Epsilon Archive for Student Projects

Abstract

Abandoned mines often face the problem of Acid mine drainage (AMD). AMD is characterized by high acidity, elevated metal concentrations, and often significant salinization making a treatment of the water necessary to prevent environmental damage and secure water availability. Especially in South Africa, where mining has a big history, solutions to treat AMD are needed.
This study evaluates the effectiveness of various nature-based materials, including limestone, zeolite, unactivated and activated bentonite, and recycling concrete, in treating synthetic AMD with the focus on heavy metals and aluminium. A batch experiment was conducted, using solid to liquid ratio of 2 and 10 g/L and a synthetic AMD based on the water analysis of Brugspruit. The research examines their impact on pH levels and their ability to reduce mineral and metal concentrations. The two main mechanisms to decrease concentration in solution are adsorption and precipitation. Adsorption is mainly attributed to zeolite and the bentonites and precipitation to limestone and concrete due to their chemical and physical properties.
Results indicate that limestone and recycling concrete are particularly effective, increasing pH to 7.3 and 8.4 respectively at a dosage of 10 g/L. Recycling concrete demonstrated superior metal removal capabilities, achieving reductions of 99.7% for aluminium, 100% for iron, 98% for nickel, 100% for zinc, and 88% for manganese. At a lower dosage of 2 g/L, only limestone significantly increased pH and effectively removed metals from the solution. Modelling the process showed, that the removal for limestone and concrete batches might not only be according to precipitation but also adsorption. This means that forming precipitates can also act as adsorbents. Adsorptive materials did not reduce elements in solution in a significant manner.
The pH value was found to be important for metal removal. Adsorptive materials that were not able to increase pH were not able to adsorb metals at low pH values. On the other hand, pH increasing materials such as limestone and concrete showed promise regarding their ability to treat AMD.
However, further investigation is needed to fully understand the exact removal mechanisms and to evaluate applicability of adsorption materials when pH is increased in a first step in a multi stage treatment.