Jonathan Pensak Pensak Associates Belmont, MA

he 1993 world market for magnetic separation equip- ment and associated engineering support most likely exceeded $100 million, and the market should grow steadily at about 5 percenvyear during the remainder of the 199Os, approaching $150 million by the year 2000 (Figure 1). This growth is driven by a number of factors, including improved magnetic separation technology, including high-gradient magnetic separa-

tion (HGMS), rare-earth high-field permanent magnets, and superconducting magnets; the increased need for high-purity chemical feedstocks; and increased pressure (and funding) for environmentally "clean" methods of purifying material. The cur- rent focus on environmental applications for magnetic separation results from improved magnetic separation technology, more stringent environmental guidelines, and increased public concern over environmental issues.

Magnetic Separation Developments Magnetic separation, which has been used by industry since

the turn of the century, is accomplished by a number of tech- niques. Initially, the technology was limited to treating minerals that were very coarse and relatively strongly magnetic. In the

1960s, researchers developed HGMS, which extended the useof magnetic separation to fine, weakly magnetic parti-

cles. In the past 10 years, researchers have increased their under-standing of the basic principles underlying both high-gradient and traditional magnetic separation

technologies. The resulting technologi- cal advances have led to improved separators as well as to the discovery of many new applications, a number of which are environmental.

While magnetic separators can perform a variety of functions, in principle they are used for three distinct processes: e Magnetic filtration (such as treating

wastewater), in which magnetizable solids are removed from a liquid

it# Removal of more strongly magnetiz-

56 The National Environmental Journal March J April 1994

Howeuer; strictly 04 the technological kind.

Although Ducon has been in business Pollution Control & Waste exceed the latest EPA,

years most of our models for Air technological advances to meet or

MODEL #

E-6

UNIFLOW'"

CAD DU-VOC

A-1 1

WI-21 CAT

/

~ O D E L T Y P ~ 1 Wet Electrostatic

Medium Energy D h a m i c Wet Scrubber Flue Gas Desulfurization Absorber Pulse-Air Baghouse VOC Recovery System Activated Carbon Adsorber Hydrofilter High Efficiency Cyclone Waste Incinerator Chemical Absorption Tower

INDUSTRIES SERVED:

Chemical, Pulp & Paper, Steel, Coal, Petrochemical, Food, Fertilizer, Detergent, Mining, & Industrial Boilers

SALES REPRESENTATIVES IN PRINCIE 'i

DUCON ENVIRONMENTAL SYSTEMS, INC. 110 BI-COUNTY BLVD., FARMINGDALE, NY 11735 USA TEL: (516) 420-4900 800-394-4990 FAX: (516) 420-4985 REGIONAL OFFICES WEST COAST: 7505 Jerez Court, Suite A, Carlsbad, CA 92009

Tel: (619) 753-4524 Fax: (619) 753-0329 ATLANTA: 1881 Murdock Rd., Marietta, GA 30062

Tel: (404) 977-1090 Fax: (404) 977-1190 .E CITIES LICENSEES THROUGHOUT THE WORLD 0 COPYRIGHT 1992 DUCON ENVIRONMENTAL SYSTEMS, INC.

CIRCLE 254 ON CARD FOR FREE INFO.

', 1

{ \

able particles from a mixture with less strongly magnetizable particles (such as cleaning coal) Concentration of valuable, more strongly magnetizable particles from a mixture with less strongly magneti- zable particles (such as recovering gold from tailings) For each of the above functions, a

magnetic field is necessary to either attract or deflect particles. For processes involving ferromagnetic par- ticles, field strengths of about 1,000 gauss (1 tesla, or 1 T) are required; for collecting paramagnetic particles, high field strengths of 1 to 5 T are needed.

Most of the recent efforts at improving magnetic separation design have been directed at cheaper and more efficient techniques for producing a high-intensity magnetic field, such as the development of rare-earth permanent magnets and superconducting magnetic separation systems. Rare-earth drum and rare-earth roll magnetic separators, which are capa- ble of generating field intensities up to 2.0 T (an order of magnitude greater than that of conventional permanent mag- nets), have been found to be very effec- tive in treating relatively coarse particle streams. (Permanent magnets, which provide a low-cost magnetic field with essentially an infinite lifetime, are suit- able for use in hostile environments as well as bench-scale laboratory settings.)

