Study On The Mechanism Of Inhibition Of Swelling And Inhibition Of Aluminum In Leaching Rare Earth Minerals From Weathered Crust Elution-deposited Rare Earth Ore By Carboxylic Ammonium Salt

Due to the rich middle and heavy rare earth?RE?,the weathered crust elution-deposited rare earth ore has high commercial value and broad application prospects.The rare earth minerals in this type of rare earth minerals are adsorbed on clay minerals in the form of hydration ions or hydroxyl hydration ions.The rare earth elements are usually enriched and recovered by chemical method through ion exchange.In the leaching process of weathered crust elution-deposited rare earth ore,exchangeable aluminum will be leached by the extractant and become the main impurity ions in the mother liquor of rare earth,which affects the subsequent processing technology and the quality of rare earth products.In the meantime,clay minerals in seam will expand because of water absorption in the process of ion-adsorption type rare earth ores's situ extraction,the phenomenon of geological disasters like landslide happen frequently for this reason.At present the commonly used on industrial leaching agent for ammonium sulfate,ammonium sulfate leaching rare earth ions can effectively but could not inhibit the leaching of aluminum,this paper adopts the column leaching way to simulate in-situ leaching technology,choose three carboxylic compounds such as ammonium acetate,tartaric acid and citric acid ammonium respectively as leaching agent,compared aluminum leaching suppression effect with ammonium sulfate,the inhibitory effect of the leaching agent on the swelling of clay minerals was also investigated.The main research contents and results are as follows:?1?The mineralogical study of weathered crust leaching rare earth ore is carried out,the distribution of rare earth and aluminum in rare earth ores was determined by EDTA volumetric method,atomic absorption spectrophotometry and fractional extraction method,and the contents of rare earth and aluminum leached in the ore samples were calculated;X-ray diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscope?SEM?and Fourier infrared spectrometer?ftir?were used to analyze the spectral characteristics of the ore.Analysis test results show that the content of rare earth in the whole phase of the ore is 0.09%,the content of rare earth in ionic phase is 0.08%,and the content of middle heavy rare earth is 46.69%.The content of heavy rare earth yttrium accounts for 30.76%of the total rare earth oxide,69.59% of the exchangeable phase rare earth and 69.65%of the exchangeable phase aluminum exists in the particle size of-0.25mm with a weight ratio of 42.61%.The content of halloysite and kaolinite in weathered clay is 64.32%and 25.67%respectively.The clay minerals are mainly composed of silicoaluminate,iron,potassium,magnesium,calcium and other compounds.Due to the highest content of elosite in mineral clay minerals,it can be considered that the exchangeable cations and adsorbed rare earth ions are mainly attached to halloysite.?2?The effects of concentration and temperature of p H,leaching on aluminum leaching were discussed.Experimental results show that when the concentration of ammonium sulfate reaches 1.50wt%,ammonium acetate reaches 1.00wt%,ammonium tartarate reaches 2.50wt%,and ammonium citrate reaches 1.00wt%,the leaching rate of rare earth has reached equilibrium.On the condition that the leaching rate of rare earth is not affected,when the concentration of ammonium acetate reaches 1.50wt%,the leaching rate of aluminum is only 12.16%,when the concentration of ammonium tartrate reaches2.50wt%,the leaching rate of aluminum is 36.37%,and when the concentration of ammonium citrate reaches 1.50wt%,the leaching rate of aluminum is 45.95%.Among the three kinds of carboxylate ammonium salts,ammonium acetate has the best effect in inhibiting aluminum leaching.When the temperature is 30?and p H=6.8?7,the inhibition rate of 1.50 wt%ammonium acetate on aluminum can reach 12.16%.?3?On the condition that the leaching rate of rare earth is not affected,intelligent dilatometer and Zeta potentiometer were used to investigate the inhibiting effect of the leaching agent on the swelling of clay minerals in weathered crust elution-deposited rare earth.The test results show that all three kinds of ammonium carboxylate salts could inhibit the swelling of clay minerals.When the concentration of leaching agent reached2.00wt%,the results showed that the swelling of clay minerals could be inhibited by three kinds of ammonium carboxylate salts.The linear expansion rate of clay minerals is only1.31%in ammonium acetate solution,3.24%in ammonium tartrate solution and 3.71%in ammonium citrate solution.After leaching with carboxylate ammonium salt,the swelling performance of tailing was reduced,and the swelling rate of tailing after reaction with2.00wt%ammonium acetate was only 1.81%,after leaching with 2.00wt%ammonium tartrate and 2.00wt%ammonium citrate,the water absorption of tailings was reduced to a certain extent,and the expansion rate was 4.71%and 5.15%respectively.In the four systems of clay-ammonium sulfate,clay-ammonium acetate,clay-ammonium tartarate and clay ammonium citrate,when the leaching concentration was 2.00wt%,the Zeta potential of the clay-ammonium acetate system was-13.02 m V,the Zeta potential of the clay-ammonium tartrate system was-19.34 m V,the Zeta potential of the clay-ammonium citrate system was-19.96 m V,and the Zeta potential of the clay-ammonium sulfate system was-20.68 m V.The Zeta potential test results were consistent with the swelling test results.?4?X-ray diffraction analysis of leached tailings shows that the leaching experiment did not change the interlayer structure of clay minerals,and the interlayer did not form interlayer complex of halloysite,which indicated that the hydration expansion of clay minerals in weathered crust leached rare earth minerals was mainly the hydration on the outer surface,and did not affect the crystal layer structure.With the leaching of carboxylate ammonium salt,the half height width of characteristic diffraction peak of kaolinite group minerals is reduced.According to the scherer formula,the size of clay particles becomes larger,the flocculation ability of clay minerals increases,and the swelling property is inhibited.?5?Infrared spectrum analysis of leached tailings shows that the strength of the absorption peak of hydroxyl group on the inner surface of halloysite after reaction with the extractant was weakened,indicating that a new hydrogen bond was formed between elosite particles,which had a direct impact on the surface hydroxyl group(3698cm^-1)of halloysite,while a smaller impact on the internal hydroxyl group(3620cm^-1).The intensity of peaks around 911cm^-1 changed to some extent,and two new absorption peaks appeared in the infrared spectrum of halloysite after the reaction with carboxylate ammonium salt,respectively 1400cm^-1 and 1560cm^-1,which could be considered as caused by the vibration of carbonyl group,indicating that acetate root,tartarate root and ammonium citrate entered into the clay mineral particles to bridge the clay mineral.