A Comparison Between Predictive Tests Results and Natural Weathering in the Figueira Mine, in Southern Brazils

Many studies on acid mine drainage (AMD) use predictive methods, such as humidity cells (HC), to study this problem, as it is often not possible to predict acid generation from field tests. However, some comparisons of HC testing with reality have proven to be unrealistic. In this study, we compared the results of the HC test with historical data from the Figueira mine, in the State of Paraná (southern Brazil). To carry out the work,we collected a fresh coal tailings sample from the Figueira Mine, and compared monthly measurements of pH and electrical conductivity (EC), and concentrations of Fe, Al, Mn, and Zn, over a 5 year period (from 2013 to 2017) with the predictive test results performed following protocol B of the ASTM D5744-13 (2018) standard. The elements were analyzed by ICP-OES. The pH and EC of the HC test were lower than the field data. The HC test underestimated the concentrations of Fe and Mn, while Al and Zn were overestimated. We believe that the overestimations were due to the aluminosilicate buffering capacity and cation exchange capacity of the soil.