Novel Wet Process Of Metal Recovery From Spent NiMo/Al₂O₃ Catalyst

With the shortage of nickel molybdenum metal and the continuous improvement of environmental protection standards for spent catalyst emission,it is becoming a general trend for the recovery and utilization of metal in spent catalyst.Currently,pyrometallurgical process is basically used for the recovery of spent catalyst in China,which has some shortcomings such as high energy consumption,complicated post-treatment and difficult cleaning and recycling.Hydrometallurgical process can be divided into acid leaching method and alkali leaching method.Acid leaching method will make most metal substances dissolve into acid,and there are many kinds and large contents of metal ions in the solution,so more chemical processes are needed to separate the metals in the subsequent work.Alkali leaching method selectively dissolves some metals,but the leaching solution may need to be acidified again to separate metal ions.Some modifiers are inevitably added in the hydrometallurgical process,which pollutes the water phase.Coalescence separation technology realizes oil-water separation by using different affinity of membrane materials to water and oil,which has no secondary pollution,low cost and simple operation.Therefore,it can be used for deep separation of oil-water emulsion and clean discharge of wastewater caused by extraction process.According to Ni Mo/Al₂O₃ spent catalyst,it is proposed to adopt the coupling process of leaching,extraction and coalescence separation to recover spent catalyst.Through the study of leaching process,nickel molybdenum metal is leached selectively,and then molybdenum metals are extracted efficiently.After extraction,the oil-containing water phase is coalescence separated by an oil-water separator,so as to improve the recovery rate of spent catalyst,realize the high-value recovery of active components of catalyst and achieve the standard discharge of wastewater.The main research work is as follows:（1）Selection of leaching process.3 processes,such as hydrogen peroxide direct leaching,hydrogen peroxide-ammonia leaching and air roasting-aqueous ammonia leaching,were compared.The effects of 3 leaching processes on the leaching rates of Ni,Mo and Al were studied.The simplicity of industrial production was evaluated.The air roasting-aqueous ammonia leaching process with high leaching rates of Mo（98.51%）and Ni（86.32%）,low cost and simple operation was selected.（2）Optimization of air roasting-aqueous ammonia leaching process.The effects of different calcination temperature,liquid-solid ratio,p H value,total ammonia concentration,leaching temperature and leaching time on leaching rate were studied by single factor experiment with controlled variable method.The results showed that the best leaching effect was obtained when the calcination temperature was 400℃,the liquid-solid ratio was 20,p H value was 9,the total ammonia concentration was 4mol/L,the leaching temperature was 70℃,and the leaching time was 30min.The leaching rates of nickel and molybdenum reached 96.32%and 86.72%,respectively.（3）Extraction process of metal components.The mechanism and thermodynamic analysis of metal extraction were carried out,and the effects of different ratios,p H value,extraction temperature and mixing time on the extraction rate were studied.The results showed that when the ratio was 1:3,p H value was equal to 9,the extraction temperature was 30℃,and the mixing time was 20min,the extraction rate of molybdenum was 98.63%,and the loss rate of nickel was less than 7%.（4）Coalescence and separation of emulsified oil and water from extraction solution.The effects of different temperature,flow rate and cycle times on separation efficiency were explored.The results show that the oil-water separation efficiency was 72.43%when the temperature was 45℃and the flow rate was 0.594 m/min.Secondly,the more the cycle times were,the better the oil-water separation effect was,and the separation efficiency was 86.73%after 5 cycles.