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VANCOUVER, British Columbia, Feb. 18, 2021 (GLOBE NEWSWIRE) -- Medallion Resources Ltd. (TSX-V: MDL; OTCQB: MLLOF; Frankfurt: MRDN) is pleased to announce the acquisition of a license for exclusive rights to Purdue University-developed rare earth element (REE) separation and purification technologies, from Hasler Ventures LLC. Medallion will further develop and commercialize this process technology which is complementary to the Company’s existing business focus

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medallion secures exclusive rights to purdue university's

The license, acquired through Hasler Ventures LLC, provides Medallion with a portfolio of technology, patents, and knowhow for ligand-assisted displacement (LAD) chromatography to deploy in the separation and purification of rare earth elements (REE). The rights assigned by Hasler Ventures and granted by Purdue are exclusive and global for use with all minerals, mineral processing by-products and mining waste feedstock, excluding coal-sourced materials

The LAD system, developed by Linda Wang, PhD, the Purdue Maxine Spencer Nichols Professor of Chemical Engineering, is built upon a well-understood and widely used platform that provides an environmentally sound method for REE separation with low technology risk

“We believe this acquisition is a pivotal moment for Medallion, that will enable substantial downstream value to be added to our existing mineral sand monazite business model as well as deliver new opportunities for sub-licensing of REE separation technology to third parties,” said Mark Saxon, Medallion President & CEO. “After extensive review (September 25, 2020) of over 25 competing separation technologies we believe this LAD technology has the potential to be REE-industry changing, and will become an important part of Medallion’s rare earth element processing capability. We are excited to be working with Linda Wang and her Purdue team.”

medallion secures exclusive rights to purdue university's

A license for the parallel application of LAD technology for coal and coal-sourced waste materials, REE magnets and batteries was signed with American Resources Corporation (NASDAQ:AREC) and announced February 2, 2021

Medallion’s licensing for the Purdue LAD technology was acquired February 17, 2020 and is through a collaboration with Hasler Ventures LLC. Hasler Ventures was formed by Dan Hasler, who retired from Purdue in March 2020. At that time, Hasler Ventures optioned the LAD technology. Hasler served Purdue as executive vice president for communications and previously served five years as president of Purdue Research Foundation, where he became familiar with Wang’s work

“Linda and her colleagues have dedicated decades of research to developing this process and her effort and innovation has delivered one of the most promising and environmentally safe methods to separate and purify rare earth elements,” Hasler said. “This LAD technology could enable the U.S. to more safely utilize these critical resources from domestic sources and aligned nations, rather than remaining reliant on Chinese suppliers and high-environmental impact solvent-based processes.”

medallion secures exclusive rights to purdue university's

Rare earth elements include the 15 elements in the lanthanide series plus scandium (Sc) and yttrium (Y). They are essential ingredients for magnets, metal alloys, polishing powders, catalysts, ceramics, and phosphors, which are important for high technology and clean energy applications. The global REE market is estimated at $US4 billion annually and growing at about 8% per year (Research and Markets estimates, January 6, 2021)

LAD chromatography was designed as a greener REE extraction and purification process compared to conventional solvent-based separation methods and aligns well with Medallion’s strategy of providing technology solutions that minimize the environmental footprint. The LAD method operates in aqueous solutions and delivers high yield while supporting superior chemical recycling, excellent productivity, and efficiency without harsh or toxic chemicals. The system design is fully scalable and can expand in line with production or demand requirements

Wang’s LAD technology was highlighted in a Journal Green Chemistry paper in 2020, entitled “Two-zone ligand-assisted displacement chromatography for producing high-purity praseodymium, neodymium, and dysprosium with high yield and high productivity from crude mixtures derived from waste magnets.” This research, which has been applied to primary raw material feedstock, has provided high-purity (>99%) Nd, Pr, and Dy with high yields (>99%) and with productivity exceeding 100x the existing market-leading technology

medallion secures exclusive rights to purdue university's

As part of the exclusive patent license for its fields of use, Medallion has committed to a three-year US$150,000 per annum sponsored research program with Purdue University to further advance the technologies, and achieve various technical milestones including operation of a demonstration plant. On commercial operation, royalty fees or sub-license fees will be payable at standard industry rates

