Method for co-production of chromate from chromite and ferrochrome

Abstract

The invention relates to a method for co-production of chromate from chromite and ferrochrome, and the method comprises the following steps: firstly, carrying out first liquid phase oxidation reaction on chromite, aqueous alkali and magnesium iron slag, and then sequentially carrying out cooling, slurrying reaction and solid-liquid separation to obtain a first reaction solid phase; then, the first reaction solid phase obtained in the step (1) is sequentially subjected to first washing treatment and second washing treatment, and a second washed liquid phase is obtained; then, evaporating and concentrating the second washed liquid phase to obtain a concentrated solution; and finally, carrying out a second liquid-phase oxidation reaction on the ferrochromium, the iron slag and the concentrated solution, and then sequentially carrying out cooling and solid-liquid separation to obtain a chromate solution. The method provided by the invention has the advantages of simple process, lower energy consumption and cost, less water consumption and the like, does not have an evaporation and concentration process of high-concentration alkali, does not discharge waste residues, has strong operability and is easy to industrialize.

Description

Technical Field

[0001] The invention relates to the fields of chromium chemical industry and chromate production, and in particular to a method for co-producing chromate with chromite ore and ferrochrome. Background Art

[0002] As an important strategic resource, chromium is widely used in the fields of steel, metallurgical-grade aerospace, etc. In recent years, with the continuous development of the economy, the demand for chromium resources has also increased. Chromite and ferrochrome are both important raw materials for the production of chromate, but the main production method of chromate is high-temperature roasting, which has the disadvantages of high production energy consumption, low chromium conversion rate and large amount of waste residue emissions, which brings great harm to the ecological environment and people's health.

[0003] In recent years, a variety of liquid phase oxidation processes have been developed for the utilization of chromium-containing resources such as chromite and ferrochrome and the production of chromate. However, the liquid phase oxidation reaction of chromite and caustic soda solution is often accompanied by problems such as high alkali concentration, difficulty in separating alkali from chromium, low alkali utilization, difficulty in evaporating concentrated alkali, low concentration of chromate solution, and the need to add other chemicals to remove silicon and aluminum impurities. In addition, the iron, silicon and other elements in chromite and ferrochrome are prone to form small particles during the liquid phase oxidation and hydrolysis process, which have high adhesion and poor filtration performance.

[0004] For example, CN106219607A discloses a method for preparing sodium dichromate, in which a circulating alkali solution is used for washing and de-alkali treatment. After de-alkali treatment, 5-10% of the alkali in the sodium chromate solution cannot be removed, resulting in large alkali losses. The alkali obtained by washing needs to be directly evaporated to a concentration of more than 65%, resulting in poor operability and easy introduction of impurities. An acidulant needs to be added to the obtained chromate solution to remove aluminum and silicon impurities therein, resulting in poor economic efficiency.

[0005] CN101817561A discloses a method for cleanly producing sodium chromate by pressure leaching of chromite, wherein the method directly uses a large amount of water to dilute the slurry after the liquid phase oxidation reaction, and the dilution liquid phase needs to add calcium oxide to remove impurities therein, and the solution after impurity removal is separated by evaporation and crystallization to obtain sodium chromate coarse crystals and sodium hydroxide solution, the coarse crystals contain sodium hydroxide and need to be washed with a saturated sodium chromate solution, and the sodium hydroxide solution needs to be further evaporated and concentrated. It can be seen that the process flow is relatively complicated, the evaporation energy consumption is high, and a certain amount of chromium slag is generated.

[0006] CN101508466A discloses an efficient, energy-saving and clean production method of chromium salts. The method uses ferrochrome and alkali to undergo a liquid-phase oxidation reaction under high pressure. The concentration of the generated chromium salt is low, and the iron oxide slag particles obtained by hydrolysis under high pressure are small, which is difficult to filter and separate, and is prone to entrainment, requiring a large amount of water and multiple washings.

[0007] In summary, the existing liquid phase oxidation technology of chromium resources still has problems such as large alkali consumption, high evaporation energy consumption and easy generation of waste residue. Therefore, it is of great significance to develop a liquid phase oxidation method for chromium-containing materials with simple process, low energy consumption and cost and less environmental impact. Summary of the invention

[0008] In view of the above problems, the object of the present invention is to provide a method for co-producing chromate from chromite and ferrochrome. Compared with the prior art, the method provided by the present invention has the advantages of simple process, low energy consumption and cost, small water consumption, no evaporation and concentration process of high-concentration alkali, no waste residue discharge, strong operability, and easy industrialization.

[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 co-producing chromate from chromite ore and ferrochrome, the method comprising the following steps:

[0011] (1) subjecting chromite, alkaline solution and ferromagnesian slag to a first liquid phase oxidation reaction, followed by cooling, slurry reaction and solid-liquid separation in sequence to obtain a first reaction solid phase;

[0012] (2) subjecting the first reaction solid phase obtained in step (1) to a first washing treatment and a second washing treatment in sequence to obtain a second washed liquid phase;

[0013] (3) evaporating and concentrating the second washed liquid phase obtained in step (2) to obtain a concentrated solution;

[0014] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction, followed by cooling and solid-liquid separation, to obtain a chromate solution.

[0015] In the present invention, chromite, alkaline solution and ferromagnesia slag are firstly used as raw materials, and a first reaction solid phase containing ferromagnesia slag is obtained through a first liquid phase oxidation reaction; then the second washed liquid phase is evaporated and concentrated to obtain a concentrated solution; thereafter, the concentrated solution, ferrochrome and iron slag are used as raw materials for a second oxidation reaction, and the concentrated solution is used as a leaching agent for ferrochrome, so that the alkali added in the system is fully utilized, the complicated alkali-chromium separation process is avoided, and the concentration of chromate in the solution is increased; and the silicon and aluminum impurities leached from the chromite in the first liquid phase oxidation reaction are oxidized by carbon in the ferrochrome in the second liquid phase oxidation reaction to generate carbon dioxide, and then the solution is acidified and removed, so that the introduction of other chemical reagents is avoided, and the production cost is reduced.

[0016] In the present invention, the method of solid-liquid separation is not particularly limited, and generally can be filtration.

[0017] In the present invention, the source of the chromite is not particularly limited, and any chromite commonly used in the art can be used. For example, the chromite mainly contains Cr 2 O 3 :30-55%,Fe 2 O 3 :10-30%,Al 2 O 3 :5-15%, MgO:8-20%, SiO 2 :3-12%. In the present invention, the chromite is generally crushed before use, and generally the chromite with a particle size of ≤75μm after crushing is used, for example, it can be 75μm, 70μm, 60μm, 65μm, 50μm or 55μm, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. In the present invention, the source of the ferrochrome is not particularly limited, and any chromite commonly used in the art can be used, for example, the ferrochrome contains 40-75% chromium, 0.25-10% carbon, and iron by mass percentage.

[0018] Preferably, the alkali contained in the alkaline solution in step (1) comprises any one of sodium hydroxide, potassium hydroxide or lithium hydroxide, or a combination of at least two of them.

[0019] Preferably, the mass concentration of the alkaline solution is 60-78%, for example, it can be 60%, 62%, 64%, 68%, 70%, 72%, 74%, 76% or 78%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the ferromagnesian slag comprises magnesium oxide and iron oxide.

