A quantitative Fourier transform infrared (FTIR) technique mas established by comparison with chemical analysis and quantitative X-ray diffraction (XRD) analysis. By the quantitative FTIR analysis of bauxite during di...A quantitative Fourier transform infrared (FTIR) technique mas established by comparison with chemical analysis and quantitative X-ray diffraction (XRD) analysis. By the quantitative FTIR analysis of bauxite during dissolution , the process of dissolution and precipitation of silica was found to occur in three stages. In the first stage, there was no precipitation of desilication product (DSP). All the silica dissolved from kaolinite went into the solution. In the second stage, the silica concentration in solution attained a maximum and then dropped very quickly. The precipitation of DSP was the main cause of the reduction of the silica concentration in solution. In the third stage, the concentration of DSP reached a constant level. The dissolution and precipitation process gradually attained an equilibrium. The mechanism of silica dissolution and DSP precipitation was discussed on the basis of the FTIR quantitative analysis of kaolinite and DSP in bauxite.展开更多
Soil secondary minerals are important scavengers of rare earth elements(REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils...Soil secondary minerals are important scavengers of rare earth elements(REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs(La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs(LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs(HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs.The substantial fractions of REEs in soils extracted byoxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile(10 %–30 %), which were similar to the mass fraction of Fe(10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.展开更多
Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion ...Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na2O-Al2O3- SiO2-CaO-TiOz-H2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to AlaTi2SiO12 at low temperatures （60-120℃）, which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2SiO12 decomposes gradually and converts to Ca3TiSi2（Al2Si0.5Ti0.5）O14 at 200 ℃ When the temperature reaches 260℃, CaTiO3 forms as the most stable titanate species for its hexagonal closest packing with O^2- and Ca^2＋. The findings enhance the under-standing of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.展开更多
文摘A quantitative Fourier transform infrared (FTIR) technique mas established by comparison with chemical analysis and quantitative X-ray diffraction (XRD) analysis. By the quantitative FTIR analysis of bauxite during dissolution , the process of dissolution and precipitation of silica was found to occur in three stages. In the first stage, there was no precipitation of desilication product (DSP). All the silica dissolved from kaolinite went into the solution. In the second stage, the silica concentration in solution attained a maximum and then dropped very quickly. The precipitation of DSP was the main cause of the reduction of the silica concentration in solution. In the third stage, the concentration of DSP reached a constant level. The dissolution and precipitation process gradually attained an equilibrium. The mechanism of silica dissolution and DSP precipitation was discussed on the basis of the FTIR quantitative analysis of kaolinite and DSP in bauxite.
基金funded by the National Natural Science Foundation of China(41420104007,41330857,and 41673135)the Guangdong Natural Science Foundation of China(S2013050014266)the One Hundred Talents Programme of The Chinese Academy of Sciences
文摘Soil secondary minerals are important scavengers of rare earth elements(REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs(La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs(LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs(HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs.The substantial fractions of REEs in soils extracted byoxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile(10 %–30 %), which were similar to the mass fraction of Fe(10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation.
基金financially supported by the National Natural Science Foundation of China(Nos.U1202274 and51504059)China Postdoctoral Science Foundation Funded Project(No.2015M581352)the Fundamental Research Funds for the Central Universities of China(Nos.N140203005 and N140204015)
文摘Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na2O-Al2O3- SiO2-CaO-TiOz-H2O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to AlaTi2SiO12 at low temperatures （60-120℃）, which is similar to anatase in crystal structure. As the temperature continues to rise, Al4Ti2SiO12 decomposes gradually and converts to Ca3TiSi2（Al2Si0.5Ti0.5）O14 at 200 ℃ When the temperature reaches 260℃, CaTiO3 forms as the most stable titanate species for its hexagonal closest packing with O^2- and Ca^2＋. The findings enhance the under-standing of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.
