MB /aqueous solution MB+/clay-Na NR /aqueous solution NR /clay-Na MG/aqueous solution MG/ clay-Na
pH MB+ (MB+)2 MB+ (MB+)n NR+H NR NR+H NR MG+ MG2+H MG+ MG2+H
3 648 - 658 *608 520.5 - 527 - 617 424 621 426
4 - - - - 519.5 - 527.5 - - - - -
5/ 5.4 668 624 - 585 521.5 - 523.5 - 617 425 619 -
6.5/ 7 647 - - 588 518 - - 460 617 424 617 426
8/ 9 668 - - 584 - 454 - 452.5 617 423 631 / 596 -
10   - - - - 451.5 - 452 Col. Col. Col. Col.
11 668 621 - 567 -   -   Col. Col. Col. Col.
12 - - - - - 451 - 450.5 Col. Col. Col. Col.
13 653 610 - 566 -   -   Col. Col. Col. Col.

MB+, (MB+)2 and (MB+)n : monomer, dimer and agglomerates forms of Methylene blue dye.
NR+H and NR: monomer and conjugate base form of Neutral red dye. Col.: colorless.
MG+ and MG2+H: monomer and protonated cations forms of Malachite green oxalate dye.
Table 2: Evolution the main absorption bands of dyes in aqueous solution and in dyes/clay-Na suspensions as a function of pH for [MB]= [NR]= [MG]=50mg/L, [Clay- Na]=0.3g/L, T=298K and contact time=60 min (MB and NR) and 80min (MG).