Kinetics And Mass Transfer In Leaching Rare Earth From The Weathered Crust Elution-deposited Rare Earth Ore

For the weathered crust elution-deposited rare earth ores, with the application and development of the green chemistry of extraction process, especially popularization of the in-situ leaching process, the high selectivity leaching, high performance and low consumption extraction technology becomes more and more important and stringent in industrial design. In order to improve extraction process with high performance and low consumption, the basie theoretic and applied experiments of leaching process have investigated in this dissertation.1 Kinetics on Leaching Rare Earth from the Weathered Crust Elution-deposited Rare Earth OresIn order to know the mechanism of the rare earth leaching and choose the more suitable technology of extraction rare earth from this ore, the kinetic of leaching rare earth from the weathered crust elution-deposited rare earth ores with ammonium sulfate solution was investigated. The effects of the main leaching parameters such as temperature and ore particle size on leaching process were examined and discussed in order to elucidate the kinetics and mechanism of leaching rare earth. It was found that the higher the leaching temperature or the smaller the ore particle size, the faster the leaching progress. The leaching mechanism was analyzed with different kinetics models. The results show that the leaching process can be described by the shrinking-core model, the leaching rate was controlled by the inner diffusion of reactants and leaching products through mineral porous layer, the leaching process follows the kinetic model 1—2/3α—(1—α)2/3=kt, the apparent activation energy was 9.24 kJ/mol obtained from calculating the experimental data and the order of the ore particle size found to be approximately 2.An empirical equation relating the rare earth leached rate constant with ore particle size and leaching temperature was established as:2 Kinetics on Leaching aluminum from the Weathered Crust Elution-deposited Rare Earth OresFor the weathered crust elution-deposited rare earth ores, the aluminum is existing as exchangeable phase state with contents of 4.56×10-2%, and is the main impurities in the rare earth leach liquor. In order to know the mechanism of the aluminum leaching and inhibit aluminium during leaching rare earth, the kinetic of leaching aluminum from the weathered crust elution-deposited rare earth ores with ammonium sulfate solution was investigated. The effects of the temperature on leaching process were examined and discussed, the leaching mechanism was analyzed with different kinetics models. The results show that the leaching process can be described with the shrinking-core model too. The leaching rate was controlled by the the ion-exchange chemical reaction controls. The leaching process follows the kinetic model 1-(1-α)1/3=kt, the apparent activation energy was 41.57 kJ/mol obtained from calculating the experimental data. An Empirical equations were established as: 1-(1-η)1/3=1.9x104·e41570/RT·t3 Mass transfer in Leaching of the weathering crust elution-deposited rare earth oresThe mass transfer in leaching of rare earth from the weathered crust elution-deposited rare earth ores with ammonium sulfate solution was investigated. The effects of the flowrate, the concentration of leach reagents and rare earth ore grade on leaching performance were examined with column leahing, these experiment datum were analyzed with the chromatographic nonequilibrium plate theory in order to elucidate the mass transfer phenomena. It was found that the relationship between the height equivalent to a theoretical plate(HETP) and leaching flowrate can be described by van Deemter equation, there is a optimum flowrate in the leaching process. The results show that the dependence of leaching efficiency on flowrate of reagents. It provides a scientific approach to leaching the weathered crust elution-deposited rare earth ores with high efficiency and low material consumption, and is applied to optimize the rare earth extraction conditions and to improve the rare earth received rate.4 Kinetics Separation Aluminum in Leaching the Weathered Crust Elution-deposited Rare Earth OresComparing with the kinetics on leaching rare earth from the weathered crust elution-deposited rare earth ores, the kinetics on leaching aluminum has a great difference. The leaching rare erath rate was controlled by the inner diffusion of reactants and leaching products through mineral porous layer, but the leaching aluminum rate was controlled by the the ion-exchange chemical reaction controls. The apparent activation energy of leach aluminum is 41.57 kJ/mol, higher than rare earth as 9.24 kJ/mol. The leach reaction speed of leach aluminum is slower than rare earth. The results show that there are kinetic separation of aluminum from rare earth in leaching process. The kinetic separation of aluminum from rare earth in leaching the weathered crust elution-deposited rare earth ores with ammonium sulfate solution was carried out. The effects of the flowrate on kinetic separation aluminum in leaching the weathered crust elution-deposited rare earth ores were examined with column leahing. It was found that there is a optimum flowrate for kinetic separation aluminum in the leaching process. The optimum condition was established:the flowrate is U=0.23mL/min, the Al/RE in leach liquor is 0.012.5 Optimisation of mass transfer in column elution of rare earths from low grade weathered crust elution-deposited rare earth oreAlong with exploitation of high-grade weathered crust elution-deposited rare earth ores during the recent decades, the quality of rare earth ores is becoming lower and lowe. It has been a serious worldwide problem that how to exploit low-grade rare earth ores availably. In order to improve extraction process from the low-grade rare earth ores, an investigation was carried out to optimize the leaching and mass transfer of rare earth metals with ammonium sulfate solution during the column elution of a low grade weathered crust elution-deposited rare earth ore. The effects of flow rate, concentration of leach reagent and ore grade on the leaching performance were examined. The experimental data was analysed using chromatographic non-equilibrium plate theory in order to elucidate the mass transfer phenomena. It was found that the relationship between the height equivalent to a theoretical plate (HETP) and the leaching flow rate can be described by the Van Deemter equation and there is an optimum flow rate in the leaching process. Compared with similar higher grade weathered crust elution-deposited rare earth ores which have a sharp peak followed by a short tail, the leach curve of low grade ores has a long tail following a broader peak.