What is Metal Leaching and Acid Rock Drainage?
• Metal leaching and add rock drainage are naturally occurring processes that are caused when minerals containing metals and sulphur (called sulphides) come in contact with both air and water. • When sulphides are exposed to water and the oxygen from air, they net (or oxidize). This oxidizing of sulphides can also produce acid. If this acid is carried by streams or other natural watercourses it is called acid rock drainage (ARD). • The acid in ARD can leach metals from surrounding rocks causing drainage that has high amounts of dissolved metals (such as iron, aluminum, copper, lead, silver, zinc). This is called metal leaching (ML). Other metals can also be leached from react in non-acidic drainage (such as selenium, zinc, molybdenum, nickel, arsenic and antimony). • Not all rocks that contain sulphide minerals will become acid generating. It depends on the amount of neutralizing minerals and materials (such as limestone) that are present in the rocks. If there is balance, or if there
