid separation;

[0066] The liquid-to-solid ratio of the water used in the water immersion to the roasted clinker is 8:1 mL / g.

[0067] Example 3

[0068] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0069] (1) chromite, sodium carbonate, and chromium iron acid leaching residue are ground and mixed in a mass ratio of 1:1.1:0.7, wherein the average particle size of the mixture is ≤40 μm, and then oxidative roasting is performed at a temperature of 950° C. for 150 minutes, followed by a second grinding to obtain a roasted clinker with an average particle size of ≤40 μm;

[0070] The content of Cr2O3 in the chromite is 43wt.%; the ferrochrome acid leaching residue comprises the following elements by mass: Cr: 43wt.%, Fe: 25wt.%, Si: 10wt.%, C: 15wt.%, and the balance is O and unavoidable impurities;

[0071] The oxidative roasting is carried out in air;

[0072] (2) soaking the roasted clinker in step (1) in water at 90° C. for 1.5 h, and obtaining a leachate and a leach residue after solid-liquid separation;

[0073] The liquid-to-solid ratio of the water used in the water immersion to the roasted clinker is 10:1 mL / g.

[0074] Example 4

[0075] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0076] (1) grinding and mixing chromium slag, potassium hydroxide, and chromium ferrochlorination decomposition slag in a mass ratio of 1:0.5:1, wherein the average particle size of the mixture is ≤38 μm, and then oxidizing and roasting the mixture at a temperature of 700° C. for 60 minutes, followed by a second grinding to obtain a roasted clinker with an average particle size of ≤38 μm;

[0077] The content of Cr2O3 in the chromium slag is 9wt.%; the ferrochromium chlorination decomposition slag comprises the following elements by mass: Cr: 31wt.%, Fe: 15wt.%, Si: 20wt.%, C: 19wt.%, and the balance is O and unavoidable impurities;

[0078] The oxidative roasting is carried out in an oxygen-rich gas;

[0079] (2) soaking the roasted clinker in step (1) in water at 85° C. for 2 h, and obtaining a leachate and a leach residue after solid-liquid separation;

[0080] The liquid-to-solid ratio of the water used in the water immersion to the roasted clinker is 4:1 mL / g.

[0081] Example 5

[0082] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0083] (1) grinding and mixing chromium slag, potassium carbonate, and chromium ferrochlorination decomposition slag in a mass ratio of 1:2:1.4, wherein the average particle size of the mixture is ≤45 μm, and then oxidizing and roasting the mixture at a temperature of 1000° C. for 30 minutes, followed by a second grinding to obtain a roasted clinker with an average particle size of ≤45 μm;

[0084] The content of Cr2O3 in the chromium slag is 9wt.%; the ferrochromium chlorination decomposition slag comprises the following elements by mass: Cr: 32wt.%, Fe: 19wt.%, Si: 18wt.%, C: 15wt.%, and the balance is O and unavoidable impurities;

[0085] The oxidative roasting is carried out in air;

[0086] (2) soaking the roasted clinker in step (1) in water at 65° C. for 2 h, and obtaining a leachate and a leach residue after solid-liquid separation;

[0087] The liquid-to-solid ratio of the water used in the water immersion to the roasted clinker is 5:1 mL / g.

[0088] Example 6

[0089] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, the method comprising the following steps:

[0090] (1) grinding and mixing chromite, potassium carbonate, and chromium chlorination decomposition slag in a mass ratio of 1:1.5:0.9, wherein the average particle size of the mixture is ≤45 μm, and then oxidizing and roasting the mixture at a temperature of 700° C. for 60 minutes, followed by a second grinding to obtain a roasted clinker with an average particle size of ≤45 μm;

[0091] The content of Cr2O3 in the chromite is 43wt.%; the chromium-iron chlorination decomposition slag comprises the following elements by mass: Cr: 35wt.%, Fe: 17wt.%, Si: 15wt.%, C: 13wt.%, and the balance is O and unavoidable impurities;

[0092] The oxidative roasting is carried out in an oxygen-rich gas;

[0093] (2) soaking the roasted clinker in step (1) in water at 85° C. for 2 h, and obtaining a leachate and a leach residue after solid-liquid separation;

[0094] The liquid-to-solid ratio of the water used in the water immersion to the roasted clinker is 4:1 mL / g.

