Computer Science
Scientific paper
Nov 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986gecoa..50.2509r&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 50, Issue 11, pp.2509-2516
Computer Science
10
Scientific paper
A newly developed mixed flow reactor was used to measure the rate of hydrolysis of wollastonite over the pH range of 3 to 8. This design avoids abrasion of the solid sample by confining it within a nylon mesh while the reacting solution is circulated over it by a stirrer. The rate of reaction was determined from the difference of the compositions of the input and output solutions following the methods used by chemical engineers for the analysis of mixed flow reactors, also called continuously stirred tank reactors (CSTR). This apparatus, constructed from easily obtainable parts, avoids many of the problems inherent in studying mineral/solution reaction kinetics in batch reactors. The hydrolysis of wollastonite CaSiO 3 + 2 H + + H 2 O = Ca 2+ + H 4 SiO 4 can be fit to a rate law of the form: dn H + / dt = k ad K H + m H + /(1.0 + K H + m H + ) where k ad = 9.80 × 10 -8 mol m -2 sec -1 and K H + = 2.08 × 10 5 . Over the pH range of 4 to 7, the data also may fit a simple linear form: dn H + / dt = - Ak + ( a H + ) 0.40 where k + = 3.80 × 10 -6 sec -1 at 25°C. The presence of calcium ion in the solution at concentrations up to 1.0 mol kg -1 produces only a minor reduction of the reaction rate. The activation energy for this reaction is 79.2 kJ mol -1 . Examination of the surfaces of the reacted grains showed no evidence of incongruent reaction leading to a product layer but did show the extensive development of etch pits leading to a rapid increase in the specific surface area. At large extents of reaction at low pH, diffusion of ions into or from these deep etch pits may limit the reaction rate.
Donald Rimstidt J.
Dove Patricia M.
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