Today, the issue of drinking water quality is receiving more and more attention. Multilevel stationary filters are the best solution in most cases, but they take up a lot of space and are expensive. A more budgetary and compact alternative to complex equipment is coagulants for water treatment.
Coagulation and flocculation wastewater treatment: what are flocculants and coagulants
A coagulant is a special substance that is added to the treated water. It is most commonly used to remove contaminants from:
- drinking water (in a country house, on a hike, etc.);
- waste and other waters in the process of their comprehensive preparation for supply to residential facilities;
- water parks, swimming pools, other artificial reservoirs;
- industrial effluents.
And also as a binding material for a number of industrial processes. The use of coagulants allows you to get rid of an unpleasant odor, a sharp taste, turbidity and extraneous shades of drinking water. Some people believe that it is unsafe to purify water using coagulants, but experts say the opposite is true. In purified water, the substance remains, but in minimal quantities, since most of it is excreted along with pollutants. This concentration is completely safe for human health.
Varieties and application of coagulants for water treatment
If all of the suspended solids in the raw water were large enough to be easily removed by known purification methods, then treatment with chemical coagulants would not be required. However, most suspended matter consists of very fine, highly dispersed solids that are largely colloidal. Because of their small size, they are not amenable to settling, flotation or filtration and must first be coagulated.
Both flocculants and coagulants are reagents that are used in the first stages of water purification from polluting particles. Coagulants combine small particles of dispersed systems into large ones under the influence of cohesive forces. The use of coagulants helps to reduce the degree of oxidation of the treated water masses, reduce the content of suspended particles in them, and improve the main technological processing processes that occur in treatment facilities and clarifiers. Floaculants provide adhesion of unstable aggressive particles and thereby intensify the process of flocculation. These substances lighten the water masses and improve the quality in a number of controlled indicators. For example, alkalinity and total iron content decrease, and the concentration of suspended particles decreases by 3-5 times.
A preliminary laboratory analysis of the composition of wastewater is required. It gives you an idea of water quality, major contaminants and allows you to create the most effective cleaning plan.
All types of reagents for drinking water treatment
The most common and effective coagulants are aluminum and iron salts. Chemical compounds formed by metals can be organic or inorganic. Each type of coagulant is designed to interact with certain substances. For wastewater treatment industrial enterprises use special substances (not the same as in everyday life). Main options:
- magnesium salts (magnesium sulfate or chloride);
- aluminosilicate solution;
- inorganic coagulant obtained from red mud;
- activated calcium aluminate;
- mineral polyreagent gel sorbent.
Consider the most popular types of aluminum-containing coagulants. The first one is aluminum sulfate Al2(SO4)3∙18H2O. In most cases, it is used in the form of solutions. Two types of substance are known - purified (looks like white pieces) and unrefined (gray-green granules).
Aluminum hydroxochloride has the chemical formula Aln(OH)(3n-m)Clm and can be produced in the form of clear solutions or yellowish granules. Advantages - good coagulating characteristics, high solubility in water, stable pH of the liquid, minimal aluminum content, efficient removal of chlorine. Aluminum hydroxochloride is a new generation coagulant. It is used to treat industrial wastewater (chemical, metallurgical industry) and drinking water.
Aluminum hydroxochlorosulfate (or HSCA) is a mixed coagulant. It shows maximum efficiency in the purification of muddy and flood waters. It can be produced in the form of a solution or a solid mass. Widely used in industry. The analogue is aluminum sulfate.
Aluminum oxychloride - formula Al(OH)mCl3n-m. It is used to purify natural waters, mainly in the cold season. The coagulant enters into quick, clear reactions with harmful substances, and can be used to treat industrial wastewater.
- Ferric chloride - has the formula FeCl3 * 6H2O. It is used to purify natural waters, industrial sludge, removes the aroma of hydrogen sulfide well.
- Ferrous sulfate - FeSO4 and Fe_2(SO_4)_3 compounds are used for water purification. Removes odors well.
Organic and inorganic coagulants include lime solutions, substances with impurities of aluminum and iron. According to their chemical composition, they all belong to salts of acids. Inorganic have a long shelf life and are not difficult to use. Organic are natural and artificial, economical in consumption, have a stable acid-base composition, effectively remove chlorine, and after the purification process is completed, they are almost completely removed from the water. Also, these substances are easy to prepare, normally interact with algae, give a minimum sediment and significantly increase the service life of stationary filtration plants.
Popular coagulants for natural water treatment
On sale are various coagulants for use at home. . Let's consider them.
Organic coagulants FLOQUAT ™ series
Organic polymeric coagulants of the FLOQUAT ™ series have a high cationic charge, therefore they effectively destabilize negatively charged colloidal particles. Compared to inorganic coagulants, polymer coagulants work in a wide range of pH and alkalinity, are economical in consumption, do not change the pH of purified water, are not afraid of chlorination, and do not add dissolved metals to purified water. Purified water has little sediment. 
