JPH03502424A - How to treat contaminated soil - Google Patents

Abstract

A process for the purification of soil contaminated with organic material is provided. The preferred process generally involves superposed attrition (35) and classification (40) processes, which lead to removal and concentration of highly comtaminated fractions. The process may also include a step of flotation (60) whereby hydrophobic materials in the soil are released to an interface with air bubbles, and are floated to the top of a flotation cell. In preferred processes according to the present invention, soil to be treated is extracted from a contaminated site, and is broken into relatively small particles. These particles are preferably treated in attrition and classification steps, to remove fine, slow settling, contaminated materials such as wood and fine soil materials. The resulting isolated coarser materials are then treated by flotation for a final polishing step. The process is particularly well adapted for use in treating soil contaminated with oil and grease materials containing PCP therein, from wood treatment plants or the like.

Description

[Detailed description of the invention] How to treat contaminated soil field of invention The present invention relates to soil purification, in particular to the purification of soil material contaminated with organic matter. present invention A special application of There is a treatment for soil. Such soils are typically made from waste from wood processing plants. Found in agglomeration sites.

Background of the invention Waste materials from many industries contain organic materials, often organic greases and oils. a In some cases, these waste oils contain highly toxic chemicals. A well-known example is , a waste material from conventional wood processing facilities.

In a typical wood processing facility, the wood is soaked or passed through two knots of oil containing a preservative. be forced to do so. For example, facilities for the treatment of telephone poles, railroad ties, etc. Use a large vat containing oil containing phenol (PCP). People like this A typical process used in the process is to prepare an organic solution containing approximately 5% FCC. include.

Waste organic material, which often contains significant amounts of PCP, is located close to the treatment facility. Often abandoned in hollow areas. This is especially true with respect to current pollution control standards. However, such treatment facilities do not provide general soaking and/or treatment methods. Understand that the system has been operating for decades with little change in nature. Must be. i.e., it has successfully existed prior to more recently imposed pollution standards. There are many sites available.

The pollution problem is exacerbated by the nature of the industry. Very often processing facilities are For a short period of time, a significant amount of timber is being sawn or built near an area where treated timber is needed. Ta. After operating adequately to meet local needs, facilities are closed and sometimes relocated. It was moved to the area of Abandoned garbage sites like this exist all over the country.

Over a long period of time, contaminated organic material is carried away by groundwater directly from the waste collection site. It seeps out and pollutes a wide area. Organic matter often contains significant amounts of highly toxic substances This leaching poses a serious health and environmental hazard.

The problem of contamination from underground organic matter has been discussed, particularly in relation to industries involving wood processing. However, the problem is that the organic waste disposed of in potholes is being used in various industries. It is recognized that the existence of The wood processing industry is a well-known and well-known We only provide examples that include PCPs, which are often particularly dangerous.

Until now, there has been no satisfactory method of treating and/or purifying whole soil. general Treatment methods may include simple incineration, microbial treatment or some combination thereof. Ru. These are not entirely sufficient, in part for reasons discussed below.

A common purification method often used is incineration. For typical incineration methods Then, a large incinerator is built near the contaminated area. large quantities of soil material from the area Dig it up and incinerate it. The incineration process generally destroys many organic materials and A large amount of ash material remains, often turning into a hard cake or block. This material is essentially are still contaminated and therefore should not be stored while leaving the excavated area open. are typically stored in abandoned garbage dumps. After the special area is cleaned, the incinerator will be It is typically dismantled and moved to a new region.

Incineration itself is generally an undesirable process. Firstly, it is an energy non- Efficiently, i.e., large amounts of energy are used to generate large amounts of contained material at sufficient temperatures. It is consumed while the incinerator is running for a sufficient time to effectively purify it. second Another issue is the gases and materials produced from incineration. Furthermore, the large amount of contamination that is formed The collected ash creates disposal problems.

The second method of purifying contaminated soil is through the use of microbial action. In general, especially oil/ It has become clear that microbial purification is undesirable for PCP problems. in the laboratory Although microbial action effectively detoxifies the material, it is rather ineffective in the field. stomach. First, temperature, humidity and oxygen regulation are extremely important and difficult to implement. or, A wide variety of chemical concentrations are found within a single dump site and from location to location. . Concentration changes lead to unpredictability. In addition, the complete microbial contribution of concentrated contaminants Detoxification takes quite a long time, during which time further leaching from the garbage dump occurs. sell. Finally, soil changes and changes in the dump surroundings may provide effective and predictable microbial growth. poses an essential obstacle to the action.

What is needed is an effective method to purify soil contaminated with organic materials or otherwise.

In general, a method that should be effective should achieve the desired result, i.e. essentially clean soil. Not only must it be affordable, but it must also be relatively inexpensive. That is, what is necessary is , provide an alternative to, or at least provide an alternative to, common soil treatment processes. It is a cost-effective method that works well.

Purpose of invention Therefore, an object of the present invention is to provide a method for purifying and treating soil contaminated with organic materials. Particularly suitable for application in the treatment of soil at waste dumps from wood processing facilities. To provide a method suitable for refining soil material contaminated with oil containing PCP. to provide a method for essentially eliminating contamination of organic materials from solid soil particles. A preferred method is provided which includes the use of attrition and classification steps and preferably superimposition. and a flotation stage to further remove contaminated organic material from coexisting soil materials. To provide a preferred method further comprising the steps for disposal by conventional processes. to provide a method for producing concentrated waste materials, and for use in conjunction with various regions. It is particularly flexible to use, relatively easy to accomplish, and relatively inexpensive. To provide a process that is inexpensive and particularly well adapted to the proposed application. It is.

Other objects and advantages of the invention are set forth in the accompanying drawings and the invention, illustrated by way of illustration. It will become clear from the following description taken together with some embodiments of the invention.

Summary of the invention The present invention results in the cleaning of contaminated soils and contaminated soils such as PCP-contaminated oil. Concerning the use of attrition and classification processes to remove organic matter.

The attrition process is a scrubbing stage. The abrasion process generally involves a high percentage of Stir the slurry containing solids with high intensity. During this process, a large number of particles / Particle contact occurs. This is because it has become weak and hard due to the contaminating organic matter. This will crush the particles.

