Geopolymeric adsorbents from fly ash for dye removal from aqueous solution

Area of Science:

• Materials Science
• Environmental Chemistry
• Inorganic Chemistry

Background:

• Coal fly ash is a significant industrial byproduct with potential for valorization.
• Basic dyes, such as methylene blue and crystal violet, are common water pollutants from textile and other industries.
• Developing cost-effective and efficient adsorbents is crucial for dye removal from wastewater.

Purpose of the Study:

• To synthesize novel inorganic polymer adsorbents from coal fly ash.
• To evaluate the efficacy of these fly ash-derived geopolymeric adsorbents for removing basic dyes from aqueous solutions.
• To investigate the influence of preparation conditions and adsorption parameters on dye removal efficiency.

Main Methods:

• Coal fly ash was treated with sodium hydroxide (NaOH) using a solid-state fusion method.
• Amorphous aluminosilicate geopolymers were formed as the adsorbent material.
• Adsorption experiments were conducted using methylene blue and crystal violet as model pollutants.
• Adsorption isotherms and kinetics were analyzed using Langmuir, Freundlich, and pseudo-second-order models.

Main Results:

• The synthesis successfully produced amorphous aluminosilicate geopolymer adsorbents from coal fly ash.
• Optimal preparation involved a 1.2:1 NaOH:fly ash weight ratio and fusion temperatures of 250-350°C.
• The synthesized adsorbents demonstrated significantly higher adsorption capacities for both dyes compared to raw fly ash and natural zeolite.
• Adsorption capacity was greater for crystal violet than for methylene blue, and was influenced by adsorption temperature.
• Adsorption data fitted well to Langmuir and Freundlich models, with the two-site Langmuir model providing the best fit.
• Adsorption kinetics followed a pseudo-second-order rate model.

Conclusions:

• Solid-state fusion of coal fly ash with NaOH is an effective method for creating geopolymeric adsorbents.
• These fly ash-derived geopolymeric adsorbents are highly efficient for removing basic dyes from wastewater.
• The adsorption process is influenced by adsorbent properties, dye type, and environmental conditions, following predictable isotherm and kinetic models.