Study On Rare Earth Elements In Phosphogypsum Leaching By Aspergillus Niger

Phosphogypsum(PG)is a waste residue produced in the production of wet-process phosphoric acid with calcium sulfate dihydrate as the main component.Because of precious rare earth elements(REEs)are contained in the PG,extracting REEs from PG is of great significance for the effective utilization of rare earth resources and the improvement of the resource value of PG waste residue.This paper takes PG as the research object,uses fungi Aspergillus Niger(A.niger)culture medium as microbial leaching agent to leach REEs from PG,studies the leaching behavior of REEs from PG in one-step,two-step and fermentation liquid systems.The main contents of this paper are as follows:(1)A.niger strain was cultured to explore the growth activity and acid production capacity,and the tolerance and adsorption of REEs of the strain were studied.The results showed that the biomass of A.niger reached the maximum on the third day of culture,and the addition of REEs had a certain inhibitory effect on the growth of A.niger strains,and A.niger strains could adsorb REEs.(2)Three methods were used to carry out the leaching experiment.The leaching effect of fermentation liquid method was better,and the leaching rate of rare earth reached 14.56%.In order to further improve the content of rare earth,Fe SO₄was added to the culture medium,and finally the leaching rate of rare earth was increased to 19.82%,an overall increase of 5.26%.The mechanism of A.niger leaching was preliminarily discussed.It was found that A.niger can produce a variety of organic acids,among which the yield of citric acid is the largest.Compared with non-biological method,biological method has the main advantage and more REEs are leached.Scanning electron microscope(SEM)results showed that the surface of the original bacteria was smooth,and the mycelia were intertwined.After leaching,a large number of granular substances appeared on the surface of the mycelia,which were seriously corroded,increasing the surface area of the fungus,and a large number of REEs were enriched on the surface and inside.(3)According to the single factor test of the leaching of REEs from PG by A.niger fermentation broth method and the orthogonal test of three factors and three levels of solid liquid ratio,temperature and oscillation rate,the optimal leaching conditions are as follows:the solid-liquid ratio is 2:1,the temperature is 30?,and the oscillation rate of shaking table is 150rpm.It is found that A.niger culture solution can leach not only REEs,but also Mg,K,Al and Fe elements in PG.In fact,the leaching of REEs from PG in A.niger culture liquid also plays a role in purifying PG,and the content of metal ions,soluble P₂O₅in the purified PG are reduced,and the subsequent application of PG in building materials will be improved.Therefore,the biological leaching of REEs by PG can not only extract valuable REEs,but also improve the purity quality of PG and the performance of building materials,with good comprehensive benefits.