Extracting tungsten from scheelite concentrate with caustic soda by autoclaving process Zhongwei Zhaoa b ⁎ Jiangtao Lia b Shibo Wanga Honggui Lia Maosheng Liua Peimei Suna Yunjiao Lia a School of Metallurgical Science and Engineering Central South University Changsha 410083 Hunan China b Key Laboratory for Metallurgy and Material Processing of Rare Metals Changsha 410083 }