| Weathered crust elution-deposited rare earth ore is the main source of medium and heavy rare earth in the world.In industry,ammonium salt is used as leaching agent to recover rare earth by heap leaching or in-situ leaching process.However,a large amount of ammonium salt leaching agent will remain in the ore body after the mine is closed by heap leaching or in-situ leaching,and its slow release will seriously affect the water system ecology in the mining area,and treatment is imminent.In this paper,the occurrence state of residual ammonium in weathered crust elution-deposited rare earth ore was studied,and the elution process of residual ammonium salts in rare earth ores was simulated by column leaching.The four common metal salts,namely monovalent potassium salt,bivalent magnesium salt,bivalent calcium salt and trivalent iron salt,were respectively used as eluting agents.The effects of eluent concentration,pH,flow rate and temperature on the elution process of residual ammonium salt in rare earth ore were discussed.The elution mechanism of residual ammonium salt was studied.This study will provide a theoretical basis and technical support for the enhancement of the efficient elution process of residual ammonium in the leaching sites of weathered crust elution-deposited rare earth ore.The main research contents and results are as follows:(1)The occurrence states and distribution characteristics of residual ammonium in the weathered crust elution-deposited rare earth ore leaching sites were studied.The results showed that residual ammonium salts mainly existed in the form of watersoluble ammonium,exchangeable ammonium and fixed ammonium.The content distribution of residual ammonium salt follows: middle-layer ore sample > deep-layer ore sample >> shallow ore sample.And the total content of water-soluble ammonium and exchangeable ammonium is about 95%,which is the main source of ammonia nitrogen pollution in ore leaching sites.The results laid the foundation for the use of different metal salts to elute residual ammonium salts.(2)The effects of potassium ion concentration,anion species,liquid-solid ratio,eluting agent pH,flow rate and temperature on the elution efficiency of residual ammonium were discussed.The results show that temperature and anion have little effect on the elution efficiency of residual ammonium,while potassium ion concentration,pH,liquid-solid ratio and flow rate have a greater effect on the elution efficiency of residual ammonium.The optimum elution conditions of residual ammonium are 0.06 mol/L of potassium ion concentration,4-6 of potassium salt solution pH,2:1 of liquid-solid ratio,0.6 m L/min of flow rate and 25 ℃ of elution temperature.At this time,the elution efficiencies of potassium sulfate,potassium chloride and potassium nitrate for residual ammonium are 95.68%,95.78% and 95.75%,respectively.The elution kinetics show that the three anions have different elution velocity for residual ammonium salts.The shrinking unreacted core model is used to fit the elution kinetics curves.The results show that the elution process of residual ammonium in rare earth ore tailings with potassium salts is controlled by the inner particle diffusing.The elution kinetic equations related to the temperature and potassium ion concentration are established.It is found that the apparent rate of elution residual ammonium follows the order of potassium chloride > potassium nitrate >potassium sulfate.The empirical reaction order and reaction activation energy follows the order of potassium sulfate > potassium nitrate > potassium chloride.(3)The effects of magnesium ion concentration,anion species,liquid-solid ratio,eluent pH,flow rate and temperature on the elution efficiency of residual ammonium were discussed.The results show that temperature and anion have little effect on the elution efficiency of residual ammonium,while magnesium ion concentration,pH,liquid-solid ratio and flow rate have a greater effect on the elution efficiency of residual ammonium.The optimum elution conditions of residual ammonium are 0.1 mol/L of magnesium ion concentration,2:1 of liquid-solid ratio,4-6 of magnesium salt solution pH,0.6 m L/min of flow rate and 25 ℃ of elution temperature.At this time,the elution efficiencies of magnesium sulfate,magnesium chloride and magnesium nitrate for residual ammonium salts are 95.17%,95.45% and 95.66%,respectively.The elution kinetics show that the three anions have different elution velocity for residual ammonium salts.The shrinking unreacted core model is used to fit the elution kinetics curves.The results show that the elution process of residual ammonium in rare earth ore tailings with magnesium salts is controlled by the inner particle diffusing.The elution kinetic equations related to the temperature and magnesium ion concentration are established.It is found that the apparent rate of elution residual ammonium follows the order of magnesium nitrate > magnesium chloride > magnesium sulfate.The empirical reaction order and reaction activation energy follows the order of magnesium sulfate > magnesium chloride > magnesium nitrate.(4)The effects of calcium ion concentration,anion species,liquid-solid ratio,eluent pH,flow rate and temperature on the elution efficiency of residual ammonium were discussed.The results show that temperature and anion have little effect on the elution efficiency of residual ammonium,while calcium ion concentration,pH,liquidsolid ratio and flow rate have a greater effect on the elution efficiency of residual ammonium.The optimum elution conditions of residual ammonium are 0.1 mol/L of calcium ion concentration,2:1 of liquid-solid ratio,4-6 of calcium salt solution pH,0.6m L/min of flow rate and 25 ℃ of elution temperature.At this time,the elution efficiencies of calcium chloride and calcium nitrate to residual ammonium are 91.85%and 92.94%,respectively.The elution kinetics show that the two anions have different elution velocity for residual ammonium.The shrinking unreacted core model is used to fit the elution kinetics curves.The results show that the elution process of residual ammonium in rare earth ore tailings with calcium salts is controlled by the inner particle diffusing.The elution kinetic equations related to the temperature and calcium ion concentration are established.It is found that the apparent rate of elution residual ammonium follows the order of calcium nitrate > calcium chloride.The empirical reaction order and reaction activation energy follows the order of calcium chloride >calcium nitrate.(5)The effects of iron ion concentration,anion species,liquid-solid ratio and temperature on the elution efficiency of residual ammonium were discussed.The results show that temperature and anion have little effect on the elution efficiency of residual ammonium,while iron ion concentration and liquid-solid ratio have a greater effect on the elution efficiency of residual ammonium.The optimum elution conditions of residual ammonium are 0.06 mol/L of iron ion concentration,2:1 of liquid-solid ratio,and 25 ℃ of elution temperature.At this time,the elution efficiencies of iron chloride and iron nitrate for residual ammonium are 97.47% and 97.53%,respectively.The elution kinetics show that the two anions have different elution velocity for residual ammonium.The shrinking unreacted core model is used to fit the elution kinetics curves.The results show that the elution process of residual ammonium in rare earth ore tailings with iron salts is controlled by the inner particle diffusing.The elution kinetic equations related to the temperature and iron ion concentration are established.It is found that the apparent rate of elution residual ammonium follows the order of iron nitrate > iron chloride.The empirical reaction order and reaction activation energy follows the order of iron chloride > iron nitrate.Both FT-IR and XPS characterization results prove that most of the residual ammonium salts were effectively removed.(6)The effects of magnesium and calcium salts with relatively low economic cost on the elution process of residual ammonium in the actual ore tailings of weathered crust elution-deposited rare earth ore leaching sites were studied.The results show that the elution velocity of magnesium sulfate to residual ammonium for the middle tailings is faster,and the elution velocity of magnesium nitrate to residual ammonium for the deep tailings is faster.Magnesium chloride and calcium chloride have relatively little effect on the elution velocity of residual ammonium,and the elution velocity of calcium nitrate to residual ammonium for middle and lower tailings is faster.Moreover,the elution efficiency of magnesium salts and calcium salts to the residual ammonium salts for most of the tailings are above 95% and 91%,respectively,confirming that both magnesium salts and calcium salts can effectively elute the residual ammonium from rare earth ore leaching sites tailings. |
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