Industrial Mining and Ore Processing
Mining and ore processing are essential industries that supply the majority of minerals, metal and gems needed to produce a wide variety of products and materials. The raw materials are ore deposits that contain valuable metallic and nonmetallic resources. These resources are mined through surface excavation or underground mining. Both surface and underground mining techniques have their own benefits and drawbacks, but surface mining continues to be the dominant method due to lower typical costs and technology development1. Both processes tend to produce large quantities of waste rock, which need to be removed to provide access to the valuable deposits but are not worth processing.
Ores, once mined, are often “concentrated” at the mine to increase the percentage of valuable material and reduce transportation costs. This concentrate is then further processed to recover the valuable material. For metal ores, the processes include smelting, refining and finishing. The concentration step typically generates large quantities of wet, very fine materials often containing various residues of processing chemicals. These “tailings” are difficult to manage because of the volumes and physical characteristics and have been involved in a number of significant pollution incidents. Tailings are often a major challenge at abandoned mines because they are frequently unstable.
The technology for smelting and refining processes has improved considerably in recent years, particularly in relation to control of dust emissions and corrosive fumes, but older facilities often lack the proper equipment and technology to prevent the release of toxic chemicals into the environment.
It is estimated that the health of nearly 7 million people is at risk from mining and ore processing locations in the countries in which Pure Earth has done investigations. These exposures result in 450,000 to 2.6 million DALYs, depending on the disability weights. Limitations in the existing methodology and gaps in underlying science mean that the analysis relies almost entirely on health outcomes associated with lead and chromium. Therefore, other substances, particularly metals such as mercury and cadmium, are not included in the current figures and the real DALY impact of this industry is likely much larger.
The most hazardous pollutants reported at Pure Earth mining and ore processing sites are lead, chromium, arsenic, cadmium and mercury. The key pollutants are identified as lead and chromium based on their respective DALYs impact while mercury is the top exposure risk in the population. Other pollutants that may be present at the mining sites include radionuclides, cyanide and other heavy metals.
The source of exposure for the population from mining and ore processing is primarily from waste products in both active and legacy pollution sites. These waste products include wastewater, waste rock (containing metal and ore), tailings, process solutions and processed ore. At abandoned or poorly closed mining sites, tailings and improperly stored waste can pollute ground and surface water, as well drastically affect agricultural activities. In poorly managed mining and processing plants, untreated waste water, slag and solid waste are often directly dumped into surface waters or may accumulate near the mines. Further environmental issues can arise as metals may be washed along with soil leading to heavy erosion and runoff contamination. The contaminated soil and water may adversely impact agricultural, food and drinking water systems.