Plot 3 in September 2009—five months after planting.
Plot 2 (left) and plot 1 in June 2010.
A composite photo of the four plots in June 2010 (left to right: plot 4, plot 3, plot 2, and plot 1).
USA - 2010
Bauxite Residue Proving Successful in Acid Mine Reclamation
At a former coal mine in Western Pennsylvania (USA), a byproduct of the alumina refining process called bauxite residue is proving successful in reclaiming a coal refuse pile with acid mine runoff.
Alcoa and the Pennsylvania Department of Environmental Protection (DEP) have partnered to demonstrate the beneficial use of bauxite residue—also known as alkaline clay after further processing—as a neutralization and soil enhancement product for the stabilization and reclamation of the Mather Mine coal refuse pile and similar mine sites across the state. The project is an example of how residual materials originating in waste streams from two industries can be combined to create a green outcome that may also have cost advantages when compared to traditional methods to handle these residuals.
Mather Mine was operational from 1925 to 1965. Coal brought to the surface was cleaned and shipped, and waste material from this process, including acid-producing pyrite, was stored onsite. Today, the approximately 36-hectare (90-acre) site houses more than 2.3 million cubic meters (3 million cubic yards) of coal refuse and 250,000 creosote railroad ties from another former company on the site. Parts of the refuse pile are on fire, there is a creosote plume contained beneath the surface, and acid mine runoff leaches into a nearby creek.
“In the initial site reclamation, we dismantled all the onsite buildings, covered up the creosote plume with coal refuse per the recommended closure plan, and graded the site in preparation for revegetation,” said Tom Kovalchuk, chief of permits and technical services for the Greensburg District Mining Office of the Pennsylvania DEP. “One of the issues is the soil is not adequate for revegetation due to its high acidity, lack of organic material and nutrients, and poor water retention and soil texture. We were looking for an alkaline material we could use to build a soil horizon with what we had available, which was acidic coal refuse.”
Alcoa’s prior use of bauxite residue as a soil enhancement had proved the material’s viability as an option. To test its appropriateness for the unique conditions found at the Mather Mine site, Alcoa and the DEP conducted laboratory-scale studies followed by the construction and systematic evaluation of four onsite vegetation test plots measuring 0.30 hectares (0.75 acres) each. The test results will be used to apply for beneficial-use designation for bauxite residue within the state of Pennsylvania, which means the material could be used for reclamation purposes without having to go through additional chemical analysis and testing.
To determine the optimum soil horizon for Mather Mine, the test plots were constructed in April 2009 with different materials:
- Plot 1: Coal refuse only (control plot).
- Plot 2: Coal refuse with 10% bauxite residue (150 metric tons) mixed into the top surface at a depth of 46 to 61 centimeters (18 to 24 inches).
- Plot 3: Same as plot 2 with the addition of compost material.
- Plot 4: Coal refuse plus 35% limestone (represents conventional reclamation).
All plots were hydroseeded, and a layer of straw mulch was added to prevent the seed from washing away. Within a month, plots 2 and 3 started growing vegetation. These two plots continued to grow vegetation faster and denser than plot 4 and sustained their moisture and greenness during the dry 2009 summer season when the grass on plot 4 turned brown. No-to-little vegetation has taken root on plot 1, which is just coal refuse. Overall, the best results through early 2010 were with plot 3.
“We don’t know what the long term will bring, but we’ve had initial success with fast growth and grass that is really dense and has great root depth,” said Kovalchuk. “We will continue monitoring to see how long this success can be sustained. In the meantime, the next step is to apply for beneficial-use designation for bauxite residue. Once we receive that, we will either finish this pile or pick a smaller pile to see what the overall impact is if we take out the unique variables—fire, creosote plume, railroad ties—we’re dealing with at the Mather site.”
Acid mine runoff is a growing issue around the world. In Pennsylvania, for example, limited government budgets and at least 100,000 hectares (250,000 acres) of government-owned land with acid mine runoff present significant reclamation challenges that require a lower-cost green solution like bauxite residue. This new approach also gives small and large mining companies a reclamation option that has the added bonus of mitigating the environmental impact of not one but two wastes—especially important to companies facing increased scrutiny on sustainable business practices.