Name: wastewater cleanup by coagulation
Uploaded: 2024-04-04T10:51:24.000Z
Duration: 1 min 6 s
Channel: JoVE

קרישה היא הצטברות של חלקיקים קולואידים ליצירת אגרגטים גדולים יותר.
טכניקה זו מיושמת לטיהור שפכים המכילים מוצקים קולואידים מרחפים, אשר בדרך כלל טעונים שלילית ומוקפים בשכבה כפולה חשמלית של יונים נספגים.
דחייה אלקטרוסטטית מונעת מהחלקיקים להתנגש, ומייצבת את הקולואיד.
כאשר מוסיפים חומרי קרישה מתכתיים, כגון אלומיניום או מלחי ברזל, הם מגיבים עם ביקרבונטים במי שפכים כדי להניב את ההידרוקסידים המתאימים.
אלה מספקים יונים נגדיים טעונים מאוד שניתן לספוג על המוצקים המרחפים ולנטרל את המטען שלהם.
ערבוב מהיר מקדם התנגשויות בין מוצקים מרחפים, אשר מתמזגים.
כעת, החלקיקים מתאחדים ויוצרים חלקיקים מעט גדולים יותר, אם כי מיקרוסקופיים, הנקראים מיקרופלוקים.
כאשר מיקרופלוקים מגיעים לגודל האופטימלי והופכים למקרופלוקים, ניתן להסיר אותם על ידי שיקוע או סינון כדי לקבל מים מטוהרים.

קרישה

Coagulation

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מוצקים קולואידים הם חלקיקים מוצקים התלויים בתמיסה. הם בדרך כלל טעונים שלילי, מושכים שכבה ראשונית קומפקטית של יונים טעונים חיובית, המושכים יותר יוני נגד ליצירת שכבה כפולה חשמלית. דחייה אלקטרוסטטית בין השכבות הכפולות הטעונות מונעת מהחלקיקים להתנגש, ומייצבת את הקולואידים. לעתים קרובות מוצקים אלו אינם רצויים מכיוון שהם יכולים להכיל רעלים שקשה להסירם. קרישה היא טכניקה המסייעת לצבור ולהסיר קולואידים, והיא ישימה לטיהור שפכים.

חומרי קרישה מתכת הם סוג אחד של חומרי קרישה שניתן להשתמש בהם בתהליך טיהור זה. כאשר מוסיפים לתמיסה הקולואידית חומרי קרישי מתכת, כגון אלומיניום או מלחי ברזל, הם מגיבים עם הביקרבונטים בשפכים כדי ליצור את ההידרוקסידים המתאימים. הידרוקסידים הללו מספקים נגדים טעונים מאוד שניתן לספוח על הקולואידים המרחפים, ולנטרל את המטען שלהם. ערבוב מהיר מבטיח פיזור של יונים טעונים מאוד אלו ולכן תדירות היווצרות של קולואידים מנוטרלים. יחד עם זאת, ערבוב מקדם התנגשויות בין הקולואידים הניטרליים, המוביל להתלכדותם כתוצאה מהאפקט ההידרופובי. עם המשך הערבוב, החלקיקים מתאחדים ויוצרים חלקיקים מעט גדולים יותר אך עדיין מיקרוסקופיים הנקראים מיקרופלוקים. כאשר מיקרופלקים מגיעים לגודל ומשקל אופטימליים והופכים למקרופלוקים, ניתן להסירם על ידי שקיעה או סינון לקבלת מים טהורים.

קרישה היא הצטברות של חלקיקים קולואידים ליצירת אגרגטים גדולים יותר.
טכניקה זו מיושמת לטיהור שפכים המכילים ...

Education

JoVE Core

Analytical Chemistry

כימיה אנליטית

Unit 1

יחידה 1

Introduction to Separation Methods

מבוא לשיטות הפרדה

KEY TERMS AND CONCEPTS

מונחי מפתח ומושגים

wastewater cleanup by coagulation

Coagulation helps remove colloidal particles from wastewater. Colloids are tiny solid particles suspended in a liquid. They are usually negatively charged, so they attract a compact first layer of positive ions. More counterions gather around them and form an electrical double layer. This charge barrier keeps the particles apart and stabilizes the colloid.

