Method for producing sodium chromate by using ferrochrome dedusting ash and calcium-free chromium slag

Abstract

The invention relates to a method for producing sodium chromate by using ferrochrome dedusting ash and calcium-free chromium slag, which comprises the following steps: adding a reaction device at a flue gas outlet of a ferrochrome smelting furnace, automatically feeding back and introducing oxygen according to the detected carbon monoxide content, and increasing the content of Na2CO3 in the dedusting ash generated by ferrochrome smelting; a mixture of the fly ash and the calcium-free chromium slag is used as a raw material, pulverized coal is used as a fuel, roasting and clinker leaching are performed in an oxygen-enriched environment, and then the chromium slag is dried for ferrochrome smelting. According to the method, the sodium chromate production process is optimized, the investment of the traditional raw materials of the chromium ore powder and the sodium carbonate is reduced, the resource recycling rate is increased, the production cost is reduced, the content of hexavalent chromium in the finally obtained chromium slag is greatly reduced, detoxification is easy, and pollution is small.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgical chemical industry, and particularly relates to a variable frequency power intelligent parallel device. BACKGROUND

[0002] Currently, there are two main methods for producing sodium chromate, one is to use calcium filler (limestone and dolomite), chromite, soda ash and a small part of calcium chromium slag mixed powder to produce by roasting, which is called calcium process. The other is to use chromite, soda ash and a small part of calcium chromium slag mixed powder to produce by roasting, which is called calcium-free process. Both of the two production processes need to discharge chromium slag. The discharge amount of chromium slag per ton of sodium chromate product produced by calcium process is 2.5-3 tons, and the discharge amount of chromium slag per ton of sodium chromate product produced by calcium-free process is 1-1.5 tons. The hexavalent chromium contained in the chromium slag is an internationally recognized carcinogen, and the hexavalent chromium contained in the discharged chromium slag is as high as 1-3% (calculated as Gr2O3), and the total chromium is as high as 8-10% (calculated as Gr2O3).

[0003] For the chromium slag discharged by these sodium chromate production processes, on the one hand, in order to meet the environmental protection requirements, the hexavalent chromium in the chromium slag needs to be detoxified first, and then filled. On the other hand, because of the scarcity of raw materials, most of the chromium ore powder used by the chromium salt factories in China is imported from countries such as South Africa. Filling will cause a lot of resource waste, so the chromium slag discharged by the sodium chromate production process will be smelted into ferrochrome alloy for further use. However, it is found after practice that although the chromium slag discharged by the sodium chromate production process can be recycled to some extent by doing so, the production cost of sodium chromate is still high, and the dust ash generated in the process of smelting ferrochrome alloy is difficult to handle, which will still cause environmental pollution. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for producing sodium chromate by using ferrochrome alloy dust ash and calcium-free chromium slag, so as to reduce the production cost of sodium chromate and reduce environmental pollution.

[0005] In order to solve the above problems, the method for producing sodium chromate by using ferrochrome alloy dust ash and calcium-free chromium slag provided by the present application comprises the following steps: Step S1: a reaction device is added at the smoke outlet of the ferrochrome alloy smelting furnace, oxygen is automatically fed according to the detected carbon monoxide content, so that all CO in the smoke dust is converted into CO2, and then the Na2O in the smoke dust is completely converted into Na2CO3, so as to increase the content of Na2CO3 in the dust ash generated in the process of smelting ferrochrome alloy; Step S2: the calcium-free chromium slag is dried and ground to 20 mesh, and the residue is ≤10.0% for standby use; Step S3: the chromium slag obtained in step S2 and the dust ash generated in the process of smelting ferrochrome alloy obtained in step S3 are mixed uniformly in a special mixing equipment according to the weight ratio of 78:22 to obtain mixed powder. Step S4: the mixed powder obtained in step S3 is sent into a rotary kiln, and sintering granulation is carried out at a temperature of 850-950 DEG C with bituminous coal as fuel, and the 1mm residue is less than or equal to 5.0%; Step S5: the granular material obtained in step S4 is subjected to oxygen-rich roasting in a rotary kiln, and the roasting is carried out with bituminous coal as fuel, the length of the high-temperature zone is greater than or equal to 28 meters, the granular material is allowed to run in the high-temperature zone for 1.1 hours, and the residence time in the rotary kiln is 3.8 hours, and sodium chromate is obtained after leaching and filtration after cooling.

