The lepidolite located in Yichun, Jiangxi Province, China, was adopted to investigate the recovery of alkali metals and leaching kinetics of lithium with sulphuric acid solution under atmospheric pressure. The results...The lepidolite located in Yichun, Jiangxi Province, China, was adopted to investigate the recovery of alkali metals and leaching kinetics of lithium with sulphuric acid solution under atmospheric pressure. The results show that the recoveries of alkali metals were achieved under the leaching conditions: mass ratio of lepidolite with particle size less than 180 μm to sulphuric acid 1.2, leaching temperature 411 K, liquid-solid ratio 2.5∶1, and leaching time 10 h. Under the selected conditions for leaching experiment, the leaching rates of lithium, potassium, rubidium and caesium are 94.18%, 93.70%, 91.81% and 89.22%, respectively. The X-ray diffraction analysis for leaching residue indicates that no insoluble product forms during leaching. The chemical compositions of leaching residue reveal that trace iron, manganese and calcium disappear after acid leaching. The kinetics of leaching process for lithium follows shrinking core model of mixed control and the apparent activation energy is 17.21 kJ/mol. The reaction orders with respect to sulphuric acid concentration and liquid-solid ratio are determined to be 2.85 and 1.66, respectively. A semi-empirical rate equation was obtained to describe the leaching process. The kinetic analysis shows that the leaching process is controlled by diffusion through the insoluble layer of the associated minerals.展开更多
Since the 1990s, the large-scale migrant labor force from rural to urban areas has made great contributions to the growth in China. However, migration does not come without costs. The potential impacts of parental mig...Since the 1990s, the large-scale migrant labor force from rural to urban areas has made great contributions to the growth in China. However, migration does not come without costs. The potential impacts of parental migration on the left-behind children have aroused wide concerns. Based on a two-wave panel dataset of nearly 10 thousand students in 166 schools from 13 counties in 5 provinces between 2014 and 2015, differences-in-differences （DID） and propensity score matching plus DID （PSMDID） approaches were used to examine the changes in academic performances before and after the parental out-migration. The results indicated that the mother only migration has a significant negative impact on the a- cademic performances of left-behind children, and it was especially true when the mother only migration lasted more than a semester. For left-behind children whose parents were out or only the father was out, their academic performances were not affected.展开更多
基金Project(2015BAB06B01) supported by the National Key Technology R&D Program of ChinaProject(2014CB643406) supported by the National Basic Research Program of China
文摘The lepidolite located in Yichun, Jiangxi Province, China, was adopted to investigate the recovery of alkali metals and leaching kinetics of lithium with sulphuric acid solution under atmospheric pressure. The results show that the recoveries of alkali metals were achieved under the leaching conditions: mass ratio of lepidolite with particle size less than 180 μm to sulphuric acid 1.2, leaching temperature 411 K, liquid-solid ratio 2.5∶1, and leaching time 10 h. Under the selected conditions for leaching experiment, the leaching rates of lithium, potassium, rubidium and caesium are 94.18%, 93.70%, 91.81% and 89.22%, respectively. The X-ray diffraction analysis for leaching residue indicates that no insoluble product forms during leaching. The chemical compositions of leaching residue reveal that trace iron, manganese and calcium disappear after acid leaching. The kinetics of leaching process for lithium follows shrinking core model of mixed control and the apparent activation energy is 17.21 kJ/mol. The reaction orders with respect to sulphuric acid concentration and liquid-solid ratio are determined to be 2.85 and 1.66, respectively. A semi-empirical rate equation was obtained to describe the leaching process. The kinetic analysis shows that the leaching process is controlled by diffusion through the insoluble layer of the associated minerals.
文摘Since the 1990s, the large-scale migrant labor force from rural to urban areas has made great contributions to the growth in China. However, migration does not come without costs. The potential impacts of parental migration on the left-behind children have aroused wide concerns. Based on a two-wave panel dataset of nearly 10 thousand students in 166 schools from 13 counties in 5 provinces between 2014 and 2015, differences-in-differences （DID） and propensity score matching plus DID （PSMDID） approaches were used to examine the changes in academic performances before and after the parental out-migration. The results indicated that the mother only migration has a significant negative impact on the a- cademic performances of left-behind children, and it was especially true when the mother only migration lasted more than a semester. For left-behind children whose parents were out or only the father was out, their academic performances were not affected.
