EP0410971A1 - Procede de traitement d'un terrain contamine - Google Patents

Procede de traitement d'un terrain contamine

Info

Publication number
EP0410971A1
EP0410971A1 EP19890902988 EP89902988A EP0410971A1 EP 0410971 A1 EP0410971 A1 EP 0410971A1 EP 19890902988 EP19890902988 EP 19890902988 EP 89902988 A EP89902988 A EP 89902988A EP 0410971 A1 EP0410971 A1 EP 0410971A1
Authority
EP
European Patent Office
Prior art keywords
soil
particles
flotation
settling
contaminated
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19890902988
Other languages
German (de)
English (en)
Inventor
George F. Bateson
Dennis D. Chilcote
Michael M. Martinson
Steven B. Valine
Adolfo R. Zambrano
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BioTrol Inc
Original Assignee
BioTrol Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by BioTrol Inc filed Critical BioTrol Inc
Publication of EP0410971A1 publication Critical patent/EP0410971A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
    • B09C1/00—Reclamation of contaminated soil
    • B09C1/02—Extraction using liquids, e.g. washing, leaching, flotation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03B—SEPARATING SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS
    • B03B9/00—General arrangement of separating plant, e.g. flow sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/02—Froth-flotation processes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/14—Flotation machines
    • B03D1/16—Flotation machines with impellers; Subaeration machines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/14—Flotation machines
    • B03D1/1406—Flotation machines with special arrangement of a plurality of flotation cells, e.g. positioning a flotation cell inside another
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
    • B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
    • B03D1/00—Flotation
    • B03D1/14—Flotation machines
    • B03D1/1443—Feed or discharge mechanisms for flotation tanks
    • B03D1/1475—Flotation tanks having means for discharging the pulp, e.g. as a bleed stream

Definitions

  • the present invention relates to soil purifi- cation and in particular to the purification of soil materials contaminated with organics.
  • a specific appli ⁇ cation of the present invention is for the treatment of soils contaminated with organic oils that contain penta- chlorophenol (PCP) . Such soils are typically found at dump sites from wood treatment plants.
  • PCP penta- chlorophenol
  • Waste materials from many industries comprise organic materials, often organic greases and oils. In some instances these waste oils include highly toxic chemicals therein.
  • a well-known example is the waste material from conventional wood treatment facilities.
  • a typical wood treatment facility wood is preserved by being soaked or dipped in a vat of oil that has a preservative therein.
  • a facility for the treatment of telephone poles, railroad ties, or the like may use large vats that contain an oil having pentachlorophenol (PCP) dissolved therein.
  • PCP pentachlorophenol
  • a typical treatment vat used for such processes contains an organic solution containing about five percent PCP.
  • Waste organics often containing a substantial amount of PCP, have often been dumped into a pit area located near the treatment facility. While this is par ⁇ ticularly disturbing with respect to current pollution control standards, it must be understood that such treatment facilities have operated for many decades with substantially little change in the overall soaking and/or treatment procedure. Thus, many sites exist which came into existence well before the more recently imposed pollution controls. The pollution problem is exacerbated by the nature of the industry. Very often a treatment facility was established, short term, near a location where a substantial amount of wood was milled, or treated wood was needed. After sufficient operation to accomodate the "local" need, the facility was closed and sometimes moved to a different location. Thus a plurality of abandoned dump sites exist throughout the country.
  • the contaminated organic materials may be leached, by groundwater, out of the immediate dump area, contaminating a widespread area. Since the organics often include a substantial amount of highly toxic materials therein, this leaching poses a substantial health and environmental hazard. It is noted that while the problem of pollu ⁇ tion from organics in soils has been described with respect to a specific industry involving wood treatment, the problem exists with respect to a variety of industries that have similarly generated organic wastes dumped into pits or the like. The wood treatment industry merely provides a well-known and notorious example, and one which often involves particularly hazardous PCPs.
  • Incineration on its own, has been a generally undesirable process. First it is energy inefficient, that is a large amount of energy is consumed in operating the incinerator at sufficient temperatures and for a sufficient length of time to lead to effective purification of the large volume of materials involved. Secondly, product gases and materials from the incinera- tion may be a problem. Further, the large amount of contaminated ash formed creates a disposal problem.
  • a second method of purifying contaminated soil is through the use of microbial action.
  • microbial purifica- tions have proved undesirable. While in the laboratory microbial action may be shown to capably detoxify material, in the field it is less efficacious.
