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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 through December 2015

South Africa Picture A
An abandoned tailing 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

South Africa Picture B
The project team expects to visit more abandoned gold mines such as this one to collect samples and characterize elemental speciation and distribution. (Photo courtesy Dr. Tutu).

In October 2014, team members Ms. Camden-Smith and Mr. Kgabo Manamela attended the 9th International Mine Closure Conference in Sandton, Johannesburg and Ms. Camden-Smith presented results from her ongoing work. The other travel related event was the visit of U.S. partner Ed Rosenberg in November. During his visit, he gave a seminar to the department and a mini-workshop to Dr. Tutu’s research group on advanced materials for metal recovery. The partners also started work on a review article about uranium removal methods that will be published in an international journal.

On the ground, the sampling trips for Ms. Camden-Smith’s project continued, one of which involved a visit to a mine water reclamation plant on the Central Rand Goldfield, Johannesburg. The project team has determined the chemical composition of the water throughout the process, i.e. from the polluted water pumped from underground to neutralization with limestone to discharge into a natural stream. They have also conducted geochemical modeling simulations of the processes involved in the evolution of the chemical composition. Mr. Manamela’s work focused on assessing the performance of the different adsorbent materials (unmodified fly ash, modified fly ash, cement and zeolite) with respect to their metal capture capability. The adsorbent materials showed a remarkable capability to remove metals at low pH regimes. For elevated metal concentrations, cement was found to exhibit excellent adsorption capability.

In the coming months, Mr. Mabape and Mr. Manamela will continue with their experimental work according to the schedule. Mr. Manamela should complete his experimental work by October 2015 and is expected to submit his dissertation by December 2015, and Mr. Mabape should complete his experimental work in June 2016. Ms. Camden-Smith will complete most of her experimental work by April 2015 and then focus on writing her thesis and journal publications. The PI will be undertaking a field trip in late January 2015 to the West Rand Goldfield, which is one of the areas where the team plans to deploy the adsorbent materials. Dr. Tutu will also visit Prof. Rosenberg’s group at the University of Montana from March 21 through April 18, 2015, before attending the International Mine Water Congress in April in Santiago, Chile. In August, Mr. Manamela will attend the International Union of Pure and Applied Chemistry (IUPAC) in Busan, South Korea.
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