Heavy metals removal from acid mine drainage using banana peels

Abstract

The sustainable removal of heavy metals from acid mine drainage (AMD) and wastewater has become a major challenge to scientists (Hossain et al., 2012), despite numerous treatment technologies. Most of the explored technologies cannot remove pollutants completely and others are too expensive and also have significant disposal challenges (Giwa et al., 2013). The need to develop a more effective and affordable technology for the removal of heavy metals from AMD is, therefore, inevitable. The banana fruit, the most abundant fruit that is almost consumed across the world its peels were explored to study their potential to remove heavy metals under AMD conditions. The banana peels were cut, washed, dried and ground into powder. Thereafter, the adsorption of zinc, copper and manganese metal ions were studied to investigate the effects of controlling parameters such as particle size, adsorbent dose, initial heavy metal ion concentration, contact time, pH and selectivity of the banana peel. Synthetic single- and ternary component solution, fortified AMD and actual AMD were used in a batch system. Langmuir and Freundlich isotherms were applied to describe adsorption equilibrium. The maximum amount of zinc, copper and manganese metal ions adsorbed, as evaluated by Langmuir isotherm were 9.017, 8.718 and 6.920 mg/g, respectively. The adsorption data fitted the pseudo second order very well and suggested that the adsorption is characterized by the valence forces through exchange of charges between banana peel powder and heavy metal ions. Continuous fixed bed column studies were conducted by using AMD at room temperature and the effects of various parameters such as flow rate (15, 30 and 45 mL/min) and bed depths (6, 12.4 and 17.8 cm) were investigated. The column bed capacity and saturation time increased with the increase of bed depth and decrease of flow rate. Furthermore, the results show that the column performed well at the lowest flow rate. The Thomas model and bed depth service time (BDST) model were applied to evaluate the breakthrough curves and to analyse the experimental data. Thomas model showed a consistent low level of regression coefficient, R2; 0.240 and 0.738 for Mn metal ion at bed depth of 6 cm and 17 cm and flowrate of 15 ml/min, respectively and 0.709 and 0.649 for Zn metal ion at bed depth of 6 cm and 17 cm and flowrate of 15 ml/min, respectively. It can be concluded that the experimental data did not fit well with this model. The BDST model showed adsorption of 150.759 and 27.722 mg/g for manganese and zinc, respectively. The results obtained in this study demonstrated that the banana peel powder can be used as an adsorbent for the removal of zinc, copper and manganese metal ions from AMD using batch and fixed bed adsorption system.