Research On The Recovery Of Molybdenum From Spent Molybdenum And Cobalt Catalysts

The development concept of contemporary circular economy and green environmental protection has become more and more popular.Under the guidance of the national policy,the recovery of molybdenum from waste molybdenum-cobalt catalyst has become a scientific research hotspot.After the spent catalyst is generally dissolved and leached out of molybdenum through acid leaching,alkaline leaching and other processes,it need to absorb and separate to recover high-purity molybdenum in the leachate.The existing recycling process has shortcomings which is not in line with the future industrial green development concept,such as long process flow,high energy consumption,low molybdenum selectivity,difficulty in waste liquid treatment and so on.Therefore,the development of a green,cheap and efficient dissolution leaching and adsorption separation technology is the focus of future research on the recovery and reuse of molybdenum in spent catalysts.Based on the current molybdenum recovery process from spent molybdenum-cobalt catalysts,it is divided into two steps:dissolution leaching and adsorption separation.The research content of this thesis is divided into two parts.One is to combine the traditional sodium roasting and water leaching method with vacuum technology to obtain a new method for recovering molybdenum from waste petrochemical catalysts.The other is to use green and pollution-free sodium alginate as raw material,and through modification,synthesize two adsorbents for efficient recovery and separation of molybdenum.The main research conclusions are summarized as follows:1.Taking spent molybdenum-cobalt catalyst as the research object,combined with vacuum technology and traditional sodiumization roasting-water leaching method,a new type of leaching process is designed,named sodiumization vacuum roasting-water leaching method.We conduct thermodynamic analysis of the relevant reactions during the sodium roasting process,and optimized the roasting time,roasting temperature,Na₂CO₃ dosage,leaching temperature,leaching time,stirring speed,liquid-solid ratio and other process conditions.The results showed that when the roasting time is 30min,the roasting temperature is 200^oC,the amount of sodium carbonate is 20%,the leaching time is 20min,the leaching temperature is 90^oC,the stirring speed is 300 rpm/min,and the liquid-to-solid ratio is 5:1,the leaching rate of Mo reaches 90.2%,and the leaching rate of Al and other elements is very low or even close to 0.In addition,by comparing the morphology characterization of vacuum and non-vacuum calcination products under the same conditions,vacuum sodium calcination can convert most of molybdenum oxide into sodium molybdate.This method can effectively leached Mo.Compared with the traditional sodium roasting method,the method has the advantages of low energy consumption,short process flow,relatively simple leaching components,and convenient subsequent processing.2.In view of the difficulty of traditional sodium alginate to have both high mechanical strength and good desorption performance,starting from the structural design of composite materials,we use sodium alginate(SA)and N,N-diethylacrylamide(DEA)as raw materials,N,N-methylenebisacrylamide(NMBA)as crosslinking agent,and ammonium persulfate(APS)as initiator A new kind of cross-linked PDEA/SA interpenetrating network polymer(PDEA/SA)was obtained by polymerization.The adsorption kinetics and thermodynamic data of PDEA/SA to Mo(VI)show that the adsorption process of PDEA/SA conforms to the zero-order,quasi-first-order kinetic models and Langmuir model.Further,We optimized the process conditions,such as the amount of NMBA added,the amount of APS added,the amount of SA,and the polymerization time.The best process conditions are:the mass ratio of NMBA,APS,and SA to DEA are:0.6,0.004,1.5,the most The best response time is 90min.When the p H of the Mo(VI)solution to be adsorbed is 3,the maximum adsorption capacity is 102.2mg/g.Under acidic conditions,the adsorption of PDEA/SA on Mo(VI)has a good separation effect with Al(III),Fe(III),Co(II),and when other metal ions in the solution appear to be the same as Mo(VI),the separation effect of the adsorbent is not ideal.By studying the desorption performance of PDEA/SA,using 1%NH₃H₂O solution as the desorption agent,when the desorption temperature is 25^oC,the desorption effect is the best and the desorption reaches equilibrium within 120 min.After 5 cycles of adsorption/desorption,61.7%of the original adsorption capacity can still be maintained,with only a slight decrease in the desorption rate,from 90.3%to 88.6%.3.Combined with ion imprinting technology,we use SA and Polyethyleneimine(PEI)as raw materials,calcium carbonate(Ca CO₃)as porogen,glutaraldehyde and calcium chloride(Ca Cl₂)as cross-linking agents for PEI and SA,respectively.The self-assembly of Mo O₄^2-and PEI was used for surface imprinting,and a porous surface imprinting PEI/SA polymer(PDA@IIP-PEI/SA)was synthesized.The adsorption kinetics and thermodynamic data show that the adsorbent has two binding sites(high affinity and low affinity sites),and the adsorption process conforms to the zero-order kinetic model and the Langmuir model.The experiment optimizes the reaction conditions during each stage of the adsorbent preparation.When the p H of the adsorption solution is 5,PDA@IIP-PEI/SA can effectively adsorb Mo(VI)in the mixed solution,and the maximum adsorption capacity is 90.2mg/g,and it has a good separation effect with Al(III),Fe(III),Co(II),Cr(VI),V(V).When the adsorbed saturated PDA@IIP-PEI/SA use 15%HCl solution as the desorbent,the desorption rate reaches 94.65%and the desorption reaches equilibrium at 160 min.After 7adsorption/desorption cycles,75.62%of the original adsorption capacity can still be maintained,and the desorption rate has no obvious change,which is stable at about 93%.