Superconducting magnetic separation systems, which offer a number advan- tages over conventional resistive or per- manent magnet systems, have contributed to the expansion of magnetic separation into new applications. Super- conducting systems can produce field strengths greater than those of conven- tional systems, can produce high mag-

netic induction in a large volume at low energy consumption, and can be made physically smaller and lighter than com- parable iron-clad devices. To date, the reduced operating cost of superconduct- ing systems (because of lower energy consumption) has been the key reason for investment in the systems. In the future, we expect that the ability of super- conducting magnets to produce extreme- ly high magnetic fields will become increasingly important, especially in envi- ronmental applications such as coal and solid waste cleaning that require high- intensity fields to be successful. Table 1 summarizes the characteristics of repre- sentative superconducting separators.

Elementary design improvements can be traced to the increased attention this field has received from many different industries that work with advanced materials and with exacting specifica- tions. These industries innately require high-purity feedstock materials for the manufacture of ceramic components, insulators, substrates, refractories, elec- trical components, specialty glasses, optical fibers, and other products.

Applications Magnetic separation offers solutions to

a number of complex problems encoun- tered in mining, chemical, biochemical, nuclear, and other industries, although the stage of development of magnetic sepa- ration equipment varies widely (Table 2). Most often, this technology is used in the production phase of industrial processes (e.g., to concentrate a mineral), but mag- netic separation is also used to treat solid wastes, wastewaters, and waste gases, as well as to manage general problems of environmental protection.

Magnetic separation can be a cost-

effective solution to many environmental problems, too, including cleaning conta- minated water, treating municipal and industrial wastewater, removing sulfur from coal, remediating soil, and separat- ing nuclear isotopes from radioactive waste spills. In addition to these applica- tions, which relate directly to the envi- ronment, magnetic separation finds additional applications in resource con- servation, another activity receiving increased public attention. For example, the steady depletion of high-grade min- eral deposits worldwide is necessitating more combined and more complete material processing, as well as the recov- ery of valuable minerals from waste sources. Magnetic separation provides a solution that is both resource-conserving and ecologically pure.

Biomagnetic Separation. Biomag- netic separation uses microorganisms that ingest ion species to accumulate enough metallic material for removal by HGMS. This process could have appli- cations in mineral processing, the treat- ment of effluents from the nuclear industry, and the recovery of precious metals in other industries. Biomagnetic separation offers the advantage of removing metal ions from a solution with high efficiency, allowing the collec- tion of these materials in a highly con- centrated material form.

Coal Purification. Magnetic separa- tion is a promising technology for the removal of sulfur and ash from coal. Stringent environmental standards are being implemented on a worldwide scale to reduce the emission levels of sulfur dioxide and ash particles from coal-burn- ing facilities. Coals generally contain 1 to

The National Environmental Journal March/AprillYY4 57

5 percent sulfur, of which one-third is car- bonaceous (organic) and two-thirds is mineral (pyrite). Methods proposed for coal purification range from froth flotation to electrostatic separation, and include HGMS. Because the dewatering of coal is a difficult and expensive process, the innate ability of magnetic separation to work dry offers a big advantage for the desulfurization of pulverized coal.

Coolant Treatment. In power plants

- both conventional and nuclear - cor- rosion products in the primary coolant (generally fine, predominantly ferromag- netic particulates) can reduce heat-trans- fer efficiencies and cause fluid-flow problems: in nuclear power plants, they can also become radioactive. HGMS is presently used to remove these particu- lates at a number of conventional power plants, and has been shown to be theo- retically effective in nuclear facilities.

I The most complete line of 1 1 solvent recovery equipment. FLAIR Environmental Products 4647 S.W. 40th Ave. Ocala, Florida 34474 Phone: 904/237-1220 FAX: 904/854-1402

CIRCLE 255 ON CARD FOR FREE INFO.

Fly Ash Beneficiation. The treatment of fly ash from pulverized coal power plants for the recovery of constituent met- als has been proposed by many industry participants as an alternative to disposal. Treatment and subsequent recovery of metals would conserve natural resources and produce many valuable minerals, including aluminum, iron, and titanium. Although the percentages of these metals in fly ash are low, the large amounts of fly ash produced in the world make it poten- tially valuable. Magnetic separation has proved quite effective in removing iron ore.

