GB866717A - Process for separating and purifying compounds of metals which form insoluble or difficultly soluble compounds - Google Patents

Abstract

A process for the separation and purification of a water insoluble or difficultly soluble metal compound from a mixture of such metallic compounds comprises extracting said water insoluble or difficultly soluble metal compound with a metal salt solution which forms with said metal compound and is capable of forming with at least one other metal compound present, soluble complex compounds, the metal salts used for the extraction being salts of aluminium, boron, scandium, zirconium, vanadium, niobium, tantalum, antimony, chromium, molybdenum, tungsten, uranium or iron. The extraction process may be repeated so as to successively separate the metal compounds forming the soluble complexes. The extracting salts may be complex, e.g. complexes of chromium, molybdenum or tungsten with oxalic acid. Aluminium salts are preferred, e.g. potassium alum, ammonium alum, aluminium nitrate, aluminium citrate and aluminium-oxalic acid (see Specification 866,718). The extraction may be performed in a column when the extracting solution may, if desired, flow in an upward direction, or in stages in a number of vessels. The extraction may be performed in an aqueous medium or in an organic solvent such of methanol or ethanol or their mixtures with water. The insoluble complexes to be separated are preferably used in a highly active form, preferably freshly precipitated and in a highly dispersed form in a solvent medium. Enforced convection, e.g. by stirring may be used. The extraction may be effected in two stages, first with the metal salt solution and then with pure solvent. The insoluble metallic compounds to be separated may be oxalates and the extraction solution may contain the preformed soluble oxalato complexes of several of the elements to be separated. Examples describe (1) the successive extraction of soluble rare earth complexes by treating a mixture of rare earth oxalates with potassium alum, and (2) the extraction of a soluble nickel complex from mixed nickel/cobalt oxalates with ammonium alum. Reference is also made to the separation of yttrium earths including scandium and yttrium by extraction of the oxalates with aluminium salts, e.g. aluminium nitrate or alum.