Qualidade da água em lagos de mineração - estudos de caso: Águas Claras e Riacho dos Machados

Abstract

Pit lakes are formed in the mine pits either in exhausted mines or abandoned ones. Their filling occurs in a natural way (precipitation and groundwater) and / or artificial (surface water). The pit lakes originated from sulfide minerals commonly have acid character and those arisen from inert minerals tend to have neutral pH. The purpose of this research is to verify the limnological characteristics, the quality of the water, the hydrodynamic behavior and the uses of the mining lakes. The case studies in this work are the Lake Águas Claras of the Mine Águas Claras (iron ore) and the lakes Cava Norte and Cava Sul of the Mine Riacho dos Machados (gold ore). The monitoring data used in this study were secondary in nature and based on these data it was performed temporal analysis, descriptive statistics, nonparametric normal distribution of data by Shapiro Wilk W test, seasonal analysis by Mann-Whitney U test for all lakes and spatial analysis Kruskal Wallis test only on lake Águas Claras. Lake Águas Claras has typical meromitic behavior (partial vertical circulations) due to the high depth (234 m) in its final configuration, it presents good water quality given the CONAMA resolution 357/05 class 2 in all parameters for data set in the analysis of descriptive statistics. There is a not a normal distribution in any parameter analyzed. There isthough a significant difference in the parameters BOD, DO, total iron, pH and temperature between the surface and bottom (spatial analysis - Kruskal Wallis test). There is a significant difference between dry and rainy periods for the parameters alkalinity, BOD, hardness, pH, temperature and turbidity at the surface and at bottom for total phosphate and turbidity. Concerning lakes Cava Norte and Cava Sul it was not possible to determine their hydrodynamic behavior as for that it is necessary for the analysis of more parameters and other tests. Lake Cava Norte received leachate from piles of mine tailings, so the pH of thelake was acid and, after correction of AMD (Acid Mine Drainage), the pH of this lake increased. Lake Cava Sul has a neutral pH. Based on the descriptive statistics, the lakes did not attend CONAMA resolution 357/05 for arsenic. The parameters that have normal distribution of data in the lakes are sulfate, for the Cava Norte and Cava Sul, and the pH for the Cava Sul; seasonality test verified that there is no significant difference between the dry and rainy period in both lakes.