WO2015150636A1 - Method for removal of sulphate from aqueous solution - Google Patents
Method for removal of sulphate from aqueous solution Download PDFInfo
- Publication number
- WO2015150636A1 WO2015150636A1 PCT/FI2015/050228 FI2015050228W WO2015150636A1 WO 2015150636 A1 WO2015150636 A1 WO 2015150636A1 FI 2015050228 W FI2015050228 W FI 2015050228W WO 2015150636 A1 WO2015150636 A1 WO 2015150636A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- aqueous solution
- suspension
- sulphate
- cells
- cell
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/463—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electrocoagulation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/24—Feed or discharge mechanisms for settling tanks
- B01D21/2433—Discharge mechanisms for floating particles
- B01D21/2438—Discharge mechanisms for floating particles provided with scrapers on the liquid surface for removing floating particles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/24—Feed or discharge mechanisms for settling tanks
- B01D21/245—Discharge mechanisms for the sediments
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D21/00—Separation of suspended solid particles from liquids by sedimentation
- B01D21/24—Feed or discharge mechanisms for settling tanks
- B01D21/2488—Feed or discharge mechanisms for settling tanks bringing about a partial recirculation of the liquid, e.g. for introducing chemical aids
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B03—SEPARATION OF SOLID MATERIALS USING LIQUIDS OR USING PNEUMATIC TABLES OR JIGS; MAGNETIC OR ELECTROSTATIC SEPARATION OF SOLID MATERIALS FROM SOLID MATERIALS OR FLUIDS; SEPARATION BY HIGH-VOLTAGE ELECTRIC FIELDS
- B03D—FLOTATION; DIFFERENTIAL SEDIMENTATION
- B03D1/00—Flotation
- B03D1/14—Flotation machines
- B03D1/1437—Flotation machines using electroflotation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
- C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
- C02F1/465—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis by electroflotation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/101—Sulfur compounds
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/10—Nature of the water, waste water, sewage or sludge to be treated from quarries or from mining activities
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/26—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof
- C02F2103/28—Nature of the water, waste water, sewage or sludge to be treated from the processing of plants or parts thereof from the paper or cellulose industry
Definitions
- Sulphate sources loading the water systems include mines, the pulp industry and effluent treatment plants.
- Typical water-soluble sulphates are, among others, sodi- urn sulphate, potassium sulphate, magnesium sulphate and ammonium sulphate.
- Sulphates are usually water-soluble and form a solution which is difficult to purify.
- Sulphate has conventionally been removed from aqueous solutions by precipitating it as calcium salt, that is, calcium sulphate. This can be done by adding calcium chloride, calcium hydroxide or calcium carbonate into the solution, the last- mentioned particularly into acidic solutions. Adding calcium chloride adds a chloride ion into the solution, which is usually undesirable in purified water.
- Adding calcium hydroxide increases the pH value of the purified water and the purified water then usually has to be neutralised thereafter.
- the use of calcium carbonate for precipitation is limited to acidic solutions, in which case the carbonate ion releases carbon dioxide.
- Calcium carbonate is obtained from limestone, which also contains considerable amounts of magnesium, which produces soluble magnesium sulphate and has a reductive effect on the amount of precipitating sulphate.
- Ettringite process Previously is known the so-called Ettringite process, which is, however, complicated and expensive and, therefore, unsuitable for purifying the large amounts of aqueous solutions produced in the mining or pulp industries or in effluent purification and for removing sulphate.
- calcium hydroxide is used to increase the pH value to about 12, whereupon the aluminium trioxide added into the suspension to be processed forms a precipitate together with the sulphate.
- This well- known sulphate precipitation method is complicated and expensive and is, therefore, for the present rarely used in industrial applications.
- Soluble sulphate ending up from effluent treatment plants in natural waters is due especially to the fact that acidic iron sulphate originating in the mining industry is intentionally added into the effluent because it precipitates phosphorus as iron phosphate.
- the soluble sulphate remains in the treated effluent.
- the only partly purified effluent contains organic matter, the bacteria responsible for oxidising which first consume the soluble oxygen from the water, and if this is lacking, take the oxygen from the sulphate.
- the sulphate converts into extremely toxic hydrogen sulphide. Hydrogen sulphide destroys organisms living in natural waters efficiently. It is, therefore, important not to discharge sulphate-containing effluents into nature.
- the aim of the invention is to provide an easy-to-use and economical process suita- ble for treating large amounts of aqueous solutions in such a way that the end result is water purified of sulphates, which can be discharged into nature without it being harmful.
- Figure 1 shows a general diagram of the device used for implementing the method of the invention according to one embodiment.
- An aqueous solution and/or suspension in a container 1 is heated to a temperature within the range +40°C-+50°C, while mixing calcium carbonate CaC0 3 into it. Increasing the temperature speeds up the process.