Particle/particle interactions also help scrub the particle surfaces free of organic matter.

size selection, filtration and screening based on relative sedimentation rates in bodies, e.g. water Including. The preferred classification process for use in the application of the present invention is that the sorting is based on relative sedimentation velocity. It is based on These include centrifugation, flocculation, cyclone, and spiral or Including the use of a Clew classifier. Sorting with a spiral or screw classifier is particularly useful. At least they are effective, relatively cheap and easy to implement. and they can be operated on a relatively large scale, even with conventional equipment. This is because that.

According to the invention, a classification step is carried out on the soil-containing slurry that has been subjected to an attrition step. In some cases, essential soil refining is carried out. In general, it is preferred that the classification step It is superimposed on the abrasion process. That is, the classification step is preferably carried out at a stage where the particles are attrited. Start before the floor has had a chance to completely precipitate. With this method, sorting can be done effectively. be exposed. In particular, if the classification is carried out in systems that are of the type that involve relative sedimentation velocities, Removal of fractions containing materials that settle out more slowly can occur during the classification process. It was found that it essentially removed contamination from the aircraft.

This results in low settling with relatively fine particles during wear! (Typically fine, low density high surface area) fraction, and it contains a substantial fraction of contaminated organic matter. , and the classification is conveniently carried out by excluding the highly contaminated fractions. Let go. As a result, the contaminated organic matter has been significantly purified or separated. Particles that settle out faster remain.

It has also been found that, in some instances, attrition and sorting can be completely separated in time. death Generally, overlapping is preferred.

According to the present invention, soil (quick sedimentation fraction from classification) can also be further purified by flotation. This can be done using Flotation generally involves the sorting of materials based on their relative hydrophobic tendencies. It is a process that includes Flotation technology is used in various industries, including mining and pumping industries. Commonly known for other purposes. Flotation techniques can also be used to perform solution separation. It will be done. Flotation technology removes organic contaminants from association with soil in an efficient and economical purification process. It is a feature of embodiments of the invention that it has been found that it can be applied to remove Ru. As a result, the final contaminant concentration in a large fraction of the soil remains at a relatively low level. Contaminated organic matter can be collected and concentrated for disposal.

A typical overall soil treatment process according to the present invention can be visualized in several stages. Ru. In the first stage, soil is excavated from the contaminated area and bulk contaminated items, e.g. Appropriate shaking or other treatment to remove solid wood, metal materials, etc. cormorant. Also at this stage, the soil material is preferably sized for the following operations: Match.

A preferred second step involves carrying out the superimposed abrasion and classification steps as already described. include. It contains small, slender, relatively contaminated soil particles and significant amounts of organic matter. Following attrition, concentration and removal of the containing fractions for disposal. For example, contaminated organic matter Small wood chips, which may contain a substantial fraction of, can be removed at this stage. Also, ratio Relatively fine soil components, such as fine clays and silicate materials, contain a significant proportion of contaminated organic matter. Can include things. These are also isolated and separated at this stage. Advantages of the entire process of the invention can be relatively inherently contaminated with organic substances or must be separated from the organic fraction. Hard to remove wood materials, fine soil particles, etc. are likely to be immediately concentrated during stage 2. The scales are then separated and, if desired, treated by effective means, followed by incineration. That is.

i.e. they are rather easily mobile and they contribute to the total bulk of the soil in the area. Comparatively speaking, the capacity is quite small. The result is a relatively small volume final incinerator ash product. , which can be handled immediately.

In a third stage, in embodiments, the soil material has a significant amount of residual material from association with the soil. Processed via flotation to remove contaminating organic materials. The flotation process is generally involves stirring the soil as a slurry or suspension with air bubbles passing through it. Sparse Aqueous contaminants, i.e. organic foam/PCP contaminants, are generally found on the soil surface and/or Water preferentially moves from the turbid liquid to the interface via air bubbles. That is, by flotation, organic materials are bumped, rubbed together, or bubbled from the soil to the interface.

Also, a significant amount of adsorbed or absorbed organic matter is difficult to wash away. Microparticles containing organic matter also move to the interface with bubbles. In addition, liquid organic matter flows toward the bubbles. Tends to move. These materials are then floated to the top of the flotation system. , from which the overflow or supernatant is skimmed off. Contaminants are easily Concentrate and dispose of by conventional means, e.g. incineration.

At the final stage, the cleaned soil is returned to the hole area or, if desired, to another location. sell. At this point, the overall contamination is fairly low, but if desired It is possible to attach. For example, further washing, flotation, etc. can be used. Also, microbial production If desired, other materials are also readily available at this point.

As can be seen from the detailed description of the invention, it typically involves the use of large amounts of water. for example, Water, used as a carrier throughout the process, carries the slurry during attrition and classification. It is also found in the material used to form and skimmed from the flotation process. It is issued. This water is inherently contaminated with contaminated organic material removed from the soil. come. An advantage of the present invention is that substantial amounts of contaminated or potentially contaminated water can be recirculated. The scales are ringed. Effective operation of the process of the present invention is based on water and/or secondary water treatment. for the essential purification of the used water, where the discharge is recycled into the control system. It is also envisioned that it would typically include cooperation with water treatment processes.

The drawings, while illustrating various objects and features, constitute a part of the specification and do not illustrate the practice of the invention. Including embodiments.

Brief description of the drawing FIG. 1 is a schematic depiction of the overall system for soil treatment of the present invention.

FIG. 2 is a schematic depiction of a flotation device for treating soil at the stage of the present invention.

Detailed description of preferred embodiments As desired, detailed aspects of the invention are disclosed. However, disclosed It should be understood that the embodiments are merely illustrative of the invention, which may be embodied in various ways. It is possible. Accordingly, the specific details disclosed herein should not be taken as a limitation, but rather as a solicitation. As a basis for the scope of requirements, and virtually any suitably detailed system. The present invention is presented in a representative manner to teach those skilled in the art to various uses of the present invention. should be interpreted as a basic basis.

Stage 1 Initial, rough screening and separation As stated in the figures, the present invention is intended to reduce the amount of soil found in waste collection sites from wood processing facilities. and applications involving the processing of materials. However, the basis of the present invention is Generally applied to soil and similar materials contaminated with various organic matter from various processes. It is understood that it is easy to understand.

That is, the specific treatments described herein should be considered exemplary only. Ru.

