With the acceleration of industrialisation, a large number of industrial enterprises have sprung up. Some enterprises lack effective environmental protection measures in the production process and recklessly discharge waste water, waste gas and waste residue containing heavy metals, organic pollutants and other harmful substances. These pollutants continue to enter the soil through atmospheric deposition, wastewater irrigation, and accumulation of waste residues, leading to a sharp rise in the content of heavy metals in the soil and a large accumulation of organic pollutants. To solve the problem of soil pollution, restore the ecological function of the soil has been imminent, then solid control equipment can play what role in soil restoration?
The importance of solid control equipment is firstly reflected in the precise separation and removal of pollutants in the soil. Different types of solid control equipment can be used for a variety of pollutants, such as heavy metals, organic pollutants, petroleum-based substances, etc., using physical, chemical or biological methods to separate them from the soil, reduce the content of pollutants in the soil, thereby reducing the harm to the soil ecosystem and human health. For example, in some oil-contaminated soil remediation projects, solid-control equipment can effectively separate the petroleum-like substances in the soil, so that the petroleum content in the soil is reduced to below the safety standard, creating conditions for subsequent soil ecological restoration.
In addition, solid control equipment can also optimise the physical properties of the soil. Many contaminated soils often suffer from structural damage, poor permeability, poor water retention and other problems. Solid control equipment can improve the particle structure of the soil through screening, crushing, mixing and other operations, increase the porosity of the soil, improve the permeability and water retention of the soil, provide a favourable environment for the survival and activities of microorganisms in the soil, and promote the natural remediation process of the soil.
一.The screening role of vibrating screens.
Vibrating screens are the pioneers of screening in solid control equipment and also play a key pre-treatment role in soil remediation. Its working principle is based on the force of vibration, which is driven by a motor to generate an excitation force that causes the screen body to vibrate at a high frequency. During the vibration process, the soil is transported to the sieve surface, and under the joint action of the excitation force and its own gravity, the soil particles jump on the sieve surface, and particles of different sizes are separated according to the size of the sieve holes. Particles larger than the sieve hole stay on the sieve surface, become the top of the sieve; smaller than the sieve hole of the particles through the sieve hole, become the bottom of the sieve, so as to achieve the purpose of soil grading according to the particle size.
Vibrating screen type is rich and diverse, common linear motion vibrating screen and circular motion vibrating screen. Linear motion vibrating screen is usually equipped with two vibration motors, when the two motors synchronously rotate in the opposite direction, the excitation force generated by the eccentric block in the direction of parallel to the motor axis cancels each other, and superimposed in the direction of perpendicular to the motor axis as a combined force, so that the trajectory of the sieve machine is a straight line. Materials on the screen surface by the vibration force and the effect of gravity, was thrown up and jumped forward for linear movement, to achieve screening. This kind of vibrating screen has the advantages of high screening precision, large processing capacity, simple structure, etc. It is suitable for fine screening of soil, and can effectively separate soil particles of different particle size ranges, providing materials with uniform particle size for subsequent restoration treatment.
Circular motion vibrating screen makes use of unbalanced heavy exciter to make the screen box vibration, and the motion trajectory is generally circular. In the screening process, the material on the screen surface is constantly turning and loosening, the fine-grained material has more opportunities to move to the lower part of the material layer and discharged through the sieve holes, and the material stuck in the sieve holes can also be jumped out, which effectively prevents the sieve holes from being clogged. Its screening efficiency is high, and it can also change the movement speed of materials along the screen surface by changing the inclination angle of the screen surface, so as to improve the handling capacity of the screen. For some difficult to screen soil materials, it can also change the relationship between the vibration direction and the direction of movement of materials by making the main shaft reverse, which further improves the screening efficiency. This kind of vibrating screen performs well when dealing with soil containing more impurities and uneven particle distribution, and can quickly and effectively separate large impurities and soil.
二.Separation and removal of impurities by desilters and desanders.
The working mechanism of sand remover and mud remover is based on the principle of centrifugal sedimentation and density difference, and through the clever structural design, it realises the efficient separation of sand and mud particles in the soil.
