Experimental Study On Vacuum Volatilization-condensation Purification Of Crude Indium

Indium is a strategic scarce resource With the rapid development of science and technology,the purity of indium products is increasingly demanded in many high-end technology fields.Vacuum distillation is widely studied and applied as a kind of indium purffication method with short process and environmental protection.The purification process of crude indium by vacuum distillation is mainly divided into two steps:the first step is to volatilize Cd,Zn,Pb and other volatile impurities by low temperature distillation;the second step is to distill indium as individually as possible by high temperature distillation,while the refractory impurities Al,Sn,Cu and Fe remain in the residues.In this way,indium can be purified by vacuum distillation at low and high temperatures.The idea of this paper is to volatilize volatile elements Cd,Zn,Pb and In into condensers with multiple condensation zones by vacuum distillation,and then control the condensation temperature of each condensation zone so that volatile metal vapors Cd,Zn,Pb and In can be condensed in different condensation zones separately.The new method only needs one vacuum distillation to separate and purify indium metal,which solves the problem of multiple distillation in the process of traditional vacuum distillation to purify crude indium.For this reason,a multi-stage condensation vacuum distillation furnace with two temperature zones was designed independently at first,and then volatilization and condensation experiments of volatile elements Cd,Zn,Pb and In were carried out with the distillation furnace.Finally,vacuum distillation and condensation experiments of crude indium were carried out.The main conclusions are as follows:(1)The theoretical condensation temperatures of volatile elements Cd,Zn,Pb and In at 10 Pa are 312?,399? 822? and 1037? respectively.(2)The volatilization experiments of volatile elements Cd,Zn,Pb and In show that the volatilization rates of Cd,Zn,Pb and In gradually increase with the increase of distillation temperature.At the distillation temperature of 1400? the volatilization rates of Cd,Zn,Pb and In all reach more than 90%.(3)The condensation experiments of volatile elements Cd,Zn,Pb and In show that the optimum condensation temperature ranges of metal vapor,Cd,Zn,Pb and In are 240??315?,370??400? 510??800? and 800??1000?.(4)The vacuum distillation and condensation purification experiments of crude indium with 99.57%purity were caried out.The experimental results show that the purity of indium is 99.99%in the primary condensation zone at the distillation temperature of 1300? and the primary condensation temperatures of 830?,880?,930?,980? and 1030? respectively.When the distillation temperature is 1188?and the temperature of the first condensation zone is 830?,the purity of indium in the first condensation zone is 99.99%.The content of impurity elements such as Cd,Zn,TI,Pb,Al,Sn,Cu and Fe all meet the national standard of 4N fine indium.