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The feasibility of using an agricultural byproduct, almond shell (Prunus dulcis), as an adsorbent in removal of basic dyes, namely, methylene blue (MB), methyl violet (MV), and toluidine blue O (TB), were evaluated in a batch adsorption process. The adsorption characteristics of MB, MV, and TB onto almond shell (AS) were investigated with respect to the changes in initial pH of dye solutions, contact time, initial dye concentration, and temperature. The dye adsorption equilibria were rapidly attained after 30 min of contact time. The adsorption kinetics were analyzed using pseudofirst-order, pseudosecond-order, Elovich, and intraparticle diffusion models and the adsorption data were well described by the pseudosecond-order model. The equilibrium adsorption data were interpreted in terms of the Langmuir, Freundlich, Temkin, and Dubinin−Radushkevich (D-R) isotherm models. The monolayer adsorption capacity of AS was found to be 51.02 mg·g−1 for MB, 76.34 mg·g−1 for MV, and 72.99 mg·g−1 for TB by using the Langmuir model equation. The thermodynamic parameters proved that the present adsorption process was feasible, spontaneous and endothermic in nature in the temperature range of (5 to 40) °C.

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The ability of activated carbon which was produced by chemical activation using zinc chloride from tea industry wastes (TIWAC) to adsorb phenol molecules from aqueous solution was tested by equilibrium, kinetic, and thermodynamic parameters. Phenol adsorption on TIWAC took place with a high yield at pH values in the range 4 to 8. The optimum contact period was observed as 4.0 h and from the adsorption graphs plotted as a function of time; it was established that phenol adsorption on TIWAC conformed more to a pseudosecond-order kinetic model. Additionally, it was determined that the adsorption rate is controlled by intraparticle diffusion as well as film diffusion. It was established that phenol adsorption on TIWAC can be better defined by the Langmuir adsorption model and its adsorption capacity was 142.9 mg·g–1 from the linear Langmuir equation. Temperature had an adverse effect on adsorption yield, and hence, the adsorption process was exothermic in our case. Moreover, increasing electrolyte concentration in the medium has a positive effect on adsorption yield. From the data obtained, it was concluded that the removal of phenol from aqueous solution by TIWAC produced from tea industry wastes with a very low cost took place with an extremely high performance.