Basic Research On Tungsten And Molybdenum Separation Based On Oxygen-containing Acid Root Morphological Monitoring

Tungsten and molybdenum often co-exist in natural resources,and the chemical properties in aqueous solution are very similar,so tungsten-molybdenum separation has always been the focus of attention.Most of the previous studies focused on changing operational parameters,technological process or developing new precipitants and extractants to optimize the separation of tungsten and molybdenum.However,the relationship between speciation and tungsten-molybdenum recovery/separation process has not been considered.To this end,this paper set up two-stage annular centrifugal contactors(ACCs)coupled electrospray-time of flight-mass spectrometry(ESI-TOF-MS)on-line monitoring platform to(1)investigate the polymerization and conversion rules of tungsten and molybdenum speciation in acidic aqueous solution,(2)study the relationship between microscopic tungsten/molybdenum.species transformation pathways and macroscopic extraction during recovery process on the basis of primary amine N192 3,(3)probe into the effect of tungsten and molybdenum speciation on the removal efficiency of tungsten as well as purification of sodium molybdate solution in tungsten-molybdenum mixture system.The results are as follows:(1)The speciation distribution of tungsten and molybdenum species in acidic aqueous solution was studied by ESI-TOF-MS characterization method,which was superior to raman method.A variety of tungsten species such as W,,W2,W4,W6,W10,W12 and various molybdenum species such as Mo1,Mo2,Mo3,Mo4 were monitored.Wn or Mon stands for the species containing n tungsten or molybdenum atoms.At the same time,the effects of sample cone voltage and source temperature on the speciation distribution of tungsten and molybdenum species were investigated.Optimum cone voltage and source temperature were 20 V,60 ?.In addition,the effects of acid type,initial solution concentration,solution pH on the morphological polymerization of tungsten and molybdenum species were further studied.The results showed that the distribution of tungsten and molybdenum species mainly depended on the pH of solution.Different acid types and initial solution concentration affected the polymerization and transformation of tungsten and molybdenum species to some extent.Molybdenum species were easier to hybridize with acid anions in solution.The schematic diagrams of the morphological polymerization of tungsten and molybdenum species in acidic aqueous solution were summarized.(2)Based on the ESI-TOF-MS coupled with two-stage ACCs on-line monitoring platform,the macroscopic extraction and microscopic tungsten/molybdenum species transformation pathways in the recovery process by primary amine N1923 were studied.The results showed that primary amine N1923 was an efficient extractant for tungsten and molybdenum extraction,and the molybdenum extraction reaction was more rapid than tungsten extraction.During the tungsten extraction process,W,was an inactive form,which only participated in the tungsten speciation equilibrium reaction rather than the extraction reaction,and W10 was more active and easier to be extracted into the organic phase than other species.During the molybdenum extraction process when MoO3Xn-(X is an acid medium anion)appeared in the initial solution,it would replace Mo4 as the active form and be preferentially extracted into the organic phase.(3)The extraction process of tungsten-molybdenum separation and the effect of speciation on tungsten removal as well as sodium molybdate solution purification were studied by the on-line monitoring platform.The results showed that tungsten was extracted preferentially over molybdenum in the competitive extraction process,and with the decrease of tungsten-molybdenum ratio,the advantages of tungsten would become more and more obvious.Various species such as Mo1-Mo5,HWO4-as well as tungsten-molybdenum hybrid species NaMoWO7-?NaMo2WO10-and NaMo3WO13-were monitored.The hybrid species would be preferentially combined with the primary amine N1923 to be extracted into the organic phase.The higher relative content of the hybrid species in tungsten speciation,the better tungsten removal.In addition the higher relative content of hybrid species in initial solution,the higher purity of the sodium molybdate solution.