Crab Shells Clean Acid Mine Drainage

Engineers at the Pennsylvania State University have found crab-shell chitin effectively raises acidity (pH) levels and reduces harmful metals in mine water.

These results may lead to the development of cost-effective treatment strategies to clean up high-risk acid mine drainage.

Acidic drainage from abandoned mines continues to contaminate tens of thousands of miles of streams in the U.S., including more than 5,000 miles in Pennsylvania.

With the support of an NSF Faculty Early Career Development Award, Rachel Brennan of Penn State tested a promising treatment option for acid mine drainage: crab-shell chitin, a waste product of the crabbing industry.

One of the most abundant natural materials in the world, chitin is used to make paper, fabrics and joint care supplements, among other products. In crustaceans such as crab and shrimp, chitin combines with calcium carbonate, the same chemical found in limestone.

In batch tests with mine water, Brennan's group found that crab-shell chitin increased the pH to near-normal levels in just six days and reduced dissolved metals like iron and aluminum by over 99 percent. After nine days, even manganese, a metal that passive treatment systems have historically failed to remove, was reduced by 81 percent and sulfate concentrations decreased as well.

Detailed investigations in Brennan's lab have shown that the complex matrix of the crab shell causes the simultaneous physical, chemical and biological changes observed with this unique substrate.

With such promising results, Brennan will extend the application of chitin to high-risk discharges where other remedies have failed, including the abandoned Klondike mine site in Cambria County, Pa.

How do you move the Planet Forward? Tweet us @planet_forward or contribute to the conversation with your own story.