What is a professional desulfurization gypsum vertical roller mill?

More than 70% of desulfurized gypsum has been used to produce sulphoaluminate cement, and there is still room for improvement; When used as Portland cement retarder, it can completely replace natural gypsum; When it is used as concrete admixture, the maximum content can reach about 40%, and there are some basic research and application research results of composite cementitious materials. In general, it is completely feasible to use desulfurized gypsum for building materials, with broad application prospects. Guikuang Machinery is a manufacturer of desulfurization gypsum vertical roller mill. Our GKLM series desulfurization gypsum vertical roller mill provides equipment support for the preparation of building materials from desulfurization gypsum. The following will introduce the application direction of desulfurized gypsum for building materials

1. Production of sulphoaluminate cement

Sulphoaluminate cement is a kind of hydraulic cementing material made by calcining limestone, bauxite and gypsum at 1250~1350 ℃, taking anhydrous calcium sulphoaluminate and dicalcium silicate as the main mineral composition, and adding appropriate gypsum to grind together. Desulfurized gypsum can replace natural gypsum to burn sulphoaluminate cement clinker, and can also replace a small amount of gypsum and clinker for common grinding.

As the main function of desulfurized gypsum to replace natural gypsum is to provide SO3, the consumption of sulphoaluminate cement clinker as raw material should be controlled at 20%~35%. At present, in order to increase the content of desulfurized gypsum, researchers have adopted different methods. An earlier method is to burn sulphoaluminate cement clinker by mixing it with aluminum phase and calcium phase solid waste materials, such as burning sulphoaluminate cement clinker by mixing coal gangue, aluminum slag, carbide slag and desulfurized gypsum. This method can further reduce the cost of raw materials for burning clinker, but the use of desulfurized gypsum is still controlled by the proportion of raw materials, The increase of consumption is small; Another novel method is to replace limestone again on the basis of replacing natural gypsum with desulfurization gypsum, that is, to use desulfurization gypsum to simultaneously provide SO3 and CaO in raw materials. This method can make the total consumption of desulfurization gypsum in raw materials of sulphoaluminate cement clinker reach more than 70%. In the future, more systematic research is needed to determine the proportion of raw materials and optimize the firing process.

It is also one of the effective ways to use desulfurized gypsum to replace part of natural gypsum after clinker burning. The addition of desulfurized gypsum, similar to anhydrite, can promote the early strength of sulphoaluminate cement, and a small amount of desulfurized gypsum (about 10%) is more conducive to the formation of ettringite. The calcination temperature of sulphoaluminate cement is lower than that of Portland cement, and the CO2 emission during burning is also significantly reduced. The production of sulphoaluminate cement in China is increasing year by year, and the application prospect of desulfurized gypsum in the production of sulphoaluminate cement is broad. If the desulfurization gypsum can be used to replace the limestone and natural gypsum in the burning of clinker at the same time as well as the later mixture for common grinding, the utilization rate of desulfurization gypsum in the production of sulphoaluminate cement can be further improved.

2. Portland cement retarder

Portland cement clinker generally needs to be mixed with an appropriate amount of natural gypsum to make cement. This is because tricalcium aluminate in the clinker will harden immediately after reacting with water. The addition of gypsum can slow down the rapid reaction between tricalcium aluminate and water. Generally, the amount of natural gypsum is 3%~5%, and there will be some changes due to the influence of gypsum purity.

Using desulfurized gypsum instead of natural gypsum as retarder in Portland cement clinker is one of the effective methods to reduce the use of natural gypsum and resource utilization of desulfurized gypsum. Compared with natural gypsum, desulfurization gypsum, as a cement retarder, can prolong the setting time by about 1h, but its dosage is more than that of natural gypsum, mainly because desulfurization gypsum contains water and impurities, which also affect the workability of cement. The moisture and impurity content of desulfurized gypsum are important factors affecting the retarding effect of cement and the quality of cement. Therefore, the key to improving the retarding effect of desulfurized gypsum and the quality of cement is to effectively remove the moisture and impurities in desulfurized gypsum, that is, the process of purification and decolorization. At present, the decolorization and purification process of desulfurization gypsum has gradually changed from physical purification method to physical chemical combination method, and the purity can reach 96% after decolorization and purification, but it is still necessary to explore a more environmentally friendly and low-cost purification method to reduce the resource utilization cost of desulfurization gypsum.

3. Mineral admixtures for concrete

The amount of desulfurized gypsum used for concrete admixture is generally less than 10%. Excessive desulfurized gypsum will generate more ettringite in the later hardening stage of the cementitious material, causing expansion and cracking of the hardened cementitious material. The thermal activation method can increase the content of desulfurization gypsum in the cementitious system. After activation at 800 ℃, when the content of desulfurization gypsum is about 18%, the 28d strength of the cementitious system is equal to that of cement paste, and the volume stability also meets the requirements. Thermal activation method can increase the content of desulfurization gypsum, but the increase range is limited. Another method that can significantly increase the amount of desulfurized gypsum in the gelling system is to adopt the curing system of standing digestion first, then moist heat curing plus natural curing, that is, digestion for 18 hours first, then steam curing at 60 ℃ for 21 hours, which can increase the amount of desulfurized gypsum to about 40% on the basis of improving the strength of the gelling system.

Desulfurized gypsum composite cementitious materials have been studied in some applications, such as: desulfurized gypsum —- secondary fly ash —- desulfurized gypsum of cement system is used for block filled walls, desulfurized gypsum composite cementitious materials are used for self leveling mortar and grouting reinforcement grout, and desulfurized gypsum lightweight modified filling materials are used for cold bending steel composite walls. In general, when FGD gypsum is used as a composite cementitious material, the early strength of the cementitious material is generally lower than that of cement paste, but its advantage lies in the long-term growth of strength. Although ettringite crystals generated by further reaction of desulfurization gypsum and hydration products are beneficial to strength, they also increase the probability of material cracking. How to balance the dosage and volume stability of desulfurization gypsum will be the key problem for desulfurization gypsum as a composite cementing material.