The first stage of the operation involves physically processing the material excavated from the dump site. Allows easy handling during subsequent purification washes and other steps. In other words, a large place Removes difficult-to-clean materials such as large stones, tree stumps, and scrap metal. Ru. Typically, to accomplish this, soil material is physically removed from the waste site. and pass through a screening device, e.g. a grizzly let

The device removes bulk contaminant materials, such as post remains, large pieces of wood, etc. from the soil. . One reason why such soil pretreatment is often necessary is that in many instances organic The collection site also contains waste items, such as old tires, unusable pieces of wood, and mechanical parts. The land will be used as a waste collection site.

Typical soil material that grizzlies pass through is large amounts of compacted or clumped material, i.e., large It is a material stuck to a solid piece of wood or earth.

This soil material typically contains approximately 100- Contains a pentachlorophenol (PCP) concentration of 2000 parts per million. nothing. This essential concentration is often 0.1-1.0% by weight of oil in the soil. This comes from the concentration of the grease. Oils and greases actually adsorb to certain components of the soil; or with certain fractions in the soil that are easily caught in woody masses or difficult to separate. meet briefly. On the other hand, PCP is typically absorbed or dissolved into oil materials. found. That is, it is often not adsorbed directly to the soil itself. That is, with these components of the soil having a disproportionate amount of oil or grease; Removing oil or grease from soil where separation of the grease is difficult is a highly toxic contamination process. This leads to the essential removal of the physical object (PCP).

At this point in the process, the soil material typically contains several basic components. Firstly, that This contains a considerable amount of wood chips. These pieces of wood are usually relatively and disproportionately High concentrations, often on the order of 500-2000 parts bar million It was found to contain contaminated PCP. The exact physical nature of this contamination is unknown . However, it is easy to understand that it is desirable to selectively remove this wood component. be understood. A significant portion of the wood components are removed during the first pretreatment step during several steps. It is possible.

First, the soil material from the grizzly bear was prepared using a conventional trommel. ) or conveyed to a crusher to essentially break up the wood chunks of the waste material. tron In the melt, the material is Water is sprayed. Typical conventional trommel application with water spray approximately 1/2 Materials with a size not larger than 2 inches are obtained.

The slurry or sludge from the trommel then further downsizes the material. For this purpose, it is preferably sent or lowered to a screen system. Generally 10-65 meters Test screening is recommended.

Multiple screening steps may be used. For example, soil material preferably about In order to make the size not larger than 20 meshes, the first screen is about 10 meshes. Leaning and a second varnish cleaning up to about 20 meshes are generally effective. Ru. Additionally, water may be added to facilitate the filtration process.

During a typical run, water added between the trommel and mesh screening to about 10-60% solids by weight, preferably 50% solids. less than. The division of the gap between water addition in the trommel and screening is divided into two necessary to facilitate one process. It is understood that different amounts of water are used. , the above merely represents the generally usable drawings.

During the process in the trommel and washing through a 20 mesh filter with lO A significant amount of wood material that does not fall apart is removed during the mesh screening stage. be done. This concentrated wood material can be collected and easily incinerated or stored for disposal. Other processing is possible. Small pieces of contaminated wood that have absorbed organic pollutants go through processes such as incineration. It is a particular advantage of the present invention that it is easily incinerated for disposal. That is, books The invention provides that these materials or fractions containing high content or concentration of contaminated organic matter are Concerning separation into relatively small volumes. , these can be incinerated relatively effectively. Ru.

FIG. 1 is a schematic representation of the process of the present invention. The following description focuses on the movement of soil materials. However, the system described does not allow for efficient use of contaminated water and water flow. Contains advantageous systems. Referring to Figure 1, the reference number 10 generally refers to step l of the process. Describe it. Citation number 11 refers to contaminated soil to Grizzly-12 for recent isolation. Indicates the sending stage.

Large contaminants, such as pillar tips, are removed at 13. Passing Grizzly-12 The material is conveyed to the trommel 14 and broken up. The quotation number 15 is general shows the flow of water to the trommel provided for the production of the slurry. trommel The slurry flow from is indicated by reference numeral 16. The material is preferably IO Sent to screening system 18 consisting of mesh sieves 19 and 20 mesh sieves. It will be done. The slurry material is made with the help of water supplied as indicated by the reference numeral 25. It is then sent through a sieve system 18. Fluid supplies I5 and 25 are trommel 14 and filtration system 18, such as by conventional valves that control the relative distribution of fluids to filtration system 14 and filtration system 18. source 26.

Larger materials, such as pieces of wood removed from filter system 18, have a reference number of 30. is removed. Pass through sieve system 18 of 20 mesh or smaller size. The soil material that passes through the soil is generally designated by tick-off 31.

Stage 2 Attrition and classification process The material removed from the physical sieve, e.g. system 18, remains essentially associated or are gathering. At this point, typical soil materials are generally still small pieces, clay ingredients, silica sand, natural organic matter, such as decomposed plant matter. It consists of many ingredients, including Is there some degree of oil and grease present in the contaminant? This soil material can prevent pollutants from being released from between the trapped internal particles, Still solidified into relatively hard particles. In a preferred application of the invention, this material The slurry is essentially concentrated, such as in a cyclone, to about 40-70% solids, and then loosening and scrubbing in an abrasion stage, e.g. in a pebble mill abrasion cell. . . During attrition, the solid slurry is subjected to vigorous agitation. This suspends solid particles. It becomes cloudy and causes a large amount of particles/particle collisions. Collisions break up the set and cause various This results in suspended particles with a size of . Contaminants Some things can break off from particles and spill into water. Float inside.

For some soils, fine-grained soil components are a relatively small proportion by weight or volume. , compared to the coarser (typically the majority) components of soil, contaminated oil and It has been shown that grease is sometimes associated with PCP in substantial and disproportionate proportions. It became clear. Although the invention does not tend to be limited to any particular theory, This phenomenon is caused by the fact that fine particles have a relatively large surface area, and organic substances are easily adsorbed onto them. It can be theorized that this is partly due to the fact that Minimum amount of non-adsorbed organic matter To some extent, it makes sense from observation that fine particles are relatively difficult to separate. It is also said. Anyway, with any associated unadsorbed organic matter, generally Separation of the fine particles also results in substantial purification of the residual material.

The classification step is carried out after attrition but essentially after precipitation, i.e. Superimposed on the abrasion stage is a preferred deaf-like feature of the present invention. This is a Although not necessary to achieve the benefits of minutes Between the classes, the advantage is that very fine (relatively high surface area) particles over large, low (relatively high surface area) ) Surface area results from the fact that particles settle faster. Generally shaped during wear and tear. very fine particles (e.g. clay) is separated by classification, and a considerable proportion of contaminated organic matter is separated and removed. becomes.

