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ADS-RPT-2021-14 <br />ESS-Nederland Mine _ 60 <br />November 4, 2021 <br />200 Lake Drive, Glasgow, DE 19702 302.731.1700 Fax 302.731.1701 <br />www.gravertech.com <br />Proprietary and Confidential <br />Page 2 of 8 <br />cadmium hydroxide (Cd(OH)2).1 Other Pourbaix diagrams show the conversion of Cd to other <br />species around a pH of 8.5 or higher. These Pourbaix diagrams are guiding documents to <br />determine how media may adsorb the contaminant. Zinc, the other major contaminant at Cross <br />is also mostly Zn2+ at a pH of 0-7.5. After 7.5, the zinc starts converting to zinc oxide. 2 <br />MetSorb® HMRG is known to remove both cations and anions, depending on the specific water <br />chemistry. There are several case studies and experimental results that show MetSorb® HMRG <br />can remove both cadmium and zinc. <br />One case study for cadmium removal concluded: <br />“Despite being at a significantly lower concentration than the other metals, cadmium <br />adsorption performance also followed a trend of steady concentration decrease over time. <br />The fine (0.1μm) filtration step reduced the starting concentration by 13% indicating the <br />presence of insoluble cadmium . The separate granular activated carbon (GAC) filtration <br />step removed only 5% of the cadmium present and not much more than the (2.7um) pre- <br />filter used prior to beginning the stirred batch equilibrium testing. The stirred batch <br />equilibrium testing demonstrated the selectivity of MetSorb® HMRG for cadmium in this <br />wastewater matrix despite the much higher concentration of other metals present. Due to <br />the evidenced selectivity, it is clear that cadmium removal will occur and that the extent of <br />reduction will be a function of media volume and contact time.” <br />This study was conducted at a customer site with over 350 ppb of cadmium. <br />In testing for zinc removal, one experimental study showed that HMRP (the powdered version of <br />MetSorb® HMRG) could remove 97% of the zinc from a pH 6.5 and a pH 8.5 solution. The zinc had <br />initial concentrations from 291-815 ppb. The measured capacity of the media for this test was <br />0.768 mg Zn/ dry gram of media. Other media specifically designed for cation removal resulted in <br />higher percent removal and capacities. <br />Another case study tested both MetSorb® HMRG and MetSorb® STG for the removal of multiple <br />metals. Both HMRG and STG removed Cd and Zn at over 7,000 bed volumes (BVs) before Zn broke <br />through (~ 800 ppb initial) and over 8,000 BVs before Cd broke through (~550 ppb initial). <br />Testing was conducted on the Cross water to confirm the capacity and effectiveness of MetSorb® <br />HMRG media relative to the specific water conditions at the Cross site. <br />3.0 Method: <br />3.1 Equilibrium batch testing - Efficiency <br />To a 125 mL polypropylene container was added 1.0 dry grams of MetSorb® HMRG and 100 mL <br />of water from Cross. This is a volume to mass ratio of 100 mL of solution per dry gram of media. <br />1 https://boris.unibe.ch/109643/1/1.4980127.pdf <br />2 https://commons.wikimedia.org/wiki/File:Zn-pourbaix-diagram.svg