Explanation of Sedimentation Process
We come across various incidents on a daily basis in which we have to separate one substance from the other to make it more useful. Different sedimentation methods are available by which we can separate substances that are mixed together. Sedimentation is the simplest separation method and an essential concept that is supposed to be understood. Its importance is unquestioned and plays a vital role in archeology. It's a natural process that can be explained as building up layers of small particles like sand or mud. Weight and sedimentation are very related.
The Sedimentation definition is given by, it also includes deposits from glacial ice and such materials collected under the impetus of gravity alone, similar to talus deposits, or accumulations of rock debris at the base of cliffs. This term is commonly used as a synonym for sedimentology and sedimentary petrology.
Sedimentation Process By an Experiment
The sedimentation process can be observed by a small experiment. Take a glass jar and fill it with a garden variety of mud. Pour some water, shake it well and keep it untouched for a few minutes.
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In a while, we can notice that the gravel and rocks have settled below, sand on above, and so on. The garden variety of mud basically has formed layers of soil based on varied, which is seen below.
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If we look at the cliff, it can be observed several layers on the surface of the cliff. These resultant layers are formed by sedimentation - the grains of sand and mud build-up over a long period of time, forming the layers. Also, fossils happen to be found in these layers. Logically, the quicker the bones are buried, and the more survival chances are more because it can be protected from scavenging animals and limited damage by weather. The rivers, lakes, and sea are the best depositors of both sand and mud are some sedimentation examples. Dinosaur fossils were found near to the sea, lakes or rivers. A land-slide, where mud and rock-fall down a hill mountain, can also lead to a sedimentation type.
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Sedimentation can also be used to separate particles based on size by applying the centrifugal force to the required solution. In the Centrifugation process, a centrifugal force is applied to a heterogeneous mixture which separates the mixture based on its density. The high dense components stay away from the centrifugal axis, whereas the less dense components stay near to the centrifugal axis by therefore separating the constituents of the mixture.
Also, sedimentation helps to determine a person's medical conditions. The sedimentation rate of RBC is one of the sedimentation examples. It is performed by measuring how long it takes the Red Blood cells (RBCs) to get settled in a test tube. As time passes by, the RBC's start to separate from the other plasma contents, they settle down at the bottom and serum will be formed above. The ESR (erythrocyte sedimentation rate) or sedimentation rate is measured simply by recording how far the top of the Red Blood Cell layer has fallen (in millimeters) from the top of the serum layer in one hour.
The water treatment plant uses the sedimentation method to pull out unwanted particles from unclean water by filtering several layers of soil and sand, allowing specific sizes of particles to pass through.
Basic Principle of Sedimentation
Suspended water solids have a specific gravity that is greater than the water tends to get settled by gravity as soon as the turbulence is retarded by granting the storage. Inorganic suspended solids have a specific gravity of about 2.65, and Organic suspended solids have a specific gravity of about 1.04
The particles having a specific gravity of about 1.20 or so readily settle down at the bottom of the tank. But to cause the settlement of lighter particles, it's difficult.
This settling down of particles at the bottom of the sedimentation tank phenomenon is called hydraulic subsidence, and each particle has its own hydraulic settling value causing hydraulic subsidence on it.
Basin, where the flow is retarded, is known as a sedimentation basin. The average theoretical time for which the water is detained in the settling tank is known as the detention period.
Types of Sedimentation
Plain Sedimentation
It is the process of settling down of solids and impurities in the raw water to the bottom of the sedimentation basin by a natural gravity force alone, with no chemical added. This is a very cheaper sedimentation method and is mostly used in every water filtration and purification system.
Sedimentation Using Clarifier and Contact
Here, the chemicals are mixed in water, and the same water is rotated with the help of pumps for a period of two hours per day, and suspended solids are settled down in the bottom of the reservoir or tank, and more.
Chemically Assisted Sedimentation or Clarification
In this process, chemicals are added to water, and through mixing, the suspended solids, and other impurities are stuck together and form floc, settling at the bottom of the basin.
Generally, the most used process is chemically assisted as horizontal sedimentation based on some assumptions. Basically, water flows through a tank in an irregular flow, and thus the intention of sedimentation is to create conditions where the flow takes place uniformly for a long enough period, permitting the maximum practical amount of floc to get settled before the water reaches the end of the tank.
FAQs on Sedimentation
1. What is the process of sedimentation in chemistry?
Sedimentation is a physical process used to separate components of a mixture, where insoluble particles suspended in a liquid settle down to the bottom. This settling occurs naturally due to gravity, as the particles are denser than the liquid they are in. The settled particles are referred to as sediment.
2. What is a common example of sedimentation that can be seen in everyday life?
A simple and common example of sedimentation is seen with muddy water. If a glass of muddy water is left undisturbed for some time, the heavier mud and sand particles will gradually settle at the bottom, leaving clearer water on top. This happens because the mud particles are insoluble and denser than water.
3. What is the primary importance of sedimentation in large-scale applications?
The primary importance of sedimentation is in the purification of water. In water treatment plants, sedimentation is a crucial step to remove large suspended solids like sand, silt, and clay from raw water. This process significantly clarifies the water before it undergoes further stages like filtration and disinfection, making the entire purification process more efficient and cost-effective.
4. How is the process of sedimentation different from decantation?
Sedimentation and decantation are two distinct but related steps in separating a mixture. Sedimentation is the process where insoluble solid particles settle down under gravity. Decantation is the subsequent step of carefully pouring off the clear liquid from the top layer, leaving the settled sediment behind. In short, sedimentation is the settling, and decantation is the separation by pouring.
5. What key factors determine how quickly sedimentation occurs?
The rate of sedimentation is influenced by several factors. The most important ones include:
- Particle Size and Density: Larger and denser particles settle much faster than smaller, lighter ones.
- Fluid Viscosity: Particles settle more slowly in a thicker, more viscous liquid (like honey) compared to a less viscous one (like water).
- Shape of the Particle: Round, spherical particles tend to settle more quickly than flat or irregularly shaped particles, which experience more drag.
6. Why can't sedimentation be used to separate salt from water?
Sedimentation is only effective for separating insoluble substances from a liquid. Salt is a soluble substance, meaning it dissolves in water to form a homogeneous solution. In a solution, the salt particles (ions) are completely integrated with the water molecules and do not exist as separate, denser particles that can settle down. Therefore, gravity has no effect, and other methods like evaporation are needed to separate the salt.
7. What are the main types of sedimentation based on particle concentration?
Sedimentation can be broadly categorised based on how particles interact with each other during settling:
- Discrete Settling: Occurs in dilute mixtures where particles are far apart and settle independently without interfering with each other.
- Flocculent Settling: Particles in the mixture clump together (flocculate) to form larger, heavier masses that settle more quickly. This is often encouraged in water treatment by adding chemicals called coagulants.
- Hindered or Zone Settling: Happens in mixtures with high particle concentrations. The particles are so close together that they hinder each other's movement, and the entire mass tends to settle as a single layer or 'zone'.