Organic flocculants flopam ™ pwg series
Organic flocculants of the FLOPAM ™ PWG series are used in combination with coagulants, help increase the size of the flakes and simplify their further removal. On sale are cationic, anionic, non-ionic flocculants with different molecular weights and charge densities in the form of powders, granules, aqueous solutions, emulsions. Polymeric flocculants have a high molecular weight, form bridges between microflakes, creating large macroflakes. They allow you to minimize settling time and maximize water quality, eliminate particle transfer, increase filter performance without capital costs. 
Water softener flosperse ™ series
The FLOSPERSE ™ series water softener is used to soften water used for domestic, drinking purposes, in food production. During the dehydrogenation in large quantities ammonia and carbon dioxide are released (due to the decomposition of organic materials). Water-soluble gases combine to form ammonium bicarbonate (formula NH4HCO3) - a substance that is a strong buffer with a pH below 7. To prevent precipitation of salts, FLOSPERSE ™ must be added (it complex forms metal ions, after which they become unavailable for precipitation from solution) .
There is nothing better than swimming in the pool on a hot summer day. In order to make such a pastime enjoyable, you should take care of the cleanliness of the pool.
The services of professionals are quite expensive, you can make the water crystal clear on your own. Quality pool cleaners can be purchased here http://www.watermart.ua/himiya-dlya-basseynov/koagulyanty-flokulyanty/ at an affordable price.
There is a huge variety of substances that can purify the water in the pool. The most popular of these are coagulants and flocculants. To date, these categories of funds include synthetic polymers of organic origin.
Until recently, inorganic substances were used for water purification, and polymers were used as additives. Gradually, organics became the main coagulant.
The use of polymer cleaners has the following advantages:
- more economical consumption, the required dose is reduced by more than ten times;
- the acidic and alkaline environment of water does not significantly affect their performance, the pH of the purified liquid remains within the normal range;
- after their use in water, the concentration of dissolved metals does not increase;
- contribute to the removal of unicellular algae;
- the precipitate formed is more easily dehydrated, processed and removed.
Differences
The main difference between coagulants and flocculants is the size of the precipitated flakes, as well as the mechanism of action. The first group of substances precipitates pollution by electrolytic action. As a result, the charge of suspended particles is neutralized, and they combine into larger associations.
The second group of reagents works in a different way, the formation of a polymer bridge between the deposited particles occurs. In this process, there is no change in the electrolytic properties of the system.
Coagulants are able to form a stable precipitate, which is filtered out when water passes through the treatment plant. However, many filters are not capable of retaining fine particles.
Flocculants are used for better water purification. These reagents combine the particles obtained during coagulation into larger flakes, which greatly facilitates their mechanical removal.
Water purification with coagulants - as we see in the video:
coagulants coagulating agents (from lat. coagulo - cause coagulation, thickening), substances whose introduction into a liquid medium containing small particles of a body causes coagulation, i.e., sticking together of these particles. Under the influence of K., large accumulations of stuck together particles are formed, which precipitate in the form of flakes or lumps (coagulate). Salts of polyvalent metals (aluminum, iron, etc.) are effective crystals for systems with an aqueous dispersion medium. Water-soluble organic high-molecular compounds (polymers), especially polyelectrolytes, are also used as K. Unlike inorganic K., they are sometimes called flocculants (see. Flocculation). K. is used to isolate valuable industrial products from production waste in various technological processes, as well as in the purification of water from natural and domestic pollution. In medicine, K. means agents that increase blood clotting, such as vikasol, gelatin solution, some drugs obtained from the blood (thrombin, fibrinogen), etc.
Big soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what "Coagulants" are in other dictionaries:
Substances, the introduction of which into liquid disperse system causes the particles of the dispersed phase to adhere to each other (coagulation). Common coagulants are polymeric surfactants used to separate complex mixtures. IN… … Big Encyclopedic Dictionary
Ov, unit coagulant, a, m. (fr. coagulant ... Dictionary of foreign words of the Russian language
coagulants- ov, pl. coagulants lat. coagulare cause coagulation, thickening. 1. honey. Medicinal substances that increase blood clotting; opposite anticoagulants. Krysin 1998. 2. chem. Substances, the introduction of which into a liquid medium containing what n. ... ... Historical Dictionary of Gallicisms of the Russian Language
Substances, the introduction of which into a liquid disperse system causes the particles of the dispersed phase to adhere to each other (coagulation). Common coagulants are polymeric surfactants used to separate complex mixtures. ... ... encyclopedic Dictionary
- (coagulantia; lat. coagulans, coagulantis causing coagulation) 1) hemostatic agents that enhance blood coagulation processes (thrombin, fibrinogen, vikasol, etc.); 2) substances used to coagulate water in the process of its ... ... Big Medical Dictionary
See Coagulation... Chemical Encyclopedia
In va, the introduction of kp into a liquid disperse system causes the particles of the dispersed phase to adhere to each other (coagulation). Widespread polymeric surfactants are used to separate complex mixtures. In medicine, K. called. in wa… Natural science. encyclopedic Dictionary
For those who just want to get clean water, without immersing themselves in the essence of the process, let's say one thing: get a high-quality coagulant of a well-known brand and strictly follow the instructions. This is all. For those who are interested in knowing how coagulation takes place, what are its chemical and physical features- This article. In simple language and in an accessible form, we will tell you how various coagulants work. And at the same time we will recommend you the most effective and efficient means that have received the most positive feedback from consumers.