Dan Hasler will join Medallion’s Advisory Board and represent Medallion Resources in sub-licensing and partnership opportunities. In connection with the transaction, Medallion entered into a license transfer agreement with Hasler Ventures pursuant to which Hasler Ventures agreed to transfer all of its interest in the license to a wholly-owned subsidiary of Medallion in consideration for, in part, one million fully paid shares in Medallion Resources Ltd to be issued to Hasler Ventures or its nominee on closing of the transaction. The transaction and the issuance of shares is subject to TSX Venture Exchange approval. The shares to be issued will be subject to a four-month hold period in accordance with applicable securities laws

Medallion’s REE Production ApproachRare earth element demand growth is closely linked to low-carbon emitting technologies, including wind energy and electromobility where efficiency is enabled by high-strength REE permanent magnets

medallion secures exclusive rights to purdue university's

The company has developed the Medallion Monazite Process, a proprietary method and related business model to achieve low-cost, near-term, REE production utilizing mineral sand monazite. Monazite is a rare earth phosphate mineral globally available as a by-product from heavy mineral sand-mining operations

The Medallion Monazite Process was developed utilizing “best available technology” (BAT) principles and is consequently a highly optimized and automated design that is transferable in location and scalable in size as REE demand grows. The process reflects the current and future expectations of REE customers in the rapidly growing electric vehicle and wind energy markets by providing the lowest impact, most sustainable and resource efficient primary raw material sourcing available

The Medallion Monazite Process utilizes by-product materials that presently pass to waste in the mineral sand industry, or to Chinese customers, and therefore additional mining is not required. The process produces zero liquid waste, has a high degree of energy and chemical reuse and regeneration, and can convert greater than 95% of monazite feed to commercial REE and phosphate products

medallion secures exclusive rights to purdue university's

As announced 25 September 2020, Medallion completed an independent comparative study of the various opportunities in REE separation, led by Dr. Dag Eriksen and Dr. Kurt Forrester. The review focused on identifying a technically and economically attractive separation method to be paired with the Medallion Monazite Process, while seeking a lower environmental impact compared to conventional solvent-based extraction methods. Some 25 different technology and business opportunities were reviewed and ranked, resulting in the current decision to invest in LAD chromatography in partnership with Purdue University

Figure 1: Rare Earth Element Magnet Supply Chain Utilizing the Medallion Monazite Process and Purdue’s LAD Chromatographyhttps://www.globenewswire.com/NewsRoom/AttachmentNg/659cb698-8294-48e7-8947-4dae071d8f41

Monazite is used today as a source of REEs in both China and India, where it is considered an attractive feedstock due to its high REE content (up to 65% REE by weight) and the relatively high abundance of the magnet metals neodymium (Nd) and praseodymium (Pr)

medallion secures exclusive rights to purdue university's

About Purdue UniversityPurdue University is a top public research institution developing practical solutions to today’s toughest challenges. Ranked the No. 5 Most Innovative University in the United States by U.S. News & World Report, Purdue delivers world-changing research and out-of-this-world discovery. Committed to hands-on and online, real-world learning, Purdue offers a transformative education to all. Committed to affordability and accessibility, Purdue has frozen tuition and most fees at 2012-13 levels, enabling more students than ever to graduate debt-free. See how Purdue never stops in the persistent pursuit of the next giant leap at purdue.edu

About Hasler Ventures LLCHasler Ventures believes that the key to a secure domestic supply chain of rare-earth metals and strategic independence in rare-earth metals from China is the ability to separate, and purify in an economical, environmentally friendly way. Purdue University invented and patented Ligand-Assisted Displacement Chromatography offers this capability to U.S producers of both recycled and ore-sourced rare-earth metals

