Model established by response surface methodology for Cu(II) removal from water with mercaptoacetyl aminomethy polyacrylamide as flocculant

The flocculation process has been validated as a highly effective technique for the removal of heavy metal ions. A novel flocculant, mercaptoacetyl aminomethy polyacrylamide (MAAPAM), was synthesized from acrylamide, sodium formate, ammonium persulfate, formaldehyde, dimethylamine, and thioglycolic acid as the raw materials. Response surface methodology (RSM) was employed to optimize the flocculation conditions for Cu(II) removal using MAAPAM. The optimal conditions for achieving the maximum Cu(II) removal efficiency of 99.21 % were a Cu(II) concentration of 7.5 mg/L, a pH of 6.1, and a MAAPAM dosage ratio to Cu(II) concentration of 5.5:1. These conditions were in close agreement with the model predictions, with a relative error of less than 0.5 %. Furthermore, the applicability of the quadratic regression model developed through RSM was rigorously evaluated. Coexisting inorganic ions (Na⁺, Ca²⁺, NO₃⁻ and SO₄²⁻) in water samples exerted a slight inhibitory effect on the removal of Cu(II) and had minimal impact on the quadratic regression model. The relative error between the measured and predicted values was maintained within ±5 %. The analysis of floc morphology and fractal dimension was conducted to investigate the flocculation mechanism. The results demonstrated that the chelation reaction between the sulfhydryl groups (—SH) in MAAPAM and Cu(II) plays a predominant role in capturing Cu(II). Additionally, the adsorption bridging and netting-sweeping mechanisms are also critical for achieving efficient removal of Cu(II) during the flocculation process.