| Iron tailings and stripped waste rocks are industrial wastes generated after mineral processing,among which mud-like fine-grained iron tailings and stripped waste rocks are unusable.The work used the mud-like fine-grained iron tailings and stripped waste rocks produced by Ansteel Group Corporation Limited’s iron ore mining in Qishan in 2020 as raw materials.Porous ceramics were prepared by air pressure foaming and gel-casting and pressureless sintering processes,and then they were used as the matrix of phase-change energy storage materials.Molten paraffin,graphite,and graphene were mixed and stirred for 1 h as phase change materials.Phase change materials were injected into the matrix of phase change energy storage materials by vacuum-melting pressure injection.It could prepare the composite phase-change energy-storage materials of iron tailings and stripped rock-based porous ceramics/paraffin as well as the composite phase-change energy-storage materials with copper particles and graphene.The mechanical and physical-chemical properties,thermophysical properties,and heat transfer process of porous-ceramic composite phase-change energy-storage materials were tested by XRF,XRD,SEM,TG-DSC,compression resistance test,and acid-and alkali-resistance test.Besides,the work studied the influence of factors such as slurry solid phase content,sintering time,sintering temperature,water-to-glue ratio,prefabricated foam ratio,and phase change material ratio on material structure and performance.The storage/exothermic cycle test of iron tailings and stripped waste rock-based multi-porous ceramic composite phase-change energy-storage materials was also carried out,and good experimental results were obtained.The main results are as follows.（1）The ratio of iron tailings to stripped waste rocks was 0.8-3.6%by taking K2O-Al2O3-SiO2ternary phase diagram as the ratio of iron tailings to stripped waste-rock ceramic raw materials.Sinter at 1150℃and preserve heat for 3 h.The results showed that the reasonable distribution ranges of SiO2,Al2O3,and K2O were 72-75%,18-21%,and 4-10%,respectively.The experimental design of the response surface was carried out by the Box-Behnken method,and data were fitted to accurately measure the effects of the raw material ratio,water-binder ratio,and sintering temperature on the compressive strength and acid-base corrosion resistance of ceramics.The analysis of variance showed that the model was significant and reliable.The three factors significantly affected the compressive strength of iron tailings and stripped waste-rock ceramics as well as the quality damage of acid-base corrosion.The optimal preparation conditions for iron tailings and stripped waste-rock ceramics were determined through model verification:the IT/WR ratio of 1.5,the firing temperature of 1120℃,the water-binder ratio of 0.35%,the compressive strength of iron tailings and stripped waste rock ceramics of 21.9 MPa,and the acid-base corrosion quality loss of 1.63%.（2）45-65%of prefabricated foams were added under optimal preparation conditions for iron tailings and stripped waste-rock ceramics.As the proportion of foams increased,the defoaming rate increased under mechanical stirring.The water-binder ratio increased and compressive strength decreased after the foams burst.Meanwhile,the porosity did not increase significantly.A significant collapse phenomenon occurred during the sintering process.Since iron tailings and stripped waste rock-based multi-porous ceramics were used as the storage matrix of phase change materials,they need to have sufficient porosity and certain compressive strength.Therefore,the proportion of foams was controlled at 50-55%.（3）The influences of heat preservation time of 2-11 h on the structure and performance of iron tailings and stripped waste rock-based multi-hole ceramics were studied under the optimal preparation conditions and the proportion of foams of 55%.The glass phases inside the porous ceramics gradually increased with the extension of insulation time.Their linear shrinkage,bulk density,and compressive strength increased,while the apparent porosity and opening pore size decreased.Comprehensive analysis showed that the porous ceramic samples prepared by heat preservation at 1120℃for 5h had the best performance,and their apparent porosity and compressive strength were 50.33%and 13.85 MPa,respectively.（4）The effects of 70-90%of paraffin and 10-30%of graphite and graphene on the phase-change temperature and latent heat of composite phase-change materials were studied in the preparation process of composite phase-change materials.The results showed that the phase transition temperature was 66.33℃and the latent heat of the phase transition was 183.28 KJ/Kg with 1%of copper particles,20%of graphene,and 80%of paraffin.Besides,paraffin had a better coating effect on both.（5）Liquid phase change materials had good wettability to porous ceramics.94.67%of the pore volume was filled under the infiltration environment of 80℃.The average thermal shock resistance number of porous ceramics was 70 in the thermal shock resistance test at the room temperature of 300℃during the infiltration process.The intensity loss rate after 70 thermal shocks was about 49.07%,with good thermal shock resistance.The integrity of the porous ceramic skeleton structure was guaranteed,and the leakage of phase change materials was avoided.Furthermore,the two had good chemical compatibility.（6）Vacuum-melting pressure injection was used to inject the phase-change materials into the matrix of iron tailings with an apparent porosity of 50.33%and the phase-change energy-storage materials of stripped waste rocks.It was heated from room temperature to 150℃for 25 minutes.Then it dropped to room temperature and continued to heat up for 25 min to 150℃for 100 melting/solidification cycle tests.The test results found that its quality loss was only 0.621%.The potential heat value decreased by 7.3%and stabilized after 75 cycles,with a small quality loss and good thermal stability.（7）The work studied the thermal conductivity of composite phase change energy storage materials of iron tailings with different porosity and porous ceramic skeletons of stripped waste rocks.When the porosity of the porous ceramic carrier increased from 50.33 to 75.16%,the thermal conductivity of the composite phase change energy storage materials decreased from 0.72 to 0.49 W/（m·K）.When 20%graphene was added to composite phase-change materials,the thermal conductivity of composite phase-change energy-storage materials increased by 66.04%.（8）A simulation experiment platform for the storage/exothermic model was constructed through COMSOL.The addition of porous ceramics greatly increased the exothermic rate.The greater the flow rate of the heat transfer fluid,the stronger the heat transfer capacity of the material.In turn,the greater the storage/exothermic rate,the higher the energy utilization efficiency.The calculation results showed that the total solidification time of the storage/exothermic system of porous-ceramic composite phase-change energy-storage material was 1,132 s.Compared with the total solidification time of 1,832 s without porous ceramics as a carrier,the heat transfer efficiency was increased by 38.21%.The results of the work showed that the preparation of porous ceramic materials from fine iron tailings and stripped waste rocks has a simple process,low cost,short preparation period,controllable sample shape,good physical and chemical properties,and high porosity.It can solve the problem of stockpiling tailings and stripping waste rocks.The prepared composite phase-change energy-storage material meets the requirements of environmental protection and energy conservation,with broad application prospects. |
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