About Medallion ResourcesMedallion Resources (TSX-V: MDL; OTCPK: MLLOF; Frankfurt: MRDN) has developed a proprietary process and related business model to achieve low-cost, near-term, rare-earth element (REE) production by exploiting monazite. Monazite is a rare-earth phosphate mineral that is widely available as a by-product from mineral sand mining operations. REEs are critical inputs to electric and hybrid vehicles, electronics, imaging systems, wind turbines and strategic defense systems. Medallion is committed to following best practices and accepted international standards in all aspects of mineral transportation, processing, and the safe management of waste materials

medallion secures exclusive rights to purdue university's

Neither TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release

Medallion management takes full responsibility for content and has prepared this news release. Some of the statements contained in this release are forward-looking statements, such as statements that describe Medallion’s plans with respect to the license for the LAD technology, the future potential of the LAD technology, the approval of the TSX Venture Exchange to the transaction and the issuance of shares and Medallion’s future REE production approach. Since forward-looking statements address future events and conditions, by their very nature, they involve inherent risks and uncertainties, including the risks related to market conditions and regulatory approval and other risks outlined in the company’s management discussions and analysis of financial results. Actual results in each case could differ materially from those currently anticipated in these statements. These forward- looking statements are based on a number of assumptions which may prove to be incorrect including, but not limited, the future potential of the LAD technology and the TSX Venture Exchange approving the transaction and the issuance of shares. In addition, in order to proceed with Medallion’s plans, additional funding will be necessary and, depending on market conditions, this funding may not be forthcoming on a schedule or on terms that facilitate Medallion’s plans. These forward-looking statements are made as of the date of this press release, and, other than as required by applicable securities laws, Medallion disclaims any intent or obligation to update publicly any forward-looking statements, whether as a result of new information, future events or results or otherwise

about us | propel industries

Propel Industries provides innovative, technologically-sound and cost-effective solutions to the crushing and screening industry. We are the strategic business division of the 57-year-old Coimbatore-based AV Group

Our product line includes a comprehensive range of Jaw crushers, Cone crushers, Vertical Shaft Impactors (VSI), Feeders, Vibrating Screens, Sand Washers and Air Classifiers. The nationwide presence of the company’s sales and service network and round-the-clock customer support make us the ultimate choice of customers

Propel is the market leader in manufacture of M-sand plants in India. M- sand is the best alternative to river sand, mining of which causes river bed erosion , increases risk of flooding and many other environmental hazards. Propel is deeply committed to provide innovative solutions to produce best quality M-sand at the cheapest price.

To be a world-class conglomerate requires commitment, perseverance and quality-rich delivery to customers. Our steadfast focus in this direction has helped us to achieve many awards, certifications and accolades

about us | propel industries

Mr. V. Senthilkumar, Managing Director of Propel Industries and has more than 30 years experience in the Engineering industry. He is a visionary leader who has great passion for design. He strives to consistently improve work management systems, quality & safety standards and places great emphasis on team building. He has received the Business Leader of Asia award from Economic Times. 

We maintain perfect quality records and we never compromise on the impeccable quality aspects of our equipment. We have an independent quality control team to ensure that only high quality equipments are delivered to our customers

At Propel, we deploy innovative production processes strengthened by cutting-edge technologies. All the equipments are of international standards and we never compromise on the stringent quality standards of our equipment, processes and personnel

about us | propel industries

Rich Heritage. We are carrying on the rich tradition and business culture of AV group at Propel Industries. Our consistent evolution helps us to offer topnotch equipment as well as tools, services and technical solutions for mining and construction industries.

