WO1997000129A1

WO1997000129A1 - Treatment of contaminated soils

Info

Publication number: WO1997000129A1
Application number: PCT/NZ1996/000056
Authority: WO
Inventors: John Pollock
Original assignee: Envirosil Limited
Priority date: 1995-06-14
Filing date: 1996-06-14
Publication date: 1997-01-03
Also published as: AU6141196A

Abstract

The treatment of contaminated soils, solids and other industrial wastes (whether liquid or solid) by the application of microfine and processed diatomaceous earths (diatomite) to reduce the presence of organic contaminants such as chlorophenols, phenols and organo-halides and where the resultant mixture is substantially chemically inert. Raw diatomite is processed by: desegregation; natural drying; treating with microwave, radio frequency or plasma radiation to remove any organic matter (if present) and to obtain the maximum surface area available; hardening by exposure to water, and further drying by natural means. The process may further include the addition of a reactive secondary material to the active surface of the diatomite by heat or chemical means; wherein the secondary material is selected from the group consisting of: an ionic material, a metallic material, a finely divided carbon, and a combination thereof.

Description

ΗTLE: TREATMENT OF CONTAMINATED SOILS

Technical Field

The invention relates to the treatment of contaminated soils, solids and other industrial wastes (whether liquid or solid) principally with contamination by chlorophenols, phenols and organo-halides. The treatment is by the application of microfine processed amorphous silica to reduce the presence of organic contaminants.

For the purposes of this specification, the contaminants and organic molecules referred to include, but are not limited to, chlorophenols, phenols and organo-halides, for example polychlorophenols (PCPs), polychlorobiphenols (PCBs), dichloro-diphenol- trichloroethane (DDT) and other dioxins, and heavy metals.

Background Art

At present it is known to treat contaminated soils and liquids with zeolites, diatomaceous earths (diatomite), or other amorphous silica products in order to further process the resultant mixture to either destructively absorb or to destroy the organic contaminants. For example, diatomite has been used in combination with a caustic liquid for retrieval of gas from a flue (US patent no. 4738690). Diatomite has been used as a water filter for returning, recycling and enhancing purified water (US patent no.5093012).

Where diatomite is being used in combination with a liquid waste there are two different processes in the manner in which the treatment proceeds. Firstly, generally the diatomite is mixed with the sludge or waste to be treated, bound in some way either alone or with another material, and then heated to a high temperature in order to reduce the contaminants to gases or to otherwise render them inert. For example, US patent no.

5102538 treats filter sludge and then subjects it to very high temperature in order to end up with the resultant inert product. US patent no. 5245120 discloses the use of a sorbent metal-reactive material with metal coated ash particles being combined together under heat to produce an insoluble metal compound.

Alternatively to the above method of treatment, the contaminant is bound in some way with a plurality of products and then heated. Examples of this can be found in US patent no. 5496404 in which the waste plus an absorbent or spent absorbents and a further additive are incinerated to produce a clinker. This is pulverised and then used as a cement base for bricks. US patent no. 5245121 discloses the use of diatomite and calcium hydroxide to combine with heavy metal wastes to produce a mixture that is heated in oxygen and incinerated at temperatures up to 1500 ° C. US patent no. 5168820 discloses a method of production of clinkers that is similar but once again incineration to high temperatures is used.

There is relatively little prior art on the pretreatment of the diatomite or the other absorbent used or absorbent used. For example, WO 90/11143 discloses a method of preparation of an absorbent in which the diatomite or zeolite is treated with an acid and then later heat treated. US patent no. 3873581 discloses a method in which activated carbon is added

(doping) to a diatomite along with a mercury reactive factor. However, the result from this is that the spent diatomite is not inert nor is there any possibility of in situ recovery of the waste.

From the above prior art it can be seen that there is no method presently available which renders a contaminated waste inert without the use of additional products to the diatomite and/or without high temperatures. Very little is available showing working on contaminated wastes or soils in situ and the only apparent known byproduct usage of the material is as a pulverised clinker or as a landfill disposal material (after heavy treatment with additional products and with the application of heat). An object of the present invention is the use of diatomaceous earth to absorb the contaminants, thus rendering contaminated soils and liquids inert, and to provide a useful and cost effective alternative to those methods already available. A further object of the invention is the preparation of the diatomite as used in the decontamination process.