What kind of chemistry is this - the reader will ask, the answer is simple: coagulants. It is this substance that is used to purify water from suspended particles. There are different cleaning methods Wastewater from impurities: filtration, settling, chemical cleaning, electrical cleaning, heat treatment.
These methods have found application in various industries, but the most common and effective of them can be considered filtration And chemical treatment.
The particle size of suspended matter in water can be so small that filtration becomes either impossible or too expensive. In some cases, you have to go to increase costs, but most often this measure is unprofitable. For example, the owner is unlikely to want to spend money on a special treatment plant, but a conventional filter does not cope with the task as successfully as required, so the owner will have to “help” a simple filter a little with the help of modern chemistry.
"What kind of chemistry is this?" the reader will ask. The answer is simple: coagulant. It is this substance that is used to purify water from suspended particles.
Coagulation- this is a special process that can be characterized by the word enlargement. That is, when a certain substance is added to the composition of muddy dirty water, all the particles that float in it and create turbidity will begin to combine into larger agglomerations, and, in the end, will become large enough to settle in the form of flakes and filter out.
In various areas of the economy and life use different types coagulants. They can be divided into two large groups: mineral And organic.
Important! Organic coagulants are more expensive and are most often used for drinking water treatment. They perform slightly better than inorganic compounds however, they are often less cost-effective.
In the case of industrial wastewater treatment, various heat carriers and circulating media, pools and reservoirs, inorganic coagulants are used:
- Ferric chloride. Strong corrodant and toxin, used in industry.
- Iron sulfate. It is used in industry for wastewater treatment, in public utilities for water treatment, and in medicine to stop blood.
- aluminum sulfate. Suitable for purification of drinking, household and industrial water for various purposes.
- aluminum oxychloride. This salt - hydroxochloride - is good for treating wastewater, tanks, pools, reservoirs.
- Aluminum hydroxochlorosulfate. This is a mixture based on aluminum sulfate. It is an excellent preparation for the treatment of flood dirty waters at temperatures below +12˚ C.
These substances are characterized by a relatively low price, availability, safety and ease of use.
The work of the coagulant: the essence of the process
The chemistry of the coagulation process involves a wide field of scientific knowledge, the understanding of which will require a certain level of specialized training. We will omit pseudo-scientific details and try to convey the essence.
How coagulants work 1 
How coagulants work 2 
How coagulants work 3 So, we have a certain volume of water contaminated with colloidal particles. These particles are so small that they pass the sand filter. Moreover, their dimensions are so small that they cannot settle to the bottom: the Brownian motion of the molecules causes these particles to constantly stay in suspension.
Attention! Once again: the smallest specks float in the water, which look like turbidity. They pass through the filter and do not settle to the bottom, as water molecules continuously “push” them from different sides, setting them in motion. As a result, it is impossible to neither filter the water nor settle the dirt to the bottom.
These particles not only do not settle and are not filtered, they also refuse to stick together into larger formations. This is because they have the same charge and repel each other as a result of electrostatic interaction forces.
Here we come to the essence of the coagulation process: after the introduction of a special reagent, the properties of the particles change, they lose their charge, and the suspension begins to stick together into larger lumps. As a result of the elimination of the effect of electrostatic repulsion, the particles approach each other enough for the attraction force to begin to act.
Approach is also prevented by the spatial volume of molecules or atomic groups, which, being in close proximity to the reacting atoms in the molecule, may prevent these atoms from coming together and reacting. This effect is leveled by adding salts and changing the acidity of the medium.
As a result, coagulants do not change chemical composition impurities or water. The main characteristic to which their influence is directed is the size of the particles. After adding, say, ferric chloride, individual corpuscles lose their charge and begin to stick together into flakes, which can then be collected or filtered.
Important! The essence of the coagulation process is to make the smallest particles large enough so that they settle to the bottom, or they are retained by the filter. This is the shortest and simplest explanation.
