Preparation And Product Development Of Phosphogypsum Composite Cementitious Materials

Phosphogypsum is the industrial solid waste produced by the reaction of phosphate rock and sulfuric acid to produce phosphoric acid.4?5 tons of phosphogypsum will be produced for every 1 ton of phosphoric acid produced.China is a big phosphoric acid producer in the world,and the emission of phosphogypsum is also the largest country.Nowadays,the global phosphorus gypsum reserves has been as high as 6 billion tons,annual emissions of phosphogypsum is still growing at a rate of about 150 million tons,the phosphorus gypsum reserves reaching 300 million tons,emissions of phosphogypsum is still growing at a rate of about 50 million tons a year,the utilization of phosphogypsum is less than 15%.At present,mainly adopts the way of storage and processing.Phosphogypsum contains a small amount of heavy metals,soluble phosphorus and soluble fluorine which a large amount of stacking will cause great harm to the surrounding soil,groundwater,atmosphere,vegetation,etc.At the same time,the stacking of phosphogypsum also occupies a large amount of land,the annual need to repair the stacking site caused by economic consumption.Therefore,the utilization of phosphogypsum has become an urgent problem.China is a country with a large population,but resources are lack.However,phosphogypsum contains abundant calcium and sulfur resources that the recycling of phosphogypsum conforms to the national sustainable development strategy and has great significance for the development of phosphorus chemical enterprises.Research papers in bulk by using phosphorus gypsum for the purpose,without calcined phosphogypsum,at 800? the calcined anhydrite,braised hot steel slag and P·? 52.5 cement as raw materials,adding a small amount of synergistic agent is prepared a high softening coefficient,high value-added hydraulic phosphorus gypsum composite gelled material,and the mechanism of the hydration process of gelled material preliminarily explored.Phosphogypsum composite cementing material is a kind of material with good water resistance and meet the standard of ordinary portland 32.5 cement.It can be used instead of cement in some fields.In addition,this paper added aggregate on the basis of phosphogypsum composite cementitious materials to design and prepare ordinary C30 concrete and dry mixed mortar.Concrete and dry mixed mortar are products with large consumption in building materials industry,and phosphogypsum can be used in it to consume a large amount of phosphogypsum.In this paper,the composition and optimization of phosphogypsum composite cementitious material are studied by experiment.Based on the optimized cementitious materials,C30 concrete and dry mixed mortar products are designed and developed,and the following conclusions are drawn:1.Through the study of proportion of phosphorus gypsum composite gelled material optimum experimental results show that:phosphorus gypsum with steel slag,P·?52.5 cement,the preparation of anhydrite modified gelled material,the experimental results it is concluded that the ratio of material quality for m(phosphogypsum):m(anhydrite):m(steel slag):m(P·? 52.5)=35:5:10:50,material softening coefficient is 0.88,3 d flexural compressive strength reached 4.9 MPa and 35.3 MPa,28 d flexural compressive strength 6.9 MPa and 51.5 MPa,respectively.2.Through orthogonal test,the influence of synergist compound on phosphogypsum composite cementifying material is explored:sodium silicate(SL)0.3%,sodium sulfate(LN)0.3%,silicon slag(GZ)0.4%and calcium lignosulfonate(MG)0.8‰are combined,and the compressive strength of cementifying material increased by 22.3%in 3 d and 20.2%in 28 d.The optimized cementitious materials for the preparation of cementitious sand test results:3 d flexural compressive strength is 4.33 MPa,24.7 MPa,28 d flexural compressive strength is 7.2 MPa,36.5 MPa,the initial setting time 245 min,the final setting time 310 min.It meets the national standard of ordinary portland cement 32.5 grade requirements.3.The microscopic analysis of cementitious materials by XRD and scanning electron microscopy(SEM)shows that the hydration products of phosphogysum composite cementitious materials include CaSO4·2H2O,AFt(ettringite),C-S-H(calcium silicate hydrate),CH(calcium hydroxide)and CaCO3.Calcium sulfate dihydrate in phosphogypsum can react with aluminum oxide and calcium oxide in cement and steel slag to form ettringite.Compared with the samples without synergist,the diffraction peak intensity of calcium silicate hydrate and ettringite in 3 d and 28 d XRD patterns is significantly enhanced,indicating that the addition of synergist promoted the generation of hydration products.According to SEM,the hydration products of cementitious materials are mainly fibrous,rod-like and plate-like in the early morphology.With the increase of hydration age,the fibrous and rod-like grow up,forming a compact large plate structure as a whole.The hydration products become denser in structure with the addition of synergist.4.Through the experiment of preparing C30 concrete with phosphogypsum composite cementitious material,the influence of sand rate and water-binder ratio on the performance of concrete is explored:the choice of sand rate is related to the corresponding index of coarse and fine aggregate,as well as the physical properties of cementitious material and the actual construction.In this paper,the cementitious material in the preparation of concrete test,with the increase of the sand ratio of concrete slump reduced,mechanical properties raised.The increase of water-binder ratio will lead to the increase of slump and expansion degree.If the water-binder ratio is too low or too high,it will cause the hydration reaction of cementing materials in concrete and affect the strength.In this test,In this test,the sand ratio is 36%and the water-binder ratio is 0.46.The best concrete performance is.5.Dry mixed mortar is prepared by different mortar ratio.The test results show that the larger the mortar ratio,the better the mortar physical and mechanical properties.Therefore,high grade mortar can be prepared when the ratio of mortar to sand is high,and low grade mortar can be prepared when the ratio of mortar to sand is low.With the addition of water-retaining agent,the water-retaining ratio of mortar increases.When the rubber sand ratio is large,the strength of mortar increases first and then decreases.When the rubber sand ratio is small,the strength of mortar decreases with the increase of water-retaining dosage.