There are basically three kinds of passive treatment technologies for treating mining influenced water (MIW):
• Biochemical Reactors (BCRs) are typically applicable to metal mine drainage with high acidity and a wide range of metals; this technology can function with or without plants.
• Aerobic Cells containing cattails, other plants, and algae are typically applicable to MIW where iron and manganese and mild acidity are problematic and/or only trace concentrations of heavy metals occur. This method also can be used to polish biochemical oxygen demand (BOD) from BCR effluent and adsorb trace metals on to iron or manganese oxides.
Most passive treatment systems employ one or more of these cell types. For novice designers, selecting the proper technologies and arranging them in a logical sequence is a problem. This paper should provide baseline guidance. While the primary focus of the article is mining influenced water, the concepts presented may be readily transferable to process waters related to oil and gas operations.
The technical community of regulators and engineers that specializes in passive water treatment should be familiar with the passive treatment “decision tree” that was published by the former U.S. Bureau of Mines about 20 years ago. The decision tree was originally intended to address MIW from coal mines. Since then, however, the breadth of passive treatment has expanded to embrace precious and base metal mines, uranium mines, and even gravel pits. Each MIW has its unique signature, either imposed by the natural geochemical conditions of the ore body and surrounding mine waste, or by resource recovery processes that may include heap leaching or traditional hydrometallurgical technologies. In the context of the elements of the periodic table, the decision tree certainly could be improved, as it was originally developed to focus on coal geology derived MIW, which typically contains acidity/alkalinity, iron, aluminum and manganese. For example, the expanded decision tree could consider residual ammonia or nitrates from blasting, cyanide from heap leach pad rinsing, trace amounts of selenium, or other parameters that may require passive treatment at a given mine, coal or otherwise. However, developing an individual decision tree for each MIW element or suite of elements and their species would be a daunting task and would probably introduce more confusion where simplicity is desired.
With apologies to Dmitri Ivanovich Mendeleev, a “Periodic Table of Passive Treatment” could become a useful design tool to satisfy the need to embrace a larger range of MIW chemistries. A single “modified” periodic table was originally presented in an earlier paper (Gusek, 2009); it focused on identifying passive treatment methods that have been observed to work on specific elements or species of elements typically found in MIW. The concept was subsequently revisited (Gusek, 2013) with a closer focus on adsorption phenomena and other processes. This article provides a summary of the two “periodic table” papers and presents the advantages and disadvantages of the various passive treatment components.
In summary, this article is an introduction to the wide range of remediation design options available to practitioners of passive treatment. It also includes a recommended “staged” approach of laboratory-, bench-, and pilot-scale testing protocols which have been shown to support successful designs, especially for MIWs with complex chemistry.
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