Who makes the best coagulants: production and distribution
Manufacturers of coagulants make up a solid list, their number has grown in Lately and is more than 15 in the country. For comparison: throughout the former Soviet Union there were only 12 productions. Modern Russia meets its needs in coagulants by 95% through domestic production.
In the Russian Federation, inorganic drugs are produced. This happened due to the economic realities of the time of construction of factories and a certain configuration of the raw material base, characteristic of our country. Historically, the first place is occupied by the preparation of aluminum-based coagulants, namely aluminum oxychloride and aluminum sulfate, as well as sodium aluminate.
Consider their differences:
As follows from the table, sodium aluminate gives the highest concentration of alumina, which means that this solution will show the highest activity in the process of water purification from suspension. At the same time, the density of impurities is also the highest, which means that after processing, excess components may remain in the water. Following a similar logic, we will come to the conclusion that aluminum oxychloride (other names: aluminum chlorhydroxide, OXA, polyaluminum hydrochloride), which demonstrates the optimal ratio of aluminum content and impurities, will be the most acceptable option.
Important! The selection of a specific substance is based on the purpose of water, the degree of contamination, temperature and method of purification. OXA is used to purify cold water with a high content of organic impurities of natural origin.
One of the most common is aluminum oxychloride. This substance works especially well at low water temperatures, within +10 ˚С, and removes organic impurities well. It is OXA that is contained in most modern coagulants for the pool.
How to Use Coagulating Agents to Clarify Pool Water
First, we will tell you what to do if you have modern equipment:
- We calculate the dose based on the volume and degree of contamination of the tank.
- Pour the required volume of liquid into the skimmer and wait for it to disperse the preparation across the pool.
- We turn off the pump and give the drug time to react within 15-30 minutes.
- We collect the sediment that has fallen to the bottom with a water vacuum cleaner or a submersible pump.
- Turn on the pump again and perform the final filtration.
The calculation of the coagulant is a separate topic, it is believed that this is something from the category of higher mathematics. Indeed, if we want to purify drinking water on a conveyor basis, we will have to calculate the consumption of the chemical very accurately, otherwise it will accumulate and poison the water. In the case of the pool, everything is much simpler.
Important! Usually the manufacturer indicates on the label the method of application of the drug. If this is not the case, then you can use the average values for each specific substance. For OCA, these values are from 20 to 50 ml of the drug per ton of water.
For those who have a homemade pool or a pool without special additional equipment
- We determine the required amount of agent, for this we calculate the volume of the pool in cubic meters, and for each cube we add from 20 to 50 ml of OXA (GOODHIM "").
- The coagulant is pre-bred in a watering can with water in a ratio of 1:5 - 1:100, that is, we take about two liters.
- Turn off the filter pump.
- We go down into the pool and start walking in a circle until the water forms a small whirlpool.
- We leave the pool and add the prepared solution to the whirlpool.
- We wait, then we collect the sediment and filter the remaining water completely.
Timely care and cleaning make the use of the pool not only pleasant, but safe and even beneficial to health. Now you can invite your friends to join the water procedures without fear of being disgraced by the state of the water in the reservoir.
Attention! Most modern manufacturers have websites where you can find contacts or shipping information. Most often, it is possible to order goods online and receive them by mail within a few days.
Conclusion
Water is a critical element for sustaining life. This applies to drinking, personal hygiene, watering plants, economic activities and production. Coagulation solved the issue of water purification and brought this process to a completely different qualitative level, and today coagulants are used almost everywhere.
Coagulants - Definition and FAQs
- What does coagulant mean? The word comes from the Latin "coagulatio" and translates as "thickening". Coagulant substances are able to combine particles suspended in water into larger lumps.
- Are coagulants and flocculants the same thing? No, not at all. These are similar drugs that can be used together.
Coagulation (from the Latin coagulatio - coagulation, thickening) - the association of particles of the dispersed phase into aggregates during collisions. Collisions occur as a result brownian motion particles, as well as sedimentation, movement of particles in an electric field (electrocoagulation), mechanical effects on the system (mixing, vibration). Characteristic features coagulation - an increase in turbidity (intensity of scattered light), the appearance of flocculent formations - floccules (hence the term flocculation, often used as a synonym for coagulation), stratification of an initially sedimentation-resistant system (sol) with the release of a dispersed phase in the form of a coagulate (sediment, cream). At a high content of particles of the dispersed phase, coagulation can lead to curing of the entire volume of the system due to the formation of a spatial network of the coagulation structure. In relatively coarse systems (suspensions) in the absence of Brownian motion of primary particles, coagulation can be judged by the change in sedimentation - from the settling of independent primary particles with a gradual accumulation of sediment (structureless sedimentation) to the settling of aggregates in a continuous layer; at a sufficiently high concentration of particles in the system, such a layer forms a clear boundary (structural sedimentation). In addition, coagulation leads to an increase in the final volume of the sediment.
