| Ion-adsorption rare earth ore contains the strategic resources of mid-heavy rare earths.At present,conventional in-situ leaching of ion-adsorption rare earth ore using ammonium salt is widely used in industry,but there is a serious problem of ammonia-nitrogen pollution.Therefore,our group proposed a new technology with magnesium salt leaching system.With this new technology,ammonia-nitrogen pollution can be eliminated from the source.However,leaching loss of calcium and soil acidification still exists in ore body after magnesium sulfate leached.For the above problems,ion-adsorption rare earth tailings was taken as an object,and deionized water,calcium chloride solution and lime water were reasonably selected as green leaching agents.Then,the leaching behaviors of calcium and magnesium were investigated,and the chemical leaching and repairing technology of the rare earth tailings leached with magnesium sulfate was proposed.The main contents are as follows:(1)The extraction and analysis methods of calcium and magnesium in different phases were studied.When the liquid-solid ratio of decarbonized water was 10:1,the water soluble calcium and magnesium in the tailings could be completely leached after leaching twice.Meanwhile,the tailings was repeatedly leached there times under the 1 mol/L ammonium acetate solution with the liquid-solid ratio of 9:1,and the water soluble and exchangeable calcium and magnesium could be leached completely.The contents of water soluble,exchangeable calcium and magnesium in the tailings can be obtained by subtraction using the results of different leaching solutions.(2)The transformation and leaching behaviors of calcium and magnesium in the tailings leached by deionized water were studied.Deionized water was used for the leaching of the rare earth tailings leached with ammonium sulfate(NH4+-leached tailing)and magnesium sulfate(Mg2+-leached tailing),and the concentrations of the cations of Mg2+,Ca2+ or NH4+in the leaching solutions decreased almost exponentially.For the NH4+-leached tailing,the content of hydrolyzable nitrogen was as high as 205.0 mg/kg even when the liquid-to-solid ratio was increased to 1.67,and serious loss of the readily-available calcium and magnesium occurred.For the Mg2+-leached tailing,the contents of readily-available magnesium and hydrolyzable nitrogen were 158.1 mg/kg and 38.1 mg/kg,respectively,which meets the requirements for plants.Serious loss of the readily-available calcium also occurred.Moreover,the problem of acidification was not solved since the pH values of both of the leached tailings were below 5.50.(3)The transformation and leaching behaviors of calcium and magnesium in the Mg2+-leached tailing leached by CaC12 solutions were studied.CaC12 solutions were used for leaching the Ng2+-leached tailing,and the concentration of CaCl2 solutions was 0.05-0.25 mol/L.With the leaching of CaCl2 solutions,the leaching curves of Mg2+were similar to that in the deionized water leaching process,and the leaching curves of calcium indicated that the leaching reaction gradually reached equilibrium as leaching progressed.The contents of the readily-available calcium in the tailings were 650.1-2333.0 mg/kg with the CaC12 concentration of 0.05-0.25 mol/L,and most of them was in the form of water soluble phase.But serious loss of magnesium occurred owing to the enhanced ion-exchange of calcium salt solutions,and the problem of acidification still exists.(4)The transformation and leaching behaviors of calcium and magnesium in the Mg2+-leached tailing leached by lime water were studied.0.02 mol/L lime water was were used for leaching the Mgig-leached tailing,the leaching curve of Mg2+ was similar to that during the deionized water and calcium chloride solution leaching,but little Ca2+was detected in the leaching solution because most of Ca2+ is electrostatically adsorbed on the tailings.The contents of the exchangeable magnesium in the leached tailings was increased,which might be attributed to back-adsorption of Mg2+ with increasing the pH values.When the liquid-to-solid ratio was 0.80,the contents of readily-available magnesium and calcium were 104.4-207.6 mg/kg and 201.7-1426.3 mg/kg,respectively.The pH range of the leached tailings was 5.50-7.75,and the mass ratio of calcium to magnesium was 1.0-13.7.Thus the problem of acidification and nutrient imbalance was solved.(5)The chemical leaching and repairing technology of Mgig-leached tailing was researched and optimized to reduce material consumption and improve leaching efficiency.The stepwise leaching with deionized water and lime water was used.When the liquid-solid ratio of deionized water and lime water was 0.13 and 0.67,the pH range of the leached tailings was 5.82-7.90,and the contents of readily-available magnesium and calcium were 122.5-206.2 mg/kg and 177.9-1282.3 mg/kg,respectively.At this time,the stepwise leaching can not only solve the problem of acidification and nutrient imbalance,but also rapidly realize the repair of Mg2+-leached tailing. |
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