COST-EFFECTIVE ACID ROCK DRAINAGE WATER TREATMENT APPLIED TO MINING-IMPACTED WATERSHEDS

摘要

The application of three different Acid Rock Drainage (ARD) water treatment technologies will be discussed. The first water treatment technology results discussed are from laboratory and field treatability studies that used low volumes of high Total Dissolved Solids (TDS) ARD water to treat much larger volumes of lower TDS water to reach applicable ecological standards in the effluent stream. The low volumes of high (TDS) lime neutralized water were mixed with the high volumes of low TDS stream water to optimize the removal efficiencies of aluminum, cadmium, cobalt, copper, iron, lead, and zinc. Average removal efficiencies of the metals from the stream water were generally greater than 95 percent. Flow conditions of the low volume high TDS water tested ranged from 10 to 300 gpm and flow of the low TDS water ranged from 3,000 to over 25,000 gpm. Iron precipitation reactions and pH values in the effluent (ranging from 6 to 8.5) were accurately controlled. The precipitated iron-rich sludge from the neutralization reactions was deposited into a large open pit. Significant cost savings using this water treatment strategy was realized when compared to a conventional lime neutralization ARD water treatment system. The second water treatment technology to be discussed uses a lime mixing apparatus (The Neutra-Mill~R) and its application to ARD impacted water-bodies. Results from hydrated lime neutralization of an approximate 90 million gallon ARD impacted tailings impoundment will be discussed. The third water treatment technology describes a system, which grinds limestone to ultra-fine grain sizes (The HALT system) resulting in rapid neutralization reactions occurring in ARD impacted water. Limestone is generally cheaper than most other sources of alkalinity and the maximum pH value that can be reached during dissolution is 8.5.