The Legacy of American Copper Smelting: Industrial Heritage versus Environmental Policy

Chapter 1. The Historic Roots of Copper Production and Smelter Pollution

Chapter 1 The Historic Roots of Copper Production and Smelter Pollution Copper has been a highly valued commodity in the global economy for eight thousand years. Its use has expanded as its specific properties—ductility, alloy-ability, corrosion-resistance, and conductivity—were successively exploited . Despite its utility, the production of copper consumed significant resources and caused visible and not-so-visible human health threats and environmental degradation from the metal’s earliest uses. Although the first smelters were small and their individual impacts minimal, as production increased both in number of furnaces and concentration of smelting works, the deleterious and environmental side effects of production increased as well. Across the globe, copper is found in three basic compounds, including native, oxide, and sulfide ores, each in combination with beneficial and sometimes detrimental or toxic components that need to be removed during smelting. Native copper is pure and, in general, only requires simple smelting to remove attached waste materials and purify the metal. Oxides are copper-oxygen compounds that are also relatively simple to smelt because oxygen easily combines with carbon in the furnace fuel and is dispelled as carbon dioxide. Sulfides, which are the most plentiful copper ores on earth, are complex copper-sulfur compounds that need to be roasted or burned separately, sometimes for weeks prior to smelting, to drive off the sulfur in combination with oxygen as sulfur dioxide. Other elements often found in copper ores that need to be removed include gold, silver, iron, arsenic, antimony , cobalt, nickel, silicon, and lead. Roots of Copper Production and Smelter Pollution 2 Copper smelting, the art and science of extracting and refining the metal from its ore is a 5,500-year-old profession. Although still debated, the precise origin of smelting technology was likely ancient Anatolia, which included parts of present-day Turkey and Iran, and spread across Asia, North Africa, and Europe. Early smelting was based on crude short blast furnaces that produced small but easily transported ingots, and became a key trade and military component of the Egyptian and later Roman Empires. These early copper blast furnace technologies ultimately evolved into a standardized , (relatively) high-output, charcoal-fueled, and water-powered industrial practice in Germany during the Middle Ages, and spread to formerly abandoned and newly discovered copper-rich regions across Europe with the diffusion of German metal workers. Thisparticulartechnologyfocusedontheblastfurnacethatsmelted copper by combining ores directly with relatively pure charcoal fuel in the vertical furnace stack and withdrawing molten semipure copper and slag waste from the furnace bottom. The long multistage smelting process began with the heap roasting of ores to remove sulfur outside of the furnace, followed by the in-furnace production of several intermediate copper compounds called mattes, each between 50% and 90% pure. The process also included several intermediate roastings outside of the furnace, ultimately resulting in a product called “black” copper, indicating that it came from a blast furnace, which was 95%–99% pure. This copper required a final refining to produce a 99.9% pure copper before it could be used in brass or bronze production (see figure 1.1). This system, however, could not be successfully implemented in late Renaissance England. Although the country was rich with copper ores, the furnaces’ reliance on wood-based, contaminant-free carbon fuels, —something in short supply in seventeenth-century England—severely restricted blast furnace integration. England, however, did ultimately develop a similar system but used a reverberatory furnace for primary smelting and refining . This furnace was more horizontal than the blast furnace and kept the ore separate from cheap, abundant, but impure coal fuel and produced “blister” copper, so-named because of its surface appearance after solidifying . Britain’s significant economic growth and industrialization in the eighteenth and nineteenth centuries, its vast empire and rich mineral and coal Figure 1.1. Generalized smelting flow diagram. This flow chart for copper production begins with mining ore, then milling to concentrate the ore and remove large portions of waste, followed by roasting of sulfide ores to remove sulfur, smelting to transform the ore into much purer metal, then refining to purify the metal for industrial uses. Although some early processes need to roast and smelt several times before refining, some later processes required multiple refining steps to get the metal ready for electrical uses. Roots of Copper Production and Smelter Pollution 4 reserves, and a timely slowdown in German production, ultimately led to its world...