WO1993015831A1

WO1993015831A1 - Sorbent for immobilization of toxic and contaminating substances

Info

Publication number: WO1993015831A1
Application number: PCT/CS1992/000027
Authority: WO
Inventors: Zdene^¿k FORMÁNEK; Jan Maloch; Vlasta PETR^¿ÍKOVÁ; Petr PU^'SCHEL; Pavel TRY^´ZNA
Original assignee: CINIS Ltd
Current assignee: CINIS Ltd
Priority date: 1992-02-05
Filing date: 1992-09-30
Publication date: 1993-08-19
Anticipated expiration: 1994-08-05
Also published as: SK278047B6; CS33492A3; CZ733U1; CZ278405B6

Abstract

The invention solves the use of ashes obtained by combustion of solid fuels at high temperatures e.g. in fuel powder kettles, if desired with addition of a biologically active substance containing bacteria causing destruction of organic matter as sorbent for immobilizing toxic and contaminating components and thus for protecting the environment from contamination with toxic elements or from their incorporation into the biosphere. The invention utilizes high sorption capacity of ashes for a very firm fixation of detrimental compounds that are thus immobilized and cannot penetrate into the biosphere. The biologically active matter, if present, causes decomposition of organic contaminants. This property is utilized e.g. so that between the source of contamination such as a dump, and the environment a barrier of an ash layer is formed, said ash having high sorption capacity so that the contaminants are immobilized by sorption on the ash and, if flooded, water gets through whilst the toxic elements are fixed. Another possibility is filtration of contaminated water through a layer of a sorbent based on the ash. The third possibility is the mixing of the contaminated material e.g. soil, with an ash sorbent.

Description

Sorbent for immobilization of toxic and contaminating substances

Field of the technology

The invention relates to a sorbent suitable for immobilization of toxic, radioactive and contaminating substances, said sorbent consisting of ashes obtained by combustion of solid fuels at temperatures higher than 1000 °C, the largest dimension of at least 30 % of sorbent particles being lower than 3 mm and its content of toxic water extractive elements lower than 1 mg. 1^-1 and radioactivity lower than 100 Bq.kg^-1, if desired with addition of a biologically active matter containing bacteria capable of destruction of organic material, e.g. hog dung water or sludge from water purification.

Prior art

For detoxication of various sorts of wastes or substrates many different technologies, preparations and means were used. The method of decontamination of the material depends on many factors that are always subordinated to the intended uses and results.

For decontamination or sanitation are used substances with high sorption capacity for the removal of contaminants, by physical or chemical sorption, the product of which possesses lower toxicity or better possibility of being captured. These sorbents are organic and inorganic substances, produced synthetically or even originating in nature.

For the liquidation of toxic heavy metals in water proved e.g. finely ground lucerne, ground needle eaves (CS 242324), chemically modified coal, (DE 3731920), CS PV 04756-90, etheri-fied phenolic resins (US 4323458) or also wool (CS 237575), among inorganic sorbents ground slag from steel plants

(US 4377483). For the purification of waste waters is in similar process used pulverized brown coal, (CS 210955), active brown coal and bentonite or calcium oxide plus bentonite (CS 266152), or also brown coal coke (DE 3913710) or oxidized coal

(DE 3912839), active coal in the form of fibers (US 4576929) or granulated (US 4954469), suspensions of paper fibers

(US 4734393} zeolite (US 4927796).

For capturing organic substances from waste waters it is also known to use polyurethane foam (DE 3718356), wood pulp, (CS 203455) or crushed rubber (DE 3923299), in some cases accompagnied by electrolysis (SU 1168512) or electrocoagulation (SU 1189811).

The removal of smelling substances was dealt with by the group of Palaty (Ochrana ovzdusi /Protection of the atmosphere/ 2/1988, 47), using cinder.