  • temperature, moisture and oxygen control may be essen ⁇ tial, and difficult to achieve.
  • chemical concentrations may be found throughout a single dump site, and from site to site. Concentration variations generate unpredictability.
  • complete microbial detoxification of concentrated contaminants may take a fairly long period of time, and during that period of time further leaching from the dump site may occur.
  • soil variations and dump site environ ⁇ ment variations pose substantial hurdles to the effec ⁇ tive, predictable, action of microbes.
  • the objects of the present inven ⁇ tion are: to provide a method for the purifying treat ⁇ ment of soils that have been contaminated with organic materials; to provide such a method especially suited for application to the treatment of soils at dump sites from wood treatment facilities; to provide such a method suitable for the purification of soil materials con ⁇ taminated with oils containing PCP therein; to provide a preferred such method which involves the utilization and preferably the superposition of attrition and classifi ⁇ cation processes to yield substantial removal of con ⁇ taminating organic materials from solid soil particles; to provide a preferred such method which further involves a step of flotation separation to further remove contaminated organic material from association with soil material; to provide such a method which yields a concentrated waste material for disposal via conventional processes; and, to provide such a process: which is particularly flexible for use in association with a variety of sites; which is relatively simple to effect; which is comparatively cost effective; and, which is particularly well adapted for the proposed applications thereof.
  • the present invention concerns the utilization of attrition and classification processes to yield cleansing of contaminated soil, to remove contaminating organics such as PCP-contaminating oils therefrom.
  • An attrition process is a scrubbing step.
  • a slurry containing a high percent of solids is subjected to high intensity agitation.
  • high intensity agitation During such a process a high number of particle/particle con ⁇ tacts occur. This tends to break up the particles, which may be weakly agglomerated due to the con ⁇ taminating organics.
  • the particle/particle interactions also help scrub particle surfaces free of the organics.
  • a classification process is a particle size separation.
  • Typical classification processes include: size separations based on relative settling velocities in a fluid, such as water; filtration; and, screening.
  • Preferred classification processes for use in applica ⁇ tions of the present invention are those in which separation is based on relative settling velocities. These include: centrifugation; flocculation; cycloning; and use of spiral or screw classifiers. Separations with spiral or screw classifiers are particularly advan ⁇ tageous, at least because: they are effective, relati ⁇ vely inexpensive and easy to effect; and, they can be operated on relatively large scales, even with conven ⁇ tional equipment.
  • a classification process is practiced on a soil-containing slurry which has been subjected to an attrition process, substantial soil purification is achieved.
  • the classification process is superposed on the attrition process. That is, the classification process is preferably initiated before particles have had a chance to completely settle from the attrition step. In this manner, separation is effi ⁇ ciently conducted.
  • the classification is of the type involving relative settling velocities, removal of a fraction containing slower settling materials during the classification pro ⁇ cedure leads to substantial removal of contaminating organics.
  • Flotation is, in general, a process involving separation of materials based on relative hydrophobic tendencies. Flotation techniques are generally known, for other pur- poses, in various industries, including the mining industry and the pulp industry. They have also been utilized to accomplish liquid separations. It is a feature of certain embodiments of the present invention that flotation techniques have been found to be adap- table to the removal of organic contaminants from asso- ciation with soil, in an efficient and economic purification process.
  • a typical overall soil treatment process according to the present invention can be visualized as broken into several stages.
  • the soil is excavated from a contaminated site and it is appropriately screened or otherwise treated for the removal of bulk contaminating items, such as large pieces of wood, metal objects or the like.
  • the soil material may be sized to a par ⁇ ticular, preferred, size for further operation.
  • the preferred second stage involves the prac ⁇ tice of superposed attrition and classification pro ⁇ Deads as previously described.
  • the soil material is treated via flotation, for the removal of substantial amounts of remaining contaminating orga ⁇ nic materials from association with the soil.
  • the flo ⁇ tation process generally involves agitation of the soil 0 as a slurry or suspension, with bubbles of air passing therethrough. Hydrophobic contaminants, i.e.
  • the typi ⁇ cal organic oil/PCP comtaminants for example, generally migrate preferentially to the interface with the air bubbles, from the soil surface and/or aqueous suspen- 5 sion.
  • the organic materials may be bumped, rubbed or drawn off the soil and into the inter ⁇ face with the bubbles.
