Adsorption mechanisms of benzohydroxamic acid and sodium oleate on calcium stannate: Combined experimental and DFT study for enhancing flotation recovery

Tin is a strategically important metal used in electronics, alloy manufacturing, and renewable energy. Approximately 80 % of global tin production is derived from cassiterite (SnO 2 ) beneficiation; The reserves of high-quality tin ore are gradually decreasing, and the research focus on tin extraction is shifting toward the recycling and reuse of tailings. However, tin and iron in tin–iron tailings are strongly intergrown, making separation challenging. Previous studies have demonstrated that a calcination roasting–magnetic separation process under a CO/CO 2 atmosphere can convert iron into Fe 3 O 4 , thereby leaving tin in the form of nonmagnetic calcium stannate (Ca 2 SnO 4 ) to achieve effective tin–iron separation. Nevertheless, the tin content in the nonmagnetic fraction is only 0.5–1.0 %, which is far below the economic threshold for recovery by fumigation. Therefore, innovative pre-enrichment strategies are urgently needed to improve tin recovery efficiency. This study explores the feasibility of flotation of synthetic calcium stannate (Ca 2 SnO 4 ) using two commonly employed collectors: sodium oleate (a representative fatty acid) and benzohydroxamic acid (a typical hydroxamic acid). The recovery performance of calcium stannate (Ca 2 SnO 4 ) was evaluated by micro-flotation tests, and the chemical interactions induced by collector adsorption, as well as the adsorption mechanism, were elucidated in depth employing FTIR, XPS, and DFT simulations. The results reveal that NaOL, with its strong ligand bonding under alkaline conditions, substantially boosts flotation recovery-reaching up to 83.56 %. These findings offer practical guidance for optimizing flotation processes in tin recovery from the tin-bearing tailings.