Acid mine drainage neutralization rate using biogenic calcite

In this study, the chicken eggshell (ES) particle size was evaluated in relation to the neutralization rate (γ) of acid mine drainage (AMD) under stirring conditions. Four treatments were carried out using three different particle sizes (<63, 250−500, and 1,410−2,000 μm). In the treatments T1−T3, the pH increase (ΔpH) was monitored every 5 min and ES was added until a pH ~6.0 was reached and the γ was calculated every 5 min. In T4, ΔpH and γ were measured every 8 hours for 48 hours, and ES particle size <63 μm was used. At the end of each treatment, the redox potential (Eh), SO42– removal efficiency (ηSO42–), and heavy metal (HM) removal efficiency (ηHM) were determined. The γ values to achieve a pH ~6.0 were 1.6×10−1, 1.1×10−1 y 6.0×10−2 min–1 for particle size of <63, 250−500, and 1410-2000 μm, respectively. However, regardless of particle size, the highest γ effect was observed within the first 5−10 min. Overall, the Eh was reduced to ca. 210 mV in all treatments. The maximum ηSO42– was ca. 70% in T1 and T4. However, the larger the particle size, the longer and higher ES concentration was needed to achieve a pH ~6.0 and the ηSO42– was lower. The maximum ηHM recorded in all treatments were 100% for Al, Fe, and Mo. The use of ES with particle size <63 μm reduced the concentration needed to reach the target pH, increased the γ, favored the ηSO42–, and removed the Fe3+ decreasing the Eh.