Material from the attrition scrubber or pebble mill, for example, is sent to a classification system. good Preferably, classification systems that rely on relative settling velocities, e.g. A classifier, or multiple counterflow screw classifiers in series, is used to move sludge or soil. used in conjunction with a flushing water stream directed against the Washing water has relatively small low sedimentation of wood particles, small low-sedimentation soil particles, e.g. clay with significant amounts of contaminants, and/or dislodge suspended organic matter. Contaminants removed by cleaning are collected and It can be concentrated and processed through incineration, etc. Easily purified or separated from contaminated organic matter These components of soil, which generally constitute an essentially small volume of soil, separated and concentrated, they are processed through conventional incineration techniques in an efficient and effective procedure. It is once again an advantage of the present invention that

It can be appreciated that a conventional screw classifier may be utilized during this stage. many kinds A wash water flow rate of 100 ml may be used depending on the system to which the process is applied. In general, screen A solids ratio range of about 10-50% is useful in a 2000-2000 mesh classifier. Typical For refining, the material entering the first screw classifier is approximately 100 parts per millimeter. Contains pentachlorophenol. In most applications, classification is used to classify organic contaminants. applied until the reduction reaches the minimum readily achievable value, typically about 10 pp11. be done. An advantage of the present invention is that it is generally the most efficient, or at least Essentially, the stages can be varied to achieve efficient operation.

The sludge material from a typical counterflow screw classifier stage of the present invention is approximately It contains 75% soil and the rest is mostly water. At this point, the soil is generally Consisting of primary silica sand with some oil and grease, much of the wood content is similar. A significant portion of fine clay or silica components and flotationable natural organic components have already been removed. be removed.

In some instances, some of these materials still exist, but there are also More cleaning than can be done in the third stage process.

Quoting Figure 1, it can be seen that downstream from the sieve system is sent to cyclone 32. . Overflow liquid is removed via line 33 and concentrated sludge is removed via line 34. and then to an attrition device, such as a pebble mill 35. Sufficient or desired slug After loosening the material and before substantial precipitation occurs, the fine product passes through line 41. and transported to the classification system 40.

In the preferred embodiment described and shown, the classification system 40 is configured with countercurrent water flow. It consists of multiple classifiers arranged in series. More specifically, the conventional screw - Classifiers 42, 43, 44 and 45 are shown arranged in series. sura The edge material is conveyed to these classifiers via lines 46, 47 and 48 so that Generally for shedding wood, natural organic matter and low sedimentation fine materials such as clay. For backflow/repression or flush/water flow, use flow lines 50, 51, 52 and 53 respectively. arise. Contaminated cleaning material is removed from the system via line 55. washed , the coarse fraction, typically the silica sand component, is removed from the system via line 56. From there, it is transported to stage 3.

Referring to the schematic diagram in Figure 1, the wash stream from the classifier through line 55 is 56 and directed to the concentration of solid material, which is passed through line 5 for incineration. It can be removed after 7 steps. Contaminated water discharged from the filter system via line 58 is Sent to Stage 3 for use.

Stage 3 Separation of organic materials from soil components by flotation The flotation process is used in the mining and pumping industries. It is known for. Flotusi Floty John - 50's Anniversary Boli Umm, Nido.

Pie Fuyuastenow, D.W., American Fist Institute On mining, metal radical, and petroleum engineers Ink 5. Niney York, 1962; Floatation, Volume ■, Ni Do, pie fuyuastenau, em, see.

American Institute on Mining, Metal Radical, and ・Petroleum Engineers, Inc. 0. Ninny York, 1976, Michal Engineers Handbook, 5th Nido, Pi Perri, Robert ・F1. McGraw-Hill Fist Book Co.: New York 1973. pp2 1-65 to 21-69. Wills, B.A.: Mineral Processing. Chikunoroshii, Bergamon Press, Ofsford, 1979. pp276- 337 and Zimmerman, R., E., and Ran. Varnish, sea 0. “Par 3; Rias Flotigion", Coal Preparation, 45th Φnido 0. Nido, Pie Leonard, Jay, W, American Institute Auto Mining, Metal Radicals, and Petroleum Engineers Ars, Inc. 2. See Niney York 1979.

These statements are cited as statements in the specification. Flotation can be provided on various machines Ru. Generally, flotation process machines fall into two basic categories: mechanical flotation machines and gas flotation machines. It is divided into selection machines. There are two types in each category, one that operates as a single tank and the other that operates as a single tank. In the Noto series, there are some that operate as storage tanks (or cells). fact Although any flotation system may optionally be used with this process, the generally preferred process is Including the use of mechanical flotation processes, alone or in series with other similar equipment. final flotation A step (polishing step) may not be required in some purification schemes.

In the application of the present invention, the basic action of flotation fractionation is to bring hydrophobic contaminants into contact with air bubbles. The process is to attach the parts to each other. Because air bubbles carry hydrophobic materials with them Climb to the top of the flotation tank. This generally involves flotation of contaminant bubbles to the top of the solution. This can be removed by overflow, skimming, etc. As a result, flotation tanks Or the solid material contained within the cell is substantially excluded from the hydrophobic material.

Specific applications of flotation techniques are included among the preferred applications of the invention. In particular, the process Removal of organic contaminants from soil and from organic matter that is not easily dissolved from soil residues. including soil separation. Grease, oil and any dissolved PCP or other toxic organic Organic components, including substances, are typically hydrophobic, i.e., amenable to removal via a flotation process.

Generally, what is required is that the machine keep the soil particles in suspension and Additionally, the system uses air to substantially move the air bubbles and hydrophobic organic matter to the air bubble surface. To ensure frequent contact between bubbles and particles, sufficient dispersion of air bubbles through the solution is Also collect air bubbles with your child.

Generally, concentrations of about 10-40% solids by weight are effective in the flotation stage. preferred Avoid high solids concentrations and/or vigorous agitation, thereby reducing attrition (particles/particulate particles). Rodion) rarely occurs. The reason for this is that attrition pulls the bubbles away from suspended particles. This reduces the time for organic matter to migrate into the bubbles. .

