Numerical Simulation Of Multiphase Flow In The Cyclonic Micro-Bubble Flotation Column

As a new type of cement,hybrid alkaline cements,which are made of low-volume clinker and high-volume pozzolanic materials like fly ash and slag et al.,can effectively alleviate problems about the high CO₂ emission in the clinker production process and the low utilization in industrial solid waste management.With these significant advantages,hybrid alkaline cements have shown incomparable potential in the transitional stage between traditional Portland cement and new alkali-activated/geopolymer cement.When it comes to the“regional shortages”of fly ash resources and“disposal ash management”of landfills,landfill ash based hybrid cements（LAC）become a one-shot solution.Focusing on the LAC material and its foamed materials,landfill ash based hybrid cements（LACF）,scientific research methods like properties test,analytical characterization,theoretical analysis and engineering application were used in this research.Meanwhile,activity improvement of partially reacted landfill ash,hydration mechanism of LAC,property influencing factor of LACF and roof-adaptive plugging mechanism of LACF were systematically studied.The main research results and innovative achievements are as follows:（1）One novel type of landfill ash based hybrid alkaline cement was developed.A systematic investigation was conducted to explore the influence of various weak base alkaline activators in terms of their types,arrangement in pairs,and content ratios on the activation of LAC materials.Results show that:（1）In this novel hybrid cement,the clinker ratio lowered to 30%,and the landfill ash ratio increased to 70%.（2）During the development process,Generally,the LAC materials achieved the strength requirement of 325 ordinary Portland cements（OPC）and closed to 425 OPC,with 2d strength up to 19.37 MPa,28d strength up to 38.9 MPa.（2）One novel activity-improving technology method,“one pretreatment,three functional effects”,was proposed.Accordingly,Characterization methods like XRD,XRF,FT-IR,SEM-EDS,and TG-DTA were employed to analyze the main components and physical-chemical properties of landfill ash after different pretreatments.Activities of landfill ash based blended cements are tested through the Blaine test,HF acid attack test,Pozzolanic test.Experimental results show that:（1）The deterioration mechanism of landfill ash resulted from the partial carbonation reaction in the calcium-rich,moisture-rich and multi-source filling environment,which resulted in solidification is revealed;（2）With grinding or sieving pretreatment to the landfill ash,its microaggregate effect is optimized（the specific surface area increased by11.93%～235.5%）,potential activity was improved（the amorphous phase content increased by 15.4～20%）,the pozzolanic property was strengthened（the Dp value increases by 21.3 to 24.4 times）.What’s more,the activity of the partially-reacted and low-activity landfill ash was quantitatively characterized and comprehensively improved.（3）The hydration mechanism of LAC materials was revealed.Characterization methods like XRD,FT-IR,SEM-EDS,and MAS-NMR were employed to investigate the hydration product identification of LAC materials.Methods like Isothermal Calorimetry,ATR-FTIR,and Strength tests were also used to explore the effect of alkali activators on the hydration product;Based on the calorimetric curve of LAC hydration,the hydration process of sodium sulfate/sodium citrate activated LAC materials was studied.Experimental results show that:（1）The mineral components,main chemical bonds/functional groups,atomic structure and microscopic morphology of hydration products of LAC materials were well identified,and the reaction product is the highly integrated symbiotic products from cement hydration and landfill ash activation;（2）The influence law of sodium sulfate/sodium citrate ratio on the hydration of LAC materials and the interaction mechanism between these two activators were revealed,in which the sodium citrate and sodium sulfate will hinder the hydration of C3S and C3A respectively,and promote the hydration of C3A and C3S respectively;（3）The hydration kinetics was calculated,at the same time,one novel hydration process model was proposed,and the hydration mechanism was revealed.（4）The influence of the law and mechanism of LACF materials was revealed.The LACF materials were prepared with the H₂O₂ chemically foaming method.Based on the significant factors like foaming agent content,surfactant content and W/S ratio to the critical properties of LACF materials,the rheology,mechanical property,density and macro/micropore structures of LACF materials were deeply investigated.The main results show that:（1）The LAC slurry well fitted with the Herschel-Bulkley rheological model.However,the continuous shearing curve LACF slurry presented a periodic variation pattern,and the superplasticizer significantly influenced the rheological performance of LAC and LACF materials;（2）The heat released by the H₂O₂ reaction promoted the LACF hydration.The surfactant shows a negative correlation within the range of 1‰～2%content.Moreover,the W/S ratio affects both the pore structures and the strength of the base;（3）The influence laws of foaming agent content,surfactant content and W/S ratio to macro/micro pore structures was revealed,and the optimal range of these factors was determined.（5）One roof-adaptive end plugging technology with LACF materials in the working face was put forward.Based on the gas concentration and temperature data from the bundle tube detection,the root reasons for air leakage in the working face and excessive CO concentration in the working face end were analyzed;One corresponding roof-adaptive end plugging technology was proposed,and the in-situ application of this technology was also conducted.During the in-situ engineering application,it shows that:（1）The air leakage mechanism based on the insufficient collapse of the triangle arch area was revealed;（2）The air leakage volume in the near-end area and middle working face area reduced by 41.8%and 71.8%,respectively;（3）the CO concentration decreased 69.18%in the return airway,and the CO concentration in the intake and return airway are both bellow the standard level.The efficiency and safety of mining work are effectively guaranteed.There are 112 figures,32 tables and 163 references in this dissertation.