The essential steps of the sulfur cycleare:Militifilftthiif•Mineralization of organic sulfur to the inorganic form, hydrogen sulfide, H2S.•Oxidation of sulfide and elemental sulfur (S) and related compounds to sulfate, SO42–.•Reduction of sulfate to sulfide.Mibilibilitifthlfdd•Microbial immobilization of the sulfur compounds and subsequent incorporation into the organic form of sulfu
These are often termed as follows: Assimilative Assimilative sulfate reduction sulfate reduction (sulfur assimilation) (sulfur assimilation) in which in which sulfate (SO42–) is reduced to organic sulfhydryl groups (R–SH) by plants, fungi and prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH. Desulfuration and Dissimilative sulfur reduction in which or g ganic molecules containing sulfur can be desulfurated, producing H2S. Note the similarity to deamination. Oxidation of hydrogen sulfide produces elemental sulfur (So), oxidation state = 0. This reaction is done by the photosynthetic f green and purple sul fur bacteria and some chemolithotr
Sulfur Reservoirs in Nature Reservoirs of sulfur atoms: su lfur i is f foun • The largest physical reservoir is the Earth's crust where lf d d i in gypsum (Ca (C SO SO4 ) an d pyr )dit(FS ite (Fe S2 ) ). • The largest reservoir of biologically useful sulfur is found in the ocean as sulfate anions (2.6 g/L), dissolved hydrogen sulfide gas, and elemental sulfur. •Other reservoirs include: e lemen ta l su-Freshwater -contains sulfate, hydrogen sulfide and ltllf lfu r-Land -contains sulfate-Atmosphere -contains sulfur oxide (SO 2 2) and methane sulfonic acid (CH3SO3-); volcanic activity releases some hydrogen sulfide into the air
When clouds are present the loss rate of SO2 is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets Hydrolysis Sulphur dioxide dissolves in water Sulphur dioxide dissolves in water and then, like carbon dioxide, and SO2· then, like hydrolyses in a series of equilibrium reactions: SO2 (g)+ H2O SO2·H2O SO H H2 O OH H + + +HSO +HSO3 HSO3-H++SO32Oxidation d. Th e m carbon dioxide, There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulphuric aci ost im por tan t oxi dati on r eacti on s ar e wi ac d e ost pota to dato eacto sae t o o e, hydrogen peroxide and oxygen (reactions with oxygen are catalysed by iron and manganese in
Soil biology can be seriously damaged by acid rain. Some tropical microbes can quickly consume acids but other microbes bl t t l t l H d kill d Th to and to lera te low p Hs an d are kille d. The enzymes o f f these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins and leach away essential nutrients and Minerals.. Acid rain can slow the growth of vulnerable forests and cause leaves and needles to turn brown and fall off cause Other p l lan leaves and needles to turn brown and fall off. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain. Oth t ts can a l lso be b d damage d by ac id ra in d b id i b tth ff t bu t the e ffec t on food crops is minimized by the application of fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but
SO2is an acid gas and thus the typical sorbent slurries or other materials used to remove the SO2from the flue gases lkliThtitkilitbbiiare alkaline. The reaction taking place in wet scrubbing using a CaCO3(limestone) slurry produces CaSO3(calcium sulfite) and can be expressed as:pCaCO3(solid) + SO2(gas) → CaSO3(solid) + CO2(gas)When wet scrubbing with a Ca(OH)2(lime) slurry, the reaction alsoproducesCaSO(calciumsulphite):also produces CaSO3(calcium sulphite):Ca(OH)2(solid) + SO2(gas) → CaSO3(solid) + H2O (liquid)A similar process is possible with magnesium hydroxide:M(OH)(lid)+SO()MSO(lid)+HO(liid)Mg(OH)2(solid) + SO2(gas) → MgSO3(solid) + H2O (liquid)Some FGD systems go a step further and oxidize the CaSO3(calcium sulphite) to produce marketable CaSO4· 2H2O (gypsum)42CaSO3(solid) + ½O2(gas) + 2H2O (liquid) → CaSO4· 2H2O
The light-induced oxidation of hydrogen sulfide for harvesting electrons during photosynthesis uses the following process: H2S -----> So + 2 H++ 2 eGreen and purple sulfur Green and purple sulfur bacteria (photosynthetic). bacteria usually (photosynthetic). Must live in the light. Cannot exist deep in the deep oceans. Environment must contain a source of hydrogen sulfide, usually arising from desulfuration of decaying organic material arising from desulfuration or from sulfate reduction. of decaying organic material These organisms are often found in waters "one level" above decaying organics or sulfate reducers where they acquire hydrogen sulfide bubbling up from below and are simultaneously illuminated by the sunlight. simultaneously illuminated by the sunlig
What is the source of hydrogen sulfide? Desulfuration of decaying organic material Sulfate reducers Volcanic activity For example, chemolithotrophs For example, chemolithotrophs near thermal vents in the light cannot near thermal vents in the deep sea harvest the energy from this source. Thus they form the foundation of whole communities in the deep sea where light cannot penetrate penetrate. When is elemental sulfur (So) oxidized? Organisms will oxidize hydrogen sulfide (H2S) until it runs out and then begin utilizing elemental sulfur. This is logical, since p more energy can be acquired from oxidizing hydrogen sulfide com pared to elemental sulfur. Use of an alternate substrate requires the expression of genes not previously expressed.
