【作者】 孙岩；

【导师】 李鹏廷；

【作者基本信息】 大连理工大学 ， 机械工程（专业学位）， 2022， 硕士

【摘要】 随着“双碳”战略目标的提出,以太阳能光伏为代表的可再生能源势力蓬勃发展。然而,光伏行业的迅猛发展不可避免地产生了大量的光伏废弃物,如废坩埚、废尾料、废硅粉以及废组件等。在金刚线切片过程中,大约有30%的高纯硅以切割废硅粉的形式被浪费掉,同时,光伏组件因使用寿命（20～25年）的限制,目前被大量废弃,而光伏玻璃占据了光伏组件中70%以上的质量,因此,切割废硅粉和光伏废玻璃在光伏废弃物中所占的比重极大。这些光伏固废造成了严重的资源浪费,甚至是环境污染,如何实现光伏固废的循环利用,尤其是多种废弃物的综合回收对光伏产业的绿色可持续性发展具有重要意义。对此,本论文提出了利用光伏废玻璃精炼提纯废硅粉的技术路线,围绕切割废硅粉中氧化层的去除和硅的分离展开研究,具体研究结果如下:（1）分析了两种光伏废弃物的物相和杂质的赋存状态。切割废硅粉中主要杂质为SiO₂表面层,含量为23.85 wt.%,此外,还有微量的Al、Ca、Fe和Ni等金属杂质,理论可以回收得到的硅含量为76.15 wt.%。光伏玻璃主要元素类型为O、Si、F、Na和Ca,其中O和Si元素含量高达59.92 wt.%,与氧化层具有高度的成分一致性。TG-DSC测试结果表明,光伏废玻璃在727℃左右发生熔化,远远低于硅的熔点,同时,光伏废玻璃与切割废硅粉之间没有化学反应发生,确保了熔炼过程中二者良好的化学稳定性。（2）研究了感应熔炼处理对两种光伏废弃物综合回收效果的影响。切割废硅粉经过直接熔炼处理后,大量的氧化层团聚在铸锭内部,严重影响了硅的回收效果。利用光伏玻璃精炼废硅粉后,铸锭中的再生硅相呈椭球状并被渣相包裹,渣硅两相之间有着清晰可见的分界面,切割废硅粉中硅得到了有效回收。不过,再生硅中仍然存在大量Al、Ca、Fe和Ni的金属夹杂物。在施加定向凝固后,EPMA测试结果显示得到的硅纯度只能达到3N级别,熔渣中Na、Ca和Mg等金属杂质的反扩散行为严重限制了定向凝固过程对硅进一步的提纯。证明定向凝固工艺不具有可行性。（3）探究了装料方式、保温时间、渣硅比三个因素对再生硅出成率的影响。得出了中间装填硅料的装料方式较为合适,并且随着保温时间的延长,硅的分离效果逐渐提升,出成率随之增加,但是,增加速率逐渐减小,保温时间为60min较为合适;随着渣硅比的增大,渣相SiO₂的衍射峰强度逐渐降低,晶体结构受到不同程度的破坏,残留在渣相中硅的数量也减少。添加光伏玻璃精炼后硅的出成率显著提高,不过,出成率的增加速率随着渣硅比的增加降低,渣硅比为1可以获得最合适的出成率,为85.6%。（4）深入探究了氧化层去除和硅分离的机制。感应加热可以有效促进熔体流动,由熔体流动产生的曳力带动SiO₂在熔体中运动并发生碰撞,形成SiO₂团簇,大尺寸的SiO₂团簇沉聚在坩埚底部,从而残留于硅锭中。润湿性实验表明,SiO₂与光伏玻璃有着极佳的亲和度,℃因此,高温精炼过程中,氧化层容易被光伏玻璃形成的液相“捕获”从而实现去除。随着渣硅比从0.5提高到1和2,渣相中网络破坏体的相对含量从6%分别提高到24%和29%。网络破坏体含量的升高破坏了熔渣网络结构,使得熔渣网络的解聚度增加,粘度降低,降低了硅的迁移阻力。更多还原