sand filter - an overview | sciencedirect topics

RSFs are not typically described as biological filters, or the biological processes are regarded as limited and secondary to the straining processes. Some studies have suggested that a combination with preozonation is required for an RSF to evolve into a biological rapid sand filter (BSF) [5]. However, it is most likely that RSF will be colonized with a microbial community, irrespective of the presence of a preceding oxidation step. The operational conditions to some extent dictate the biological processes in the filters. For example, the high filtration rate (low contact time) implies that less time is available for any biological process. As a result, such a filter favors the development of bacterial species that grow rapidly on easily available BOM, while complex organic compounds may not be removed biologically. The small sand grains provide a tremendous surface area for colonization. Biomass concentrations in RSF can vary considerably, ranging in one broad study between 20 and 2000 ng ATP cm−3 (Table 1). However, knowledge about the required biomass start-up times and presence of specific microbial communities in RSF systems is severely limited. The regular backwashing of RSF has three obvious implications for the filter biology: (1) no permanent vertical biomass gradient develops in the filter, meaning a rather homogeneous distribution of the biomass concentration and composition in the filters; (2) no real schmutzdecke develops, which results in limited retention capabilities for pathogens; and (3) the concentration of protozoa will be limited if the backwash cycle is faster than the reproductive cycle of the organisms [11]. Backwashing might reduce the biomass concentration in RSFs by as much as 20%, although the impact of backwashing on filter performance is not regarded as significant [7]

Sand filters are widely used in water purification and remove suspended matter by a completely different mechanism. Instead of the water passing through small orifices through which particles cannot pass, it runs through a bed of filter medium, typically 0.75 mm sand 750 mm deep. The orifices between such sand particles are relatively large, but dirt is adsorbed onto the large surface area presented by the medium. The pressure loss rises as the dirt builds up and the filter must be cleaned when it reaches about 3 m WC, otherwise the dirt can be pushed right through the filter

sand filter - an overview | sciencedirect topics

Filter backwashing normally needs low-pressure compressed air and a flow of filtered water about ten times the rated filter throughput. These backwashing arrangements are critical, and providing the large flow of backwash water, as well as drainage for its disposal, can often create difficulties. Given good backwash arrangements, and on a water low in suspended matter, sand filters are simple, reliable, cheap and have low operating costs

Sand filters vary in sophistication. A simple filter will remove most particles down to 5 μm. Multi-media filters which use sand and anthracite, and possibly a third medium, in discrete layers, can yield very efficient filtration down to 2 μm. Granular activated carbon can be used instead of sand to add some measure of organic removal to the filtration process. The quality produced by any filter depends largely on the efficiency of the backwash. Sand filters in some form provide a satisfactory solution for the majority of water-filtration problems

Sand filters are typically designed to give 24 hrs or more between backwashing. Trouble follows quickly if for some reason filter runs become short, because then the filtered water used for backwashing uses up a large percentage of the filtered water and the net output of water falls sharply

sand filter - an overview | sciencedirect topics

Rapid sand filter (RSF) evolved at end of 19th century in the United States of America. It became popular in 1920s because it required lesser necessary facilities with respect to SSF. Unlike slow sand filters, RSF involves only physical process because of absence of biological layer (biofilm) on filter media. Coarse-grained sand and gravels efficiently remove suspended solid by straining and adsorption. RSF must be aided with pretreatment (sedimentation and flocculation) and posttreatment (disinfection) steps to remove pathogens and prevent fouling. It requires lesser area for construction as compared to SSF for treatment of unit volume of water. RSF is constructed in a rectangular tank usually made up of concrete. Three to five layers of graded gravel are installed at the bottom of tank over a network of drainage pipes placed on the floor. Filter media that is coarse sand with a diameter ranging from 0.4 to 0.6 mm is filled over gravel layer. As coarse sand provides larger void as compared with fine sand of SSF, RSF achieves a higher rate of filtration. Gravel layer prevents sand from being drained out during filtration. Also, it facilitates even distribution of water through filtration media during backwash. Top of the RSF is either open for supernatant water (gravity filter) or closed (pressure filter) (O'Connor and O'Connor, 2002)

