Why are clay minerals adsorbent?

People with a little common sense know that clay is adsorption, and clay has sticky properties as the name suggests, but why clay has adsorption, do you know the deeper reason? Let's take a look at what clay is and why it has this property. Clay is a kind of clayey soil with relatively few sand particles, and it is not easy for water to pass through it, and it has good plasticity.

Generally clay is made of silicate.

Minerals of the same class are formed after weathering on the earth's surface.

The adsorption of clay minerals can be divided into three categories, namely: physical adsorption, chemical adsorption and ion exchange adsorption. First of all, physical adsorption refers to the adsorption due to the gravitational action between the adsorbent and the adsorbate, which is due to the large surface area of the adsorbent itself.

proportion, so the adsorption capacity is very strong. The second is chemisorption, which refers to the chemical bond between the adsorbent and the adsorbate.

Adsorption by force. The adsorption effect is based on the chemical bonds created between the forces of yin and yang, so that there must be a positive charge around an object.

Another object has a negative charge around it, so that a gravitational attraction of positive and negative attracts is created.

The third is ion exchange adsorption, which refers to cations such as Ca2+, Mg2+, H+, K+, NH4+, Na+, Al3+, etc.

and anions such as SO42-, Cl-, PO32- and NO3- in solution.

Electrons are exchanged with each other to achieve a typical equilibrium effect. Ion exchange adsorption can be divided into cation exchange adsorption and anion exchange adsorption according to different electrical properties. The factors affecting the size of anion and cation exchange in clay are mainly as follows.

One is the type of clay minerals, and different types of clay minerals are different. The second is the particle density of clay minerals, which corresponds to different clay densities.

The third is the pH of the solution.

These are inseparable from chemistry, if students who are good at chemistry can continue to study in depth, I will not describe them in detail here.

Because the edge of the clay mineral crystal is positively charged, the anionic group can be adsorbed on the edge of the clay mineral by electrostatic attraction. In the presence of a neutral electrolyte in the medium, inorganic cations can act as a "bridging" between the clay mineral and the anionic polymer, allowing the polymer to adsorb on the surface of the clay mineral.

Because clay minerals have a large surface area, they have a strong adsorption capacity, and clay minerals carry many unsaturated charges that attract other charges to adsorb.

The crystal structure of mineral soil is a layer chain structure, which determines its good adsorption performance and plasticity because of its special structure, which can be applied in mining, building materials, fertilizer and other industries.

The reason why clay minerals have physical adsorption is that it has a large specific surface area, so the adsorption capacity is very strong.

The main secondary minerals in the soil are clay minerals.

Clay minerals are a composite aluminum-silicate.

Crystals, in the form of flakes, are made up of unit cells composed of silicon wafers and aluminum sheets.

The basic unit of a silicon wafer is a silicon-oxygen tetrahedron.

The basic unit of the aluminum sheet is the aluminum-hydroxide octahedron.

Clay minerals are mainly divided into three types: kaolinite, illite and montonite, depending on the combination of silicon wafers and aluminum flakes.

Kaolinite: The crystal layer structure is composed of a silicon wafer and an aluminum wafer stacked on top of each other.

The main characteristics are: the particles are coarse, and they are easy to absorb water and expand, lose water and shrink, or have poor hydrophilic ability.

Monterite: The crystal layer structure is composed of two silicon wafers sandwiched between an aluminum wafer.

The main characteristics are: fine particles, with significant water absorption and expansion, water loss and contraction characteristics, or strong hydrophilic ability.

Illite (a product of the weathering of mica in an alkaline medium): a three-layer structure formed by two layers of silicon wafers sandwiched by a layer of aluminum, but with potassium ion bonding between the crystal layers (the bond strength is weaker than that of kaolinite and stronger than Montesite).

Electrophoresis: A phenomenon in which charged particles move towards an electrode opposite to their electrical properties under the action of an electric field.

Electroosmosis: In the electric field, the solution is relatively charged due to the adsorption of positive and negative ions in the water by the porous support, and the solution moves in a certain direction under the action of the electric field. Xiangzhi.

The surface of flaky clay particles often has an unbalanced charge, usually a negative charge, due to:

1.Dissociation: dissociation of certain minerals on the surface of the crystal in an aqueous medium (cation diffusion in water, anion.

left on the surface).

2.Adsorption: Some minerals on the surface of the crystal adsorb some charged ions in the aqueous medium to the surface of the particles.

3.Isomorphic replacement: The aluminum inside the crystal is replaced by magnesium or iron.

Electric double layer: The negative charge on the surface of the particles, which constitutes the inner layer of the electric field, the cations and water molecules in the water that are attracted to the surface of the particles.

The outer layer that makes up the electric field. (The surface properties of clay minerals directly affect the properties of water in the soil, so that cohesive soil has many characteristics that non-cohesive soil does not have).

Specific surface area. The sum of the surface area possessed by a unit mass of soil particles.

Primary minerals are generally coarse, granular, and the scale in the three directions is basically on the same order of magnitude, and the specific surface area is small.

The clay particles are fine, mostly flake-like, and have a large specific surface area.

The specific surface area of kaolinite is 10 20 square meters per gram, illite is 65 100 square meters per gram, and Monte stone is 800 square meters per gram.

The specific surface area of clay minerals directly reflects the intensity of the interaction between soil particles and the surrounding medium (water), which is an important indicator to represent the characteristics of cohesive soil. However, for coarse-grained soil, because its surface is not charged, the specific surface area is not of much significance, and the inter-particle arrangement and roughness should be considered.

the proportion of needle flakes and the roundness of the particles (which ultimately affects the shear strength).