[0006] Preferably, in step S1, the negative pressure, the composition and the flow of the flue gas are detected, and the amount of oxygen introduced into the inside of the reaction device is automatically controlled according to the detected carbon monoxide content, so that the Na2CO3 content in the dusting ash generated by the smelting of ferrochrome alloy is greater than or equal to 92%.

[0007] Preferably, in step S2, the content of Cr2O3 in the calcium-free chromium residue is 8-10%.

[0008] Preferably, in step S5, the reaction temperature of the high-temperature zone is 1100-1200 DEG C.

[0009] Compared with the prior art, the present application has the following advantages: In the present application, a reaction device is added at the flue gas outlet of a ferrochrome smelting furnace, so that the sodium oxide in the dusting ash is converted into sodium carbonate as much as possible, which is convenient for repeated recycling, and then the dusting ash and the calcium-free chromium residue generated by the production of sodium chromate are used as raw materials for the production of sodium chromate, on the one hand, the input of traditional raw materials such as chromite is reduced, the resource utilization rate is improved, and the industrialized continuous production is realized, and the cost is reduced by more than 20% compared with the traditional production cost of using chromite powder and soda ash, on the other hand, after the calcium-free chromium residue generated by the production of sodium chromate is recycled for many times, the content of hexavalent chromium in the final chromium residue is greatly reduced, which is easy to detoxify and has little pollution. BRIEF DESCRIPTION OF DRAWINGS

[0010] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0011] Figure 1 The process flow chart provided for the embodiments of the present application. DETAILED DESCRIPTION

[0012] Embodiment 1 A method for producing sodium chromate by using ferrochrome dusting ash and calcium-free chromium residue: Step S1: a reaction device is added at the flue gas outlet of a ferrochrome smelting furnace, when the negative pressure is -5 Pa, the flue gas flow is detected to be 85600 m 3 / h, and the carbon monoxide content is 44.3 m 3 / h, automatically feedback oxygen 22.1m 3 / h, make all CO in the smoke dust convert into CO2, and make Na2O in the smoke dust convert into Na2CO3 completely, so as to increase the content of Na2CO3 in the dusting ash generated by smelting ferrochrome alloy to 93%.

[0013] Specifically, the negative pressure, smoke composition and flow are detected, and appropriate oxygen is automatically controlled to be introduced into the reaction device according to the detected carbon monoxide content. The main reaction in the reaction device is: 2CO+O2=2CO2, CO2+Na2O=Na2CO3. During the smelting process, sodium oxide is precipitated into the dusting ash at high temperature. The reaction device is added at the outlet of the smelting furnace to increase the conversion rate of sodium oxide into sodium carbonate, so that the sodium carbonate can be recycled and reused (combined with calcium-free chromium residue to be used as raw material for producing sodium chromate), and industrial continuous production is realized. This part is the same as the subsequent examples.

[0014] Step S2: The calcium-free chromium residue is dried and ground to 20 mesh, and the residue is 10.0% for use. The content of Cr2O3 in the calcium-free chromium residue is 9.5%.

[0015] Step S3: The chromium residue obtained in step S2 is mixed with the dusting ash generated by smelting ferrochrome alloy obtained in step S3 in a mixing device according to a weight ratio of 78:22 to obtain a mixed powder, wherein the content of Na2CO3 in the dusting ash is 93%.

[0016] Step S4: The mixed powder obtained in step S3 is sent into a rotary kiln, and bituminous coal is used as fuel to sinter and granulate at a temperature of 930℃, and the residue on a 1mm sieve is ≤5.0%.

[0017] Step S5: The high-temperature granular material obtained in step S4 is oxygen-enriched roasted in a rotary kiln, and bituminous coal is used as fuel. The length of the high-temperature section is 28 meters. The granular material is allowed to run in the high-temperature zone for 1.1h, and stays in the rotary kiln for 3.8h. After cooling, sodium chromate is obtained by leaching and filtering.

[0018] The total chromium content in the chromium residue is measured to be 5.1%, and the leaching rate of hexavalent chromium is 99.4%. The obtained chromium residue is dried and then used for smelting ferrochrome alloy. During the smelting process, sodium oxide is precipitated into the dusting ash at high temperature and becomes sodium carbonate, which is recycled and reused, realizing industrial continuous production. The method provided by the present application is used to produce sodium chromate, which reduces the cost by 23% compared with the traditional production method using chromium ore powder.