RSF is not as good as SSF for pathogen removal because pore size of medium is larger and it lacks biofilm. However, RSF removes suspended solid along with biological particles. Prominent biological particles retained by RSF include algal microcolonies (5–20 μm), protozoan cysts (3–10 μm), bacterial cells (0.2–2 μm), and virus particles (0.01–0.1 μm). Rose (1988) reported removal of Giardia and Cryptosporidium. The deposition of microorganisms and other particles in filters depends on transportation efficiency and retention in surface pore of filter media. Theoretical model for collection of microorganism on anthracite and sand media suggested lowest removal of individual bacterial cells in comparison to free suspended viruses, protozoa, or microbial aggregates and other particulates. In fact, removal of nanoscale particles such as viruses is governed by diffusion while protozoans are removed by cumulative effect of sedimentation and interception. Removal mechanism for suspended bacterial cells involves diffusion, differential sedimentation, and interception. Effective grain size is an important factor of collection of viruses and bacteria on media surface, whereas removal of protozoa and microbial aggregates is chiefly influenced by hydraulic loading rates. Therefore, the model suggests that smaller grain size media is major factor for removal of freely suspended viruses and other nanosized particles, and lower hydraulic loading rates would be improving removal efficacy for protozoan pathogens. Other factors that were not included in the model such as net surface charge on the filter media and microbial surfaces; media properties (type, size, and depth); hydraulic loading rates; upstream chemical use (oxidants and/or coagulants); water quality variables; flow control; and backwashing and postbackwashing practices may also significantly influence pathogen removal efficiency of filter media. Additional factors such as pH, ionic strength, temperature of effluent; concentration, molecular size, and charge density of dissolved organics; and particle characteristics influence removal efficiency. For example, high ionic strength reduces the electric double layer around microorganisms and filter media, thereby increasing attachment efficiency between the two. Backwashing of filter media in RSF may release pathogen from RSF granules. Pathogen removal in water treatment system was observed in many experimental studies. Removal of Giardia cysts and Cryptosporidium oocysts was shown to be affected by extent of filter maturation and application of coagulant chemicals. Treatment of coagulated primary effluent through RSF demonstrated approximately 1 log unit decrease in fecal coliform, pathogenic bacteria (Salmonella and Pseudomonas aeruginosa) and enteroviruses, 50%–80% of protozoan (Giardia and Entamoeba histolytica) cysts, and 90%–99% of helminth ova (Adelman et al., 2012; Hoslett et al., 2018; Jiménez et al., 2009)

Typical of this class is the rotary vacuum drum filter shown in Figs. 26.7 and 26.8. Other types include cross-flow membrane filtration, “DynaSand®”-type continuous sand filters, as shown in Fig. 26.6, and rotary vacuum disk filters

sand filter - an overview | sciencedirect topics

Continuous sand filters (see Fig. 26.6) are gravity-driven depth filters with countercurrent flows of filter sand and dirty fluid. Dirty fluid is introduced into the bottom of the structure, and clean fluid is collected at the top. An airlift pump carries dirty sand from the bottom of the structure to a pneumatic sand washer at the top

The principle of operation makes for a tall thin structure, and the location of the sand washer and instrumentation require maintenance access to the top of the structure. There is consequently a platform with a handrail covering most of the top of the vessel, accessed by a hooped ladder

Sand filters use either graded sand (fine to coarse or heterogeneous) or coarse monograde sand (uniform size or homogeneous). No single media specification (size and depth) can be applied universally for all waters; the choice depends on the water quality and upstream processes, filtered water quality objectives, cleaning method, filtration rate and length of filter runs. In graded sand filters the bed depth typically comprises 0.7 m of 0.6–1.18 mm fine sand (effective size 0.63–0.85 mm), 0.1 m of 1.18–2.8 mm coarse sand, 0.1 m of 2.36–4.75 mm fine gravel and 0.15 m of 6.7–13.2 mm coarse gravel. The effective size, d10, is defined as the size of aperture through which 10% by weight of sand passes. For applications requiring a finer sand, the two upper layers are changed to 0.7 m of 0.5–1.0 mm sand (d10=0.54–0.71 mm) and 0.1 m of 1.0–2.0 mm coarse sand, the gravel layers remaining the same. Depending on the slot size of the underlying filter nozzles, the bottom gravel layer can be omitted and replaced by more of the next layer. The homogeneous sand filter has a 0.9–1 m deep bed of typically 0.85–1.7 mm sand (d10=0.9 mm) placed on a 50 mm layer of 4–8 mm or 75 mm of 6.7–13.2 mm gravel. Homogeneous sand of effective size up to 1.3 mm has also been used. The stated size ranges for sand and gravel are generally 5 and 95 percentiles. For estimating the sand depth some employ the rule that the depth of sand should be ≥1000 times its effective size (Kawamura, 2000). Pilot studies may be done to confirm sand depth, for large plants in particular

