Process for removing sulfate ions from aqueous streams

Claim 2

A process for removing dissolved sulfate ions from an aqueous stream comprising the steps of (a) contacting the sulfate-containing stream which is essentially free of organic materials with at least 4 gram moles of gaseous hydrogen per gram-ion of sulfate, at least 0.05 gram mole of gaseous CO 2 per gram-ion of sulfate, and an aqueous anaerobic mixed liquor containing group Desulfovibrio sulfate-reducing bacteria, trace nutrients, and a suspension of calcium carbonate to maintain a mixed liquor pH of between about 5.5-8, said contacting conducted at a temperature between 0° and 60° C. for a time sufficient to convert the sulfate ions to sulfide ions; (b) removing the sulfide ions from the mixed liquor by transforming them into either a vapor or solid phase; and (c) separating the sulfide-containing phase from the mixed liquor.

Claim 3

The process of claim 1 wherein the separated mixed liquor is recycled to step (a).

Claim 4

The process of claim 1 wherein the pH of the mixed liquor is in the range of about 6.5-7.5 and the sulfate-containing stream is aqueous sulfuric acid.

Claim 5

The process of claim 1 wherein at least part of the sulfide ions are derived from soluble salts and are removed from solution and transferred into the solid phase by mixing Fe(OH) 3 with the mixed liquor by which water-insoluble iron sulfides are formed and which are removed from the mixed liquor.

Claim 6

A process for removing dissolved sulfate ions from an aqueous stream comprising the steps of (a) continuously feeding the sulfate-containing stream essentially free of organic materials, at least 4 gram moles of gaseous hydrogen and at least 0.05 gram mole of gaseous CO 2 per gram-ion of sulfate to an oxygen-free fermentation zone containing an aqueous anaerobic mixed liquor containing group Desulfovibrio sulfate-reducing bacteria, phosphorus, nitrogen and iron nutrients and a suspension of calcium carbonate to maintain the pH of the mixed liquor between about 6.5-7.5, said fermentation zone maintained at a temperature in the range of about 0°-40° C.; (b) continuously contacting the sulfate-containing stream, hydrogen, carbon dioxide and mixed liquor for a time sufficient to convert sulfate ions to sulfide ions; (c) continuously feeding ferric hydroxide to the fermentation zone and forming ferric sulfide therein; (d) continuously removing from the fermentation zone a portion of the mixed liquor containing ferric sulfide, removing ferric sulfide from the mixed liquor and recycling the mixed liquor to the fermentation zone; and (e) continuously removing from the fermentation zone a second portion of the mixed liquor, retaining the solids from this portion and returning them to the fermentation zone and discharging liquid effluent.

Claim 7

A process for removing dissolved sulfate ions from an aqueous stream comprising the steps of (a) continuously feeding the sulfate-containing stream essentially free of organic materials, at least 4 gram moles of gaseous hydrogen and at least 0.05 gram mole of gaseous CO 2 per gram-ion of sulfate to an oxygen-free fermentation zone containing an aqueous anaerobic mixed liquor containing group Desulfovibrio sulfate-reducing bacteria, phosphorus, nitrogen and iron nutrients and a suspension of calcium carbonate to maintain the pH of the mixed liquor between about 6.5-7.5, said fermentation zone maintained at a temperature in the range of about 0°-40° C.; (b) continuously contacting the sulfate-containing stream, hydrogen, carbon dioxide and mixed liquor for a time sufficient to convert sulfate ions to sulfide ions; (c) continuously feeding ferric hydroxide to the fermentation zone and forming ferric sulfide therein; (d) continuously removing from the fermentation zone a portion of the mixed liquor containing ferric sulfide, removing ferric sulfide from the mixed liquor and recycling the mixed liquor to the fermentation zone; and (e) continuously removing from the fermentation zone a second portion of the mixed liquor, retaining the solids from this portion and returning them to the fermentation zone and discharging liquid effluent.

Claim 8

The process of claim 5 wherein the sulfate-containing stream is aqueous sulfuric acid.

Claim 9

The process of claim 1 or claim 5 wherein the bacteria are Desulfovibrio desulfuricans.