Residual peanut shells as zinc ions biosorbent: analysis of variables, removal mechanisms and disposal

The degradation of surface water quality is a consequence of human activities, particularly industrial and agricultural processes. Biosorbents are widely recognised as cost-effective adsorbents and numerous studies have demonstrated their efficacy in removing heavy metals from aqueous solutions. This study aims to elucidate the optimal conditions and the primary mechanisms involved in the removal of Zn(II) ions using ground peanut shells as adsorbent. The adsorption experiments were carried out in batch mode, with different parameter variations. The biomass was subjected to a series of analytical techniques to determine its physicochemical and environmental characteristics. Different kinetic models of the process were studied and adsorption isotherms were used to analyse the biosorption process. The optimal conditions for zinc removal were obtained at a biomass concentration of 50 g/L, an initial pH of 6.1, and a contact time of 120 min. Using these parameters, approximately 84 % of the metal was removed. Furthermore, peanut shells contaminated with zinc do not show significant changes in their ecotoxicological properties when disposed of on land. The results show that peanut shells are a promising and cost-effective alternative biosorbent for the removal of zinc ions from aqueous media, where cation exchange mechanism is of great importance. • Peanut shells can remove up to 70 % of zinc ions from aqueous solutions. • The adsorption mechanism of zinc could be in the order of 50 % due to ion exchange. • The ecotoxicological impact of biomass before and after zinc adsorption is similar. • Peanut shells represent an economical and effective alternative for remediation.