These are often termed as follows: Assimilative Assimilative sulfate reduction sulfate reduction (sulfur assimilation) (sulfur assimilation) in which in which sulfate (SO42–) is reduced to organic sulfhydryl groups (R–SH) by plants, fungi and prokaryotes. The oxidation states of sulfur are +6 in sulfate and –2 in R–SH. Desulfuration and Dissimilative sulfur reduction in which or g ganic molecules containing sulfur can be desulfurated, producing H2S. Note the similarity to deamination. Oxidation of hydrogen sulfide produces elemental sulfur (So), oxidation state = 0. This reaction is done by the photosynthetic f green and purple sul fur bacteria and some chemolithotr
Sulfur Reservoirs in Nature Reservoirs of sulfur atoms: su lfur i is f foun • The largest physical reservoir is the Earth's crust where lf d d i in gypsum (Ca (C SO SO4 ) an d pyr )dit(FS ite (Fe S2 ) ). • The largest reservoir of biologically useful sulfur is found in the ocean as sulfate anions (2.6 g/L), dissolved hydrogen sulfide gas, and elemental sulfur. •Other reservoirs include: e lemen ta l su-Freshwater -contains sulfate, hydrogen sulfide and ltllf lfu r-Land -contains sulfate-Atmosphere -contains sulfur oxide (SO 2 2) and methane sulfonic acid (CH3SO3-); volcanic activity releases some hydrogen sulfide into the air
When clouds are present the loss rate of SO2 is faster than can be explained by gas phase chemistry alone. This is due to reactions in the liquid water droplets Hydrolysis Sulphur dioxide dissolves in water Sulphur dioxide dissolves in water and then, like carbon dioxide, and SO2· then, like hydrolyses in a series of equilibrium reactions: SO2 (g)+ H2O SO2·H2O SO H H2 O OH H + + +HSO +HSO3 HSO3-H++SO32Oxidation d. Th e m carbon dioxide, There are a large number of aqueous reactions that oxidize sulfur from S(IV) to S(VI), leading to the formation of sulphuric aci ost im por tan t oxi dati on r eacti on s ar e wi ac d e ost pota to dato eacto sae t o o e, hydrogen peroxide and oxygen (reactions with oxygen are catalysed by iron and manganese in
Soil biology can be seriously damaged by acid rain. Some tropical microbes can quickly consume acids but other microbes bl t t l t l H d kill d Th to and to lera te low p Hs an d are kille d. The enzymes o f f these microbes are denatured (changed in shape so they no longer function) by the acid. The hydronium ions of acid rain also mobilize toxins and leach away essential nutrients and Minerals.. Acid rain can slow the growth of vulnerable forests and cause leaves and needles to turn brown and fall off cause Other p l lan leaves and needles to turn brown and fall off. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain. Oth t ts can a l lso be b d damage d by ac id ra in d b id i b tth ff t bu t the e ffec t on food crops is minimized by the application of fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but
SO2is an acid gas and thus the typical sorbent slurries or other materials used to remove the SO2from the flue gases lkliThtitkilitbbiiare alkaline. The reaction taking place in wet scrubbing using a CaCO3(limestone) slurry produces CaSO3(calcium sulfite) and can be expressed as:pCaCO3(solid) + SO2(gas) → CaSO3(solid) + CO2(gas)When wet scrubbing with a Ca(OH)2(lime) slurry, the reaction alsoproducesCaSO(calciumsulphite):also produces CaSO3(calcium sulphite):Ca(OH)2(solid) + SO2(gas) → CaSO3(solid) + H2O (liquid)A similar process is possible with magnesium hydroxide:M(OH)(lid)+SO()MSO(lid)+HO(liid)Mg(OH)2(solid) + SO2(gas) → MgSO3(solid) + H2O (liquid)Some FGD systems go a step further and oxidize the CaSO3(calcium sulphite) to produce marketable CaSO4· 2H2O (gypsum)42CaSO3(solid) + ½O2(gas) + 2H2O (liquid) → CaSO4· 2H2O
The light-induced oxidation of hydrogen sulfide for harvesting electrons during photosynthesis uses the following process: H2S -----> So + 2 H++ 2 eGreen and purple sulfur Green and purple sulfur bacteria (photosynthetic). bacteria usually (photosynthetic). Must live in the light. Cannot exist deep in the deep oceans. Environment must contain a source of hydrogen sulfide, usually arising from desulfuration of decaying organic material arising from desulfuration or from sulfate reduction. of decaying organic material These organisms are often found in waters "one level" above decaying organics or sulfate reducers where they acquire hydrogen sulfide bubbling up from below and are simultaneously illuminated by the sunlight. simultaneously illuminated by the sunlig
What is the source of hydrogen sulfide? Desulfuration of decaying organic material Sulfate reducers Volcanic activity For example, chemolithotrophs For example, chemolithotrophs near thermal vents in the light cannot near thermal vents in the deep sea harvest the energy from this source. Thus they form the foundation of whole communities in the deep sea where light cannot penetrate penetrate. When is elemental sulfur (So) oxidized? Organisms will oxidize hydrogen sulfide (H2S) until it runs out and then begin utilizing elemental sulfur. This is logical, since p more energy can be acquired from oxidizing hydrogen sulfide com pared to elemental sulfur. Use of an alternate substrate requires the expression of genes not previously expressed.
Comments
Post a Comment