Scale-up factors, kinetics, passivation and sludge analysis for electrochemical removal of malachite green oxalate dye

A new approach has been proposed to predict the effectiveness of electrocoagulation (EC) process to treat synthetic dye solution containing malachite green oxalate or Basic Green-4 (BG 4). Process intensification was used to optimise the EC operational parameters. Constant current batch galvanostatic studies were carried out under a single-pair Al electrode system at spacing (0.3–2 cm), dipped area (12–31 cm2), current (0.1–0.5 A), time (0–70 min) and dye concentration (10–1000 mg/L). Maximum dye removal efficiency >96 was attained within 10 min of the EC process with dye concentrations ranging from 100 to 1000 mg/L at optimal parameters of 6.98 pH, 0.5 cm spacing, 8 cm dipped length and 17.86 mA/cm2 current density. The dye removal and functional groups were verified by Fourier transform infrared spectroscopy (FTIR) and UV/Vis measurements. The field emission scanning electron microscope (FESEM) results revealed that the sludge containing dye particles included more carbon and small amounts of Na and Cl. According to the atomic force microscopy (AFM) findings, there was evidence of polynuclear aluminium floc production and pitting corrosion. Furthermore, PI values of 0.769 to 1 and 0.328 to 0.443 show that the particles in both EC supernatants are linear polynuclear groups with varying sizes. A linear association with R2 of 0.96 was found in the kinetic analysis between the loading concentration (Ci) and the optimal removal time (ORT). Based on ORT estimates, operating costs (OC) were calculated, and for Ci >806.33 mg/L, EC was determined to be cost-effective.