  • fine particles having a substantial amount of organics adsorbed or absorbed thereon, and from which scrubbing of organics may be
  • the cleansed soil may be returned to the pit area, or elsewhere, as desired. At this point overall contamination is relatively low,
  • Water typically involves use of large amounts of water.
  • Water for example, is used as a carrier throughout the process, is used to form slurries during attrition and classification, and is also found in the skimmed material from the floation process. This water becomes substantially contaminated with the contaminating organic materials removed from the soil. It is an advantage of the present invention that a substantial amount of recirculation of con ⁇ taminated or potentially contaminated water may be pro- vided. It is also envisioned that effective operation of processes according to the present invention will typically involve cooperation with water treatment pro ⁇ Grandes for substantial purification of the water used, allowing for re-cycling of water and/or discharge to secondary water treatment systems.
  • Fig. 1 is a schematic representation of an overall system for the treatment of soil according to the present invention.
  • Fig. 2 is a schematic representation of a flo ⁇ tation device for treating soil according to a step of the present invention.
  • the present invention is described herein for applications involving the treatment of soil and materials found at dump sites from wood treatment facilities. It will be understood, however, that the principles of the present invention are generally applicable to soils and similar materials contaminated with a variety of organics from a variety of processes. Thus the specific treatment described herein is to .be considered exemplary only.
  • excavated material from the dump site is physically treated so that it can be readily handled during the later purifi ⁇ cation washes and other steps. That is, any large unma ⁇ nageable materials such as large rocks, tree stumps, scrap metal or the like are removed.
  • the soil material is physically removed from the dump site, and is passed through a screening device, such as a grizzly. In this apparatus the bulk contaminating materials such as pole butts, large wood blocks, or the like are removed from the soil.
  • a screening device such as a grizzly.
  • the bulk contaminating materials such as pole butts, large wood blocks, or the like are removed from the soil.
  • organic dump sites are also used as dump sites for waste items such as old tires, unusable pieces of wood, machinery parts or the like.
  • soil material which passes through the grizzly includes a large amount of chunk or agglo- merated material, i.e. material stuck together in large clumps or clods. While concentrations may vary con ⁇ siderably, from a typical waste dump this soil material typically includes a pentachlorophenol (PCP) con- centration of about 100 to 2000 parts per million. This substantial concentration often results from a con ⁇ centration of oil and grease in the soil of about 0.1 to 1.0 percent by weight. The oil and grease may actually be adsorbed upon certain components of the soil, or it may simply be trapped in the clumps, or it may simply be associated with certain fractions in the soil from which separation is difficult.
  • PCP pentachlorophenol
  • PCP highly toxic contaminant
  • the soil material at this point of the process typically contains several basic components.
  • a substantial portion of the wood component is removable during a first stage pre-treatment process in several manners.
  • the soil material from the grizzly is conveyed into a conventional trommel or mill to substan- tially break up the clumps of dirt materials.
  • the material is sprayed with water, to facili ⁇ tate the breaking-up process and the removal of unde- sired components.
  • a typical, conventional, trommel application with a water spray yields material sized to no greater than about one-half inch.
  • the slurry or sludge from the trommel is then preferably passed or discharged onto a screen system, to further size the material downwardly.
  • a screening of 10-65 mesh is desirable. Multiple screening steps may be used. For example, a first screening to about 10 mesh, and a second screening to about 20 mesh, to preferably size the soil material to no greater than about 20 mesh, is generally effective. Further water may be added to facilitate the filtering process.
  • the total amount of water added during both the trommel and mesh screening processes is such as to result in about 10-60% solids, by weight, and preferably less than 50% solids.
  • the split between water addition in the trommel and during screening may be as necessary to facilitate the two pro ⁇ Waits. It will be understood that a variety of amounts of water may be used, the above merely generally repre ⁇ senting operable figures.
  • Fig. 1 is a schematic representation of a pro ⁇ cess according to the present invention. Although the following descriptions focus on the movement of soil materials, it is noted that the scheme depicted includes an advantageous system of water flow, making efficient use of contaminated water. Referring to Fig. 1, the reference numeral 10 generally designates stage 1 of the process.
  • Reference numeral 11 illustrates a step of loading contaminated soil into grizzly 12, for initial separation. Large contaminants, such as pole butts and the like, are removed at 13.
  • the material which passes through the grizzly 12, is conveyed into a trommel 14 and is broken therein.
