Capacitive deionization process for water desalination and novel adsorbents for selective removal of selenium and arsenic from contaminated water

M. Parans Paranthaman, S.F. Evans, M.R. Ivancevic, C. Tsouris, A.M. Levine, R.J. Lee
Oak Ridge National Laboratory,
United States

Keywords: capacitive deionization, selenium and arsenic removal, tire derived carbon support, adsorbents, water treatments

Summary:

Potable water is a very scarce, critical resource on Earth. Part of USA, as well as countries including China, India, and other African states already experience water scarcity. Putting this into perspective, times of water scarcity affect nearly four billion people and this problem is expected to compound as population growth continues and living standards improve. Better water management can improve water availability, but other advancements are also necessary to provide water resources for the near future. Water purification technologies currently include distillation , electrodialysis, and membrane filtration methods. Researching alternative desalination techniques that are both energy efficient and economically feasible is important. One such method is capacitive deionization (CDI). CDI is a more cost-effective and efficient water purification method. CDI operate at ambient pressures, low temperatures, and low cell voltages, allowing for cheap, scalable systems. CDI is more efficient than the current industry standard, reverse osmosis, at lower salt concentrations. Waste-tire derived carbon [1-7] coated with polyaniline was used to form a composite electrode material for CDI process in this work [8]. In a batch cell testing with 1.2 V applied potential, the salt adsorption capacity measured in mg of salt adsorbed per gram of active material, in a 1500–1700 ppm KCl solution was measured at 14.2 mg/g. Scale-up of the process with ionic membrane- assisted CDI led to improvement in salt adsorption capacity at 18.9 mg/g. Further, cycling tests revealed that the electrodes had comparable or better longevity compared to most of the other CDI materials, retaining >92.8% charging capacity after 300 cycles. High adsorption capacities for other salts such as LiCl, NaCl, MgCl2 and CaCl2 have been found. In addition, waste tire-derived carbon has been used as a support for magnetic nanoparticles that selectively adsorb selenite (Se(IV)) ions from contaminated water has been developed [9]. Carbon-supported magnetic nanoparticle adsorbents displayed higher adsorption values of 48 ± 5 mg/g capacity with >99% Se removal at pH 3, 5, and 7 from 5 to 50 ppm selenite concentrations. Similar results have been obtained with arsenic as well. These improvements will expand the range of water sources that can be treated, as well as easing adsorbent collection through magnetic separation. We will report in detail about the CDI process coupled with use of magnetic adsorbents for selenium and arsenic removal.