| Phosphogypsum is a solid waste in the process of wet production of phosphoric acid from phosphate rock.China’s annual output of phosphogypsum is about 75 million tons,and the accumulation amount is nearly 300 million tons.The large accumulation of phosphogypsum has caused damage to land resources and ecological environment.Therefore,increasing the utilization of phosphogypsum resources is in line with the national concept of ’carbon neutralization and carbon peak’,and can achieve certain social and economic benefits.The purpose of this paper is to improve the resource utilization of industrial waste phosphogypsum.Firstly,the process conditions of preparing AⅡ by calcining phosphogypsum were explored,and the optimum preparation process of AⅡ was determined.Secondly,by exploring the influence of activator and surfactant on the performance of AⅡ,the optimal ratio was compounded to solve the problem of poor self-gelling of AⅡ,which provided a new idea for the activation and modification of AⅡ,and its hydration process,hydration products and hydration mechanism were preliminarily explored.Finally,on the basis of the modified AⅡ,high titanium slag and vitrified microbeads were used as aggregates to design the products of ordinary plastering gypsum and lightweight plastering gypsum mortar and analyze the economic benefits.The resource utilization of phosphogypsum was realized and the problem of phosphogypsum accumulation was solved.In this paper,by exploring the best preparation process of AⅡ,and its excitation modification,and using it as the main material to prepare ordinary plastering gypsum and lightweight plastering gypsum mortar products,the preparation products are optimized and economically analyzed,and finally the following conclusions are drawn:1.The preparation process of AⅡ from phosphogypsum was studied and the performance of AⅡ was tested by using 2.0%potassium alum.The results showed that the optimal preparation conditions of AⅡ were calcination temperature 800℃,calcination time 2h,specific surface area 560.8m2/kg.The content of AⅡprepared under this process condition was 70.51%,and the compressive strength of AⅡ at 3d and 28d was 15.42 MPa and 28.24 MPa,respectively.2.The effects of activator and surfactant on the mechanical properties of AⅡ were studied.The results showed that potassium alum had the best excitation effect in sulfate activator.The 28 d flexural and compressive strength of the specimens with 2.0%potassium alum were 5.54 MPa and 26.11 MPa,respectively.The hydration rate increased from 25.92%to 78.28%.Among the non-sulfate activators,K2Cr2O7 has the best excitation effect.The 28 d flexural and compressive strength of the specimens with 1.0%K2Cr2O7 content are 7.99 MPa and 27.36 MPa,respectively,and the hydration rate is increased to 53.54%.The 28 d flexural and compressive strength of the specimens using 0.5%potassium alum and 0.4%K2Cr2O7 were 7.10 MPa and 31.63 MPa,respectively.Under the synergistic dosage of 2.0%potassium alum and 1.5‰ LA-1 and 0.5‰ LAS,the 28 d compressive strength of the specimens increased from 26.11 MPa to 36.48 MPa and 34.42 MPa,which increased by 38.71%and 30.87%.3.The effects of activators and surfactants on the hydration mechanism of AⅡ were studied.The results showed that both potassium alum and K2Cr2O7 changed the concentration of Ca2+and SO42-in the liquid phase and increased the supersaturation of the liquid phase.Under the synergistic dosage of 2.0%potassium alum,1.5‰ LA-1 and 0.5‰ LAS,respectively,the surfactant LA-1 and LAS increased the absolute value of Zeta potential on the surface of gypsum particles in the system.4.The microscopic analysis of the hydration products by SEM shows that under the conditions of 2.0%potassium alum,1.0%K2Cr2O7,0.5%potassium alum and 0.4%K2Cr2O7,2.0%potassium alum and surfactant 1.5‰ LA-1 and 0.5‰ LAS,the crystal form of hydration 28 d is mostly prismatic and rod-shaped.Among them,the crystal form doped with K2Cr2O7 is flocculent as a whole,and the crystal form coordinated with surfactant is mostly prismatic,and the crystal form is more slender,smaller,and the crystals are intertwined to form a more compact structure.5.Through the preparation test of ordinary plastering gypsum mortar,it is shown that the performance of mortar decreases with the increase of mortar ratio.When the mortar ratio is 9:1,8:2,7:3,only 0.1‰ LAS can be added to meet the requirements of the standard for mortar performance indicators.When the cement-sand ratio is 6:4,the water retaining agent HPMC0.4‰,the adhesive VAE0.5%,0.2‰ LAS should be added.When the cement-sand ratio is 5:5,it is necessary to add water-retaining agent HPMC0.6‰,adhesive VAE1.0%,0.2‰LAS.6.Through the preparation test of lightweight plastering gypsum mortar,it is shown that the material ratio of 92%AⅡ,8%vitrified microsphere,1.0‰ water retaining agent HPMC,2.0‰ foaming agent LAS and 0.5%adhesive VAE can meet the requirements of the standard for mortar performance indicators.7.The design of the proposed annual treatment of 80,000 tons of AⅡ production mortar factory for economic benefit analysis shows that the total investment of the project is expected to be CNY 243,439,000,of which the fixed asset investment is CNY 18.546,600.After the completion of the project,the annual production cost is CNY 57.973,200,the annual sales volume is CNY 63.6 million,and the net profit is CNY 4.782,800.It is expected that all investment can be recovered within 6 years,with a profit rate of 19.65%. |
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