title: Swelling related to ettringite crystal formation in chromite ore processing residue.
abstract: Several million tons of Chromite Ore Processing Residue (COPR) were deposited at two sites in New Jersey and Maryland, USA, and over time they exhibited extensive heaving phenomena. Ettringite, a needle-shaped mineral and an expansive mineral commonly recognized in the literature concerning cement- and soil, has been identified extensively in numerous COPR samples collected from these sites. It was therefore believed that ettringite formation and its crystal growth are strongly associated with COPR heaving. We investigated the correlation between ettringite and the heaving phenomena in COPR materials that contained no initial ettringite. Two identical COPR samples were exposed to a 4% w/w sulfate solution (25 degrees C, 50 degrees C) in a confined swell test apparatus. Both swell test samples were analyzed by means of X-ray powder diffraction. The peak intensities of newly formed ettringite were more pronounced in the sample tested at 50 degrees C, and swell development was only observed in this sample. Scanning electron microscopy analyses revealed well-crystallized ettringite needles exceeding 40 microm in length for this sample, while ettringite crystals less than 15 microm in length formed in the sample tested at 25 degrees C. Therefore, the results suggest that the quantity of ettringite and the extent of crystallization play a key role in the heave of COPR.
authors.affiliation: W.M. Keck Geoenvironmental Laboratory, Center for Environmental Systems, Stevens Institute of Technology, Hoboken, NJ 07030, USA. dmoon@stevens.edu
authors.forename: Deok Hyun
authors.initials: DH
authors.lastname: Moon
authors.forename: Dimitris
authors.initials: D
authors.lastname: Dermatas
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Wazne
authors.forename: Adriana M
authors.initials: AM
authors.lastname: Sanchez
authors.forename: Maria
authors.initials: M
authors.lastname: Chrysochoou
authors.forename: Dennis G
authors.initials: DG
authors.lastname: Grubb
mesh_terms: D017608:Chromium Compounds / Q000737:chemistry*; D019411:Clinical Laboratory Techniques; D003460:Crystallization; D008396:Maryland; D008903:Minerals / Q000737:chemistry*; D008906:Mining; D009515:New Jersey; D012996:Solutions; D013431:Sulfates; D013696:Temperature; D017155:Wettability; D014961:X-Ray Diffraction
chemical_list: D017608:Chromium Compounds; D008903:Minerals; D012996:Solutions; D013431:Sulfates; C501337:ettringite