Theoretical Basis for the Separation of W and Mo with Manganese Dioxide: A Speciation-Based Approach
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LYBDENUM and tungsten are both the important high-tech metals and their high-purity products are vital for developing advanced materials.[1] However, the effect of lanthanide contraction makes the atomic radii and electronic structures of Mo and W almost same to each other.[2] as a result, separation of these two metals is one of the most difficult problems in extractive metallurgy.[3] The separation difficulty lies in the complexity of the metals ion species in aqueous solution and the similarity of the extraction behaviors of Mo and W in most cases.[4] So far, most available methods for separation of Mo and W from mixed solutions are based on either solvent extraction[5–7] or ion exchange.[8,9] However, in the solvent extraction process, the organic phase is relatively unstable and the extracting agent is expensive;[10] the method of ion exchange has several YUNFENG SONG, JIALIANG ZHANG, and LIHUA HE, Doctoral Students, XINGYU CHEN, Associate Professor, and ZHONGWEI ZHAO, Professor, are with the School of Metallurgy and Environment, Central South University, Changsha 410083, China, and also with the Key Laboratory of Hunan Province for Metallurgy and Material Processing of Rare Metals, Changsha 410083, China. Contact e-mail: [email protected] Manuscript submitted August 30, 2014. Article published online December 17, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
drawbacks, such as poor selectivity, complicated operation process and unsatisfactory production efficiency. At present, hydrated oxides and hydroxides have been widely used to adsorb microamounts of metal ions, owing to their simple and effective operability.[11,12] Compared with W, Mo has a greater affinity for sulfur and it is easily to be adsorbed by metal sulfides in the form of Mo-S bond.[13,14] Relatively, W has a greater affinity for oxygen than Mo, so it is expected that W can be adsorbed onto metal oxides more easily than Mo. Thus means, perhaps efficient separation of Mo and W would be achieved, once certain kind of oxides or hydroxides adsorbent with high selectivity for W is developed. In fact, molybdenum and tungsten compounds are widely distributed in nature and their differences in behavior are well studied in thalassochemistry, geochemistry, biochemistry, and other subjects.[15–19] Researchers have observed that the content of W increases markedly in sedimentary rock, which contains abundant oxides of iron and manganese such as pyrolusite.[20] Moreover, it is noteworthy that the tungsten abundance is extremely low in oceans, normally less than 0.2 to 1 9 1012, while the average content of W can reach up to 111.3 9 106[21] in manganese nodules (a kind of clot with iron and manganese oxides or hydroxide), especially in the manganese micronodules of the Pacific. Literatures[22,23] VOLUME 47B, FEBRUARY 2016—675
also show that under conditions of thalassochemical circumstance, the adsorption ratios of Mo and W onto hydrated manganese oxide are 25 and 99 pct, respectively. All above facts indicated that manganese oxides should be able to efficiently and sel
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