THE STOICHIOMETRIC MODELLING OF THE EXCHANGE EXTRACTION OF Mg, Ca AND Na WITH POTASSIUM DL-2-ETHYLHEXYLPHOSPHATE FROM CONCENTRATED BRINES

摘要

An organic phase comprising potassium di-2-ethylhexylphosphate (KD) with some free acid (HD) in xylene diluent was used to extract calcium, magnesium and sodium from chloride brine containing each of the elements. The stoichiometry of two possible extraction reactions was studied by testing the agreement between the experimental data and the respective equilibrium models. For calcium and magnesium the reactions tested were: and M~(2+)_a + 2KD_(org) <-> MD_(2 org) + 2K~+_a M~(2+)_a + KD_(org) + HD_(org) <-> MD_(2 org) + K~+_a H~+_a Whilst the former reaction gave good agreement only at higher concentrations of potassium, the latter equation involving the free acid, gave an excellent fit. The equilibrium constant was K_(ex) = 1.82 x 10~(-3). Extraction of sodium from a synthetic brine containing 0.1 mol/dm~3 NaCl in 2.0 mol/dm~3 KC1 provided evidence that the extracted complex is polymerised to a variable extent and contains excess extractant of formula, Na_mD_(m+1) with m = 4 to 12 including one extra HD or KD unit.