Coagulants are substances capable of inducing or accelerating coagulation. The introduction of coagulants into the system is widely used to facilitate the processes associated with the need to separate the substance of the dispersed phase from the dispersion medium (sedimentation of suspended particles during water treatment, enrichment of mineral raw materials, improvement of the filtration characteristics of sediments, etc.). Coagulation plays an important role in water treatment processes to remove suspended colloidal particles that can give drinking water an unpleasant taste, color, odor or turbidity. Under the action of coagulants, dispersed colloidal particles are combined into large masses, which then, after flocculation, can be removed by such methods of separating the solid and liquid phases as sedimentation, flotation and filtration.
Salts of polyvalent metals (aluminum, iron, etc.) are effective coagulants for systems with an aqueous dispersion medium. The following aluminum-containing coagulants are used in water treatment: aluminum sulfate, aluminum oxychloride, sodium aluminate and, to a much lesser extent, aluminum chloride.
Aluminum sulfate Al 2 (SO 4) 3 18H2O is a crude technical product, which is grayish-greenish pieces obtained by treating bauxites, nephelines or clays with sulfuric acid. It must have at least 9% Al 2 O 3 , which corresponds to a content of about 30% pure aluminum sulfate. It also contains about 30% insoluble impurities and up to 35% water.
Purified aluminum sulfate (GOST 12966-85) is obtained in the form of plates of a grayish-pearl color from the crude product or alumina by dissolving in sulfuric acid. It must have at least 13.5% Al2O3, which corresponds to a content of 45% aluminum sulfate. In Russia, a 23–25% solution of aluminum sulfate is also produced for water treatment. When it is used, there is no need for special equipment for dissolving the coagulant, as well as simplifying and reducing the cost of loading and unloading and transportation. In addition to water treatment, aluminum sulphate is used in large
quantities in the pulp and paper industry for paper sizing and other purposes; it is used in the textile industry as a mordant for dyeing cotton, woolen and silk fabrics, for tanning leather, for preserving wood, and in the artificial fiber industry. In this regard, in this review, when estimating the production volumes of coagulants, the consumption of Al 2 (SO 4) 3 in other industries will be taken into account, and then these data will be excluded from the consumption structure. The coagulating properties of Al 2 (SO 4) 3 are due to the formation of colloidal aluminum hydroxide and basic sulfates as a result of hydrolysis. In the process of coagulation of Al(OH)3, colloidal particles of impurities present in water are captured and released together with aluminum hydroxide in the form of gelatinous flakes. Al(OH) 3 has hypersensitivity to the pH and temperature of the treated water. The isoelectric region for aluminum hydroxide, where it has the lowest solubility, corresponds to pH = 6.5-7.5. At lower pH values, partially soluble basic salts are formed, at higher pH values, aluminates. At a source water temperature below 4°C, as a result of an increase in the hydration of aluminum hydroxide, the processes of coagulation of its impurities and decantation of flakes slow down, filters quickly become clogged, a precipitate of aluminum hydroxide is deposited in pipes, residual aluminum enters the filtrate, and hydroxide flakes are formed in water after supply to consumers.
In the cold season, when treating water with a high content of natural organic matter aluminum oxychloride (OXA) is used. OXA is known under various names: polyaluminum hydrochloride, aluminum chlorhydroxide, basic aluminum chloride, etc. and has general formula Al(OH)mCl3n-m. During water treatment, these compounds can form monomeric, polymeric and amorphous structures.
Inorganic cationic coagulant OXA has the ability to form complex compounds with a wide range of organic and inorganic substances in water. It differs fundamentally from conventional aluminum salts in that it has a so-called surface acidic shell, which ensures the highest efficiency of water purification from suspended solids and metals. The practice of using aluminum oxychloride has demonstrated a number of advantages that directly affect the economic performance of its use (including in comparison with traditionally used aluminum sulfate):
Being a partially hydrolyzed salt, aluminum oxychloride has a greater ability to polymerize, which accelerates flocculation and sedimentation of a coagulated suspension;
Aluminum oxychloride has been confirmed to work over a wider pH range than aluminum sulfate;
The decrease in alkalinity during coagulation with aluminum oxychloride is significantly less. This, along with the absence of the addition of sulfates, leads to a decrease in the corrosiveness of water, the exclusion of stabilization treatment, an improvement in the condition of the city's water distribution network and the preservation of the consumer properties of water during transportation, and also allows you to completely abandon the use of alkaline agents and leads to savings in them at the middle station. water treatment up to 20 tons monthly;
Low residual aluminum content at high administered doses;
Reducing the working dose of the coagulant by 1.5 - 2.0 times compared with aluminum sulfate;
Delivery in a ready-made working solution, which makes it possible to refuse the process of coagulant dissolution, leading to energy savings for stirring at the middle station up to 100 thousand kW/h annually;
Reduction of labor intensity and operating costs for storage, preparation and dosing of the reagent, improvement of sanitary and hygienic working conditions.