Gas Filtration. Steelmaking processes produce large emissions of fumes con- taining substantial amounts of iron-bear- ing dust particles that must be removed before the gas is discharged into the atmosphere. HGMS has been shown in pilot plants to be a potentially efficient and economical method for emission control of dust from basic oxygen furnaces and possibly from electric-arc furnaces.

Magnetic Ore Purification. Magnetic separation is an established technique for the beneficiation of strongly magnet- ic ores and for the removal of ferromag- netic impurities from mixtures. The advent of HGMS, however, has extend- ed the use of magnetic separation to weakly magnetic ore, to the advantage of many branches of the mining industry that were unable to use it in the past. In fact, even though mineral treatment is the oldest application of magnetic sepa- ration, its large-scale use has not been realized because cost-effective, versatile magnetic separation has not been avail- able, and because the fundamental prin- ciples of HGMS were not sufficiently understood by the mining industry. Mag- netic separation can be used for the treatment of many different minerals, including iron, manganese, tin, tungsten, copper, lead, and gold. It can also be used to recover minerals from beach sands and solid wastes.

Microorganism Separation. HGMS has been used in biotechnology applica- tions to remove viruses, bacteria, algae, and red-tide plankton from waste streams. The technology is effective in biotechnology on nonmagnetic particu- lates, such as microorganisms, through the process of “seeding.” In this tech- nique, fine, submicron magnetic seed particles introduced into solution adhere to the target organism’s surface, making them susceptible to separation. An alter-

58 The National Environmental Journal March/Aprill994

native technique uses larger magnetic particles, which attract target organisms to their surface. There is great potential for HGMS in this area, especially in the final cleanup and isolation of proprietary or hazardous organisms.

Nuclear Fuel Processing. As shown by pilot projects conducted by the U.S. Department of Energy, HGMS is effec- tive in reprocessing spent irradiated fuel from nuclear reactors. Efficiencies of concentrating insoluble fission products with HGMS are comparable to those from centrifugation, which is presently the method of choice.

Recyclables Processing. Tradition- ally, eddy-current separators and elec- trostatic separators have been used to separate aluminum from plastic in this labor-intensive processing of commin- gled recyclables. Recently, however, the magnetic field strengths of conventional magnetic separators have become strong enough to induce large enough flocs in metal particles for practical application in the scrap metal industry.

Wastewater Treatment. Large amounts of wastewater in the steel indus-

try contain fine magnetic particles (it gen- erally requires more than 25,000 gallons of water to produce 1 ton of steel). HGMS and the newer wet high-intensity magnetic separation have demonstrated the same efficiency as traditional sepa- ration methods (such as sedimentation and flocculation), but at substantially higher flow rates (3 to 10 times greater).

Water Filtration. The use of mag- netic separation for the filtration of river water has been studied using the mag- netic seeding technique. Adding mag- netic particles and coagulants to a stream creates flocs of impurities mixed with the magnetic particles. In combination with HGMS or new perma- nent magnet systems, this form of seeding has been shown to be effec- tive at removing impurities from streams and rivers.

Other Applications. Emerging appli- cations of HGMS include purification of feedstock materials used in manufactur- ing many new materials, including alloys, electrical components, grinding and pol- ishing compounds, insulators, optical fibers, refractories, specialty ceramic

for a low cost lagoon system If you're upgrading a lagoon system or constructing a new one, use the Bio-Separator floating baffle-the most practical and economic approach for lagoon

standards and the

of the cost of conventional activated sludge systems. The Bio-Separator also maintains quality and requires little service. Bio-Separator

For complete information,Call Bill Watkins at 803 794-2543, ThermaFab, Inc. 200 Rich Lex Drive, Lexington,SC 29072, 1-800-762-1 712

-, by ThermaFab

Think $AFE.T.WAY to store & pour

hazardous material.

CIRCLE 257 ON CARD

NFPA 30 CABNETS lollow or insulated doul falls exceed NFPA 30 onstruction - I' thick institutional luality walls with rabbet- id doors& optional leak- roof sump. Up to 200% iecondaiy containment. ? o h convey material

3

I iandlingllo&.