The sorption of pyridine from waste waters by fly ash from power plants has been described by Gulíková, Diploma work of the Technical University for emistry and technology, Prague 1984, the decreasing of the phenol content in water by fly ash has been described by Günther and Frotcher (Wasserwirtschaft-Wassertechnik, 11, 416, 1961), Thickening of liquid biological waste is object of the CS a.o. 260625, here, however, simple filtration is concerned. For the filtration of smoke gases after dry desulfuration the use of ash from fluidized bed has been described (DE 3721251).

One of the greatest disadvantages of all organic sanation and decontamination means is their instability, where e.g. the lucerne (alfalfa) with adsorbed toxic substances is decomposed on the dump, liberating toxic substances. The disadvantage of synthetic sorbents is their selectivity for the given type of the contaminant, and mainly their high price.

The hitherto described processes using the products of coal combustion as the sorbent do not define exactly the material: This makes the process irreproducible. Particularly these processes do not define the composition of the sorbent itself, so that they do not distinguish the ashes, i.e. the more coarse particles from. fly ash, i.e. from the finest particles wherein the contaminating elements are enriched. In the use of the ashes there occurs the sorption, but simultaneously the desorption of the enriched ashes, so that the total result may be negative in spite of the fact that some substances were adsorbed. Cinder or clinker, on the contrary, as a very coarsely granulated material, has a very small specific surface and its sorption capacity is small. Similarly the asches from the fluidized bed have considerably different properties because they have been produced at temperatures lower than

1000 °C and are therefore not molten and partly deprived of trace elements.. These shortcomings in the definition of sorbents originated from the fact that up to now the causal connection between the physico-chemical properties of the ash and its possibilities of binding toxic and contaminating substances polluting the environment were not known.

The fly ash, i.e. the smallest particles not caught in the separators and escaping from the stack into the atmosphere is enriched by toxic elements. In its aqueous extract is therefore an increased concentration of toxic trace elements and is worthless in the utilization in the sorption. (Bezčinský L., Pilátovά B. - Chemical composition of the emissions from the coal combustion and in further selected technologies-Final Research Report UVP Praha, 1985, Bezaδinsky M. - Emission factors of trace elements from energetic sources - Candidate Disertation work ČVÚT Praha, faculty of mechanical engineering, 1985,

Natusch-Characterization of trace elements in fly ash, Conference about heavy metals, Toronto, 1975, Hrubý V., Kusý V. - Ekological problems in coal combustion. - Chem. prύmysl 26/51, 1976, No. 6, page 303, Hrubý V., Kusý V., Research of sorption and desorption of sulfur dioxide in the fly ash from thermal power plants - closing report VÚHU Most 1973). Neither cinder ar ashes from the fluidized bed, nor the fly ash thus do not fulfil the condition of the definition of the sorbent according to the invention where the grain size and composition of the aqueous extract are defined.

Substance of the invention

The above mentioned shortcomings removes the sorbent for the fixation of toxic, radioactive and contaminating substances, the essence of which consists in that it is composed of the ashes obtained by combustion of solid fuels at temperatures above 1000 °C, said ashes being formed of at least 30% of particles having their longest dimension lower than 3 mm and having the content of water extractive elements lower than 1 mg. 1 and the radioactivity is lower than 100 Bq. kg , if desired with addition of 0 - 20 % as dry substance, of a biologically active material containing bacteria capable of destructing organic matter, e.g. hog dung water or water work sludge.

Ash seperated in mechanical or electro-static separators is, as a result of high combustion temperature, deprived of a considerable part of originally present toxic trace elements.

The part of toxic elements which remains in the ash is firmly built in and is but partly and very uneasily extractive. This ash has, however, due to the impaired balance and due to a considerable large specific surface the capability of binding firmly organic as well as inorganic substances by physical and chemical sorption. This capability have the ashes in dry or fresh state as well as in wet state after the floating.

Wet ash - molten alumosilicate- forms on its surface a layer of hydrated species and these hydrated species of various alumosilicates - hydrogels - are also active as excellent sorbents. Large specific surface makes also possible an intensive analysis of the microflora, as far as the ash is mixed with a biologically active matter, whereby the efficiency of the decontamination furthermore increases.

