Residual color profiles of reactive dyes mixture during a chemical flocculation process

Residual color profiles of reactive dyes during a chemical flocculation process were simultaneously determined by employing a multiple linear regression (MLR) method. The color removal processes for a single dye of Reactive Black KN-B (KN-B), a binary mixture of KN-B and Reactive Violet K-3R (K-3R), and a ternary mixture of KN-B, K-3R and Reactive Red K-2BP (K-2BP) by using poly(epicholorohydrin-diamine) (PEPIDA) were investigated. It was shown that free dye, complex of dye + PEPIDA as well as the light scattering by the fine particles of the flocs are the three components that responded for the residual color in the samples of single reactive dye. In the mixtures of 50 mg/L K-3R + 50 mg/L K-2BP, K-3R was preferentially removed in the region of insufficient dosage of PEPIDA (<34 mg/L). The residual color is related to the concentration of two free dyes, two complexes of dye + PEPIDA and fine flocs dispersed in solutions. In the sample of the ternary mixture, the dye removal is in the order of K-3R, K-2BP and KN-B in the region with shortage dosage (PEPIDA:dye < 0.33, w/w). In the over-dosed region (PEPIDA:dye > 0.45, w/w), the residual color in the samples is mainly from the re-stabilized complexes of dye + PEPIDA. The light scattering by the particles is another reason for the decrease ca. 1–4% in color removal efficiency. At the optimal dosage area (PEPIDA:dye = 0.35–0.38, w/w), the color removal efficiencies for the dyes are greater than 90% under the conditions used. The binding constants for K-3R, K-2BP and KN-B onto PEPIDA were estimated to be 9.31 × 106, 1.86 × 106 and 6.72 × 105 L/mol, respectively.