| A novel separation method was presents for recovery and separation of molybdenum(VI)from aqueous solution: an aqueous two-phase system composed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)tri-block copolymer nonionic surfactant L35 and sulfate.In the absence of any extractant case,it can efficiently extract and separate molybdenum for four kinds of aqueous two-phase systems composed of L35-sulfate(Li2SO4/Na2SO4/(NH4)2SO4/MgSO4).The effects of related factors on phase equilibrium and distribution of molybdenum in aqueous two-phase systems were investigated.The results on phase equilibrium of L35-sulfate aqueous two-phase systems indicated that the tie-line length and phase difference increase as the increase of the system composition;the biphasic area slightly increases with the increase of temperature.The tie-line length sequence for four systems is as follows: Na2SO4>Li2SO4>(NH4)2SO4,indicating that the bigger biphasic area is and the higher phase separation ability is.The empirical equations of Othmer-Tobias and Bancroft were used to correlate the tie-line data of L35-sulfate aqueous two-phase systems and the correlation results are of higher accuracy.The effects of p H,L35 concentration,sulfate concentration,molybdenum concentration and temperature on the extraction performance of molybdenum were investigated.The experimental results showed that the distribution of molybdenum in aqueous is strongly dependent on the p H value of the system;The extraction rate and distribution coefficient of molybdenum increase with increasing concentration of L35 and sulfate;the extraction rate and distribution coefficient increase first and then decrease with the increase of Mo concentration;in the range of 303.15 K-343.15 K,the extraction rate and the distribution coefficient of molybdenum decrease with the increase of temperature.FTIR analysis showed that molybdenum has no obvious interaction with the oxyethylene units in L35 micellar phase.DLS potential analysis showed that the apparent potential of L35 micellar phase changed from positive to negative before and after extraction.Therefore,the molybdenum extraction mechanism can be inferred that the polymolybdate anion is extracted into L35 micellar phase based on electrostatic attraction by micellar solubilization in the role of salting-out effect of phase-forming sulfate and relatively high hydrophobic nature of polymolybdate anion.The effects of temperature-pH,temperature-(NH4)2SO4 concentration and temperature-phase ratio on stripping were investigated by using(NH4)2SO4 aqueous solution to strip molybdenum(VI)loaded in L35 micellar phase.The experimental results showed that the stripping rate of molybdenum increased as the increasing of p H value;when the temperature increased from 323.15 K to 353.15 K,the stripping rate increased gradually;and the stripping rate increased rapidly and then increased slowly as(NH4)2SO4 concentration increased;but the stripping rate decreased with increasing phase ratio;stripping temperature is the main factor on influencing stripping.The results on the separation of molybdenum and associated cations Cu(II),Co(II),Ni(II),Mn(II),Zn(II),Fe(III),Al(III)showed that the extraction rate of molybdenum(VI)gradually decreased as the increasing of seven metal cations concentration,the addition of charge modifier octadecyl amine ethoxylate ether(1815)can effectively improve the extraction rate of molybdenum(VI)and inhibite the extraction of other metal cations,to realize the efficient separation of molybdenum(VI)and low concentration of associated cations.Similar results were observed in the separation of molybdenum and high concentration N i(II)or Fe(III),the temperature rising lead to a bad separation efficiency,but the extraction rate of molybdenum increased and the extraction rate of other metal cation decreased with the increase of concentration of 1815,then the better separation performance is realized. |
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