Experimental design and modelling of removal of dyes using nano-zero-valent iron: a simultaneous model

The aim of the present study is to remove dyes from aqueous solutions since the dye compounds are harmful to human life and the environment. Nano-zero-valent iron particles were synthesised and used to remove the synchronisation of Direct Red-31 (DR-31) and Direct Brown-2 (DB-2). Nano-zero-valent iron particles were characterised using SEM (scanning electron microscopy) and XRD (X-Ray Diffraction) analysis. The effects of five influential variables were investigated on the dye removal including DR-31 and DB-2 concentrations (4-20 mg L-1), NZVI dosage (0.15-0.95 g), pH of the solution (5-9) and contact time (20-140 s). In order to improve the conditions, the response surface methodology (RSM) approach was applied using the central composite design (CCD). The response for the removal of DR-31 and DB-2 was predicted second-order polynomial models. The Analysis of Variance (ANOVA) presented that second-order models, with high F-value, were so remarkable in order to eliminate the simultaneity of dyes. Based on the results of the perturbation plot, NZVI dosage and pH of the solution had the most effect on the removal of the dye mixture compared to three other factors. The optimum variables are achieved: NZVI dosage (0.75 g), DR-31 concentration (12.00 mg L-1), DB-2 concentration (12.00 mg L-1), contact time (110.00 s) and pH of the solution (6). Under optimal conditions, the removal rate of DR-31 and DB-2 was 91.03% and 94.57%, respectively. The NZVI can be used effectively to salvage pollution problems posed by anionic dyes in the environment.