Acid Mine drAinAge ( AMd ) MAnAgeMent 285 Acid Mine drAinAge ( AMd ) MAnAgeMent
AMd is recognized as one of the most serious environmental problem in the mining industry. the problem of acid mine drainage (AMd) has been present since mining activity began thousands of years ago. Mining activity has disrupted the hydrology of mining areas so badly that it is extremely difficult to predict where water would eventually re-emerge. its causes, treatment have become the focus of number of researchers. this paper describes Acid Mine drainage (AMd) generation and its associated pollution. Jr. of Industrial Pollution Control 23 (2)(2007) pp 285-297
PASSIVE TREATMENT OF COAL MINE DRAINAGE 1
Passive treatment systems utilize chemical and biological processes to neutralize acidity and decrease concentrations of metals. These systems have been successfully applied at numerous coal mine discharges over the past 20 years. The three most commonly applied passive unit operations are aerobic ponds/wetlands, anoxic limestone drains (ALDs), and reducing and alkalinity producing systems (RAPS). The selection of the most effective unit operation, or combination of unit operations, is based on water quality. The unit operations are sized based on flow or contaminant loads. Net alkaline water is treated with ponds and aerobic wetlands that promote iron oxidation, precipitation, and settling. Empirical data have shown that 10 - 20 grams of iron is typically removed per square meter of surface area of the pond or wetland. Net acidic water with low ferric iron and aluminum levels can be treated with ALDs, which are used to add bicarbonate alkalinity (typically 100 - 300 mg/L of alkalinity as CaCO3). To attain near maximum levels of alkalinity, ALDs are sized to maintain a 12 -15 hour detention time. Net acidic water containing ferric iron or aluminum is treated using RAPS, which add bicarbonate alkalinity via sulfate reduction and limestone dissolution. The amount of alkalinity generated is dependant on influent water quality, but empirically has been found to range from 15 - 60 grams of alkalinity (as CaCO3) per square meter of pond surface. Many of these systems are constructed to facilitate flushing of retained metals, however, the ability of these systems to maintain adequate permeability has not been determined.
The micro-mechanical behaviour of artificially cemented sand particles under compression and shear
The mechanical behaviour of cemented sands at macro-scale has been widely studied in the past, while there is still a lack of laboratory test data for the micro-mechanical response. Therefore, a series of uniaxial compression and tangential shear tests on artificially cemented sand particles have been conducted using a microscope to observe their behaviour. First, the consistency of cemented particles with different cementing agents is discussed. Three breakage modes are proposed according to the images taken using a microscope camera. A new parameter named ‘local roundness at contact’ is introduced to emphasise the effect of contact morphology on sample strength. Moreover, the effect of bond thickness on the mechanical response of cemented particles has been investigated. Finally, the shear strength parameters of artificially cemented sand samples have been determined for two different sample diameters.