Application and modification methods of phosphogypsum_Industrial additives

Background and overview^[1][2]

Phosphorus-containing gypsum is a by-product in the production of wet phosphoric acid. Due to different production processes, there are phosphorus-containing dihydrate gypsum (CaSO₄·2H₂O) and hemihydrate gypsum (CaSO₅·1/ 2H₂Quenching agent O). In addition to calcium sulfate, the main ingredients also contain a small amount of undecomposed phosphate rock powder, free phosphoric acid, iron phosphate, aluminum phosphate and fluorosilicate and other impurities. The purer ones can be used as raw materials for making cement, sulfuric acid, ammonium sulfate and building materials. It can also be used in some alkaline soils, which can utilize the water-soluble phosphorus pentoxide and improve the soil. Its sulfate radical is also needed for sulfur-deficient soil.

Modification^[2]

Phosphogypsum is a solid waste from the phosphate fertilizer industry. Generally, approximately 5-6 tons of phosphogypsum are produced for every ton of phosphoric acid produced, and 2.5-5 tons of phosphogypsum are emitted for every ton of diammonium phosphate produced. At present, whether abroad or domestically, the comprehensive utilization rate of phosphogypsum is relatively low, and it is mainly processed by stockpiling. The cumulative discharge of phosphogypsum in my country is nearly 100 million tons, which is the largest type of gypsum waste. The discharged phosphogypsum residue occupies a large amount of land, forming slag mountains and seriously polluting the environment.

At present, the output of phosphogypsum is large, but its utilization rate is very low. There are many reasons for the low utilization rate of phosphogypsum, but the most important one is that the surface properties of phosphogypsum are poor, resulting in a relatively single utilization route. By analyzing and understanding the properties of phosphogypsum, CN201810143006 explored a phosphogypsum modification method with simple equipment and low cost, thereby improving the surface properties of phosphogypsum and expanding the comprehensive utilization of phosphogypsum.

A method for modifying phosphogypsum, the steps are as follows:

1) Grind the phosphogypsum in a grinder and pass it through a mesh sieve to obtain product A;

2) Put product A and quicklime into a stirring and heating device, stir and mix evenly, adjust the pH value of the mixture to 10, and obtain product B;

3) Heat and stir the product B, and control the temperature to 120°C. After heating and stirring for 70 minutes, product C is obtained;

4) Add 0.75% by mass of titanate coupling agent, 0.75% by mass of aluminate coupling agent, 0.5% by mass of liquid paraffin and 1.5% by mass of product C in sequence. % stearic acid, before adding, the above additives were diluted with equal mass of industrial ethanol, and the heating and stirring process was continued, and the temperature was controlled to 100°C, and the heating and stirring process was carried out for 50 minutes, and finally the modified phosphogypsum was obtained.

Phosphogypsum is modified through the above method, and the surface properties of the modified phosphogypsum are greatly improved, which expands its industrial application and improves the utilization value of phosphogypsum. Experiments have shown that modified phosphogypsum produced by traditional processing methods has agglomeration, and the 45-micron test sieve residue is usually greater than 3%. The modified phosphogypsum prepared by the invention is tested with a 45 micron test sieve. The sieve residue is ≤0.3%, the activation mass fraction is ≥90%, and the oil absorption capacity is ≤70mL/100g. It meets the standard requirements and can be used as PVC, PP, etc. Used as filler in the processing of plastic products.

Micronization^[3]

A method for preparing active phosphogypsum micropowder, the steps are as follows:

1) Put phosphogypsum powder and calcium oxide with a particle size of 20 microns into a stirring and heating device, stir and mix, adjust the pH value of the mixture to 10, and obtain product A;

2) Heat and stir product A, control the temperature to 120°C, and heat for 70 minutes to obtain product B;

3) Add 2% by mass of aluminate coupling agent to product B. When adding the aluminate coupling agent, dilute it with industrial ethanol of the same quality, continue heating and stirring, and control the heating temperature to 90 ℃, heat and stir for 40 minutes, and finally obtain activated phosphogypsum micron powder.

Using the above method to surface-treat phosphogypsum micropowder, the surface properties of the obtained phosphogypsum micropowder are greatly improved, expanding its industrial application and improving the utilization value of phosphogypsum. Phosphogypsum micropowder produced by traditional processing methods has agglomeration, and the residue on the 45-micron test sieve is usually greater than 3%. This phosphogypsum micropowder is tested with a 45 micron test sieve. The sieve residue is ≤0.3%, the activation mass fraction is ≥90%, and the oil absorption is ≤69mL/100g. It meets the standard requirements and can be used as a processing filler for PVC, PP and other plastic products. use.

Apply^[4-5]

A kind of phosphogypsum ceramsite for soilless cultivation and its preparation method. After drying the phosphogypsum, clay, shale and bauxite are prepared into additive powder, and the additive powder is modified with urea phosphate. Then the phosphogypsum and modified additive powder are mixed and granulated into particles, and then undergo steam curing or drying treatment, so that the prepared ceramsite has better bulk density, better cylinder pressure strength, better air permeability and better water retention performance. , after being used to prepare soilless cultivation substrates for crop cultivation, it can improve the quality of crop growth and the quality of Bayer curing agent for crop growth products.

A high-strength phosphogypsum permeable brick and its manufacturing method. The permeable brick uses phosphogypsum, activated water quenching slag, and epoxy resin as main raw materials, and is produced through thorough mixing, molding, curing and other processes of materials. High-strength phosphogypsum permeable bricks, in which the dosage of phosphogypsum is 40% to 80% of the total components. The permeable bricks made have high strength and low production cost, which broadens the comprehensive utilization rate of phosphogypsum.�It can effectively alleviate the pressure of comprehensive utilization of solid waste in the development process of the phosphorus chemical industry.