磷钨杂多酸的萃取

Solvent Extraction of Phosphotungstic Acid

实验获知,N,N-二(1-甲基庚基)-乙酰胺(N503)的萃取效果优于醇、酮类萃取剂;有机相中加入长碳链酸性含磷萃取剂(OA-4),显示了一定的协萃效应。以5份N503-10份OA-4-20份TBP-65份磺化煤油(体积比)为萃取体系,在[HCl]=5mol/L,相比1∶1,[WO_3]_(2)=50.11g/L,W/P=11.9时,进行文题研究,结果表明:D_W≈1.16×10~3,用2mol/L氨水反萃,单级反萃率≈60%。初步探讨了协萃机理,在[HCl]=4～6mol/L时,N503-OA-4萃取磷钨酸为离子缔合萃取。N503质子化后,与磷钨杂多酸根阴离子缔合,OA-4则作为配位体进入协萃络合物以降低络合物的亲水性,进一步提高分配比。其协萃络合物的组成认为是(?)_2^+·[HPW_(12)O_(40)]^(2-)·(HA)

The extraction of heteropoly phosphotungstic acid in strong hydrochloric acid, particularly in 5 mol/L HCl, was studied. It was shown that the extraction capability of N, N-di(1-methylheptyl)-acetamide (N503) is apparently higher than that of the commonly used alcohols and ketones. Under the adopted experimental conditions, the addition of an acidic phosphorus-containing extraetant (OA-4) to the organic phase shows there is a certain synergistic effect. The synergistic coefficient R is greater than 1. Distribution coefficient is quite large when using N 503-OA-4 pair to extract phosphotungstic acid from 5 mol/L hydrochloric acid solution (when[WO_3]=50.11g/L and (W/P)=11.9, the value of D_w is approximately equal to 1.16×10~3). TBP was used as modifier to improve the solubility of the synergistic complex in the organic phase and to speed up the phase separation rate. 2mol/L ammonia water was chosen as stripping agent. The percentage back-extraction of a single stage is about 60%. Preliminary work on synergistic mechanism was attempted. The process in which phosphotungstic acid is extracted by N503-OA-4 in 4～6 mol/L HCl was shown as ionpair formation mechanism. OA-4 was regarded as a ligand in the synergistic complex. The possible form of the complex was suggested as[N503·H]_2^+·[HPW_(12)O_(40)]^(2-)·(HA)