Macauba palm (Acrocomia aculeata) cake from biodiesel processing: An efficient and low cost substrate for the adsorption of dyes

The potential of natural and heat-treated Macauba palm cake as adsorbent for the removal of Methylene Blue (MB) and Congo Red (CR) from solution has been investigated. Equilibrium adsorption was attained in <7 h and the process was favored at pH 5.0 for MB and pH 6.5 for CR with an adsorbent (g):adsorbate (mL) ratio of 1:200 and an initial concentration of adsorbate of 25 mg L−1. The maximum adsorption capacities of the natural and heat-treated materials were, respectively, 25.80 and 32.30 mg g−1 for MB, and 32.00 and 20.30 mg g−1 for CR. The isotherm model proposed by Sips represented most adequately the adsorption of MB and CR. The adsorptions of the dyes were best described in terms of a pseudo second-order reaction. Thermodynamic parameters such as ΔHo, ΔSo and ΔGo were calculated. The adsorption process was found to be endothermic and spontaneous. Macauba palm cake is adequate for the removal of waste dye from industrial effluents by virtue of its abundance, low cost and efficiency of adsorption.

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► The system is cheap and efficient for the removal of dyes.
► Macauba palm cake has been shown to be a suitable adsorbent for the removal of Methylene Blue and Congo Red from solution.
► The natural palm cake was more efficient in the removal of Congo Red than Methylene Blue.
► Heat treatment eliminated some volatile components from the cake, increasing the efficiency of adsorption of Methylene Blue.
► Macauba palm cake thus has potential as a low-cost natural biosorbent for the removal of waste dye from industrial effluents.