Eco-friendly iron removal from contaminated water using chemically modified rice straw: Adsorption mechanisms and performance

The availability of water does not always guarantee its quality, particularly when it is contaminated with iron (Fe), which poses health risks such as kidney failure, cardiovascular diseases, and digestive disorders. This study evaluates the potential of rice straw -modified Ca(OH)₂ (Rs-OCa) as an adsorbent for removing Fe(II) ions from groundwater. Rice straw, a widely available agricultural waste in Indonesia, was chemically modified to enhance its adsorption capacity by increasing active sites, removing lignin, and improving its affinity for metal ions. FTIR analysis confirmed the presence of hydroxyl (-OH) and carboxyl (-COOH) functional groups, while XRD analysis revealed both crystalline and amorphous structures that contribute to stability and adsorption efficiency. Adsorption tests indicated optimal Fe(II) removal at pH 4–5 with an adsorbent dose of 0.75 g per 100 mL of solution. The adsorption isotherm followed the Langmuir model, with a maximum adsorption capacity (Qₘ) of 22.47 mg/g, indicating a homogeneous monolayer adsorption mechanism. The Freundlich model (KF = 8.91 mg/g, n = 2.5) further confirmed surface heterogeneity and high adsorption efficiency at low Fe (II) concentrations.The results demonstrate that Rs-OCa is an effective, economical, and environmentally friendly adsorbent for iron removal from contaminated water.