A Green Ammonia Complexation Method (ACM) for Accurate Copper Grade Determination in Copper Ores: An Eco-Friendly Alternative to Toxic Ammonium Bifluoride Masking Agent

Abstract

Conventional iodometric methods for copper determination in ores rely on toxic ammonium bifluoride (NH₄HF₂) as a masking agent, which poses health hazards, environmental toxicity, and pH-dependent systematic errors (recovery 85–95%). In this study, a novel Ammonia Complexation Method (ACM) is developed as a safer and more accurate alternative. At pH ≈ 10.5–11, Cu²⁺ forms a stable tetraamine complex [Cu(NH₃)₄]²⁺, while interfering ions (Fe³⁺, Al³⁺, Mn²⁺, Pb²⁺, As) precipitate as hydroxides and are removed by filtration. After decomplexation and redissolution, the liberated iodine is titrated with standardized thiosulfate. Validation using three real copper ore samples from Iran and comparison with ISO methods showed that ACM achieves recovery values of 97.53–99.47% and RSD below 1% (0.24–0.59%), outperforming ISO methods (recovery 93.46–103.98%, RSD up to 4.01%). ICP-OES confirmed residual interferences below 0.1 mg/L. The proposed ACM eliminates toxic fluoride reagents, reduces chemical hazards, and provides superior accuracy and precision for routine copper grade determination.