The synergic extraction of ni from ammoniacal sulfate solution by mixtures of lix 64n and kelex 100 was studied using slope analysis, continuous variation, and mathematical modeling. This extractant pair was discovered as part of a study to find extractants that perform at the higher ph level needed for leaching cu, ni, and CO, and thus eliminate ammonia stripping and recharging steps in current processes. Ni was more efficiently extracted at higher ph with the lix 64n-kelex mixture than with either extractant alone. A model is proposed based on four different stoichiometries, each contributing to the overall reaction. The four ni-lix 64n-kelex species are 1/2/0, 1/0/3, 1/1/1, and 1/2/1. Ammonia is coextracted, but can be selectively scrubbed with 2 g/l h2so4. Ni can be selectively stripped from the ni- and cu-loaded extractants with 10 g/l h2so4; then cu is stripped with 150 g/l h2so4. A continuous process was simulated with a batchwise circuit, which showed no loss of extraction efficiency in 10 cycles.