Discoloration of textile effluent by natural clay improved through the presence of dyeing additives

The aim of this work was to investigate the possible mechanisms of adsorption of anionic dyes from effluents onto natural clay, and particularly the influence on the adsorption of dyeing additives, released in the effluents with the dyes. Batch experiments with an anionic dye (RR120) at different conditions showed that the adsorption was enhanced at high ionic strength, low pH and in the presence of the additive such as CHT Catalase derived from enzymatic products. On the contrary, the presence of another additive, Duralkan (nitrogenated polycondensate, formaldehyde and metal free), had a negative effect. Experimental methods, such as Fourier transform infrared spectroscopy, electrophoretic mobility and streaming induced potential, allowed us to evidence that CHT Catalase when mixed with RR120 neutralizes the dye and decreases the repulsion between RR120 molecules and the clay negative surfaces, thus favouring adsorption. However, the additive Duralkan does not neutralize the dye, but interacts with the clay, thereby competing with the dye for the clay surface reactive sites, leading hence to adsorption reduction. The efficient discoloration of effluents by clay suggests that in overall, the negative effect of some additives on adsorption is overcome by the positive effect of others. Thus, crude clay may be a promising adsorbent to treat effluents containing dyes and chemical additives.