Various fabrications of flotation devices can be utilized with the process of the present invention. these are , for example, developed for other uses, operated with suitable stirring speeds and air bubble flows. including a moving flotation machine. Such devices produce air by simple suction of air from the atmosphere. This includes systems that generate bubbles and systems that use fractional blowers or compressed air sources. flotation machine available Or the cells are, for example, Denver Equipment Division, Joy Manufacturing Company, Colorado Springs, Colorado 80 901. Outkumbu Oy, Nisbuu 20. Finland, and Wenco, Sa. Obtained from Crament, CA 95852. Such devices generally Although developed for use in the mining industry, they are easily amenable to the application of the present invention. can be adapted to

Referring to Figure 1, stage 3, the flotation stage, is generally indicated at reference number 60. .

If the pre-treatment in stage 2 provides sufficiently purified soil material, the soil material can e.g. For example, it is transported to the flotation cell 61 through a flow path 62. As already shown, e.g. The Clew classifier is used to clean well-polished or otherwise uniformly sized soil particles. When used to clean and transport from a typical pillar processing dump, the cleaning material must be It consists of approximately 85-95% soil and contains 55-20 pp PCP. Sufficient amount of materials along with water is sent via line 63 to flotation cell 61 for cell operation. stir Start and maintain a suitable speed to prevent substantial settling of the material. That is, this is actually The speed is high enough to keep qualitatively all particles in suspension. Air bubbles flow through the flotation cell during operation. formed within. These air bubbles, typically numerous microbubbles, are caused by atmospheric suction. Or it can be formed through a blower or compressed air source or other equipment. generally sufficient foam shape The formation ensures effective flotation of organic materials from soil materials for effective purification. done for the sake of The organic material trapped in the air bubbles floats to the top of the machine, From there, by overflow or by using conventional mechanical foam skimmers etc. can be removed through passage 64. Similarly, fine soil with adsorbed organic matter The particles also collapse into bubbles.

For stage 3, reference number 60, as shown in Figure 1, a high degree of cleaning is achieved. In , a second flotation cell 0 is shown used in series with the first cell 61 . cell The downstream from 61 is sent to self 0 by flow path 71. water for foam formation is sent to self 0 via line 73. Remove overflow or bubbles at 74 75 for downstream or refined soil. The clean soil is separated from the water at 76 and removed at 77. It will be done. Transport water may be removed at 78 and recycled to backwash to stage two.

In the preferred embodiment shown, the foam from 64 and 74 is concentrated while there The water removed is sent to water purification system 80. Purified water can be stored in a water storage tank 81, It can also be used throughout the process.

In FIG. 2, a typical flotation cell for use in the system of the present invention is schematically depicted.

In FIG. 2, cells are generally designated by the reference numeral 100.

Cell 100 includes a tank portion 101 in which water and contaminated soil, typically sludge, are stored. Lee is discarded for processing. Sludge or slurry 10 in tank 101 2 stirs faster with the stirrer/aerator 103. Special stirrer 103 shown includes a plurality of wings 105 thereon, which rotate quickly to violently stir the water. Turn and keep solid soil material from settling at the bottom of the tank. Air bubbles are generally Stirring cone with airflow indicated by arrow +07! In the high vertical area between 05 and stator It is formed. The foam spreads throughout the slurry or sludge, allowing soil particles to come across it. The organic matter moves to the interface with the air bubbles, and the organic matter moves within the foam of the bubbles 110. surface to the top of the tank. The bubbles then appear as indicated by reference numeral 112. , skimming or overflow 111. mixed in tank The three components (air, soil and water) are introduced via lines 115 and 116, respectively. shown as being done. Downstream is via an outlet 120 actuated by a valve 121. displayed so that they can be removed.

Figure 2 is intended to be schematic only, and various special mechanical configurations may be used. That is understood.

In the system of the present invention, stirring speed, air bubble size and concentration, water concentration, and tank internal residence time to reach the highest, or at least the desired level of efficiency and purity. It can be changed to Flotation cells can be operated in closed, batch, recirculating or entirely continuous operation. It is understood that it is difficult to move.

In general, continuous systems are more efficient full-on systems.

Referring again to Figure 1, downstream from the flotation system is generally designated by the reference numeral 75. . The material generally contains less than 10 ppm PCP, preferably 5 ppm PCP. Contains purified soil containing P or less. At this relatively low concentration, PCP is essentially shows almost no problems. Optionally, in some applications of the invention, the soil is more To obtain the above purification, it is dried and returned to the hole area along with the active microbial components. child At relatively low PCP concentrations, microbial action is more effectively accommodated and regulated. It can be done.

The skimmed or overflow material from the flotation cell can be concentrated if desired. and can be incinerated. Send some mixed water to a water treatment facility, etc. Can be done. Foaming agents may be added during flotation. Foaming agents are generally stable foaming agents. changes the surface tension of water, which in a sense facilitates the formation of The foaming agent is methyl alcohol. Contains mill alcohol and pine oil. These typically have a flotation device width of approximately 0,0 1-0.27! Can be used in amounts of bs foaming agent/ton of soil.

PH adjustment, surfactant, temperature adjustment The general process is described without any special adjustment of pH and without the use of added surfactants. did. In general, many of the soil treatment processes of the present invention require efficient removal of organic contaminants. can be obtained without special pH adjustment or use of surfactants.

pHH adjustment can be done at most stages if deemed necessary. interface Active materials can also be introduced at various stages to facilitate the removal of organic material from the solid particles.

The process is generally effective at ambient temperature, but may be carried out over a wide range of temperatures. How much In that example, temperature regulation may be used to facilitate certain steps.

Model test facility The process already described is very flexible. That is, if the device does not perform the described unconventional When configured for sequential operation, it can be carried out using entirely conventional process equipment.

The specific equipment to be used will depend on the characteristics of the soil being treated and the contaminants it contains. It can change depending on the characteristics of the object. Soil composition and particle size range and contaminant concentration and gender As quality varies, the individual details of the process may vary accordingly. For example, there is In the system, no flotation step is required. In other systems, a single flotation cell offers effective purification. In yet other systems, multiple cells in series may be all that is needed to serve is required.

In general, it is best to determine what specific equipment is needed before assembling the entire scale treatment facility. Therefore, it is preferable to estimate the special areas to be treated.

To achieve this, suitable A mobile, small-scale facility will be constructed using appropriately prepared equipment. like this Through this configuration, evaluations of soil and soil refining processes can be made. With this procedure , the most efficient use of the flotation process along with other purification steps can be determined.

The operation of this process will be further understood by reference to the following test examples and examples.