  • Reference numeral 15 generally designates flow of water into the trommel, to provide for production of a slurry.
  • the slurry flow out of the trommel is designated by reference numeral 16.
  • This material is directed toward a screening system 18, pre ⁇ ferably comprising a 10 mesh screen 19 and a 20 mesh screen 20.
  • the slurry material is directed through the screen system 18, with aid of water provided as indi- cated at reference numeral 25.
  • fluid feeds 15 and 25 may be provided from a single source 26, with conventional valves or the like controlling rela ⁇ tive distribution of fluid into the trommel 14 and the filter system 18.
  • Large materials such as wood chips or the like removed from the filter system 18 are shown taken-off at reference numeral 30.
  • Stage 2 The Attrition and Classification Processes
  • the material removed from a physical screen such as system 18 may still be substantially clumped or agglomerated.
  • a typical soil material generally comprises numerous components including: still smaller pieces of wood material; clay components; silica sand; and, natural organic matter such as decomposing plant material or the like. Due in part to the presence of the oils and greases in the contaminants, this soil material may still be clumped into relatively hard glo ⁇ bules, preventing release of contaminants from between trapped inner particles.
  • the slurry of this material is concentrated substantially, in a cyclone or the like, to about 40-70% solids, or more, and is then broken up and scrubbed in an attrition step, such as in a pebble mill, attrition cell, or the like.
  • the slurry of solids is subjected to intense agitation. This suspends the solid particles, and causes a great deal of particle/particle bumping.
  • the bumping breaks up the agglomerates, resulting in suspended particles of a variety of sizes. Some of the contaminating organices are rubbed off of the particles, and float in the water.
  • a classification step is practiced after attrition, but before substantial settling, i.e., it is superposed on the attrition step. This is not required for the achievement of some advan ⁇ tages, but it does generate a more efficient separation.
  • advantage is taken of the fact that larger, low (relative) surface area particles settle faster than very fine (relatively high surface area) particles.
  • the very fine particles for example, clay
  • the material from the attrition scrubber or pebble mill is directed, for example, into a classifica ⁇ tion system.
  • a classification system relying on relative settling velocities is used, such as a countercurrent screw classifier, or a plurality of countercurrent screw classifiers in series, with a washing water flow directed against movement of the sludge or soil.
  • the washing water removes: relatively small, slow settling, particles of wood; small, slow settling, particles of soil such as clay having substan ⁇ tial amounts of contaminant thereon; and/or, floating organics.
  • the contaminants removed by washing can be collected, concentrated and treated via incineration or the like.
  • the classifi ⁇ cation is applied until reduction of organic contaminant has reached a readily achievable minimum, typically about 10 ppm.
  • An advantage to the present invention is that for specific operations stages can be varied, in order to achieve an overall most efficient, or at least substantially efficient, operation.
  • the sludge material from a typical counter- current screw classifier step, according to the present invention includes about 75% soil, by weight, the remainder being substantially water.
  • the soil generally comprises primarily silica sand with some oil or grease thereon, much of the wood component having already been removed as well as a substantial portion of the fine clay or silica component and any flotable natural organic components. In some instances, some of these materials will still be present, however, and further cleansing with respect to them may be accomplished in a third stage treatment.
  • underflow from the screen system 18 is shown directed into cyclone 32.
  • Overflow liquid is removed via line 33, and the concentrated sludge is transported via line 34 to attrition equipment such as a pebble mill 35.
  • attrition equipment such as a pebble mill 35.
  • the finer product is transported to classification system 40 via line 41.
  • the classification system 40 comprises a plura ⁇ lity of classifiers arranged in series, with a counter- current wash flow. More specifically, conventional screw classifiers 42, 43, 44 and 45 are shown arranged in series.
  • a counter- current flushing or washing water flow to generally remove wood, natural organics, and slow settling, fine materials such as clay occurs via flow lines 50, 51, 52 and 53, respectively.
  • the contaminated wash material is removed from the system via line 55.
  • the washed, coarser fraction typically primarily a silica sand com ⁇ ponent, is removed from the system via line 56, whereby it is transported into Stage 3.
  • the wash flow from the classifiers, through line 55 may be directed through screen 56, to lead to concentration of solid materials which can be removed via line 57 for incineration.
  • Contaminated water released from the filter system 56, via line 58 may be directed into Stage 3 for use.
