Enrichment of Rare Earth from Low Concentration Rare Earth Sulfate Solution by Calcium Oxide Precipitation

The process of rare earth enrichment from the leaching liquor of ion-adsorption type rare earths ore by calcium oxide precipitation could eliminate ammonia nitrogen pollution existing in the traditional precipitation process of ammonium bicarbonate. It couldsupply calcium ions for Mg-Ca compound leaching agent, realizing the effective circulation of magnesium and calcium. Therefore, in order to provide data basis for calcium oxide precipitation process, the calcium oxide was used as precipitant to enrich rare earth from low concentration rare earth sulfate solution. The study showed that the rare earth precipitation efficiency could reach more than 99% when the end pH value was 9.5 in the calcium oxide precipitation process. Moreover, it was determined that the optimum precipitation conditions in 45 ℃, a feeding speed of 1.5 ml•min-1, 0.5 mol•L-1 calcium oxide slaking solution (COH-), 200 ml of washing water, led to 83.81% rare earth purity in the precipitate product. However, the sulfate ions would coordinate precipitation and form the alkaline rare earth sulphate, which made the content of SO3 in the precipitate product up to 12.30%. In order to reduce the content of SO3, sodium acetate, sodium hydroxide and sodium succinate were used as washing agentsto agitator washing the rare earth hydroxide cake. With the competitive coordination between the anion and the sulfate, the rare earth purity increased to 85.83%, 90.40% and 93.09%, respectively. Therefore, the qualified mixed rare earth oxide of ion-adsorption type rare earths ore was expected to obtain by controlling the conditions in the calcium oxide precipitation and the sodium hydroxide washing process. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.