Sodium aluminate NaAlO 2 is a white solid piece with a pearly sheen at the break, obtained by dissolving aluminum hydroxide or oxide in a solution of sodium hydroxide. Dry commercial product contains 55% Al 2 O 3 , 35% Na 2 O and up to 5% free alkali NaOH. Solubility of NaAlO 2 - 370 g/l (at 20 o C). Bulk weight 1.2−1.8 t/m3. Aluminum chloride AlCl 3 is a white crystalline powder with a density of 2.47 g / cm 3, with a melting point of 192.4 ° C. The solubility of aluminum chloride in 100 g of water at 20 ° C is 46 g, the compound decomposes in hot water. Al 2 Cl 3 ·6H 2 O crystallizes from aqueous solutions with a density of 2.4 g/cm 3 , spreading in air. When heated, it splits off water and HCl to form Al2O3. Aluminum chloride is used mainly as a catalyst in the cracking of petroleum products, as well as for a number of organic syntheses. However, in some cases, it is used as a coagulant. At low water temperatures during the flood period, aluminum hydroxide can be used as a coagulant. Iron-containing coagulants are also used in water treatment:
ferric chloride, iron (II) and iron (III) sulfates, chlorinated ferrous sulfate. Ferric chloride FeCl 3 ·6H 2 O (GOST 11159−86) is a dark crystals with a metallic sheen, very hygroscopic, so it is transported in sealed iron barrels. Anhydrous ferric chloride is obtained by chlorinating steel chips at a temperature of 700 ° C, and also as a by-product in the production of metal chlorides by hot chlorination of ores. Contains at least 98% FeCl 3 in the commercial product. Density 1.5 g/cm 3 . Ferrous oxide sulfate FeSO 4 7H 2 O (iron vitriol according to GOST 6981−85) is a transparent greenish-blue crystals, easily turning brown in air as a result of the oxidation of iron (II). The marketable product is produced in two grades (A and B), containing respectively not less than 53% and 47% FeSO 4 , not more than 0.25 - 1% free H 2 SO 4 and not more than 0.4 - 1% insoluble sediment. The density of the reagent is 1.5 g/cm3. The industry also produces a 30% solution of iron (II) sulfate containing up to 2% free sulfuric acid. It is transported in a rubberized container. Oxidation of iron hydroxide (II), which is formed during the hydrolysis of ferrous sulfate at a water pH of less than 8, proceeds slowly, which leads to its incomplete precipitation and unsatisfactory coagulation. Therefore, before the introduction of ferrous sulfate, lime or chlorine, or both reagents together, are added to the water, thereby complicating and increasing the cost of water treatment. In this regard, ferrous sulfate is mainly used in the technology of lime and lime-soda water softening, when the pH value is maintained within 10.2–13.2 when magnesium hardness is eliminated and, therefore, aluminum salts are not applicable.
Iron sulfate (III) Fe 2 (SO 4) 3 2H 2 O is obtained by dissolving iron oxide in sulfuric acid. The product is crystalline, very hygroscopic, soluble in water. Its density is 1.5 g / cm 3. The use of iron (III) salts as a coagulant is preferred over aluminum sulfate. Their use improves coagulation at low water temperatures, the process is little affected by the pH of the medium, the decantation of coagulated impurities is accelerated and the settling time is reduced (the density of iron (III) hydroxide flakes is 1.5 times greater than that of aluminum hydroxide). Among the disadvantages of iron (III) salts
is the need for their exact dosage, since its violation leads to the penetration of iron into the filtrate. Flakes of iron hydroxide (III) are deposited unevenly, and therefore, remains in the water a large number of fine flakes entering the filters. These shortcomings are largely eliminated by adding aluminum sulfate.
Chlorinated ferrous sulfate Fe 2 (SO 4) 3 + FeCl 3 is obtained directly at water treatment complexes by treating a solution of ferrous sulfate with chlorine, introducing 0.160 - 0.220 g of chlorine per 1 g of FeSO 4 7H 2 O. Mixed aluminum-iron coagulant is prepared from solutions of aluminum sulfate and ferric chloride in a ratio of 1:1 (by weight). The recommended ratio may vary depending on the specific conditions of the treatment plant. The maximum ratio of FeCl 3 to Al 2 (SO 4) 3 when using a mixed coagulant by weight is 2:1. Water treated with a mixed coagulant, as a rule, does not form deposits even at low temperatures, since the formation and sedimentation of flocculation ends mainly before the filters; the flakes are deposited evenly, and a more complete clarification of the water is achieved. The use of a mixed coagulant can significantly reduce the consumption of reagents. The components of the mixed coagulant can be introduced either separately or after mixing the solutions. The first method is more flexible in the transition from one optimal ratio of reagents to another, however, with the second one, it is easier to do dosing.
