Alkaline Leaching Of Indium In Indium Zinc Ferrite Under Ultrasonic-Microwave Field Action

Indium is a rare scattered metal with excellent properties,which is widely used in aerospace,electronics and energy fields.Since there is no separate deposit,indium is mainly extracted from non-ferrous metal smelting leaching slag.Among them,indium in the form of interstitial and substitutional solid solution exists in the zinc ferrite lattice to form indium zinc ferrite(Zn Fe_2-xIn_xO₄).In the process of acid leaching indium from slag,there are problems such as many impurity components,difficult separation,and long process flow.The alkali leaching method can effectively reduce the accompanying components of indium.However,the lattice structure of indium zinc ferrite is stable,and it is difficult to effectively leaching indium by conventional alkali leaching,and external field strengthening is an effective method.Based on this,this paper uses ultrasonic and microwave external fields to carry out alkaline-enhanced leaching of indium zinc ferrite,and studies the influence of different processes on its leaching.The results are as follows:（1）The optimum process conditions for the preparation of indium zinc ferrite are the calcination temperature of 900℃and the time of 2 h.The maximum solid solution amount of indium in the zinc ferrite lattice is x=0.1;when the solid solution amount is higher than x=0.2,indium cannot be completely dissolved in the lattice.In this paper,the leaching raw material,ω（In）=4%indium zinc ferrite is irregular spherical with an average particle size of 0.5-1μm.（2）The reaction of alkaline leaching of indium from indium zinc ferrite includes the solid solution release of indium and the dissolution of In（OH）₃.Without an external field at 25℃,the alkaline leaching reaction of indium proceeded slowly,and the leaching rate of indium was only 20.5%in 150 min.Under the ultrasonic field,the leaching rate of indium reached 30.2%in 30 min;if the ultrasonic time continued to increase,the leaching rate decreased due to the decomposition of the indium salt.The effect of ultrasonic external field on the alkaline leaching of indium is mainly reflected in its cavitation vibration and heating effect.The optimal conditions under ultrasonic field:leaching time 30 min,solid-liquid ratio 1:30 g/m L,ultrasonic power 1000 W,sodium hydroxide concentration 11 mol/L.Although ultrasonic alkali leaching released part of the indium from the lattice,it did not collapse the octahedral lattice of zinc ferrite.（3）At 50℃in a water bath,the leaching reaction basically tends to the limit at 30min,and the leaching rate of indium is 33.5%,which is close to the effect of ultrasonic field.Compared with 25℃（20.5%）without external field,the effect of reaction temperature on alkaline leaching of indium is obvious.Continue to increase the leaching time to 90 min,and the leaching rate is greatly reduced due to the decomposition of the indium salt.Under the microwave field,the leaching rate of indium reached 51.25%with the power of 500 W and 90 min;Due to the intermittent nature of the microwave field,the leaching rate of indium shows a dynamic fluctuation and rising trend;and the selective action of microwaves makes the indium salt produced more stable,and the leaching rate will not drop significantly.Alkaline leaching of indium does not require high microwave power,and the leaching rate is basically unchanged within 100 W-450 W.The optimal conditions under microwave field:reaction temperature 40℃,solid-liquid ratio 1:30 g/m L,sodium hydroxide concentration 11 mol/L,continuous microwave action for 5 min or intermittent microwave action for 90 min.Although microwave alkaline leaching can release indium from the lattice,it does not collapse the octahedral lattice of zinc ferrite.（4）Under the superimposed compound field,the indium leaching rate showed a fluctuating trend,up to 34.5%,which was not significantly improved compared with the single-field leaching.Under the sequential compound field,the leaching rates of ultrasonic followed by microwave and microwave followed by ultrasonic are not high,less than 20%,and the strengthening effect on alkaline leaching of indium is small.（5）The optimum kinetic model for alkaline leaching of indium at 25℃without external field and ultrasonic field is the Avrami model,the unreacted nucleation model was suitable for the water bath without external field at 50℃and microwave field,and the linear correlation coefficients were all above 0.98.The activation energies₍（6） of the indium leaching reaction in the water bath and microwave field are 25.287 k J/mol and 25.787 k J/mol,respectively,which are not much different;the frequency factor AK’is quite different,which are 1978.31 and 5218.68.The promotion effect of microwave field on alkaline leaching of indium is mainly reflected in the increase of frequency factor,that is,the vibration effect of microwave on molecular level.The main mode of action of ultrasonic and microwave fields is to enhance the release of indium from the zinc ferrite lattice.