Remediation of Dye-Polluted Solutions by a New Tannin-Based Coagulant

Tanfloc is the name of a new tannin-based coagulant with a natural origin. It was tested on several dye-polluted aqueous solutions, namely, those containing triphenylmethane (Eriochrome Cyanine R), indigoid (Carmine Indigo), azoic (Chicago Sky Blue 6B, Palatine Fast Black WAN, or Acid Red 88), or anthraquinonic dyes (Alizarin Violet 3R). Particularly the removals of Alizarin Violet 3R and Palatine Fast Black WAN were studied. According to the classical influence-of-variable method, Tanfloc present a high coagulating activity, as a relatively low dose (200 mg . L-1) can remove almost all of the initial dye concentration of Palatine Fast Black WAN (0.03 mmol . L-1). pH seems to negatively affect the dye removal process, whereas temperature is not an important factor. In addition, a design of experiments based on the response surface method led to the evaluation of the effective interaction between coagulant dosage and initial dye concentration, so an optimal point was established for Palatine Fast Black WAN with a coagulation capacity (q) equal to 0.61 mmol . g(-1). Freundlich and Langmuir models were applied, and adjusted r(2) correlation factors were above 0.85 in all cases.