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Acid Rock Drainage

Acid Rock Drainage (ARD) occurs when sulphide minerals from overburden, waste rock, and tailings deposits are exposed to naturally occurring oxidizing conditions. The principle minerals involved include: pyrite (FeS2), chalcopyrite (CuFeS2), and pyrrhotite (Fe(1-x)S (x = 0 to 0.2)). The oxidation of sulphides in the presence of water can generate acidic drainage. This drainage raises two problems: the generation of acidity which is also known as acid rock drainage (ARD) or acid mine drainage (AMD) and the subsequent release of dissolved metals (metal leaching) into the surrounding environment. As the drainage becomes more acidic, its capacity to leach out other elements from the rock, such as heavy metals, increases and can result in the water bearing a number of harmful constituents. As a result of these interactions, polluted water can drain away from the exposed rock and have a significant impact at the mine site and the surrounding areas including bodies of water (river, lakes, and groundwater), wildlife and/or inhabitants if the appropriate prevention and management strategies have not been adopted. Although this is a natural process, mining activities and excavation can trigger this phenomenon by exposing large surface areas of rock to water and oxygen, increasing the reaction rate compared to natural conditions. Not all mining operations that expose sulphide bearing rocks result in ARD. In some situations the sulphide minerals may be non-reactive or they may even have a buffering capacity to neutralize any acid released from sulphide oxidation which consequently results in a metal leaching problem without an ARD problem. ARD potential is often initially estimated using rapid, accurate determinations on the likelihood of a sample to exhibit characteristics of generating acid. The following reactions explain the process:

2FeS2 + 2H2O + 7O2 → 4H+ + 4SO4 2- + 2Fe2+ 4Fe2+ + O2 + 4H+ → 4Fe3+ + 2H2O Fe3+ + 3H2O → Fe(OH)3 ↓ + 3H+ 2FeS2 + 14Fe3+ + 8H2O → 15Fe2+ + 2SO4 2- + 16H+

AGAT Laboratories offers full-service analysis capabilities for ARD testing, We offer a complete range of solid phase geochemical analysis, static testing, leaching procedures (Shake Flask Extraction (SFE), Synthetic Precipitation Leaching Procedure (SPLP), and Toxicity Characteristic Leaching Procedure (TCLP)), Net-Acid Generation (NAG), and Kinetic Testing. We offer these services nationally to both the Environmental and Mining Sectors and the analysis are performed at our laboratory in Burnaby, British Columbia.

AGAT Laboratories’ Burnaby laboratory is accredited to ISO/IEC 17025 for specific tests as listed on our current scope of accreditation from the Canadian Association for Laboratory Accreditation (CALA). Our Acid-Base Accounting Procedures are accredited for Paste pH, Sulphate Sulphur, Total Sulphur, and Neutralization Potential.

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