RCLE 258 ON CARD-

*Pallet design allows easy portability for cement as needed.

foundation sized

*Type I Non-combustible patented high security 12 GA

Investment Value of Institutional Quality

A Good Deal Better/ Your Best Bul

$AFE.T.WAAY MANUFACTURING, INC.

P.O. Box 288 Rockton, IL 61072 P.O. Box 688 * Youngstown, OH 4450

CIRCLE 256 ON CARD FOR FREE INFO.

The National Environmental Journal March/Aprill994

Toll-lree: 1-800-222-2600 Ext. 245

59

A Sentry symbolizes reliability, hard work, long hours and safety. Now you can have a sentry work for you- the Sentry Gas Monitoring System! H A complete gas risk management

system, not just an alarm system H MODBUS@ communication interface H Combustible gas, oxygen

deficiency and toxic gas sensors H Real-time and historical data H Analog and printer output H One-person auto-adjusting

calibration and self-diagnostics H FM approved You can trust Sentry to man its post and reliably monitor hazardous gas conditions. No other system provides you with all of these benefits. Yet Sentry’s price is lower thansystems with less capability. Let Sierra Monitor be your partner in managing hazardous gas risk throughout your plant. As a major supplier of gas detection systems for the military and industry, we have the technical expertise to meet your exact needs. Call 408-262-661 1 to put a Sentry to work for YOU!

S M ! K s i e r r a monitor corporation 1991 Tarob Ct., Milpitas, CA 95035 Phone 408-262-661 1 Fax 408-262-9042

Sensor systems and gas detection

Others 1 % Lumber and wood products 2% 1 I Electronic eauioment 3%

minerals (excluding fuel) 4% sporation equipment 4%

Paper/paper products 6%

Bituminous coal and

bricated metal products 7%

achinery (excluding electrical) 7% Primary metals 8%

components, specialty glasses, and substrates. In addition, HGMS has been proposed for the removal of contaminants from oil and other hydrocarbons.

Competitive Techniques Many of the advances in magnetic separation design have

been driven by the need to compete with other processes in these application>_&presentative competitive technologies for environmental applications include the following.

Coal Cleaning. The use of a magnetic cyclone has been explored by the US. DOE and by private research groups for separating magnetite in coal cleaning. Although the cyclone does not require high fields or feed pressures, it does not appear to be effective on very fine particles. Other proposed techniques would use bacteria to leach impurities such as pyrite from coal, but these techniques have not been used because they are too slow and they do not reduce the coal ash content. Chemical techniques exist for separating coal and pyrite, but they tend to be expensive and often produce toxic waste products.

Gas Filtration. An electrostatic agglomerator theoretically could be effective at controlling fine particles. After successful agglom- eration, particles would be removed by conventional equipment, such as a cyclone, filters, or an electrostatic precipitator. Another potential technique for cleaning gas emissions is an electroflu- idized bed, which has been shown to be theoretically capable of a 90 percent efficiency in removing submicron particles.

Solid Waste Cleanup. For solid wastes, no technique exists that is as effective as magnetic separation on such a large variety of materials. The overall cost of magnetic sepa- ration of solid wastes compares favorably with that of tradi- tional disposal methods when the material being separated is toxic (e.g., certain heavy metals).

Market Projections Although the market for the preliminary processing of miner-

als (e.g., classifying, separating, concentrating, and cleaning) has declined recently, this decline can be attributed to the gen- eral global recession and the depressed state of the mining industry and forecast that the market for magnetic separators will grow at 5 percentlyear for the near term. Applications that will grow most rapidly over the next five years include coal sep- aration, nuclear fuel processing, wastewater cleanup (industrial and municipal), and traditional mineral applications. Market

CIRCLE 261 ON CARD FOR FREE INFO. 60 March/Aprill994

\

potential for wastewater treatment is greatest in Europe because water quality environmen- tal regulations there are more stringent than in the United States.

The superconducting segment of the market has been somewhat flat after the initial suc- cesses of some large units, but as acceptance of the technology improves and the reliability of existing units becomes more widely known, this segment of the market will increase dra- matically. Flare-earth permanent magnet sys- tems will grow dramatically over the next decade. Machines are being developed that use these magnets and that compete favorably with the best resistive units available.

