Info

Bulk density, normal

2-15 lb/ft3

Mesh Sizes (normal)

4-40 and finer mesh

Property

Characteristic

Softening Point

1600-2000° F

Fusion Point

2300-2450° F

Specific Heat

0.2BTU/lb-°F

Thermal Conductivity

0.27-0.41 BTU.in/h.ft2 °F

Clay - The use of clay based flocculating agent(s) in conjunction with a strong metal precipitator has proven successful in many wastewater treatment applications where the objectives are aimed at metals removal. Clay based flocculants cleans the wastewater and in some cases replaces multistage conventional treatment system and saves the traditional operational difficulties of treatment with several chemicals such as metal hydroxide precipitation, coagulant, flocculants and other methods. Commercial clay-based flocculants usually consist of bentonite and other proprietary ingredients. These products are in a granulated form to minimize any dust exposure. Betonite mixtures are often used for removing many wastewater constituents including, but not limited to heavy metals, oil and grease, pigments, and phosphates. It encapsulates the metals and other wastewater constituents in a clay barrier, producing an easily disposable waste sludge and treated water. Industrial wastewater from rinses and cleaning operation can be mixed with the flocculant at an average of < 1 % (by weight) dosage rate in a mixing tank. Even though the process of flocculation takes few minutes, a rapid multi-stage complex chemistry starts working. These hidden reaction stages, simulate the

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex; filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies: the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation; an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate; and it is necessary to account for the method of application and characteristics of filter aids.

phenomena of attraction, coagulation, precipitation, and separation of metals, oil, grease, and pigment due to a strong affinity of muti-layer positively charged of the bentonite crystal structure and other blended additives in each package. Depending on the constituent of the effluent, blended specialty products are formulated such that in addition to metal removal, it has added -value chemistries that have strong tendencies to remove chlorinated solvents as well as oil & grease -all in one chemical package system. After addition of the flocculant, the fully reacted mass is a bonded and complex formula that strongly encapsulates wastewater contaminants. These bonds are generally categorized as weak Van der Waals, as well as strong electrostatic forces. The clay has also tendency to entrap and agglomerate the surrounding suspended solids very efficiently. During this stage, some Pozzolanic reactions also occur, in which, a cementatious particles settles down to bottom of the reaction vessel. It is very interesting that the entire microencapsulation process occurs in few minutes as long as the granulated clays are fed into the system, leaving clear solution for reuse, recycle, or discharge. The solidified and flocculated waste sludge is often classified as non-leachable and in many occasions, depending the waste stream, it may pass the TCLP and STLC tests. If the test passes, it confirms that contaminant is surrounded by a barrier of clay particles and is not accessible to external leaching solutions or processes. Cellulose fiber is applied to cover metallic cloths. The fibers form a highly compressed cake with good permeability for liquids, but a smaller retention ability for solid particles than that of diatomite or perlite. The use of cellulose is recommended only in cakes where its specific properties are required. These properties include a lack of ashes and good resistance to alkalies. The cost of cellulose is higher than those of diatomite and Perlite.

Sawdust may be employed in cases where the suspension particles consist of a valuable product that may be roasted. For example, titanium dioxide is manufactured by calcining a mixture of sawdust and metal titanium acid. The mixture is obtained as a filter cake after separating the corresponding suspension

Charcoal is not only employed in activated form for decoloring and adsorbing dissolved admixtures bat also in its unactivated form as a filter aid. It can be used in suspensions consisting of aggressive liquids (e.g., strong acids and alkalies). As with sawdust, it can be used to separate solids that may be roasted. On combustion, the charcoal leaves a residue of roughly 2 percent ash. Particles of charcoal are porous and form cakes of high density but that have a lesser retention ability than

Fly ash has a number of industrial filtering applications but primarily is applied to dewatering sewage sludge. The precoat is built up to 2-in. thick from a 60 percent solid slurry. On untreated sludges, filtration rates of 25 lb/ft2-hr are obtainable. This rate can be doubled with treated sludges. The sludge is reduced from a liquid to a semidry state. Fly ash may also be used as a precoat in the treatment of

