Mining Mirror January 2019 | Page 23

Mining in focus Tailings dams usually only hit the headlines when they fail, resulting in the loss of life and catastrophic environmental damage. As a result, the proper design, management, construction, and monitoring thereof are vital, writes Nicolaas C Steenkamp. A tailings dam exists because of the processing of ore. When raw ore is mined, it is processed in several ways. In the majority of precious and base metal operations, the ore rock is crushed, and then milled before being processed. Most of these processes use a significant amount of water. Once the processing is complete, the waste material, referred to as tailings, are pumped to mining residue storage facilities, or what is generally better known as tailings dams. A tailings dam is the physical structure that holds, or impounds, the tailings pond, which serves the dual role of containing the fine material and recycling the water to be reused in processing. The tailings are piped out in slurry form to the pond, where solids settle to the bottom and the water on top is pumped via a reclamation barge back into the mill. There are a number of tailings facility construction methods, which include valley impoundments, ring-dyke impoundments, in-pit impoundments, and special dug-pit impoundments. Need for tailings dams Prior to the 19th century, most run-off from mines were disposed of in water systems. Tailings dams were also not needed in most cases, as operations were relatively small compared to modern operations today. Due to the development in processing methods and mine equipment, operations are now able to mine deposits well into lower-grade material, resulting in an increase in mining process fines. In the past century, there has been a lot of advances in the design of tailings facilities. Tailings dam designs depend on the topography of the ground and the material available to build it. The tailings facilities can be built by earth-filled structures or built from the waste rock generated during mining. The pond is built by forming an embankment of waste rock at the onset of mine construction. Tailings are piped in and deposited at the crest of the embankment where they drain to form a beach. The beach is an important buffer between the dam’s embankment and water in the pond area. The general approach to building a tailings dam is to separate the tailings into coarse- and fine-grained material www.miningmirror.co.za JANUARY 2019 MINING MIRROR [21]