Date Palm Stones as an Eco-Friendly Natural Adsorbent for Basic Blue 41 Dye Removal from Wastewater: Batch Adsorption Study

Abstract

Discharge of textile effluents containing synthetic dye is still one of the more obstinate environmental challenges in many developing locations. The present work has focused on the investigation of raw date palm (Phoenix dactylifera) stones, which are an abundant agricultural by-product in Iraq, as a low-cost natural adsorbent for the removal of Basic Blue 41 (BB41), a cationic azo dye, from aqueous solution. The material was not subjected to any chemical or thermal activation, only washed, dried, powdered and sieved below 125 µm. FTIR, XRD and FESEM were used to evaluate the surface and structural properties and the point of zero charge was determined to be close to 6.3. Batch studies were conducted to investigate the effect of solution pH, adsorbent dose, contact time, initial dye concentration and temperature. The removal increased significantly with pH from 2 to ∼8. This is consistent with electrostatic interaction between the protonated dye and the more negative biosorbent surface. Equilibrium was reached in around 75 min and uptake increased with increasing temperature. The kinetics data were better fit by the pseudo second order model and the equilibrium data by the Langmuir isotherm with a maximal monolayer capacity of about 48 mg/g. Thermodynamic analysis showed a positive value of ΔH° (about +21.5 kJ/mol) and negative values of ΔG° indicating an endothermic and spontaneous process. The results show that untreated date palm stones could be used as a real low-cost and practical adsorbent for waste water containing cationic dyes, while valorising a waste stream.

Highlights
● Raw, unmodified date palm stone powder was used to adsorb Basic Blue 41 dye.
● No chemical or thermal activation was applied, which keeps the process low-cost.
● Adsorption followed pseudo-second-order kinetics and the Langmuir isotherm.
● The maximum monolayer capacity reached about 48 mg/g at the optimum conditions.
● The process was endothermic, spontaneous and driven mainly by electrostatic attraction.