Process Control And Element Behavior Of Naturally Cooled Yellow Phosphorus Slag Based Glass-ceramics

Yellow phosphorus is an important chemical raw material and is used widely in various industrial applications.Additionally,produces a byproduct during the hot process of phosphorus chemical industry in Yunnan,Guizhou,Sichuan and Hubei provinces of China.The main method to dispose of yellow phosphorus slag is to store it in open air.This not only takes up a lot of land resources,but also pollutes the surrounding environment.In recent years,more and more attention is paid on safe disposal of yellow phosphorus slag.Recently,water quenched yellow phosphorus slag has found its use in cement and concrete mixtures,both of which are of low value.In order to make full use of the high-temperature slag discharged directly from the production process of yellow phosphorus,the naturally cooled yellow phosphorus slag has been taken as the research object in this paper.First,the high value-added glass-ceramics with high performance were prepared by adding auxiliary materials.Additionally,the existence of different elements in the heating process was studied by using the software Factsage 6.4.Furthermore,the effects of different nucleating agents,different amounts of slag and flux on prepared glass-ceramics were also explored.Secondly,the effects of different sintering factors(temperature,pressure and time)on the glass-ceramics prepared by sintering method were discussed.Finally,the finite element method was used to establish the thermally conductive model of microcrystalline glass during the preparation of glass-ceramics.Then,the optimum heating.rate.of thecrystallization process was determined.Moreover,the preliminary energy consumption for preparing the glass-ceramics was also analyzed.The results showed that in CaO-Al2O3-SiO2 system,the addition of K2O and Na2O lowered the forming temperature of the molten phase of slag,while the addition of MnO2 and Fe2O3 promoted the decomposition of F-containing minerals.In addition,the analyses of Ca,Al,Si,As,F,S and P at different temperatures showed that SiO2 and Ca3Al2Si3O12 began to change into CaSiO3 and CaAl2Si2O8(respectively)when the temperature was increased to 450 ?.Nevertheless,the molten slag phases of CaO(slag),Al2O3(slag)and SiO2(slag)appeared at 950 ?.In addition,the maximum rate of melting for CaO(slag),Al2O3(slag)and SiO2(slag)was observed to be between 1100 and 1150 ?,whereas all of the Al-containing phase melted at 1150 ?.Most of the sulfur in the system underwent transformation due to the decomposition of CaSO4(s)into SO2(g)and SO3(g),while P remained in phosphate during the conversion of fluorapatite(CaiO(PO4)6F2)into calcium phosphate(Ca3(PO4)2).As for F element,it existed in solid CaF2 and fluorapatite(Ca10(PO4)6F2)at low temperature,and gradually changed to CaF2 and MgF2 slag(liquid phase)with increasing temperature,while also forming a minute quantity of gas phase(SiF4).Additionally,arsenic existed in calcium arsenate(Ca3(AsO4)2)and most of it,changed into gas phase(AsF3),while a little was converted to liquid phase(As2O3-slag).The crystallization behaviors of TiO2,Fe2O3,MnO2,P2O5 and CaF2 crystal nucleating agents on naturally cooled slag glass-ceramics were also studied.Ca(Mn2+,Ca)Si2O6)and iron wollastonite type solid solutions((Ca,Fe)SiO3)were found in the glass-ceramics free of crystal nucleating agents.Then,light-yellow glass-ceramics with superior properties were obtained for Fe2O3 dosage of 2 wt.%.However,when 8 wt.%MnO2 was added,it yielded purple glass-ceramics.Therefore,the main crystal phases were CaSi03 and Ca5(PO4)3F when the content of P2O5 was 4 wt.%.Moreover,when 4 wt.%CaF2 was added,glass-ceramics with dense grain structure and CaSiO3(Wollastonite-2M),CaSiO3(Wollastonite-1A)and CaF2-dominating phase were obtained.It was found that for CaO-Al2O3-SiO2 based glass-ceramics,adding K2O-SiO2-Al2O3 directly to the hot-state yellow phosphorus slag at high temperature was beneficial.The addition(K2O-SiO2-Al2O3)not only lowered the melting temperature,but also yielded thebest product.The glass-ceramics prepared by sintering method were investigated through uniform design experiments and single factor experiments.The crystallinity of the sample was found to be highest when the sintering temperature,pressure and time were 1000 ?,12 MPa and 30 min,respectively.Based on the above analyses,it can safely be concluded that the sintering temperature significantly influenced the crystallinity,specific surface area,pore volume and average pore size of the product.Simulation results indicated that the heating rate from room temperature to nucleation temperature(25-790 ?)should be controlled at 2-4 ?/min,and at below 2 ?/min from nucleation temperature to crystallization temperature(790-1080 ?).