What Is Gravity Separation?

Gravity separation refers to the separation and sorting process of solid materials in water and air based on the law of gravity movement. In the field of waste management and re-recycling, it can be roughly divided into two processes: gravity settlement and gravity separation.

Gravity sedimentation of solid particles can be performed in the liquid or gas phase. Gravity sedimentation of solid particles in the liquid phase is one of the important methods for purifying wastewater and recovering useful components from wastewater or solid-liquid suspension liquid phase. Its basic principle It is the solid particles or particle aggregates that settle freely from the liquid phase under the action of its own gravity, so as to achieve the purpose of separating the solid phase from the liquid phase. The sedimentation treatment process can be a process in the entire treatment process, or it can be used as the sole treatment method. According to the purpose of solid-liquid separation, gravity sedimentation has different application methods such as precipitation, concentration and clarification. Its main uses can be summarized as follows:

(1) Used for the treatment of urban sewage and industrial wastewater, to remove the precipitation of solid suspended solids in wastewater.

(2) When industrial wastewater is treated by chemical method, the combined crystal or chemical is separated from the liquid phase by gravity sedimentation method.

There are many types of gravity sedimentation equipment. First, the equipment that settles the solid phase in the liquid phase. When it is used for the purification and recovery of sewage and waste liquid, it is often called a sedimentation tank, while it is used for solid waste and separation and dehydration operations. Thickener. Sedimentation tanks used for wastewater treatment can be divided into advection type, vertical flow type, radial flow type and inclined plate type inclined tube sedimentation tanks according to the direction of water flow in the pool.

Gravity sorting refers to the sorting process of separating solids with different specific gravity based on the difference in the density of the separated materials under the action of gravity. Unlike gravity sedimentation, gravity sorting has some selectivity. Gravity sorting is mostly performed in aqueous media, and there are many sorting methods. Such as chute sorting, shaker sorting, jig sorting and heavy media sorting. Gravity sorting can also be performed in air.

Gravity separation chute sorting

Tank sorting is the process of layering and dividing the solid particles in the flow of the chute slant. According to the thickness of the particles and the density of the particles. The typical chute can be classified as a representative. Its main feature is that the first-rate chute is bent into a spiral shape around the vertical axis, and the cross section of the spiral groove is part of a parabola or ellipse. After the slurry is fed from the upper end of the spiral groove, the material moves along the inclined plane, and the rotary motion is performed around the central axis of the spiral groove along the groove surface. Under the combined action of gravity, water current impact force and centrifugal force, the solid particles are layered according to the density along the vertical direction of the thickness of the water layer, and also divided into zones according to the density along the radial direction. Large-density particles along the bottom of the tank are subject to less water impact and greater friction. They move slowly along the tank and suffer less centrifugal force. Therefore, the particles will mainly move to the inner edge of the chute under the action of gravity separation. The particles are pushed to the outside of the chute mainly by centrifugal separation. After the materials are sorted by the spiral chute, they are divided into heavy, light and intermediate products at the lower end of the tank, which can be intercepted separately as required.

Gravity separation shaker sorting

Shaker sorting is also called flow film sorting. All shaker sorting equipment basically consists of three parts: bed surface, frame and transmission mechanism. The bed surface of a typical shaker is approximately rectangular or diamond-shaped. It is driven by a transmission device to perform an asymmetrical reciprocating motion back and forth. The bed surface has a relatively obvious inclination in the transverse direction, and a feed trough and a water trough are arranged above it. There are grid bars (complex bars) or grooves along the longitudinal direction on the bed. The height of the grid bars gradually decreases from the driving end to the opposite side.

The important feature of shaker sorting is that the pulsation of the water flow caused by the shaking of the bed surface and the vortex formed by the lateral water flow flowing through the bed strips causes the fine particles to drill through the gap between the particles when the material is dispersed in the tank and preferentially sink At the bottom. As a result of layering, coarse and light particles are in the uppermost layer, followed by fine and light particles, again coarse and heavy particles, and the bottom layer is fine and heavy particles. This kind of separation, which is called dissociation and delamination, promotes the delamination of the particle group according to the density, which is more perfect than the delamination of a general flat chute, and the separation effect is better. At the same time, the eddy current formed in the groove can also clean the small-density particles mixed in the high-density particle layer, thereby improving the sorting effect.

Gravity separation jig sorting

Jig sorting refers to the process of sorting solid materials according to different densities in alternating water flows. Its working principle is to use an eccentric link mechanism or a cam lever mechanism to push the rubber diaphragm to reciprocate under the action of a rubber diaphragm, thereby forcing the water flow to generate up and down pulse action in the jigging room. When the material is fed into the sieve plate of the jig chamber, a material layer of a chamber is formed, which is called a bed. As the water flow rises, the bed is pushed and loosened. Create favorable spatial conditions for relative displacement between particles of different densities. When the water flow decreases, the bed is in a tight state. After repeated and tightness of the bed, high-density particles gradually move to the lower layer, while low-density particles The upper layer collects light and heavy products of different densities through corresponding discharge devices.

Gravity separation of heavy media

Heavy medium separation is a gravity separation process that separates materials of different densities in a medium with a density greater than water. Its basic principle is Archimedes' Law. When sorting, the density c of the sorting medium should be between the low density (1) and high density (2) materials, that is, c <1 <2. Regardless of their particle size and shape, the high-density materials in the sorting medium sink and are concentrated at the bottom of the sorting equipment; the small-density materials float and are concentrated and discharged at the top of the sorting equipment to obtain two kinds of products, light and heavy.

Gravity separation

Air separation, also known as air separation, is a gravity separation method that uses air as a sorting medium to separate solid particles according to density and particle size under the action of air flow. In waste treatment, it is currently widely used for sorting waste. ^[2]