Disclosure of the Invention

The preparation of refined and processed diatomite includes the following steps: desegregation and natural drying; treating with microwave, radio frequency or plasma radiation to remove any organic material (if present) and to obtain the maximum surface area available; hardening by exposure to water for up to seven days; and further drying by natural means.

The desegregation is preferably by mechanical flailing. The treatment may also include "doping" of the activated surface by addition of appropriate ionic or metallic materials and combined by heat or chemical means to the base material of the diatomite silica. Alternatively, or additionally, very finally divided carbon may be associated with the base material. This can be used as an energy source or as a catalyst to assist in the purification process. In some instances iron and iron alumina may be present in the pore lining with the activated carbon. The metallic materials which may be added may include small portions of any or all of the following: magnesium, potassium, iron, sodium, tungsten, gallium.

Radiation, or exposure to infrared radiation, may be used in addition to dry the material. After it has been dried the diatomite can be hardened by exposure to water in soaking tanks for up to seven days.

Preferably the diatomite includes diatoms that have dimensions 25 micron by 11 micron by 1 micron thick, preferably predominantly of the Cymbella type.

The present invention further provides a process for the treatment of contaminated solids or liquids, said process including the following steps: adding prepared diatomite (as described above) to the liquid or solid (containing contaminants) at between 0.05% and 1000% by weight for a predetermined time to permit reaction of the diatomite with organic contaminants in liquids or solids to produce a substantially chemically inert material.

More preferably the percentage addition of the diatomite is between 0.1% and 20% by weight. The reaction times will vary, depending upon a number of factors:- the temperatures surrounding the soil treatment area or the temperature of the liquid being treated, the nature ofthe contaminants, the degree of bonding or coalescence between the contaminant and the waste being treated, the soil area of the contaminant and of the waste being treated, the chemical concentration in the waste being treated and any surrounding water. Preferably the average treatment time is for between 24 hours to 28 days.

Best Mode of Carrying Out the Invention

The above process for the treatment of contaminated liquids or solids can be applied in situ. The diatomite may be applied as a solid (a fine amorphous solid) or in a slurry form, either hot or cold, using water as the solvent. Preferably the concentration of the diatomite in the slurry varies between 25% to 45% by weight. Deflocculants may be added, for example 0.5% by weight of sodium hexametaphosphate or sodium silicate. Alternatively, the diatomite may be applied as part of a steam injection into the contaminant to be treated.

The dosage for such steam injection has been found in practice to be optimum between 0.1 to 2.5 % by weight of the soil content. A slurry is made (for steam injection) at the above concentrations and injected into a high pressure steam line, for injection into the contaminated soil, at concentrations between 1 to 10 % by weight of the steam jet.

The application and rates of reaction are governed by whether the diatomite is added in solid or liquid form, and by the particle size of the material to which it is added and by the uniformity of distribution of the diatomite.

The reaction times will vary, depending on a number of factors: the temperature surrounding the soil treatment area; the type of soil; and the degree of bonding between the contaminant.

EXAMPLES

1. Preparation

(a). Preparation of diatomite for use to treat contaminated soils.

Alumina dross and diatomite are mixed 50-50 by volume. Water is added up to 5:1 by volume, until a fluid gel is obtained. More water and sodium chloride at 0.2% by weight is added to this solution and the resultant mix is treated and dried under microwave heating for 30 minutes at 0.8 kW in a plastic container.

The crystalline solid material is extracted by known method, and washed on filter paper prior to being used, and dried at 120 ° C for 16 hours.

(b). Where diatomite is to be added (at a concentration shown in the table below) into a filter column, the material is treated by revolving in a drum in order to aggregate the material. This material is then discharged using continuous discharge sheets and dried, by heating to 600° C. A soaking period of up to 12h hours is used to harden the material. The material is then combined with silica sand and anthracite of filter grade for placement as filter media.

