Comparative performance and techno-economic evaluation of pristine and hybrid Sn- and Mg- based coagulants for the removal of Cr(VI) and fluoride ions

The persistent co-occurrence of fluoride (F − ) and hexavalent chromium (Cr(VI)) in water systems raises significant concerns and highlights the need for effective treatment. Coagulation technology prompts significant research efforts toward the use of new economically viable coagulants. This study evaluates a series of novel coagulants, such as, inorganic SnCl₄ and MgO, as well as hybrid polymer-metal systems (Sn, Mg or Sn/Mg) based on chitosan (CS), starch (ST) and poly(vinyl alcohol) (PVA), for the comparative removal of F − and Cr(VI) under single and co-contamination conditions. In addition, the work incorporates an economic assessment, delivering a comprehensive cost-performance analysis that integrates treatment effectiveness with material and operational expenses. For Cr(VI) removal, SnCl₄ achieves the highest efficiency (99.8%) under acidic conditions (pH 5) with a low production cost (€0.05/mL), making it the most favorable option from a cost–performance standpoint. CS@Sn also performs effectively under the same conditions but is less economically competitive (€0.14/mL). In contrast, F − removal is optimized at pH 3 (84.3%), where ST@Mg combines outstanding removal efficiency with the lowest production cost (€0.04/mL), highlighting its suitability as a cost-effective coagulant. The integrated framework enables mechanistic differentiation and identifies the most effective and economically viable coagulant.