THE SOLVENT-EXTRACTION OF NICKEL FROM ACIDIC SOLUTIONS USING SYNERGISTIC MIXTURES CONTAINING PYRIDINECARBOXYLATE ESTERS .2. SYSTEMS BASED ON ALKYLSALICYLIC ACIDS

The synergistic solvent extraction of nickel and cobalt by pyridinecar boxylate esters (2-, 3- or 4-C5H4N.CO.OR) in admixture with 3-bromo-or 3-nitro-derivatives of 5-alkylsalicylic acids was studied. Nickel is extracted more strongly than cobalt in all cases and, for systems cont aining a given pyridinecarboxylate, the pH,, values (pH values for 50% extraction) of both metals decrease in the order: alkylsalicylic acid > bromo-derivative > nitro-derivative. For systems containing a given salicylic acid, the separation between the pH(50) values for nickel a nd cobalt was found to increase in the order: pyridine 2-ester < 4-est er approximate to 3-ester. The extractability of divalent base metals from sulphate solutions by mixtures of isodecyl 3- or 4-pyridinecarbox ylate and 3-bromo- or 3-nitro-5-nonylsalicylic acid in Shellsol K decr eases through the series: Cu > Ni > Co approximate to Zn > Ca > Mg. In single-stage batch extraction experiments with a simulated leach liqu or containing Ni 2.2, Cu 0.5, Ca 0.4 and Mg 5.0 g dm(-3) (and smaller amounts of other base metals), adjustment of the equilibrium pH value to between 3.3 and 4.0 with magnesium oxide gave extractions of nickel and copper of 97-100%, with co-extractions of calcium and magnesium o f < 0.5 and < 0.1%, respectively. Amongst the metals present in lower concentrations, manganese (2-5%) and lead (5-10%) were extracted only slightly whereas cobalt (40-80%), zinc (15-65%) and iron (100%) were m ore strongly extracted.