EP0195071A1 - Microbiological method for the removal of contaminants from coal - Google Patents

Abstract

Contaminants in carbon are eliminated by the organic action of strains of Thiobacillus ferrooxidans, Thiobacillus thiooxidans, Thiobacillus thioparus, Thiobacillus neopolitanus, Thiobacillus acidophilus, Euglenoids, Cyanochlorophytes, in a predetermined sequence of treatment stages, when burned, causes less pollution and is a more efficient source of energy. The contaminating substances eliminated are generally oxidized iron and sulfur compositions which can be converted into usable products.

Description

MICROBIOLOGICAL METHOD FOR THE REMOVAL OF CONTAMINANTS FROM COAL

FIELD OF INVENTION

This invention relates to a process by which iron, sulfur and other impurities may be removed from coal to produce a high carbon content fuel composition, as well as separately useful quantities of iron, sulfur and other by¬ products.

BACKGROUND OF THE PRIOR ART

Coal, a fossil fuel, is an abundant energy source found in the eastern and western United States. Significant re¬ serves of coal contain an iron pyrite contaminant which, when burned produces sulfur dioxide particulates, which are con¬ sidered by some to mix with water vapor and produce sulfuric acid and "acid rain"-. The burning of coal contaminated with iron pyrite also prevents the total combustion of the coal and inhibits the release of its maximum BTU energy potential.

Present techniques for the removal of iron pyrite contam¬ inants generally do not separate iron and sulfur from the coal as separate compositions, but rather include the elements in a sludge waste product. Microbiological tech¬ niques are known to provide such separations; however, they require extended time periods to be effective.

OBJECTIVES OF THE INVENTION

It is an objective of this invention to provide a process by which contaminating iron pyrite and organic impur¬ ities may be removed from coal by a microbiological process that results in the separation of impurities at a signifi- cantly faster rate than other known methods. A decrease in pollution and an increase in energy efficiency of burned coal will thereby be achieved.

It is a further objective to provide a process by which the impurity components may be further separated from each other to create by-products in useful forms.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of an apparatus configur¬ ation useful in the process.

Figure 2 shows a multiple stage process.

Figures 3-9 are microphotographs showing action of the biological media in a slurry at various steps of the process of Figure 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Coal contaminated with iron pyrite, organic sulfurs and other impurities, is, in accord with the general method of the invention, crushed and mixed with acidified bog water under pressure and then introduced to a media comprising a mixture of selected chemolithotrophic bacteria and algal species. Bacterial action separates the iron, sulfur and other impurities from the coal and binds the organic and inorganic elements to oxygen, forming sulfate and metallic oxides and/or hydroxides. Centrifugation then separates the coal fines from the oxidized impurities, which are trapped in a mat of bacterial produced lipophosphates. The hydrophobic characteristic of "clean" coal fines causes them to rise to the top of the separator tank, while the heavier impurity- laden mat sinks to the bottom. The discarded mat can then be processed to reduce oxides and/or hydroxides, making sulfur and heavy metals reclaimable. The end result is a "clean" composition of a high carbon coal.

In the preferred embodiment, a high, sulfur coal from the mines is provided in an aqueous mixture with a selected group of bacteria: Thiobacillus ferrooxidans, Thiobacillus thio- oxidans, Thiobacillus thioparus, Thiobacillus neopolitanus, and Thiobacillus acidophilis maintained at temperature of between 20 and 35 degrees Celsius at atmospheric pressure. While temperature and pressure are not critical, it is noted that a higher temperature or pressure, will increase the speed of processing; the amount of bacteria employed and time of reaction will vary depending on the amount of contaminant iron and sulfur assumed to be in the coal. Oxygen is supplied to support aerobic bacteria in the form of Euglenoid ^'algal species; aeration, glu'tathione reductase, and a Redox catalyst such as Bovine cytochrome "C" (or other appropriate sulfhydrase) is added as an oxidizing agent. EDTA is added as a non-specific iron chelator [Krumbein, W. E., ed. Microbial Geochemistry, Blackwell Scientific Publications, London, 1983, at Chapter 6 "The Microbial Iron Cycle" by Nealson, K. H., p. 167] to further speed the process by increasing the redox potential to an optimum range, which is from 300 to 700 millivolts for iron and from 200 to 500 millivolts for sulfur. Depending upon the amount of iron pyrite in the coal, the time required to remove the iron, sulfur and other impurities from the coal and to chelate these compositions to the lipophosphate mat from the bacterium and to oxidize them will take from 3 to 5 hours. The mixture is then centrifuged to separate the coal from the iron oxide, sulfur and other impurities. A magnetic attrac¬ tion means introduced into the lipophosphate mat and its oxidized impurities in the centrifuge tank will remove iron compositions; rust (formed ferric compounds) may be removed from the- separated iron by running the mat through a carbon¬ ized steam bath. Sulfur is reduced to hydrogen sulfide, which is further broken down into hydrogen gas and elemental sulfur, which is insoluble in water. The sulfur is suctioned off and then dried. After removal of the impurity-laden mat, the coal-water slurry is moved into a neutralization tank and/or other station for drying and compaction before combus¬ tion, or mixed with oil and blown into the boiler.

