Study On Recycling Of Rare Earth From Waste Process Fluorescent Powders

Nowadays there is a lot of waste rare earth in solid waste disposal as afluorescent lamp in the world every year. These not only pollute the environment, doharm to human body health, but also cause rare earth waste of resources. Rare earth isof strategic resources in the world today. How to effectively use and protect the rareearth resources are the important task of our country. Researches on how to deal witha lot of waste comprehensive in China rare earth fluorescent lamps (including otherwaste fluorescent lamp), the protection of environmental health, realizing the rareearth resources recycle, have the important practical significance.In this paper, we take the waste in the production process of fluorescent lamps(also called process waste powder) as the research object, and studied the leachingprocess, dynamics and precipitation separation of rare earth in the process wastepowder. We investigated the leaching effect of rare earth in the two different wastepowders by different leaching conditions or the leaching effect of rare earth under thecondition of ultrasonic. The purpose of studying the precipitation effect of rare earthin the leaching solution under different precipitation conditions is to get the bestprecipitation rate.The results show that the rare earth leaching effect of two kinds of different craftwaste powder is better in the hydrochloric acid. The rare earth leaching rate improveswith the increase of hydrochloric acid concentration, reaction time, liquid-solid ratioand reaction temperature. At the temperature of343K, controlling the hydrochloricacid concentration of3mol·L-1, reaction time at6h and liquid-solid ratio of6:1, therare earth leaching rate of process waste powderⅠreaches95.98percent. At the roomtemperature, controlling the hydrochloric acid concentration of4mol·L-1, reactiontime at6h and liquid-solid ratio of5:1, the rare earth leaching rate of process wastepowderⅡreaches92.71percent. Ultrasonic has a certain impact on the rare earthleaching of process waste powders. Under the same condition, the ratio of rare earthleaching with ultrasonic can be increased by10%.Leaching kinetics analysis shows that whether or not use ultrasonic, the rareearth leaching process of process waste powders is controlled by internal diffusionreaction. Under the condition of ultrasonic and non-ultrasonic, the apparent activationenergy of rare earth leaching reaction is20.53kJ·mol-1and26.09kJ·mol-1respectively.By comparing the apparent activation energy, further evidence proves that ultrasonicis helpful to rare earth leaching. The result of the rare earth precipitation in the leaching solution shows that whenthe rare earth precipitated directly from leaching solution with oxalic acid, the rareearth deposit rate enhanced with the increase of the mount of oxalic acid, theextension of the settling time and the increase of reaction temperature. At roomtemperature, when the amount of70g·L-1oxalic acid is40mL and precipitation timeat4hours, the rare earth precipitation rate in the leaching liquid reaches93.31%, andrare earth oxide is48.52%. When using a two-step precipitation with ammonia andoxalate, the rare earth precipitation rate improves as the dosage of ammonia andoxalate acid increases, also in proportion to the precipitation time and reactiontemperature. At the temperature of70°C, the dosage of ammonia at the concentrationof70g·L-1is15mL and the oxalic acid is30mL with the precipitation time of4h,the rare earth precipitation rate in the leaching solution reaches96.35%, and rare earthoxide is86.25%.The purity of rare earth oxide precipitation increased by37.74%thanthe primary.