These suspended solids can be a problem because they may contain toxins that are hard to remove. Coagulation is used to make the particles clump together so they can be taken out of water. In wastewater treatment, metal coagulants are often used for this step. Aluminum salts and ferric salts are common examples.

When these coagulants are added, they react with bicarbonates in the wastewater and form the matching hydroxides. The hydroxides supply highly charged counterions that can adsorb onto the colloids. This neutralizes the particle charge. Rapid mixing spreads the ions through the solution and increases the chance that neutralized colloids will form.

Mixing also helps the particles collide. After they lose their charge, they can come together because of the hydrophobic effect. Continued mixing makes them join into slightly larger microscopic particles called microflocs. When the microflocs grow to the right size and weight, they become macroflocs and can be removed by sedimentation or filtration to produce clean water.

Wastewater Cleanup by Coagulation

states of matter and phase changes

Heating and Cooling During Phase Changes

Heating and cooling can change a substance from one state of matter to another. These phase changes depend on internal energy, which is the total kinetic energy of particles and the potential energy from their interactions. In the condensed phases, stronger intermolecular forces and the pressure on the substance affect that internal energy. The internal energy is highest in the gaseous state, lowest in the solid state, and in between for the liquid state. Phase transitions happen when...

distillation: vapor&ndash;liquid equilibria

Distillation and Boiling Point Changes

Distillation separates a miscible liquid mixture by using differences in boiling points. It works best when the two liquids have a significant boiling point gap, usually at least 20°C. In this process, the mixture is heated until the more volatile component reaches its bubble point and begins to vaporize. The vapor then rises into a condenser. A condenser is a glass tube with separate inner and outer sections. Cold water flows through the outer section and cools the vapor in the inner section,...

filtration

Filtration Setup and Filtrate Collection

Filtration separates a solid from a liquid by passing a suspension through a porous medium. The solid stays on the filter, and the liquid, called the filtrate, passes through. This makes filtration a physical separation process, not a chemical change. The filtering medium is chosen for the purpose of the separation, the amount of material, and the nature of the precipitate. A good filter medium should be inert, mechanically strong, nonabsorbent toward dissolved materials, and able to let...

centrifugation

Centrifugation for Separating Particles

Centrifugation separates particles in a liquid by using differences in size and density. The sample is placed in centrifugation tubes and spun at high angular velocity. This creates centrifugal force, which makes the different components move at different rates. After spinning, the supernatant, or liquid above the settled material, is decanted. In some cases, the pellet is kept for further purification. In other cases, the supernatant is kept and may be spun again for additional processing. <br...

sublimation

Sublimation in Separation and Purification

Sublimation is the direct change of a solid into a gas. It skips the liquid state. A common example is solid carbon dioxide, or dry ice, which turns into gaseous carbon dioxide at standard pressure and room temperature. The phase diagram shows when sublimation can happen. This process occurs at the solid-gas boundary. It is not seen above the triple point of a substance. The reverse process is deposition, which is when a gas changes directly into a solid. Sublimation and deposition can help...

recrystallization: solid&ndash;solution equilibria

recrystallization-solidsolution-equilibria

Recrystallization for Purifying Solid Compounds

Recrystallization is a way to purify solid compounds by using differences in solubility. It does not involve a chemical reaction. Instead, it relies on physical properties of the desired compound and the impurities. The process is based on solid-solution equilibrium, also called solubility equilibrium. In this equilibrium, a component is split between the solid phase and the solution phase. At equilibrium, the chemical potential of that component is the same in both phases. To begin...

crystal growth: principles of crystallization

crystal-growth-principles-of-crystallization

Crystal Formation Through Supersaturation

Crystal formation through supersaturation begins when a solution contains more dissolved solute than it can normally hold. In crystallization, atoms or molecules line up into a rigid crystal lattice so the system can lower its energy. To start the process, the solute concentration and the solution temperature must be adjusted so the supersaturation ratio, S, is greater than one. Supersaturation can be increased in two main ways. One method is to concentrate the solution by evaporating the...

precipitation and co-precipitation

Selective Ion Separation by Precipitation

Selective ion separation by precipitation is used to isolate ions from a solution. In qualitative inorganic analysis, ions that form sparingly soluble precipitates with the same reagent can be separated by using differences in their solubility products. A solubility product is the limit at which an ionic solid begins to form from dissolved ions. One example is the separation of Cu(II) and Fe(II) ions as insoluble sulfides. Copper(II) sulfide is first precipitated by adding acidic H2S. The acid...

