Abstract
The production of Acid Mine Drainage (AMD) which is highly acidic, usually contains high concentrations of metals, sulphates, salts, and radioactive material which if left untreated, can contaminate ground and surface watercourses, damaging the health of plants, humans, wildlife, and aquatic species. Traditionally, the treatment of AMD consists of its neutralisation with limestone (CaCO3) or similar materials. However, the high cost of AMD remediation has resulted in the search for alternative liming substitutes which are low cost, readily available, and easily regenerated. This thesis aims to demonstrate that pervious concrete permeable reactive barrier (PERVC-PRB) can be effective in treating polluted or acidic water and effectively removes undesirable contaminants, as an alternative treatment method for addressing the AMD problem. Furthermore, it aims to show that PERVC can be effective in treating polluted mine water to meet the national limits applicable to the discharge of wastewater into a water resource without causing adverse impacts. A column study was conducted to investigate the potential use of PERVC for the removal of heavy metals from AMD. The study was done using AMD collected from a gold mine (WZ) and a coalfield (TDB). Pervious concrete mixtures consisting of Portland cement CEM I 52.5R with or without 30% fly ash (FA) were prepared at a water-cementitious ratio of 0.27 and then used to make cubes which were employed in the reactor columns. It was found that the removal efficiency levels of Al, Fe, Mn, Co, Ni were 75%, 98%, 99%, 94%, 95% for WZ and 87%, 96%, 99%, 98%, 90% for TDB, respectively. The high rate of acid reduction and metal removal by PERVC is attributed to the dissolution of portlandite which is a groundmass constituent of concrete. Precipitation of metal hydroxides seems to be the dominant metal removal mechanism. A batch study for effective removal of heavy metals present in polluted mines using pervious concrete was also conducted, for recovery of water from AMD. The effectiveness of PERVC adsorbent in removing heavy metals was compared with that of zero-valent iron (ZVI) which v is the most commonly used reactive material in PRBs. PERVC mixtures consisted of 6.7 mm granite aggregate and ordinary Portland cement CEM I 52.5R (CEM I) or cement containing 30% Class F fly ash (30%FA). ZVI comprised 25% iron grit GH18 of size 1.0 to 1.4 mm, 25% iron grit GH80 of size 0.18 to 0.42 mm, 25% fine silica sand of 0.4-0.85 mm size, 25% coarse silica sand of 0.8-1.8 mm size. The PERVC and ZVI media were used to conduct batch reactor tests with AMD for a period of 43 days using a ratio of one litre of reactive material to three litres of AMD. CEM I effectively removed Al, Fe, Zn, Mn, Mg, and Cu from both WZ and TDB with efficiency levels of 98% to 100% while the removal efficiency of the same elements using ZVI was 12 to 99%. ZVI exhibited low removal levels of Mn, Mg and Cu with removal efficiencies of 44, 12, 70% respectively. Although PERVC removed more heavy metals and with greater efficiency than ZVI, the PERVC – treated water showed high pH levels and exhibit elevated Cr6+ concentrations, owing to leaching from the cement and fly ash materials used in PERVC mixtures. PERVC mixtures were found to be better sorbents and gave better water quality than the treatment done using ZVI...
Ph.D. (Civil Engineering)