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First, flocculation and condensation
In solid-liquid suspension systems, the process of forming aggregates is called flocculation or flocculation. The aggregates thus formed are called flocs. Chemicals that promote the flocculation process are called flocculants.
However, due to historical reasons, in the current literature, the terms "Flocculation" and "Coagulation" are often confused or common. In recent years, there has been a clear distinction between the different angles in the literature: (1) according to the mechanism of the suspension "Destabilization", or the formation of aggregates: "flocculation" means Forming close aggregates; (2) according to the chemical used, flocculation is made of organic high molecular polymer, and the inorganic chemical is used for coagulation; (3) according to the engineering operation steps, flocculation is through the mechanical machinery of the particles. The migration step leads to the formation of aggregates (collisions between particles after slurrying); coagulation is the adjustment of chisel by chemicals; (4) according to the application of some engineering, flocculation is still the step of particle migration, while condensation shows as overall The process of aggregation.
In short, aggregates formed by flocculation can be disturbed and disintegrated by relatively weak mechanical forces or due to changes in physical forces at the interface of solid and suspended media, for example, the resulting flocs are agitated. It can be broken, and once the agitation stops, it will re-form the floc. According to the newer definition, flocculation refers to the action produced by the use of high-molecular flocculants (such as starch or polyelectrolytes), which connect solid particles together in a linear polymer form by "Bridging". Forming an arbitrary, three-dimensional, loose, porous structure. That is to say, only the effect of generating flocculation by the "bridge action" of the polymer can be called "flocculation" or "flocculation".
The application of flocculants plays a very important role in the flotation process. The fine ore of the ore contains a flocculation process before it adheres to the bubble during the flotation process; in order to prevent the loss of the concentrate, the sedimentation of the concentrate fine particles is accelerated in the concentrate concentrator, and if necessary, a flocculant is added to Reduce the loss of concentrate in the overflow of the concentrator; some concentrates are difficult to filter, and adding flocculant can greatly increase the filtration speed and reduce the moisture in the filter cake. The more important application is the purification of tailings water to prevent the tailing water from polluting the surrounding environment of the mine. The purified water can be recycled and reused to save water and reduce production costs. As for the application of flocculants in other chemical industries, the scope is even broader.
Second, inorganic salt flocculant
Strictly speaking, inorganic salts should be coagulants and are often included in the classification of flocculants. Aluminum salts: include aluminum sulfate, polyaluminum chloride, sodium aluminate and the like. Aluminum salts are generally prepared as a concentrated solution for storage and then temporarily diluted during use.
Commercial aluminum sulfate contains 14 crystal waters, Al 2 (SO 4 ) 3 ·14H 2 O, which is stable in nature and can be stored for a long time without deterioration. It is mostly used for water purification.
The polyaluminum monochloride is a partial hydrolysis product of aluminum trichloride, abbreviated as PAC, and its experimental formula is Al(OH) 1.5 (SO 4 ) 0.125 CI 1.25 , and the product is in a solution state. It is generally considered to have a stronger and faster flocculation effect than aluminum sulfate.
Iron salts: hydrated ferric iron ions stronger than the acidic aluminum ions, as the flocculent mainly ferric chloride, ferric sulfate and ferrous sulfate.
The active silica can be used as an anionic flocculant. Lime can promote flocculation and is often referred to as an auxiliary flocculant. Magnesium bicarbonate is used in the backwater system, and bentonite and other clays are added as flocculating aids.
Third, organic polymer flocculant
The polymer flocculants are water-soluble polymers with an average molecular weight ranging from about 10 3 to 5 × 10 6 and a maximum of 20 × 10 6 . If some subunits have a charge in a polymer molecule, they are called polyelectrolytes. The subunit has a positive charge, such as a polyamine salt, which is called a cationic polymer; a subunit has a negative charge, such as sodium polyacrylate, which is called an anionic polymer; a subunit having both positive and negative charges in the molecule, called Amphoteric polymer. Uncharged subunits, such as polyoxyethylene, pure polyacrylamide, are referred to as nonionic polymers.
The synthetic high-molecular flocculant may be in the form of a powder, a granule, a bead, an aqueous solution, a hydrosol, or a water-oil emulsion. The higher their molecular weight, the greater the viscosity of their aqueous solution.
Cationic polymer flocculants are mainly quaternary ammonium salts. Cationic polymer flocculants containing organic tetravalent sulfides (é”) or containing phosphonium (PR 4 + ) groups have been reported but have not been applied.
The anionic polymer flocculant is mainly a carboxylic acid group. Generally, the higher the molecular weight, the better, and the strong anionic type and low molecular weight polymer have the action properties of the dispersant.
The main representative of the nonionic polymeric flocculant is pure polyacrylamide or polyacrylamide having a carboxyl group of less than 1%.
