| Phosphogypsum is the industrial solid waste produced by the production of phosphoric acid.The crystal of gypsum in phosphogypsum is influenced by the growth environment,and most of the crystals are sheet or flaky,so it cannot be used as gypsum building materials for their improper macroscopic mechanical and physical properties.To make phosphogypsum become a building cementitious material with good performance,at the same time reduce the experimental costs and improve the experimental efficiency,the purpose of this study is to improve the morphology of gypsum crystals by chemical intervention(adding a crystallize agent)by using the technology of trans crystal and computer simulation,in order to obtain high performance phosphogypsum,with the help of computer simulation technology and macroscopical experiment and microscopic characterization,the multi-dimensional,micro structure and deep analysis of chemical transformation of phosphor building gypsum crystal is carried out.Finally,the purpose of screening the best crystal modifier by using the simulation model is achieved.At present,the crystal form of gypsum crystal is mainly adjusted by chemical doping crystal modifier,the variety of crystal modifiers and the effect are different.Through previous experiments and related research,it was found that organic acid carboxylate spacings less than or larger than 3 C atoms do not possess the effect of crystallize.Single organic acids also do not possess the function of crystallize,the inorganic salts with high valence cations have stronger trans crystal effect.Based on the above research,this paper first selected the selection of the trans crystal agent,and made a preliminary screening,Succinic acid,which has the rules of molecular structure and without auxiliary functional groups,is used as an initial crystallize agent,the adsorption properties of succinic acid on the surface of phosphogypsum were investigated.In order to study the effect of changing organic acid structure(adding auxiliary functional groups)on the transformation effect of gypsum crystal,malic acid and malic acid with hydroxyl and carbon carbon double bond on the basis of succinic acid molecular structure were selected as research objects.In order to study the effect of different mass fraction of crystallize agent on the effect of crystallize,we also selected the inorganic salt crystallization agent aluminum sulfate containing high valence cation as the research object,and analyzed the influence of aluminum sulfate on the transformation effect of phosphor building gypsum crystal.This selection of potassium sodium tartrate,magnesium acetate,aluminum sulfate and potassium sulfate 4 kinds of crystal modifier as the research object,study the different types of crystal modifier also act on the superposition effect of phosphorus gypsum crystal effect.The specific research contents are as follows:(1)For chemically doped single organic acid phosphorus building gypsum,on the basis of the density functional theory and the theory of molecular dynamics.Through the adsorption model of organic acid and crystal surface,the different adsorption mode,different structure and crystal surface reaction of organic acids are calculated and simulated.It is found that the double bond oxygen atoms in succinic acid carboxyl group are vertically adsorbed on the Ca atoms on the crystal plane,and for chemisorption,the order of the effect of organic acids on crystal plane transformation is:malic acid>maleic acid>succinic acid.(2)For chemically doped single inorganic salt crystal modifier of phosphorus building gypsum,according to molecular dynamics and crystallography theory,in the present study,both the crystalline type of gypsum crystal and the attachment energy of its main crystal planes have been calculated based on attachment energy(AE)model.This model is used to calculate the optimum mass fraction of aluminum sulfate to adjust the morphology of the crystal.(3)On the basis of molecular dynamics,the effect of superposition effect of different types of trans crystal agents on phosphogypsum crystals at the same time is studied.The composition of compound crystal agent which has good influence on the crystal is synthetically analyzed.Based on the above-mentioned crystal-growth mechanism,theoretical model and crystal-transition effect system,the microstructure and mechanical properties were studied by conventional chemical analysis combined with microscopic test methods such as SEM,XRD and X-ray photoelectron spectroscopy,The simulation results were verified.The results show that the experimental results are basically consistent with the computer simulation results.By analyzing the effect of succinic acid on the crystal morphology and surface electron binding energy of phosphogypsum,the flexural and compressive strength of phosphogypsum products under different amounts of succinic acid was detected.The surface chemistry of hydroxyl and Ca has indeed taken place.After the reaction with malic acid,the compressive strength and flexural strength of the phosphate building gypsum test block were the largest and the crystal shape was closer to the short columnar column,followed by maleic acid and succinic acid.The experimental results show that the morphology and mechanical properties of the phosphorus gypsum after the reaction with 2.5wt%Al2(SO4)3 are better.Phosphate building plaster added 0.15%aluminum sulfate and 0.03%potassium sodium tartrate,the maximum compressive strength and flexural strength of the test block are 22.31Mpa and 6.44MPa,respectively.To sum up,through the experimental verification and microscopic characterization analysis,the relevant computer models can well reflect the objective facts,and provide a good support for the research of phosphogypsum crystal transformation effect. |
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