Hexavalent Chromium Mitigation with Antimony-Based Additives: A Focus on Operator Exposure and Sb Speciation

Over the past decades, increasing attention has been devoted to worker safety and environmental sustainability in cement production, particularly in reducing water-soluble hexavalent chromium [Cr(VI)]. Directive 2003/53/EC sets a limit of 2 mg/kg for Cr(VI) in cement due to its toxicity and allergenic potential. Consequently, several additives have been developed to convert Cr(VI) into the less toxic and insoluble Cr(III). Among them, Sb(III) compounds have demonstrated superior performance over traditional reducers. This study compares two antimony-based additives: a liquid formulation and a microgranular product with controlled-release technology. Citric acid–EDTA extraction followed by speciation analysis confirmed the stability of Sb(V)-citrate complexes, allowing accurate differentiation between Sb(III) and Sb(V) and preventing oxidation artifacts. Furthermore, the optimal extraction conditions were identified to extract approximately 60% of Sb2O3 from the microgranular additive. These extraction protocols were applied to cement premixes containing total chromium levels of 40 ppm and 80 ppm, respectively. HPLC-ICP-MS/MS analyses revealed distinct Sb(III)/Sb(V) speciation profiles. Inhalable dust exposure was then assessed by sampling air during handling operations. The chemical speciation of antimony is crucial for risk assessment in the cement industry, as Sb(III) is significantly more toxic than Sb(V), with studies reporting its carcinogenic potential and respiratory toxicity upon inhalation (Ribeiro et al., 2020). Approximately 1000 L of air were collected over 5 hours using glass fiber filters, simulating operator exposure to airborne antimony species. The results provide valuable insights into occupational safety related to additive formulation and Sb speciation.