Synthetic flocculants which have been put into production in China are: polyacrylamide, polyoxyethylene, polyvinyl alcohol, polyacrylic acid, polyvinylpyrrolidone and the like. The most widely used in the beneficiation process is still polyacrylamide. The products are colloidal and powder.
The application range of commonly used flocculants is listed in Table 1. The more famous synthetic organic flocculants are listed in Table 2. The foreign synthetic flocculant brand number is listed in Table 3. [next]
Table 1 Examples of common flocculant application ranges
Types of | Application range | ||
Inorganic salt | Aluminum salt | Clarification of urban water supply, decolorization and sedimentation - flocculation, clarification of industrial water, Industrial, urban waste sedimentation, phosphate precipitation - flocculation | |
Iron salt | Phosphate precipitation - flocculation; industrial and municipal waste sludge precipitation and dewatering | ||
lime | pH adjustment (water, wastewater, pulp, etc.), carbonate precipitation (water supply softening), Sugar refining auxiliary flocculant, phosphate precipitation in sludge treatment, auxiliary flocculant, etc. | ||
Synthetic organic polymer | Degree of ionization | Molecular weight | |
Cationic (40~80%) | 1~5×10 6 | Industrial and municipal waste sludge dewatering, black liquor clarification when manufacturing TiO 2 | |
Cationic (40~80%) | 10 5 ~ 10 6 | Iron ore concentrate and tailings, coal slag concentrate (as an auxiliary flocculant), industrial and municipal waste dewatering | |
Cationic (40~80%) | 10 3 ~ 10 5 | Concentration of iron concentrates and tailings, dewatering of municipal and industrial waste sludge | |
Cationic (1~10%) | 1~5×10 6 | Municipal and industrial waste residue, sludge dewatering, purification of refined pulp in sugar industry | |
Anionic (10~40%) | 1~5×10 6 >5×10 6 | Aluminum plant red mud (iron oxide) concentrated | |
Anionic (80~100%) | >5×10 6 | Cinder concentration and dehydration, aluminum sludge dehydration, sugar industry syrup purification | |
Anionic (1~10%) | 1~5×10 6 >5×10 6 | a flocculant used after chemical precipitation, Concentration of potassium salt tailings (clay fine mud), ore flocculant | |
Non-ionic | Ibid. | Mineral flocculant, acid slurry and concentrate concentrate, Weakly acidic waste residue, uranium extract sedimentation | |
Starch starch | Precipitate | Aluminum plant red mud (iron oxide) concentrated, quartz iron shale selective flocculation | |
Ancient ear glue | Settling agent extract uranium, gold ore residue was extracted aid | ||
Protein glue | Uranium acid extract sedimentation, wine, alcoholic beverage clarifying agent | ||
Table 2 Famous synthetic organic flocculant structure
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Table 3 Foreign synthetic flocculant brand number
Product grade | Factory | Types of |
Accofloc Amerfloc Aquafloc Aronfloc Betz Polymer Bozefloc Calgon Catfloc Coagulant Aid Cyfloc Drewfloc Diacler Fennofloc Flocogil Floerger Hercofloc Himoloc Hi-Set Magnafloc Magnifloc Montrek Nalco Nalcolyte Nopcofloc PEI Percol Polyfloc Polyox Praesrol Primafloc Purifloc Rohafloc Sandoles Sanfloc Sanploy Sedipur Separan Sumifloc Superfloc Versa-TL Zetag | 1.Mitsui-Cyanamid (Japan) 2.Drew Chemical Corp (US) 3.Dearborn chemical (US) 4.Toagosei chemical Industry Co. (Japan) 5.Betz Laboratories , Inc, (US) 6.Nobel-Hoechst (French) 7.The Calgon Corp (Merck & Co.) (US) Same as above Same as above 8. Ametlean Cyanamid Co (US) Same as 2 9. Mitsubishi Chemical Industrier (Japan) 10. KEMIRA Oy (Finland) 11. Rhone-Poulenc (French) 12.Floerger (French) 13.Hercules, Inc (United States) 14.Kyoritsu Yuki (Japan) 15.Dai-Ichi Kogyo Seiyuku Co. (Japan) 16.Allied Colloids Ltd. (UK) Same as 8 17.The Dow Chemical Co. (US) 18.Nalco Chemical Co. (US) Same as above 19.Dialmond Shamrock (US) Same as 17 Same as 16 Same as 7 20.Union Carbide Corp (United States) 21.Chemische Fabrik Stockhausen & Cie (West Germany) 22.Sandoz (US) Same as 17 23.Rohm GmbH (West Germany) Same as 22 24. Sanyo Chemieal Industries (Japan) 25. Sankyo Chemical Industries, Ltd (Japan) 26.BASF AG (West Germany) Same as 17 27.Sumitomo Chemical Co.Ltd. (Japan) Same as 8 28.Natiooal Starch Corp (United States) Same as 16 | a Abc a a a } abc Abc Abc a a a Abc Ab a a a Abc Ab Ab Ab Abc Ab a Ab C Abc b Ab Ab Bc Ab Ab Ab Ab Ab Abc c a |
Note: a—nonionic, anionic and cationic polyacrylamides;
B—polyamines, quaternary ammoniums;
C—epoxidized polymer (POE) and others. [next]
Fourth, natural polymer flocculant
The first flocculant used to purify drinking water comes from natural products (almonds, beans and stone fruits). The current natural polymer flocculants include starch, various types of starch derivatives, vegetable gums, seaweed extracts, cellulose. Derivatives, proteins and tannins, among which the most important and most used are starch, followed by Guargum. Natural flocculants are cheaper than synthetic flocculants, but they are used in high amounts and are prone to deterioration. Synthetic flocculants have gradually replaced natural flocculants. For example, in the uranium extraction process, polyacrylamide replaces the protein colloidal flocculant.
