D2EHPA/氯化钠强化萃取赤泥酸浸液中钪及抑制铁的实验研究

Enhanced extraction of scandium and inhibiting of iron from acid leaching solution of red mud by D2EHPA and sodium chloride

本文提出利用D2EHPA(P204)、磷酸三丁酯(TBP)和氯化钠(NaCl)从赤泥酸浸液中选择性萃取钪的方法。研究了P204浓度(XP204)、氯化钠浓度(C_(NaCl))、pH值、反应时间、搅拌速度和O/A等参数对酸浸液中钪萃取与铁分离效果的影响。利用傅立叶变换红外光谱(FT-IR)和萃取热力学理论阐述了浸出液中钪的萃取机理,通过溶液热力学理论解释抑制铁萃取的作用机制。结果表明:在溶液pH值为1.2、搅拌速度为200 r/min、反应时间为6 min、C_(NaCl)为75 g/L、X_(P204)为0.75的条件下,钪、铁的单级萃取率和β(Sc/Fe)分别为99.1%、9.4%和1061.2,钪与铁的分离效果较好。Sc─O振动吸收峰的形成有利于P204萃取赤泥酸浸液中的钪。通过向赤泥浸出液中添加NaCl,溶液中铁离子会形成[FeCln]^(3−n)络合物,增加氯离子浓度,络合物中n值升高,[FeCln]^(3−n)的价态降低,从而抑制了P204萃取浸出液中的铁。依据McCabe-Thiele图谱进行了三级逆流萃取实验,该反应的吉布斯自由能变为−5.93 kJ/mol,焓变为23.45 kJ/mol,熵变为98.54 J/(mol·K),表明该过程可自发进行且为吸热反应,适当增加反应温度有利于钪的萃取回收。

D2EHPA(P204),tri-butyl-phosphate(TBP)and sodium chloride(NaCl)were attractive for selective extraction of scandium from acid leaching solution of red mud.The extraction parameters of P204 concentration(X_(P204)),NaCl concentration(C_(NaCl)),pH value,reaction time,stirring speed and O/A were investigated to extract scandium and separate iron from the acid leaching solution.The extraction mechanism was analyzed by Fourier transform infrared spectroscopy(FT-IR)and thermodynamic theory.The single-stage extraction efficiency of scandium,iron andβ(Sc/Fe)were 99.1%,9.4%and 1061.2,respectively,with C_(NaCl) of 75 g/L and XP204 of 0.75 at solution pH value of 1.2 and stirring speed of 200 r/min for 6 min,in which a good separation effect of scandium and iron was obtained.The vibration absorption peak Sc─O was contributed to the extraction of scandium with P204.The complex[FeCln]^(3−n) existed in the solution with adding NaCl into the acid leaching solution.The value of n was higher and the valence state of the complex[FeCln]^(3−n) was lower with an increase of chloride concentration,which restricts the extraction efficiency of iron with P204.The extraction of three stages in the counter-current simulation experiments was carried out according to the McCabe-Thiele diagram.Gibbs free energy change(ΔG)of−5.93 kJ/mol,enthalpy change(ΔH)of 23.45 kJ/mol and entropy change(ΔH)of 98.54 J/(mol·K)were obtained in the solvent extraction proces,which indicate that the extraction reaction is easily spontaneous and endothermic and a proper increase of temperature is conducive to the extraction of scandium.