  • Flotation processes are known in the mineral industry and the pulp treatment industry; see for example. Froth Flotation - 50th Anniversary Volume, Ed. by Fuerstenau, D.W., American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., New York, 1962; Flotation, Volumes I and II, Ed. by Fuerstenau, M.C., American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., New York, 1976; Chemical Engineer's Handbook, 5th Ed.; Ed. by Perry, Robert F., McGraw-Hill Book Co.; New York 1973, pp. 21-65 to 21-69; Wills, B.A. ; Mineral Processing Technology, Pergamon Press, Oxford, 1979, pp.
  • Flotation may be provided in a variety of machines. Generally, flotation process machines are separated into two basic cate ⁇ gories, mechanical flotation machines and pneumatic flo- tation machines. Within each category are two types, those operated as a single tank, and those operated as a bank of tanks (or cells) in series.
  • any flo ⁇ tation system may be optionally utilized in association with the present process, however generally preferred processes will involve the use of a mechanical flotation device, either alone or in series with other such devices. It is noted that final flotation steps (polishing steps) may not be required in some purifica ⁇ tion schemes.
  • the primary function of a flotation separation in an application according to the present invention is to allow hydrophobic contaminants to contact and adhere to air bubbles. The air bubbles rise to the top of the flotation device, carrying the hydrophobic material with them. This generally results in formation of a con ⁇ taminated froth at the top of the solution, which can be overflowed, skimmed or otherwise removed. As a result, the solid material contained within the flotation tank or cell is substantially purged of the hydrophobic material.
  • a unique application of flotation technology is involved in preferred applications of the present invention.
  • the process involves the removal of organic contaminants from soil, and separa- tion of soil particles not readily disassociated from organics, from the remainder of the soil.
  • the organic components including the greases, oils and any dissolved PCP or other toxic organics, are typically very hydrophobic and thus susceptible to removal via the flotation process.
  • the machine maintain the soil particles in suspension and further that the system generate sufficient disper ⁇ sion of air bubbles throughout the solution, with colli ⁇ sion of air bubbles with particles, to ensure high frequency of contact between the air bubbles and the particles for substantial transport of hydrophobic orga ⁇ nic material to the air bubble surface.
  • a concentration of about 10-40% solids, by weight, in the flotation step is effective.
  • Preferably high solids concentration, and/or intense agitation, are avoided so that little attrition (particle/particle collision) occurs.
  • attrition would tend to pull bubbles off of floated particles, thus allowing less time for transport of organics to the bubbles.
  • manufactures of flotation equip ⁇ ment can be utilized in association with processes according to the present invention. These include, for example, flotation machines developed for other uses, operated with appropriate stirring velocity and air bubble flow. Such devices include systems which generate air bubbles by a simple draw of air from the atmosphere, and also those which utilize separate blowers or pressurized air sources.
  • Usable flotation machines or cells are available, for example, from the Denver Equipment Division, Joy Manufacturing Company, Colorado Springs, Colorado 80901; Outokumpu Oy, Espoo 20, Finland; and, Wemco, Sacramento, California 95852. Such devices are generally developed for use in the mining industry, however they can be readily adapted to application according to the present invention.
  • Stage 3 i.e, the flota ⁇ tion stage, is generally indicated at reference numeral 60.
  • the soil material is transferred into a flotation cell 61, as for example along flow path 62.
  • a series of screw classifiers is used to wash and transfer sufficiently ground up or otherwise sized particles of soil, from a typical pole treatment dump the washed material comprises about 85-95% soil by weight, and contains 5-20 ppm PCP.
  • the material is directed into a flotation cell 61, along with a suf- ficient amount of water via line 63 for cell operation. Agitation is started, and is maintained at a rate appropriate to inhibit any substantial settling of material, i.e., that is a sufficiently high rate to maintain substantially all particles in suspension. Air bubbles are formed in the flotation cell, during opera- tion.
  • air bubbles typically numerous micro bubbles, may be formed by an atmospheric draw, or through the provision of a blower or source of pressurized air or the like. Generally sufficient bubble formation is created to ensure effective flota ⁇ tion of the organic material from the soil material, for effective purification.
  • the organic material trapped in the air bubble froth is floated to the top of the machine, wherefrom it can be removed by overflow or by use of conventional mechanical skimmers or the like, along path 64. Similarly, any fine soil particles having organics adsorbed thereon will also tned to flat to the froth.
