Optical In Situ Monitoring of Acid Mine Drainage Remediation: Laboratory and Model Investigation

A permeable reactive barrier (PRB) can be deployed to remediate acid mine drainage. The performance of a PRB material under different boundary conditions (pH, flow velocity, and sulfate concentration) was investigated in a series of column experiments applying in-situ optical sensing methods for pH and oxygen detection. The reactive material consisted of organic components (compost, wood, and coconut shell) mixed with calcium carbonate and fine gravel. The input concentrations were around 1000 mg/L for iron and 3000 mg/L for sulfate, and the pH value was 6.2. The remediation efficiency of iron was 14.6% and of sulfate 15.2%, but was expected to scale up when moving to a field-site PRB with greater thickness. The iron and sulfate removal was influenced by decreasing the flow velocity and increasing the sulfate input concentration and the pH value. In an experiment with low pH boundary conditions (pH = 2.2), acidity was neutralized in the PRB by calcium carbonate during an experiment duration of 47 days. The modeling program MIN3P was used to create a simulation of the laboratory experiments. This helps to design parameters, for example, the residence time in the PRB, which is necessary for close to 100% remediation efficiency. This study shows the application of optical oxygen and pH monitoring in PRBs. In this context, they can be used to monitor the stability of a PRB for the remediation of acid mine drainage (AMD).