Experimental investigations of a[sub Ca[sup 2+]]/a[sub CO[sub 3][sup 2[minus]]] ratio on the kinetics of calcite precipitation: Implications for the rate equation and trace element incorporation

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6136726

Winter, D J; Burton, E A ^[1]

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1. Northern Illinois Univ., DeKalb, IL (United States). Dept. of Geology

Experiments investigating the influence of a[sub CA[sup 2+]]/a[sub CO][sub 3[sup 2[minus]]] (C/C) solution ratio on calcite precipitation rates indicate that the traditional forms of rate laws for carbonate precipitation are incorrect. Precipitation rates are highly dependent on the C/C ratio of the solution and thus, rate expressions based solely on carbonate species or on the ion activity product do not accurately depict precipitation rate dependence. The effect of C/C ratio on the rate of calcite precipitation in CaCl[sub 2]-NaHCO[sub 3] solutions was investigated at six different calcium concentrations, ranging from 0.1M to 0.001M Ca[sup 2+]. Rates were measured using the pH-stat method under constant solution compositions at 25 C and 10[sup [minus]2] atm P[sub CO[sub 2]] over a range in saturation states from slightly less than 2 to about 8 in each solution. Over the ranges in calcium concentrations and saturation states tested, C/C ratios varied from less than 1 to greater that 200,000. Results indicate that precipitation rates at constant saturation state increase by over an order of magnitude as C/C decreases over this range. For example, at a saturation state of 5, calcite precipitation rates are 25 times slower in a solution of 0.1M CaCl[sub 2] (C/C of about 40,000) than in a solution of 0.001M CaCl[sub 2] (C/C of about 1). In addition to modification of the form of rate law, these data also require re-evaluation of parameters controlling trace-element incorporation into calcite. Most all previous studies have linked trace-element incorporation to Mg[sup 2+]/Ca[sup 2+] solution ratios, to precipitation rate and, in some cases, to solution a[sub CA[sup 2+]]. The influence of C/C ratio on precipitation rate requires that this parameter also be considered in trace-element incorporation studies.

• OSTI ID: 6136726
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALCITE
PRECIPITATION
CALCIUM CARBONATES
CALCIUM CHLORIDES
CARBON DIOXIDE
KINETICS
PARTIAL PRESSURE
SODIUM CARBONATES
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM HALIDES
CARBON COMPOUNDS
CARBON OXIDES
CARBONATE MINERALS
CARBONATES
CHALCOGENIDES
CHLORIDES
CHLORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
MINERALS
OXIDES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
SODIUM COMPOUNDS
580000* - Geosciences