Starch contains two "glycans", namely amylose and aleose starch. Generally contain more amylopectin manifold, higher molecular weight, up to 106, it may be used to make aluminum as red mud flocculants. Starch made from corn, wheat, sorghum, rice, potatoes, and cassava can be used as a flocculant. Starch can also be processed into a variety of flocculants, either cationic or anionic.
Sodium carboxymethyl cellulose, which has a degree of substitution of generally 0.4 to 1.5, is characterized by stable nature and is not easily biodegradable or hydrolyzed.
Tannins are also reported to be a flocculating agent, see British Patent No. 1310491 of 1973.
Five, selective flocculant
In a stable suspension containing two or more components, after adding a certain polymer flocculant, the flocculant produces selectivity between the different components due to the different surface properties of the two components. Adsorption, sedimentation by "bridge" to produce flocs; while the other component is still dispersed in the suspension, so as to achieve the purpose of separation of the two components, this effect is called selective flocculation. (Also called "preferred flocculation"); a flocculant that can do this is called a selective flocculant.
In the flotation industry, research on selective flocculation has been intermittent for nearly 60 years since the beginning of the 20th century, and was not applied until 1974. Cleveland-Crafts Steel Company of the United States used tapioca starch in research and later in production. The use of corn starch as a selective flocculant for the treatment of very fine-grained quartz iron gangue was successful. In 1974, a concentrating plant with an annual output of 4 million tons of concentrate was established and put into production.
The partially hydrolyzed polyacrylamide is selectively flocculated to achieve the separation of the very fine feldspar -hematite artificial mixture. By changing the anionic properties of polyacrylamide, it is possible to preferentially flocculate hematite or preferentially flocculate silicates from a mixture. For example, strong anionic polyacrylamide promotes selective flocculation of hematite; while weak anionic forms preferentially flocculate silicates. Polyacrylamide flocculation can also choose cassiterite; Selective Flocculation and artificial quartz mixed mineral galena; selecting flocculation chrysocolla quartz. Also tested for the sorting of kaolin and clay. Hydrolyzed polyacrylamide was tested for selective flocculation of kaolin and bauxite.
Sodium carboxymethyl cellulose, polyacrylamide, etc. may be used synthetic tannin manganese selective flocculation sludge. Carboxymethyl cellulose can be used for selective flocculation selective flocculation of iron and chromium lead, zinc sulphide ore, tapioca may also be used to selectively flocculate clay iron-containing material desliming. Selective flocculation of coal and clay with sodium polymethacrylate. Selective flocculation of copper uranium mica with polyoxyethylene.
In recent years, many units in China have studied and obtained results on selective flocculants and their effects. The flocculating agent used includes: sodium humate, ammonium humate, nitrated humic acid, hydrolyzed polyacrylamide, sulfonated polyacrylamide, starch, acorn starch, planan meal and the like.
Dispersant
Corresponding to the flocculating agent is a dispersing agent. Any agent capable of suspending solid fine particles in a flotation slurry may be referred to as a dispersant. They must be capable of adsorbing on the substrate for dispersion and imparting a negative charge. The dispersing agent mainly includes polycondensed phosphate (polyphosphate), organic polymer, inorganic salt and organic compound. Some common dispersants are shown in Table 4.
Table 4 Dispersant
Inorganic dispersant | Organic dispersant | Organic polymer dispersant |
Sodium hydroxide Water glass Aluminum silicate Al 2 (SiO 3 ) 3 Sodium tripolyphosphate (STPP) Sodium hexametaphosphate (NaPO 3 ) 6 Tetrasodium pyrophosphate Na 4 P 2 O 7 Sodium fluoride Sodium carbonate Sodium boron (borax) Sodium aluminate NaAlO 2 or Na 3 AlO 3 | Sodium citrate Sodium gluconate Sodium soda Sodium tartrate ascorbic acid Polyamines Amino alcohols Phosphonate Sulfonate | Glucuronic acid Alginic acid Casein Gelatin Lecithin Tannin Lignosulfonate Degraded glycans a variety of synthetic polymers |
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