Using the HClO₄-H₂O₂ System for Efficient Platinum Leaching: Optimal Conditions and Kinetics

This work studies the kinetics of platinum leaching using HClO₄ and H₂O₂. The experiments are carried out by dissolving small pieces of high-purity platinum with an irregular shape. The knowledge obtained can be useful for leaching minerals with disseminated native platinum in refractory minerals, such as silicates, of which there are large quantities in nature but are not processed due to their great refractoriness. The results show that increasing the temperature and the HClO₄ concentration increases the leaching rate. Interestingly, for each HClO₄ concentration, an H₂O₂/HClO₄ = 2.5 ratio exists that optimizes the leaching kinetics. The best operating conditions are ≈70 °C, [HClO₄] 3 m, and [H₂O₂] 7.2 m. From kinetic analysis, it is concluded that the leaching process is governed by a mixed control stage (diffusion in the boundary layer and surface chemical reaction). In addition, it is proposed that the leaching process mechanism is supported by fundamental thermodynamic and experimental results, highlighting the importance of chlorine gas for this novel extraction method that reaches elevated recoveries. This process is also interesting because the chemical system can potentially weaken the crystallographic structure of silicates (very important), increasing the feasibility of extracting the partially not-liberated precious metals.