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Title: Ab initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution: OH{sup {minus}} catalysis

Abstract

The generally accepted mechanisms of quartz dissolution in basic pH solutions can be summarized as (a) direct attach by H{sub 2}O on a negatively charged surface site and (b) catalysis by hydroxide ion (OH{sup {minus}}) on a neutral surface site. In order to test these proposals and to understand the full dynamics of the dissolution processes from first principles, we have carried out high level ab initio molecular orbital calculations to study the following reactions: (HO){sub 3} Si-O-Si(OH){sub 2}O{sup {minus}} + H{sub 2}O {r_arrow} (HO){sub 3}Si-OH + {sup {minus}}O-Si(OH){sub 3} (HO){sub 3}Si-O-Si(OH){sub 3} + OH{sup {minus}} {r_arrow} (HO){sub 3}Si-OH + {sup {minus}}O-Si(OH){sub 3}. Disilicic acid, (HO){sub 3}Si-O-Si(OH){sub 3}, and its-1 deprodonated form, (HO){sub 3}Si-O-Si(OH){sub 2}O{sup {minus}}, have been chosen to simulate the neutral and negatively charged quartz surface site, respectively. Their reactions with OH{sup {minus}} and H{sub 2}O, which lead to the hydrolysis of the Si-O bond, have then been thoroughly investigated. Based on our ab initio calculations, we have discovered some interesting consequences: (1) OH{sup {minus}} attach on the hydroxyl surface will lead to the deprotonation of the surface by transferring one H to the OH{sup {minus}}, resulting in a H-bonded H{sub 2}O adsorption onto a negatively charged Si-O{supmore » {minus}} site. This process is equivalent to H{sub 2}O attack on the negatively charged Si-O{sup {minus}} surface. (2) The next step involves the formation of a negatively charged fivefold coordinated Si species; this step has to overcome a large energy barrier (18.91 kcal/mol). (3) The final step is the rupture of the Si-O-Si bond to form {equivalent_to}Si-OH...{sup {minus}O}-Si{equivalent_to}, with a much smaller energy barrier (4.49 kcal/mol). 61 refs., 11 figs., 6 tabs.« less

Authors:
;  [1]
  1. Yale Univ., New Haven, CT (United States)
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
471507
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 60; Journal Issue: 13; Other Information: PBD: Jul 1996
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; QUARTZ; DISSOLUTION; HYDROXIDES; CATALYSIS; CHEMICAL REACTION KINETICS; EVALUATION; ANIONS

Citation Formats

Xiao, Yitian, and Lasaga, A C. Ab initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution: OH{sup {minus}} catalysis. United States: N. p., 1996. Web. doi:10.1016/0016-7037(96)00101-9.
Xiao, Yitian, & Lasaga, A C. Ab initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution: OH{sup {minus}} catalysis. United States. doi:10.1016/0016-7037(96)00101-9.
Xiao, Yitian, and Lasaga, A C. Mon . "Ab initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution: OH{sup {minus}} catalysis". United States. doi:10.1016/0016-7037(96)00101-9.
@article{osti_471507,
title = {Ab initio quantum mechanical studies of the kinetics and mechanisms of quartz dissolution: OH{sup {minus}} catalysis},
author = {Xiao, Yitian and Lasaga, A C},
abstractNote = {The generally accepted mechanisms of quartz dissolution in basic pH solutions can be summarized as (a) direct attach by H{sub 2}O on a negatively charged surface site and (b) catalysis by hydroxide ion (OH{sup {minus}}) on a neutral surface site. In order to test these proposals and to understand the full dynamics of the dissolution processes from first principles, we have carried out high level ab initio molecular orbital calculations to study the following reactions: (HO){sub 3} Si-O-Si(OH){sub 2}O{sup {minus}} + H{sub 2}O {r_arrow} (HO){sub 3}Si-OH + {sup {minus}}O-Si(OH){sub 3} (HO){sub 3}Si-O-Si(OH){sub 3} + OH{sup {minus}} {r_arrow} (HO){sub 3}Si-OH + {sup {minus}}O-Si(OH){sub 3}. Disilicic acid, (HO){sub 3}Si-O-Si(OH){sub 3}, and its-1 deprodonated form, (HO){sub 3}Si-O-Si(OH){sub 2}O{sup {minus}}, have been chosen to simulate the neutral and negatively charged quartz surface site, respectively. Their reactions with OH{sup {minus}} and H{sub 2}O, which lead to the hydrolysis of the Si-O bond, have then been thoroughly investigated. Based on our ab initio calculations, we have discovered some interesting consequences: (1) OH{sup {minus}} attach on the hydroxyl surface will lead to the deprotonation of the surface by transferring one H to the OH{sup {minus}}, resulting in a H-bonded H{sub 2}O adsorption onto a negatively charged Si-O{sup {minus}} site. This process is equivalent to H{sub 2}O attack on the negatively charged Si-O{sup {minus}} surface. (2) The next step involves the formation of a negatively charged fivefold coordinated Si species; this step has to overcome a large energy barrier (18.91 kcal/mol). (3) The final step is the rupture of the Si-O-Si bond to form {equivalent_to}Si-OH...{sup {minus}O}-Si{equivalent_to}, with a much smaller energy barrier (4.49 kcal/mol). 61 refs., 11 figs., 6 tabs.},
doi = {10.1016/0016-7037(96)00101-9},
journal = {Geochimica et Cosmochimica Acta},
number = 13,
volume = 60,
place = {United States},
year = {1996},
month = {7}
}