Laboratory Example.

(a). Treatment of contaminated soils. A standard garden soil was used, ensuring that it was uniform throughout. The sample was divided into seven separate samples. The first sample was set aside as a control. The other samples were dosed with PCPs at a concentration of 0.1% by weight of oven-dried soil. Samples A-G were tested for PCP concentration by the techniques outlined below prior to being treated with diatomite.

Diatomite (as prepared by the first method under Example 1 above) was added to the soil samples B-G as set out below in the table. The samples were stored for two weeks before being analysed. The samples were tested for leachable PCPs.

The extraction technique used was US EPA Toxicity Characteristic Leaching Procedure; TCLP: Extraction Fluid #1: US EPA Methods 13111. The analysis was by aeetylation CCNS. The results are set out in table 1 below.

TABLE 1

Control Mix B Mix C Mix D Mix E Mix F Mix G

Diatomite/ - 2% 1% 2% 5% 5% 1% Alumina

Total < 10 50,000 50,000 50,000 50,000 50,000 50,000

P.C.P. Initial (Total) p.p.b

Final < 10 < 10 < 10 < 10 < 10 < 10 < 10 (leachable)

(based on dry soil) with density of 1.0 kg/m³ p.p.b. = parts per billion.

3. Tar Treatment

The tar used in the field trials included various contaminants (these are set out in table 2), cyanides, phenols, and heavy metals. The processed material is stored in sealed rubbish skips while analysis was carried out. Full mixing ratios were tested as follows:- A 25 litres Tar/m³ diatomite

B 32.5 litres Tar/m³ diatomite (large container) C 32.5 litres Tar/m³ diatomite (small container) D 67.5 litres Tar/m³ diatomite

The material sat in sealed containers after being mixed (in a truck mounted concrete

mixer). The extraction techniques used were those listed above under Treatment of Contaminated Soils. All results below were in parts per million (ppm).

The amount of leachable polyaromatic hydrocarbons were found to be as follows at seven days: TABLE 2 ' Chemical " Untreated A B C D Ave Limit Tar

Naphthalene 14718 1120 1244 1126 455 986.3

Acenaphthylene 6600 312 285 346 239 295.5

Acenaphthene 5906 208 218 177 128 182.8

Fluorene 376 66 58 56 56 59

Phenanthrene 1729 54 72 63 68 64.25

Anthracene 10953 18 13 10 17 14.5

Fluoranthene 5835 26 25 23 9.9 20.98

Pyrene 2576 62 32 23 39

Benzo-k-fluoranthene 624 0.5 0.3 0.4 0.4

Benzo-a-pyrene 988 0 0.4 0 0 0.1 0.2

Dibenzo-a,h- 282 0 0 0 0 0 anthracene

TOTAL PAH (ppm) 55.25 1.87 1.95 1.82 0.97 1.66 2

The material was treated at seven days for cyanides, with test results being as set out in table 3.

TABLE 3

Days A B C D Mean Limit

0 14.3 14.3 14.3 14.3 14.3 0.1 7 1.1 0.3 0.4 0.3 0.53 0.1

The levels of phenols in the samples were tested at 0 days, 1 day, 7 days, and 28 day intervals. The results are as set out in Table 4.

TABLE 4

Days A B C D Mean Limit

0 11132 11132 11132 11132 11132 10

1 18.7 35.5 46.0 67.1 41.8 10

7 16.8 32.9 40.6 46.4 342 10

28 12.4 18.0 25.9 32.8 22.3 10

Metals in the tar samples were also tested. The limits in the Table 5 below are expressed in terms of total metal and leachable trace levels.

TABLE 5

With the very low specific gravity of the diatomite, the types of volumes that are being used in the above examples are of the order of a ratio 1:15 Tar/diatomite.

Thus the level of all hazardous materials present in tar can be reduced to a level where the material, once dried to a usable form, can be safely used as landfill, or after natural drying, as a construction material.

