• Cu2+ activates cassiterite flotation by forming Cu–O bonds and promoting OHA adsorption, enhancing recovery.
• Cu2+ depresses calcite flotation by consuming OHA through precipitation and complexation, reducing collector availability.
• The study provides a mechanistic model for Cu2+ interaction with OHA on mineral surfaces, aiding in selective flotation.
• Findings are crucial for optimizing cassiterite flotation in the presence of unavoidable metal ions, improving tin recovery efficiency.