Acid Drainage and Metal Leaching Prediction: Where have we been and Where do we Need to Go - An Historical Perspective
Symposium 2015 Rouyn-Noranda
Mr Ronald V.Nicholson (EcoMetrix Incorporated)
The effects of mine drainage reportedly date back to Southern Spain almost 3000 years before present and the “poisonous” qualities in mine drainage from ores was made in Agricola’s treatise, De Re Metallica, in 1556. Acidic soils and drainage in North America were observed to be associated with coal mining in the eastern Appalachian region of the USA in the 1940s. After recognizing the cause of acidic conditions as weathering of iron sulphide minerals in disturbed mine materials at the earth surface, efforts were made to develop prediction techniques. The concepts of acid potential (AP) and neutralization potential (NP) were developed in the 1960s with acid base accounting (ABA) introduced in the literature in the early 1970s. Acid conditions at metal mines were “unexpectedly” observed in the 1960s in Canada.
Our current approach to assessing acid generating characteristics and metal leaching are based on a USEPA report authored by Sobek and others in 1978. While the initial purpose of prediction was related to acidic coal spoils and the potential for revegetation, water quality soon became the major focus of attention. While vigorous scientific debate and discussion ensued on the approaches to prediction, the questions gradually turned from “yes or no” to quantifying effects on water quality, including those for neutral drainage conditions. As the science of prediction has matured since the 1970s, there has been a shift to prevention and mitigation strategies for mine materials that represent risks to water quality. And while we have advanced substantially in our understanding of weathering of mine materials and their influence on water quality, there are ongoing debates on methods of interpretation. The challenge of time-dependent processes and the scarcity of full scale “tests” have left many questions yet to answer in our quest to manage risks to the environment from mine wastes. Examples of accomplishments and future challenges will be discussed.