Effect of residual polyacrylamides on the flotation performance: mechanisms, process impacts and water treatment for recycling and reuse

• Residual PAMs accumulate in recycled flotation water and alter mineral processing. • PAMs depress the flotation of ores through adsorption mechanisms. • No clear residual PAM concentration thresholds to predict depressive flotation effects. • PAM effects on flotation depend on polymer type, conformation and water chemistry. • Combined or hybrid treatments provide the highest (> 90%) PAM removal efficiency. Residual polyacrylamides (PAMs) from tailings thickening and dewatering accumulate in recycled flotation water. The high molecular weight polymers persist through water reuse and interact with mineral surfaces and flotation reagents, modifying surface charges, hydrophobicity, aggregation behavior and leading to significant variations in flotation performance. A comprehensive evaluation of PAM adsorption mechanisms on key mineral phases under recycled-water conditions and their implications for flotation performance was conducted. Complementary characterization tools, including mineralogy, physicochemistry, and microflotation tests were compared. Results showed that, at the mineral–water interface, PAMs adsorb through electrostatic interactions, hydrogen bonding, or metal–ligand coordination, thus altering surface charge, hydrophobicity, and bubble–particle attachment. High ionic-strength matrices typical of recycled water (Ca 2+ , Mg 2+ , SO 4 2- , residual reagents) and pH enhance PAM adsorption through mixed electrostatic–hydrogen bonding interactions. Depending on polymer characteristics, molecular conformation, and process conditions, PAMs may behave as depressants, markedly decreasing flotation recovery and selectivity. Such behavior complicates process optimization and underlines the absence of clear thresholds defining critical PAM concentrations in flotation circuits. Treatment processes (advanced oxidation, biological, and hybrid), with efficiency up to 90%, allow PAMs removal from recycled water and the mitigation of detrimental metallurgical impacts. Overall, this study provides an integrated assessment of residual PAMs in froth flotation circuits, emphasizing their action mechanisms, impacts on ores flotation behavior, and promising treatment processes for sustainable water recycling.