Performance evaluation of eggshell waste material for remediation of acid mine drainage from coal dump leachate

In this study, eggshell (ES) powder was evaluated as a cheap and biocompatible waste material for the pretreatment of acid mine drainage (AMD) leachate from coal dump. First, the composition of the AMD and physiochemical properties of the ES powder were determined using various standard characterization techniques. Then the removal efficiency of the target metal contaminants and the acid-neutralisation effect were explored in batch and kinetic set-ups. Thereafter, the settling rate of sludge formed after separately reacting ES and limestone powders with AMD was explored. Results revealed that the AMD leachate was highly acidic and contaminated with both cations and anions. Thermogravimetric analysis (TGA) and X-ray fluorescence (XRF) analyses demonstrated that ES powder was thermally stable up to 700 degrees C and CaO was the main component, respectively. Scanning electron microscopy (SEM) and EDX spectra confirmed the removal of contaminants. Both the decrease in particle size and increase in mass of ES enhanced the treatment efficiency. Although complete Fe and Al removal was achieved, Mn and sulphates posed a challenge as they were partially removed. Meanwhile, ES demonstrated superior acid-neutralizing effect to limestone and the mine water clarity and pH were shifted to acceptable levels. Both Fe and Al removal proceeded through an exothermic process while it was opposite for Mn. Kinetics were rapid and the sludge from ES powder settled faster compared with that from limestone powder. Cost analysis indicated that significant financial savings can be realised by substituting limestone with ES material. The findings suggest that ES waste could be an efficient and cheap material in the pre-treatment of AMD effluents.