  • a second flotation cell 70 is shown used in series with the first cell 61 to achieve a high degree of cleansing.
  • the underflow from cell 61 is directed to cell 70 along flow path 71.
  • Water, for froth formation is directed into cell 70 via line 73.
  • the overflow or froth is removed at 74, and the underflow, or purified soil, at 75.
  • the clean soil is separated from the water at 76, and is removed at 77.
  • the carrier water is removed at 78, and may be cycled into backwash for Stage 2.
  • froth from
  • a typical flotation cell for use in a system according to the present invention is schemati ⁇ cally depicted.
  • the cell is generally designated at reference numeral 100.
  • the cell 100 includes a tank portion 101 into which water and con- taminated soil, typically as a slurry, are dumped for treatment.
  • the sludge or slurry 102 within tank 101 is rapidly agitated by an agitator/aerator 103.
  • the par ⁇ ticular agitator 103 shown includes a plurality of vanes 105 thereon which rapidly rotate to churn the water, and keep the solid soil material from settling in the bottom of the tank.
  • Air bubbles are formed in a high sheer zone between the agitation cones 105 and the stator, with air flow being generally represented by arrows 107.
  • soil particles are encountered, organics transfer to the interface with the air bubble, and the organics float to the top of the tank in the form of froth 110.
  • the froth is then removed via skimming or overflow 111, as indicated at reference numeral 112.
  • the three com- ponents which are mixed in the tank are represented as being introduced via lines 115 and 116, respectively. Underflow is shown removable via the port 120, operated by valve 121.
  • FIG. 2 is intended to be schematic only, and that a variety of specific mechanical structural arrangements can be utilized.
  • agitation speed, air bubble size and concentration, water concentration, and retention time in the tank may be varied to achieve an optimum, or at least a desired level of efficiency and purification.
  • the flotation cell may be operated on a closed, batch, cycle, or with a continuous run therethrough. Generally, a continuous system will provide for a more efficient overall operating system.
  • underflow from the flotation system is generally designated at reference numeral 75.
  • This material includes the purified soil, generally containing less than 10 pp PCP, and pre- ferably 5 ppm PCP or less.
  • the PCP may pose substantially little problem.
  • this soil can be dried and transferred back to the pit area with an active microbial agent therein, to obtain even further purification. It is noted that at this relatively low PCP concentration, microbial action may be more effectively undertaken and controlled.
  • the skimmed or overflow material from the flo- tation cell can be concentrated, if desired, and inci ⁇ nerated.
  • the water, somewhat contaminated, can be directed to a water treatment facility or the like.
  • Frothers may be added during flotation. Frothers generally change the surface tension of the water in a manner facilitating formation of a stable froth phase. Frothers include methyl amyl alcohol and pine oil. They may typically be used in an amount of about 0.01-0.2 lbs. frother/ton of soil in the flotation device.
  • the particular equipment to be used may vary depending on the specific nature of the soil being treated, and the specific nature of the con- taminant contained therein. As soil composition and particle size ranges and contaminant concentration and nature vary, individual specifics of the treatment may be changed accordingly. For example, in some systems no flotation step may be necessary. In other systems, a single flotation cell may be all that is needed to acco- modate efficient purification, whereas in still other systems a plurality of cells in series may be required.
  • PCP pentachlorophenol
  • the soil sample contained a substantial amount of wood therein. Originally the soil, classified to less than one-half inch, contained about 18% water. The overall PCP concentration in the sample was about 250 ppm. The sample contained a variety of sizes of par- ticulates and could be sized accordingly. It was generally found that the PCP concentration varied throughout the size range of the particles, being higher in size fractions coarser than 20 mesh and finer than 150 mesh, as shown in Table 1.
  • This separation step was undertaken to elimi ⁇ nate handling difficulties created by the wood content of the soil and to confirm PCP distribution in the soil. 5
  • the process involved screening to minus 10 or 20 mesh to remove the bulk of the coarse wood, and is described above as occurring in Stage 1.
  • the test soil was subjected to both dry and wet screening. ...The dry screening was merely, a cursory 0 test to remove the bulk of the coarse wood.
  • the soil sample was first dried at 75° Centigrade to at least 16 hours.
  • the dry soil was then screened through a 10 mesh screen, using a manually sha ⁇ ken, frame-mounted screen.
  • the plus 10 mesh and minus 5 10 mesh fractions were anlyzed for PCP.