Magnetic separation is being used in an increasingly diverse range of industries (Fig- ure 2). A typical company selling magnetic separation equipment divides 85 percent of its sales among 20 different industry groups. There are only six major producers of mag- netic separation equipment worldwide, five U.S. firms and one British firm. These compa- nies rarely sell equipment “off the shelf”; rather, they provide engineering and technical advice to a client.

For free catalog 1-800-242-3910

716-424-2140 713-956-2833 714-955-3930 Rochester, NY Houston, TX Imine. CA

CIRCLE 263 ON CARD FOR FREE INFO.

We do. That’s who. And we’ve been making these machines since 1889.

EXTRUDERS FEEDERS WASTE CHOPPERS PUGMILLS and for mixing, reduce lumps to 2” fine chop filter cakes HIGH SHEAR MIXERS aqqlomeration and and feed uniformly and other soft. stickv for intimate mixina of densification of from very dry to . solids sludges, solids a i d waste materials sludge-consistency liquids

DISINTEGRATORS to crush and size soils, clays and other tough materials

J.C. STEELE & SONS, INC. P.O. Box 1834, Statesville, NC 28687, Tel: 704/872-3681, FAX: 704/878-0789

CIRCLE 262 ON CARD FOR FREE INFO.

Suresh D. Pillai, Ph.D. Environmental Science Program Texas A&M University Research Center El Paso, TX

lobally, there is an increasing demand for efficient drinking

water and wastewater treat- ment systems. In the United States, under the Surface Water Treatment Rule (S WTR), all community and non-commu- nity public water systems are required to provide disinfection to control the protozoan para- site Giardia lamblia, as well as enteric viruses and bacteria (Regli et al., 1991). To comply with these current regulations and with possible future requirements, water treatment providers must start using microbial pathogen detection methods that are specific, sen- sitive, rapid, and cost- effective.

Need for Better Detection Methods

Most of the methods currently used to detect specific and indicator bacteria rely on culture techniques that involve filtering samples through 0.45-pm membranes and incubating the mem- branes on culture media in Petri dishes to permit the growth of bacterial popu-

66 DNA:DNA hybridizations use specific genetic sequences as “probes” to detect nucleic acid sequences in a sample. 99 lations. Most of these methods require a minimum of 48 hours for complete verification of the results. The methods to detect protozoa such as Giardia sp. and Cryptosporidium sp. (which has caused major disease outbreaks in Wisconsin and othgr areas) and infec- tious viruses a

ments such as so water are in a “via

tially still cause infection

media due to variou factors (Roszak and C

detect specific organisms by initially increasing the numbers of specific nucleic acid sequences in the sample. The Polymerase Chain Reaction (PCR) is a patented gene amplification tech-

spread use and is finding increasing commercial applications in environmen- tal microbiology, clinical microbiology, and industrial microbiology.

Both the DNA:DNA hybridization methods and the PCR amplifications (when employed for detecting specific microorgy ims) are targeted to spe- cific ge e sequences present in the tar- get/Organisms. By circumventing the n$ed to culture the microorganisms on /media, not only has the speed of detec- tion been shortened to about 5 hours for the PCR technique, but the speci- ficity and the sensitivity have also been improved significantly. In addition, these methods have also been shown to detect the “non-viable” organisms, which is one of the major limitations of the present methodologies. Both the

nology that has already found wide- ~~

7 .

amplification and nucleic acid tech- \ niques can be used to detect specific viral, and protozoan species

less time than the con-

hycleic Acid DNkDNA ‘ Hybridization

\ hybridizations use specific genetic sequences as “probes” to detect specific nucleic acid sequences in a sample. Amplification techniques use specific genetic sequences as “primers” to

This method involves the use of a spe- cific genetic “probe” to detect comple- mentary sequences in the presence of a variety of other non-homologous seauences in a samDle. as shown in

# I

F i g k 1. The initial step is the binding of single-stranded nucleic acid target sequence@) to nylon or nitrocellulose membranes. The sequence-specific probe (isotopically or non-isotopically labeled) is then added, and in the pres- ence of appropriate buffer solutions, is allowed to hybridize to the target

tection