| Summary: | Seed husk of Bengal gram (SHBG) (Scientific Name: Cicer arietinum) was used as an adsorbent for the removal of a direct dye namely Congo red (CR), two basic dyes namely methylene blue (MB) & rhodamine-B (RB) and an acidic dye namely acid blue 25 (AB) from aqueous solutions with equilibrium isotherms. The effect of particle size, of mass of adsorbent, of agitation speed of shaker and of temperature of dye solutions was studied for understanding the interaction of dyes with adsorbent. The uptake of dyes by the adsorbent was increasing with increasing mass of the adsorbent, decreasing with increasing size of the adsorbent, and increasing with increasing agitation speed and temperature. The adsorption capacity for each dye-adsorbent system was determined by using the Langmuir isotherm. The adsorption capacity of adsorbent for MB, RB, CR and AB was 333.33, 133.34, 78.12 and 5.56 mg g−1, respectively. The experimental data fit well with the Langmuir and Freundlich models. The standard enthalpy change of adsorption for MB, RB, CR and AB was 13.5, 10.97, 4.01 and 6.72 kJ mol−1, respectively. The average standard entropy change of adsorption for MB, RB, CR and AB is 58.2957, 36.869, 13.2138 and −3.4179 kJ mol−1, respectively. The adsorption of two basic dyes is much higher than that of the direct and acid dyes.
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