Abstract:Molybdenum was extracted by hydrometallurgy leaching from low grade molybdenum calcine. The mineral compositions of the calcine roasted from low grade molybdenum concentrate were tested by X-ray diffraction. The results indicate that the leaching rate by ammonia is low because of the existence of molybdate and low state of molybdenum phase in the molybdenum calcine. The strengthening leaching for low grade molybdenum calcine by HNO₃/NH4NO₃ pretreatment was investigated. The results show that the undissolved molybdate is translated into dissolved molybdate in ammonia leaching by the HNO₃/NH₄NO₃ pretreatment. Meanwhile, the loss of molybdenum is restrained with the effect of acid and salt. Thus, the comprehensive recovery rate of molybdenum is improved. The operating parameters of optimum process is established as follows: HNO₃ concentration is 120 g/L, NH₄NO₃ concentration 100 g/L, liquid-solid ratio 3:1, pretreating time 120 min, reaction temperature 90 ℃. Compared with the direct ammonia leaching without pretreatment, the molybdenum content in the ammonia leaching residue reduces from 20.00% to 5.13%, and the comprehensive recovery rate of molybdenum increases from 75.90% to 95.38% with the processing of pretreating-ammonia leaching.

Key words: low grade molybdenum concentrate; molybdenum calcine; undissolved molybdate; pretreatment; ammonia leaching