A novel process of extracting niobium, yttrium, and cerium from a low-grade niobium-bearing ore by the roasting (NH 4 ) 2 SO 4 -Na 2 SO 4 -H 2 SO 4 system was experimentally studied. The influences of various factors, such as roasting temperature, roasting time, mass ratio of agents-to-ore and particle size fraction on the extraction of valuable metals were comprehensively investigated. It is found that the roasting Na 2 SO 4 -H 2 SO 4 system is effective to extract the niobium, yttrium, and cerium. The obtained optimum conditions for the extraction of Nb, Y, and Ce are roasting temperature of 300°C, roasting time of 3 h, mass ratio of Na 2 SO 4 :H 2 SO 4 :Ore of 0.5:1.0:1.0, and particle size fraction of -74 lm (*95 %). Under the optimum condition, the maximum recovery of Nb, Y, and Ce can reach 90.53 %, 92.15 %, and 98.04 %, respectively. All the results generated from this study will provide the fundamentals for Nb, Y, and Ce extraction from a niobiumbearing ore with low-grade.
The microorganism trench-leaching process of a low-grade uranium ore with a high content of fluorine was experimentally studied through the technique of Real-time PCR by using the fluorine-tolerance bacteria of Retech-3 as the leaching-ore bacteria. It was found that the Retech-3 strains of fluorine-tolerance domestication grown well in a fluoride solution with concentration of 0.0~3.0 g·L-1, and the oxidation of Fe2+ ions to Fe3+ ions occurred rapidly to promote the extraction of uranium. The experimental results showed that the bioleaching rate (89.82%) of uranium can be improved of 13.80% than acid leaching in 30 days with 65 kg ore and its particle size of-6 mm (fraction of 100%) in trench. The Real-time PCR analysis of microbial population compositions revealed that Retech-3 strains were mainly composed of Leptospirillum sp. and Acidithiobacillus sp. in the leaching process. The obvious improvements of fluorine-tolerance domestication of bacteria and the uranium leaching process will provide fundamentals for the smooth utilization of a high fluorine-containing uranium ore with the aid of microorganism trench-leaching.
In this work, the monitoring of bacterial and chemical dissolution of massive bornite was performed using cyclic voltammetry (CV); the mineral surface was examined using scanning electron microscopy (SEM) and the elements were indentified by Energy Dispersive X-ray Analysis (EDXA). The electrolyte employed for the electrochemical tests was the medium used for bioleaching the electrodes (3.0 g•dm-3 (NH4)2•SO4, 0.5 g•dm-3K2HPO4, 0.5 g•dm-3 MgSO4•7H2O and 0.1 g•dm-3 Ca(NO3)2).The results showed differences in voltagramms carried out by Acidithiobacillus ferrooxidans and Acidithiobacillus caldus: In bioleached electrodes tested in the presence of Acidithiobacillus ferrooxidans, the anodic and cathodic current signals were larger than with Acidithiobacillus caldus The analysis of CV results allowed attributing the different peaks observed in both the direct and reverse potential scanning to the oxidation of bornite to a secondary copper mineral(chalcocite and covellite) and its reduction via different non stoichiometric copper sulphides intermediaries. Surface evidences were produced by SEM, and chemical elements evidences were also investigated by EDAX.
The present work investigated the comparison of the effects of Na2SO3 and Na2SiO3 on thiourea stabilization, and a systematic study was undertaken to establish the effects of these stabilizers on the stability of alkaline thiourea, both qualitatively and quantitatively. The effects of these stabilizers on the activation energy of alkaline thiourea gold leaching was also studied. The results showed that sodium silicate was more suitable as a stabilizer in this system than sodium sulfite because the peak current of gold dissolution with sodium sulfite was higher than that with sodium silicate, but the inhibition of thiourea decomposition by the former was less obvious than that of sodium silicate in the cyclic voltammetry curve. The quartz crystal microbalance results showed that the quality decreased to about 100 ng cm2 in the presence of a stabilizer, while it increased to 300 ng cm2 in the absence of the stabilizer. It is inferred that gold can be dissolved by alkaline thiourea in the presence of a stabilizer, while it cannot without a stabilizer because of the decomposition of thiourea. This assumption was confirmed by atomic force microscopy measurements. The surface activation energy of Au dissolution decreased from 183.76 to 98.07 kJ/moL with the addition of sodium silicate, indicating that Au dissolution was promoted with the chemical.
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