THE KINETICS OF SILICA-WATER REACTIONS
THE KINETICS OF SILICA-WATER REACTIONS
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DOI：
10.1016/0016-7037(80)90220-3
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发表时间：
1980-01-01
影响因子：
5
通讯作者：
BARNES, HL
中科院分区：
文献类型：
--
作者：
RIMSTIDT, JD;BARNES, HL
根据SiO2（s）+2 H2O（l）= H4 SiO 4（aq）反应中反应物的化学计量比和活度，导出了0-300° C范围内SiO2-水反应的微分速率方程（α H 4 SiO 4 β t）PTM=（A M）（γ H4 SiO4）（k+ a SiO 2 a 2 H 2 O− k_a H 4 SiO 4）其中（A M）=（固相和水相之间的相对界面面积/系统中水的相对质量），k+和k−分别是溶解和沉淀的速率常数。所有二氧化硅相沉淀的速率常数为log k−=− 0.707− 2598 T（T，K），该反应的Eact为49.8 kJ mol− 1。与石英、方石英或无定形二氧化硅反应的相应平衡常数表示为log K= a+ bT+ cT。使用K= k+ k−，k表示为log k+= a+ bT+ c T，并计算相应的活化能：a B c E法案（kJ mol-1）石英1.174-2.028 x 10 3-4158 67.4-76.6 α-方石英-0.739 0-3586 68.7 β-方石英-0.936 0-3392 65.0无定形二氧化硅-0.369- 7.890 x 10-4 3438 60.9-64.9在将二氧化硅饱和溶液冷却至平衡温度以下时，二氧化硅溶解度的降低导致过饱和度的增加，这往往会提高沉淀速率，但速率常数迅速降低，这往往会降低沉淀速率。这些相互竞争的效应导致最大降水速率比饱和温度低25-50° C。在低于最大速率的温度下，二氧化硅通常通过非常慢的反应速率淬灭成溶液。因此，如果样品取自高度断裂区域上方最热、流速最高的温泉，石英地质温度计将给出最准确的结果。
A differential rate equation for silica-water reactions from 0–300° C has been derived based on stoichiometry and activities of the reactants in the reaction SiO 2 (s)+ 2H 2 O (l)= H 4 SiO 4 (aq)(∂ a H 4 SiO 4∂ t) PTM=(A M)(γ H 4 SiO 4)(k+ a SiO 2 a 2 H 2 O− k_a H 4 SiO 4) where (A M)=(the relative interfacial area between the solid and aqueous phases/the relative mass of water in the system), and k+ and k− are the rate constants for, respectively, dissolution and precipitation. The rate constant for precipitation of all silica phases is log k−=− 0.707− 2598 T (T, K) and E act for this reaction is 49.8 kJ mol− 1. Corresponding equilibrium constants for this reaction with quartz, cristobalite, or amorphous silica were expressed as log K= a+ bT+ c T. Using K= k+ k−, k was expressed as log k+= a+ bT+ c T and a corresponding activation energy calculated: a b c E act (kJ mol-1) Quarts 1.174-2.028 x 10 3-4158 67.4–76.6 α-Cristobalite-0.739 0-3586 68.7 β-Cristobalite-0.936 0-3392 65.0 Amorphous silica-0.369-7.890 x 10-4 3438 60.9–64.9 Upon cooling a silica-saturated solution below the equilibrium temperature, the decreasing solubility of silica causes increasing super saturation, which tends to raise the precipitation rate, but the rate constants rapidly decrease, which tends to lower the precipitation rate. These competing effects cause a maximum rate of precipitation 25–50° C below the saturation temperature. At temperatures below that of the maximum rate, silica is often quenched into solution by very slow reaction rates. Consequently, the quartz geothermometer will give the most accurate results if samples are taken from the hottest, highest flow rate, thermal springs which occur above highly fractured areas.