In order to strengthen the leaching procedure,the chemical processes of leaching rare earths (RE) from the weathered crust elution-deposited rare earth ore were investigated frow the viewpoints of kinetics,hydrodynamic and mass transfer.The results show that the leaching hydrodynamics follows the Darcy law.The leaching kinetics can be described by the shrinking core model;the leaching process is controlled by diffusion of porous solid layer;and the mass transfer can be described with Van Deemter equation.This provides a theoretic basis and a scientific approach with high efficiency and optimized extraction conditions in industrial practice.
To understand the flotation mechanism of bastnaesite using reactive oily bubble, the interaction between bastnaesite parti-cles and reactive oily bubbles was investigated by electro-kinetic studies, induction time measurements and small-scale flotation ex-periments. The bastnaesite flotation could be seen as a hetero-coagulation between bastnaesite particles and reactive oily bubbles which was confirmed by the zeta potential distribution and induction time measurements from pH 4.8 to pH 9.0. The small-scale flotation tests were consistent with the hetero-coagulation results, and showed a better flotation of reactive oily bubble than air bubble among all pH range. The interaction force between bastnaesite particles and reactive oily bubbles was evaluated by the classical DLVO theory. It indicated that the attachment could be predicted well by the DLVO theory only in a restricted pH range due to the absence of hydrophilic interaction repulsion force and chemical interaction force.
Cerium carbonate powders were produced in a submerged circulation impinging stream reactor （SCISR） from Ce（NO3）3· 6H2O. NH4HCO3 was used as a precipitant in the reaction. Cerium carbonate powders were roasted to produce ultra-fine cerium dioxide （CeO2） powders. The optimal conditions of such production process were obtained by orthogonal and one-factor experiments. The results showed that ultra-fine and narrowly distributed cerium carbonate powders were produced under the optimal flowing conditions. The concentrations of Ce（NO3）3 and NH4HCO3 solutions were 02,5 and 0.3 mol · L^-1, respectively. The concentration of PEG4000 added in these two solutions was 4 g · L^-1. The stirring ratio, reaction temperature, feeding time, solution pH, reaction time and digestion time were 900 r · min^- 1,80 ℃, 20 min, 5 - 6, 5 min and 1 h, respectively. The final product, CeO2 powders, was obtained by roasting the produced cerium carbonate in air for 3 h at 500 ℃. The finally produced CeO2 powders were torispherical particles with a narrow size distribution of 0.8 -2.5 μm. The crystal structure of CeO2 powders belonged to cubic crystal system and its space point 5 group was OH^5-FM3M. Under optimal conditions, powders produced by SCISR were finer and more narrowly distributed than that by Stirred Tank Reactor （STR）.