  • the dry screened material showed a significant and dispropor ⁇ tionate accumulation of PCP in the plus 10 mesh frac ⁇ tion, which was determined to contain a significant amount of wood. The results of this screening are reported below in Table 2.
  • the -10 mesh slurry in the tub was allowed to settle for 72 hours and the aqueous phase or supernatant (first wash) was siphoned off and collected. This wash was analyzed as a slurry (solids plus solution) but was also filtered to determine the weight of solids remaining in suspension. The settled solids were reslurried with an equal weight of water and were allowed to settle for 15 minutes. The supernatant (second wash) was again siphoned, collected, and ana ⁇ lyzed. The reslurrying step was repeated two more times for a total of four washes. A dark slime layer (slimes) that settled on the top of the' sandy soil was left until the last siphoning operation when it was removed, dried, weighed and analyzed. After the slime layer was removed, the final settled solids were collected, dried, weighed and analyzed (-10 mesh). Typical assays of the products from the washing cycles are reported in Table 4. Table 4
  • the slurry from the wet screening operation cannot be readily filtered due to the presence of oil and fine particles.
  • the slimes contain a suspension of finely divided soil, small pieces of wood, and oil. Methods for the cleaning of this suspension include flo ⁇ tation, centrifugation, settling, and combinations thereof. Certain of these processes may be undertaken in Stage 2, discussed above, and include treatment in an attrition scrubber or pebble mill to further break up agglomerates and scrub particle surfaces before pro ⁇ cessing this slurry in a classifier to wash out fine or floatable contaminated material. As a result of such operations, products containing relatively concentrated amounts of PCP and oil/grease components can be isolated for disposal. In particular, fine clay particles and small wood pieces are removed by this process.
  • the soil material is ultimately treated via flotation to achieve reduction of PCP con ⁇ centration, or concentration of other contaminants, to a minimum, or at least to below a desired value.
  • This is a particularly effective way of obtaining a relatively clean silica sand material.
  • flotation can be used advantageously at the head of the flowsheet to separate intractable slimes; i.e. the fines containing a substantial amount of organics not amenable to scrubbing, for additional processing in a centrifuge or the like.
  • Soil contaminated with PCP was wet screened at 10 mesh to remove coarse wood.
  • the -10 mesh fraction of the soil was slurried with water at a pulp density of 50% solids.
  • the pulp was brought to the desired tem ⁇ perature, pH was adjusted, and surfactant was added.
  • the slurry was scrubbed (intensely agitated) in a baffled vessel using a shrouded impeller rotating at 1000 rpm.
  • the pH was maintained constant throughout the duration of the test. At the end of the scrubbing period the slurry was allowed to settle for 5 minutes and the aqueous phase or supernatant was siphoned off and collected.
  • a 3.5 inch by 2.5 foot screw classifier with a capability for bed washing by means of bottom-bed water injection was used for this testwork.
  • the feed to the classifier was the -10 mesh fraction from a sample of screened soil contaminated with PCP. This sample was slurried to 50% solids with tap water and scrubbed in a mixing tank, for one hour under intense agitation. The slurry was fed to the classifier and the sand ' discharge and fluid overflow (first overflow) were collected. The fluid overflow was allowed to settle and the dark layer of slimes that settled out on top of the fine sand was selectively removed and analyzed separately (slimes).
  • the remaining fluid overflow was ana- lyzed as a slurry but also filtered to determine the weight of solids remaining in this suspension.
  • the sand bed in the classifier was removed (first bed), dried, weighed, and analyzed.
  • a sample of the first sand discharge (first product) was taken for analysis.
  • the remaining first sand discharge was slurried with tap water and fed back into the empty classifier to produce a second overflow and second sand discharge.
  • the sand product from the classifier was sampled for analysis (second product) and recycled two more times without removing the bed to simulate cleaning of the sand in a multi-stage system.
  • Experimental results are presented in Table 6.
  • PCP Fluid Solids PCP split Stream (liters) (grams) ppm %
  • polishing opera- tion may be used to reduce the PCP content of the final soil by as much as 50%.
  • the solid material in the froth appeared to be mostly clay.
  • the sand material was released in a relatively clean form. Results also indi ⁇ cated that it appears beneficial to operate at a basi- city within the pH range of 7-8.