Polymeric flocculants are high molecular weight organic chains with ionic or other functional groups incorporated at intervals along the chains. Because these compounds have characteristics of both polymers and electrolytes, they are frequently called poly electrolytes. They may be of natural or synthetic origin. All synthetic polyelectrolytes can be classified on the basis of the type of charge on the polymer chain. Thus, polymers possessing negative charges are called anionic while those carrying positive charges are cationic. Certain compounds carry no electrical charge and are called nonionic polyelectrolytes. Because of the great variety of monomers available as starting material and the additional variety that can be obtained by varying the molecular weight, charge density, and ionizable groups, it is not surprising that a great assortment of polyelectrolytes are available to the wastewater plant operator. Extensive use of any specific polymer as a flocculant is of necessity determined by the size, density, and ionic charge of the colloids to be coagulated. As other factors need to be considered (such as the coagulants used, pH of the system, techniques and equipment for dissolution of the poly electrolyte, and so on), it is mandatory that extensive jar testing be performed to determine the specific polymer that will perform its function most efficiently. These results should be verified by plant-scale testing. Types of polymers vary widely in characteristics. Manufacturers should be consulted for properties, availability, and cost of the polymer being considered. Dry polymer and water must be blended and mixed to obtain a recommended solution for efficient action. Solution concentrations vary from fractions of a percent up. Preparation of the stock solution involves wetting of the dry material and usually an aging period prior to application. Solutions can be very viscous, and close attention should be paid to piping size and length and pump selections. Metered solution is usually diluted just prior to injection to the process to obtain better dispersion at the point of application. Two types of systems are frequently combined to feed polymers. The solution preparation system includes a manual or automatic blending system with the polymer dispensed by hand or by a dry feeder to a wetting jet and then to a mixing-aging tank at a controlled ratio. The aged polymer is transported to a holding tank where metering pumps or rotodip feeders dispense the polymer to the process. It is generally advisable to keep the holding or storage time of polymer solutions to a minimum, one to three days or less, to prevent deterioration of the product. Selection must be made after determination of the polymer; however, type 316 stainless steel or plastics are generally used. The solution preparation system may be an automatic batching system that fills the holding tank with aged polymer as required by level probes.

Ultra High Molecular Weight Flocculants - Water soluble polymers with an average molecular weight of > 106 g/mol are generally considered to be high molecular weight flocculants. In recent years there has been a trend for flocculants to be manufactured with ever increasing molecular weight. This new generation of flocculants are referred to as 'ultra high molecular weight'. The use of flocculants with ultra high molecular weights can lead to stronger floes compared to lower molecular weight alternatives. The floe strength is of particular importance where high degrees of mixing energy prevail at the flocculant dosing point of a given dewatering application. Typically, the process operator has no control over this mixing shear, and consequently the choice of flocculant is paramount for ensuring that effective flocculation and subsequent solid/liquid separation occurs. A further advantage of high molecular weight flocculants is their propensity for dose efficient performance. The nature of high molecular weight flocculants, with long chain lengths, increase the likelihood of effective inter-particle polymer bridges compared to lower molecular weight, shorter-chain-length analogues. This dose efficient performance is desirable as a means of minimizing the cost of chemical pre-treatments that aid solid/liquid separation unit operations.

Sewage Sludge Pre-treatment Flocculants - Sewage sludge must be dewatered to facilitate economic disposal. Dewatered sludge decreases the cost of transportation to landfill, or if the sludge is to be incinerated the removal of water combustion. Ultra high molecular weight cationic flocculants are increasingly used for pre-treatment of sewage sludge prior to dewatering because they are particularly effective in the thickening of surplus activated sludges and centrifuge applications. Centrifuges exert a very large shearing force on floes as they enter the centrifuge bowl. The resilience of floes formed with ultra high molecular weight flocculants, readily explain the usefulness of such flocculants for centrifuge applications. It can be observed that increasing molecular weight has improved the dose-efficiency of the flocculant, making the product more cost-effective.

Red Mud Flocculation - In the Bayer process, crushed bauxite is digested in concentrated sodium hydroxide in order to dissolve and extract aluminium. An insoluble residue known as red mud is produced, which is composed primarily of iron oxides, quartz, sodium aluminosilicates, calcium carbonate, calcium aluminate and titanium dioxide. To recover the aluminium, the solid red mud must be removed from the liquor, This is typically achieved by a series of sedimentation tanks referred to as the 'wash train'. The sediment from the primary sedimentation is washed in order to recover entrained aluminium rich liquor. This washing process is repeated several times. The use of ultra high molecular weight anionic flocculants promote a desirable sedimentation rate at an economic dose, and can lead to a more compact sediment than that obtained using lower molecular weight flocculants. The more compact the sediment, the greater the liquor recovery, and therefore the higher the aluminium recovery.

