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Congo red (CR), an anionic dye, is very harmful to the environment and should be removed via an easy and inexpensive technique. The adsorption of CR from an aqueous solution onto a mixture of illite-kaolinite clay minerals and surfactant-modified illite-kaolinite was investigated at different temperatures. The characterization of the raw clay mixture and the organified sample was confirmed with X-ray diffraction, FTIR spectroscopy, nitrogen gas adsorption at 77 K and transmission electronic microscopy techniques. Factors influencing the adsorption such as pH, adsorbent dosage and temperature were tested. The thermodynamic parameters G˚, H˚and S˚have been calculated, and it was found that the adsorption is exothermic in nature. The isotherm data were fitted by the linear form of the Langmuir and Freundlich models and showed a good fit with the Langmuir approach. The maximum adsorption capacity of surfactant-modified clay (83 mg/g) was found to be around 14 times higher than that of unmodified clay. Kinetic studies of CR on illite-kaolinite and organified illite-kaolinite were evaluated by pseudo-first-order and pseudo-second-order models.

a b s t r a c tAdsorption technology is one of the most promising technologies to remove heavy metals from water. This paper aims to remove arsenite As(III) from contaminated water using a less costly, easier to handle and efficient absorbent. Purified natural clay was characterized and tested as an adsorbent. Mineralogical and textural analysis showed that this adsorbent is a nonswelling clay mineral (illite + kaolinite) and a mesoporous material with specific surface area S BET = 128 m ). The adsorption equilibrium studies revealed that Freundlich isotherm was followed with a better correlation than the Langmuir isotherm, moreover, it was intra particle diffusion controlled. The adsorption of As(III) onto the mixture illite-kaolinite was significant in the pH range 9-10.8 with a maximum adsorption capacity q max = 233.1 mg·g -1 . At 298 K, the thermodynamic investigation indicates that the adsorption processes is spontaneous (∆G°a ds = -9.3 kJ·mol -1 ) and exothermic (∆H°a ds = -4.58 kJ·mol -1 ). The ∆S°a ds parameter was found to be +15.8 J·mol -1 ·K -1 meaning an increase in the randomness of the processes at the surface of clay particles.