COLUMN BIOLEACHING IN A VOLCANIC ROCK TYPE URANIUM DEPOSIT, SOUTHEAST-CHINA

摘要

The Xiangshan uranium deposit is one of the biggest volcanic rock type uranium mines in China. The ore is complex with a high content of clay minerals. Currently, high-grade uranium ore is leached by conventional agitation hydrometallurgy, but the production is costly and the economic efficiency is poor. Low-grade ore is leached by the percolation leaching method, however fines cause the heap to be compacted and clayey, resulting in distinctly decreased permeability.In this paper, a heap bioleaching technology is developed for this deposit. Mineralography study using EPMA shows that the dominating uranium minerals are brannerite and pitchblende. Refractory native brannerite accounts for about half the content. These uranium minerals are associated with pyrite and fluorite, and are semi-encapsulated by them or commonly at their edges. There is significant apatite and illite, which can produce mud and clay during heap leaching. The process is carried out in two stages, comprising an acid pre-leaching stage followed by a bioleaching stage. It is found that most of acid is consumed in the pre-leaching acidification stage. The hexavalent uranium is preferentially leached in the initial stage. The acid consumers existing in the ore have an adverse impact on uranium leaching, and acidification with higher acid in the initial stage can significantly promote uranium leaching. It is shown that the bioleaching of uranium yields better results than acid leaching. Rotating drum technology is one of the important methods to solve the problem of unevenness of the ore in the column during the bioleaching process. The leaching results show that the acid consumption is low at 6.8% and the leaching rate is high at 90%, with a leaching period of 126 days. Through the study of the change in chemical composition during the leaching process, it is proven that the leaching of uranium is closely related to the leaching of pyrite, so that the leaching of pyrite has a beneficial effect.