In the embodiment of Figure 1, coal from the mine, 1, is fed to a vat, 2, where it is crushed and mixed with steam under pressure to produce a maximum substrate area for the chemolithotrophic bacteria to act upon.

Following the crushing and washing of the coal, the base of the vat is removed to expose a sieve, 3, through which water and the particulate coal flows into tank, 4..

Tank 4 is fed from a breeding tank, 5, supporting a mixture of chemolithophic bacteria: Thiobacillus thio- oxidans, Thiobacillus ferrooxidans, and Thiobacillus thioparus, and the bacterium Thiobacillus neopolitanus. Compositions separated from the coal; Fe_0, and sulfur, bind to the pili of the bacteria; pili of T. thioparus and T^ thiooxidans display an affinity for sulfur and pili of T. ferrooxidans display an affinity for iron. T. neopolitanus appears to produce one or more enzymes of unconfirmed composi¬ tion, which speed the reproduction rate of the others. The process is further improved by photosynthetic growth of the algae of Euglena.

After the introduction of the bacteria to the ground coal, the mixture is then directed to a holding tank, 6, in which because of the production of sulfuric acid, the pH will become approximately 1.5 to 3.0. From the holding tank, after the passage of a period of time sufficient for bacter¬ ial action to achieve the desired separation, the mixture is passed to a centrifuge, 7, where the coal is separated from the aqueous mixture. The iron and sulfur components separ¬ ated in the centrifuge may be removed through means connected to the centrifuge shown at 7A and 7B. A sulfuric acid by-product may be removed through conduit, 8, and separately utilized. Alternatively the low pH may be raised to 6 or 7 by titration with phenophethalian solution and liquified calcium carbonate in tank, 9. The hydrated coal particles are then moved out through a pipeline, 10, such as a coal slurry or fluidized bed, or direct boiler feed. Alterna¬ tively, the water is drained off, heated, and reused as steam in the initial step through conduit, 11.

In the process of Figure 2 , coal fines, 20, are mixed with acidified bog water, 21, comprised of peat, sphagnum and spring water and carried to a first tank, 22, where they are mixed with a culture from breeder tank, 23, comprised of acidified bog water (pH 2-3.5, temp. 20 -30 C) containing Thiobacillus ferrooxidans, T. thiooxidans, T. thioparus, T. acidophilis, T. neopolitanus, Euglena gracilis, E. acus, E. acus-(gracilis peat), E. mutabilis and others. "Bog water" is generally a mineral water seasoned with peat and sphagnum having an acid pH. A sample analysis is set forth in follow¬ ing Table I identifying characteristics of a "new" bog (a fresh mixture of water, peat and sphagnum) and a mature bog comprising the same mixture aged at room temperature with aeration for a period of a month.

TABLE I New Bog Mature Bog pH 6.9 2.62

Total Hot Acidity 8 381 mg/L CaC0₃

Mineral Acidity 8 381 mg/L CaC0₃

Total Alkalinity 110 mg/L CaC0₃

Total Fe ppm 0.38 6.25

Total Cu ppm 0.14 0.19

Al ppm 1.09 6.90

S0₄ ppm 63 1, ,763

Total PO. ppm 1.89 4.37

NO., - N ppm 5.96 0.516

N0₂ - N ppm 0.04 0.04

COD ppm 705 674

Spec. Cond. u hmos 1,550, -000 13,_r200 The presence of secondary bacterial forms, such as Beggiatoa, Sphaeotilus natans, Leucothrix, and Leptothrix, which are aerobic, like the Thiobacillus will enhance the second oxidation phase, as will the facultative anaerobic Cyanochlorophyta alga, such as Oscillatoria, and the anaerobic photosynthetic bacteria found at low oxygen inter¬ faces, such as Chromatium, Thiopedia, Thiospirilium, Chlorobium and Rhodospirilium. These former organisms, like the Beggiatoa and Leucothrix, ingest sulfur as granules, rather than chelate it prior to oxidation. "Gro-lites" provide illumination in a spectrum pattern that stimulates photosynthetic bacteria and cause the Erylenoids to photosyn- thesize and produce nutrients and oxygen. This mixotrophic culture is ecologically balanced, synergistic, symbiotic and self-sustaining. The addition of catalysts,^' such as glutathione reductase, bovine cytochrome "C", EDTA and Vitamin B- -, enhance and speed up life-sustaining, chelation and oxidation functions and since they are necessary for the reactions to occur, but not used up during the reactions, tend to be maintained over a period of 2-4 weeks before they need to be replenished or supplemented.