Aluminum sulfate is the most common coagulant used in water treatment for drinking and industrial water treatment. The simplest and oldest method of obtaining crude aluminum sulphate is the boiling of uncalcined but dried kaolin with sulfuric acid. The degree of conversion of Al2O3 clay into sulfate does not exceed 70–80%.
The products obtained by this method - crude aluminum sulphate or coagulants - harden after boiling and are not subjected to additional processing. They contain all impurities of raw materials.
To obtain purified aluminum sulfate, insoluble impurities are separated, which greatly complicates the production process. An improvement of this method was the decomposition of kaolin with excess sulfuric acid to increase the degree of extraction of Al2O3 and the neutralization of excess acid with nepheline. The successful use of nepheline as an additive to kaolin served as the basis for the production of nepheline coagulant from nepheline alone (without kaolin):
(Na, K) 2 O Al 2 O 3 2SiO 2 + 4H2SO 4 → (Na, K) 2 SO 4 + Al 2 (SO 4) 3 + 4H 2 O + 2SiO 2
Nepheline coagulant
When mixing nepheline concentrate with tower sulfuric acid without subsequent dilution with water, the mixture quickly thickens, since the water in it binds with the formed salts into solid crystalline hydrates. This is accompanied by a strong increase in temperature, causing significant vaporization, which leads to a sharp increase in the volume of the mixture, which turns into a solid porous mass, easily crumbling into powder. This product, consisting of a mixture of aluminum sulfate, potassium, sodium alum, SiO 2 and other impurities that were in nepheline and formed during its treatment with sulfuric acid, is called nepheline coagulant. It would be more correct to call it the crude nepheline coagulant, in contrast to the purified nepheline coagulant, which is a mixture of products obtained by crystallization of the solution after separation of the silica precipitate from it. The reaction temperature, the amount of evaporated water, the yield and properties of the coagulant depend on the concentration of the initial acid. Aluminum bisulfate was found in the product obtained by decomposition of nepheline with 63-84.5% acid. This is due to the incomplete neutralization of sulfuric acid. The presence of hygroscopic acid salts in the coagulant causes it to absorb moisture from the air. As a result of watering the product, further decomposition of unreacted nepheline occurs. This process of "ripening" proceeds slowly in air for about 12 days, due to the coating of grains of unreacted nepheline with coagulant crystals. When crystals are dissolved in water, the process of further decomposition accelerates and ends in cold water for an hour, and in hot water for 5 minutes. Thus, the slowdown in the interaction of nepheline with concentrated sulfuric acid (above 63% H 2 SO 4) is due to the lack of water in the liquid phase. With the highest rate, nepheline decomposes with 47-73% sulfuric acid. Obtaining the crude nepheline coagulant is carried out by mixing the nepheline concentrate with tower sulfuric acid in boilers with mixers and pouring the resulting pulp until it thickens into the apparatus for "maturation", i.e. mass solidification.
The solid mass is crushed. When nepheline is mixed with 92% sulfuric acid, the reaction is very slow and the unthickened slurry can easily flow into the auger trough where water is added to dilute the acid. After that, the reaction goes very quickly, and the mass, intensively mixed by the screw and moved along the apparatus, quickly hardens, turning into small grains. The mixing process is carried out in two devices connected in series. Acid and nepheline concentrate are fed continuously into one of the mixers. The resulting slurry flows into the second mixer, from where it exits from its lower part through a hydraulic seal into the ladle batcher. The outgoing pulp should contain from 1.5 to 4% excess sulfuric acid (depending on the quality of the nepheline). By excess is understood the acid contained in the pulp in excess of the amount that can react by the end of the process during hydration. From the bucket feeder, the pulp enters the screw reactor, where water is added at the rate of diluting the acid to 70−73% H2 S O 4 . The residence time of the mass in the screw-reactor is 28−30 sec and the degree of decomposition of nepheline during this time reaches 85−88%. From the reactor, the dry friable mass with a temperature of 80–100°C enters the warehouse, where the product ripens and cools for 2–4 days. The production of 1 ton of nepheline coagulant by this method requires: 0.32 tons of nepheline flour (up to 1% moisture) or 0.105 tons of Al 2 O 3 (100%), 0.378 tons of sulfuric acid (100%). The technology for the production of nepheline coagulant has been implemented at OAO Svyatogor, as well as at OAO Apatit, where the resulting reagent is used to thicken apatite and nepheline concentrates. The industrial process for the complex processing of nephelines was developed by Soviet specialists and tested at the Volkhov Aluminum Plant in 1952. The essence of the process is the sintering of nepheline with limestone at a temperature of 1250-1300 ° C. The resulting mass is leached with an aqueous alkaline solution, the sodium aluminate solution is separated from sludge, then freed from SiO 2, precipitating it in an autoclave at a pressure of about 0.6 MPa, and then with lime at atmospheric pressure, and decompose the aluminate with gaseous CO 2 . The resulting Al(OH) 3 is separated from the solution, and then used for its intended purpose: when interacting with sulfuric acid, aluminum sulfate is obtained, when calcined (t ~ 1200 o C) - alumina. With this method of processing nepheline, in addition to alumina and aluminum sulfate, soda ash, potash and cement are obtained. A similar technology for producing aluminum sulfate from nepheline is currently used at the Achinsk Alumina Refinery.
