Phytostabilization Technology for Mining Wastes in Arid and Semiarid Environments: Plant-Microbe-Metal Indicators to Predict Sustainability

Problem: 

Mine tailings are a significant health risk to nearby populations and they require novel remediation approaches that are economical and low input. In arid regions, mine tailings and their associated contaminants are prone to wind-borne dispersion and water erosion. Capping mine tailings sites with soil, gravel, or even cement is an accepted although often impermanent way to reduce wind and water erosion. Revegetation is considered a cost-effective and more permanent alternative to these capping strategies. The challenge is that mine tailings have no nutrients or soil structure. This is exacerbated by conditions of drought and salinity in arid and semi-arid regions. Additionally, the mineral separation process is only partially efficient, and after the milling processes, some of the metal-containing minerals are left behind as small tailings particles. As a result of these combined factors tailings do not readily support plant growth and can remain barren for decades or longer.

At the University of Arizona, Drs. Raina Maier and Jon Chorover are developing a feasible revegetation strategy for the phytostabilization of metal contaminants in mine tailing piles in arid and semi-arid ecosystems. Phytostabilization is a remediation technology that results in the vegetation of mine tailings with sufficient coverage to reduce wind and water erosion. It seeks to accumulate metals in the root zone, rather than to extract them into above-ground biomass, so as to prevent metals from entering the food chain. Little information is available on the effects of organic matter (compost) addition and the evolution of associated microbial communities on plant establishment and on metal bioavailability, solubility, and speciation.

Previous work on the project determined the conditions required to grow metal- and drought-tolerant plant species in mine tailings dirt under greenhouse conditions. The current projects seeks to translate the findings into the field, by establishing a plant cover in a pilot plot on the Iron King mine tailings Superfund site in Dewey-Humboldt, AZ.

Significance: 

Sustainable management of mining wastes is a global challenge facing the mining industry. This field study at the Iron King Mine Superfund site combines biological, chemical, and physical measurements to describe the revegetation process and will provide a minimum of five years of information that can be used to assess phytostabilization as a remediation technology.

Specific Aims: 

Aim 1: Define the phylogenetic and functional diversity of the microbial community responsible for acidification of pyritic legacy mine tailings. 

Aim 2: Identify mechanisms of root-microbe-metal interactions in established plant fertility islands that immobilize contaminant metals during phytostabilization of mine tailings.

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