Microbial desulfurization of coal

Claim 2

A process for the removal of pyrite from coal which comprises the steps of: preparing an aqueous slurry containing finely-divided coal particles of a size sufficient to expose a substantial fraction of the total surface of the pyrite in the coal; maintaining the pH of the slurry at a value between about 1.5 and 6; maintaining the slurry at a temperature of between about 10° and 35° C.; providing an oxygen or oxygen-containing atmosphere in contact with the slurry; and subjecting the slurry to the action of iron and sulfur oxidizing microorganisms selected from the Thiobacillus ferrooxidans group while agitating the slurry for a period of time sufficient to oxidize and solubilize substantially all of the pyrite in the coal, the initial concentration of the microorganisms being in a range of between about 3×10 10 and 1×10 12 cells per gram of pyrite present in the coal slurry.

Claim 3

The process as defined by claim 1 wherein the slurry contains between about 2.5 and 40% by weight coal.

Claim 4

The process as defined in claim 1 wherein the finely-divided coal particles are of a size no larger than about 200 mesh.

Claim 5

The process as defined by claim 1 wherein the pH of the slurry is maintained at a value between about 1.5 and 3.5.

Claim 6

The process as defined by claim 1 wherein the pH of the slurry is periodically adjusted by the addition of a base to neutralize the acid generated during the leaching process.

Claim 7

The process as defined by claim 1 wherein a portion of the aqueous slurry or slurry liquid is treated with a base to neutralize the acid generated during the leaching process and is then recycled to maintain a substantially constant pH in the slurry.

Claim 8

The process as defined by claim 1 wherein the slurry is maintained at a temperature of between about 15° and 33° C.

Claim 9

The process as defined by claim 1 wherein the oxygen concentration within the slurry is maintained between about 4 and 30 parts per million in solution.

Claim 10

The process as defined by claim 1 wherein the slurry is agitated by bubbling air, oxygen or oxygen-enriched air through the slurry.

Claim 11

The process as defined by claim 1 wherein the oxygen or oxygen-containing atmosphere is enriched with carbon dioxide.

Claim 12

The process as defined by claim 10 wherein the concentration of carbon dioxide is in a range of up to about 2% by volume of the oxygen or oxygen-containing atmosphere.

Claim 13

The process as defined by claim 1 wherein nutrients are added to the slurry for growth of the microorganisms.

Claim 14

The process as defined by claim 12 wherein the nutrients consist of nitrogen and phosphorous-containing compounds.

Claim 15

The process as defined by claim 13 wherein the concentration of the nitrogen and phosphorous-containing compounds is maintained in the range of from about 1×10 -3 to 6×10 -2 weight percent nitrogen and from about 5×10 -3 to 2×10 -2 weight percent phosphorous.

Claim 16

The process as deinfed by claim 1 wherein the slurry is filtered to separate the solid coal after removal of the pyrite from the coal.

Claim 17

The process as defined by claim 1 wherein the finely-divided coal particles are rinsed with water prior to preparation of the coal slurry.

Claim 18

The process as defined by claim 1 wherein the slurry liquid containing the finely-divided coal particles is treated with activated carbon to remove inhibitory organic compounds.

Claim 19

A process for the removal of pyrite from coal which comprises the steps of: preparing an aqueous slurry containing finely-divided coal particles of a size no larger than about 200 mesh; maintaining the pH of the slurry at a value between about 1.5 and 3.5; maintaining the slurry at a temperature of between about 15° and 33° C.; bubbling air, oxygen or oxygen-enriched air through the slurry; subjecting the slurry to the action of Thiobacillus ferrooxidans for a period of time sufficient to oxidize and solubilize substantially all of the pyrite in the coal, the initial concentration of the Thiobacillus ferrooxidans being in the range of between about 3×10 10 and 1×10 12 cells per gram of pyrite present in the slurry; and separating the slurry into a liquid and solid phase to recover the desulfurized solid coal.

Claim 20

A process for the removal of pyrite from coal which comprises the steps of: preparing an aqueous slurry containing finely-divided coal particles of a size no larger than about 200 mesh; maintaining the pH of the slurry at a value between about 1.5 and 3.5; maintaining the slurry at a temperature of between about 15° and 33° C.; bubbling air, oxygen or oxygen-enriched air through the slurry; subjecting the slurry to the action of Thiobacillus ferrooxidans for a period of time sufficient to oxidize and solubilize substantially all of the pyrite in the coal, the initial concentration of the Thiobacillus ferrooxidans being in the range of between about 3×10 10 and 1×10 12 cells per gram of pyrite present in the slurry; and separating the slurry into a liquid and solid phase to recover the desulfurized solid coal.

Claim 21

The process as defined by claim 18 wherein the pH of the slurry is maintained at a value between about 1.5 and 2.8.

Claim 22

The process as defined by claim 18 wherein the pH of the slurry is maintained at a value between about 1.7 and 2.3.

Claim 23

The process as defined by claim 18 wherein the pH of the slurry is periodically adjusted by the addition of a base to neutralize the acid generated during the leaching process.

Claim 24

The process as defined by claim 18 wherein a portion of the aqueous slurry or slurry liquid is treated with a base to neutralize the acid generated during the leaching process and is then recycled to maintain a substantially constant pH in the slurry.

Claim 25

The process as defined by claim 18 wherein the slurry is maintained at a temperature of about 28° C.

Claim 26

The process as defined by claim 18 wherein the oxygen concentration within the slurry is maintained between about 4 and 30 parts per million in solution.

Claim 27

The process as defined by claim 18 wherein the air, oxygen or oxygen enriched air contains carbon dioxide.

Claim 28

The process as defined by claim 25 wherein the concentration of carbon dioxide is in a range of up to about 2% by volume of the air, oxygen or oxygen enriched air.

