Remediation of acid mine drainage using ash derived from the co-calcination of eggshells and Amarula peels: Insights into chemical attenuation and mechanisms

Acid mine drainage (AMD) has been a prime concern for mining houses, largely due to its worrisome toxicological impacts that wreak havoc on receiving aquatic ecosystems. Conventional chemicals that are often used to treat AMD include, but are not limited to, limestone, quicklime, and hydrated lime. These chemicals remain widely trusted; however, they are non-renewable and require mining, which, to a larger extent, destabilizes the environment and its integrity to foster life. For these reasons, herein, a sustainable bio-composite derived from Amarula peels (AMP) and chicken eggshell (CE) biomass was facilely developed for the treatment of real AMD from coal. Optimization was done using the one-factor-at-a-time pedagogy. Specifically, the bio-composite was synthesized by blending AMP and CE at a 1:1 (wt:wt%) solid-to-solid ratio, and subsequently co-calcined at 750℃ and 850℃. Characterization was fulfilled using X-ray Fluorescence (XRF) and X-ray Diffraction. Results confirmed the ash to primarily constitute lime (CaO) and portlandite (Ca(OH)₂). XRF analysis confirmed the CaO content to be 53.5% and 84%, after calcination at 750℃ and 850℃, respectively. These results demonstrate that calcination significantly impacts the physicochemical properties of calcined ash. Depending on the CaO content, the ash prepared at 850 °C was preferred to treat AMD. The pH of AMD was observed to increase from pH 2.26 to >12, thus demonstrating the neutralization capacity of the synthesized ash. Optimum time was observed to be 10 min of mixing, where >99.99% of Fe, Al, Mn, Mg, Ni, Pb, and Zn, whilst sulfate registered close to 86% removal efficacy. This material has demonstrated the potential to treat AMD. However, future work should consider integrating this method with other technologies to enhance the quality of treated AMD. In addition, the market analysis, cost-benefit analysis, and scalability of the technology must be investigated.