sand filter - an overview | sciencedirect topics

Some filter plant designers use the term ‘hydraulic size’ in place of effective size (Stevenson, 1994). This is defined as the size particles would have to be, if all were the same size, in order to match the surface area of a sample covering a range of sizes. For media with size range 1:2, the hydraulic size is approximately 1.36× the lower size in the range; e.g. for 0.85–1.7 mm sand the hydraulic size is 1.16 mm

Other filter media such as anthracite (Section 9.7), granular activated carbon (GAC; Section 9.9), garnet, pumice (Farizoglu, 2003), expanded clay particles and glass are also used in filtration applications. Garnet is a dense (s.g. 3.8–4.2) medium which is used as the bottom layer of multimedia filters containing anthracite and sand. It occupies about 15% of the bed depth and the effective size could be as low as 0.35 mm; being dense, it requires about three times the wash rate as anthracite to give the same bed expansion. Pumice and expanded clay are porous media and could be used in biological filtration (Section 10.28). Glass is a suitable filter medium of similar specific gravity to sand

where d60 is the size of aperture through which 60% of sand passes. UC values should be less than 1.6 and usually lie between 1.3 and 1.5. Lower UC values would make the medium costly as a high proportion of fine and coarse medium is discarded and higher values would reduce the voidage. Typically sand has a voidage of 37–40%, defined as: 100×(particle density−bulk density)/particle density. Loss in weight on ignition at 450°C should be <2% and the loss in weight on acid washing (20% v/v hydrochloric acid for 24 hours at 20°C) should be <2%. The sand should be tested for friability (BW, 1996) to ensure that washing operations do not produce fines

sand filter - an overview | sciencedirect topics

Rapid sand filters are divided into two main types: (1) gravity filters and (2) pressure filters. The principles of the two types of filters are identical. The pressure filter is operated at elevated pressures, thus prolonging the filter cycle and/or increasing the rate of flow of water through the filter. Gravity filters are commonly operated at 2 GPM/sq ft*, whereas pressure filters are operated at 3 GPM/sq ft and higher

The rapid sand filter is operated with clarification ahead of the filter. This step reduces the load on the filter, allowing longer filter runs and high-quality effluent at higher flow rates. Rapid sand filters have a layer of sand on layers of graded gravel and do not utilize a “Schmutzdecke” layer for the filtration action. Instead, the particulate matter is adsorbed on the sand in the layers below the surface. A considerable amount of support for the adsorption of solids (causing turbidity) as the predominant removal mechanism of rapids and filters was gained from the report of O'Melia and Crapps (1964) in their study on the chemical aspects of filtration

Rapid sand filters are customarily operated with sand on top of a graded gravel bed. A considerable amount of interest, however, has been shown in some areas in the use of sized coal in place of sand. Coal has the advantage of lower density, occupying greater volume per unit weight and, more important, requiring lower velocity of the backwash water to suspend the coal bed during the washing or scrubbing cycle. Coal, however, is soft and abrades rapidly with reduction in particle size. This results in losses during the backwash cycle and, consequently, coal replacement is much more frequent than that of sand

sand filter - an overview | sciencedirect topics

A skid-mounted bank of three high-rate rapid sand filters ready for shipment to the field is presented in Figure 7.7. Figure 7.8 is a cutaway drawing of a high-rate rapid sand filter showing the internals and the media. Figure 7.9 shows the inlet distributor, whereas Figure 7.10 shows the bottom drain collector for a high-rate rapid sand filter. The openings are spaced to obtain an equal flow through each

