The Research On Comprehensive Utilization Of Iron-base Nickel-chromium Alloy

The recycling production of non-ferrous metals have a significant role in the expansionof non-ferrous metal resources, reducing production and consumption, saving infrastructureinvestment, lowering production costs, reducing environmental pollution and increasingsocial benefits. For this reason, comprehensive recycling the non-ferrous metals of secondaryresources is more practical.This paper mainly studies the comprehensive utilization of Nickel Chromium Iron-basesuper-alloy. The first, using membrane electrolysis to dissolve the Nickel Chromium Iron-basesuper-alloy, prepared anode leaching solution, studied the process in detail, focused on thecurrent density, anode acidity, the polar distance and cell voltage, and so on. Investigatedthese condition's effect to electrolysis efficiency and energy consumption. Secondly,researched the separated treatment and comprehensive utilization of the Fe²⁺,Cr³⁺in anodicleaching solution, and carried out the in-depth analysis to various process conditions, focusedon studying pH,temperature,ion concentration,reaction time and other conditions of theseparation process.An investigation is made of the dissolution process of Nickel Chromium Iron-basesuper-alloy. in hydrochloric acid system by using membrane electrolysis method. Byoptimizing experimental conditions, the operation condition for membrane electrolysisprocess was decided. The results show that under the conditions of voltage1.5V,averagecurrent density500A/m2,Ni2+concentrations1mol/L,anolyte acidity1mol/L,polar distance20mm,temperature40℃, average current efficiency can be up to90%,energy consumption is1200KWh/t or so. In the membrane electrolysis process, with the voltage increased, the powerconsumption was a corresponding increase; voltage is too low, the efficiency is too low. Withthe temperature increased, the current density would increased, the electrolytic consumptionwould droped. However, the temperature should be controlled within the membranewithstanding range. Under these conditions, energy consumption can be maintained at a lowerlevel. Using membrane electrolysis, acid utilization rate is high, no waste acid excluding. Theacidity of the anolyte can be controlled at a very low level, the follow-up separated processesis conducive to deal with. Using membrane electrolysis to dissolve iron nickel chromiumsuperalloys, the technology is feasible, easy to operate.Using the method of goethite to separate the Fe²⁺from the anolyte, after optimized theconditions, determined the operating conditions of the method of goethite. Studies show: oneof the key factors in the method of goethite is to control the pH of the solution, we adopted to adjust pH at different stages. In the beginning, adjusted pH=1.7, the later reaction, transferredto pH=2.5. because lower pH is favorably generate crystalline β-FeOOH; The same time, thedifference pH value of iron completely precipitated with chromium ions beganningprecipitated is small, if the pH value is high, although the iron separation is complete, therewill be some chromium hydroxide precipitation generated, impacted the chromium recovery;if pH value is too low, iron separation will fail to meet requirements. At high temperaturescolloidal Fe(OH)₃tend to be unstable, and easily formate goethite; goethite crystallization is achemical crystallization process, the increase of temperature will speed up the reaction rate;at high temperature, crystallization is big, the filtration is well. So we identified as thereaction temperature around95℃. To get the well crystalled and filtered goethite precipitation,would need a longer reaction time; the same time, using the air to oxidize iron, the oxidativecapacity of the air is weak, the process would take a long time to oxidize the divalent ironions. In order to obtain high iron separated rate, to determine the reaction time was120min ormore. At large concentration of Fe²⁺, reaction rate is relatively fast, as the concentration ofFe²⁺in the solution is gradually reducing, the reaction rate becomes slower and slower. Theinitial concentration is too high, it will lengthen the cycle of the iron separated reaction.Goethite precipitation roasted at650°C for two hours, obtained the completly crystallizationof Fe₂O₃.After the ion of iron separated, the Cr³⁺is separated by chemical precipitation method.The chromium exist the form of Cr³⁺in the anolyte, the Cr³⁺easily hydrolysis into theprecipitation of Cr(OH)₃. The solubility of Cr(OH)₃is very low, at298K, the equilibriumconstant K=6.3×10-31. We adopt to improve the pH, let it hydrolysis and precipitate, andachieve the purpose of Cr³⁺separated. The best precipitated reaction conditions of therecovery of chromium ion is at90℃, the concentration of chromium ions is at4～6g/L,pH=6.0. In this condition, the recovery rate of chromium is up to92%, the filtration is well,the concentration of chromium in the filtrate can be reduced to about1mg/L. Theprecipitation went through washing, drying, and roasting at600℃for1h. Cr(OH)₃precipitation completely dehydrated into Cr₂O₃, generated the integral structure of Cr₂O₃After the ion of iron and chromium separated, anolyte is solution of NiCl₂...