Study On The Mechanism Of Uranium And Thorium In Immersion And Leaching Experiment Of Associated Radioactive Waste Residue Of Rare Earth Ore

China is one of the largest countries with rare earths in the world.The exploitation of rare earth minerals produces a large amount of waste residue.The radionuclide-bearing rare earth slags stacked in open air are subjected to natural conditions such as weathering and rainfall,and radionuclides?U?Th,?are eluted into the ecosystem,causing huge hidden dangers to human health.The research object of this study is 4 kinds of rare earth ore wastes of different types,namely uranium thorium slag?S1?,neutralization slag?S2?,Sichuan rare earth?S3?and radium slag?S4?,and these 4 rare earth slags are The particle size classification process is divided into small particle size sieved slag and large particle size unscreened slag.The radioactivity specific activity of the rare earth slag was measured,and its radioactive level was analyzed.Static and dynamic leaching experiments were set up to study changes in the pH and uranium concentration of the leachate and the leachate,the amount of uranium leachate,and the leaching of rare earths.The influence of slag radionuclides U content,so as to get a general understanding of the release and migration of U in the four kinds of rare earth ores,and provide scientific basis for the scientific treatment of rare earth slag and prevention of radioactive pollution.The main conclusions of the experiment are as follows:?1?S1 and S3 are strongly acidic slags.S2 and S4 are weakly acidic and neutral slags,have similar pH with high water content.The order of the radionuclides specific activity of the four rare earth slags was radium slag?S4?>uranium&thorium slag?S1?>neutralization slag?S2?>Sichuan rare earth?S3?,radium slag has the strongest radiocative,Sichuan soil is the weakest.?2?Dynamic leaching experiment:during the first period of leaching,acid slags S1?S3?and S4 pH of the leached leachate of screening slag was smaller than that of unscreened slag,and screening slag leachate pH of alkaline slag S2 is always larger than unscreened slag in two leaching cycles.After the second period of leaching,the pH of the slag leachate of S1 and S3 unscreened is gradually smaller than the slag of the slag.S4 is the pH of the unscreened slag leachate which is greater than the sieving slag.The leaching cycle time interval has a certain recovery of slag acid precipitation.U concentration decreased with the increase of leaching amount.The concentration of leachate U from S1 and S3 slags?S1-G,S3-G?is significantly higher than that of slags?S1-WG,S3-WG?,and S2 and S4?S2-WG?.S4-WG)The concentration of the leachate U is higher than that of the slag?S2-G,S4-G?,but as the leaching time increases,the unconcentrated slag U concentration is higher than the sieving slag at different times.?3?Static immersion experiment:S1,S2,S3 pH increased in different degrees,S4 in the immersion time the pH change first rose and then decreased.With the increase of the soaking time,the pH value of the large particle size unscreened slag leachate is smaller than that of the small size sieved slag.The U concentration of the leaching solution of the four kinds of rare earth slag is basically the same,the overall trend is upward and there are two rapid and slow changes in the U concentration.In the leaching liquid of the same kind of slag of different particle sizes,the U concentration of S1 slag that has been sifted is always greater than that of unscreened slag,and that of S2,S3,and S4 is that the unscreened slag is greater than the slag that has been sieved.?4?In dynamic leaching experiment and static immersion experiment,the concentration of leaching liquid and leaching liquid ²³²Th was positively correlated with slag and leaching liquid and pH of leaching solution.When the leaching solution of the dynamic leaching experiment is weakly acidic and alkaline,the concentration of ²³²Th in the leaching solution will rise with the increase of pH.The concentration of ²³²Th in the leaching solution of the static immersion experiment increased with the increase of pH,whether the leaching solution was acidic or alkaline.?5?The uranium releases from the same or similar acid-alkaline slag during leaching and immersion experiments have similar laws.The maximum value of leaching of uranium in each month of leaching experiment occurred in March to June,and the amount of leaching was positively correlated with the simulated acid rain leaching.The time interval during the leaching cycle is beneficial to the recovery of U precipitation capacity,and the leaching amount of uranium in the leaching experiment is much larger than that in the immersion experiment.?6?The radionuclide content of rare earth slag changes after leaching.The specific activity of ²³⁸U,²²⁶Ra,²³²Th,and ⁴⁰K before leaching of uranium slag G?S1-G?is larger than that of leaching.The specific activity of ²³⁸U before leaching of slag?S4?is significantly larger than that of leaching,and slag of radium G?S4-G?is about 6 times lower than that before leaching after leaching experiment,slag WG?S4-WG?is reduced by about 10 times,and ²²⁶Ra?²³²Th,and ⁴⁰K are relatively stable.The specific activities of the remaining leaching slag ²³⁸U?²²⁶Ra?²³²Thand ⁴⁰K were all larger than those before leaching after leaching experiment.