[0095] Example 7

[0096] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that the ferrochromium acid leaching residue in step (1) is adjusted to include the following elements by mass: Cr: 30 wt.%, Fe: 30 wt.%, Si: 2 wt.%, C: 10 wt.%, and the balance being O and unavoidable impurities; other conditions are the same as those in Example 1.

[0097] Example 8

[0098] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that the ferrochromium acid leaching residue in step (1) is adjusted to include the following elements by mass: Cr: 45 wt.%, Fe: 8 wt.%, Si: 10 wt.%, C: 10 wt.%, and the balance is O and unavoidable impurities; other conditions are the same as those in Example 1.

[0099] Example 9

[0100] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that the ferrochromium in step (1) is adjusted to include the following elements by mass: Cr: 55 wt.%, Fe: 30 wt.%, Si: 17 wt.%, C: 1 wt.%, and the balance is O and unavoidable impurities; other conditions are the same as those in Example 1.

[0101] Example 10

[0102] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that the mass ratio of chromite ore to ferrochrome acid leaching residue in step (1) is 1:3; other conditions are the same as those in Example 1.

[0103] Example 11

[0104] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material. Except that the oxidative roasting temperature in step (1) is 300° C., other conditions are the same as those in Example 1.

[0105] Example 12

[0106] This embodiment provides a method for extracting chromium by oxidative roasting of a chromium-containing material. Except that the oxidative roasting temperature in step (1) is 1200° C., other conditions are the same as those in Example 1.

[0107] Comparative Example 1

[0108] This comparative example provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that no ferrochromium acid leaching residue is added in step (1); other conditions are the same as those in Example 1.

[0109] Comparative Example 2

[0110] This comparative example provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that no ferrochromium acid leaching residue is added in step (1); other conditions are the same as those in Example 3.

[0111] Comparative Example 3

[0112] This comparative example provides a method for extracting chromium by oxidative roasting of a chromium-containing material, except that no ferrochromium chlorination decomposition slag is added in step (1); other conditions are the same as those in Example 4.

[0113] After the clinker, leachate, and leach residue obtained in the above examples and comparative examples were assayed, the oxidation rate of chromium after roasting in step (1), the leaching rate of chromium after step (2), and the chromium content (as Cr2O3) in the leach residue were calculated. The results are shown in Table 1.

[0114] Table 1 Chromium oxidation rate, leaching rate and chromium content of leached residue in each embodiment and comparative example

[0115]

[0116]

[0117] From Table 1 we can see that:

[0118] (1) The methods for extracting chromium by oxidative roasting of chromium-containing materials provided in Examples 1-6 of the present invention employ a specific additive mixed with the chromium-containing material and an alkali to achieve efficient extraction and recovery of chromium from the chromium-containing material and the additive, with a chromium oxidation rate greater than 93%, a chromium leaching rate greater than 99%, and a chromium content (calculated as Cr2O3) in the leached residue less than 2 wt.%;

[0119] (2) From the comparison between Example 1 and Example 7, it can be seen that when the mass ratio of Fe to Cr in the additive is too large, although it does not affect the oxidation rate of chromium and the subsequent chromium leaching rate, due to the generation of excessive ferrate, there is residual ferrate in the roasted clinker, and the iron content in the solution after leaching is high, which affects the purity of chromium in the leachate; from the comparison between Example 1 and Examples 8-9, it can be seen that when the Fe content in the additive is too low, it is not conducive to strengthening the roasting and chromium extraction, resulting in a decrease in the oxidation rate of chromium in the roasted clinker; when the C content in the additive is too low, it is not conducive to increasing the calorific value of the roasting process, and at the same roasting temperature, it leads to the disadvantages of incomplete roasting of the material and high energy consumption;

[0120] (3) A comprehensive comparison of Example 1 and Example 10 shows that when the amount of additives used is too much, due to the large amount of additives added, part of the additives do not participate in the reaction, so the chromium oxidation rate is not further improved and the chromium content of the slag is increased;

[0121] (4) From the comparison between Example 1 and Examples 11-12, it can be seen that when the oxidation roasting temperature is too low, the roasting is incomplete, resulting in a low chromium extraction rate; when the oxidation roasting temperature is too high, the material becomes hardened during the roasting process, which is not conducive to the leaching of chromium and increases energy consumption;

[0122] (5) Comparison of the embodiment with comparative examples 1-3 shows that when no additive is added, it is not conducive to the efficient extraction and recovery of chromium from the chromium-containing material, the oxidation rate of chromium in the roasted clinker is greatly reduced, and the chromium content (in terms of Cr2O3) in the leached slag is increased.