Obtaining purified aluminum sulfate from aluminum hydroxide or aluminum oxide (alumina)
Most Russian producers of aluminum sulfate use aluminum hydroxide or aluminum oxide (alumina) as a raw material.
2Al(OH) 3 + 3H 2 SO 4 → Al 2 (SO 4) 3 + 6H 2 O
Al 2 O 3 + 3H 2 SO 4 → Al 2 (SO 4) 3 + 3H 2 O
In the production of purified aluminum sulfate by dissolving aluminum hydroxide (or aluminum oxide) in sulfuric acid, the process is carried out as follows. The reaction kettle (steel tank lined with acid-resistant bricks over a layer of diabase tiles) is simultaneously loaded with aluminum hydroxide, sulfuric acid and water in an approximately stoichiometric ratio corresponding to a product content of approximately 90% Al 2 (SO 4) 3 18H 2 O and 10% free water.
Stirring is carried out with live steam, maintaining the temperature at the level of 110-120 ° C, and it is completed after 20-30 minutes, when the amount of free sulfuric acid in the sample of the reaction mass becomes less than 0.1%. The reaction mass containing 13.5−15% Al 2 O 3 (in the form of aluminum sulfate), to accelerate the subsequent crystallization, is cooled in the reactor to 95 ° C, blowing air through it for 10 minutes. Then it is poured onto a crystallization table equipped with an automatic machine for cutting the solidified product. Crystallization of the melt on the table lasts about 50 minutes and the same time takes the extraction of the product from the mold, which has an area of 32-34 m2 (capacity of about 6 tons).
The consumption of materials per 1 ton of product is: 0.142 tons of aluminum hydroxide (in terms of Al2O3) and 0.40 tons of sulfuric acid (100%). Crystallization is also carried out on the outer surface of a horizontal rotating drum cooled from the inside - on cooling or crystallization rollers. The drum is partially immersed in the melt located in the pallet, having a temperature of 90−100 o C. Crystallization on the rollers facilitates working conditions, ensures a continuous production mode, and improves the commercial properties of the product. A flake product removed from the rollers containing 13.5−14% Al 2 O 3 during storage
caking. A non-caking product is obtained by increasing the content of Al 2 O 3 to 15.3−15.8% (15.3% corresponds to the concentration of Al 2 O 3 in Al2(SO4)3·18H2O crystalline hydrate). With a roller drum length of 2.2 m and a diameter of 1.8 m (heat exchange surface 12.4 m2), when discharging a product with a content of 13.5–14% Al 2 O 3 , the number of revolutions of the drum is 4.3 per minute and the average the working capacity of the rollers is 2.4 t/h; when the product containing 15.3–15.8% Al2O3 is released, the drum makes 1–1.2 rpm and the productivity decreases to 1 t/h.
To obtain a non-caking product, it is also proposed to mix the aluminum hydroxide slurry with 60% sulfuric acid, taken in an amount of 95-97% of the stoichiometric, and the resulting solution with a temperature of 100 ° C is directed to cold rollers for crystallization. The product contains an admixture of basic salt. A continuous process for the production of aluminum sulfate has been patented, in which an aqueous suspension of Al(OH) 3 and sulfuric acid in a stoichiometric ratio are fed at high speed by metering pumps into the mixing nozzles of the reactor, in which the mass is at least 30 seconds. It is then cooled to below 100° C. in a flow cooler and forced through nozzles or slits to form a finely granular product.
Obtaining aluminum oxychloride
Crystals of aluminum oxychloride Al 2 (OH) 5 Cl 6H2O are obtained by dissolving freshly precipitated aluminum hydroxide in a 0.5−1% solution of hydrochloric acid. The reagent contains 40−44% Al 2 O 3 and 20−21% NaCl. Available in the form of a 35% solution. In addition, aluminum polyoxychloride is obtained by reacting HCl with pure aluminum:
2Al(OH)3 + HCl → Al 2 (OH) 5 Cl + H2O
2Al + HCl + 5H 2 O → Al 2 (OH) 5 Cl + 3H2