[0021] Preferably, the ferromagnesian slag also contains alkali and chromate.

[0022] Preferably, the ferromagnesian slag is leached slag from a liquid phase oxidation reaction of chromite ore.

[0023] Preferably, the ferromagnesian slag contains 10-35% chromate by mass percentage, for example, it can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32% or 35%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] Preferably, the ferromagnesian slag contains 25-55% alkali by mass percentage, for example, it can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 50%, 52% or 55%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] Preferably, the mass of the ferromagnesian slag in the first liquid-phase oxidation reaction accounts for 2-80% of the mass of the chromite ore, for example, it can be 2%, 4%, 6%, 12%, 24%, 36%, 48%, 60%, 70% or 80%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] Preferably, the mass ratio of alkali to chromite in the first liquid-phase oxidation reaction is (3-6):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or 6:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In the present invention, the first liquid-phase oxidation reaction is a common reaction in the art for preparing chromate using chromite. An oxidizing gas is introduced into the first liquid-phase oxidation reaction, and the oxidizing gas includes any one of air, oxygen or ozone or a combination of at least two thereof. The conditions of the first liquid-phase oxidation reaction, such as the partial pressure, temperature, and time of the oxidizing gas, can adopt common parameters in the art. For example, the partial pressure of the oxidizing gas in the first liquid-phase oxidation reaction is 1-5MPa, for example, 1MPa, 2MPa, 3MPa, 4MPa or 5MPa; the temperature of the first liquid-phase oxidation reaction is 260-350°C, for example, 260°C, 280°C, 300°C, 320°C, 340°C or 350°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable; the time of the first liquid-phase oxidation reaction is 2-5h, for example, 2h, 3h, 4h or 5h, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0028] Preferably, the cooling temperature in step (1) is 100-150°C, for example, it can be 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In the present invention, the cooling temperature is controlled within a specific range and the cooling temperature is made relatively high because the cooled product is then mixed with a diluent to undergo a slurry reaction, which can improve the overall heat utilization rate.

[0030] Preferably, the cooling method in step (1) includes flash evaporation.

[0031] In the present invention, flash cooling is preferably used because the waste heat of flash cooling can be fully utilized, the amount of cooling water used can be reduced, the operation is simple, and the maintenance is easy.

[0032] Preferably, the slurrying reaction comprises: adding a diluent to the reaction product obtained from the first liquid phase oxidation reaction, and then slurrying.

[0033] In the present invention, the diluent is generally selected from water or a post-washing liquid, for example, it can be the first post-washing liquid phase. In the present invention, the liquid-to-solid ratio of the diluent and the reaction product is not particularly limited. Under the condition of ensuring the filtering performance and the small amount of water, a suitable liquid-to-solid ratio can be selected as required, for example, the liquid-to-solid ratio can be 1:1.

[0034] Preferably, the slurrying temperature is 80-110°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C or 110°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the slurrying time is 0.2-2 h, for example, it can be 0.2 h, 0.4 h, 0.6 h, 0.8 h, 1 h, 1.2 h, 1.4 h, 1.6 h, 1.8 h or 2 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, after the solid-liquid separation in step (1), a first reaction liquid phase is obtained.

[0037] Preferably, the first reaction liquid phase is used as an alkaline solution or the first reaction liquid phase is supplemented with alkali and then returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution.

[0038] In the present invention, the purpose of returning the first reaction liquid phase is that the alkali content in the first reaction liquid phase is relatively high, and a small amount of alkali can be added or directly used for liquid phase oxidation reaction, which is beneficial to the full utilization of high-value alkali and avoids the evaporation of high-concentration alkali.

[0039] Preferably, the first reaction solid phase obtained in part of step (1) is directly returned to the first liquid phase oxidation reaction system as ferromagnesian slag without being washed.

[0040] In the present invention, the main component of the first reaction solid phase is ferromagnesia slag, which is used as a seed to return to the reaction system of the first liquid phase oxidation reaction. The advantage is that the ferromagnesia slag particles contained therein are larger, and the entrainment of chromium and alkali is less, which is beneficial to reduce the loss rate of chromium and alkali and increase the concentration of chromate in the solution. The unwashed first reaction solid phase is preferably used as the seed because the unwashed solid phase contains a higher content of alkali. Direct reuse reduces the pressure of subsequent washing and is beneficial to the precipitation of ferromagnesia slag.

[0041] Preferably, in step (2), the first washing treatment and the second washing treatment each independently comprise countercurrent washing.

[0042] Preferably, the number of stages of the first washing treatment is at least 1, for example, it can be 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] Preferably, the number of stages of the second washing treatment includes 3-8 stages, for example, it can be 3, 4, 5, 6, 7 or 8, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] Preferably, in the first washing treatment and the second washing treatment, the washing time of each stage is independently 0.5-2h, for example, it can be 0.5h, 0.6h, 0.8h, 1h, 1.2h, 1.4h, 1.6h, 1.8h or 2h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, the liquid-to-solid ratio of the first washing treatment is less than the liquid-to-solid ratio of the second washing treatment.

[0046] In the present invention, the first washing treatment is controlled to be carried out at a lower liquid-solid ratio, so that a first washed liquid phase containing a higher alkali and chromium concentration can be obtained, and the first washed liquid phase is used as a diluent of the product after the first liquid-phase oxidation reaction for slurry reaction, which can increase the return amount of alkali and increase the filtration performance of the product after the first liquid-phase oxidation reaction. In the present invention, the second washing treatment is controlled to be carried out at a higher liquid-solid ratio, which can further improve the cleanliness of the second washed solid phase, and the obtained second washed liquid phase can be used as a leaching agent for ferrochrome in the second liquid-phase oxidation reaction after evaporation and concentration, further fully utilizing the alkali added in the system, avoiding a complicated alkali and chromium separation process, and increasing the concentration of chromate in the solution.

[0047] In the present invention, the liquid-to-solid ratio refers to the ratio of the mass of the liquid to the mass of the solid during washing.

[0048] Preferably, the temperature of the first washing treatment is 80-100°C, for example, it can be 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C, 98°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] Preferably, the liquid-to-solid ratio of the first washing treatment is (0.5-2):1, for example, it can be 0.5:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.6:1, 1.8:1 or 2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] Preferably, the first washing treatment obtains a first washed liquid phase and a first washed solid phase.

[0051] Preferably, after the first washing, the solid phase is subjected to a second washing treatment.

[0052] Preferably, the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent.

[0053] In the present invention, the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent, which can increase the return amount of the alkali and improve the filtration performance of the product after the first liquid phase oxidation reaction.

[0054] Preferably, the temperature of the second washing treatment is 60-90°C, for example, it can be 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] Preferably, the liquid-to-solid ratio of the second washing treatment is (3-8):1, for example, it can be 3:1, 4:1, 5:1, 6:1, 7:1 or 8:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] Preferably, part of the second washed liquid phase obtained in the second washing treatment is used as washing liquid in the first washing treatment.

[0057] Preferably, the second washing treatment further produces a second washed solid phase.

