Abstract
Dyes used by the textile, tannery, and food industries tend to pollute water bodies and must be removed to get clean water. Hydroxyapatite (HAP) was synthesized from eggshells using the wet precipitation process. The as-synthesized HAP was characterized using Fourier Transform Infrared (FTIR) and X-ray powder diffraction (XRD). The synthesized HAP was mixed with three different clays: halloysite (HNT), kaolinite (KAO), and bentonite (BENT). The removal efficiency values of methylene blue (MB) from the data showed that HAP-BENT adsorbents had higher values, followed by HAP-HNT and then HAP-KAO adsorbents. The combined masses of 24 mg, 34.5 mg, and 33 mg (representing 20%, 15%, and 10% of HAP-BENT mass) had average adsorption capacity values of 20.7 mg/g, 17.2 mg/g, and 17.9 mg/g, respectively. For each mass percentage, the adsorption capacity values were found to decrease with adsorbent dosage. The HAP-BENT composites had removal efficiency values of 98.4, 91.9%, and 91.9%, respectively. Adsorption data for the HAP-BENT adsorbents were found to be well described by the Langmuir isotherm model and pseudo-second-order kinetic model. The effect of temperature on adsorption capacity was evaluated and thermodynamical modeling was undertaken. The thermodynamical modeling predicts that based on the value of the change in enthalpy and Gibbs free energy the process was exothermic and spontaneous. This work confirms the potential of HAP-clay composites in removing MB from water.
Highlights
Dyes used by the textile, tannery, and food industries tend to pollute water bodies and must be removed to get clean water
Hydroxyapatite (HAP) was synthesized from eggshells using the wet precipitation process. e as-synthesized HAP was characterized using Fourier Transform Infrared (FTIR) and X-ray powder diffraction (XRD). e synthesized HAP was mixed with three different clays: halloysite (HNT), kaolinite (KAO), and bentonite (BENT). e removal efficiency values of methylene blue (MB) from the data showed that HAP-BENT adsorbents had higher values, followed by HAP-HNT and HAP-KAO adsorbents. e combined masses of 24 mg, 34.5 mg, and 33 mg had average adsorption capacity values of 20.7 mg/g, 17.2 mg/g, and 17.9 mg/g, respectively
Characterization of Adsorbents. e results of the FTIR analysis of synthesized HAP samples are plotted in Figure 3(a) for the calcined hydroxyapatite and crushed or powdered eggshell (EggS) samples. e carbonate functional group showed up within the range 1395–1600 cm−1 (]3; asymmetric stretch vibration) and 873–889 cm−1 (]2; out-of-plane bend vibration). e crushed eggshell showed this carbonate functional group at 1026 cm−1
Summary
Dyes used by the textile, tannery, and food industries tend to pollute water bodies and must be removed to get clean water. E HAP-BENT composites had removal efficiency values of 98.4, 91.9%, and 91.9%, respectively. Researchers have shown that several conventional methods and remediation methods to treat these polluted water sources are often not effective in dye removal [9]. Bagane and Guiza [15] showed that clay is able to remove MB due to its high surface area as it showed an adsorption capacity of 300 mg/g. Kaolin as a dye adsorbent was studied by Ghosh and Bhattacharyya [14] who showed that NaOH was able to improve its adsorption capacity through purification and treatment
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