Sustainable and Low-cost Hydroxyapatite/Starch for the Removal of Methylene Blue from Aqueous Solutions

Hydroxyapatite/starch (HA/Star-n; « n » represents the weight ratio of HA to Star ) bio-composite was obtained by in situ chemical precipitation of calcium hydroxide using phosphoric acid in the presence of starch. Analysis through FTIR and XRD confirmed the formation of hydroxyapatite within the polymer matrix. To date, no work was reported in the literature concerning the use of composites based on hydroxyapatite and native starch as adsorbent in the treatment of wastewaters. For this, the elaborated HA/Star-n composite was used for the removal of methylene blue (MB) from aqueous solution through batch experiments. The effect of pH (2-12); contact time (5-180 min) and dye concentration (15-100 mg/L) was explored. The results prove that the optimum pH for MB removal by the bio-composite is pH= 6. Conversely, pure HA showed minimal removal efficiency at this pH. Further, kinetic study revealed that the adsorption of MB onto HA/Star-n is a rapid process described by pseudo-second order model. Results from the dye concentration study suggest that the adsorption efficiencies of the elaborated bio-composite can exceed 90% with an adsorption capacity of 45.51 mg/g demonstrating that HA/Star-n has a great potential as an adsorbent for the removal of MB from aqueous solution.