Adsorption of Malachite Green Using Alkali-Modified Fish Scale Bioadsorbents

Abstract

The removal of toxic Malachite Green (MG) dye from water was studied using low-cost fish-scale biosorbents chemically activated with NaOH and KOH. The fish scales were cleaned, ground and soaked in 0.3 M NaOH or KOH (24 h), then rinsed and oven-dried to produce two adsorbents (FS-NaOH, FS-KOH) Batch experiments examined the effects of solution pH (3–11), adsorbent dose, and temperature (20–40 °C) on MG uptake. Equilibrium data were fitted to Langmuir and Freundlich isotherms. The NaOH-treated scales showed higher adsorption capacity than KOH-treated. Removal efficiency increased with higher pH and larger adsorbent dose, reaching >95% at optimal conditions. The data best fit a Langmuir model (monolayer adsorption), with maximum capacities on the order of 10–20 mg·g⁻¹ (FS-NaOH) and lower for FS-KOH. Kinetic analysis indicated pseudo-second-order behavior. The results demonstrate that alkali-modified fish scales are effective biosorbents for MG, with NaOH activation yielding superior performance.