| With the rapid progress in display manufacturing technology in recent years,cathode ray tubes(CRT)are gradually replaced by advanced display products,resulting in a vast number of obsolete CRTs.A huge amount of waste CRTs are generated in China every year,and there are plenty of waste CRTs being transferred from developed countries to China through illegal means,such as Europe,America and Japan.It is verified that the lead-containing CRT funnel glass is a hazardous waste,which may pose considerable threats to the environment and also endanger human beings if disposed improperly.Therefore,it is of great importance to develop an economical and effective approach for comprehensive reutilization of obsolete CRT funnel glass.In this study,an approach for lead extraction from waste CRT funnel glass through the lead smelting process was presented.The technological conditions were optimized,and the effects of various factors on metallurgical performance of the slag and refractory corrosion were studied.Furthermore,a novel process for extracting lead from funnel glass and simultaneously producing glass-ceramics was developed according to the principle of lead recovery from funnel glass by lead smelting.The approaches proposed in this study can radically remove the potential threats of lead in funnel glass and achieve significant environmental and economic benefits.The main contents and conclusions of the present work are given as follows.(1)The feasibility of lead extraction from funnel glass by smelting with low lead slag or high lead slag was examined.Results show that lead can be recovered from funnel glass by smelting with low lead slag or high lead slag.The optimum conditions for low lead slag smelting are glass addition of 10-20 wt%,reductant addition of 1.0?smelting temperature of 1250°C and reducing time of 1.5 h.On these conditions,the lead and zinc recovery is up to 75% and 85%,respectively,and lead content in slag is below1.2 wt%.For high lead slag smelting,the optimum conditions are glass addition of10-30 wt%,reductant addition of 0.9,CaO/Si02 ratio of 0.8,smelting temperature of1200°C and reducing time of 60 min,where a high lead extraction yield of 97%,a zinc recovery over 90% and a lead content in slag below 2 wt% are successfully obtained.(2)The effect of Ca0/Si02 ratio and FeO on the breaking temperature,slag viscosity,activation energy for viscous flow and slag structure of the CaO-SiO2—6iFeOM-12wt%ZnO—3wt%AbO3 slags were studied.The breaking temperature of the slag initially increases and then decreases with the increasing CaO/Si?2 ratio,whereas lowers consistently by the addition of FeO.The slag viscosity and activation energy for viscous flow both decrease as the CaO/Si?2 ratio or FeO content increases.This variation tendency is more pronounced at lower CaO/Si?2 ratio and FeO content.The silicate network structure can be depolymerized by the addition of CaO and FeO,resulting in the decrease of Q2 and Q3 structural unit of silicate network structure and hence the reduced degree of polymerization(DOP)of the slag.(3)The effect of ZnO and K2 O on the breaking temperature,slag viscosity and activation energy for viscous flow,phase relations and structure of the CaO-SiO2-“FeO”—ZnO-Al2O3—(R2O)slag system were studied.Results show that the slag viscosity and activation energy for viscous flow decrease continuously with increasing ZnO content from 0 wt% to 20 wt%,while the breaking temperature decreases at first and then increases.Si?2 is prone to combine with ZnO to form willemite,and the crystallization capacity of the slag increases with ZnO addition.ZnO reduces the DOP of the slag,and the depolymerization mechanism could be explained by the transformation of Qn species expressed as Q1-f-Q32Q2.The precipitation temperature of melilite and olivine in the slag decreases with the increasing K2 O addition from 0 wt% to 5 wt%.The liquid phase region enlarges and gradually moves to the Si-and Ca-rich region by the addition of K2 O.The slag viscosity and activation energy for viscous flow increase at first and then decrease with increasing K2 O content.The effect of K2 O on aluminate structure is prior to that of silicate structure.(4)The chemical corrosion behavior of magnesia-chromite refractory in slags with different funnel glass additions was studied using a rotating finger corrosion test.The corrosion mechanism of slag on refractory was achieved by SEM-EDS analysis and Factsage calculation,and the corresponding control measures were proposed.It is found that the main corrosion mechanism of magnesia-chromite refractories in ZnO-containing fayalite slags is the dissolution of magnesia into the slag.The addition of funnel glass causes the increase of MgO solubility in the slag.A(Zn,Fes Mg)0 solid solution layer is observed in the reaction interface of slag-refractory,which can restrain the diffusion and dissolution of MgO into slag as well as the slag penetration into the refractory.The viscosity of the slag increases with the addition of funnel glass,and hence the slag penetration capacity into refractory reduces.The dissolving capacity of MgO in slag decreases with the increase of CaO/Si?2 and FeO/Si?2.The dissolved amount of MgO into slag significantly increases when K2 O addition is increased from 0 wt% to 3 wt%.(5)A novel process for lead extraction from funnel glass and simultaneously producing glass-ceramics was developed.The influences of various factors on lead extraction efficiency and lead content in glass were investigated.Additionally,the effects of crystallization temperature and crystallization time on the properties of glass-ceramics were studied.In the case of funnel glass addition of 40?80 wt%,the optimum reductant addition,CaO/Si?2 ratio,smelting temperature and holding time for lead recovery are 1.0,0.3?0.6,1450 oC and 2 h,respectively.Under these conditions,more than 92% of lead can be extracted from the funnel glass and a low lead content in the produced glass-ceramics materials below 0.6 wt% was successfully achieved.The optimum crystallization temperatures for FG40-80 glass-ceramics samples are 975°C,925°C,950°C,925°C and 900°C,respectively,and the optimum crystallization times are4 h,4 h,3 h,3 h and 2 h,respectively. |
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