The main clay minerals include kaolinite, illite, montmorillonite, vermiculite and sepiolite minerals.

Clay minerals are some hydrous silicate minerals containing aluminum, magnesium and other predominant. Except for the sepiolite and the slope stone with a chain layered structure, the rest have a layered structure. The particles are extremely fine, generally less than millimeters.

It has different degrees of plasticity after adding water. Main function: Mainly used as ceramics and refractory materials, and used in petroleum, construction, textile, papermaking, paint and other industries.

Answer]: There are three ways to form minerals in the clay pre-clay soil: it is related to weathering, and the types of weathered original rocks and media conditions such as water, climate, landform, vegetation and time determine the mineral species and whether they are preserved or not; Hydrothermal reflux and hot spring water act on the surrounding rocks, which can form alteration and enrichment belts of clay minerals. Clay minerals are produced by sedimentation and diagenesis.

The type of affinity clay mineral can affect the process and results of clay hydration. Different kinds of clay minerals have different chemical and physical properties, which can affect their hydration process and the properties of their hydration products. Generally speaking, clay minerals mainly include illite, chahormontmorillonite, kaolin, talc, etc.

The following are the effects of different clay mineral species on clay hydration:1Illite:

Illite has a large number of interlayer water molecules, and when the water molecules enter the interlayer, they will form hydrogen bonds with the surface of illite, resulting in an increase in the interlayer distance. Illite is easy to form colloids after hydration, and has high viscosity and viscosity. 2.

Montmorillonite: Montmorillonite has more functional groups such as oxides and hydroxyl groups than illite, so its hydration process is more complex. Montmorillonite is also easy to form colloids after hydration, but compared with illite, its viscosity and viscosity are low.

3.Kaolin: Kaolin belongs to a cross-linked polymer, and its hydration process is mainly achieved through hydrogen bonding between hydroxyl and alumina.

Kaolin can form colloids after hydration and has a high viscosity and viscosity. 4.Talc:

The structure of talc is relatively simple, and since its surface has no electric charge, talc is not easily hydrated in water. When talc is hydrated, the colloids formed have a lower viscosity and viscosity. In conclusion, the type of clay minerals has a great influence on clay hydration.

Different kinds of clay minerals need to be treated and utilized in different ways to get the best results.

Clay minerals with different shed types also show great differences in their water absorption and gel properties, so the type and amount of clay minerals can affect the hydration properties of clays. Generally speaking, when the clay contains more quartz, feldspar and other minerals that cannot absorb water, the hydration properties of the clay will be relatively poor; When the clay contains more illite, clay minerals and other parts that can strengthen the hydration properties of the clay, the hydration properties of the clay will be better.

At the interface between the clay particles in the mud and the decomposition medium water, the phenomenon of automatically concentrating the molecules or ions in the medium is called clay adsorption. Because the surface of clay particles usually has a negative charge, it can adsorb various hydration cations in the medium, so that the surface of the clay particles forms a layer of hydration film with a certain thickness, which is called the hydration of clay. The adsorption and hydration of clay are important factors that stabilize the mud dispersion system.

By adjusting with different chemical treatment methods and controlling its adsorption and hydration, various types of slurries with different properties can be obtained.

a) Adsorption properties of clay.

The adsorption of clay in mud, like the adsorption of many other objects, can be divided into three types: physical adsorption, chemical adsorption and ion exchange adsorption.

Physical adsorption is the adsorption caused by the interaction force between molecules, which is caused by the surface energy of surface molecules. Its adsorption force is weak and easy to desorption, and the adsorption speed is fast. There is a wide range of physical adsorption between the clay particles and the molecules or ions of the treatment agent in the slurry.

Chemical adsorption is the adsorption of chemical bonds between adsorbed substances, and its adsorption force is strong. It is not easy to desorption, and the adsorption speed is slow. Chemical adsorption is also widely present in slurries.

Ion exchange adsorption is physico-chemical adsorption and is widely present in slurries. It is the main adsorption effect of clay in the mud, and is the basis for the chemical treatment and performance adjustment of the mud. Because the surface of the clay particles is negatively charged, cations can be adsorbed, and the adsorbed cations are exchangeable, that is, they are exchanged with other cations present in the mud, and this exchange is reversible.

The properties and quantity (exchange capacity) of clay particles adsorbed cations have a very important impact on the dispersion and stability of clay particles in the mud.

b) Hydration of clays.

The hydration of clay refers to the state and ability of adsorbed molecules on the surface of clay particles in the mud. The surface of the clay particles can directly adsorb polar water molecules – adsorption of water. More importantly, the surface of clay particles is negatively charged, and a large number of cations dispersed in the mud can be adsorbed to achieve hydration, so that a layer of hydration film is formed on the surface of the clay particles, thereby producing hydration.

The hydration of clay is an important factor affecting the performance of water-based mud, and the dispersion, stability and coagulation and precipitation of clay particles in the mud depend to a large extent on the hydration of clay particles.

3) An electric double layer on the surface of clay particles in the mud.

The negative charge on the surface of clay particles in water can generate an electric field, which can attract exchangeable cations around it to form an electric double layer through electrostatic action. Only a part of the cations adsorbed around the clay particles move together with the clay particles, and this part attracts a relatively strong cation layer with the clay, which is called the adsorption layer; The other part of the cation is slightly farther away from the clay particles and does not move with it, and the layer where this part of the cation is located is called the diffusion layer.

The electric double layer theory of the surface of clay particles in mud is the theoretical basis for chemical treatment of mud with electrolyte.