Drainage and Retention Aids - Paper formation is critical for both aesthetic and practical reasons i.e. visual appearance and paper strength, respectively. Increased mixing, which improves the distribution of fibre and filler within the paper has been highlighted as a means of achieving a superior formation. Drainage and retention aids are added to induce the rapid and efficient release of water and to capture and retain the filler within the paper. Over the last decade, the throughput rate on paper machines has increased significantly, while the length of the paper machine, specifically the drainage area, has decreased. Due to the requirements and changes described above, the use of highly soluble, ultra high molecular weight flocculants as drainage and retention aids has increased. A more robust, shear stable floe is produced which withstands the increased mixing intensities and dewatering forces and leads to a better drainage and retention performance compared to lower molecular weight analogues.

Crosslinked Flocculants - The accepted theory of flocculation dictates the need for a water-soluble polymer, which is as linear as possible. However, controlled levels of polymer crosslinking or branching can provide unexpected benefits to enhance solid/liquid separation. The mechanism by which crosslinked flocculants operate is not well documented. It is possible that the crosslinked polymer lies on the surface of a solid particle and, by virtue of its structure, a proportion of the polymer charge is available to interact with adjacent particles, i.e. the crosslinked polymer cannot fully adsorb all its charge to one particle. One could perceive the charge remains available even after a transient bond has been broken. Thus, flocculation and re-flocculation mechanisms may explain the unique dewatering characteristics engendered by crosslinked flocculants. In recent times, the trend has been for manufacturers to develop commercially available flocculants that contain higher levels of crosslinking.

Sewage Sludge Pre-treatmentFlocculants - Highly crosslinked cationic flocculants have gained popular use in the pre-treatment of sewage sludge prior to dewatering by gravity belt thickening and centrifugation. In the laboratory the maximum filtrate volume (after a drainage time of 5 seconds) increases with the degree of flocculant crosslinking. This rapid rate of filtration observed in the laboratory translates into increased throughput rates when highly crosslinked flocculants are used on full-scale plants. As the degree of flocculant crosslinking increases, so does the flocculant dose requirement to achieve the desirable enhanced performance. A similar increase in dose requirement is necessary in order to gain performance benefits of highly crosslinked flocculants, when used to pretreat sludge prior to centrifugation. Advantages of highly crosslinked flocculants for centrifugation are increased throughput rates, increased percentage solid content of centrifuge cakes and cleaner centrâtes.

Encapsulated Flocculants - A recent innovation in commercially available flocculants is a counter ionic system, where one charged moiety is encapsulated and suspended in the counter charged product. This facilitates a mechanism of delayed release of the encapsulated product.

Coal Slurries - Two component treatments prove to be effective on a commercial scale for coal slurry flocculation. The use of encapsulated flocculant suspended in a counter charged flocculant provides the robustness of traditional dual component systems, but with additional performance advantages, which include reduction in filter cake moisture content and an increased throughput rate. Figure 5 illustrates the typical filter cake moisture content obtained by a conventional treatment system compared to the encapsulated treatment system using coal tailings as the substrate.

Microparticulate Systems - Although dual combination treatment systems comprising microparticles and flocculants have been used in the paper industry since the 1980s, it is only recently that there has been a general trend for paper mills to switch from conventional single component systems to dual systems.

Microparticle/Flocculant - In the past few years the use of microparticles in conjunction with ultra high molecular weight flocculants as drainage and retention aids has grown. The more compact, shear stable floes produced by the cationic flocculant followed by the anionic microparticle give technical improvements in both paper formation and dewatering and retention of fibre and fines within the paper. In general terms, the former is regarded as a more powerful drainage and retention system compared to the latter.

Low Molecular Weight Flocculants - Contrary to the trend to increase molecular weight, which has resulted in the commercial availability of ultra high molecular weight (HMW) flocculants, there are a number of applications where low molecular weight (LMW) flocculants are gaining considerable credibility.

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