[0058] Preferably, the second washed solid phase is used as raw material for ironmaking.

[0059] In the present invention, the solid phase after the second washing is composed of relatively clean ferromagnesian slag, which can be used as raw material for ironmaking.

[0060] Preferably, the temperature of the evaporation concentration in step (3) is 105-150°C, for example, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C or 150°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] Preferably, the mass concentration of alkali in the concentrated solution is 10-25%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22% or 25%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] In the present invention, the concentrated solution contains silicon and aluminum impurities remaining after the chromite is subjected to the first liquid phase oxidation reaction. The present invention uses the concentrated solution and ferrochrome as raw materials to carry out the second liquid phase oxidation reaction, and can utilize the carbon in the ferrochrome to oxidize and generate carbon dioxide, and then acidify the solution to remove silicon and aluminum impurities, avoid using other chemical reagents, avoid introducing impurities, and reduce production costs.

[0063] Preferably, the iron slag in step (4) comprises iron oxide.

[0064] Preferably, the iron slag also contains chromate.

[0065] Preferably, the iron slag is leached slag from a liquid phase oxidation reaction of ferrochrome.

[0066] Preferably, the iron slag contains 10-55% iron oxide by mass percentage, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or 55%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] Preferably, the iron slag contains 0.5-5% chromate by mass percentage, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] Preferably, the mass of the iron slag in the second liquid-phase oxidation reaction in step (4) is 1-40% of the mass of the ferrochrome, for example, 1%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0069] Preferably, the mass ratio of alkali to ferrochrome in the second liquid-phase oxidation reaction is (0.72-1.35):1, for example, it can be 0.72:1, 0.8:1, 0.85:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1 or 1.35:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0070] In the present invention, the second liquid-phase oxidation reaction is a common reaction in the art for preparing chromate using ferrochrome. An oxidizing gas is introduced into the second liquid-phase oxidation reaction, and the oxidizing gas includes any one of air, oxygen or ozone or a combination of at least two thereof. The conditions of the second liquid-phase oxidation reaction, such as the partial pressure, temperature, and time of the oxidizing gas, can adopt common parameters in the art. For example, the partial pressure of the oxidizing gas in the second liquid-phase oxidation reaction is 3-8MPa, for example, 3MPa, 4MPa, 5MPa, 6MPa or 8MPa; the temperature of the second liquid-phase oxidation reaction is 250-320°C, for example, 250°C, 260°C, 280°C, 300°C or 320°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable; the time of the second liquid-phase oxidation reaction is 3-6h, for example, 3h, 4h, 5h or 6h, but is not limited to the listed values, and other values ​​not listed within the numerical range are equally applicable.

[0071] Preferably, the cooling temperature in step (4) is 70-100°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0072] Preferably, the solid-liquid separation in step (4) also obtains a second reaction solid phase.

[0073] Preferably, part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without being washed.

[0074] In the present invention, the second reaction solid phase contains iron slag, and unwashed iron slag is used as seed crystal because the obtained iron slag particles are larger and carry less chromium and alkali, which can reduce the loss rate of chromium and alkali and increase the concentration of chromate in the solution.

[0075] Preferably, part of the second reaction solid phase is used for iron smelting or preparation of red iron oxide after the third washing treatment.

[0076] In the present invention, after the third washing treatment, a third washed solid phase is obtained, which is composed of relatively clean iron slag and can be used for ironmaking or preparing red iron oxide. After the third washing treatment, a third washed liquid phase is also obtained, and after evaporation and concentration, the third washed liquid phase is mixed with a chromate solution to prepare related products.

[0077] As a preferred technical solution of the present invention, the method comprises the following steps:

[0078] (1) subjecting chromite, an alkaline solution having a mass concentration of 60-78% and ferromagnesia slag to a first liquid phase oxidation reaction; the ferromagnesia slag contains magnesium oxide and iron oxide, and also contains 10-35% of chromate and 25-55% of alkali, the mass of the ferromagnesia slag in the first liquid phase oxidation reaction accounts for 2-80% of the mass of the chromite, and the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is (3-6):1;

[0079] The reaction product after the first liquid phase oxidation reaction is flash-cooled at 100-150° C., and then a diluent is added to the reaction product, and slurried at 80-110° C. for 0.2-2 hours, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase;

[0080] The first reaction liquid phase is returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution or as an alkaline solution after the first reaction liquid phase is supplemented with alkali, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesia slag without being washed;

[0081] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 80-100° C. and a liquid-to-solid ratio of (0.5-2):1, wherein the first washing treatment includes at least one stage of countercurrent washing, and the washing time of each stage is 0.5-2 hours, to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0082] The first washed solid phase is subjected to a second washing treatment at a temperature of 60-90° C. and a liquid-to-solid ratio of (3-8):1, wherein the second washing treatment comprises 3-8 stages of countercurrent washing, and the washing time of each stage is 0.5-2 hours, to obtain a second washed liquid phase and a second washed solid phase;

[0083] The second washed solid phase is used as raw material for ironmaking; part of the second washed liquid phase is used as washing liquid for the first washing process;

[0084] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 105-150° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 10-25%;

[0085] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction at a temperature of 250-320° C., wherein the iron slag comprises, by weight percentage, 10-55% of iron oxide and 0.5-5% of chromate, the weight of the iron slag in the second liquid phase oxidation reaction accounts for 1-40% of the weight of the ferrochrome, and the weight ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is (0.72-1.35):1, and then cooling at 70-100° C., and then solid separation to obtain a second reaction solid phase and a chromate solution;

[0086] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing, and part of the second reaction solid phase is used for iron smelting or preparation of red iron oxide after the third washing treatment.

[0087] Compared with the prior art, the present invention has the following beneficial effects:

[0088] (1) The present invention uses chromite, alkaline solution and ferromagnesia slag as raw materials to carry out a first liquid phase oxidation reaction to obtain a first reaction solid phase containing ferromagnesia slag. The first reaction solid phase is not washed and has large particles, which is suitable for returning to the first liquid phase oxidation reaction as a seed crystal, and has less entrainment of chromium and alkali, which is beneficial to reducing the loss rate of chromium and alkali and increasing the concentration of the chromate solution. The first reaction liquid phase returns to the first liquid phase oxidation reaction and serves as a leaching agent for chromite ore, which can fully utilize the alkali added to the system, avoid the complex process of separating the alkali and chromium, and further increase the concentration of the chromate solution.

[0089] (2) In the present invention, the cooling temperature after the first liquid-phase oxidation reaction is controlled to be relatively high because the cooled product is further combined with the diluent to undergo a slurry reaction, so that the slurry reaction can fully utilize the waste heat. In addition, the heat generated during the flash evaporation process can also be further utilized, thereby improving the overall heat utilization rate and reducing energy consumption.

[0090] (3) In the present invention, the liquid-to-solid ratio of the first washing treatment is controlled to be lower than that of the second washing treatment, so that washing can be performed at a lower liquid-to-solid ratio to obtain a first washed liquid phase with higher chromium and alkali concentrations, and the first washed liquid phase is used as a diluent for the slurry reaction, which can increase the return amount of alkali and improve the filtration performance of the material after the slurry reaction; then, the solid phase is further washed at a higher liquid-to-solid ratio to obtain ferromagnesian slag that can be used for ironmaking, and the obtained second washed liquid phase is evaporated and concentrated in the second liquid phase oxidation reaction as a leaching agent for chromium and iron, which can further fully utilize the alkali added to the system, avoid the complicated chromium and alkali separation process, and increase the concentration of the chromate solution.

