CONDENSATION OF SILICA FROM SUPERSATURATED SILICIC-ACID SOLUTIONS
CONDENSATION OF SILICA FROM SUPERSATURATED SILICIC-ACID SOLUTIONS
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DOI：
10.1016/0021-9797(80)90081-8
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发表时间：
1980-01-01
影响因子：
9.9
通讯作者：
SLAUGHTER, J
中科院分区：
文献类型：
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作者：
MAKRIDES, AC;TURNER, M;SLAUGHTER, J
在pH(4.5~6.5)、温度(75~105℃)、盐度和硅酸浓度(700~1200ppm)范围内，研究了硅酸过饱和卤水中二氧化硅的缩合反应。通过对钼酸盐反应性硅酸的分析，跟踪了缩合过程。SiO_2凝聚的等温速率是过饱和度(C、Ce)、pH和盐度的函数。在过饱和度小于约3的情况下，存在一个明显的过渡期，在此期间，溶液中硅酸的脱除率低于分析技术的检测下限。在约2.0的过饱和度下，这段时间相当于数百分钟。成核颗粒的生长是活化控制的，至少在一开始是这样。初级原子核的半径约为几埃量级。最终会产生几百埃的粒子。成核和生长速度随着pH的增加而增加，对于每个pH单位大约增加10倍。PH的依赖关系与SiO(OH)3−是反应物种之一的假设一致。冷凝的速度增加了含盐量。实际上，较高的盐浓度会增加过饱和度并导致更快的成核。在初始硅酸浓度一定的情况下，温度(75~105℃)对缩合速率影响不大。这一结果表明，较高温度下的速率增加被过饱和度的减少所抵消。在成核的二氧化硅颗粒中加入硅酸的活化能约为17千卡/摩尔。沉淀二氧化硅与卤水的界面能约为45erg/cm2。氯化钠、氯化钾、氯化镁对凝聚速率无明显影响。氟化钠对凝聚速率有很大的影响；15-100ppm的氟离子大大加速了凝结。
Condensation of silica from brines supersaturated in silicic acid was studied over a range of pH (4.5–6.5), temperature (75–105° C), salinity, and silicic acid concentration (700 to 1200 ppm as SiO 2). The course of condensation was followed by analyzing for molybdate-reactive silicic acid. The isothermal rate of SiO 2 condensation is a function of supersaturation (C C e), pH, and salinity. At supersaturations less than about 3, there is an apparent transition period during which the rate of removal of silicic acid from solution is below the detection limit of the analytical technique. This period amounts to several hundred minutes at supersaturations of about 2.0. Growth of nucleated particles is activation controlled, at least initially. The primary nuclei have radii of the order of a few angstroms. Particles of several hundred angstroms are produced eventually. Nucleation and growth rates increase with increasing pH approximately by a factor of 10 for each pH unit. The pH dependence is consistent with the hypothesis that SiO (OH) 3− is one of the reacting species. The rate of condensation increases salt content. In effect, higher salt concentrations increase supersaturation and lead to faster nucleation. Temperature (75–105° C) has little effect on condensation rate at a fixed initial silicic acid concentration. This result suggests that the increase in rate at higher temperatures is counterbalanced by a decrease in supersaturation. The activation energy for addition of silicic acid to a nucleated particle of SiO 2 is about 17 kcal/mole. The interfacial energy between precipitated silica and the brine is about 45 erg/cm 2. NaCl, KCl, and MgCl 2 have no specific effect on condensation rate. NaF has a large effect on rate; 15 to 100 ppm of fluoride ion accelerate condensation substantially.