Separation and Recovery of Chromium and Aluminum in the Leaching Solution of Waste Nickel-Base Superalloys
Chromium and aluminium were extracted and separated from the sulphuric acid leach solution of nickel-based high-temperature alloys by the co-precipitation method,and based on thermodynamic analysis,the optimum process flow and technical parameters for chromium-aluminium precipitation and separation were studied and determined.The thermodynamic analysis shows that the Cr3+and Al3+in the solution can be completely precipitated in the pH range of 4.5-5.5,while Ni2+and Co2+not be precipitated.Under the condition where sodium hydroxide adjusting the pH of the leaching solution to 4.76 and reacting at 80 ℃ for 20 min,Cr3+,Al3+,Co2+and Ni2+undergo hydroxide precipitation,with precipitation rates of 99.95％,99.99％,17％and 18.3％,respectively.The analysis of Eh-pH of the Me-OH-system shows that,when the pH is＞13,E(CrO42-/CrO2-)-0.4 V＜0,Cr3+is easily oxidized to CrO42-.At this point,Al(OH)3 dissolves to form AlO2-,while nickel and cobalt hydroxides do not dissolve.The precipitate is dissolved at pH 14 with an H2O2 addition of 0.2 mol/L.Chromium and aluminium enter the solution in the form of CrO42-and A1O2-,respectively,and nickel and cobalt still exist in the form of the residue;CrO42-in the solution react with barium chloride to form BaCrO4 precipitate,with a precipitation rate of 99.83％.Subsequently,the solution pH is adjusted to 7 with sodium hydroxide,causing Al(OH)3 to precipitate and achieving the purpose of chromium and aluminium separation and recovery.This study provides an efficient and feasible process method for the recovery of valuable metals from nickel-based high-temperature alloys.
chemical precipitationthermodynamic analysisco-precipitationseparation extractionchromium and aluminum separation
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