MSGID: 1:317/3 648007f7   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    The problems with coal ash start smaller than anyone thought    
    How well toxic elements leach out of coal ash depends on the ash's   
   nanoscale composition    
      
     Date:   
         June 6, 2023   
     Source:   
         Duke University   
     Summary:   
         Burning coal doesn't only pollute the air. The resulting ash   
         can leach toxic chemicals into the local environments where   
         it's kept. New research shows that the toxicity of various ash   
         stockpiles relies heavily on its nanoscale structures, which vary   
         widely between sources. The results will help researchers predict   
         which coal ash is most environmentally dangerous.   
      
      
         Facebook Twitter Pinterest LinkedIN Email   
      
   ==========================================================================   
   FULL STORY   
   ==========================================================================   
   Everyone knows that burning coal causes air pollution that is harmful to   
   the climate and human health. But the ash left over can often be harmful   
   as well.   
      
   For example, Duke Energy long stored a liquified form of coal ash in 36   
   large ponds across the Carolinas. That all changed in 2014, when a spill   
   at its Dan River site released 27 million gallons of ash pond water into   
   the local environment. The incident raised concerns about the dangers   
   associated with even trace amounts of toxic elements like arsenic and   
   selenium in the ash.   
      
   Little was known, however, about just how much of these hazardous   
   materials were present in the ash water or how easily they could   
   contaminate the surrounding environment.   
      
   Fears of future spills and seepage caused Duke Energy to agree to pay $1.1   
   billion to decommission most of its coal ash ponds over the coming years.   
      
   Meanwhile, researchers are working on better ways of putting the ash to   
   use, such as recycling it to recover valuable rare earth elements or   
   incorporating it into building materials such as concrete. But to put   
   any potential solution into action, researchers still must know which   
   sources of coal ash pose a hazardous risk due to its chemical makeup --   
   a question that scientists still struggle to answer.   
      
   In a new paper published June 6 in the journal Environmental Science:   
   Nano, researchers at Duke University have discovered that these answers   
   may remain elusive because nobody is thinking small enough. Using one of   
   the newest, most advanced synchrotron light sources in the world -- the   
   National Synchrotron Light Source II at Brookhaven National Laboratory   
   -- the authors show that, at least for selenium and arsenic, the amount   
   of toxic elements able to escape from coal ash depends largely on their   
   nanoscale structures.   
      
   "These results show just how complex coal ash is as a material," said   
   Helen Hsu-Kim, professor of civil and environmental engineering at   
   Duke University.   
      
   "For example, we saw arsenic and selenium either attached to the surface   
   of fine grain particles or encapsulated within them, which explains   
   why these elements leach out of some coal ash sources more readily   
   than others."  It's long been known that factors in the surrounding   
   environment such as pH affect how well toxic elements can move from source   
   to surroundings. In previous research, Hsu-Kim showed that the amount   
   of oxygen in a toxin's surroundings can greatly affect its chemistry,   
   and that different sources of coal ash produce vastly different levels   
   of byproducts.   
      
   But just because one source of coal ash is high in arsenic doesn't   
   necessarily mean that high amounts of arsenic will leach out of   
   it. Similarly, various sources of ash respond differently to the same   
   environmental conditions. The problem is complex, to say the least. To   
   take a different approach, Hsu-Kim decided to take an even closer look   
   at the source itself.   
      
   "Researchers in the field typically use x-ray microscopy with a resolution   
   of one or two micrometers, which is about the same size as the fly ash   
   particles themselves," Hsu-Kim said. "So if a single particle is a single   
   pixel, you're not seeing how the elements are distributed across it."   
   To shrink these pictures' pixels to the nanoscale, Hsu-Kim turned to   
   Catherine Peters, professor of civil and environmental engineering at   
   Princeton University, and her colleagues to acquire time on the National   
   Synchrotron Light Source II. The futuristic machine creates light   
   beams 10 billion times brighter than the sun to reveal the chemical and   
   atomic structure of materials using light beams ranging from infrared   
   to hard X-rays.   
      
   Brookhaven's capabilities were able to provide the researchers a   
   nanoscale map of each particle along with the distribution of elements   
   in each particle. The incredible resolution revealed that coal ash is   
   a compilation of particles of all kinds and sizes.   
      
   For example, in one sample the researchers saw individual nanoparticles of   
   selenium that were attached to bigger particles of coal ash, which is a   
   chemical form of selenium that probably isn't very soluble in water. But   
   most of the ash had arsenic and selenium either locked inside individual   
   grains or attached at the surface with relatively weak ionic bonds that   
   are easily broken.   
      
   "It was almost like we saw something different in every sample we looked   
   at," Hsu-Kim said. "The wide array of differences really highlights why   
   the main characteristic that we care about -- how much of these elements   
   leach out of the ash -- varies so much between different samples."   
   While nobody can say for sure what causes the coal ash to develop its   
   unique composition, Hsu-Kim guesses that it is likely mostly related to   
   how the coal was originally formed millions of years ago. But it might   
   also have something to do with the power plants that burn the coal. Some   
   plants inject activated carbon or lime into the flue gas, which captures   
   mercury and sulfur emissions, respectively. At 1000 degrees Fahrenheit,   
   toxins such as arsenic and selenium in the flue are gaseous, and the   
   physics that dictate how the particles will cool and recombine to form   
   ash is uncontrollable.   
      
   But regardless of the how, researchers now know that they should be paying   
   closer attention to the fine details encapsulated within the end results.   
      
   This work was supported by the U.S. Department of Energy   
   (DE-FE0031748) and the National Institute of Environmental Health   
   Sciences (5U2C-ES030851). This research utilized U.S. DOE Office of   
   Science User Facility resources at the Stanford Synchrotron Radiation   
   Lightsource facility operated by SLAC National Accelerator Laboratory   
   (DE-AC02-76SF0051) and at the Hard X-ray Nanoprobe (HXN) Beamline at   
   3-ID of the National Synchrotron Light Source II facility operated by   
   Brookhaven National Laboratory (DE-SC0012704).   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Petroleum # Fossil_Fuels # Energy_Policy #   
                   Energy_and_Resources   
             o Earth_&_Climate   
                   # Energy_and_the_Environment # Environmental_Science #   
                   Hazardous_Waste # Environmental_Issues   
       * RELATED_TERMS   
             o Volcanic_ash o Coal o Pyroclastic_flow_from_volcanoes   
             o Fireworks o Volcano o Fossil_fuel o Pompeii o   
             Making_existing_structures_earthquake_resistant   
      
   ==========================================================================   
   Story Source: Materials provided by Duke_University. Original written   
   by Ken Kingery. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Nelson A Rivera, Florence T Ling, Zehao Jin, Ajith Pattammattel,   
      Hanfei   
         Yan, Yong Chu, Catherine Peters, Heileen Hsu-Kim. Nanoscale   
         heterogeneity of arsenic and selenium species in coal fly ash   
         particles: Analysis using enhanced spectroscopic imaging and   
         speciation techniques. Environmental Science: Nano, 2023; DOI:   
         10.1039/D2EN01056A   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230606111655.htm   
      
   --- up 1 year, 14 weeks, 1 day, 10 hours, 50 minutes   
    * Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)   
   SEEN-BY: 15/0 106/201 114/705 123/120 153/7715 218/700 226/30 227/114   
   SEEN-BY: 229/110 112 113 307 317 400 426 428 470 664 700 291/111 292/854   
   SEEN-BY: 298/25 305/3 317/3 320/219 396/45   
   PATH: 317/3 229/426