The dependence of dissolution rates on grain size for some fresh and weathered feldspars.
The dependence of dissolution rates on grain size for some fresh and weathered feldspars.
复制标题
一些新鲜和风化长石的溶解速率对晶粒尺寸的依赖性。
DOI：
10.1016/0016-7037(92)90009-8
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发表时间：
1992
影响因子：
5
通讯作者：
C. Anbeek
中科院分区：
文献类型：
--
作者：
C. Anbeek
来自自然风化矿物碎片的地面样品仍然可以包含相当大比例的风化BET表面积。如果这种样品中的新鲜研磨表面和自然风化表面具有不同的溶解速率，则必须根据这两种类型的表面用动力学模型来解释数据。提出了这样一个动力学模型。该模型被用来重新检查九种不同的自然风化长石的磨粒级分的文献数据。对样品中新鲜和风化表面的溶解反应BET与测量的BET表面积的比率作为颗粒尺寸的函数进行了分析。对于自然风化表面，该模型强烈地表明，反应性BET与测量的BET表面积之比要么与颗粒尺寸无关，要么随着颗粒尺寸的减小而增加。如果是这样的话，研磨不会破坏，而且可能会产生风化的活性表面积(相对于风化的表面积)。对于刚磨光的表面，反应性BET与测量的BET表面积之比与颗粒尺寸近似成正比。因此，研磨破坏了所有粒度的新鲜活性表面积(相对于新鲜表面积)。对基本上含有新鲜BET表面的样品的额外溶解实验仅证实了这一发现。在文献中，来自大的自然风化碎片的研磨样品经常暗示仅含有新鲜的BET表面。如果单位新鲜BET表面积的溶解速率与颗粒大小大致无关，则可以解释观察到的溶解速率。然而，事实上，在自然风化矿物碎块的研磨过程中，有两个(部分)抵消过程似乎是活跃的。这些是1.(1)新磨制的BET与测量的(新磨制的和自然风化的)BET表面积的比率增加和2.(2)单位新鲜BET表面积的溶解速率的降低.这些观察表明，当归一化到新的BET表面时，速度常数和溶解速率仅在一个颗粒尺寸下有效.初步计算进一步表明，与自然风化的长石表面相比，新鲜长石表面的溶解速率(归一化为溶解反应的BET表面)大约高两个数量级。
Ground samples from naturally weathered mineral fragments can still contain substantial proportions of weathered BET surface area. If the freshly ground and naturally weathered surfaces in such samples have different dissolution rates, data must be interpreted by a kinetic model in terms of both types of surface. Such a kinetic model is presented. The model was used to reexamine literature data for ground size fractions from nine different naturally weathered feldspars. Ratios of dissolution-reactive BET to measured BET surface area were analyzed as a function of the grain size, both for the fresh and weathered- surfaces in the samples. For the naturally weathered surfaces, the model strongly suggests that the ratio of reactive BET to measured BET surface area is either independent of the grain size or, alternatively, increases with decreasing grain size. If so, grinding does not destroy, and possibly creates, weathered reactive surface area (relative to weathered surface area). For the freshly ground surfaces, the ratio of reactive BET to measured BET surface area was approximately directly proportional to the grain size. Thus, grinding destroys fresh reactive surface area (relative to fresh surface area) at all grain sizes. Additional dissolution experiments on samples essentially containing fresh BET surfaces only have confirmed this finding.In the literature, ground samples from large naturally weathered fragments are frequently implied to contain fresh BET surface only. Observed dissolution rates can then be explained if dissolution rates per unit of fresh BET surface area are approximately independent of the grain size. In fact, however, two (partly) counteracting processes appear to be active during grinding of naturally weathered mineral fragments. These are1.(1) increase of the ratio of freshly ground BET to measured (freshly ground plus naturally weathered) BET surface area and2.(2) decrease of the dissolution rate per unit of fresh BET surface area.These observations demonstrate that rate constants and dissolution rates, when normalized to fresh BET surface, are valid at one grain size only. Tentative calculations further suggest that dissolution rates, normalized to dissolution-reactive BET surface, are approximately two orders of magnitude higher for fresh feldspar surfaces than for naturally weathered feldspar surfaces.