Alkaline Fusion Mechanism And Application Of Aluminate Rare Earth Phosphors

The reuse and recycling of rare earth elemnts(REEs)from the end-of-life rare earth goods is an efficient way to solve the problem of rare earth resources.Aluminate rare earth phosphor is widely used in the word because of its good luminous efficiency and practical value.Aluminate phosphor mainly consists of blue phosphor(BaMgAl10O17:Eu2+,BAM)and green phosphor(CeMgAl11O19:Tb3+,CMAT).BAM and CMAT cannot be dissolved by either acid or alkali at room temperature because of their high bond strength.So as to the traditional recycling process has lower leaching rare of REEs.Our team put forward the dual hydrochloric acid dissolution(DHA)process,in which alkaline fusion was used to recycle REEs form waste phosphor.Alkaline fusion process can effectively improve the REEs recycling rate.However,basic theory and research regarding alkaline fusion are almost lacking and alkaline fusion process can also be further improved.In this work,a series of alkaline fusion experiments of BAM/CMAT were performed with six reactants to separately elucidate the structure decomposition of aluminate phosphor.Kinetic parameters of alkaline fusion were obtained via four model-free calculation methods.BAM and CMAT have similar crystal structure,so as to they can share similar reaction process or mechanism.Rare earth ions were bonded with free oxoanion(OH-,CO32-,O2)preferentially to escape from the BAM/CMAT structure.This view can be used to explain explain the recovery principle and moving trajectory of REEs.By discussing the previous alkaline fusion hypothesis,a new theory,Cation-Oxoanion Synergies Theory(COST),was proposed to elucidate the structure decomposition of aluminate phosphor.COST can be described as follows:Both alkali metal cations(Na+,K+)and free oxoanion have contribution to the decomposition of aluminate phosphors.On the mirror plane,alkali metal cations would substitute rare earth ions,while free oxoanion can bond with rare earth ions.These two ionic forces ensure that rare earth ions can be substituted.This substitution would cause more oxygen vacancies and interstitial ions,resulting in lattice distortion.Then the unstable crystal structure break down into smaller blocks.This theory can significantly benefit REEs recycling technology,and supplement the alkaline fusion technology theory.DHA process was performed on pilot scale to analyze the economic benefits and environmental assessment.For processing one tone waste phosphor,the total products value(USD 12,329)is about 4 times of the direct input costs(USD 3,196),indicating that the process itself is valuable.The potential environmental effects of DHA process were assessed by reference to the technical framework of life cycle assessment.During the studied environmental impact categories,DHA process had a larger contribution to water use and global warming than others。According to the evaluation of the process,a pre-treatment of silicon powder was proposed to improve the DHA process.300 mesh(48 μm)physical screening was chosen to separate silica,and about 56%of silica was removed from the waste phosphor,thus 0.215 t caustic soda,0.538 t hydrochloric acid and 0.8 m3 water were saved accordingly for per ton waste phosphor treatment.Rare earth resources shortage is a common problem in the world.It is very meaningful to make reasonable arrangements for the management of rare earth resources from the aspects of substitution,regulation,reduction and recycling.The current crisis of rare earths and other materials that are in short supply is an important learning experience,in which we can learn how to quickly deal with similar resource shortage.