Test example 1 Characterization of soil contaminated with PCP Contaminated soil collected from the waste collection site of a former treatment plant was used for the following test measurements. . The three major impurities involved are pentachlorophenol (PCP) and grease/oil. It was an ingredient. The soil samples contained significant amounts of wood. Initially, the soil was 1/2 It was classified into smaller sized pieces and contained about 18% water. The total PCP concentration in the sample was approximately 25 It was 0 ppm. The sample contains fine particles of various sizes, and the size varies accordingly. I couldn't get it to match. Generally, the PCP concentration is It varies throughout the body, and as shown in Table 1, it is coarser than 20 mesh and 150 mesh. It was found that the fraction size was higher than that of Nyu. The data is a rough sketch A two-step process of leaning and fine screening or classification results in highly concentrated PCPs. Reveals soil particles by removing a small fraction of the original material that has been reduced. He suggested that it be cleaned thoroughly. The wood concentration in soil samples is together with the wood particles contained in the pieces was found to be approximately 5-10% by weight. . Grease/oil concentrations were generally about 4 (1-80 times) greater than PCP concentrations.

Table 1 Typical distribution of pentachlorophenol in soil 3M 13.4 1.33 3016M 62.6 6.23 42410M 29.6 2.95 71520 M 302.8 30.14 31035M 1g6.2 18.53 22265M 204.4 20.34 124100M L12.7 1 1.42 120150M 49.2 4.90 141-150M 41.9 4.16 504 1004.8 100.00% Test example 2 Dry and wet screening This separation step is aimed at removing handling difficulties caused by the wood content of the soil and We attempted to confirm the distribution of PCP in soil. The process is carried out at 1O or 20 meshes. step l as described above, including cleaning to remove coarse wood particles. It is done.

The test soil was subjected to dry and wet screening. Dry screening is It is just a cursory test to remove coarse wood particles. for dry screening First, the soil samples were first dried at 75 degrees Celsius for at least 16 hours. then dry soil was passed through a 10-meter sieve using a hand-vibrated sieve with a frame. I sifted it. The fraction of plus lO mesh and minus 10 mesh PCP was analyzed. The dry screened material may contain a significant amount of wood. It was found that the plus lO mesh fraction had a considerable amount of unbalanced PCP. showed accumulation. The results of this screening are reported in Table 2 below.

Table 2 Assaying fractions from dry screening For wet screening, Pour an amount of tap water equal to the weight to be separated into a large tank. a mountain of soil, Place it on a 10-meter sieve fitted with a frame, keeping the sieve partially submerged in water. I shook it.

The +lO mesh fraction remaining on the sieve is then poured into as little water as possible. Washed and collected. The process was repeated until all soil samples were screened. + The IO mesh section was dried and sampled for analysis of PCP. This dry type +1 A secondary sample of the 0 mesh product was sieved into 5 size fractions. . Typical fractions derived from +lO mesh product screening The results are shown in Table 3.

Table 3 of the fraction derived from the +10 mesh obtained by wet screening. assay The IO mesh slurry in the aquarium was allowed to settle for 72 hours to remove the aqueous layer or supernatant (secondary liquid). Purified matter) was taken out with a siphon and collected. This wash is a slurry (solids plus solution) Analyzed as, but also filtered to determine the weight of solids remaining in suspension. did. The precipitated solids were re-slurried with an equal weight of water and allowed to settle for 15 minutes. . The supernatant (secondary wash) was again siphoned, collected, and analyzed. reslurry - Step 1 was repeated two more times and washed four times with water. Sedimentation on top of sandy soil Leave the dark layer (sludge) on until the final siphon operation and remove it. , dry, weighed, and analyzed. After removing the sludge layer, collect the final precipitated solid. It was then analyzed by dry method and gravimetric analysis (-10 mesh). Raw from wash cycle Typical assays for the products are reported in Table 4.

Table 4 Wet screening and cleaning of soil Product Liquid Dry Solid Percent Blue Liter Gram Solid Assay pmPcP + 10 2.280 6.9 556.4- l0M 27,250 83.5 135. 2 Hedoro 50 0.16 567.81 Washed items 24.85 12.4 0.04 1:(,82 Next wash 22.40 2,266.9 6.9 159. 03rd wash 16.90 gll, 2 2.5 63 ．． 04th wash 1.00 -0- 10.0 total 32,640.5 100.0 calculated head 304. A special slurry of supernatant It was allowed to settle for 72 hours before being picked up. That is, this wash contains only a very small amount of solids. Not included.

From these results, wet screening can be used to detect PCP in the −10 m The content was obviously reduced. A large proportion of PCP is found in washes, where In the case PCP was present in solution and also associated with the suspension of wood and clay materials. Canada In addition, wet screening also removed relatively soil containing high PCP values. It is an effective means to separate wood flag silane (-1O mesh sieve). It turns out. The wood fraction can then be easily incinerated.

Example 3 flotation The slurry that has gone through the wet screening operation is contaminated due to the presence of oil and fine particles. It can't be filtered anymore. Hedoro (slin+es) is fine soil, wood chips and oil suspensions. The cleaning methods for this suspension include flotation, centrifugation, and sedimentation. including lees and combinations thereof.

Some of these methods are carried out in the second step, as described above, and include a polishing scrubber. Further grind the agglomerates and scrub the surface of the abrasive particles in a bar or pebble mill. This step is carried out in a classifier to clean fine or flotationable contaminants. Including processing rallies.

The result of such operations is a relatively concentrated concentration of PCP and oil and/or grease. The product is separated as waste. especially fine clay particles and small wood Debris is removed in this step.

Soil samples are ultimately subjected to flotation to reduce PCP concentrations, or concentrations of other contaminants. A reduction below a minimum value or at least a desired value is preferred. this is, It is particularly effective as a method for obtaining relatively clean silica sand material.

The flotation process with pretreatment (washing) begins with wet screening up to the IO mesh. It was carried out on soil. The slurry after the screening operation was heated to 120 rpm. The mixture was stirred in a flotation machine. The solids content of the slurry was approximately 106%. sura Lee was flotated for 15 minutes without adding any foaming agent. From the top and bottom of the cell sampled and measured. The results are shown in Table 5.

