The Preparation Of New Type "Dry Water" Powder And The Study Of Its Inhibition Mechanisms On Thermal Spontaneous Combustion Of Pyrite

Pyrite is prone to thermal spontaneous combustion in nature,causing mine fires and other hazards.Fire accidents caused by spontaneous combustion are one of the major safety issues for mines.Many accidents have occurred in recent decades,causing not only a large number of staff casualties and environment pollution,but also huge economic losses and resources waste.Thus the development of prevention technology will reduce the frequency of mine fires and effectively mitigate the harm caused by such accidents.Now,the most widely used fire prevention and control method is based on inhibitor,which is a substance that can retard or inhibit the natural oxidation of sulfide ore.The fire extinguishing agent has the similar characteristics to inhibitor.The fire extinguishing agent is used to prevent and control the mine fire.Dry water powder is a new type of high-efficiency “green clean fire extinguishing agent”.It has good fluidity,high fire extinguishing efficiency,good cooling effect and no harm to the environment.Therefore,dry water powder is selected as inhibitor for spontaneous combustion of pyrite.The research work of this thesis consists of the following parts.(1)Preparation and basic performance characterization of dry water powder.The formation mechanism of dry water powder is analyzed.The dry water powder is prepared by mechanical stirring method.The preparation steps of dry water powder are introduced.The effects of mass ratio of hydrophobic fumed silica to water,stirring speed,stirring time and impeller shape on the morphology of dry water powder are compared by appearance observation and microscopic image method.The optimal preparation conditions of dry water powder are obtained: the mass ratio of hydrophobic fumed silica to the deionized water is 9:100,and stirring speed is 6000 rpm.The stirring time is 150 s,and the stirring impeller shape is a multi-blade blade high-type mixing head.The dry water powder prepared under this condition has a uniform shape and good dispersibility.According to the standard performance parameters,basic properties of dry water powder and modified dry water powder with ammonium dihydrogen phosphate are tested.The bulk density method is used to measure bulk density of dry water powder and modified dry water powder to be 0.38g/mL and 0.42/mL.The flowability of dry water powder powder is measured by repose angle method.The outflow velocities of conventional and modified dry water are 1.63mL/s and 1.59 mL/s,respectively,and repose angles are 35.3° and 36.2°.The dry water products have good fluidity.The stability of dry water powder and modified dry water powder are measured by centrifugation and pressure.Dry water powders have a certain stability and the maximum pressure is 1000 g.Water loss rates of the conventional and modified dry water powder are tested by gravimetric method.The results indicate that dry water products are dehydrated quickly in the open space and the water is completely evaporated after 7 days.In the closed space,the water can be maintained.The dry water powder must be stored in a confined space as much as possible to avoid prolonged squeezing and violent shocks.(2)Experimental study on factors affecting pyrolysis of pyrite.The pyrolysis experiment of pyrite is carried out by using a synchronous thermal analyzer to investigate the effects of different heating rates,different inhibitors and different mass fraction inhibitors on the pyrolysis reaction of pyrite.The heating rates are 10K/min,15K/min and 20K/min,and the mass fractions are 5%,10% and 15%.The inhibitors are ammonium dihydrogen phosphate,dry water powder and modified dry water powder.By analyzing the thermogravimetric curve,it is concluded that heating rate,inhibitor and different mass fraction inhibitors have an effect on the pyrolysis reaction process of pyrite.The higher the heating rate promotes the decomposition of pyrite.The higher the inhibitor mass fraction,the better inhibition of pyrite pyrolysis reaction.The inhibitory effect of modified dry water powder on the pyrolysis reaction of pyrite is optimal.(3)Study on pyrolysis inhibition mechanism of pyrite.The mass spectrometry of pyrolysis products of pyrite and its mixtures containing ammonium dihydrogen phosphate and dry water powder is carried out by thermogravimetry-mass spectrometry.According to the comparative analysis of mass spectrum,it is observed that the pyrolysis inhibition effect of pyrite is better than that of ammonium dihydrogen phosphate.The inhibition mechanisms of conventional and modified dry water powder and ammonium dihydrogen phosphate on pyrite pyrolysis reaction are analyzed.(4)Study on the mechanism of thermal pyrolysis kinetics of pyrite.The activation energy of pyrite and its mixture is calculated by Flynn-Wall-Ozawa(FWO)method.The experimental results show that ammonium dihydrogen phosphate,dry water powder and modified dry water powder can improve the activation energy required for pyrolysis reaction of pyrite.The inhibitory effect of modified dry water powder is better than ammonium dihydrogen phosphate and dry water powder.(5)Study on the combustion and explosion inhibition performance.The pure pyrite and the inhibitors containing different mass fractions(5%,10%,15%)(ammonium dihydrogen phosphate,dry water powder and modified dry water powder)are tested and calculated by burst point measurement.The explosion temperature of 5-second burst lag period of each sample is studied to study the effect of the inhibitor on the combustion and explosion performance of pyrite.After adding different mass fractions of dry water powder and ammonium dihydrogen phosphate,5-second retardation burst temperature of pyrite mixture is higher than that of pure pyrite.Under the 5% mass fraction,the burst point temperature of dry water and pyrite mixture is lower than that of ammonium dihydrogen phosphate and pyrite.For 10% and 15% loading,dry water mixture has a higher burst temperature than ammonium dihydrogen phosphate mixture;For 15% loading,the explosion point of modified dry water and pyrite is highest.It can be concluded that these three inhibitors have a good inhibitory effect on the ignitability of pyrite,and the modified dry water powder has the best inhibitory effect.