Claim 29

The process as defined by claim 18 wherein nitrogen and phosphorous-containing compounds are added to the slurry as nutrients to promote the growth of the microorganisms.

Claim 30

The process as defined by claim 27 wherein the concentration of the nitrogen and phosphorous-containing compounds is maintained in the range of from about 1×10 -3 to 6×10 -2 weight percent nitrogen and from about 5×10 -3 to 2×10 -2 weight percent phosphorous.

Claim 31

The process as defined by claim 18 wherein the slurry is filtered to separate the solid coal after removal of the pyrite from the coal.

Claim 32

The process as defined by claim 18 wherein the finely-divided coal particles are rinsed with water prior to preparation of the coal slurry.

Claim 33

The process as defined by claim 18 wherein the slurry liquid containing the finely-divided coal particles is treated with activated carbon to remove inhibitory organic compounds.

Claim 34

A cyclic process for the removal of pyrite from coal which comprises: (a) forming an aqueous coal slurry by contacting together finely-divided coal particles and water; (b) maintaining the pH of the slurry at a value between about 1.5 and 3.5; (c) maintaining the slurry at a temperature of between about 10° and 35° C.; (d) providing an oxygen or oxygen-containing atmosphere in contact with the slurry; (e) subjecting the slurry to the leaching action of iron and sulfur oxidizing microorganisms selected from the Thiobacillus ferrooxidans group while agitating the slurry for a period of time sufficient to oxidize and solubilize substantially all of the pyrite in the coal, the initial concentration of the microorganisms being in a range of between about 3×10 10 and 1×10 12 cells per gram of pyrite present in the slurry; (f) separating the slurry into a liquid and solid phase to remove the desulfurized solid coal; (g) treating the liquid phase so as to neutralize acid generated during desulfurization; (h) removing precipitates from the liquid phase; (i) passing the liquid phase into contact with additional water and finely-divided coal particles to form fresh slurry; and (j) treating the fresh slurry by repeating steps (b) to (i).

Claim 35

A cyclic process for the removal of pyrite from coal which comprises: (a) forming an aqueous coal slurry by contacting together finely-divided coal particles and water; (b) maintaining the pH of the slurry at a value between about 1.5 and 3.5; (c) maintaining the slurry at a temperature of between about 10° and 35° C.; (d) providing an oxygen or oxygen-containing atmosphere in contact with the slurry; (e) subjecting the slurry to the leaching action of iron and sulfur oxidizing microorganisms selected from the Thiobacillus ferrooxidans group while agitating the slurry for a period of time sufficient to oxidize and solubilize substantially all of the pyrite in the coal, the initial concentration of the microorganisms being in a range of between about 3×10 10 and 1×10 12 cells per gram of pyrite present in the slurry; (f) separating the slurry into a liquid and solid phase to remove the desulfurized solid coal; (g) treating the liquid phase so as to neutralize acid generated during desulfurization; (h) removing precipitates from the liquid phase; (i) passing the liquid phase into contact with additional water and finely-divided coal particles to form fresh slurry; and (j) treating the fresh slurry by repeating steps (b) to (i).

Claim 36

The cyclic process as defined by claim 32 wherein the finely-divided coal particles are of a size no larger than about 200 mesh.

Claim 37

The cyclic process as defined by claim 32 wherein the pH of the slurry is maintained at a value between about 1.5 and 2.8.

Claim 38

The cyclic process as defined by claim 32 wherein the pH of the slurry is maintained at a value between about 1.7 and 2.3.

Claim 39

The cyclic process as defined by claim 32 wherein the slurry is maintained at a temperature of between about 15° and 33° C.

Claim 40

The cyclic process as defined by claim 32 wherein the oxygen concentration within the slurry is maintained between about 4 and 30 parts per million in solution.

Claim 41

The cyclic process as defined by claim 32 wherein the slurry is agitated by bubbling air, oxygen or oxygen-enriched air through the slurry.

Claim 42

The cyclic process as defined by claim 32 wherein the oxygen or oxygen-containing atmosphere is enriched with carbon dioxide.

Claim 43

The cyclic process as defined by claim 39 wherein the concentration of carbon dioxide is in a range of up to about 2% by volume of the oxygen or oxygen-containing atmosphere.

Claim 44

The cyclic process as defined by claim 32 wherein nitrogen and phosphorous-containing compounds are added to the slurry as nutrients to promote the growth of the microorganisms.

Claim 45

The cyclic process as defined by claim 41 wherein the concentration of the nitrogen and phosphorous-containing compounds is maintained in the range of from about 1×10 -3 to 6×10 -2 weight percent nitrogen and from about 5×10 -3 to 2×10 -2 weight percent phosphorous.

Claim 46

The cyclic process as defined by claim 32 wherein the liquid phase is treated with lime or limestone in order to neutralize the acid that is produced during the process and to precipitate sulfate.

Claim 47

The cyclic process as defined by claim 32 wherein a portion of the separated liquid phase is passed into contact with additional water and finely-divided coal particles to form the fresh slurry without neutralizing acid or removing precipitates from said portion of the liquid phase.

Claim 48

The cyclic process as defined by claim 32 wherein the finely-divided coal particles are rinsed with water prior to preparation of the coal slurry.

Claim 49

The cyclic process as defined by claim 32 wherein the slurry liquid containing the finely-divided coal particles is treated with activated carbon to remove inhibitory organic compounds.

Claim 50

The cyclic process as defined by claim 32 wherein coal slurry is treated in a continuous manner following steps (b) to (j) inclusive.

Claim 51

The cyclic process as defined by claim 33 wherein coal slurry is treated in a discreet manner following steps (b) to (j) inclusive.