SOLVENT-EXTRACTION OF NICKEL FROM ACIDIC SOLUTIONS USING SYNERGISTIC MIXTURES CONTAINING PYRIDINECARBOXYLATE ESTERS .1. SYSTEMS BASED ON ORGANOPHOSPHORUS ACIDS

The solvent extraction of nickel from acidic solutions by pyridinecarb oxylate esters (2-, 3- and 4-C5H4N.CO.OR) mixed with organophosphorus acids (R(2)POOH, (RO)RPOOH and (RO)(2)POOH) in toluene was investigate d for both series of compounds in which R = n-octyl, 2-ethylhexyl and cyclooctyl. Substantial synergistic effects were observed, which incre ased in the orders: pyridine 2-ester < 3-ester < 4-ester, and: phosphi nic < phosphonic < phosphoric acid. The extractability of divalent bas e metals from sulphate solutions by mixtures of isodecyl 4-pyridinecar boxylate and di(2-ethylhexyl) phosphoric acid in Shellsol K decreases through the series Cu > Ni > Zn, Co > Ca > Mg. In a batch countercurre nt experiment, a simulated leach liquor containing Ni 2.1, Cu 0.5, Ca 0.4 and Mg 5.0 g dm(-3) (initial pH 3.00) was extracted with the mixed reagent (0.50 M) in four stages at unit phase ratio, without pH adjus tment. Recoveries of nickel and copper were 93 and 100%, with co-extra ctions of calcium and magnesium of 10 and 1%, respectively. In a simil ar experiment using isodecyl 3-pyridinecarboxylate in place of the 4-i somer, the overall extractions were nickel 80, copper 100, calcium 17 and magnesium 3%.