Method for assisting reduction decomposition of ardealite by adopting hydrogen

Abstract

The invention discloses a method for reducing and decomposing ardealite under the assistance of hydrogen, which comprises the following steps: mixing crushed and sieved ardealite and lignite, placing the mixture in a tubular furnace, and reacting for 1-2.5 hours in a hydrogen atmosphere with the volume concentration of 20-100% at 700-800 DEG C to obtain a calcium sulfide product; according to the method, efficient resource utilization of the phosphogypsum can be achieved, meanwhile, the emission amount of CO2 is greatly reduced, and the method is simple and easy to implement and can play a reference role in industrial production and market popularization and application.

Description

Technical Field

[0001] The invention belongs to the field of resource utilization of phosphogypsum solid waste, and specifically relates to a method for reducing and decomposing phosphogypsum by using hydrogen to assist. Background Art

[0002] Phosphogypsum is a solid waste produced in the process of producing phosphate fertilizer using wet phosphoric acid in industry. In the wet phosphoric acid process, five tons of phosphogypsum are produced for every ton of phosphoric acid produced. The stockpile of phosphogypsum in my country has reached 870 million tons, with an annual increase of about 80 million tons. In addition, my country started late in the resource utilization of phosphogypsum, and currently the excess phosphogypsum is still mainly piled up in large quantities. However, phosphogypsum is also an important renewable resource. However, due to the complexity of its composition, it contains a small amount of impurities such as incompletely decomposed phosphate rock, soluble nitrate salts, fluoride, etc., which makes it difficult to utilize it harmlessly.

[0003] As early as 1915, Muller and Kuhner proposed a method of decomposing phosphogypsum using coke as a reducing agent under high temperature conditions, thus laying the foundation for the production process of hollow rotary kilns and rotary kilns with vertical drum preheaters to decompose phosphogypsum to produce sulfuric acid and cement. In the research on reducing atmospheres, CO as a reducing atmosphere for the thermal decomposition of phosphogypsum can effectively reduce the initial decomposition temperature and increase the decomposition rate and decomposition rate, but CO is an important raw material for the production of organic chemicals, and using it as a reducing atmosphere for the decomposition of phosphogypsum will bring cost pressure to industrial production. Therefore, in order to find a cheaper and more readily available atmosphere to replace CO as a new research target, some researchers use H2S in exhaust gas as a reducing atmosphere for phosphogypsum, but the research is not deep enough and the process is not yet mature, so it cannot be applied to actual production.

[0004] In the current industrial decomposition process of bulk solid waste phosphogypsum, the decomposition method adopted is one-step or two-step. The main solid product produced by the former is calcium oxide, while the mutual product of the latter is first calcium sulfide and then calcium oxide. In the process, a large amount of carbon dioxide is produced, which brings serious environmental pollution problems. In the current method of preparing calcium sulfide by decomposing phosphogypsum, the decomposition temperature is 900-1200℃. Therefore, it is necessary to select other more suitable reducing agents or methods to achieve the effect of low temperature and low carbon in the thermal decomposition of phosphogypsum. Summary of the invention

[0005] In view of the difficulty in resource utilization of phosphogypsum, the present invention provides a method for low-temperature reduction and decomposition of phosphogypsum using hydrogen to assist, the solid phase products obtained by this method are all calcium sulfide, and sulfur dioxide accounts for the majority of the gas phase products, thereby achieving the purpose of low-temperature and low-carbon reduction and decomposition of phosphogypsum. This method effectively reduces carbon dioxide emissions and also achieves the purpose of recycling phosphogypsum.

[0006] The method of the present invention using hydrogen to assist the reduction and decomposition of phosphogypsum is as follows: 1. Grind the phosphogypsum and lignite separately, sieve them, and mix the sieved raw materials evenly at a mass ratio of phosphogypsum to lignite of 10-12:1; 2. Place the mixture in a tubular furnace, pass hydrogen (N2 as carrier gas) with a volume concentration of 25%-70%, control the gas flow rate at 100mL / min, react at 700℃-800℃ for 1-2.5h to obtain calcium sulfide product.

[0007] Compared with the existing decomposition technology, the advantages of the present invention are: 1) The present invention adopts hydrogen as a reducing atmosphere for the first time; the method of the present invention can completely decompose calcium sulfate in phosphogypsum to generate calcium sulfide, and the calcium sulfide product is more conducive to reuse; 2) During the low-temperature decomposition process, carbon emissions are greatly reduced, achieving the goal of low carbon, reducing pollutant emissions during the decomposition of phosphogypsum, and also bringing higher economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is the XRD pattern of the product of Example 1; Figure 2 is the XRD pattern of the product of Example 2; Figure 3 is the XRD pattern of the product of Example 3; Figure 4 is the XRD pattern of the product of Example 4; Figure 5 This is the XRD pattern of the product of Example 5. DETAILED DESCRIPTION

