Alkaline leaching characteristics of uranium from Lincang coal: Correlation with the dissolution of coal humic substances

The characteristics involving the leachability of uranium from coal by utilizing sodium carbonate-bicarbonate mixtures and the role of coal humic substances dissolution in the leaching procedure were investigated. Alkaline leaching is an effective method to extract uranium from coal without reducing the usability of coal. Under the optimum leaching condition, viz. liquid/solid (L/S) ratio = 20: 1 and [CO32]/[HCO3-] ratio = 2: 1, the leaching efficiency increases from 80.50 +/- 0.24% at 10 degrees C to 96.29 +/- 0.70% at 90 degrees C with the leaching agent concentration of 0.6 mol/L. As the primary form of uranium in the coal, the organic-bound uranium decreases by 64.95 +/- 3.25 mg/kg after leaching at ambient temperature of 25 degrees C, and is the main source of the alkalineleached uranium. Besides, the uranium is linearly and significantly correlated with the dissolved organic carbon (DOC) in the leachate (R-2 = 0.916, p < 0.01) before the leaching equilibrium. The fluorescence excitationemission matrix (EEM) analysis, coupled with parallel factor (PARAFAC), peak-picking and fluorescence regional integration (FRI) analysis, shows that the leaching concentration of uranium is closely correlated with the fluorescence components represented humic acid (HA)-like substances in leachate, with R-2 values around 0.8 and p < 0.05. Thus, we hypothesize that the dissolution of HA-like substances can be the key factor for the alkaline leaching of uranium from the coal.

Automated summary

The study investigated the leachability of uranium from coal using sodium carbonate-bicarbonate mixtures and the dissolution of coal humic substances in the leaching process. It was found that under optimal conditions, the leaching efficiency of uranium from coal increased with temperature and leaching agent concentration. The dissolution of HA-like substances was hypothesized to be a key factor in the alkaline leaching of uranium from coal, as indicated by the significant correlation between uranium concentration and fluorescence components in the leachate.