The Leaching Research On Difficult-to-Infiltrate Weathered Crust Elution-Deposited Rare Earth Ore

The weathered crust elution-deposited rare earth ore is rich in medium and heavy rare earths,and its efficient mining has great commercial value and strategic significance.At present,ammonium salt is mainly used as a leaching agent in industry,and rare earths are recovered by heap leaching or in-situ leaching.There are more mines with poor permeability found in actual mining,which results in lower mine production efficiency or difficult-mined-mines.In this paper,we studied the permeation law of ammonium salt solution as leaching agent in the ore body for such difficult-to-infiltrate weathering crust elution-deposited rare earth ore,and proposed to improve the permeation velocity of leaching agent in difficult-to-infiltrate weathering crust elution-deposited rare earth ore body by changing the initial moisture content of ore and adding the leaching-aid reagent.The effects of the initial moisture content of ore and the leaching-aid reagent on the leaching process of difficult-to-infiltrate weathering crust elution-deposited rare earth ore were discussed in detail to enrich the theoretical foundation of difficult-to-infiltrate weathering crust elution-deposited rare earth ore and provide a scientific basis for strengthening rare earth leaching and lowing impurities leaching out from difficult-to-infiltrate weathering crust elution-deposited rare earth ore.The main research contents and results are as follows:(1)The effects of ore loading height,differential pressure and initial moisture content of ore on the infiltration process of the leaching agent were investigated.It is found that the seepage of the leaching agent solution in the ore body is in accordance with Darcy's law.With the increases of initial moisture content,height of ore loaded and differential pressure,the permeation velocity increases.With the decrease of height of ore loaded,increase of initial moisture content and increase of differential pressure,the time of forming the steady flow field decreases.(2)The effect of initial moisture content of ore on the leaching process of difficult-to-infiltrate weathering crust elution-deposited rare earth ore was investigated.The results show that the initial moisture content effectively increasesthe leaching velocity of rare earth(RE)and aluminum(Al)and has no effect on the leaching efficiency of RE and Al.The optimum leaching conditions are 20 % of initial content of ore,0.24 mol/L of ammonium concentration,1:1 of liquid-solid ratio and5.5~6.0 of initial leaching agent pH.At this time,the leaching rates of rare earths and aluminum were 95.35 % and 96.46 % respectively.The effect of initial moisture content of ore on the leaching dynamics of RE and Al were analysis by kinetic equations.The results show that the initial moisture content effectively increases the leaching velocity of RE and Al and the leaching process of rare earth and aluminum controlled by internal diffusion kinetics.The effect of the initial moisture content of ore on the mass transfer process of RE and Al was studied by using the theory of chromatography.The results show that the higher the initial moisture content,the smaller the theoretical plate height(HETP)and the higher the leaching and mass transfer efficiency of RE and Al.(3)The assisted leaching effects of ammonium formate,hydroxypropylmethyl cellulose and sesbania gum were compared.The results show that the ammonium formate has better effect of assisting leaching.With ammonium formate was used as leaching-aid agent,the effects of the concentration of ammonium formate,leaching temperature,liquid-solid ratio and pH of leaching solution on the leaching rate of rare earth and aluminum were investigated.The results show that increasing the compound concentration of ammonium formate,leaching temperature and liquid-solid ratio can effectively increase the leaching rate of rare earth.At the same time,it was also found that ammonium formate can effectively inhibit the leaching of Al.When the concentration of ammonium formate is 0.032 mol/L,the leaching rate of Al is only38.86 %,which is reduced by 57.60 % compared with 96.46 % for leaching without ammonium formate,but the lower pH would reduce the aluminum inhibition effect of ammonium formate.Dynamics model was used to analyze the kinetics of ammonium formate assisted leaching process.The results show that increasing the compound concentration of ammonium formate and leaching temperature can effectively increase the leaching velocity of rare earth,and the leaching process of RE and Al controlled by internal diffusion kinetics.The activation energy of RE leaching reaction is 15.83 kJ/mol,andthe activation energy of Al leaching reaction is 9.60 kJ/mol.The effect of ammonium formate used as leaching-aid agent on the mass transfer process of RE and Al was investigated using the theory of chromatography.The results show that the higher the leaching temperature and the greater the liquid-solid ratio,the smaller the HETP and the higher the mass transfer efficiency of RE and Al.(4)The inhibition mechanism of aluminum leaching by ammonium formate was studied.It was found that in the range of pH 5.5-8.0,ammonium formate converted the ion-exchanged aluminum to the adsorbed hydroxy aluminum and then stayed in the tailings without being leached,thereby significantly reducing the leaching rate of Al.The above results show that the initial moisture content and the ammonium formate as a leaching-aid agent,can effectively accelerate the leaching velocity of rare earth during the mining process of difficult-to-infiltrate weathering crust elution-deposited rare earth ore,significantly shorten the production cycle,and increase production efficiency.At the same time,ammonium formate can effectively inhibit the leaching of impurity aluminum from rare earth ore,reduce the cost of later removal of impurities,and increase the purity of rare earths.