Rapid removal of cationic dyes from water by coprecipitation with aluminum hydroxide and sodium dodecyl sulfate

• Coprecipitation with aluminum hydroxide and sodium dodecyl sulfate (SDS) was designed.
• SDS induced the coagulation of aluminum hydroxide and the removal of cationic dyes.
• Nearly complete removal was achieved by using 100 mg L−1 each of SDS and Al(III).
• The proposed method was applicable to wastewaters containing dissolved organic substances.

A coprecipitation method using sodium dodecyl sulfate (SDS) and aluminum hydroxide was designed for the efficient removal of three cationic dyes: methylene blue (MB), malachite green (MG), and crystal violet (CV), from water. The coprecipitation occurred by the hydrolysis of Al(III) ions in the presence of SDS far below the critical micelle concentration. Microscopic observation and spectrometric analyses clearly indicated the sorption of SDS into the precipitate. A molecular probe study using 1-phenyl-N-naphthylamine suggested that the precipitate provided hydrophobic regions suitable for incorporating hydrophobic ion-pairs of cationic dyes with dodecyl sulfate ions. In the pH region from 7.9 to 8.6, the use of 100 mg L−1 each of SDS and Al(III) allowed nearly complete (>99%) removal of three cationic dyes that had hardly (<4%) been removed by the conventional coagulation method using aluminum hydroxide. The proposed method was successfully applied to the treatment of different wastewater samples containing dissolved organic substances and superior to the admicellar sorption method using SDS-coated aluminum hydroxide.