[0009] The present invention is further explained by examples below, but these examples do not limit the scope of protection of the present invention. The methods in the examples are conventional methods unless otherwise specified, and the reagents used are conventional commercial reagents or reagents prepared according to conventional methods unless otherwise specified; In the embodiment, the phosphogypsum and coal are from Yuntianhua Group, the calcium sulfate content in the phosphogypsum is 80%, and the C content in the lignite is 62%; Example 1: Method for low-temperature and low-carbon reduction decomposition of phosphogypsum using hydrogen 1. Grind the phosphogypsum and lignite separately, pass the phosphogypsum through a 100-mesh sieve and the lignite through an 80-mesh sieve, and mix the phosphogypsum and lignite evenly at a ratio of 10:1; 2. Put the mixture into a small porcelain boat and place it in a tube furnace. Pass N2 containing 35% hydrogen by volume. The gas flow rate is controlled at 100 mL / min. React at 700 ° C for 1.5 h to obtain calcium sulfide. The XRD pattern of the reaction product is shown in Figure 1 , it can be seen from the figure that except for the silicon dioxide originally contained in the phosphogypsum, the calcium sulfate has been completely converted into calcium sulfide, and the conversion rate of calcium sulfide reaches 100%.

[0010] Example 2: Method for low-temperature and low-carbon reduction decomposition of phosphogypsum using hydrogen 1. Grind the phosphogypsum and lignite separately, pass the phosphogypsum through a 100-mesh sieve and the lignite through an 80-mesh sieve, and mix the phosphogypsum and lignite evenly at a ratio of 12:1; 2. Put the mixture into a small porcelain boat and place it in a tube furnace. Pass N2 containing 25% hydrogen by volume. The gas flow rate is controlled at 100 mL / min. React at 750°C for 1.5 h to obtain calcium sulfide. The XRD pattern of the reaction product is shown in Figure 2 , it can be seen from the figure that except for the silicon dioxide originally contained in the phosphogypsum, the calcium sulfate has been completely converted into calcium sulfide, and the conversion rate of calcium sulfide reaches 100%.

[0011] Example 3: Method for low-temperature and low-carbon reduction decomposition of phosphogypsum using hydrogen 1. Grind the phosphogypsum and lignite separately, pass the phosphogypsum through a 100-mesh sieve and the lignite through an 80-mesh sieve, and mix the phosphogypsum and lignite evenly at a ratio of 12:1; 2. Put the mixture into a small porcelain boat and place it in a tube furnace. Pass N2 containing 50% hydrogen by volume. The gas flow rate is controlled at 100 mL / min. React at 700 ° C for 1.5 h to obtain calcium sulfide. The XRD pattern of the reaction product is shown in Figure 3 , it can be seen from the figure that except for the silicon dioxide originally contained in the phosphogypsum, the calcium sulfate has been completely converted into calcium sulfide, and the conversion rate of calcium sulfide reaches 100%.

[0012] Example 4: Method for low-temperature and low-carbon reduction decomposition of phosphogypsum using hydrogen 1. Grind the phosphogypsum and lignite separately, pass the phosphogypsum through a 100-mesh sieve and the lignite through an 80-mesh sieve, and mix the phosphogypsum and lignite evenly at a ratio of 12:1; 2. Put the mixture into a small porcelain boat and place it in a tube furnace. Pass N2 containing 60% hydrogen by volume. The gas flow rate is controlled at 100 mL / min. React at 700 ° C for 1.5 h to obtain calcium sulfide. The XRD pattern of the reaction product is shown in Figure 4 , it can be seen from the figure that except for the silicon dioxide originally contained in the phosphogypsum, the calcium sulfate has been completely converted into calcium sulfide, and the conversion rate of calcium sulfide reaches 100%.

[0013] Example 5: Method for low-temperature and low-carbon reduction decomposition of phosphogypsum using hydrogen 1. Grind phosphogypsum and lignite separately, and pass phosphogypsum through a 100-mesh sieve; 2. Put the phosphogypsum into a small porcelain boat and place it in a tube furnace. Pass N2 containing 65% hydrogen by volume. The gas flow rate is controlled at 100 mL / min. React at 750°C for 1.5 hours to obtain calcium sulfide. The XRD pattern of the reaction product is shown in Figure 5 ,It can be seen from the figure that without the addition of lignite, calcium sulfate is not completely converted into calcium sulfide, except for the silicon dioxide originally contained in the phosphogypsum, and some calcium sulfate still exists.

Claims

1. A method for reducing and decomposing phosphogypsum using hydrogen, characterized in that: The crushed and sieved phosphogypsum is mixed with lignite and placed in a tubular furnace, and reacted for 1-2.5 hours at 700°C-800°C in a hydrogen atmosphere with a volume concentration of 25%-70% to obtain a calcium sulfide product.

2. The method for reducing and decomposing phosphogypsum using hydrogen as an aid according to claim 1, characterized in that: The mass ratio of phosphogypsum to lignite is 10-12:1.

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