Study On Technology And Properties Of Porous Ceramics Prepared From Rare Earth Tailings Of Maoniuping

Maoniuping rare earth deposit is the largest producing area of rare earth in Sichuan Province.After recovering bastnaesite,barite and fluorite from rare earth ore,a large number of rare earth tailings are produced.How to realize the high-quality utilization of the rare earth tailings is the key to alleviate the environmental problems caused by the stacking of rare earth tailings and realize its resource utilization.In this paper,rare earth tailings are used as the main raw materials,Kaolin Tailings and feldspar tailings are added to meet the requirements of firing ceramic formula.Porous ceramics were prepared by direct foaming method.The effects of mineral composition and chemical composition of tailings,formula of porous ceramic body,type and dosage of foaming agent and sintering system on the properties of porous ceramics were studied.Finally,the process parameters of porous ceramics were optimized in combination with orthogonal experiments.The main conclusions are as follows:(1)The main minerals of rare earth tailings are quartz,albite,microcline,mica and calcite,and their chemical compositions are Si O₂,Al₂O₃,Ca O,Fe₂O₃,K₂O and a small amount of Ca F₂ and Sr O;the main phases of Kaolin Tailings is kaolinite,and contains a small amount of pyrite,anatase and calcite.And their chemical compositions are Si O₂,Al₂O₃,Ti O₂,Fe₂O₃and Ca O;the main phases of feldspar tailings are quartz,albite and potash feldspar.The main chemical compositions are Si O₂,Al₂O₃,K₂O,Na₂O and Fe₂O₃.(2)With rare earth tailings as the main raw material,kaolin tailings and feldspar tailings were added,and combined with K₂O-Al₂O₃-Si O₂ ternary phase diagram,the formula of porous ceramics was designed.The formula of ceramic body was determined as 60 wt.%of rare earth tailings,15 wt.%of kaolinite tailings and 25 wt.%of feldspar tailings.The composition range of leucite in ternary phase diagram was the formula area.(3)Carbon powder,calcium carbonate,soluble starch and silicon carbide were selected as foaming agents.Through the analysis of the foaming mechanism of the four foaming agents and the comparison of the properties of the samples,silicon carbide was the most suitable.foaming agent for the preparation of porous ceramics.The porosity,flexural strength,bulk density and water absorption of porous ceramics are 68.2%,2.08 MPa,670 kg/m³ and 1.4%,respectively.(4)Through single factor experiments,the optimum preparation conditions of porous ceramics were determined as follows:0.5 wt.%silicon carbide,sintering temperature1140?,holding time 20 min,pre-sintering temperature 1020?,pre-sintering time 40 min.The porosity,flexural strength,bulk density and water absorption of porous ceramics were73.5%,1.72 MPa,438 kg/m³ and 1.5%,respectively.(5)In order to optimize the process parameters of porous ceramics,the optimal process conditions of porous ceramics were determined by orthogonal experiment of five factors and four levels,including sintering temperature,holding time,pre-sintering temperature,pre-sintering time and foaming agent dosage.The results show that the sintering temperature is the most important factor affecting the properties of porous ceramics;the optimum technological conditions are sintering temperature 1145?,holding time 15 min,pre-sintering temperature 1030?,pre-sintering time 40 min,0.5 wt.%silicon carbide content.The porosity,flexural strength,bulk density,water absorption and thermal conductivity of porous ceramics were 76.2%,1.37 MPa,387 kg/m³,2.3%and 0.051 W/m·K,respectively.(6)Herein,rare earth tailings as the main raw material,the porous ceramics prepared by the direct foaming method meet the performance requirements of T/CECS 480-2017"Foaming Ceramic Insulation Board Application Technical Regulations",and can be used as insulation material for the wall insulation system.