Table 5 Flotation liquid of 10 mesh slurry by wet screening Solids Measured value PCP product (liter) (gram) PCPp pm Content % Habe 2.0 102.0 117.5 32.5 Ant-Flow 4.0 300.0 122.2 67.5 The results obtained from this experiment were Flotation on the pre-treated material through the cleaning process has a lower concentration of contaminants compared to the feed material Generates a large amount of foamy fluid material without any difficulty in handling. However, under The flow contains 3/4 of the solids and is fully capable of settling. In conclusion, sludge treatment By the early part of the process flow sheet, flotation It is not necessarily practical to implement this. Rather, it is generally Continuous cleaning operations that reduce the difficulty of Lee treatment and further reduce contaminant content. Preferably made. This is achieved by using the second stage method, as described above. can. Alternatively, at the beginning of the flowsheet, a difficult sludge: i.e. , which are not amenable to scrubbing and require special treatment such as sedimentation. It is effective to use flotation to separate fine materials including organic materials.

Example 4 scrubbing In a planned experimental program that required 30 different experiments, The effect of scrubbing on I considered it. In this experimental design, temperatures of 25-65°C, 10-+5 min. time, pH of 5-11, o, i-0, 51 bs/small ton soil.

Soil contaminated by PCP is wet-filtered using a lO mesh to remove coarse wood chips. soil The fraction of the soil up to 10 mesh is dense pulp with a solids content of 50%! It(p slurry with water at ulp density). Bring the valve to the desired temperature and p Adjust H and add surfactant. Covered stirrer rotating at 1000 rpm Scrub the slurry (with vigorous stirring) in a divided container using . The pH is kept constant during the test. At the end of the scrubbing period, rinse the slurry for 5 minutes. Allow to stand, and collect the aqueous layer or supernatant using a siphon. Remaining precipitated solids reslurried to 50% solids content using fresh water and stirred for 15 seconds; Let settle for 5 minutes and collect the supernatant with a siphon. The collected siphon liquid is fine particles. sieve through a 48-mesh sieve to remove wood fibers. precipitated The solids are filtered and the filtrate is combined with the siphon sample to form the final suspension. . The filtered solids and the xylem fraction of 48 metsunyu were dried overnight at 75°C. Dry and grind to 100 mesh pieces. PCP for soil, liquid and water parts Measure.

Statistical analysis of the results showed that the residual PCP in soil is linear with respect to pH and time. In a relationship. The least influential factor is surfactant concentration, which Whether the surfactant is anionic, cationic, or anionic-nonionic do not have. The most influential factor is PH. Removal of PCP from soil Cent (PR) can be expressed by the following equation.

PR=39.89-0.187X (min) -1, 96X (pH) Example 5 Cleaning scrubbing soil with classifier After the flotation test as described in Example 3, the soil remaining in the flotation machine is removed by an agitator. After stopping the rotation, it showed a precisely sorted precipitation pattern. Faster, without exception A black layer of precipitated wood and soil later forms on top of the sandy material. Ru. From this, we conclude that the classifier is rather highly contaminated by PCP. It is estimated that it can be used to remove light components. This test equipment 3.5 inch long x 2.5 inch wide foot section that can be washed with a fixed jet of water. A screw classifier was used. The feedstock for the classifier is screened PCP This is the fraction up to 1O mesh of the contaminated soil sample. This sample is tap water. Slurry to 50% soil and scrub for 1 hour with vigorous agitation in a mixing tank. I clicked. This slurry is passed through a classifier to remove sandy waste and overflow (first overflow) was collected. Let the overflow stand still and let it settle on the fine sand. The black layer of the filter was selectively removed and analyzed separately (Hedoro).

The remaining overflow (first overflow) was only analyzed as slurry. The suspension was filtered and the weight of solids remaining in the suspension was also measured. Sand in the classifier The bed was removed (first bed), dried, weighed, and analyzed. First sandy discharge ( The first product) was subjected to analysis. The remaining first sandy waste was slurried with tap water. , back into the empty classifier to produce a second overflow and a second sandy effluent. I set it.

The sand treated by the classifier is sampled for analysis (second product) and bed The sand was recirculated two more times without being removed to simulate a multi-stage sand cleaning system. . The experimental results are shown in Table 6.

Table 6 Washing liquid of 10 mesh soil by screw classifier Solid matter PC P amount PCP process (liter) (gram) ppm Content% feedstock 20000 105.5 product Hedoro 2365 194.5 21.2 1st bed 3630 31.2 5.2 First product 124 8.4 Second product 122 7.2 0.2nd product 3 Product 126 7.5 Final bed 2000 8.0 0.7 Final product 10831 B , 1 4.121056 103.1 100.0 The above data is Qualitative amounts of PCP removal can be achieved by using a classifier before introducing the soil material into a flotation cell etc. This supports the results that can be achieved by However, during the recirculation of classified sand No further substantial PCP removal is observed at this stage. This is a classification The residual PCP in the sandy product is fixed in particles of similar size and density to sand particles. This suggests that Separation of PCP from these particles is demonstrated in Example 6. As mentioned in This can be easily done by using line steps. Alternatively, the residual portion of PCP and oil/grease materials can be removed in a flotation machine as described in Example 7. Wear.

Test example 6 Confirmed in soil cleaning test example 5 using multi-stage classification with intermediate stage scrubbing. Continuing with the manufacturing process, this test was carried out by adding sandy waste to the same classifier simulating the following steps: To remove the heads in a laboratory screw classifier before recycling the output product It was designed to better simulate a group of classifiers. Also, intermediate stage scrubber scrubbing the classified sandy discharge product at 210 rpm in a flotation machine. It was simulated by In detail, 110 meshes of soil contaminated with PCP The sample was slurried with tap water to a solids content of 50%, scrubbed in a flotation machine, and It was fed to the Liu classifier. Overflow of classifier (first slurry) and sand discharge was collected. Remove the sandy bed (first bed) remaining in the classifier. , dried, weighed and analyzed. A sample of the sandy discharge was analyzed (first sand) and the remaining The sandy product was slurried with tap water and heated at 2100 rpm for 15 minutes in a flotation machine. attribution scrubbing and empty classifier for second stage of cleaning. I returned it. This cycle was repeated twice for a total of three stages of purification. The results are in Table 7. Shown below. This data shows that with the appropriate intensity of intermediate scrubbing, soil Clean from 120 ppm PCP to approximately 5-105-1 Opp in 3 steps. showed that it is possible to

Table 7 Soil cleaning feedstock by multi-stage classifier with intermediate stage scrubbing 12000 120 products 1st slurry 83 916.3 14.9 86.1 1st slurry Tsudo 2080.0 49.6 7.2 1st sand 65.2 8.2 0.0 Second slurry 76 113.6 0.3 1.4 2nd bed 2155.0 12. 8 1.9 2nd sand 56.8 9.1 0.0 maximum Final slurry 45 22.7 0.2 0.6 Final bed 　　　　　1520.0　　　? , 1 0.8 final sand 4550.0 6.3 2.0 Calculated feedstock value 125.3 Test example 7 Cleaning soil by flotation As mentioned earlier, the final removal of PCP from the soil, i.e. the refinement stage, is accomplished by flotation. was achieved. This unique stage has very low PCP and is not necessarily at the dump site. Final soil production that can be processed in a manner that does not require special handling. guide things.

