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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).

The project group continued their research work and conducted multiple related trips and exchanges during the first quarter of 2015. In January, Dr. Tutu led a field expedition to Potchefstroom to identify future sampling sites for the aspects of the project. He then visited Prof. Ed Rosenberg and his group at the University of Montana in Missoula, MT from March 21 – April 18. During his visit, he presented a seminar to the department and the Rotary Club of Missoula entitled “Understanding and responding to contaminants in gold mining environments”. Dr. Tutu, along with team member Ms. Camden-Smith, also attended the 10th International Conference on Acid Rock Drainage held in Santiago, Chile where Ms. Camden-Smith presented a paper entitled “Chemical transformations of metals in gold tailings.”

With regard to ongoing project research, Ms. Camden-Smith completed a study that used geochemical modelling to assess the possibility of reducing limestone dosages and the amount of sludge produced at a mine water treatment plant. A manuscript is being prepared on this work for publication in an internationally acclaimed journal. Mr. Manamela completed studies on the adsorption capacities of unmodified and modified fly ash and cement. The results showed that adsorption is independent and that raw fly ash has good adsorption capabilities, but its modification with sodium hydroxide was found to enhance adsorption only slightly. Cement was found to exhibit elevated adsorption capacities. The mixed adsorbents gave impressive improvements on sorption capacity and removal efficiencies of both untreated and treated fly ash. The finding showed that with a little amount of cement, adsorption capacities of a waste material such as fly ash could be greatly improved.

In the coming months, Team member Ms. Camden-Smith will attend the Young Water Professionals Conference to be held in August where she will present a paper on her findings and is also expected to submit her thesis in November. Mr. Mabape will continue the work on functionalizing zeolite to get various types of zeolite for the adsorption of different elements in contaminated water and Mr. Manamela will continue his experimental work that will include making bricks (proxies for reactive barriers) using various mixes of cement, fly ash, and sand. This mix may include slag, depending on its availability.
 
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