| Phosphorus tailings are solid wastes produced during the process of phosphorus tailings beneficiation and enrichment.The beneficiation methods of associated minerals are different.Reverse flotation of phosphorus tailings is mainly aimed at carbonaceous associated ore,and the main mineral composition is dolomite,residual fluorapatite and a small amount of quartz.At present,it is pointed out that phosphorus tailings can be used as inert cement filler.However,the activity of phosphorus tailings is low,and some phosphoric acid will dissolve out.In addition,there are few researches on the toxicity of phosphorus tailings used as concrete and its influence on concrete properties.Therefore,the effects of toxicity and fineness on the activity and ion leaching of phosphorus tailings were analyzed.The effects of phosphorus tailings on the working performance,mechanical properties and durability of concrete are analyzed.Firstly,X-ray fluorescence spectrometer(XRF),X-ray diffraction analyzer(XRD),scanning electron microscopy-energy spectrometer(SEM-EDS),laser particle size analyzer,Fourier transform infrared spectrometer(FTIR)and synchronous thermal analyzer(TG-DSC)were used to analyze the chemistry,mineral composition,morphology and particle size distribution of phosphorus tailings.The feasibility of phosphorus tailings as mineral admixture was analyzed according to the limestone technical index in GB/T 51003-2014"Technical Specification for Application of Mineral Admixture".The results show that the phosphorus tailings mainly consist of lamellar dolomite and a small amount of flotation reagent remains in the tailings.Phosphorus tailings contain less heavy metal ions.The methylene blue and fluidity of phosphorus tailings meet the technical requirements of limestone powder in GB/T51003-2014 Technical Specification for Application of Mineral Ad Mixtures.With the average particle size of phosphorus tailings reduced to 25μm,the 28d activity can reach74%.Secondly,the method of grinding modification,grinding phosphorus tail powder to 4 different fineness.The effects of different fineness of phosphorus tailings on the setting time of cement,the water requirement of standard consistency and the strength,consistency and shrinkage of cement sand were analyzed.The effects of phosphorus tailings on cement hydration,slurry filling,hydration phase and microstructure were analyzed by means of hydration thermal analyzer,mercury injection meter,X-ray diffraction analyzer and scanning electron microscope-energy spectrum.The results showed that with the average particle size of phosphorus tailings decreased from 30μm to 15μm,the setting time increased by 140 min,the compressive strength increased by6.1MPa,the ion dissolution increased significantly,the F~-concentration increased by10 mg/L,the cement hydration induction period was prolonged,the rate of acceleration period was increased,the total heat release in 70h was increased,and the porosity of cement sand was reduced.Phosphorus tailings react with hydration products to form hydrotalcite in the later stage of hydration.Finally,cement,phosphorus tailings,machine-made sand,stone and water reducing agent were used to adapt C40 concrete.The effects of different phosphorus tailings content on the working performance,mechanical properties and durability of concrete were analyzed.Cement,fly ash,phosphorus tailings,machine-made sand,stone and water reducing agent are used to match different grades of concrete such as C30,C40,C50 and C60.The results show that with the increase of phosphorus tailings content,the slump of concrete will be higher,and the mechanical properties and durability will be worse.However,when the content of phosphorus tailings is 10%,the loss of mechanical properties and durability of concrete is less than 5%,and when the content of phosphorus tailings is 20%,the loss of mechanical properties and durability of concrete is about 10%.When the content of phosphorus tailings is 30%,the concrete performance will be rapidly reduced. |
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