[0019] Example 2 A method for producing sodium chromate by using calcium-free chromium residue and dusting ash of ferrochrome alloy: Step S1: A reaction device was added to the flue gas outlet of the ferrochrome alloy smelting furnace. When the negative pressure was -4 Pa, the flue gas flow rate was detected to be 84900 m³ / s. 3 / h, carbon monoxide content is 43.8m 3 / h, automatically feeding in 21.8m of oxygen based on the detected carbon monoxide content. 3 / h, so that all CO in the flue dust is converted into CO2, and the Na2O in the flue dust is completely converted into Na2CO3, thereby increasing the Na2CO3 content in the dust generated from ferrochrome alloy smelting to 92%.

[0020] Step S2: After drying the calcium-free chromium slag, grind it to 20 mesh, and sieve the residue to 10.0% for later use. The Cr2O3 content in the calcium-free chromium slag is 9%.

[0021] Step S3: The chromium slag obtained in step S2 and the dust generated from the smelting of ferrochrome alloy obtained in step S3 are mixed evenly in a mixing device at a weight ratio of 78:22 to obtain a mixed powder, wherein the Na2CO3 content in the dust is 92%.

[0022] Step S4: The mixed powder obtained in step S3 is fed into a rotary kiln and sintered and granulated at a temperature of 910°C using bituminous coal as fuel. The residue on a 1mm sieve is ≤5.0%.

[0023] Step S5: The high-temperature particles obtained in step S4 are calcined in a rotary kiln with oxygen enrichment. Bituminous coal is used as fuel for calcination. The high-temperature section is 28 meters long. The particles are allowed to run in the high-temperature zone for 1.1 hours and stay in the rotary kiln for 3.8 hours. After cooling, sodium chromate is obtained by leaching and filtration.

[0024] The total chromium content in the chromium slag was measured to be 5.1%, and the leaching rate of hexavalent chromium was 99.2%. After drying, the obtained chromium slag was used to smelt ferrochrome alloys. During the smelting process, sodium oxide precipitated into the dust at high temperature and was converted into sodium carbonate for repeated recycling, realizing continuous industrial production. The method provided by this invention reduces the cost of producing sodium chromate by 21.5% compared with the traditional method of producing sodium chromate from chromium ore powder.

[0025] Example 3 A method for producing sodium chromate using ferrochrome alloy dust and calcium-free chromium slag: Step S1: A reaction device was added to the flue gas outlet of the ferrochrome alloy smelting furnace. When the negative pressure was -3 Pa, the flue gas flow rate was detected to be 84,500 m³ / s. 3 / h, carbon monoxide content is 43.5m 3 / h, automatically feeding in 21.7m of oxygen based on the detected carbon monoxide content. 3 / h, so that all CO in the flue dust is converted into CO2, and the Na2O in the flue dust is completely converted into Na2CO3, thereby increasing the Na2CO3 content in the dust generated from ferrochrome alloy smelting to 91.5%.

[0026] Step S2: After drying the calcium-free chromium slag, grind it to 20 mesh, and sieve the residue to 10.0% for later use. The Cr2O3 content in the calcium-free chromium slag is 8.5%.

[0027] Step S3: The chromium slag obtained in step S2 and the dust generated from the smelting of ferrochrome alloy obtained in step S3 are mixed evenly in a mixing device at a weight ratio of 78:22 to obtain a mixed powder, wherein the Na2CO3 content in the dust is 91%.

[0028] Step S4: The mixed powder obtained in step S3 is fed into a rotary kiln and sintered and granulated at a temperature of 900°C using bituminous coal as fuel. The residue on a 1mm sieve is ≤5.0%.

[0029] Step S5: The high-temperature particles obtained in step S4 are calcined in a rotary kiln with oxygen enrichment. Bituminous coal is used as fuel for calcination. The high-temperature section is 28 meters long. The particles are allowed to run in the high-temperature zone for 1.1 hours and stay in the rotary kiln for 3.8 hours. After cooling, sodium chromate is obtained by leaching and filtration.

[0030] The total chromium content in the chromium slag was measured to be 5.3%, and the leaching rate of hexavalent chromium was 99.1%. After drying, the obtained chromium slag was used to smelt ferrochrome alloy. During the smelting process, sodium oxide precipitated into the dust at high temperature and was converted into sodium carbonate for repeated recycling, realizing continuous industrial production. The method provided by this invention reduces the cost of producing sodium chromate by 21% compared with the traditional method of producing it from chromium ore powder.

