Removal of Methyl Orange and Malachite Green from Model Waters Using Pumice Stone as an Adsorbent

Water pollution by synthetic dyes represents a pressing global environmental concern due to the persistence and toxicity of these contaminants. In Mexico, the Atoyac River, spanning the states of Puebla and Tlaxcala, has been identified as a severely impacted water body, with high concentrations of dyes primarily discharged by the textile industry. Among the various treatment technologies explored, adsorption has emerged as a highly effective and sustainable method owing to its simplicity, cost-effectiveness, and high removal efficiency. In this study, natural pumice powder, abundantly available in the central region of Mexico, was investigated as an eco-friendly adsorbent for the removal of methyl orange (MO) and malachite green (MG) from model aqueous solutions. The material was used without any chemical modification, achieving adsorption capacities of 4.8 mg/g for MO and 9.2 mg/g for MG with adsorbent doses of 0.1 g and 0.05 g, respectively. The adsorption process was found to be independent of pH, allowing for operation under neutral conditions. Besides, high removal efficiencies were attained with contact times as short as 15 minutes. Kinetic modeling revealed that the adsorption data for both dyes best fit the pseudo-second-order model, indicating a rapid and chemically controlled mechanism. These results demonstrate that using natural pumice powder offers a viable, low-cost, and environmentally sustainable alternative for the remediation of dye-contaminated water bodies such as the Atoyac River.