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Partnerships for enhanced engagement in research (PEER) SCIENCE
Cycle 2 (2012 Deadline)

Development of advanced composite materials and geopolymers for the removal of uranium and toxic elements from gold mine-polluted water

PI: Hlanganani Tutu (University of the Witwatersrand)
U.S. Partner: Edward Rosenberg (University of Montana)
Project Dates: August 2013 to February 2015

South Africa Picture A
An abandoned talling storage facility with an efflorescent crust, which leaches metal pollutants into the water at the start of the rainy season (Photo courtesy Dr. Tutu).

The Witwatersrand Basin in South Africa faces challenges of water pollution, largely due to acid mine drainage (AMD) emanating from gold mining activities. AMD in the region includes a wide range of toxic elements such as uranium, arsenic, lead, mercury, and other metals. Most of the AMD emanates from inactive or abandoned mine facilitie, with sources including tailings storage facilities, tailing ponds, waste rocks, abandoned mine shafts, and open pits. Because of lack of funding for treatment of such facilities, surface and groundwater resources are continually contaminated, which has far-reaching implications for communities where these are the only water sources available. Two remediation approaches for the polluted water will be studied in this PEER Science project. The first will focus on the remediation of tap water used by households drawing water from mine-polluted aquifers. Silica polyamine composites (SPC) for the removal of uranium and attendant toxic elements will be developed for use in faucets (tap filters) and in columns that can be inserted into drinking water holding containers such as kettles and water jars. Commercially-available adsorbents tend to be expensive and out of reach for poor communities such as the ones affected by AMD in the study area. Affordable ones such as activated carbon are not very effective for removal of uranium and other elements such as arsenic. To this end, the study will explore ways of augmenting activated carbon with SPC for improved removal of these elements. The second approach will focus on bulk remediation at the sources of contamination. This will entail developing cost-effective geopolymeric materials using fly ash from coal mining, slag from furnace smelters, and a silicate binder. This material will be used in concrete mixes to form porous reactive barriers that will be erected at mine-polluted sites to intercept the polluted water flow, providing an adsorption surface for toxic elements and improving the quality of exiting water.

In the course of the proposed work, particular attention will also be paid to the potential recovery of low levels of precious metals (gold and silver) contained in gold mine-polluted water. Once allowed to load onto the adsorbents over time, these and other metals can be desorbed by an acid leach and concentrated using precious metal and uranium-selective SPC and recovered for economic use, thus providing the possibility of an in situ “smart” mining technique. This way, the costs of remediation can be decreased further or, better still, forgone. The results of this study will have applications in most mining industries in South Africa. In addition, the project will provide an opportunity for students to participate in applied and fundamental academic research.

Summary of Recent Activities

This research team began experimental work on their project in October 2013, focusing on contaminants likely to be found in gold-mine water, as well as the materials likely to be effective in filtering out these contaminants. An experiment on the leaching and microwave digestion of fly ash was commenced, and waste material composed of phosphygypsum from coking operations was also studied. In addition, the team conducted batch experiments on the adsorption capacity of the phosphonated silica polyamine composite polymer BPAP as a possible filter for contaminated water. This was done to assess the possibility of using the polymer for the adsorption of uranium and carbonates.
 
A workshop on geochemical modelling was held February 3-7, 2014 to teach students involved in the project various aspects of computer modelling related to water chemistry and remediation.  A workshop on the development of materials for adsorbent systems will be held in June 2014 at the University of the Witwatersrand, immediately after which the project team and U.S. partner Ed Rosenberg will meet with the Cancer Association of South Africa to discuss the design of clean-water systems and identify the communities to which these systems will be deployed. Other plans include site visits to collect water samples from a stream in Johannesburg impacted by gold mining. The presence and density of uranium and other elements in the water will be determined using geochemical modelling.
 
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