Determination of Antimony in Antimony Ores Using Carbon Reduction-Assisted Digestion Coupled with Inductively Coupled Plasma-Optical Emission Spectrometry

Refractory antimonate minerals (e.g. tripuhyite) are difficult to decompose completely using conventional acid digestion methods, often leading to underestimated results in antimony determination. Although alkaline fusion and microwave digestion have been applied, these approaches may suffer from reagent interference or require specialized equipment. In this study, a novel sample pretreatment strategy based on an in situ carbon reduction mechanism was developed. The method employs a mixed acid system consisting of tartaric acid, hydrofluoric acid, nitric acid, and sulfuric acid. Under high-temperature conditions, concentrated sulfuric acid carbonizes tartaric acid to generate strongly reducing elemental carbon in situ, which efficiently reduces Sb(Ⅴ) to Sb(Ⅲ). This process suppresses the formation of antimonate precipitates and enables the complete dissolution of refractory antimonate minerals, thereby improving the accuracy of antimony determination in antimony ores. The content of antimony was determined by inductively coupled plasma-optical emission spectrometry (ICP-OES). The optimized conditions involved the use of 1.0 mL of 10% tartaric acid as the carbon source in the mixed acid system, with assisted digestion at 180℃. Subsequently, 10 mL of concentrated nitric acid was used as the extraction acid to simultaneously extract antimony and remove residual carbonaceous material. The method exhibited a relative standard deviation (RSD) of 0.23%–1.74% and a detection limit of 17.7 μg/g. Spike recoveries ranged from 96.2% to 104.4%, meeting the requirements of The Specification of Testing Quality Management for Geological Laboratories (DZ/T 0130.3-2006). Validation using certified reference materials and real samples showed that the measured values for reference materials were consistent with certified values, while results for real samples agreed well with those obtained by the atmospheric closed-vessel microwave digestion method, demonstrating the accuracy and reliability of the proposed method. The digestion was carried out under atmospheric open conditions, eliminating the need for specialized equipment. When combined with ICP-OES determination, the method enabled rapid analysis of large batches of antimony ore samples and remained accurate even for high-grade samples containing up to 40% antimony.