[0123] The applicant declares that the present invention is intended to illustrate the detailed structural features of the present invention through the above-described embodiments, but the present invention is not limited to the above-described detailed structural features. This does not mean that the present invention must rely on the above-described detailed structural features in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for selected components, additions of auxiliary components, and selection of specific embodiments, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for extracting chromium by oxidative roasting of chromium-containing materials, characterized in that: The method comprises the following steps: (1) Grinding and mixing the chromium-containing material, alkali and additives, and then oxidizing and roasting to obtain roasted clinker; The additive comprises the following elements by mass content: Cr: 30wt.%~60wt.%, Fe: 10wt.%~30wt.%, Si: 1wt.%~20wt.%, C: 5wt.%~30wt.%, and the balance is O and inevitable impurities; the mass ratio of Fe to Cr in the additive is (0.4~0.8):1; the mass ratio of the additive to the chromium-containing material is (0.1~2):1; The temperature of the oxidation roasting is 600-1000°C; (2) Leaching the roasted clinker in step (1) to obtain a leachate and a leach residue.

2. The method according to claim 1, characterized in that The chromium-containing material in step (1) includes chromite and / or chromium slag.

3. The method according to claim 1, characterized in that The base in step (1) includes any one of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide, or a combination of at least two thereof.

4. The method according to claim 1, wherein The mass ratio of the alkali in step (1) to the chromium-containing material is (0.5-2):

1.

5. The method according to claim 1, wherein The additive in step (1) comprises any one of ferrochrome, ferrochrome acid leaching residue or ferrochrome chlorination decomposition residue, or a combination of at least two of them.

6. The method according to claim 1, wherein The mass ratio of the additive to the chromium-containing material in step (1) is (0.2~1.5):

1.

7. The method according to claim 1, characterized in that After grinding and mixing in step (1), the average particle size of the mixed material is ≤74 μm.

8. The method according to claim 1, characterized in that The oxidation roasting time in step (1) is 10 to 400 minutes.

9. The method according to claim 1, characterized in that The oxidative roasting in step (1) is carried out in air and / or oxygen-rich gas.

10. The method according to claim 1, characterized in that The step (1) further includes a second grinding after the oxidation roasting.

11. The method according to claim 10, characterized in that After the second grinding, the average particle size of the roasted clinker is ≤74 μm.

12. The method according to claim 1, characterized in that The leaching method in step (2) includes water immersion.

13. The method according to claim 1, wherein The liquid-to-solid ratio of the leached liquid to the roasted clinker in step (2) is (2-10):1 mL / g.

14. The method according to claim 1, wherein The leaching temperature in step (2) is 50-100°C.

15. The method according to claim 1, wherein The leaching time in step (2) is 1 to 5 hours.

16. The method according to claim 1, wherein Step (2) further includes solid-liquid separation after the leaching.

17. The method according to claim 1, wherein The chromium content in the leached residue in step (2) is less than 2 wt.%.

18. The method according to claim 1, wherein The method comprises the following steps: (1) After grinding and mixing the chromium-containing material, alkali and additives, the average particle size of the mixture is ≤74 μm, and then oxidizing and roasting the mixture at a temperature of 600-1000°C for 10-400 minutes, and then performing a second grinding to obtain a roasted clinker with an average particle size of ≤74 μm; The chromium-containing material includes chromite and / or chromium slag; the alkali includes any one of sodium carbonate, potassium carbonate, sodium hydroxide or potassium hydroxide, or a combination of at least two of them; the mass ratio of the alkali to the chromium-containing material is (0.5-2):1; the additive includes the following elements by mass content: Cr: 30wt.%-60wt.%, Fe: 10wt.%-30wt.%, Si: 1wt.%-20wt.%, C: 5wt.%-30wt.%, and the remainder is O and unavoidable impurities; the mass ratio of Fe to Cr in the additive is (0.4-0.8):1; the additive includes any one of ferrochrome, ferrochrome acid leaching residue or ferrochrome chlorination decomposition residue, or a combination of at least two of them; the mass ratio of the additive to the chromium-containing material is (0.1-2):1; (2) Leaching the roasted clinker in step (1) at a temperature of 50-100° C. for 1-5 hours, and obtaining a leachate and a leach residue after solid-liquid separation; The liquid-to-solid ratio of the leached liquid to the roasted clinker is (2-10):1 mL / g; The chromium content in the leaching residue is less than 2 wt.%.

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