coagulation

Coagulation helps remove colloidal particles from wastewater. Colloids are tiny solid particles suspended in a liquid. They are usually negatively charged, so they attract a compact first layer of positive ions. More counterions gather around them and form an electrical double layer. This charge barrier keeps the particles apart and stabilizes the colloid. These suspended solids can be a problem because they may contain toxins that are hard to remove. Coagulation is used to make the particles...

electrodeposition

Electrodeposition for Metal Ion Separation

Electrodeposition separates metal ions from a solution by using an electric current and an electrolytic cell. The cell has an anode and a cathode. When current flows, oxidation happens at the anode. At the cathode, metal ions gain electrons, undergo reduction, and deposit on the large metal surface. This method works well when metals have very different reduction potentials. Copper and nickel in the same solution can be separated this way. First, the solution is made acidic. Then current is...

extraction: partition and distribution coefficients

extraction-partition-and-distribution-coefficients

Solvent Partitioning in Chemical Extraction

Solvent partitioning in chemical extraction describes how a solute spreads between two immiscible solvents. Immiscible solvents do not mix, such as an aqueous phase and an organic phase. The distribution law, also called Nernst's distribution law or the partition law, explains how that solute is shared at a constant temperature and equilibrium. At equilibrium, the ratio of solute concentrations in the two solvents stays constant. For extraction from water into an organic solvent, this...

extraction: effects of ph

pH Control in Liquid Extraction

pH control in liquid extraction changes how amines and acids move between organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes. The charged form is usually more soluble in the aqueous phase. For a weak base such as an amine, the neutral form is called B. Its partition coefficient, K, describes how the neutral molecule distributes between the two liquids. If the conjugate acid of the amine is soluble only in the aqueous phase, while the base...

extraction: advanced methods

Chelate Extraction for Metal Ion Separation

Chelate extraction is a way to separate metal ions by using an organic ligand, or chelating agent, to form an uncharged metal complex. The chelating agent needs hydrophobic groups, and it must act as a weak acid so it can lose a proton and bind to the metal. Most organic ligands used for this method are not stable in water or are insoluble in the aqueous phase. For that reason, the chelating agent is first placed in the organic phase. It then moves into the aqueous phase, where the...

chromatography: introduction

Chromatography: Separation by Polarity

Chromatography separates compounds by how they divide between a stationary phase and a mobile phase. The stationary phase is the material that holds the compounds for a time. The mobile phase is the solvent that carries the solutes to be analyzed. In column chromatography, a mixture flows through the stationary phase. The compounds separate based on their structure and polarity. Solutes that interact weakly with the stationary phase move faster through the column and exit first. Solutes that...

dialysis

Dialysis Separation by Diffusion

Dialysis separates small molecules from larger ones by diffusion through a semipermeable membrane. It is a purification method used to remove unwanted ions or small organic molecules from a sample while keeping larger analytes in place. The membrane is usually made of cellulose acetate or cellulose nitrate. Its pores are typically about 1 to 5 nm wide. Molecules such as chloride, sodium, and glucose can pass through these pores. Larger molecules, including proteins, hormones, and enzymes, are...

volatilization

Mass Loss in Gravimetric Analysis

Volatilization gravimetry is a way to measure mass loss in a sample by driving off a volatile substance. It helps estimate how much volatile material is present. In this method, a known amount of sample is heated to a high temperature in a crucible or another suitable vessel. As the sample heats, the volatile substance evaporates. The vapor is then completely removed from the crucible, either by continued heating or by bubbling an inert gas through the vessel. The non-volatile part stays...

ion exchange

Ion Exchange Resins and Charged Molecules

Ion exchange chromatography separates charged molecules from a solution by swapping them with mobile, or active, ions on a stationary phase. It is used to separate ions, soften and deionize water, and purify solutions. The method depends on a solid column made of high-molecular-weight, chemically stable polymers that are crosslinked to make them porous and essentially insoluble. These polymers are functionalized with either acidic or basic groups. When acidic groups are present, the resin is a...

key terms and concepts

Learn how coagulation removes charged colloids from wastewater. See how metal coagulants, mixing, microflocs, and macroflocs help purify water.

Wastewater Cleanup by Coagulation | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Wastewater Cleanup by Coagulation

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