Rare earth extraction and separation from mixed bastnaesite-monazite concentrate by stepwise carbochlorination-chemical vapor transport

• Published in: Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2002-10, Vol.33 (5), p.661-668
• Main Authors: WANG, Zhi-Chang, ZHANG, Li-Qing, LEI, Peng-Xiang, CHI, Ming-Yu
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Metallurgical fundamentals; Metals. Metallurgy; Production of metals
• ISSN: 1073-5615; 1543-1916
• DOI: 10.1007/s11663-002-0018-1

A stepwise carbochlorination-chemical vapor transport (SC-CVT) process is proposed for the rare earth extraction and separation from a mixed bastnaesite-monazite concentrate based on thermodynamic and kinetic analysis using carbon as reductant, chlorine gas as chlorination agent, SiCl sub 4 as defluorination agent, and AlCl sub 3 as vapor complex former. Between 500 deg C and 800 deg C, apparent activation energy of the carbochlorination within 2 hours changed from 22 to 16 kJ/mol roughly for the initial half hour and final 1 hour, respectively, in the absence of SiCl sub 4 ; but these values reduced to 15 and 2.1 kJ/mole under 2 kPa of SiCl sub 4 gas. The rare earth chloride yield for 2 hours was 56 to 88 mol pct in the absence of SiCl sub 4 and 92 to 99 mol pct in the presence of SiCl sub 4 ; but carbochlorination at above 1000 deg C yielded a large amount of acid-insoluble residue. This, together with the negligible equilibrium vapor pressure of ThCl sub 4 at below 600 deg C, suggests that carbochlorination of the mixed concentrate at temperatures as low as 500 deg C in the (Cl sub 2 + SiCl sub 4 ) atmosphere is suitable for rare earth extraction and thorium-free volatile by-product release, which is different from the conventional Goldschmidt process at 1000 deg C to 1200 deg C. The CVT reaction of the carbochlorination product was performed at 800 deg C for 0.5 hours in the (Cl sub 2 + SiCl sub 4 + AlCl sub 3 ) atmosphere and then at 1000 deg C for 6 hours in the (Cl sub 2 + AlCl sub 3 ) atmosphere along different temperature gradients, leading to complete thorium removal and efficient rare earth separation, respectively. Their combination allows an efficient and environmentally conscious extraction and separation of rare earth elements from the mixed concentrate.