Soil contaminated with PCP is treated in five stages, including scrubbing at pH 9. A scrubbed soil slurry was prepared as a selection test feedstock. solid slurry The content was adjusted to 33% and flotation was carried out for 5 minutes.

Conditioned with 0.3 bond pine oil or a small ton of MIBC/soil and an additional 10 Flotated for a minute. Another test was conditioned with a small ton of 0.1 bond pine oil/soil for 10 minutes. This was done by carrying out two stages of flotation by whisking for 5 minutes. . The foam product, underflow solids and underflow filtrate are combined and PC It was subjected to P analysis.

Representative results are shown in Table 8 below.

Table 8 Refinement of scrubbed soil by flotation Fluid Solid PCP PCP process (Liters) (Grass ) ppm Content% feed material 500 9 ．． 2 bubbles 0.4 1.8 2J 18.8 underflow Solid 494.5 4.6 47.0 Filtrate 1.4 1.2 34.2 Calculated feedstock value 9.6 From the above data that matched for all tests, the refinement operation was It can be concluded that it can be used to reduce P content by 50%. Most of the solid ingredients in the foam looks like clay. The sandy material was separated in a relatively clean manner. The result is also , that it appears to be beneficial to operate at a basicity within the pH range of 7-8. Indicated.

Although specific embodiments of the invention have been described above, except as claimed, It is not intended to be limited by the particular steps, forms or devices described and illustrated.

air FIG. 2 Submission of translation of written amendment (Article 184-8 of the Patent Act) August 8, 1990 9 nights

Claims (15)

[Claims] 1. A process for treating soil contaminated with organic material; the process comprises: (a) subjecting the soil to a friction process to loosen it into particles that are suspended in a liquid; and coarse particles. (b) separation of a fraction containing relatively fine particles from a fraction containing For removal, it involves subjecting the contaminated soil to a classification process. 2. The classification process determines the fraction containing fast-settling particles by their relative settling velocities. Claim 1 comprising the separation of a fraction containing relatively fine, low-sedimentation particles from the sample. process. 3. The claim is that the classification step is carried out before the safe settling of the suspension from the attrition step. Steps 1 and 2. 4. The stage of wear and tear is (a) forming a slurry of soil material of 10 mesh or less in water; - contains 40-70% solids by weight, and (b) the slurry is passed through an attrition mill. 4. The process of claim 3, comprising passing. 5. (a) The stage of classification is carried out in the soil as part of the fraction containing particles of low sedimentation. Claims 1, 3 and 4 comprising the substantial removal of relatively fine particulate clay components from process. 6. In the flotation cell, the fraction containing fast settling particles is separated from the particles and the organic matter in the soil selectively distributing hydrophobic materials containing fine particles of air at a sufficient concentration to encounter the bubbles at the interface. The method of claim 3 comprising the step of subjecting the soil to a flotation process containing suspended particles in the presence of foam. Process. 7. Process for treating soil contaminated with organic materials; Selective distribution of hydrophobic materials containing organic matter and a sufficient concentration of foam to encounter the interface at the interface It involves a flotation stage involving flotation particles of soil in the presence of microbubbles of air. 8. The process of claim 7, wherein the organic matter comprises an oil with dissolved pentachlorophenol. . 9. Process for treating soil contaminated with organic materials; the process consists of (a) removing the soil from the environment; Screening to form material with a size smaller than that of a sieve. and (b) disintegrating the material into fine particles suspended in a liquid, into materials no larger than a sieve. Subjecting to an abrasion process (c) From the fraction containing fast-sedimenting particles to relatively fine particles based on the relative sedimentation velocity. A classification process is applied to contaminated soil to separate and remove fractions containing low-sedimentation particles. The classification stage is carried out before complete settling of the suspension from the attrition stage. and (d) subjecting the fast settling material from step (c) to a flotation step; The flotation stage involves the selective separation of organic matter into the scrubbed material and soil in a flotation cell. Hydrophobic materials meet the interface with bubbles, which allows organic matter to flow through the scrubbed material. Air particles of sufficient concentration to be separated from the feedstock and flotated into the upper part of the flotation cell. comprising flotated soil material in the presence of microbubbles; including the stages of 10. (a) Materials whose classification stage is smaller than the sieve are transferred to the classification system by backwashing with water. including (b) fractions thereby containing small wood materials and relatively fine contamination; Soil particles include soil, wood-containing fractions and generally a disproportionate amount of contaminants 10. The process of claim 9, wherein relatively fine contaminated soil material is selectively removed. 11. (a) Claim 10 in which the classification system includes a plurality of screw classifiers arranged in series. process. 12. (a) The flotation stage is rapid through several flotation cells arranged in series with precipitated material. 11. The process of claim 10, comprising a transition. 13. (a) A claim in which the soil is sieved to 10 mesh or less before the attrition stage. 10 steps. 14. Treatment process for soil contaminated with organic materials; the process is (a) from the waste collection site; To remove volumetric items from the soil by digging and grizzly passage (b) Crushing the soil into small particles with a trommel (c) ) screening small particles to 10 mesh or less (d) minus 10 subjecting the mesh material to an attrition process to break the material into particles suspended in the liquid; (e) contains relatively fine, low-sedimentation, particles from the fraction containing fast-settling particles; Performing a classification process on contaminated soil to separate and remove fractions (f) subjecting the fast settling material from step (e) to a flotation step; In the flotation cell, the scrubbed material and soil organic matter are selectively distributed with hydrophobic materials and encounters the interface with bubbles, whereby organic matter is decomposed from the scrubbed material. , and the presence of microbubbles of air in sufficient concentration to float in the upper part of the flotation cell. The lower step involves the inclusion of suspended soil material. 15. (a) from the classification stage to the complete settling of the suspension from the attrition stage; , the process of claim 15.