[0091] (4) In the present invention, silicon and aluminum impurities remaining after the chromite undergoes the first liquid-phase oxidation reaction enter the concentrated solution, and the concentrated solution and ferrochrome are used as raw materials for the second liquid-phase oxidation reaction. The carbon in the ferrochrome can be oxidized to generate carbon dioxide, and then the solution is acidified to remove the silicon and aluminum impurities, thereby avoiding the introduction of other chemical reagents and impurities, thereby reducing production costs. In addition, part of the iron slag obtained from the second liquid-phase oxidation reaction is returned to the second liquid-phase oxidation reaction without washing, and the advantages of larger iron slag particles and less alkali and chromium entrainment are utilized to reduce the loss rate of chromium and alkali, thereby further increasing the concentration of the chromate solution.

[0092] (5) The method provided by the present invention does not require the evaporation and concentration process of high-concentration alkali, has strong operability, low water consumption in the overall process, no waste residue discharge, low production cost, simple process, and is easy to industrialize and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 It is a flow chart of the method described in Example 1 of the present invention. DETAILED DESCRIPTION

[0094] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0095] Example 1

[0096] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment contains Cr in terms of mass percentage. 2 O 3 :48.5%,Fe 2 O 3 :15.70%,Al 2 O 3 :7.22%,MgO:8.13%,SiO 2 :5.51%;

[0097] The ferromagnesian slag used in this embodiment is the leached slag of the liquid phase oxidation reaction of chromite, and its mass accounts for 2% of the mass of the ferrochromite, wherein it contains 25% of sodium chromate, 40% of sodium hydroxide, 9.48% of magnesium oxide, and 18.29% of iron oxide by mass percentage;

[0098] The iron slag used in this embodiment is the leached slag of the liquid phase oxidation reaction of ferrochrome, and its mass accounts for 2% of the mass of ferrochrome, wherein it contains 35.36% of iron oxide and 3.44% of chromate by mass percentage;

[0099] The ferrochrome used in this embodiment contains 52.23% chromium, 2.46% carbon, and 38.17% iron by mass percentage;

[0100] The schematic diagram of the method is shown in Figure 1 As shown, the following steps are included:

[0101] (1) subjecting chromite (particle size ≤ 75 μm), an alkali solution (the alkali is sodium hydroxide) having a mass concentration of 68.23%, and ferromagnesia slag to a first liquid phase oxidation reaction in a high pressure reactor at a temperature of 340° C. for 4 h, wherein the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is 4:1, and an oxidizing gas (air) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 5 MPa;

[0102] The reaction product after the first liquid phase oxidation reaction is flash-cooled at 100° C., and then a diluent (pure water) is added to the reaction product, wherein the liquid-to-solid ratio of the diluent to the reaction product is 1:1, and slurrying is performed at 80° C. for 2 hours, followed by solid-liquid separation to obtain a first reaction solid phase and a first reaction liquid phase;

[0103] After adding alkali to the first reaction liquid phase, it is returned to the reaction system of the first liquid phase oxidation reaction as an alkali solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesia slag without being washed;

[0104] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 80° C. and a liquid-to-solid ratio of 0.6:1, wherein the first washing treatment is a single-stage countercurrent washing for 2 hours to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0105] The first washed solid phase is subjected to a second washing treatment at a temperature of 80° C. and a liquid-to-solid ratio of 8:1, wherein the second washing treatment is 8-stage countercurrent washing, and the washing time of each stage is 2 hours, to obtain a second washed liquid phase and a second washed solid phase;

[0106] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0107] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 110° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 10%;

[0108] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction in a high pressure reactor at a temperature of 300° C. for 4 hours, introducing an oxidizing gas (oxygen) into the second liquid phase oxidation reaction, wherein the partial pressure of the oxidizing gas is 6 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 0.9:1, and then cooling at 70° C., and then solid separation to obtain a second reaction solid phase and a chromate solution;

[0109] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing. Part of the second reaction solid phase is subjected to the third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for iron smelting or preparing red iron oxide. A third washed liquid phase is also obtained, which is evaporated and concentrated and mixed with a chromate solution to prepare related products.

[0110] Example 2

[0111] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment is the same as that in Example 1.

[0112] The ferrochrome used in this embodiment contains 52.20% chromium, 6.15% carbon, and 36.22% iron by mass percentage;

[0113] The ferromagnesian slag used in this example is the first reaction solid phase returned in Example 1, accounting for 5.00% of the mass of the chromite ore;

[0114] The iron slag used in this embodiment is the second reaction solid phase returned in Example 1, accounting for 5.00% of the mass of the ferrochrome;

[0115] The alkaline solution used in this embodiment is: sodium hydroxide is added to the first reaction liquid phase returned in Example 1 until the mass ratio of the alkali in the alkaline solution to the mass ratio of the chromite is 4.5:1;

[0116] The diluent used in this example is the first post-washing liquid phase returned in Example 1;

[0117] The washing liquid used in the first washing treatment of this embodiment is the second washed liquid phase obtained in Example 1;

[0118] The method comprises the following steps:

[0119] (1) subjecting chromite (particle size ≤ 75 μm), an alkaline solution and ferromagnesia slag to a first liquid phase oxidation reaction in a high pressure reactor at a temperature of 300° C. for 5 h, wherein the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is 4.5:1, and an oxidizing gas (oxygen) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 4 MPa;

[0120] The reaction product after the first liquid phase oxidation reaction is flash cooled at 110° C., and then a diluent is added to the reaction product, wherein the liquid-to-solid ratio of the diluent to the reaction product is 1:1, and slurrying is performed at 85° C. for 1.5 hours, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase;

[0121] The first reaction liquid phase is returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesian slag without being washed;

[0122] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 85° C. and a liquid-to-solid ratio of 0.8:1, wherein the first washing treatment is a single-stage countercurrent washing for 2 hours to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0123] The first washed solid phase is subjected to a second washing treatment at a temperature of 70° C. and a liquid-to-solid ratio of 7:1, wherein the second washing treatment is a 6-stage countercurrent washing, and the washing time of each stage is 1.5 h, to obtain a second washed liquid phase and a second washed solid phase;

[0124] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0125] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 120° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 15%;

[0126] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction in a high pressure autoclave at a temperature of 290° C. for 4 h, introducing an oxidizing gas (oxygen) into the second liquid phase oxidation reaction, wherein the partial pressure of the oxidizing gas is 6.5 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 0.9:1, and then cooling at 80° C., and then solid separation to obtain a second reaction solid phase and a chromate solution;

[0127] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing. Part of the second reaction solid phase is subjected to the third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for iron smelting or preparing red iron oxide. A third washed liquid phase is also obtained, which is evaporated and concentrated and mixed with a chromate solution to prepare related products.

[0128] Example 3

[0129] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment is the same as that in Example 2.

