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TOPO体系萃取分离铑与铱
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摘要
铑在氯化物溶液中的化学性质十分复杂,它的分离与纯化一直是贵金属提取冶炼中的难题。
     本文研究了活化—溶剂萃取技术分离铑的TOPO体系,以SnCl_2为活化试剂,从Rh(Ⅲ)—Sn(Ⅱ)—Cl~-体系中的萃取Rh(Ⅲ),考察了SnCl_2加入量,酸度,萃取剂浓度,料液恒温时间等条件对Rh(Ⅲ)萃取率的影响。在相比为1:1,Sn:Rh:4:1(摩尔比),恒温时间为1h,酸度为3mol·L~(-1)盐酸,一级萃取率可达98%以上,而且分相速度快。用加KClO_3的4mol·L~(-1)盐酸反萃,一级反萃率达95%。研究结果表明,含铑料液经SnCl_2活化处理后,能显著提高铑的被萃取性能,指出了活化—溶剂萃取技术分离回收铑的应用可行性。
     本文还研究了在TOPO体系中,应用活化—溶剂萃取技术于Rh(Ⅲ)和Ir(Ⅳ)的选择性分离,研究结果表明:
     在Ir(Ⅳ)和Rh(Ⅲ)的混合液的萃取体系中,在含氯化亚锡的RhCl_6~(3-)和IrCl_6~(2-)初试料液中IrCl_6~(2-)被还原为IrCl_6~(3-),IrCl_6~(3-)不能被TOPO萃取,RhCl_6~(3-)被还原为Rh(Ⅰ),同时与SnCl_3~(3-)进一步络合形成一个双核桥联基配合物阴离子[Rh_2Cl_(6-n)(SnCl_3)_n]~(4-)(n=2—4),可以被TOPO萃取。
     在反萃取体系中HCl和KClO_3的混合溶液产生具有很强的氧化性的氯气,可以利用它的氧化性来反萃铑。在反萃过程中,在络阴大离子中的Rh(Ⅰ)和SnCl_3~-被氧化为Rh(Ⅲ)和Sn(Ⅳ),破坏了[Rh_2Cl_(6-n)(SnCl_3)_n]~(4-)(n=2—4)的结构,Rh(Ⅲ)被反萃到水相中。由于受到IrCl_6~(3-)与IrCl_6~(2-)离子间价态变化的高频率性的微弱影响,在萃取过程中有一小部分IrCl_6~(2-)可能被TOPO萃取。在强氧化性的溶液中IrCl_6~(2-)不发生变化而仍然在有机相中,最后可以被硝酸反萃回收。无论在萃取还是在反萃铑的过程中,由于TOPO萃取SnCl_3~-和SnCl_6~(2-)阴离子的萃取率很高,SnCl_3~-和SnCl_6~(2-)始终保持在有机相中。最终所有的锡可以被氢氧化钠反萃下来,TOPO得到循环利用。
     应用斜率法讨论了萃合物中各组分的物质的量的比,用紫外光谱UV,红外光谱FT—IR研究了探讨了TOPO萃取体系萃取铑的萃取机理。
The separation and purification of rhodium from the other precious metals is one of the more difficult areas in precious metal refining, due mainly to the complex solution chemistry of rhodium in chloride solution.
    In this paper ,Tin (II) chloride was used as labilizing reagent, and the results of a systematic study on the solvent extraction of rhodium with tri-n-octylphosphine oxide(TOPO) in aqueous solution of Rh(III)-Sn(II)-Cr system by activation-solvent extraction technology are given. The effects of the molar ratio of Sn to Rh , TOPO concentration, acidity, aging time ect. were inspected. The optimum extraction conditions are as follows: the amount of added stannous chloride is four times that of Rh according to the molar ratio of Sn to Rh, the temperature of complex reaction 60℃, aging time 1 h, phase ratio 1:1, the Rh percentage extraction was over 98% .The percentage of stripping may reach to 95% through one stage with 4 mol·L~(-1) hydrochloric acid containing potassium chlorate. The results of this study show that the extraction of rhodium can be improved observably by the labilizing progress with SnCLl_2 and indicate the feasibility of recovery and purification of rhodium by activation-solvent extraction technology.
    In the TOPO system , activation-solvent extraction technology was put forward to separate Ir(IV) and Rh(III) ions from a mixed chloride solution by extraction of rhodium .Stannous chloride was added to the original solution containing IrCl_6~(2-) and RhCl_6~(3-) ions before extraction. IrCl_6~(2-) was reduced to IrCl_6~(3-) , which cannot be extracted by TOPO, and RhCl_6~(3-) was reduced to Rh(I), which was further complexed with SnCl_3~- forming a bi —nuclei bridged complex anions of the form[Rh_2Cl_(6-n)(SnCl_3)_n]~(4-)(n=2—4) and were extracted by TOPO simultaneously.
    A mixed solution of HC1 and KClO3 in which the strong oxidant chlorine was produced was used for stripping the rhodium. During the stripping process, both Rh(I) and SnCl_3~- in the complex anions were oxidized to Rh(III) and Sn(IV) destroying the structure of the [Rh_2Cl_(6-n)(SnCl_3)_n]~(4-)(n=2 — 4) anions; Rh(III)was stripped into the aqueous solution . The process was affected only slightly by the characteristic hing frequency of between IrCl_6~(2-) and IrCl_6~(3-) ions;a little amount of IrCl_6~(2-) might be extracted by TOPO in the course of extracting rhodium . IrCl_6~(2-) remained in the organic phase experiencing no change in the strong oxidative environment can be stripped with nitric acid. Because of their high percent extraction by TOPO, the SnCl3"" and SnCl_6~(2-) anions are always kept in the organic phase whether in the process of extraction or stripping the rhodium. Finally, all of the tin was stripped by sodium hydroxide and reclaimed. Meanwhile the TOPO was
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