Organophosphorus acids for hydrometallurgical extraction : the synthesis of di(2-methylcyclohexyl)-, di(3-methylcyclohexyl)-, di(4-methylcyclohexyl)-, di(3,5-dimethylcyclohexyl)-, di(4-t-butylcyclohexyl)-, di(cyclohexylmethyl)- and dicyclohexyl- phosphinic; cyclohexylmethyl monocyclohexylmethylphosphonic; di(2-methylcyclohexyl)-, di(4-methylcyclohexyl)-, di(cyclohexylmethyl)- and di(cyclohexylethyl)- phosphoric acids and their evaluation as potential hydrometallurgical extractants for cobalt or nickel
The syntheses and characterisation of di(cyclohexylmethyl), di(2-cyclohexylethyl), di(2-methylcyclohexyl) and di(4-methylcyclohexyl) phosphoric acids; cyclohexylmethyl phosphonic acid monocyclohexylmethyl ester, di(cyclohexylmethyl), di(4-methylcyclohexyl), di(4-tert- butylcyclohexyl), di(3-methylcyclohexyl), di(3,5-dimethylcyclohexy) and di(2-methylcyclohexyl) phosphinic acids are reported. Problems encountered and how they were resolved during the preparation of the above organophosphorus acids are reported and discussed in detail. These acids are then evaluated as potential hydrometallurgical extractants, for the separation of cobalt from nickel in acid leach liquors, and compared with two commercially available extractants, namely di(2-ethylhexyl)phosphoric acid (D2EHPA) and di(2,4-4- trimethylpentyl)phosphinic acid (Cyanex 272). The effects of variablest such as metal feed solution concentration, extractant concentration, diluent, modifier and temperature are examined experimentally in order to determine which factors are important for optimisation of an extraction system. The extraction characteristics for each acid as a function of pH are presented graphically and the pHO 5 values, distribution coefficients and separation factors are calculated. The dialkylphosphinic acids are found to exhibit much greater selectivity, for cobalt over nickel, than the dialkylphosphoric acids. It is postulated, that steric crowding of the phosphorus atom, by the hydrocarbon groups attached to the phosphorus, increases the selectivity of an extractant. This effect is particularly apparent in the dialkylphosphinic acids with di(2-methylcyclohexyl)phosphinic acid giving the best selectivity; much better than the commercially available Cyanex 272. Several of the dialkylphosphinic acids, evaluated as extractants in this thesis, are protected by a British Patent Application.