[0130] The ferrochrome used in this embodiment contains 56.60% chromium, 6.44% carbon, and 34.59% iron by mass percentage;

[0131] The ferromagnesian slag used in this example is the first reaction solid phase returned in Example 2, accounting for 2.00% of the mass of the chromite ore;

[0132] The iron slag used in this embodiment is the second reaction solid phase returned in Example 2, accounting for 10.13% of the mass of ferrochrome;

[0133] The alkaline solution used in this embodiment is: the first reaction liquid phase returned in Example 2;

[0134] The diluent used in this example is the first post-washing liquid phase returned in Example 2;

[0135] The washing liquid used in the first washing treatment of this embodiment is the second washed liquid phase obtained in Example 2;

[0136] The method comprises the following steps:

[0137] (1) subjecting chromite (particle size ≤ 75 μm), an alkaline solution and ferromagnesia slag to a first liquid phase oxidation reaction at a temperature of 320° C. for 4 h in a high pressure reactor, wherein the mass ratio of alkali to chromite in the first liquid phase oxidation reaction is 3.5:1, and an oxidizing gas (ozone) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 1 MPa;

[0138] The reaction product after the first liquid phase oxidation reaction is flash cooled at 120° C., and then a diluent is added to the reaction product, wherein the liquid-solid ratio of the diluent to the reaction product is 1:1, and slurrying is performed at 90° C. for 1 hour, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase;

[0139] The first reaction liquid phase is returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesian slag without being washed;

[0140] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 90° C. and a liquid-to-solid ratio of 1:1, wherein the first washing treatment is a single-stage countercurrent washing for 1 h, to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0141] The first washed solid phase is subjected to a second washing treatment at a temperature of 80° C. and a liquid-to-solid ratio of 5:1, wherein the second washing treatment is a 5-stage countercurrent washing, and the washing time of each stage is 1.5 hours, to obtain a second washed liquid phase and a second washed solid phase;

[0142] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0143] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 130° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 18%;

[0144] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction in a high pressure autoclave at a temperature of 280° C. for 5 h, introducing an oxidizing gas (oxygen) into the second liquid phase oxidation reaction, wherein the partial pressure of the oxidizing gas is 7 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 0.95:1, and then cooling at 80° C., and then solid separation to obtain a second reaction solid phase and a chromate solution;

[0145] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing. Part of the second reaction solid phase is subjected to the third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for iron smelting or preparing red iron oxide. A third washed liquid phase is also obtained, which is evaporated and concentrated and mixed with a chromate solution to prepare related products.

[0146] Example 4

[0147] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment is the same as that in Example 3.

[0148] The ferrochrome used in this embodiment contains 40.33% chromium, 9.77% carbon, and 45.61% iron by mass percentage;

[0149] The ferromagnesian slag used in this example is the first reaction solid phase returned in Example 3, accounting for 7.00% of the mass of the chromite ore;

[0150] The iron slag used in this embodiment is the second reaction solid phase returned in Example 3, accounting for 18.27% of the mass of ferrochrome;

[0151] The alkaline solution used in this embodiment is: the first reaction liquid phase returned in Example 3;

[0152] The diluent used in this example is the first post-washing liquid phase returned in Example 3;

[0153] The washing liquid used in the first washing treatment of this embodiment is the second washed liquid phase obtained in Example 3;

[0154] The method comprises the following steps:

[0155] (1) subjecting chromite (particle size ≤ 75 μm), an alkaline solution and ferromagnesia slag to a first liquid phase oxidation reaction in a high pressure reactor at a temperature of 330° C. for 3 h, wherein the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is 3.5:1, and an oxidizing gas (oxygen) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 3.5 MPa;

[0156] The reaction product after the first liquid phase oxidation reaction is flash-cooled at 130° C., and then a diluent is added to the reaction product, wherein the liquid-to-solid ratio of the diluent to the reaction product is 1:1, and slurried at 100° C. for 0.5 h, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase;

[0157] After adding alkali to the first reaction liquid phase, it is returned to the reaction system of the first liquid phase oxidation reaction as an alkali solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesia slag without being washed;

[0158] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 95° C. and a liquid-to-solid ratio of 1.2:1, wherein the first washing treatment is a single-stage countercurrent washing, and the washing time is 0.5 h, to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0159] The first washed solid phase is subjected to a second washing treatment at a temperature of 85° C. and a liquid-to-solid ratio of 4:1, wherein the second washing treatment is a 4-stage countercurrent washing, and the washing time of each stage is 1 hour, to obtain a second washed liquid phase and a second washed solid phase;

[0160] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0161] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 140° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 20%;

[0162] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction in a high pressure reactor at a temperature of 310° C. for 5 h, introducing an oxidizing gas (ozone) into the second liquid phase oxidation reaction, wherein the partial pressure of the oxidizing gas is 3 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 0.72:1, and then cooling at 90° C., followed by solid separation to obtain a second reaction solid phase and a chromate solution;

[0163] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing. Part of the second reaction solid phase is subjected to the third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for iron smelting or preparing red iron oxide. A third washed liquid phase is also obtained, which is evaporated and concentrated and mixed with a chromate solution to prepare related products.

[0164] Example 5

[0165] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment is the same as that in embodiment 4.

[0166] The ferrochrome used in this embodiment contains 74.27% chromium, 0.25% carbon, and 23.84% iron by mass percentage;

[0167] The ferromagnesian slag used in this example is the first reaction solid phase returned in Example 4, accounting for 10% of the mass of the chromite ore;

[0168] The iron slag used in this embodiment is the second reaction solid phase returned in Example 4, accounting for 20% of the mass of the ferrochrome;

[0169] The alkaline solution used in this embodiment is: sodium hydroxide is added to the first reaction liquid phase returned in Example 4 until the mass ratio of the alkali to the chromite in the alkaline solution is 6:1;

[0170] The diluent used in this example is the first post-washing liquid phase returned in Example 4;

[0171] The washing liquid used in the first washing treatment of this embodiment is the second washed liquid phase obtained in Example 4;

[0172] The method comprises the following steps:

[0173] (1) subjecting chromite (particle size ≤ 75 μm), an alkaline solution and ferromagnesia slag to a first liquid phase oxidation reaction at a temperature of 350° C. for 2 h in a high pressure reactor, wherein the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is 6:1, and an oxidizing gas (oxygen) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 2 MPa;

[0174] The reaction product after the first liquid phase oxidation reaction is flash cooled at 140° C., and then a diluent is added to the reaction product, wherein the liquid-to-solid ratio of the diluent to the reaction product is 1:1, and slurrying is performed at 110° C. for 0.5 h, followed by solid-liquid separation to obtain a first reaction solid phase and a first reaction liquid phase;

[0175] After adding alkali to the first reaction liquid phase, it is returned to the reaction system of the first liquid phase oxidation reaction as an alkali solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesia slag without being washed;

[0176] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 100° C. and a liquid-to-solid ratio of 1.4:1, wherein the first washing treatment is a single-stage countercurrent washing for 1.5 h to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0177] The first washed solid phase is subjected to a second washing treatment at a temperature of 90° C. and a liquid-to-solid ratio of 3:1, wherein the second washing treatment is a 5-stage countercurrent washing, and the washing time of each stage is 0.5 h, to obtain a second washed liquid phase and a second washed solid phase;

[0178] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0179] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 150° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 22%;

[0180] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction in a high pressure autoclave at a temperature of 320° C. for 3 h, introducing an oxidizing gas (oxygen) into the second liquid phase oxidation reaction, wherein the partial pressure of the oxidizing gas is 4 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 1.35:1, and then cooling at 100° C., and then solid separation to obtain a second reaction solid phase and a chromate solution;

[0181] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing. Part of the second reaction solid phase is subjected to the third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for iron smelting or preparing red iron oxide. A third washed liquid phase is also obtained, which is evaporated and concentrated and mixed with a chromate solution to prepare related products.