【Abstract】 With the introduction of the"carbon peaking and carbon neutrality"strategy,the renewable energy industry,represented by solar photovoltaics（PV）,is booming.However,the rapid development of the PV industry has inevitably generated a large amount of PV waste,such as waste crucibles,waste tailings,silicon kerf waste（SKW）and waste modules.In the diamond wire cutting process,about 30% of high purity silicon is wasted in the form of SKW.Meanwhile,PV modules are currently discarded in large quantities due to the limitation of their service life（20-25 years）,while PV glass waste（PVGW）occupies more than 70%of the mass of PV modules,thus cutting SKW and PVGW account for a huge proportion of PV waste.These PV solid wastes have caused serious waste of resources and even environmental pollution.How to realize the recycling of PV solid wastes,especially the comprehensive recycling of multiple wastes is of great significance to the green and sustainable development of the PV industry.In this regard,this thesis proposes a technical route for refining and purifying SKW using PVGW,which revolves around the removal of the oxide layer and the separation of silicon in SKW,with the following specific research results:（1）The physical phase and impurity fugacity states of the two types of PV waste were analyzed.The main impurities in the SKW are the SiO₂ surface layer with a content of 23.85wt.%,in addition to traces of metallic impurities such as Al,Ca,Fe and Ni,which can theoretically be recovered to obtain a silicon content of 76.15 wt.%.The main element types of PVGW are O,Si,F,Na and Ca,of which O and Si elements contain up to 59.92 wt.%,with a high degree of compositional consistency with the oxide layer.TG-DSC test results showed that the melting of PVGW occurred at around 727℃,far below the melting point of silicon,while no chemical reaction occurred between the PVGW and the SKW,ensuring that the good chemical stability of the two during the melting process.（2）The effect of induction melting treatment on the comprehensive recovery effect of two types of PV waste was investigated.After direct melting of the SKW,a large amount of oxide layer is agglomerated inside the ingot,which seriously affects the silicon recovery effect.After refining the SKW using PVGW,the recycled silicon phase is ellipsoidal and wrapped by the slag phase,with a clearly visible interface between the slag and silicon,and the silicon in the SKW is effectively recovered.However,a large amount of metal inclusions of Al,Ca,Fe and Ni are still present in the recycled silicon.After application of directional solidification,the EPMA test results showed that the purity of the silicon could only reach the 3N grade,and the back-diffusion behavior of the metal impurities such as Na,Ca and Mg in the slag severely limited the further purification of the silicon by the directional solidification process.This proves that the directional solidification process is not feasible.（3）The influence of three factors,namely loading mode,holding time and slag/silicon mass ratio,on the yield of recycled silicon was investigated.It was found that the loading mode with middle loading of silicon was suitable,and with the extended holding time,the silicon separation effect gradually improved and the yield increased,however,the rate of increase gradually decreased,and the holding time of 60 min was suitable;As the slag to silicon ratio increases,the intensity of the diffraction peaks of SiO₂ in the slag phase gradually decreased,the crystal structure was damaged to varying degrees and the amount of silicon remaining in the slag phase was reduced.The silicon yield increased significantly with the addition of PVGW refining,however,the rate of increase of the yield decreased gradually and the most suitable yield of 85.6% was obtained with a slag/silicon ratio of 1.（4）The mechanism of oxide layer removal and silicon separation was investigated.Induction heating can effectively promote melt flow.The drag force generated by the melt flow drove SiO₂ to move and collide in the melt,forming SiO₂ clusters,so that large-sized SiO₂ clusters settled at the bottom of the crucible and remained in the silicon ingot.Wettability experiments showed that SiO₂ had an excellent affinity with PVGW,therefore the oxide layer was easily captured by the liquid phase formed by the PVGW,thus removed during the high temperature refining process.As the slag to silicon ratio increased from 0.5 to 1 and 2,the relative content of network breakers in the slag phase increased from 6% to 24% and eventually to 29%.The increase in network breakers destroyed the network structure of the slag,increased the degree of depolymerization of the slag network,reduced the viscosity of the slag phase and facilitated the migration of silicon.更多还原