Study On Operational Conditions And Disturbance Mechanism Of Leaching Indium From Waste LCD Screens By Oxalic Acid Reactor

As a kind of precious and scarce metal,indium has been widely used in the manufacture of LCD screens.With the continuous acceleration of the upgrading of electronic equipment,indium showed the characteristics of increasing demand and decreasing reserves.Consequently,recycling indium from waste LCD screens became an inevitable choice.We have studied on the leaching of indium from waste LCD screens by the fermentation broth of Aspergillus niger,and clarified that oxalic acid was the effective component for leaching.In this paper,based on the preceding work,the best operating conditions for leaching of indium from waste LCD screens by oxalic acid in the self-made simple reactor was investigated and the kinetic process of the reaction was analyzed.Then,the reason for concentration change of indium in the leachate was explained.Finally,an efficient method for the enrichment and separation of indium from leachate was proposed.The main conclusions were as follows:（1）An easy-to-operate oxalic acid reactor was made and the main factors affecting the leaching efficiency,including oxalic acid concentration,ITO glass powder dosage,temperature,stirring speed and powder particle size,were investigated.The results showed that the optimal operating conditions were 0.2 mol/L oxalic acid,300g/L ITO glass powder dosage,90℃ and 500 rpm.Under the optimal condition,indium was completely leached within 10 minutes,and the indium concentration maintained stable for 20 minutes.The total kinetic equation could be described as1-2/3η -（1-η）^2/3=5.6614×10^-52T^22.5911C^0.4231W^0.3647t,indicating that temperature was the most important factor affecting the reaction rate.Contrast to the flask system,the reactor achieved the reduction of oxalic acid concentration by 3/5,the increase of ITO glass powder dosage by 6 times,the reaction time of complete leaching by 7/9 and the longer indium concentration maintaining duration at the same time,which greatly improved the economic and technical feasibility of leaching of indium from waste LCD screens by oxalic.（2）The key element resulted in a concentration decrease of indium in the leachate was determined by the analysis of leaching process under different conditions,the monitoring records of various metal concentration changes during leaching process,and the simulation of leachate when different kinds of elements coexist with indium which was achieved by metal chloride,indium chloride and oxalic acid solution.The results showed that the formation of ferrous oxalate would not cause the decrease of indium concentration,while calcium,barium,strontium and magnesium would all cause coprecipitation of indium by the formation of oxalate precipitates,of which strontium and magnesium would not work in the system due to a high concentration request.Between calcium and barium,the latter played a major role,but a decrease in the total indium loss was showed due to its lower concentration and weaker binding capacity to oxalate ions than calcium.（3）Coprecipitation mechanism of barium to indium in the oxalic acid leachate was determined according to the characterization of precipitation products（XRD\BET\SEMEDS\FTIR）and the verification of coprecipitation mechanism,and a method of separating and enriching indium from the leachate by adding barium to enhance the coprecipitation was proposed according to it.The results showed that there are both mixed crystal coprecipitation and adsorption coprecipitation in the coprecipitation process,and the latter played a major role.Adding 1.52 g barium chloride per liter of leachate and then react for 10 min,99.37% of indium could be separated by precipitation.The relative content of indium in the precipitated product reached 14.55%,and its grade was greatly improved compared to the natural minerals of indium.