When the soil mixture containing sand particles, mud particles and pollutants enters the cyclone of the desander or desilter in a tangential manner under a certain pressure, it instantly generates a strong rotary motion. Due to the difference in the density of sand and mud particles and soil mixture, under the joint action of centrifugal force, centripetal force, buoyancy and fluid traction, sand and mud particles of greater density are subjected to greater centrifugal force, are thrown to the outer wall of the cyclone, and spiral downward along the inner wall of the cyclone, and ultimately discharged from the underflow port; and relatively small density of the liquid and part of the fine particles in the centre of the formation of the upward cyclone, and discharged through the overflow port.
Take the common desander as an example, its cyclone diameter is generally larger, usually between 150 – 300mm, can effectively separate the particle size greater than 44μm sand. The desander has a strong processing capacity and can be configured with multiple cyclones according to actual demand to meet the processing capacity requirements of soil remediation projects of different sizes. The cyclone diameter of the desilter is relatively small, generally in the range of 50 – 100mm, mainly used for separating mud particles with a particle size of 15 – 44μm, which has a good effect on the separation of finer particles in the soil.
Desanders and desilters have the remarkable features of simple structure, stable operation and large treatment capacity. Their structure mainly consists of cyclone, inlet pipe, overflow pipe and underflow pipe, etc. There are no complicated moving parts, which reduces the probability of equipment failure and lowers the maintenance cost. During operation, it can work continuously and efficiently as long as stable inlet pressure and flow rate are ensured. Moreover, due to its large processing capacity, it is able to carry out preliminary separation of a large amount of contaminated soil in a short period of time, providing favourable conditions for the subsequent remediation process.
三.Sedimentation and separation of centrifuges.
The working principle of centrifuges is based on a strong centrifugal field. When the centrifuge rotates at high speed, the soil mixture in the drum is affected by centrifugal force, and particles of different density and particle size will produce different motion trajectories, thereby achieving efficient separation.
Taking the sedimentation centrifuge as an example, when the soil suspension enters the high-speed rotating drum, under the action of centrifugal force, the solid phase particles with higher density (such as heavy metal particles, soil particles attached with some organic pollutants, etc.) will quickly settle to the drum wall to form sediment; while the liquid phase with lower density (including water and partially dissolved pollutants) will gather in the center area of the drum and be discharged through the overflow port.
For some particles with tiny particle sizes, such as colloids and fine heavy metal particles, it is difficult to effectively separate them by traditional gravity sedimentation methods. The centrifuge can provide strong centrifugal force to enable these tiny particles to achieve sedimentation and separation in a short time. For example, when treating contaminated soil containing heavy metals such as lead and mercury, the centrifuge can efficiently separate solid phase particles with a particle size range of 2-44μm from the soil liquid phase, greatly improving the removal efficiency of heavy metals. At the same time, the centrifuge can also separate heavy crystals in the soil. These heavy crystals may combine with pollutants in the soil, affecting the properties and remediation effect of the soil. Through the separation effect of the centrifuge, they can be removed from the soil, creating favorable conditions for subsequent remediation work.
Technical advantages in soil remediation
The centrifuge has shown many significant technical advantages in soil remediation. First, its efficient separation ability enables it to quickly process a large amount of contaminated soil. In some large-scale soil remediation projects, the centrifuge can run continuously, processing tens or even hundreds of cubic meters of soil per hour, greatly shortening the remediation cycle
Secondly, the centrifuge has extremely high separation accuracy for tiny solid particles. In soil remediation, many pollutants such as heavy metals and organic pollutants are often attached to tiny soil particles, and traditional separation methods are difficult to effectively remove them. The centrifuge can accurately separate these tiny particles from the soil with its powerful centrifugal force, greatly reducing the content of pollutants in the soil.
In addition, the centrifuge has good adaptability. It can achieve the best separation effect by adjusting parameters such as speed and drum radius according to different soil properties and pollution types. For soil with heavy texture, the centrifuge can appropriately increase the speed and enhance the centrifugal force, so as to better achieve solid-liquid separation; for soil with more complex pollution, the centrifuge can also achieve the ideal remediation effect through multiple separations and process adjustments.
The application of centrifuges in soil remediation can also achieve resource recycling. During the separation process, some useful materials such as sand, gravel, metals, etc. can be recycled and reused, reducing resource waste and reducing remediation costs. For example, when dealing with contaminated soil containing metal impurities, the centrifuge can separate the metals. After further purification, these metals can be put back into industrial production, realizing the recycling of resources.
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