Dialkyl Pyridinedicarboxylates’ Extraction Ability toward Copper(II) from Chloride Solutions and Its Modification with Alcohols Mariusz B. Bogacki, Artur Jakubiak, Ge ´ rard Cote, † and Jan Szymanowski* Institute of Chemical Technology and Engineering, Poznan University of Technology, Pl. Sklodowskiej-Curie 2, 60-965 Poznan, Poland Dipentyl pyridinedicarboxylates (denoted hereafter as L) with different positions of the ester groups were synthesized and used for copper(II) extraction from chloride solutions containing up to 10 mol‚L -1 Cl - . The effect of decanol addition on copper extraction was studied. A molecular modeling technique was used to estimate the structures of extractants, copper complexes, and associates with alcohol. It was found that the ability of pyridinecarboxylates to extract copper depends on the aqueous phase composition and the position of the ester groups in the pyridine ring. All the investigated compounds except dipentyl pyridine-2,6-dicarboxylate extract copper(II) by formation of CuCl 2 L 2 complexes. Dipentyl pyridine-2,6-dicarboxylate forms another type of complex, probably CuCl 2 L. However, this compound is not suitable for copper extraction as its copper complex precipitates. Dipentyl pyridine-3,5-dicarboxylate was found to be the most suitable extractant among the various compounds listed. Finally it is shown that the possibilities to modify the extraction ability of pyridinecarboxylates with a hydrophobic alcohol such as decanol are relatively weak. Some enhancement was, however, observed when 20% of decanol was added to the organic phase containing dipentyl pyridine-3,5-dicarboxylate. 1. Introduction The success of the hydrometallurgical technique using extraction of copper with hydroxyoximes and electro- winning in the processing of the oxide ores and various wastes has attracted interest in applying this technology for copper recovery from other raw materials, including sulfidic ores, which constitute the principal raw material for copper production (Szymanowski, 1993). However, the recovery of copper from sulfide ores is more complex than that from oxide ores. Basically, the latter were treated in the past as an off-balance copper resource which provided a strong argument for design- ing the above-mentioned technology allowing their exploitation. Competition of other hydrometallurgical methods, including those applying cementation or cop- per electrowinning directly from the solution after leaching with sulfuric acid, was insignificant due to both the low quality of produced copper and the economy of the processes. A totally distinct situation is associated with applica- tion of the hydrometallurgical technique for processing sulfide ores for which, almost exclusively, pyrometal- lurgical techniques have been applied. Neverthless, such techniques constitute a serious hazard for the environment by emitting toxic heavy metals and sulfur dioxide, and under the increasing pressure of environ- mental concerns and associated legislation, alternative routes to produce copper from sulfidic ores are investi- gated. It is, however, clear that the developing pro- cesses which are based on hydrometallurgy cannot yet compete with the well-established pyrometallurgical processes. It may only be of accessory value, helping to process raw materials unfavorable for pyrometallur- gical processes, e.g., complex ores which cannot be concentrated effectively by flotation or specific cuprif- erous materials and typical sulfide ores occurring in amounts too small for construction of a large, economi- cally profitable pyrometallurgical installation. The first modern attempt was the Arbiter process in which sulfide concentrate was leached with ammonia in the presence of oxygen and copper was extracted from ammonia solutions with hydroxyoximes (Khun et al., 1974). However, after 7 years of operation the instal- lation was closed. The newest effort was done by ICI which developed the CUPREX process. The copper concentrate is leached with ferric chloride, giving a solution containing up to 60 g L -1 of Cu, 150 g L -1 of Fe, and 8 mol‚L -1 Cl - . Copper is then recovered by solvent extraction with pyridine-type extractant ACOR- GA CLX-50 (Dalton et al., 1983, 1984, 1987, 1988, 1991). The active component of this commercial extractant is an ester of pyridine-3,5-dicarboxylic acid, probably diisodecyl pyridine 3,5-dicarboxylate, and the ICI pat- ents indicate that this type of pyridine compound is particularly suitable for the extraction of copper(II) from chloride systems through a solvation mechanism. ACOR- GA CLX-50 is capable of transferring large amounts of copper with no need for pH adjustment or control and with very high selectivity over a wide range of metals and metalloids (Dalton et al., 1982; Soldenhoff, 1987). In previous work (Szymanowski et al., 1993; Cote et al., 1994), we have investigated copper(II) extraction by model pyridinemonocarboxylates and compared the results with those obtained for ACORGA CLX-50. In particular, we have modeled the extraction equilibrium at constant water activity and constant total concentra- tion of ionic or molecular species dissolved in the aqueous solution (i.e., by keeping constant, but not necessarily equal, the values of the activity coefficients of all the species involved in the system). The influence of the position of the ester group in the pyridine ring on the extraction ability of pyridinemonocarboxylates was also discussed. Pyridinemonocarboxylates form more stable copper(II) complexes than ACORGA CLX- 50 and can therefore efficiently extract this metal even * Author to whom correspondence should be addressed. † Laboratoire de Chimie Analytique (Unite ´ associe ´e au CNRS No. 437), ESPCI, 10 rue Vauquelin, 75005 Paris, France. 838 Ind. Eng. Chem. Res. 1997, 36, 838-845 S0888-5885(96)00281-3 CCC: $14.00 © 1997 American Chemical Society