The sand filter designs use either graded sand (fine to coarse or heterogeneous) or coarse monograde sand (uniform size or homogeneous). There is no single media specification (size and depth) that can be applied universally for all waters. The choice depends on the water quality and upstream processes, filtered water quality objectives, cleaning method, filtration rate and length of filter runs. In graded sand filters the bed depth typically comprises 0.7 m of 0.6–1.18 mm fine sand (effective size 0.75 mm), 0.1 m of 1.18–2.8 mm coarse sand, 0.1 m of 2.36–4.75 mm fine gravel and 0.15 m of 6.7–13.2 mm coarse gravel. For applications requiring a finer sand the two upper layers are changed to 0.7 m of 0.5–1.0 mm sand (effective size 0.55 mm) and 0.1 m of 1.0–2.0 mm coarse sand, the gravel layers remaining the same. Effective size = size of aperture through which 10% by weight of sand passes (D10). Depending on the slot size of the nozzles the bottom gravel layer can be omitted and replaced by more of the adjoining media. The homogeneous sand filter has a 0.9–1 m deep bed and typically of 0.85–1.7 mm of sand (effective size 0.9 mm) placed on a 50 mm layer of 4–8 mm or 75 mm of 6.7–13.2 mm gravel. Homogeneous sand of effective size up to 1.3 mm has also been used. The stated size ranges for sand and gravel are generally 5 and 95 percentiles. For estimating the sand depth some employ the rule that the depth of sand should be ≥1000 times its effective size (Kawamura, 2000). Some filter plant designers use the term ‘hydraulic size’ in place of effective size (Stevenson, 1994). It is defined as the size particles would have to be, if all were the same size, in order to match the surface area of a sample covering a range of sizes. For media with size range 1:2 hydraulic size is approximately 1.36 × the lower size in the range, for example for 0.85–1.7 mm sand it is 1.16 mm

Other filter media such as anthracite (Section 8.6), granular activated carbon (Section 8.8), garnet, pumice (Farizoglu, 2003), expanded clay or glass are used in filtration application. Garnet is a dense (s.g. 3.8–4.2) medium which is used as the bottom layer of multimedia filters containing anthracite and sand. It occupies about 15% of the bed depth and the effective size could be as low as 0.35 mm. Being dense, it requires about 3 times the wash rate as anthracite to give the same bed expansion. Pumice and expanded clay are porous media and could be used in biological filtration (Sections 10.12 and 10.29). Glass is a suitable filter medium of similar specific gravity to sand

sand filter - an overview | sciencedirect topics

The sand should be of the quartz grade with a specific gravity in the range 2.6–2.7. The uniformity coefficient (UC) should be less than 1.6 and usually lies between 1.3 and 1.5. Bulk density is about 1.56 g/cc

where D60 is the size of aperture through which 60% of sand passes and D10 is the size of aperture through which 10% of sand passes. Lower UC values would make the medium costly as a high proportion of fine and coarse medium is discarded and higher values would reduce the voidage. Typically sand has a voidage of 37–40%. Voidage = 100 × (particle density—bulk density)/particle density. Loss in weight on ignition at 450°C should be <2% and the loss in weight on acid washing (20%undefinedvv hydrochloric acid for 24 hours at 20°C) should be <2%. The sand should not be too friable to ensure that washing operations do not produce fines. It should therefore be tested for friability (BW, 1996)

Pressure sand filters (PSF) are used in many industrial applications including a DM plant and often are popularly termed rapid sand bed filters. APSF consists of a pressure vessel that is normally vertical or horizontal, in rare occasions, depending on the layout of the plant. The filter vessels are generally of welded mild steel construction lined with rubber/epoxy. A minimum of 50% freeboard is provided over the filtering bed depth to enable efficient backwash

sand filter - an overview | sciencedirect topics

Graded silica quartz sand and anthracite supported by layers of graded underbed, consisting of pebbles and gravels, are provided with a water inlet at the top. Incoming water is distributed uniformly throughout the cross-section of the filter to ensure that there are no preferred fluid paths where the sand may be washed away and jeopardize filter action. The bottom drainage system is kept to collect filtered water