4. Tar Treatment Example

A further tar treatment was conducted for testing for phenols with a variety of ratios of diatomite to tar at room temperature under dry conditions. These are as set out in Table 6 and on the accompanying graph. On the accompanying graph, the phenol is represented in grams per cubic metre.

TABLE 6

Sample No. Diatomite/Tar 11 days 25 day 31 day ratio Total phenol Total phenol Total phenol gm^"3 gπr³ gm^"3

1 10:1 77.2 38.6 30.6

2 20:1 45.3 15.6 1.6

3 30:1 27.3 15.4 2.5

4 40:1 20.3 2.3 1.0

5 - 2.3 - -

*1 (outside) 10:1 - 31.9

Day 0: 13600 micrograms per gram of phenols in all samples of tar. The diatomite was at 27.6% moisture content and was pretreated to an aggregate of less than 1.5 mm (screened).

Claims

1. A process for the treatment of contaminated solids or liquids, in which the contaminants aie organic molecules which include chlorophenols, phenols and organo- halides and other dioxins, and heavy metals, εaid process including the following steps: adding prepared diatomaceous earth (diatomite) to the liquid or solid (containing contaminants) at between 0.05% and 1000% by weight for a predetermined time to permit reaction of the diatomite with organic contaminants in liquids or solids, until the resultant mixture is substantially inert.

2. A process for the treatment of contaminated solids or liquids as claimed in claim

1 wherein the percentage addition of the diatomite is between 0.1% and 20% by weight.

3. A process for the treatment of contaminated solids or liquids as claimed in claim 1 wherein if the contaminant to be treated is contained in a liquid then the ratio of liquid to diatomite required is in the range 1:10 to 1:40 by volume.

4. A process for the treatment of contaminated solids or liquids as claimed in claim

3 where in the resultant mixture is air dried, compressed, and used for construction purposes.

5. A process for the treatment of contaminated solids or liquids as claimed in claim 1 or claim 2 wherein said diatomite is in a slurry using water as a solvent, with the concentration of the diatomite in the slurry being 25 to 45 % by weight.

6. A process for the treatment of contaminated solids or liquids as claimed in claim

4 wherein a deflocculant is added to the slurry at a concentration in the range 0.01 to 1% by weight.

7. A process for the treatment of contaminated solids or liquids as claimed in either claim 1 or claim 2 wherein said diatomite is applied to liquid or solid to be treated via a steam injection, said diatomite being in a concentration in the steam injection in the range 0.1 to 2.5 by weight. δ. A process for the treatment of contaminated solids or liquids as claimed in any one of the preceding claims wherein the contaminant is contained in a liquid or solid that is treated in situ with the diatomite.

9. A process for the treatment of contaminated solids or liquids as claimed in any one of the preceding claims wherein said predetermined time is in the range 1 to 60 days.

10. A process for the treatment of contaminated solids or liquids as claimed in claim 9 wherein said time is between 25 and 31 days.

11. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite, said process including the steps of: desegregation of the raw diatomite; natural drying; treating with microwave, radio frequency or plasma radiation to remove any organic material (if present) and to obtain the maximum surface area available; hardening by exposure to water for up to seven days; and further drying by natural means.

12. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite as claimed in claim 11 wherein said desegregation is by mechanical failing.

13. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite as claimed in either claim 11 or 12 wherein a secondary material is combined with the diatomite, to the active surface of the diatomite by heat or chemical means.

14. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite as claimed in claim 13 wherein said secondary material is selected from the group consisting of: an ionic material, a metallic material, a finely divided carbon, and a combination thereof. 15. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite as claimed in claim 14 wherein said metallic material includes small portions of a metal selected from the group consisting of: magnesium, potassium, iron, sodium, tungsten, gallium, and a combination thereof.

16. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite as claimed in any one of claims 11 to 15 wherein the diatomite includes a predominance of diatoms having dimensions 25 micron by 11 micron by 1 micron thick.

17. A process for the refinement and preparation of diatomaceous earth (diatomite) to form prepared diatomite as claimed in any one of claims 11 to 16 wherein the diatomite includes a predominance of the C mbella type.