[0182] Example 6

[0183] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment is the same as that in Example 5.

[0184] The ferrochrome used in this embodiment contains 66.74% chromium, 3.40% carbon, and 30.53% iron by mass percentage;

[0185] The ferromagnesian slag used in this example is the first reaction solid phase returned in Example 5, accounting for 20% of the mass of the chromite ore;

[0186] The iron slag used in this embodiment is the second reaction solid phase returned in Example 5, accounting for 30% of the mass of the ferrochrome;

[0187] The alkaline solution used in this embodiment is: sodium hydroxide is added to the first reaction liquid phase returned in Example 5 until the mass ratio of the alkali to the chromite in the alkaline solution is 5:1;

[0188] The diluent used in this example is the first post-washing liquid phase returned in Example 5;

[0189] The washing liquid used in the first washing treatment of this embodiment is the second washed liquid phase obtained in Example 5;

[0190] The method comprises the following steps:

[0191] (1) subjecting chromite (particle size ≤ 75 μm), an alkaline solution and ferromagnesian slag to a first liquid phase oxidation reaction at a temperature of 280° C. for 4.5 h in a high pressure reactor, wherein the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is 5:1, and an oxidizing gas (a mixture of air and ozone) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 5 MPa;

[0192] The reaction product after the first liquid phase oxidation reaction is flash-cooled at 150° C., and then a diluent is added to the reaction product, wherein the liquid-to-solid ratio of the diluent to the reaction product is 1:1, and slurried at 110° C. for 1 hour, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase;

[0193] After adding alkali to the first reaction liquid phase, it is returned to the reaction system of the first liquid phase oxidation reaction as an alkali solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesia slag without being washed;

[0194] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 100° C. and a liquid-to-solid ratio of 2:1, wherein the first washing treatment is a single-stage countercurrent washing for 1 hour to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0195] The first washed solid phase is subjected to a second washing treatment at a temperature of 90° C. and a liquid-to-solid ratio of 8:1, wherein the second washing treatment is a three-stage countercurrent washing, and the washing time of each stage is 1 hour, to obtain a second washed liquid phase and a second washed solid phase;

[0196] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0197] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 125° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 25%;

[0198] (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction in a high pressure autoclave at a temperature of 260° C. for 6 hours, wherein an oxidizing gas (a mixture of air and ozone) is introduced into the second liquid phase oxidation reaction, the partial pressure of the oxidizing gas is 6 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 1.15:1, and then cooling at 90° C., followed by solid separation to obtain a second reaction solid phase and a chromate solution;

[0199] Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing. Part of the second reaction solid phase is subjected to the third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for iron smelting or preparing red iron oxide. A third washed liquid phase is also obtained, which is evaporated and concentrated and mixed with a chromate solution to prepare related products.

[0200] Example 7

[0201] This embodiment provides a method for co-producing chromate from chromite and ferrochrome. The chromite used in this embodiment is the same as that in Example 6.

[0202] The ferrochrome used in this embodiment contains 48.82% chromium, 5.43% carbon, and 41.09% iron by mass percentage;

[0203] The ferromagnesian slag used in this example is the first reaction solid phase returned in Example 6, accounting for 40% of the mass of the chromite ore;

[0204] The iron slag used in this embodiment is the second reaction solid phase returned in Example 6, accounting for 40% of the mass of the ferrochrome;

[0205] The alkaline solution used in this embodiment is: the mass ratio of the alkali to the chromite in the alkaline solution is 4:1 by adding sodium hydroxide to the first reaction liquid phase returned in Example 6;

[0206] The diluent used in this example is the first post-wash liquid phase returned in Example 6;

[0207] The washing liquid used in the first washing treatment of this embodiment is the second washed liquid phase obtained in Example 6;

[0208] The method comprises the following steps:

[0209] (1) subjecting chromite (particle size ≤ 75 μm), an alkaline solution and ferromagnesia slag to a first liquid phase oxidation reaction at a temperature of 260° C. for 5 h in a high pressure reactor, wherein the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is 4:1, and an oxidizing gas (a mixture of air and ozone) is introduced into the first liquid phase oxidation reaction, and the partial pressure of the oxidizing gas is 1.5 MPa;

[0210] The reaction product after the first liquid phase oxidation reaction is flash-cooled at 130° C., and then a diluent is added to the reaction product, wherein the liquid-to-solid ratio of the diluent to the reaction product is 1:1, and slurried at 100° C. for 1.5 hours, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase;

[0211] The first reaction liquid phase is returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesian slag without being washed;

[0212] (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 100° C. and a liquid-to-solid ratio of 1:1, wherein the first washing treatment is a single-stage countercurrent washing for 1 hour to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent;

[0213] The first washed solid phase is subjected to a second washing treatment at a temperature of 80° C. and a liquid-to-solid ratio of 5:1, wherein the second washing treatment is a 4-stage countercurrent washing, and the washing time of each stage is 1 hour, to obtain a second washed liquid phase and a second washed solid phase;

[0214] The solid phase after the second washing is composed of ferromagnesian slag, which is used as raw material for ironmaking; part of the liquid phase after the second washing is used as washing liquid for the first washing process;

[0215] (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 130° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 23%;

[0216] (4) subjecting the ferrochrome, iron slag and the concentrated liquid obtained in step (3) to a second liquid phase oxidation reaction in a high pressure autoclave at a temperature of 250° C. for 6 hours, introducing an oxidizing gas (a mixture of air and ozone) into the second liquid phase oxidation reaction, wherein the partial pressure of the oxidizing gas is 4 MPa, and the mass ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is 0.85:1, followed by cooling at 80° C., and then solid separation to obtain a second reaction solid phase and a chromate solution; a portion of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing, and a portion of the second reaction solid phase is subjected to a third washing treatment to obtain a third washed solid phase, the main component of which is iron slag, which is used for ironmaking or preparing red iron oxide, and a third washed liquid phase is obtained, which is evaporated and concentrated and then mixed with a chromate solution to prepare related products.

[0217] Example 8

[0218] This embodiment provides a method for co-producing chromate from chromite and ferrochrome, which is different from Embodiment 2 only in that the liquid-to-solid ratio of the first washing treatment is 0.2:1.

[0219] Example 9

[0220] This embodiment provides a method for co-producing chromate from chromite ore and ferrochrome, which is different from Embodiment 2 only in that the liquid-to-solid ratio of the first washing treatment is 5:1.

