Research On Recycling Process Of Nickel-based Superalloy Scrap

In this master's thesis,scrap nickel base superalloy is recovered by the combined process of smelting and hydrometallurgy.The technological process of"alloying with gallium-dissolution-chemical impurity removal-separation of cobalt and nickel-separation and extraction of gallium"is proposed in this thesis.Low melting point metal gallium was used as alloying element for the first time to alloying the scrap nickel base superalloy,so as to effectively reduce the difficulty of dissolving and leaching of the scrap nickel base superalloy and improve the dissolution and leaching efficiency of scrap alloy by alloying with gallium.In this thesis,alloying process of the scrap nickel base superalloy and gallium,dissolution leaching efficiency of the scrap nickel base superalloy and new alloy,leaching liquefaction and nickel cobalt extraction separation,gallium separation in impurity removal precipitation were studied respectively.It is feasible to use gallium as an alloying element to alloying the scrap nickel base superalloy.The microstructure of the scrap nickel base superalloy can be completely changed by alloying.Two groups of optimized alloying process parameters were obtained:(1)In argon atmosphere,the processing temperature is 1000?,the mass ratio of gallium to the scrap nickel base superalloy is 1.0 and the holding time is 6 h,under the condition of alloying processing?new alloy can be obtained.(2)In argon atmosphere,the processing temperature is 900?,the mass ratio of gallium to the scrap nickel base superalloy is 1.8 and the holding time is 8 h,under the condition of alloying processing?new alloy can be obtained..When the temperature was 25?,the ratio of volume to mass was 12 and the reaction time was 6 h,the leaching rates of nickel,cobalt and gallium in the?new alloy were 97.69%,97.38%and 99.12%,respectively.When sulfuric acid concentration is 6 mol/L,the mass ratio of sodium chlorate to the new alloy is 2,the temperature is 75?,the liquid-solid ratio(m L:g)is30,and the reaction time is 8 h,the dissolution leaching efficiency of the?new alloy is much higher than that of the original nickel-based superalloy.The leaching rates of nickel,cobalt and gallium are 98.67%,98.48%and 99.87%respectively.The above results show that gallium alloying treatment can effectively reduce the difficulty of dissolution and leaching of the scrap nickel base superalloy and improve the efficiency of dissolution and leaching of the scrap nickel base superalloy.By adjusting the p H of leaching solution with 1 mol/L Na₂CO₃ solution to 5.07,gallium and chromium plasma in the solution can be effectively removed,and the deposition rates of nickel and cobalt are only 0.46%and 0%.Meanwhile,99.97%of gallium in the solution is enriched in the impurity removal precipitation,which is conducive to the subsequent separation and recovery of gallium.The solvent extraction method was used for the nickel and cobalt separation experiment of the simulated solution,and the optimized technological parameters of the nickel and cobalt extraction separation were obtained:the initial p H value of the extract was 3.0,the volume concentration of the extractant P507 was 10%,the saponification rate of P507 was 55%,the ratio of O/A was 1:2,and the oscillation time was 5 min.The single stage extraction rate of nickel was 0.78%,the single stage extraction rate of cobalt was 68.08%,and the extraction and separation coefficient of nickel and cobalt was 271.41.Nickel in the loaded organic phase can be removed by washing with 0.01 mol/L dilute hydrochloric acid solution(p H value around 2.0).The back extraction rate of nickel in single-stage washing is 63.8%,while that of cobalt is only0.48%In this case,the nickel removal effect of single stage washing is better.The gallium element in impurity removal precipitation was separated by experiments.In this paper,gallium containing filter residue was dissolved in 1 mol/L HCl solution,and then the p H value of the solution was adjusted to 11?12 by 1 mol/L Na OH solution,which could separate and remove impurities such as chromium and iron.Optimized gallium extraction and separation process parameters were obtained:when compared with O/A at 2:1 and extraction time at 15 min,the extraction rate of gallium could reach more than 99%when the hydrogen ion concentration of the extract was 6 mol/L and the volume fraction of TBP was 20%.