Leaching And Separation Of Lanthanum And Cerium From Spent FCC Catalyst

Fluid Catalytic Cracking（FCC） catalyst is a new product of China National PetroleumCorporation Lanzhou Filiale. It has gain priority share in domestic and internationalmarkets. Rare earth modified FCC catalysts possess high activity, good selectivity, highstability, good regeneration performance and strong anti-poisoning ability, and have beenwidely used in fluid catalytic cracking unit (FCCU). After a long time of recycling,however, the catalytic activity of rare earth modified FCC catalysts decreases, needremoval of some spent catalyst and supplement some fresh one for the maintenance ofcatalytic cracking activity. Due to the spent FCC catalysts with some heavy metals such asrare earth, Al, Fe, Ni and V, direct landfill is not desirable after primary pretreatment. Thiswill result in the waste of limited rare earth resources and the undesirable problems ofecological environmental pollution because the heavy metals are accumulated in the soil.This thesis consists of three parts:Chapter1is a survey of the preparation and modification of FCC catalysts, the structureand reasons and the environmental pollution of the spent FCC catalysts.Chapter2studied acid leaching conditions for spent FCC catalyst, including species ofleaching acid, leaching acidity, leaching temperature, leaching time, ratio of solid to liquid,pretreatment temperature of spent FCC catalysts and stirring rate.Chapter3investigated the precipitation, separation and purification of rare earths fromacid leaching solutions. Effect of acidity, concentration and temperature on theprecipitation and separation of lanthanum and cerium from acid leaching solutions wasexamined using oxalic acid as a precipitant. Further purification was discussed for theprecipitated rare earth compounds.It has been found that saticfactory recovery was achieved through hydrochloric acidand nitric acid leaching of rare earths from spent FCC catalyst under the optimizedconditions. The leaching efficiency of lanthanum and cerium is more than90%. Theprecipitation and separation of lanthanum and cerium from acid leaching liquids was examined using oxalic acid as a precipitant. The obtained purity of mixed rare earth oxidewas superior to95%.