Filtration Methods Separation

Filtration Methods Steps of Filtration

I. Filtration

1. Definition: Filtration is a method of separating a solid substance dissolved in a liquid from a liquid.

2. Principle: When filtering, the liquid passes through the holes in the filter paper, while the solid substance remains on the filter paper, thus separating the solid from the liquid.

3. Methods of operation:

For example: purification of crude salt (ask students to design the experimental steps) to show the crude salt, so that students can see the sand and other insoluble solids on the crude salt for students to think.

(Demonstration experiment) crude salt purification

Summarize:

(1) Steps:

① Dissolve crude salt in a beaker

② Filtering

(2) Notes:

A stick: the filter paper is tightly adhered to the inner wall of the funnel

Two low: the filter paper is lower than the edge of the funnel 0.5cm

filtrate below the edge of the filter paper

three leaning: the lower end of the funnel against the inner wall of the beaker

glass rod leaning on the three layers of filter paper

beaker leaning on the glass rod to pour the liquid

(3) the role of the glass rod

Dissolution - to accelerate the dissolution

Filtration --Drainage

Filtration is a method used to separate intolerable solids from soluble solids.

What are some of the methods of filtration based on process?

Filtration methods according to the driving force of the process, filtration can be divided into: ① gravity filtration, the operating driving force is the suspension itself, the column static pressure, generally not more than 50kPa, this method is only suitable for dealing with the large particle size, less content of the slurry; ② pressure filtration, with a pump or other means of pressurizing the slurry, which can produce a higher operating pressure, generally up to 500kPa or more, can effectively deal with the difficult to separate the slurry; ③ vacuum filtration. Separation of the slurry; ③ vacuum filtration, vacuum at the bottom side of the filtration medium, the resulting pressure difference is usually no more than 85kPa, suitable for slurry containing mineral or crystal particles, and easy to wash the cake; ④ centrifugal filtration, the operating pressure is the centrifugal force generated by the slurry layer, easy to wash the cake, the resulting cake contains less liquid, suitable for crystalline and fibrous materials filtration.

There are many types of filtration equipment. Usually the implementation of gravity filtration, pressurized filtration and vacuum filtration machine called filter; the implementation of centrifugal filtration machine, called centrifugal filter.

Steps of Filtration

Filtration is a process of separating solid particles suspended in a liquid or gas. Its basic principle: under the action of pressure difference, the liquid (or gas) in suspension through the permeable medium (filter media), solid particles for the medium to be retained, so as to realize the separation of liquid and solid.

1) to realize the two conditions of filtration:

① with the necessary equipment to achieve the separation process;

② filtering media on both sides to maintain a certain pressure difference (driving force).

2) The commonly used filtration methods can be divided into gravity filtration, vacuum filtration, pressurized filtration and centrifugal filtration.

The gravity pressure difference is formed by the height of the slurry column; the driving force for vacuum filtration is the vacuum source.

3) Filtration has characteristics: In essence, filtration is a multi-phase fluid through the porous media flow process.

① Fluid flow through porous media belongs to the very slow flow, that is, seepage flow. There are two influencing factors, one is the macroscopic hydrodynamic factors, and the other is the microscopic physicochemical factors.

② The suspension of solid particles in the five is continuously deposited in the pore space inside the medium or on the surface of the medium, and thus the filtration resistance in the filtration process is increasing.

4) Classification of filtration: divided into two categories, respectively: cake filtration and deep filtration, cake filtration application surface filter, deep filtration, solid particles are retained in the pores inside the medium.

5) Cake filtration and deep filtration:

① Cake filtration is usually a high concentration of suspension, its volume concentration is often higher than 1%. If the flocculant is added to the slurry, some low concentration of the suspension can also be used cake filtration.

② deep filtration from a very dilute suspension of fine solid particles, it is usually used for liquid purification. In the case of similar efficiency, the starting pressure of the deep filter is generally higher than the surface filter, and with the increase in the number of particles collected, the pressure drop will gradually increase.

6) The purpose of filtration: in the recovery of valuable solid phase, or to obtain valuable liquid phase; or both collected or both discarded as waste.

1, incompressible cake filtration process

(1) incompressible cake filtration process

Incompressible cake: filtration, the liquid flowing through the cake through the surface of the transport volume transferred to the solid particles of a trailing stress, the force through the point of contact with the particles forward and gradually accumulated along the flow direction. If the structure of the cake in this accumulated trailing stress under the action of the particles do not move with each other, the porosity of the cake does not produce changes, it is said that this cake is incompressible cake.

The reasons for the industrial compression of the cake: ① in the slurry in fact, very few individual particles, and there are often varying degrees of agglomeration, agglomeration interface can not withstand the trailing stress of the liquid and deformation of the cake; ② -10μm particles are almost always on the surface of the salt film, the salt film in the fluid will produce deformation; ③ solid particles in the role of coagulants or flocculants to form cohesive or flocs have only a very small The solid particles formed under the action of coagulants or flocculants have only a small anti-shear property, and are very easy to produce deformation under the action of liquid.

What are the common filtration methods?

In slurry filtration, there is a driving force to overcome the resistance of the cake and the resistance of the filter media.

So according to the different driving force, the filtration method can be divided into the following categories: 1. gravity filtration that is, the filtrate is under its own gravity through the filtering medium and be discharged; 2. pressurized filtration that is, the use of slurry or vacuum compressor on the slurry to exert pressure, forcing the liquid through the filtering medium; 3. vacuum filtration vacuum pump vacuum suction caused by the use of the filtrate through the filtering medium and was sucked out; 4. centrifugal filtration using the centrifugal pump to filter the liquid through the filtering media and was sucked out; 4. 4. centrifugal filtration using centrifugal force to exclude the liquid in the slurry; 5. magnetic and vacuum filtration combined with the use of magnetic force and vacuum suction, forcing the filtrate through the filtration medium and be discharged. Mainly used for magnetic products.

Gaoke Machinery.

How to do filtration operation?

The filtration operation requires "one post, two low, three rely on".

A stick, even if the filter paper is wet, close to the inner wall of the funnel, no residual air bubbles. (To prevent air bubbles from slowing down the filtration speed.)

One stick, even if the filter paper is wet, close to the inner wall of the funnel, without residual bubbles.

Two low, the edge of the filter paper is slightly lower than the edge of the funnel. The liquid level is lower than the edge of the filter paper. (Prevent the liquid from being filtered.)

Three.

Third, the beaker should be poured with the mouth of the beaker against the glass rod. The lower end of the glass rod rests against the three layers of filter paper. , the mouth of the long side of the lower end of the funnel is against the inner wall of the beaker.

Extended information:

Choice of materials for the experiment:

The size of the funnel depends primarily on the amount of precipitate to be filtered or the amount of solids precipitated , rather than on the volume of liquid. A larger amount of precipitate or solids will result in a larger funnel being selected and vice versa. Funnel cone angle should be 60 °.

The diameter of the pipe is appropriate, too thick to maintain the water column, too fine water flow rate is slow, filtration takes too long. The end of the pipe diameter should be slightly inclined.

The choice of filter paper is based on the experiment to determine. Filter paper is divided into qualitative filter paper and quantitative filter paper. Qualitative filter paper is mainly used to study the physical and chemical properties of substances in filtration operations; quantitative filter paper is mainly used for quantitative analysis of substances.

In secondary school experiments, filtration operations are often used in qualitative experiments, so most of the qualitative filter paper. Selected filter paper into the funnel, the edge of the paper should be lower than the edge of the funnel about 5 mm is appropriate.