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  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Soil Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • Biotechnology (AREA)
  • Processing Of Solid Wastes (AREA)

Abstract

La présente invention décrit un procédé servant à épurer un terraen contaminé par des matières organiques. Le procédé préféré comporte généralement des opérations d'abrasion (35) et de classifications (40) superposées, qui produisent l'extraction et la concentration des fractions fortement contaminées. Le procédé peut également comporter une étape de flottation (60) par laquelle les substances hydrophobes contenues dans le sol sont libérées à une interface avec des boules d'air et sont amenées par flottation au sommet d'une cellule de flottation. Dans les procédés préférés décrits par la présente invention, la terre à traiter est extraite du site contaminé et est broyée en particules relativement fines. Ces particules sont de préférence traitées par des opérations d'abrasion et de classification, destinées à extraire les substances contaminées en fines particules à sédimentation lente, telles que le bois et les fines particules terreuses. Les particules plus grossières isolées qui en résultent sont ensuite traitées par flottation en vue d'une opération de polissage finale. Ledit procédé est particulièrement bien adapté pour être utilisé dans le traitement de terrains contaminés par des huiles organiques et des matières grasses contenant du pentachlorophénol (PCP), qui proviennent par exemple d'installations de traitement du bois ou similaire.
EP19890902988 1988-02-08 1989-02-06 Procede de traitement d'un terrain contamine Withdrawn EP0410971A1 (fr)

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US153240 1993-11-16

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DE4395836T1 (de) * 1992-11-19 1995-01-26 Tdk Corp Filter des Typs mit abgelagerter Schicht
CN111068887A (zh) * 2019-12-26 2020-04-28 沈丹 一种基于细化土壤的土壤修复装置

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NL9301555A (nl) * 1993-09-08 1995-04-03 Saskia Mosmans Werkwijze en inrichting voor het reinigen van verontreinigd bodemmateriaal.
JP4646047B2 (ja) * 2000-11-01 2011-03-09 株式会社鴻池組 汚染土壌の浄化方法及びそれに用いる分離装置
JP4568893B2 (ja) * 2001-02-26 2010-10-27 Ｄｏｗａエコシステム株式会社 汚染土壌の浄化法
JP4697719B2 (ja) * 2001-03-01 2011-06-08 株式会社鴻池組 汚染土壌の浄化方法及びそれに用いる分離装置
JP4599766B2 (ja) * 2001-06-21 2010-12-15 Ｊｆｅエンジニアリング株式会社 土壌洗浄方法および装置
JP4640673B2 (ja) * 2005-10-06 2011-03-02 清水建設株式会社 高濃度油分汚染土壌の浄化方法
JP5276779B2 (ja) * 2006-06-09 2013-08-28 五洋建設株式会社 ダイオキシン類によって汚染された底質・土壌の浄化方法
JP5327580B2 (ja) * 2008-04-23 2013-10-30 清水建設株式会社 浮遊選鉱装置
JP5397847B2 (ja) * 2009-03-23 2014-01-22 太平洋セメント株式会社 重金属含有土壌の浄化方法
JP5702567B2 (ja) * 2010-09-14 2015-04-15 Ｄｏｗａエコシステム株式会社 汚染土壌の浄化方法および浄化装置
JP5845658B2 (ja) * 2011-06-28 2016-01-20 株式会社大林組 汚染土壌の浄化方法及びシステム
JP5834272B2 (ja) * 2011-09-20 2015-12-16 株式会社湘南数理研究会 汚染土の除染方法
FR2990364B1 (fr) * 2012-05-11 2014-06-13 Commissariat Energie Atomique Procede de decontamination radioactive d'une terre par mousse de flottation a air disperse et ladite mousse
JP6114136B2 (ja) * 2013-07-30 2017-04-12 株式会社オメガ 汚染土壌の分級選別装置
JP6391012B2 (ja) * 2014-02-19 2018-09-19 清水建設株式会社 砒素汚染土壌の洗浄方法
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DE4395836T1 (de) * 1992-11-19 1995-01-26 Tdk Corp Filter des Typs mit abgelagerter Schicht
DE4395836C2 (de) * 1992-11-19 2003-02-20 Tdk Corp Filter mit Dielektrischen Schichten
CN111068887A (zh) * 2019-12-26 2020-04-28 沈丹 一种基于细化土壤的土壤修复装置
CN111068887B (zh) * 2019-12-26 2022-02-08 福建龙源环境工程技术有限公司 一种基于细化土壤的土壤修复装置

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WO1989007014A1 (fr) 1989-08-10

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