Patent GB-866714-A (GB)
Title: Process for the separation and purification of difficultly separable elements
IPC: C01F17/229
Filed: 1957-04-26
Abstract: Precipitation or crystallisation to effect separation or purification of difficultly separable elements, is effected in a liquid medium by changing one of the parameters that effect precipitation or crystallisation (such as temperature, degree of dilution or pH) up to, but not beyond, the point when crystal nuclei are formed as determinable by the Tyndall effect, and thereafter maintaining said parameters unchanged until separation of the so-induced precipitate or crystallisation is complete.  The liquid system is maintained substantially homogeneous with respect to said parameters during the process by vigorous agitation.  It is preferred that the alteration of the parameter be slow, for example the temperature being altered at not greater than 0,1  DEG C. per minute, pH at not greater than 0,1 per hour or concentration at a rate not greater than 1 relative per cent. per hour.  As a modification, the parameter or parameters may be altered up to the onset of visible turbidity and the parameter thereupon immediately changed by the addition of a counter-agent to that which it would have been at the onset of the formation of crystal nuclei as determined by the Tyndall effect, the parameter being thereafter maintained unchanged.  Seeding may be effected by adding finely divided crystal nuclei at the onset of the Tyndall effect.  The specification refers to fractional precipitation of rare earth oxalate complexes from solutions of their complexes with aluminium oxalic acid by dilution with water at 70-80 DEG C. and to the decomposition of rare earth complexes with aluminium oxalic acid by the addition of oxalic acid and a mineral acid.  The process is also applicable to the separation of other elements forming water-insoluble oxalates, e.g. Ca, Sr, Ba, Ra, Fe, Co, Ni, platinum metals, the elements of the manganese group, zirconium, hafnium, gallium, indium, thallium, and transuranic elements.  Besides aluminium oxalic acid complexes there may be used oxalic acid complexes of other metals, e.g. chromium, molybdenum, vanadium or uranium and besides oxalic acid complexes of the said metals with other di- and tri-basic organic acids may be used, e.g. tartaric or citric acid.  Specification 866,718 is referred to.ALSO:Precipitation or crystallization to effect separation or purification of difficulty separable elements, is effected in a liquid medium, by changing one of the parameters that effects precipitation or crystallization (such as temperature, degree of dilution or pH) up to, but not beyond, the point when crystal nuclei are formed as determinable by the Tyndall effect, and p  thereafter maintaining said parameters unchanged until separation of the so-induced precipitate or crystallization is complete.  The liquid system is maintained substantially homogeneous with respect to said parameters during the process by vigorous agitation.  It is preferred that the alteration of the parameter be slow, for example the temperature being altered at not greater than 0.1 DEG  C. per minute, pH at not greater than 0.1 per hour, or concentration at a rate not greater than 1% relative per hour. As a modification, the parameter or parameters may be altered up to the onset of visible turbidity and the parameter thereupon immediately changed, by the addition of a counter-agent, to that which it would have been at the onset of the formation of crystal nuclei as determined by the Tyndall effect, the parameter being thereafter maintained unchanged.  Seeding may be effected by adding finely divided crystal nuclei at the onset of the Tyndall effect.  The Specification refers to fractional precipitation of rare earth oxalates from solutions of their complexes with aluminium oxalic acid by dilution with water at 70-80 DEG  C., to the decomposition of rare earth complexes with aluminium oxalic acid by the addition of oxalic acid and a mineral acid; to the fractional crystallization of lanthanumpraseodymium-ammonium nitrate by crystallization after inoculation, to the separation of zirconium and hafnium by fractional crystallization of the ammonium or potassium double fluorides after inoculation with hafnium-free zirconium ammonium fluoride for example, to the separation of barium and radium by their bromides, and to niobium/tantalum separation with potassium double fluorides. A further example relates to the separation of platinum and palladium from a solution of their chlorides by adding caustic soda or ammonia hydroxide, palladium being precipitated first and then the other platinum metals whilst platinum remains in solution to the end. Specification 866,718 is referred to.