A mathematical modeling method was developed by the Bureau of Mines for the prediction of the principal equilibrium species in the solvent extraction of copper. The use of models for predicting the amount of metal extracted can reduce the amount of experimental work required to characterize a system for purposes such as optimization studies. Models were developed for the extraction of copper from ammoniacal sulfate and carbonate solutions with commercially available extractants commonly used by industry. Results from laboratory shakeout tests compared well with predictions of the equilibrium concentrations of copper and ph values. For example, the loading of copper onto the solvent was predicted for most cases within +/-5 pct of the measured values, and the ph to within +/-0.1 Ph unit in sulfate systems and +/-0.2 Ph unit in carbonate systems. Both mechanistic and empirical extraction equations were developed from laboratory data for copper and ammonia. The empirical-based models were slightly more accurate than the mechanistic-xdsed models. Industrial-level concentrations of the aqueous and organic constituents were used in this work. Independent variables included copper concentration, ionic strength, and initial ph of the aqueous phase; extractants, diluents, and their concentration in the organic phase; and temperature.