Process Optimization Of Leaching Ion Adsorption Rare Earth By Calcium Chloride And Aluminum Sulfate In Stages

After developing for decades,a great achievements have been made for the high efficiency leaching process of ion adsorption rare earth（IARE）.However,with the increase of development demand and environmental awareness,the exploitation of IARE is seriously restricted due to the problems such as ammonia nitrogen pollution and soil erosion.Therefore,it is urgent to develop an novel extraction process of IARE to meet the requirements of medium and heavy rare earths.In this paper,a new process for leaching IARE by calcium chloride and aluminum sulfate solutions in stages is successively proposed by comparing the leaching efficiency（LE）of several electrolyte solutions and the corresponding change of zeta potential of clay mineral particles in tailings.Meanwhile,lime water eluting is used to protect the tailings from pollutant emission and soil erosion.Selecting three raw ores as representative,leaching conditions,such as the types and concentrations as well as the dosages of leaching agents,the dosage ratio of different reagents,the consumption of lime and water in tailing cure are optimized with respecting to the LE of IARE,the concentration of aluminium,uranium and thorium,and the Zeta potential of clay minerals.The results show that the LE of IARE by several electrolytes follows the order of aluminum sulfate>ammonium sulfate>magnesium sulfate>magnesium chloride>calcium chloride.Therefore,the requirements of high-efficiency leaching IARE can not be met only by calcium chloride,but can realized by the cooperation strengthen of aluminum sulfate.When leaching IARE by calcium chloride and aluminum sulfate in stages with a overall liquid-solid ratio of 1:1,the suitable concentration and p H of calcium chloride solution are 0.3-0.6N and 6.5-7.5respectively,the concentration of aluminum sulfate is between 0.1-0.2N,and liquid-solid ratios of calcium chloride and aluminum sulfate solutions to ore weight are 0.6-0.8 and 0.2-0.4 respectively.With these conditions,more than 90%of IARE enter the leachate of calcium chloride and more than 85%of the uranium enter the leachate of aluminum sulfate.The absolute values of the zeta potential of clay minerals after leaching are lower than that of the original ore.Especially,the zeta potential of clay minerals in the tailings leached by aluminum sulfate is close to 0 m V,which is beneficial to reduce soil erosion or landslide collapse due to soil agglomeration.The new process can improve both the LE of IARE and the safety of tailings.More importantly,the leaching agent used in this process can be extracted from the waste water and residue in rare earth extraction separation process,and is beneficial for the utilization of waste resources.At the same time,pollutants emission and soil erosion tailings can be reduced by eluting with lime water.Therefore,tailings leached by different electrolytes were eluted by lime and water via column eluting method.The dependence of pollutants emission amount on the dosages of deionized water and lime water,and relationship with the type and amount of leaching reagents,as well as the occurrence form of residual Al³⁺in tailings before and after tailing eluting were investigated.The results show that compared with the water eluting of tailings after ammonium sulfate and magnesium sulfate leaching,the lime water eluting can reduce the water amount by 30%.After leached by calcium chloride,lime water eluting can reduce the water amount by 45%.Only controlling the p H of elutent between 6 and 9,the NH₄⁺content in elutent of tailing leached by ammonium sulfate can be reduced to below 25μg/m L,and the Al³⁺content in elutent of tailing leached by aluminum sulfate can be reduced to less 1μg/m L.After eluting with lime and water,the water-soluble aluminum content in tailings leached by calcium chloride and aluminum sulfate in stages is close to the original value of their raw ores.However,the content of aluminum hydroxide was increased by2.4–3.2 times.These results demonstrated that the existing form of aluminum in tailings is water insoluble,the content of aluminum in elent can meet the requirement of water emission.Therefore,lime water eluting is a good method for curing the security of tailings after IARE leached by various electrolyte solutions,and shows a good application prospect in the exploitation of IARE resource.