Comparative assessment of methylene blue removal using gypsum and red ceramic waste as low-cost adsorbent

Dyes present in industrial effluents, when improperly discharged, tend to cause serious environmental and societal problems. The adsorption method is an efficient and low-cost technique for treating industrial effluents. Various residues have been studied to add value to them and reduce costs, thus promoting a sustainable process. Construction waste has generated negative environmental impacts and land occupation. Gypsum residue (GR) and red ceramic residue (RCR) are commonly found in the building and demolition of houses and structures. This study aimed to investigate the adsorption kinetics and isotherms of methylene blue (MB) on the surface of untreated and NaOH-treated GR and RCR, comparatively, to assess their potential as adsorbent materials. Both GR and RCR were characterized, and kinetic and isotherm models were applied. No significant differences were observed in the chemical composition or surface physical structure of the adsorbents. The kinetic study showed that adsorption equilibrium was rapidly achieved, between 5 to 30 minutes for GR and 2 to 5 minutes for RCR. The highest removal percentages were found for RCR, reaching up to 99% MB removal. Adsorption capacities (qm) were also higher for the RCR adsorbent, reaching a value of 7.61 mg g-1 under untreated conditions.