Study On Extraction Of Rare Earth By P507 - N235 Extraction

Rare earth（RE） is widely used in optical material, electronic material and magneticmaterials due to particular physical and chemical properties, and thus becomes the strategicresources in the fields of high technology. As acid phosphonic type of extractant, P204and P507are commonly used to separate RE to obtain individual RE elements in the modern industry,however, this extraction process simultaneously generates large amount of NH4+because ofammonia saponification which has caused serious environmental problems.In this paper, a double-solvent system of P507and trialkylamine(N235), which extract REions and acids respectively, was designed for RE extraction without saponification. Researchershave demonstrated the feasibility for the whole scheme while some problems still exist. Forexample, the system easily generated the third-phase besides the aqueous and organic phase whenusing the kerosene as diluents, and the researchers had not made a systemic research on theextraction ability and the separation factors of RE. Aiming at overcoming the shortcomingsproposed in the former research, this paper optimized the organic phase of extraction system.Furthermore, the saturated capacity of extraction, the distribution ratio and the separation factorsunder the new system were studied. Finally, the law of stripping organic phase with RE byhydrochloric acid, the related parameters of recycling organic phase and the extractionmechanism under the new system were studied.The reasons for producing the third-phase in organic phase with RE were analyzed and thesolution was proposed. Good performance could be obtained when using kerosene mixed withcyclohexane as diluents and the different extraction system was choosen according to thedifference balanced acidity to extract RE: the system of30%P507+25%N235+15%kerosene+30%cyclohexane and30%P507+25%N235+22.5%kerosene+22.5%cyclohexane were emploiedwhen extracting the light and the heavy RE elements, respectively. The optimal conditions ofextracting single rare earth were determined as follows by extracting Nd3+with P507-N235system: the oscillation time was5mins, the phase ratio was1:1, the pH of the feed was2~3.Under these conditions, the extraction ability for the RE of the new system increased with theincreasing of atomic numbers, which was in accordance with the law of positive extraction.The optimal extracting RE conditions determined by La/Ce with P507-N235system were asfollows: the oscillation time was8mins, the phase ratio was1:1, the concentration of the feedwas1mol·L-1. Under these conditions, the separation factors were measured in different pH anddifferent component of the feed in the P507-N235system. The results showed that, the separationfactors of the P507-N235system was higher than that of P507-kerosene system when extractingthe light RE elements, and it is lower than the P507-kerosene system when extracting the heavyRE elements.In this experiment, hydrochloric acid was used to strip the organic phase with RE to obtain asingle RE element, and the single-step stripping factors increased with the decreasing of thephase ratio and the increasing of the hydrochloric acid concentrations. The single-step strippingfactors was larger than94%and the second stripping factors could reach more than98%whenthe phase ratio was1:0.8and the acid concentration was4mol·L-1. The organic phase with acidscould be recycled when the pH of the organic phase was5or higher. The recovery rate of theorganic phase could reach95.20%when the organic phase was stripped by the water whose phaseratio was1:2for9times. The composition of extracted species was speculated based on the dependence of startingmolar of P507(N235) and extraction volume of Nd3+in the P507-N235system, it consumed4molP507and4mol N235to extract1mol Nd3+, and the chemical equation was speculated as NdCl3（a）+4R3N（o）+4HA（o） REA3(R3N HA)3(R3N HCl).