| Compared with the traditional leaching methods with the defect of low efficiency,high cost and high pollution,microbial leaching has significant advantages of low cost,high efficiency and green environmental protection,and can extract mineral resources efficiently.Fungal leaching is a new method for mineral extration,and Aspergillus niger(A.niger)has been used widely.During the leaching process,the mycelia of A.niger can encase ore particles to form bio-ore pellets of A.niger-ore under certain conditions.In this study,A.niger and uranium ore were taken as research objects to carry out experiments,and the effects of different leaching conditions on the morphology and leaching effect of bio-ore pellets of A.niger-uranium ore were analyzed.On this basis,the research on optimization of parameters of uranium extraction was carried out.The achievements are summarized as follows:(1)The effects of leaching time,spore inoculum,type and concentration of carbon source,incubation temperature,initial pH,rotate speed and pulp density on morphological characteristics of bio-ore pellets of A.niger-uranium ore and uranium extraction were investigated by singer factor experiments,respectively.The results show that A.niger has three morphologies under different leaching conditions,including compact bio-ore pellets of A.niger-uranium ore,loose bio-ore pellets of A.niger-uranium ore and dispersed mycelia.(2)Under the conditions of 2-4 days leaching time,spore inoculum of 10~7-10~9 spores/L,concentration of carbon source 20-30 g/L,incubation temperature of 25-30?,initial pH 5-7,150-200 rpm and pulp density of2-4%,bio-ore pellets of A.niger-uranium ore can be formed.And under the conditions of 4 days leaching time,spore inoculum of 10~8 spores/L,sucrose concentration of 25 g/L,incubation temperature of 30?,initial pH 6,150 rpm and pulp density of 2%,the compact bio-ore pellets of A.niger-uranium ore are formed and uranium recovery is up to 76.26%.Furthermore,the relationship of uranium extraction with the morphological characteristics of bio-ore pellets of A.niger-uranium ore was also examined.When the compact bio-ore pellets A.niger-uranium ore were formed,the uranium leaching effect was much better.(3)The optimization of uranium extraction experiments using response surface methodology(RSM)was carried out.According to the results of single factor experiments,the positive and negative levels of seven factors in the RSM experiments were selected.The main affecting factors were screened by choosing the uranium recovery.Plackett-burman experiments and the steepest ascent experiments were used to screen out the main influencing factors and central point for extraction uranium.Then,RSM was designed to study the interaction between different factors and optimize parameters of uranium extraction.The main factors affecting uranium extraction are as follows:pulp density,rotate speed,incubation temperature.The optimist extraction conditions are incubation temperature of 30?,171 rpm and pulp density of 0.5%,which can get79.16%of uranium from its ore. |
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