The binding of the sorbed harmful substances is very firm so that even a long time contact with water, either rain or underground, lasting even more than 5 years does not cause extraction of toxic and contaminating substances. A contingent acidity, of the rain is neutralized, moreover, by alkaline components of the ashes.

Examples of the invention

The use of the ash as a sorbent according to the invention may be realized e.g. in the following way:

In all cases there was used a floated ash from the power plant Prunéřov. The ash contains 92 % of particles smaller than 3 mm, 85 % smaller than 1 mm, 54 % smaller than 0.5 mm and 15 % smaller than 0.2 mm. The content of all recorded elements in the aqueous extract is lower than 0.5 mg.1^-1.

1) During the buiding the dump of toxic waste there was formed in the subsoil and on the walls of the dump a layer of ash 0.8 m thick.

In such set up dump the toxic components are firmly bound, the rain water, however, penetrates the dump so that no problems with the drainage occur as in the case of clay or plastics tightening layers. In the water from the subsoil of the dump no toxic trace elements were found in a concentration higher than 0.5 g.1^-1.

2) In purification of water in a swimming pool the circulation water in an amount of 1 1 passed over an ash layer 0.7 m thick, 12.5 m² surface.

The P_H of water decreased from 8.4 to 6.8, the content of ammonia sank from 0.3 mg. 1 to 0.15 mg. 1^-1, BSK₅ sank from 1.95 onto 0.81 mg. 1^-1.

3) In final purification of city waste waters the water from the septic was led over an ash layer 1.5 m thick. The chemical oxygen consumption sank from the original 180 mg. 1^-1 to 50 mg. 1^-1 of biological oxygen consumption from 180 mg. 1^-1 to 12 mg. 1^-1. 4) Industrial fertilizer containing 50 mg Cd. kg^-1 was mixed with the ash in the relation of 1 : 1. The aqueous extract content sank onto 0.2 mg.1^-1.

5 ) The soil was contaminated by phenolic waters in an amount of 2 mg of phenol on kg. To the soil 10 % of the ash and 20 % of a water work sludge, conteining 5 % of dry substance were added. After 2 months the content of phenol sank to 0.1 mg.kg^-1. While in the control sample without ash addition the content of phenol did not change outside of the experimental error.

Industrial utility

The sorbent according to the invention can be used in all cases, where the penetration of toxic substances from the surface into the underground or surface water, soil or other components of the environment is to be barred or removed, especially when the concentrations of said substances are low.

The matter is that the purification of contaminated water or final purification of water into the water work, dumping toxic wastes from the industry and agriculture, building of security barriers of such dumps.

Another field of utilization is the immobilization of toxic and contaminating substances which have already penetrated into the environment or into the soil, e.g. from the fertilizers, industrial and agricultural wastes or from the atmospherical fall-out. In the cases the toxic and contaminating substances remain in the soil, they are, however, firmly bound onto the ash so that their detrimental effect cannot develop.

In case of organic contaminating substances and utilizing of the ash sorbent with an admixture of a biologically active matter the contaminants are not only caught, but also rapidly decomposed, so that the sorbent is automatically regerated and its capacity grows, theoretically, in an unlimited manner . The same effect is achieved in purification of some organically contaminated waters where the contaminant itself starts the accelerated decomposition reaction on the ash surface.

Claims

C l a i m

Sorbent for fixation of toxic, radioactive and contaminating substances, characterized by that it consists of ashes obtained by combustion of solid fuels at temperatures higher than 1000 °C and consisting of at least 30 of particles smaller than 3 mm and has the content of water extractive elements lower than 1 mg.1^-1 and radioactivity lower than 100 Bq.kg^-1, if desired with addition of 0 to 20 % of biologically active substances, as dry substance, containing bacteria acting destructively onto organic matters, e.g. hog dung water or water purification sludge.