Extractive Metallurgy Over the Millenia
Mining and, indeed, ore processing have been around for thousands of years, with evidence of lead smelting discovered as early as 4000 BCE in the Fertile Crescent. The processing of ore to extract and purify metals presented significant technological challenges and so the development of pyrometallurgy, hydrometallurgy and electrometallurgy were not concurrent. Pyrometallurgy primarily uses heat to separate metal from impurities in the ore. An enduring image of early pyrometallurgy depicts crucibles with molten metal being poured as enormous fires burn in the background.
Long associated with the eternal puzzle of alchemy, hydrometallurgy uses chemicals and chemical bonding to extract pure metal from ore. Its broad use is first documented at the end of the first millennium in China and was developed in response to reduced availability of high-quality copper ore. The growth of technology and breakthroughs in chemistry at the end of the 19th and into the early 20th centuries, coupled with an ever-growing demand for metals in the age of electronics, has launched hydrometallurgy into a period of rapid development.
Electrometallurgy is the use of electricity and magnetism to extract pure metals from ore.
The youngest branch of extractive metallurgy has expanded with the advent of improved materials as well as new techniques in electrochemistry and engineering. Science and methods continue to mature, guaranteeing that electrometallurgy will gain importance as the world’s appetite for more and rarer metals continues to grow.
Most metal refining today includes processes from more than one type of extractive metallurgy.
As the Industrial Age drew to a close and the Information Age dawned, the demand for ever more and ever rarer metals exploded alongside the industry’s ability to meet those needs with improved technology and processes. In fact, a broad range of hydrometallurgical processes are used today to extract more than 70 metals, including gold, silver, copper and zinc. Additionally, low grade ore that was previously discarded as worthless, can now be economically processed, significantly increasing the world’s ore supply.
Expanding technology, and the associated demand on resources, shows no signs of abating. In fact, with the current drive for renewable energy and reduction in fossil fuel use, the IEA’s predicts the number of electric vehicles and wind turbines, along with solar power and other infrastructure adaptation by 2030 would require approximately double the current global production of copper alone. Other metals (aluminum, zinc, lithium, cobalt, silver, uranium) will experience similar increased demand.
There are costs associated with the exponential growth of production, and those costs can be staggering. In the past decade, it was estimated that, on an annual basis and excluding coal, overall mining waste amounted to approximately 1.8 billion tons in the U.S. alone. In fact, mining waste accounts for nearly half of all solid waste generated in the U.S. The accumulated mining waste already generated over past decades probably exceeds 55 billion tons. To help visualize this incomprehensible statistic, imagine collecting the world’s accumulated mining waste and spreading it out in a uniform thickness. It very likely would cover 52,000 square miles (approximately the size of Ireland) to a depth of over six and a half feet.
The imminent explosion of mining production, and the correlated volume of waste, is of major concern to industry, governments and populations worldwide. Currently, tailings comprise approximately 30% (or 500 million tons) of the total waste stream from mining activities. More than half of that volume is disposed of in tailings ponds. This means that tailings ponds are inevitably multiplying as well; both in size and number. Twenty years ago, over 3,500 tailings dams were counted worldwide. In Alberta, Canada, where the world’s oil sands are centered, well over one 1.6 trillion liters of tailings are stored, and that volume increases by 25 million liters each day. Today, Alberta’s tailings ponds alone cover close to 155 square miles, an area about five times the size of Manhattan.
Clearly, mine waste and its environmentally acceptable storage, constitutes the largest disposal problem on the planet. Even as it enjoys explosive growth, the mining industry must unquestionably be concerned about the enormous footprint it leaves, but the design and management of tailings ponds merits special concern.