Study On The Extraction Of Rare Earth From Waste CRT Phosphors

With the rapid upgrading and renewing of electronic products, the electronic productsincluding the CRT monitors are or are going to be on their last legs at present. The rare earthphosphors painted on CRT screen are usually burned, dumped in landfills or discarded, whichnot only pollutes the environment, but also wastes the rare earth resources. Therefore, carryingout a research into the extraction of rare earth from waste Cathode Ray Tube (CRT) phosphorshas important practical significance. However, the present researches are focused on thefluorescent powder used for lamp, and there are few researches about the extraction of rare earthfrom waste CRT phosphors.The study on the extraction of rare earth from waste CRT phosphors is carried outaccording to the features and occurrence state of the rare earth in the phosphors, using themethods of dilute acid pretreatment process, acid leaching of the rare earth phosphor, DDTCpurification and oxalic acid precipitation. The research work will be aimed at studying the newtechnology of extracting rare earth from waste CRT phosphors, in order to reduce the wastephosphors’ harm to environment, at the same time, recycle the rare earth resources from thephosphors. Following are the main research areas:(1) The effects of hydrochloric acid concentration, pretreatment temperature andpretreatment time on the extraction of rare earth from waste CRT phosphors were studied.(2) The experiment of leaching the rare earths from pretreated material was studied, whichmainly investigated the influence of hydrochloric acid concentration, reaction time, reactiontemperature and solid to liquid ratio on the extraction of rare earth.(3) The method of DDTC precipitation was used to remove impurities from leachingsolution, which mainly investigated the influence of pH value and dosage ratio of DDTC on theremoval of impurities.(4) Using the way of oxalic acid precipitation to recycle the rare earths, and then sinteringthe precipitate at high temperature. This experiment mainly discussed the effects of the oxalicacid dosage, calcination temperature and time on rare earth products.The research results show that the mainly rare earth elements in waste CRT phosphorsare Yttrium and Europium, and the total content of rare earth (in the form of oxide) is20.53％.The optimum conditions of dilute acid pretreatment process are as follows: hydrochloric acid concentration0.8mol·L-1, reaction temperature65℃and leaching time2h. Under theoptimum conditions, the removal rate of impurities and rare earths are26.49%and5.77%,respectively. The best conditions for leaching the rare earths from pretreated material are asfollows: hydrochloric acid concentration5mol·L-1, reaction temperature80℃and leachingtime5h, at this time, the leaching rate of rare earths is94.26%. When the pH value ofleaching solution is5~5.5and the dosage ratio of DDTC is6:1, the impurity removal effect isbest. The oxalic acid dosage is more than10percent of the theoretical dosage during recyclingrare earths, and under this condition, the precipitation rate of rare earth is96.17%. The optimumcondition of sintering process is performed at900℃for2h. The granularity analysis resultsshow that the particles are well scattered, and its D50is13.059μm. It was analyzed andcharacterized by x-ray diffraction(XRD) and scanning electron microscopy(SEM).Testresults showed that the final rare earth products are cubic crystal system Y2O3, in whichlamella crystals are closely integrated with each other and form a compact structure.