Chitosan/nanohydroxyapatite composite based scallop shells as an efficient adsorbent for mercuric ions: Static and...

Area of Science:

• Materials Science
• Environmental Science
• Chemical Engineering

Background:

• Mercury contamination poses a significant environmental and health risk.
• Developing efficient and sustainable adsorbents for mercury removal is crucial.
• Chitosan and nanohydroxyapatite are promising materials for water remediation.

Purpose of the Study:

• To synthesize and characterize chitosan/nanohydroxyapatite composites from scallop shells.
• To evaluate the adsorption performance of these composites for mercury (Hg+2) removal.
• To investigate the static and dynamic adsorption behavior and reusability of the optimal composite.

Main Methods:

• Composite preparation using varying chitosan: nanohydroxyapatite ratios.
• Characterization using TGA, XRD, N2 adsorption/desorption, SEM, Zeta potential, and FTIR.
• Static adsorption studies varying adsorbent dosage, pH, time, and Hg+2 concentration.
• Dynamic adsorption studies evaluating bed height, flow rate, and Hg+2 concentration.
• Desorption and reusability tests using EDTA solution.

Main Results:

• BET surface area ranged from 189 to 512 m²/g.
• CP12 composite showed maximum static adsorption capacity of 111.6 mg/g, fitting Langmuir isotherm and pseudo-second-order kinetics.
• Optimal dynamic adsorption occurred at 3 cm bed height, 2.0 mL/min flow rate, and 300 mg/L Hg+2 concentration.
• Breakthrough and exhaustion times were 9 h and 21 h, respectively.
• Yoon-Nelson and Thomas models best described the dynamic breakthrough curve.
• Maximum desorption efficiency was achieved with EDTA, and CP12 showed validity over three adsorption-desorption cycles.

Conclusions:

• Chitosan/nanohydroxyapatite composites from scallop shells are effective for mercury removal.
• CP12 exhibits excellent adsorption capacity and reusability, making it a viable adsorbent for mercury remediation.
• The study provides valuable insights into the application of sustainable materials for wastewater treatment.