After one hour in the first tank, the chelation of impurities is complete and low pH oxidation is well underway, due to the production of sulfhydrase and ferrooxidase enzymes produced by the Thiobacillus groups . T. ferrooxidans and T. acidophilis appear to be the main producers of the ferro- oxidases and smaller amounts of the sulfhydrases. T. thio- oxidans and T. thiopanus appear to produce only sulfhydrases. T. neopolitanus appears to produce sulfhy- drases and an enzyme of unconfirmed composition which, when present, speeds up and enhances the reproduction rates of the other four species of Thiobacillus. The oxidation process is further improved by the photosynthetic activity of the Euglenoid species.

The coal-fines mixture then passes into second tank, 25. Yellow, 26, and green, 27, lights at 5* intervals around the tank keep the oxygen production at a high level. The pH gradually increases to 3.5 to 4.5, which in turn activates the photosynthetic bacteria that ingest sulfur granules not yet oxidized. A lag phase of 20-30 minutes occurs, and the coal-fines mixture empties into third tank, 28.

Peat and sphagnum is introduced into third tank from vessel, 29, . and the oxidized impurities, now becoming entrapped in a "slime" lipophosphate mat, adhere to the sphagnum and peat. After one hour, third tank, 28, empties into fourth tank, 30.

Oxidation and deposition continue in fourth tank, 30, for one hour. All of the first four tanks rotate slowly to keep the contents well-mixed. This assures access of the bacteria to the coal-fines surface and inhibits the formation of the "mat" on the coal-fines.

The material then passes into a fifth tank, 31, then is cleaned in a cyclone-centrifuge, 32, which spins rapidly for about one hour to separate the coal-fines, "soup" and impurities-laden peat and sphagnum. The hydrophobic cleaned coal-fines move to a froth flotation tank, 33, or series of cells, where they are mixed with clean water for one hour, then sent into slurry and blown with oil into the coal-users combustion unit. The "soup" is returned to the hydro-bog, 21, after cleaning in a secondary water treatment tank, 34. The impurity-laden peat and spagnum are removed as by tray means, 35, for processing back into reclaimed, reusable sulfur and heavy metals. A water source for various process stages is shown interconnected at 40. Figures 3-9 depict in sequence the state of the microbiological cultures in the stages of the five tanks of the process of Figure 2. Figure 3 is a 200x magnification showing the density of microorganisms in the absence of any coal, in the breeder tank, 23. Figure 4 shows the beginning of oxidation and chelation of microorganisms to impurities in the coal fine mixture in the first process tank, 22. The mixture in the second tank, 25, is shown in Figure 5, after a residence time of approximately two hours (200x) and shows the ongoing oxidation of iron and sulfur. Figure 6 (200x) shows the mat of lipophosphate bacterial enzymes, oxidized iron and sulfur and coal fines beginning to form on the peat and sphagnum particles introduced in tank, 28, and Figure 7 is a lOOOx microphotograph, oil immersion and gram stained, showing bacterial action depositing sulfate and metallic oxides on the sphagnum particles as occurs in third and fourth tanks, 28 and 30. Figure 8 and Figure 9 are respectively 200x microphotographs of the slurry in fifth tank, 31, and the supernatant liquid found in reservoir, 34, after the centri¬ fuge removes the cleaned coal fines from the slurry. to

When burned, the coal thus cleaned by the foregoing processes will not produce pollution as the iron and sulfur contaminants have been removed. Additionally, since the coal is "clean", it is a more efficient energy source, as less of the coal needs to be combusted to create a given amount of energy.

Adaptions of the process include the removal of other unwanted materials, such as clay, by floculation immediately after the pulverization step. The system may be made anaero¬ bic to accommodate chemolithotrophic anaerobes such as Desulfo- vibro and the system may be accommodated to other bacteria which remove other pollutants and contaminants, such as salt, copper, etc.

