Water Resources Research Act Program

Details for Project ID 2009SD137B

Acidic Leaching Tests to Determine Arsenic Mobility from Concrete-Encapsulated Limestone Waste

Institute: South Dakota
Year Established: 2009 Start Date: 2009-03-01 End Date: 2011-02-28
Total Federal Funds: $24,262 Total Non-Federal Funds: $48,522

Principal Investigators: Arden Davis, David Dixon, Marion Hansen

Project Summary: Limestone-based material has clearly shown the ability to remove arsenic and other metals from drinking water. The technology offers the potential for low-cost disposal of waste product after arsenic removal, either in an ordinary landfill or by recycling in concrete. Disposal of arsenic-enriched waste is critical for commercial viability of removal technologies. The ability to recycle the waste material in concrete will add a significant economic benefit, further reducing overall costs. Other methods of arsenic removal suffer from the disadvantage of higher disposal costs because of the potential for leaching of arsenic from the waste product. Research by the principal investigators has shown that the limestone waste product, after encapsulation in concrete, passes the Toxicity Characteristic Leaching Procedure (TCLP) test. However, the longer-term stability of concrete-encapsulated limestone waste has not been determined under acidic conditions. If limestone waste is recycled in concrete works such as sidewalks and pavements, stability of the encapsulated waste under typical weathering conditions is crucial. This project will investigate acidic leaching of arsenic from limestone waste after encapsulation in concrete. The tests will be indispensable in determining the longer-term stability of concrete-encapsulated waste when exposed to weathering or acidic conditions. If leaching of arsenic is minimal, the research will help demonstrate the potential for recycling of the waste material, thereby decreasing overall costs of limestone-based technology. In laboratory tests with limestone-based material, arsenic-contaminated water will be run through limestone material until breakthrough arsenic concentrations are reached. Breakthrough curves will be plotted for the tests. Breakthrough in this study will occur when the arsenic concentration goes from undetectable to 10 ppb, the new drinking water standard. The waste material then will be removed, encapsulated in concrete, and tested for leaching potential under acidic conditions such as rainwater and weak sulfuric acid solutions. If successful, the proposed work could give limestone-based technology a distinct advantage for use in small rural water systems. The objectives of this work are to: 1) Remove arsenic from water in laboratory tests and determine the mass of arsenic adsorbed on limestone. 2) Remove the limestone waste material after breakthrough and encapsulate it in concrete. 3) Conduct acidic leaching tests on the concrete-encapsulated arsenic and determine the long-term suitability for recycling of the encapsulated waste material in concrete. The research presented in this proposal will focus on improving the economic advantages of disposal of limestone-based material by recycling in concrete, which could significantly broaden potential applications of limestone-based arsenic removal methods. Overall goals include application as a pilot study at a wellhead with naturally occurring arsenic contamination, and commercial viability of the technology. The leaching tests in this work are designed to determine the stability of the concrete-encapsulated waste material and the potential mobility of arsenic contaminants. Rainwater and infiltrating water under acidic conditions that comes into contact with the waste could potentially leach toxins from the material. The U.S. Environmental Protection Agencys D List indicates the maximum concentration of arsenic for toxicity characteristic is five parts per million (ppm). Previous work by the researchers has shown that waste product from limestone-based material, after arsenic removal, is considered benign and suitable for disposal in a landfill. Testing is needed for long-term stability of limestone waste, however, if it is to be used in concrete that will be exposed to acidic conditions and weathering. The proposed research will help demonstrate the viability of this approach.