REMOVAL OF THE SYNTHETIC AZO PIGMENT NAPHTHOL RED (PR170) BY ADSORPTION ONTO SILICA (SiO2) FROM AQUEOUS SOLUTIONS

Synthetic dyes are extensively used in many industrial fields, such as textile, paper, leather tanning, food processing, plastics, cosmetics and printing industries. Synthetic dyes are complex organic molecules resistant to many agents (e.g., detergents) and exhibit a considerable structural diversity. Among them, most of the dyes currently used in the industry are azo derivatives and their wastes are toxic and carcinogenic posing a serious hazard to aquatic living organisms1. The adsorption of dyes from aqueous solution has proven to be an excellent approach to treat effluents as well as an economical method for dye removal2. Naphthol Red (PR170) is a very important type of azo pigment mainly applied in fields like coatings and inks, but no adsorption studies were carried out to develop a strategy to reduce the discharge of this dye in the effluents. In the present work, the removal of Naphthol Red by adsorption on silica (SiO2) was investigated. In particular, the effects of the pH of the solution, the particle size (granulometry) and the pore size (porosity) of the adsorbent on the process were in batch evaluated. Due to the low water solubility of Naphthol Red, the suspensions were prepared in a water/dimethylformamide (10% v/v) mixture, in an ionic medium 0.1 M NaCl. Our findings show that the adsorption on silica removes 95% of the pigment from aqueous solutions (pH = 7.00, CPR170 = 4.00 mg L-1).