EXAMPLE I

A bench scale operation of the method is accomplished as follows:

Equal quantities of each of the certified bacterial strains Thiobacillus ferrooxidans, Thiobacillus thiooxidans, Thiobacillus thioparus and Thiobacillus acidophilis are added to a like quantity of Thiobacillus neopolitanus in the ratio of approximately 4,000,000 per ml. in acidified bog water. These bacteria cultures were obtained as verified strains from the American Type Culture Laboratories and Depository in Rockville, Maryland. The T. thioparus and T. ferrooxidans were provided live in vitro. The others were freeze dried in a skim milk culture and were prepared approximately two weeks before use.

It is believed that the T. neopolitanus enhances the reproduction replication rate of the other bacteria, which in the above mixture have been observed to replicate ten times within a day, especially when "wild" cultures from active bogs are added to the ATCC cultures. In using the mixture of bacteria in the foregoing process, it is preferred to use a beginning solution of a concentration of approximately 10 to 10 bacteria per 1 ml. of media. This range is approximate because individual bacteria vary in size. Other concentra¬ tions are feasible depending upon factors such as ultimate dilution of the slurry, proportions of coal fines introduced and relative impurity level in the coal. The suspected enzyme enhancing this phenomena is as yet unconfirmed.

To the mixture of the bacteria in the bog water there is added a further volume of 10 ml. bog water medium and .5 gram glutathione reductase (an oxidizing sulfhydrase catalyst), 10 conventional hypodermic units of bovine cytochrome "C", 1 gram of EDTA, 1 gram of Vitamin B,_, and 10 grams of high sulfur coal. After a period of about four hours, oxidized sulfur in sulfate form is observed and iron is observed to separate from the mixture as a ferrous oxide, which become enmeshed in a "slime" lipophosphate mat. The clean, clean- fines are observed to float to the top. In the bacterial action, the bacteria chelate and oxidize the sulfur and metal, which form a cohesive lipophosphate mat.

The coal fines used in the foregoing example range from 60 to -300 mesh and comprise a bituminous coal with a high iron pyrite contamination obtained in Perry County, Ohio from a glaciated formation including further deposits of lime- IZ stone, dolomite, magnetite, limonite and sulfur at the terminal morine of the glacier. Upon combustion after drying, the coal separated in the foregoing example burned completely and left no residue.

EXAMPLE II

The procedure of Example I was followed using comparable fines of a pure "clean" Cannelton Coal from Fayette County, West Virginia. No biological reaction occurred using this coal sample which did not have an iron pyrite component. The bacterial retained their original integrity.

EXAMPLE III

The procedure of Example I was followed using sulfur flowers and "pure iron pyrite" obtained from Carolina Biologi¬ cal Supply Co. in Burlington, North Carolina and dibenzothio- phane from Kodak. There was observed to be an extremely vigorous chelation and oxidation of the chemicals.

These Examples II and III provide positive evidence that the bacteria involved in the method and composition of the invention do in fact react with the iron pyrite and organic sulfur contaminants of a coal composition as is set forth in Example I.

Variations to the method, the biologically active agents used and the apparatus of the foregoing invention should be evidence to those of skill in the art.

Claims

WHAT IS CLAIMED IS: 13

1. A met_hod for the removal of iron pyrite and other impurities from coal by subjecting the coal to the action of a mixotrophic culture of bacterial and algal species in an aqueous bog water solution.

2. A method according to claim 1 wherein coal is crushed and mixed with acidified bog water to produce a slurry which is then exposed to action of the chemolitho- trophs and other bacteria in an environmentally appropriate media to support a bateriological system and the slurry is thereafter centrifuged to separate solid components.

3. A method of claim 2 in which a quantity of sphagnum and peat is introduced into the slurry after exposure to the bacterial and algae species for an extended period of time whereby impurities are deposited on the sphagum and peat, and thereafter the solution is exposed to a magnetic means to remove the impurities deposited on the mat of sphagnum and peat.

4. A system according to claim 1 wherein the iron and sulfur components of the iron pyrite and organic sulfur contaminants are removed to result in the creation of iron and sulfur by-products in a useful form.

5. A system according to claim 3 wherein the ferric oxide is removed by running the separated iron component, through a carbonized steam bath.

6. A system according to claim 3 wherein the hydrated coal particles are removed from the water solution and dry coal is produced.

7. A system according to claim 3 wherein other unwanted materials are removed by floculation after the pulverization step.

8. A system according to claim 3 which is adapted to anaerobic bacteria or Desulfovibro.

9. A mixture of the bacteria strains Thiobacillus ferrooxidans, Thiobacillus thiooxidans, Thiobacillus thio¬ parus, Thiobacillus neopolitanus, Thiobacillus acidophilus, Euglenoids, Cyanochlorophyta and secondary aerobic and anaero¬ bic bacterial groups useful in the removal of contaminants from coal in accordance with the process of claim 1.