State Water Resources Research Institute Program

Project ID: 2008SD130B
Title: Thermal Stability of Limestone Waste for Recycling after Arsenic Removal from Drinking Water
Project Type: Research
Start Date: 3/01/2008
End Date: 2/29/2009
Congressional District: SD First
Focus Categories: Toxic Substances, Treatment, Water Supply
Keywords: Arsenic; arsenic removal; drinking water; recycling; cement; disposal
Principal Investigators: Davis, Arden D (S.D. School of Mines and Technology); Dixon, David J. ; Hansen, Marion
Federal Funds: $ 12,467
Non-Federal Matching Funds: $ 24,935
Abstract: Limestone-based material has demonstrated 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 during the manufacture of cement. Research by the principal investigators has shown that the waste product from the limestone-based technology passes the Toxicity Characteristic Leaching Procedure (TCLP) test. Disposal of arsenic-enriched waste is critical for commercial viability of removal technologies. Low-cost disposal of waste in an ordinary landfill gives the method an advantage that could help communities meet the new maximum contaminant level for arsenic. The ability to reuse or recycle the waste material in the manufacturing of cement would add a significant economic benefit, further reducing overall costs. Other methods of arsenic removal, such as iron-based material, suffer from the disadvantage of higher disposal costs because of the potential for leaching of arsenic from the waste product.

This project will investigate recycling of waste product during the manufacturing of cement, and will focus on thermal stability tests. The tests, if successful, will help demonstrate the potential for recycling of the waste material, thereby decreasing overall costs of limestone-based technology. Ground water from City Well No. 4 at Keystone, South Dakota, will be used as the water source. In laboratory tests with limestone-based material, arsenic-contaminated water will be run through the 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 for thermal stability testing and leaching potential. 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. Determine breakthrough of arsenic in ten column tests using limestone-based material as the treatment media and Keystone city well water as the arsenic source.
  2. Remove the waste material after breakthrough and conduct analysis for thermal stability.
  3. Analyze thermal stability test results, and determine the suitable for reuse or recycling of the waste material during the manufacturing of cement.

The research presented in this proposal will focus on improving the economic advantages of disposal of limestone-based material by reuse or recycling, e.g., in a kiln feed during the manufacturing of cement, 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 thermal stability tests in this work are designed to determine the stability of the waste material and the potential mobility of contaminants in wastes. Infiltrating water and other liquids that come into contact with the waste can potentially leach toxins from the material. The U.S. Environmental Protection Agency's 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 thermal stability of limestone waste, however, if it is to be used in the manufacture of cement. The proposed research will help demonstrate the viability of this approach.

Progress/Completion Report, 2008, PDF
Final Report, 2009, PDF

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