The sensitivity of different minerals to chemical weathering

2019-05-15 10:54 admin
The mechanical transport of sediment in rivers can be described by the velocity-particle diagram, i.e. Hjulstrr m diagram (Fig. 10-3). In the picture. In the transporting area, the debris particles migrate with the flow mechanically in three ways: roll, jump and suspension, and when the flow velocity decreases, they are collected. Deposition. The area settled on the river bed. Small particles can move in suspension when the velocity is very slow, while large-sized debris requires a higher velocity to be transported. When the velocity of flow increases to 1. In the denudation zone, the riverbed can be eroded and the sediment can be re-transported.
 
For example, 0.lmm particles are in Figure 10-3 at a 10 cm/s flow rate. Carry. Zone, it will move with the current. When the flow rate is lower than lcm/s, it will precipitate in the river bed. Once the particles of o.lmm precipitate, they will be stripped off the riverbed at about 3ocm/s or higher velocity and carried by the river water and continue to migrate. As can be seen from Figure 10-3, in the Eustrome diagram. Denudation. And. Carry. The boundaries of the zones are wide in the fine grains. This is because the cohesive force between the deposited clay and silt particles is greater than that of sand particles, and it is easier to compact and consolidate and more difficult to denudate.
 
Moreover, the sedimentary surface of clay and silty sand is more compact and smooth than that of sand, which is more conducive to the development of laminar flow. Obviously, the higher the degree of consolidation of sediments, the smaller the porosity and the smoother and denser the surface, the higher the velocity required for erosion. However, the development of desert soils is slow in Yostrom illustration leaching. However, affected by wind-dust deposition, desert soils often contain various clay minerals, showing the illusion of weathering. Chemical weathering is carried out on the earth's surface. It is a complex combination of physical and chemical interactions between the lithosphere and the atmosphere, hydrosphere and biosphere. Chemical weathering is caused by thermodynamically unstable minerals adapting to the supergene environment rich in water and atmospheric gases. The newly formed substances in the chemical weathering process of Tartar are usually poorly crystallized or not) in parent rocks.
 
The principal component analysis of products in different stages of rock weathering can be used to calculate the gain and loss of components in chemical weathering process. But it is not easy to quantitatively determine the mineral composition of weathering products, just as it is difficult to determine the mineral composition of latent quality or vitreous volcanic rocks. The program for calculating standard minerals in volcanic rocks can also be used to estimate the mineral composition of some weathering products.
 
The sensitivity of different minerals to chemical weathering varies greatly, that is to say, some silicate minerals are easier to decompose than others, which can be related to the Bowen reaction series, that is, minerals crystallized from magma at high temperature are easier to weathering than minerals crystallized at lower temperature. However, to understand the different weathering sensitivities of minerals, background knowledge of ion and mineral stability in aqueous solutions is also needed.
 
Clay minerals are the main products of chemical weathering and an important component of most sedimentary rocks. Clay minerals are mainly layered silicate clay minerals, which are composed of two structural plates with different chemical composition and coordination number. One is tetrahedral sheet (T), which is composed of silicon-oxygen tetrahedron, and the other is octahedral sheet (0), which is composed of hydroxides of aluminium. A13 + ions are located in the center of the octahedral. The chemical diversity of clay minerals is due to the replacement of A13 + in octahedral slices and Si4 + in tetrahedral slices. A13+ in octahedral slices can be replaced by Fe', Fez+, Mg', Zn', Li + and CG +, and Si4 + in tetrahedral layer is replaced by A1a +. The charge imbalance caused by substitution in tetrahedral wafers can be compensated by additional cations in the octahedral layer. However, the net negative charges generated in tetrahedral and octahedral sheets can be neutralized by cations adsorbed on the surface of tetrahedral sheets, so that each clay unit is connected to each other. The clay adsorbing Na+, CaZ+, or M+ has larger interlayer voids than K-clay, and the cations between layers are replaced by water molecules, so they will expand in water. Because of the existence of surface charge, clay minerals and other particles can form colloidal suspension in diluted electrolyte solution. The polarity of charges carried by different colloidal particles depends on the pH value of the solution. In addition to the strong acid environment at pH 2.0, clay minerals, quartz, feldspar and manganese oxides are all iron oxides with negative charges. In the case of pH 5-9, hydroxides can be positively charged or negatively charged aluminum oxides and hydroxide particles are positively charged except at pH S. The ability of clay minerals to absorb displaceable ions is called cation exchange capacity (CEC).

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