COAL ASH MEETS CITRIC ACID (IMAGE) DOE/Sandia National Laboratories Caption Sandia National Laboratories researcher Guangping Xu adds coal ash into a citric acid mixture. This solution will be fed into a reactor — operating at about 70 times atmospheric pressure — where supercritical carbon dioxide aids citric acid in extracting rare-earth metals. Credit Rebecca Lynne Gustaf Usage Restrictions None License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.