| The weathering crust elution-deposited rare earth ore is rich in middle and heavy rare earth.It is a kind of rare earth mineral resource which is widely distributed.And also,it is a kind of rare earth ore,which has considerable commercial value and strong market competitiveness.At present,the main leaching agent in industry is ammonium sulfate,and rare earth is leached by in-situ leaching process.However,the leaching agent,uesd in the process of leaching weathering crust elution-deposited rare earth ore,is poor in penetration effect and long in leaching period,leading to remain a large amount of liquid in ore bodies,and resulting in low recovery rate of resources,serious pollution of ecological environment and other outstanding problems.Carboxyl compounds are a new and promising leaching agent in recent years.It can not only increase the leaching rate of rare earth and reduce the using amount of leaching agent,but also accelerate the permeation process and shorten the leaching period.Although there have been many achievements in improving the leaching rate of rare earth with carboxyl compounds,still lacking reasonable and systematic discussion on the permeation law and mechanism of the leaching process of rare earth ore.Thus,in this paper,ammonium acetate,tartrate and ammonium citrate were used as leaching agents,and simulating the in-situ leaching process with column leaching experiment.Discussing the influence of experiment factors,which include leaching agent concentration,leaching agent p H,leaching temperature,particle size and porosity,on the leaching process of weathering crust elution-deposited rare earth ore with carboxyl compounds.Besides,from the two aspects—Zeta potential and wettability,to discuss the permeation mechanism of leaching rare earth ore from weathering crust with carboxyl compounds.The experimental results were as follows:?1?The effects of leaching agent concentration,leaching agent p H,leaching temperature,particle size and porosity on permeation rate of leaching weathering crust elution-deposited rare earth ore with carboxyl compounds in different hydraulic gradients were discussed.It was found that the permeation rate increasing linearly with the increase of hydraulic gradient,which indicated that the permeation process obeyed Darcy's law?R2>0.98?.Both fluid and orebody properties had an effect on the permeability of ore bodies.The smaller liquid viscosity,the thinner water film thickness,the stronger adsorption,the less the precipitate,all would lead to the better permeation effect.And also,The larger particle size and porosity,could increase the unit seepage flow,and resulting in the better permeability.Considering both with permeation effect and rare earth leaching rate,the concentrations of ammonium acetate,ammonium tartrate and ammonium citrate were 1.00 wt.%,2.50 wt.%,0.70 wt,%respectively,and the permeability coefficients were 2.64×10-4cm/s,1.86×10-4cm/s,2.62×10-4cm/s,respectively.Furthermore,The maximum of permeability coefficients of ammonium acetate,ammonium tartrate and ammonium citrate appeared in p H=5.00,p H=6.00,p H=7.00,which were 2.99×10-4cm/s,1.90×10-4cm/s,2.69×10-4cm/s,respectively.The permeability coefficients of three carboxyl compounds were as followed:CH3COONH4>C6H5O7?NH4?3>C4H4O6?NH4?2.?2?The variation law of Zeta potential on clay mineral surface under different kinds and concentrations of solution,p H,experimental temperature,rare earth ore sample particle size were discussed.It showed that the property of the liquid and the rare earth sample property would have an effect on the Zeta potential value of the rare earth sample surface.The higher Zeta potential,the smaller thickness of the double electric double layer on the surface of the rare earth sample surface,the smaller permeability coefficient.The higher solution concentration,the higher the Zeta potential value on the rare earth sample surface.Ammonium acetate,ammonium tartrate and ammonium citrate appeared the minimum Zeta potential values at p H=5.00,p H=6.00,p H=7.00,which were-22.8mv,-27.38mv,-45.46mv,respectively.when the concentration of ammonium acetate was1.00 wt.%,the concentration of tartrate was 2.50 wt.%and the concentration of ammonium citrate was 0.70 wt.%,the effect of temperature on the Zeta potential on the surface of the rare earth sample surface was not obvious.With the increase of the grain size,the Zeta potential value of its surface was reduced,and the thickness of the electric double layer was thin,which leaded to the increase of macroscopic permeability coefficient.?3?The effects of ore sample size,the leaching agent types and concentration,temperature and p H on the surface chemical properties of rare earth ore sample were discussed.The results showed that when the particle size of rare earth ore sample was smaller than 0.106mm,the surface free energy was 62.365m J/m2,and the polar component was 64.96%?40.512m J/m2?.When the particle size of rare earth ore sample was in the range of 0.106?0.150mm,the surface free energy was 53.576m J/m2and the polar component was 59.28%?31.601m J/m2?.When the particle size of rare earth ore sample was in the range of 0.150?0.250mm,the surface free energy was 47.681m J/m2and the polar component was 54.04%?25.767m J/m2?.When the particle size of rare earth ore sample was in the range of 0.250?0.850mm,the surface free energy was42.814m J/m2and the polar component was 50.10%?21.447m J/m2?.It was indicated that the smaller grain size of the rare earth sample,the greater free energy of the surface,and the thicker water film thickness was formed on the surface of the rare earth sample surface during the permeation process,which meant that it was more unfavorable to the seepage of the liquid in the ore body.The decrease of the solution surface tension could enhance the wettability of the rare earth sample surface in the process of leaching the rare earth,so as to increase the water film thickness on the rare earth sample surface,and making the permeability coefficient smaller.The larger solution concentration,the smaller surface tension.The maximal value of the surface tension of the ammonium acid,tartaric acid and citric acid were at p H=5.00,p H=6.00 and p H=7.00,which were56.69 m N/m,57.80 m N/m and 58.28 m N/m,respectively,which were matched with the minimum point of the Zeta potential value and the maximum point of the permeability coefficient.With the increase of the temperature,the change of the surface tension value of the three carboxyl compounds was not obvious.The contact angle of the carboxyl compound on the surface of the rare earth sample was consistent with surface tension,and it was also in accordance with the permeability rule of leaching process.The above results show that both fluid properties and orebody properties would affect the permeability during the leaching of weathering crust elution-deposited rare earth ore with carboxyl compounds.Combining with these three considerations,ammonium acetate was the best leaching agent in the three carboxyl compounds.The optimum conditions for column leaching were as followed:the ammonium acetate concentration was 1.00 wt.%,the initial p H was7.00,the leaching temperature was 25?,and the permeability coefficient of leaching rare earth ore from weathering crust with ammonium acetate was 2.64×10-4cm/s. |
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