Dissolution of quartz in aqueous basic solution, 106-236 degree C: Surface kinetics of perfect crystallographic faces

Journal Article · Wed Oct 31 23:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90109-X· OSTI ID:6262080

Gratz, A J; Bird, P; Quiro, G B ^[1]

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1. Univ. of California, Los Angeles (USA)

Past work on dissolution kinetics of minerals has focused on particulates and the total transfer of material to solution. The authors look instead at local topography of single crystals. Etching of quartz in alkali hydroxide solutions produces four types of features: flat-bottomed negative crystals with facets for walls, believed to nucleate on microfractures; jumbo pits, giant etch pits cored by dislocations and often with hollow cores; small pits, also believed to be dislocation-cored; and etch tunnels extending from some jumbo pits. A transition from selective etching to nonselective etching occurs as a function of ionic strength, with small pits forming only at ionic strengths below {approximately}0.005 m. This transition is attributed to the decrease in Debye-Hueckel length with increasing solution strength. The authors introduce the negative crystal method, whereby dissolution rates of nominally perfect crystal faces are obtained by measuring the size of individual negative crystals during a sequence of dissolution steps. Rates are obtained to {approximately}4% accuracy, with temperature control of {plus minus} 1.25{degree}C. Using this method, they find apparent activation energies for dissolution of the prism and for an average of the rhombs to be 86.39 and 90.19 kJ/mol, respectively, with corresponding pre-exponential factors of 2.99 {times} 10{sup 9} and 1.43 {times} 10{sup 10} {mu}m/h.

• OSTI ID: 6262080
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:11; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACID NEUTRALIZING CAPACITY
ACTIVATION ENERGY
BUFFERS
CHALCOGENIDES
CHEMISTRY
CRYSTAL FACES
DISSOLUTION
ENERGY
KINETICS
LEACHING
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
QUARTZ
REACTION KINETICS
SEPARATION PROCESSES
SILICON COMPOUNDS
SILICON OXIDES
SOLUBILITY
SURFACE PROPERTIES
WATER CHEMISTRY