[0031] Example 4 A method for producing sodium chromate using ferrochrome alloy dust and calcium-free chromium slag: Step S1: A reaction device was added to the flue gas outlet of the ferrochrome alloy smelting furnace. When the negative pressure was -2 Pa, the flue gas flow rate was detected to be 84,000 m³ / s. 3 / h, carbon monoxide content 43m 3 / h, automatically feeding in 21.45m³ of oxygen based on the detected carbon monoxide content. 3 / h, so that all CO in the flue dust is converted into CO2, and the Na2O in the flue dust is completely converted into Na2CO3, thereby increasing the Na2CO3 content in the dust generated from ferrochrome alloy smelting to 91%.

[0032] Step S2: After drying the calcium-free chromium slag, grind it to 20 mesh, and sieve the residue to 10.0% for later use. The Cr2O3 content in the calcium-free chromium slag is 9.2%.

[0033] Step S3: The chromium slag obtained in step S2 and the dust generated from the smelting of ferrochrome alloy obtained in step S3 are mixed evenly in a mixing device at a weight ratio of 78:22 to obtain a mixed powder, wherein the Na2CO3 content in the dust is 91%.

[0034] Step S4: The mixed powder obtained in step S3 is fed into a rotary kiln and sintered and granulated at a temperature of 880°C using bituminous coal as fuel. The residue on a 1mm sieve is ≤5.0%.

[0035] Step S5: The high-temperature particles obtained in step S4 are calcined in a rotary kiln with oxygen enrichment. Bituminous coal is used as fuel for calcination. The high-temperature section is 28 meters long. The particles are allowed to run in the high-temperature zone for 1.1 hours and stay in the rotary kiln for 3.8 hours. After cooling, sodium chromate is obtained by leaching and filtration.

[0036] The total chromium content in the chromium slag was measured to be 5.6%, and the leaching rate of hexavalent chromium was 99%. After drying, the obtained chromium slag was used to smelt ferrochrome alloy. During the smelting process, sodium oxide precipitated into the dust at high temperature and was converted into sodium carbonate for repeated recycling, realizing continuous industrial production. The method provided by this invention reduces the cost of producing sodium chromate by 20% compared with the traditional method of producing it from chromium ore powder.

[0037] The technical solution provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for producing sodium chromate using ferrochrome alloy dust and calcium-free chromium slag, characterized in that, The method includes: Step S1: Add a reaction device to the flue gas outlet of the ferrochrome alloy smelting furnace. Based on the detected carbon monoxide content, oxygen is automatically fed in to convert all CO in the flue gas into CO2, which in turn promotes the complete conversion of Na2O in the flue gas into Na2CO3, thereby increasing the Na2CO3 content in the dust generated from ferrochrome alloy smelting. Step S2: Dry the calcium- and chromium-free slag and grind it to 20 mesh. The residue on the sieve should be ≤10.0% for later use. Step S3: The chromium slag obtained in step S2 and the dust generated from the smelting of ferrochrome alloy obtained in step S3 are mixed evenly in a special mixing equipment at a weight ratio of 78:22 to obtain a mixed powder. Step S4: The mixed powder obtained in step S3 is fed into a rotary kiln and sintered and granulated at a temperature of 850-950℃ using bituminous coal as fuel, with a sieve residue of ≤5.0% on a 1mm sieve. Step S5: The granular material obtained in step S4 is oxygen-enriched and roasted in a rotary kiln using bituminous coal as fuel. The high-temperature section is ≥28 meters long. The granular material is allowed to run in the high-temperature zone for 1.1 hours and stay in the rotary kiln for 3.8 hours. After cooling, it is leached and filtered to obtain sodium chromate.

2. The method for producing sodium chromate using ferrochrome alloy dust and calcium-free chromium slag as described in claim 1, characterized in that, In step S1, the negative pressure, flue gas composition and flow rate are detected, and an appropriate amount of oxygen is automatically introduced into the reaction device based on the detected carbon monoxide content, so that the Na2CO3 content in the dust generated from ferrochrome alloy smelting reaches more than 92%.

3. The method for producing sodium chromate using ferrochrome alloy dust and calcium-free chromium slag as described in claim 1, characterized in that, In step S2, the Cr2O3 content in the calcium-free chromium slag is 8-10%.

4. The method for producing sodium chromate using ferrochrome alloy dust and calcium-free chromium slag as described in claim 1, characterized in that, In step S5, the high-temperature calcination reaction temperature is 1100-1200℃.

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