Study On The Technology Of Separation Of Lanthanum From Acid Leaching Solution Of Fly Ash

Rare earth elements have important applications in the metallurgical industry, electronics, telecommunications, agriculture, military and other fields, which enjoy the "industrial MSG" reputation. In order to obtain high-purity individual rare earth products, the usual method is to futher separate the rare earth mixture from the rare earth deposits, which is exploited from the mine. Although China’s rare earth resources are abundant, the reserves are still limited. Furthermore, the current extraction agents which commonly used in industry are ammoniated. It will produce large amount of ammonia nitrogen waste, which heavily polluted environment. Since China is a large country of coal consuming, and therefore generats a large amount of fly ash every year. It is found that in some areas, the coal fly ash has high content of rare earth elements, and some even reaches the industrial grade, and they can be used as the rare earth resources. In this thesis, the starting solution was the pickle liguor which was obtained after extracting the aluminum from the fly ash in Shenhua Company, and extract the rare earth elements from the pickle liguor. The obtained mixture of rare earth concentrate was used as the preliminary solution. There are two methods of separating the lanthanum element from the preliminary solution were designed, namely the multi-stage extraction and impregnation resins methods. Both approaches used unpurified Cyanex272 as the extraction solvent because it can be used without saponification, consequently it will effectively reduce the pollution.Firstly, this paper studied the multi-stage countercurrent extraction separation for extraction of lanthanum. In the hydrochloric acid system with unpurified Cyanex272 as extracting agent and sulfonated kerosene as diluent, we discussed the effect of the concentration of the organic phase, pH value of the aqueous phase of the extracted equilibrium, A/O, the shock time and standing time on the distribution ratio and separation coefficient of La, Ce, Nd, which have higher levels in the pre-solution. The best experimental conditions for the extraction of lanthanum:The volume fraction of extractant is 30%, pH value of the aqueous phase of the extracted equilibrium is 2.2, A/O is 1:1, the shock time is 3 min and the standing time is 15 min. Optimum extraction stages of the separation of lanthanum under the preferred conditions determined by Graphic theory is 3 stages, we simulated three-stage countercurrent extraction with three separation funnels to separate La from preliminary solution, enriching lanthanum in the raffinate. The finally purity of lanthanum in the obtained solution is more than 90%, and the extraction rate of lanthanum is more than 85%.Considering the problem of extraction solvent recycling, using a concentration of 0.25mol/L hydrochloric acid reextraction. Reextraction rate can reach 99%, after reextraction the extracting agent can be reused. Experiment results show that after repeated using the extraction solvent 4 times extraction rate decreased slightly because of the loss of a small amount of extraction solvent every completion of the extraction. As long as added a small amount of extracting solvent, it can be used again.This paper also studied the process conditions of Cyanex272 resin-impregnated method to separation lanthanum ion and prepared Cyanex 272 impregnating resin. The static adsorption saturation capacity of Cyanex272 impregnating resin was tested and the effect of pH of adsorption process on the adsorption saturation capacity was discussed, we found that adsorption capacity at pH 4.5 is suitable. At pH 4.5, the adsorption reached equilibrium in 40 minutes. Adsorption capacity of Cyanex272 impregnating resin is about 8.7mg/g dry resin when adsorption reached equilibrium.The paper discussed the factors of dynamic adsorption separation conditions of three elements (La, Ce, Nd) and chose the best conditions of separation of lanthanum. The factors are:pH value, flow rate of the initial rare earth solution, resin column packing height, concentration and flow rate of elution hydrochloric acid, loaded amount of resin and so on. The best conditions are as followes:the resin loading rate is 0.8%, flow rate of the initial rare earth solution is 1ml/min, the resin column packing height is 120 mm (resin column diameter is 20mm), the concentration of elution hydrochloric acid is 0.00625mol/L, the flow rate of eluent hydrochloric acid is 1ml/min. In optimum conditions, more than 95% purity of lanthanum in the solution can be obtained, and the extraction rate of lanthanum can be more than 90%. If extraction rate of La is more than 99%, the purity of the solution of lanthanum is also can reach 90%.It was also considered that the recycling times of Cyanex272resin-impregnated, after ten cycles of use, the amount of resin mass is reducd to 1.94%, the amount of resin adsorption capacity is reducd to 0.54mg/g dry resin. It is shown that Cyanex272 impregnated resin can be recycled at least more than ten times.Compared multistage extraction method with resin-impregnated method in separation lanthanum from hydrochloric acid solution, both processes can achieve the purpose of lanthanum separation, but resin-impregnated method is better than the multi-stage extraction.