Water Resources Research Act Program

Details for Project ID 2018MT325B

Reducing Acid Rock Drainage Volume using Passive Solar Evaporation Islands

Institute: Montana
Year Established: 2018 Start Date: 2018-03-01 End Date: 2019-02-28
Total Federal Funds: $15,000 Total Non-Federal Funds: $30,000

Principal Investigators: Katherine Zodrow

Abstract: Acidic mine waste (AMW) affects numerous drainages in Montana, and the release of AMW into natural waters threatens human and ecosystem health. One type of AMW, acid rock drainage, ARD, is a result of erosion of sulfidic minerals that creates sulfuric acid and dissolved metals. Several technologies may be used for the treatment of AMW, including passive wetlands and active treatment with lime. Implementation of these treatment technologies could potentially benefit from a process that reduces AMW volume, which would decrease the requisite size of water treatment reactors, decreasing cost and land area required. Likewise, volume reduction could potentially reduce the risk of spills or accelerate evaporative treatment of AMW. For example, enhancing evaporation in the Berkeley Pit could prolong the time to reach the critical level, where groundwater flow reverses, and starts flowing away from the Pit. This process may be utilized in holding ponds, tailings ponds or other evaporation ponds containing acidic mine waste. The proposed research explores implementation of Passive Solar Evaporation Islands (PSEIs) for AMW volume reduction. PSEIs consist of a floating carbon-based material (Figure 1) incorporated onto an upcycled plastic bottle. Coated bottles will be arranged into large rafts or islands. This “island” floats in AMW-filled lagoons or retention ponds. When exposed to sunlight, water within the material evaporates from the surface. Because the surface of the material is a stronger absorber of solar energy than water, the evaporation rate is accelerated. The base of the material is a semi-porous sponge that simultaneously insulates the material from the water, allowing it to store heat, and draws water up through its pores using capillary forces. The result is a floating island that acts as both a straw and a heat reservoir, enhancing evaporation and reducing volumes of AMW. The proposed project will be broken down into two phases. First, PSEIs will be fabricated and evaluated for stability in acidic water. Evaporation rates and scaling (the deposition of minerals) will be evaluated, determining material effectiveness and long-term viability. During the second exploratory phase, the materials will be tested using real ARD from Butte, and the influence of material properties on performance will be addressed. Findings will be shared with the public through an engineering design fair, a conference paper, and a children’s museum exhibit. Two recommendations set forth by the Montana State Water Plan will be addressed in this study. Notably, (1) to protect ecological health and the environment through treatment of a hazardous waste, AMW, and (2) to deliver water-related education and outreach by training a student in laboratory techniques and communication, presenting results at an engineering design fair attended by the public, and developing an exhibit for Butte’s children’s science museum, the Science Mine. Thus, the project will both address the environmental hazard posed by AMW and increase public awareness of the problem and solutions.