1. Concept:
Adsorption: It is a phenomenon in which a substance in a liquid (or gas) increases or decreases at a phase interface.
Positive adsorption: When a certain substance is added, the surface energy of the solution is lowered, the concentration of the surface layer solute is greater than the concentration inside the solution, and the concentration is increased. This substance is called a surfactant.
Negative adsorption: When a certain substance is added, the surface energy of the solution is increased, the concentration of the surface layer solute is less than the concentration inside the solution, and the concentration is lowered. This substance is called a non-surfactant.
Adsorption amount: When the adsorption reaches equilibrium at a certain temperature, the number of moles of adsorbate adsorbed per unit area is usually expressed by “Γâ€.
2. Significance:
Adsorption is a major form of phase interaction in the float process, in addition to absorption, adhesion and multiphase chemical reactions. Studying the adsorption phenomenon in the flotation process is of great significance for exploring the flotation theory and guiding the flotation practice.
Second, the type of adsorption:
Adsorption is divided into physical adsorption and chemical adsorption. The difference between the two: whether the chemical bond between the chemical particle on the adsorption surface and the adsorbate occurs. The adsorption caused by the chemical bond force is called chemical adsorption; the adsorption caused by the molecular bond force is called physical adsorption.
Physical adsorption: molecular adsorption, double layer diffusion layer adsorption, semi-adhesive semi-adsorption.
Chemical adsorption: ion adsorption, double layer inner layer adsorption and characteristic adsorption.
1. Molecular adsorption: dissolved solutes in solution,
Adsorption to the solid-liquid, gas-liquid phase interface in molecular form is called molecular adsorption. The result of the adsorption does not change the electrical properties of the mineral surface.
2. Ion adsorption: Solute ions are adsorbed on the surface of minerals, called ion adsorption.
(1) Positioning adsorption: The adsorption of the positioning ions in the positioning layer has strong selectivity and non-substitution, and the result is electrical.
(2) Exchange adsorption: Another ion on the surface of an ion exchange mineral adsorbs on the surface of the mineral.
Positioning adsorption and exchange adsorption often occur simultaneously, often forming insoluble salts on the mineral surface, which can change the electrical properties (including quantity and symbol) of the mineral surface.
3. Double layer adsorption:
(1) Adsorption of the inner layer of the electric double layer---position adsorption (2) adsorption of the outer layer of the electric double layer:
Tight layer adsorption: electrostatic force, van der Waals force and chemical bond force.
Diffusion layer adsorption: electrostatic force.
4. Semi-micelle adsorption: The non-polar end of the long hydrocarbon chain undergoes association under the action of van der Waals force to form a colloid-like structure.
5. Characteristic adsorption: adsorption in addition to electrostatic adsorption in the adsorption of electric double layer. Has a special affinity for a certain component of the solution.
3. Gas---adsorption of liquid interface Foaming agent is a kind of surface active material. At the gas-liquid interface, the monolayer is oriented to adsorb molecules. The non-polar group penetrates the gas phase through the interface. The base remains in the liquid.
The non-polar groups interact with van der Waals forces, and the polar groups repel each other and attract the water dipoles.
The adsorption equation (self-learning) obeys the Gibbs adsorption equation.
4. Adsorption of solid--liquid interface 1. Influencing factors
(1) The structure and properties of the adsorbent and adsorbate and the number of active sites in contact with each other.
During the flotation process, the mineral acts as a adsorbent, gas or solvent as the adsorbate.
Regularity: A. The polar adsorbent is easy to adsorb the absorbing adsorbate or electrolyte ion.
B. The non-polar adsorbent is easy to adsorb non-polar adsorbate.
(2) The solute that can reduce the free energy of the solid-liquid interface is more adsorbed.
(3) Solutes with less solubility are more easily adsorbed.
(4) The same mineral may have different adsorption properties.
(5) The temperature has an influence, the adsorption is exothermic, the temperature rises, and the adsorption amount decreases.
2. Adsorption equation (self-study)
3. Types of adsorption of chemicals on mineral surfaces (1) Classification according to the morphology of adsorbed products on the surface of minerals: molecular adsorption, ion adsorption, (semi) micelle adsorption.
(2) Classification by adsorption: exchange adsorption, competitive adsorption, and characteristic adsorption.
(3) Classification according to the position of ions adsorbed in the electric double layer: adsorption inside and outside the electric double layer.
(4) Classification according to the action attribute between adsorbate and adsorbent: physical and chemical adsorption.
4. Points to add (1) Physical and chemical adsorption in the same system coexist and are not mutually exclusive.
(2) The two may undergo mutual transformation as conditions change.
(3) Chemical adsorption When the conditions are suitable, it can develop into a surface chemical reaction.
(4) Physical adsorption is the adsorption of "non-site" nature, and the effect is lack of selectivity;
Chemisorption is a "site-specific" adsorption that is selective.
(5) The surface of the mineral can adsorb the solvent in addition to the adsorbed solute, and there is interaction and competitive adsorption between the components, which leads to the complication of solid-adsorption.
(6) The speed is slow and requires a certain amount of contact time----pulp preparation.
5. Adsorption of solid--liquid interface The hydration and electrical properties of the solid surface are the result of adsorption.
Physical adsorption: electrostatic force or van der Waals force, such as: hydration.
Characteristic adsorption: characteristic adsorption of physical properties;
Chemical properties of adsorption.
Chemical adsorption: molecular adsorption and ion adsorption.
The solid-liquid interface adsorption obeys the Langmuir adsorption equation.
V. Adsorption of liquid---liquid interface Two liquids that are incompatible with each other have a liquid-liquid interface. Valuable in the flotation process is the emulsification of oil and water. This mixture is stirred to form an O/W or W/O emulsion.
From the point of sorting and separation, the O/W type is the basic form of oil flotation, pellet flotation and emulsification flotation. In the foam flotation, the O/W type is the basic form of the distribution of hydrocarbon oil flotation agent in the slurry.
There are many emulsification treatment methods for flotation reagents, but surfactants are added to reduce the oil-water interface free energy, and an emulsion with suitable dispersion and high stability can be obtained.
The structure of the oil-water interface adsorption layer:
The system consists of three separate phases: oil, water and mesophase.
The mesophase is a surfactant and an auxiliary adsorption layer. The surface tension on both sides is a double film (bending), and the oil phase is infiltrated into the intermediate layer to expand to a depth of 4/5 double film. Water molecules and counterions enter the 1/5 thickness of the intermediate phase. Since it contains multiple components in the middle, it is also called a mixed film.
Oil---the flat adsorption layer of water, under the action of pressure gradient and oil penetration, causes the expansion to extend to the oil side and the water side to equalize the pressure, and at the same time, the curvature forms a spherical emulsion.
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