[0221] Example 10

[0222] This embodiment provides a method for co-producing chromate from chromite and ferrochrome, which is different from Embodiment 2 only in that the liquid-to-solid ratio of the second washing treatment is 1:1.

[0223] Embodiment 11

[0224] This embodiment provides a method for co-producing chromate from chromite ore and ferrochrome, which is different from Embodiment 2 only in that the liquid-to-solid ratio of the second washing treatment is 10:1.

[0225] Example 12

[0226] This embodiment provides a method for co-producing chromate from chromite ore and ferrochrome, which is different from the method of embodiment 2 in that the liquid-to-solid ratio of the first washing treatment is 7:1, and the liquid-to-solid ratio of the second washing treatment is 0.2:1.

[0227] Comparative Example 1

[0228] This comparative example provides a method for co-producing chromate from chromite and ferrochrome, which is different from Example 2 only in that step (3) and step (4) are not performed, that is, a second washed liquid phase is obtained after the second washing treatment. The content of the components in the second washed liquid phase is detected by titration, and the concentration of sodium hydroxide in the second washed liquid phase is 113 g / L, and the concentration of sodium chromate is 215 g / L; the content of aluminum and silicon in the second washed liquid phase is detected by dilution ICP analysis, and the aluminum content in the second washed liquid phase is 4.59 g / L and the silicon content is 2.45 g / L.

[0229] The mass concentration of sodium hydroxide and the mass concentration of sodium chromate in the first reaction liquid phase obtained in Examples 1-12 were detected by titration analysis; the content of components contained in the chromate solution was detected by titration analysis; the mass percentage of chromium in the second washed solid phase, i.e., ferromagnesia slag, and the mass percentage of chromium in the third washed solid phase, i.e., iron slag, were detected by ICP analysis after melting. The pH value of the chromate solution and the third washed liquid phase was measured by a pH meter. The above results are shown in Table 1.

[0230] Table 1

[0231]

[0232] From the data of Table 1 and Comparative Example 1, the following points can be seen:

[0233] (1) From the data of Examples 1-7, it can be seen that the method provided by the present invention can make the concentration of the obtained chromate solution reach 402.33 g / L or more, the mass percentage of chromium in the ferromagnesian slag reaches less than 0.65%, and the chromium content in the iron slag reaches less than 0.89%. It can be seen that the chromium recovery rate in the present invention is high, and the loss of chromium is effectively avoided; and the purity of chromate is high, and the content of impurities such as silicon and aluminum is low, the aluminum content reaches less than 0.017 g / L, and the silicon content reaches less than 0.019 g / L, which effectively avoids the introduction of other chemical reagents to remove silicon and aluminum impurities, thereby reducing production costs; the pH values ​​of the obtained chromate solution and the liquid phase after the third washing are both about 7, indicating that the recovery rate of the alkali is high, and the overall process water consumption is low, and no waste residue is discharged.

[0234] (2) From the comparison between Example 2 and Example 8-9, it can be seen that the liquid-solid ratio of the first washing treatment in Example 2 is 0.8:1, compared with 0.2:1 and 5:1 in Example 8-9, respectively. Although the liquid-solid ratio of the first washing treatment in Example 8 can increase the concentration of alkali and chromium in the first reaction liquid phase to a certain extent, which is beneficial to the leaching of chromium, it will also cause operational difficulties, increase the difficulty of subsequent washing, and make the chromium content in the ferromagnesian slag higher; In Example 9, the liquid-solid ratio of the first washing treatment is increased, resulting in a decrease in the concentration of alkali and chromium in the first reaction liquid phase, thereby resulting in a decrease in the leaching rate of chromium in the chromite, an increase in the chromium content in the ferromagnesian slag, a large loss of chromium, and serious environmental pollution. It can be seen that the preferred control of the liquid-solid ratio of the first washing treatment in the present invention can improve the recovery of chromium, transfer chromium to the chromate solution, reduce the difficulty of treatment, and reduce pollution to the environment.

[0235] (3) From the comparison between Example 2 and Example 10-11, it can be seen that the liquid-solid ratio of the second washing treatment in Example 2 is 7:1. Compared with 1:1 and 10:1 in Examples 10-11, respectively, the lowering of the liquid-solid ratio of the second washing treatment in Example 10 leads to an increase in the chromium content in the ferromagnesian slag, resulting in an increase in the loss of chromium; although the increase of the liquid-solid ratio of the second washing treatment in Example 11 can reduce the chromium content in the ferromagnesian slag, the degree of reduction is limited, and the amount of washing water is increased, which increases the subsequent evaporation energy consumption. It can be seen that the present invention preferably controls the liquid-solid ratio of the second washing treatment within a specific range, which can improve the recovery of chromium, transfer chromium to the chromate solution, reduce water consumption, and reduce energy consumption.

[0236] (4) From the comparison between Example 2 and Example 12, it can be seen that the only difference between Example 12 and Example 2 is that the liquid-solid ratio of the first washing treatment is greater than the liquid-solid ratio of the second washing treatment. The data show that the concentrations of alkali and chromate in the first reaction liquid phase in Example 12 are greatly reduced, and the chromium content in the ferromagnesian slag is also greatly increased. It can be seen that the present invention preferably controls the liquid-solid ratio of the first washing treatment to be less than the liquid-solid ratio of the second washing treatment, so that chromium can be transferred to the chromate solution and the loss of chromium can be reduced.

[0237] (5) From the comparison between Example 2 and Comparative Example 1, it can be seen that the difference between Comparative Example 1 and Example 2 is that step (3) and step (4) are not performed, that is, evaporation concentration and second liquid phase oxidation reaction are not performed. In Comparative Example 1, the chromium concentration in the liquid phase after the second washing is obviously low, and the liquid phase after the second washing contains a lot of sodium hydroxide and silicon and aluminum impurities. The silicon and aluminum impurities need to be removed by adding additional reagents, which is costly, and sodium hydroxide is difficult to separate from the chromate solution. In general industry, the liquid phase after the second washing is subsequently acidified to prepare sodium chromate and generate sodium sulfate, which not only loses high-value sodium hydroxide, but also increases the amount of acid used.

[0238] In summary, the method provided by the present invention can make full use of the alkali added to the system, avoid the complicated process of alkali and chromium separation, and obtain a high-concentration chromate solution. Through the combination of the first liquid phase oxidation reaction and the second liquid phase oxidation reaction, silicon and aluminum impurities can be effectively removed, and the introduction of other chemical reagents can be avoided. In addition, the overall process has low water consumption, no waste residue discharge, low production cost, simple process, and easy industrial application.

[0239] 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 co-producing chromate from chromite ore and ferrochrome, characterized in that: The method comprises the following steps: (1) subjecting chromite, alkaline solution and ferromagnesian slag to a first liquid phase oxidation reaction, followed by cooling, slurry reaction and solid-liquid separation in sequence to obtain a first reaction solid phase; (2) subjecting the first reaction solid phase obtained in step (1) to a first washing treatment and a second washing treatment in sequence to obtain a second washed liquid phase; (3) evaporating and concentrating the second washed liquid phase obtained in step (2) to obtain a concentrated solution; (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction, followed by cooling and solid-liquid separation, to obtain a chromate solution.