The selection of the sand’s grain size is important because smaller sand grains provide an increased surface area and, consequently, more decontamination at the water outlet that, on the other hand, demands extra pumping energy to drive the fluid through the bed. In an attempt at a compromise, grain sizes are generally selected in the range 0.5 to 1.50 mm. A sand bed depth of ∼0.5 to 2.0 m is recommended regardless of the application of which the ratio of quartz sand and anthracite is ∼7 to 50

Raw water flows downward through the filter bed and the suspended matter is retained on the sand’s surface and between the sand grains immediately below the surface. Rapid-pressure sand bed filters are typically operated with a feed pressure of 1 to 4 kg/cm2. The differential pressure (DP) across a clean sand bed usually is insignificantly low. The DP gradually builds up for a given flow rate as particulate solids are captured in the bed; this may not be uniform with depth. For obvious reasons, buildup would be more at the higher level with the concentration gradient decaying rapidly

sand filter - an overview | sciencedirect topics

This type of filter captures particle sizes down to very small ones. In fact there is no true cutoff size below which particles would not be arrested. Interestingly, the shape of the characteristic curve of efficiency versus filter particle size is a U one with the highest rate of particle capture for the smallest and largest particles, with a plunge in between for mid-sized particles. When the pressure loss, or flow, is unacceptable, it is sensed by a pressure drop across the PSF of ∼0.5 kg/cm2. The filter is then taken out of service and cleaning of the filter is effected by flow reversal or the bed is backwashed or pressure-washed to remove the accumulated particles. Backwashing of pressure filters normally is done once every 24 hours while the system is online

During backwash, the sand becomes fluidized and the expansion in volume may go up to about 30%, which allows the sand grains to mix, and the particulate solids are driven off as they start rubbing together. The smaller particulate solids are then forced out with the backwash fluid. The fluidizing flow requirement is typically 5 to 30 m3/hr/m2 of filter bed area, depending on the depth of the bed, for a short period (i.e., for a few minutes only). The filter backwash fluid is taken to a common inlet chamber of raw water pumps. The backwashing process would cause sand loss though not significantly noticeable, thus requiring periodic top up of sand in the bed

To assist in cleaning the bed, the backwash operation is often preceded by air agitation through the under drain system. The process of air scouring agitates the sand with a scrubbing action, loosening the intercepted particles. After backwashing, the filter is ready to be put back into service. For a 500 MW TPS, the typical backwashing flow rate would be between 25 to 30 m3/hr/m2 of bed area and the air-flow rate would be 50 m3/hr/m2 of filter bed area

sand filter - an overview | sciencedirect topics

Conventional downflow sand filters are effective for solid–liquid separation at flow rates up to about 15 m3/h m2 of filter area, although higher rate downflow filters are available (depending upon input quality). With proper selection of filter media, gelatinous as well as granular suspended matter can be filtered out, without a rapid differential pressure build-up as pathways through the bed become blocked

The bed is cleaned by a reverse, upward flow of filtrate water, sufficient to expand and fluidize the granules of the bed. After sufficient cleaning, the bed particles settle back into place under the influence of gravity. If the particles are all of the same material (i.e. have the same density), then the largest ones will typically settle at the bottom of the bed and the smallest ones at the top. This is the wrong way around from a filtration point of view, which is best achieved under downflow conditions by having the largest pores (created by the largest particles) at the top of the bed, first meeting the incoming raw water

Typical filter media for the downflow filter consist of selected silica sands, and coal or anthracite, which are tough inert solids, and available in a range of particle sizes. One solution to the problem of optimizing the pore size profile in the bed is to use layers of different solids, with different densities. If the denser material also has the smallest particle size, then the layers will resettle after backwashing with the finest at the bottom and the coarsest on top

sand filter - an overview | sciencedirect topics

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