2. The method according to claim 1, characterized in that The alkali contained in the alkaline solution in step (1) includes any one of sodium hydroxide, potassium hydroxide or lithium hydroxide, or a combination of at least two thereof; Preferably, the mass concentration of the alkaline solution is 60-78%; Preferably, the composition of the ferromagnesian slag includes magnesium oxide and iron oxide; Preferably, the ferromagnesian slag also contains alkali and chromate; Preferably, the ferromagnesian slag is leached slag from a liquid phase oxidation reaction of chromite; Preferably, the ferromagnesian slag contains 10-35% chromate by mass percentage; Preferably, the ferromagnesian slag contains 25-55% alkali by mass percentage; Preferably, the mass of the ferromagnesian slag in the first liquid phase oxidation reaction accounts for 2-80% of the mass of the chromite ore; Preferably, the mass ratio of alkali to chromite in the first liquid phase oxidation reaction is (3-6):

1.

3. The method according to claim 1 or 2, characterized in that: The cooling temperature in step (1) is 100-150° C. Preferably, the cooling method in step (1) includes flash evaporation; Preferably, the slurrying reaction comprises: adding a diluent to the reaction product obtained by the first liquid phase oxidation reaction, and then slurrying; Preferably, the slurrying temperature is 80-110°C; Preferably, the slurrying time is 0.2-2h; Preferably, after the solid-liquid separation in step (1), a first reaction liquid phase is obtained; Preferably, the first reaction liquid phase is used as an alkaline solution or the first reaction liquid phase is supplemented with alkali and then returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution; Preferably, the first reaction solid phase obtained in part of step (1) is directly returned to the first liquid phase oxidation reaction system as ferromagnesian slag without being washed.

4. The method according to any one of claims 1 to 3, characterized in that: Step (2) the first washing treatment and the second washing treatment each independently comprise countercurrent washing; Preferably, the number of stages of the first washing treatment is at least 1; Preferably, the number of stages of the second washing treatment includes 3-8 stages; Preferably, in the first washing treatment and the second washing treatment, the washing time of each stage is independently 0.5-2h; Preferably, the liquid-to-solid ratio of the first washing treatment is less than the liquid-to-solid ratio of the second washing treatment; Preferably, the temperature of the first washing treatment is 80-100°C; Preferably, the liquid-to-solid ratio of the first washing treatment is (0.5-2):1; Preferably, the first washing treatment obtains a first washed liquid phase and a first washed solid phase; Preferably, the solid phase after the first washing is subjected to a second washing treatment; Preferably, the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent; Preferably, the temperature of the second washing treatment is 60-90°C; Preferably, the liquid-to-solid ratio of the second washing treatment is (3-8):1; Preferably, part of the second washed liquid phase obtained in the second washing treatment is used as washing liquid in the first washing treatment; Preferably, the second washing treatment further obtains a second washed solid phase; Preferably, the second washed solid phase is used as raw material for ironmaking.

5. The method according to any one of claims 1 to 4, characterized in that: The temperature of the evaporation concentration in step (3) is 105-150° C. Preferably, the mass concentration of alkali in the concentrated solution is 10-25%.

6. The method according to any one of claims 1 to 5, characterized in that: The iron slag in step (4) comprises iron oxide; Preferably, the iron slag also contains chromate; Preferably, the iron slag is leached slag from a liquid phase oxidation reaction of ferrochrome; Preferably, the iron slag contains 10-55% iron oxide by mass percentage; Preferably, the iron slag contains 0.5-5% chromate by mass.

7. The method according to any one of claims 1 to 6, characterized in that: Step (4) the mass of the iron slag in the second liquid phase oxidation reaction accounts for 1-40% of the mass of the ferrochrome; Preferably, the mass ratio of alkali to ferrochrome in the second liquid-phase oxidation reaction is (0.72-1.35):

1.

8. The method according to any one of claims 1 to 7, characterized in that: The cooling temperature in step (4) is 70-100°C.

9. The method according to any one of claims 1 to 8, characterized in that: The solid-liquid separation in step (4) also obtains a second reaction solid phase; Preferably, part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without being washed; Preferably, part of the second reaction solid phase is used for iron smelting or preparation of red iron oxide after the third washing treatment.

10. The method according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: (1) subjecting chromite, an alkaline solution having a mass concentration of 60-78% and ferromagnesia slag to a first liquid phase oxidation reaction; the ferromagnesia slag contains magnesium oxide and iron oxide, and also contains 10-35% of chromate and 25-55% of alkali, the mass of the ferromagnesia slag in the first liquid phase oxidation reaction accounts for 2-80% of the mass of the chromite, and the mass ratio of the alkali to the chromite in the first liquid phase oxidation reaction is (3-6):1; The reaction product after the first liquid phase oxidation reaction is flash-cooled at 100-150° C., and then a diluent is added to the reaction product, and slurried at 80-110° C. for 0.2-2 hours, and then solid-liquid separation is performed to obtain a first reaction solid phase and a first reaction liquid phase; The first reaction liquid phase is returned to the reaction system of the first liquid phase oxidation reaction as an alkaline solution or as an alkaline solution after the first reaction liquid phase is supplemented with alkali, and part of the first reaction solid phase is directly returned to the reaction system of the first liquid phase oxidation reaction as ferromagnesia slag without being washed; (2) the first reaction solid phase obtained in part of step (1) is subjected to a first washing treatment at a temperature of 80-100° C. and a liquid-to-solid ratio of (0.5-2):1, wherein the first washing treatment includes at least one stage of countercurrent washing, and the washing time of each stage is 0.5-2 hours, to obtain a first washed solid phase and a first washed liquid phase, and the first washed liquid phase is returned to the reaction system of the slurry reaction as a diluent; The first washed solid phase is subjected to a second washing treatment at a temperature of 60-90° C. and a liquid-to-solid ratio of (3-8):1, wherein the second washing treatment comprises 3-8 stages of countercurrent washing, and the washing time of each stage is 0.5-2 hours, to obtain a second washed liquid phase and a second washed solid phase; The second washed solid phase is used as raw material for ironmaking; part of the second washed liquid phase is used as washing liquid for the first washing process; (3) the second washed liquid phase obtained in part of step (2) is evaporated and concentrated at a temperature of 105-150° C. to obtain a concentrated solution, wherein the mass concentration of alkali in the concentrated solution is 10-25%; (4) subjecting the ferrochrome, iron slag and the concentrated solution obtained in step (3) to a second liquid phase oxidation reaction at a temperature of 250-320° C., wherein the iron slag comprises, by weight percentage, 10-55% of iron oxide and 0.5-5% of chromate, the weight of the iron slag in the second liquid phase oxidation reaction accounts for 1-40% of the weight of the ferrochrome, and the weight ratio of alkali to ferrochrome in the second liquid phase oxidation reaction is (0.72-1.35):1, and then cooling at 70-100° C., and then solid separation to obtain a second reaction solid phase and a chromate solution; Part of the second reaction solid phase is directly returned to the second liquid phase oxidation reaction system as iron slag without washing, and part of the second reaction solid phase is used for iron smelting or preparation of red iron oxide after the third washing treatment.

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