- the calcium carbonate is in powder form and it is added and mixed into the aqueous solution and/or suspension in an amount which increases the pH of the aqueous solution and/or suspension to a value of approximately 8.4, the amount being sufficient in relation to the amount of sulphate to be precipitated. Irrespective of the calcium carbonate content, the pH reaches a constant value and the pH value does not have to be separately adjusted.
- the aqueous solution and/or suspension is pumped from the container 1 through an electrolytic cell 2 provided with an aluminium electrode. Aluminium hydroxide and hydrogen gas are produced in the cell 2 by means of an electric current.
- the cell may be, for example, of the type described in patent publication
- the cells may be aluminium cells with one or more electrodes.
- the aqueous solution and the sulphate-containing suspension contained by it are conveyed from the cell 2 into a precipitation basin 3, which is connected to a collection basin 5 through a flow channel 4 close to the bottom.
- a precipitation basin 3 which is connected to a collection basin 5 through a flow channel 4 close to the bottom.
- the flow channel 4 may be, for example, a belt conveyor or several screw conveyors, by means of which the precipitate is conveyed into the collection basin or directly to the filter. If so desired, some polymer may be added after the cell 2, which stabilises the precipitate and flock produced.
- the aqueous solution and the suspension are cooled or allowed to cool in the collection basin 5 to a temperature of typically below 30°C, in which it crystallises and forms a solid substance which rises to the surface of the water, resembles ice, floats, and contains uniform blocks, "a flock". It has been found that during cooling, the flock crystallises into a coarsely structured or spongy "sulphate ice" which is lighter than water and rises to the surface and can thus be easily removed, for example, by scraping with a scraper conveyor 8 and conveying through a pipe or chute 6 to further treatment.
- the "sulphate ice” formed is a metal complex compound which contains aluminium and calcium in addition to sulphate and, depending on the solution purified, may also con- tain sodium, potassium and magnesium and small amounts of other metals, chloride and other anions.
- a complex compound typically also contains crystal water.
- Sulphate can be removed from an aqueous solution or suspension also by filtering at the basin 3 precipitate stage.
- the precipitate is formed by means of a molecular sieve provided by aluminium hydroxide to which the sulphate, calcium and other ions formed in the electrolysis adhere.
- the aqueous solution and/or suspen- sion purifying or purified in connection with the formation of the precipitate or flock can, if necessary, be conveyed back to the aqueous solution and/or suspension to be purified in order to reduce its conductance typically to a value of less than 4 mS/cm (e.g. 3.5 mS/cm) for the electrolysis treatment.
- this is implemented with a pipe 7 which extends from the bottom of the rear part of the con- tainer 5.
- the aqueous solution and/or suspension purifying or purified in connection with the formation of the precipitate or flock can be conveyed to another electrolytic cell 12 for further purification.
- each cascade stage may be a desired number of cells 2 in parallel to provide sufficient treatment capacity.
- the aluminium cells may also be arranged in such a way that they form a horizontal channel system through which the sulphate-containing water is passed.
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Water Supply & Treatment (AREA)
- Life Sciences & Earth Sciences (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Hydrology & Water Resources (AREA)
- Organic Chemistry (AREA)
- Biotechnology (AREA)
- Water Treatment By Electricity Or Magnetism (AREA)
Abstract
A method for the removal of sulphate from an aqueous solution and/or suspension. An aqueous solution and/or suspension is heated to a temperature within the range +40°C-+50°C and calcium carbonate is added and mixed into the aqueous solution (1) and/or suspension in an amount which increases the pH of the aqueous solution and/or suspension to the value of 8.4. The aqueous solution and/or suspension is pumped through an electrolytic cell or set of cells (2) provided with an aluminium electrode and aluminium hydroxide is produced in the cell or set of cells by means of an electric current. The precipitate or flock formed is separated from the aqueous solution and/or suspension removed from the cell or set of cells.
Description
Method for removal of sulphate from aqueous solution
Sulphate sources loading the water systems include mines, the pulp industry and effluent treatment plants. Typical water-soluble sulphates are, among others, sodi- urn sulphate, potassium sulphate, magnesium sulphate and ammonium sulphate. Sulphates are usually water-soluble and form a solution which is difficult to purify. Sulphate has conventionally been removed from aqueous solutions by precipitating it as calcium salt, that is, calcium sulphate. This can be done by adding calcium chloride, calcium hydroxide or calcium carbonate into the solution, the last- mentioned particularly into acidic solutions. Adding calcium chloride adds a chloride ion into the solution, which is usually undesirable in purified water. Adding calcium hydroxide increases the pH value of the purified water and the purified water then usually has to be neutralised thereafter. The use of calcium carbonate for precipitation is limited to acidic solutions, in which case the carbonate ion releases carbon dioxide. Calcium carbonate is obtained from limestone, which also contains considerable amounts of magnesium, which produces soluble magnesium sulphate and has a reductive effect on the amount of precipitating sulphate.
Previously is known the so-called Ettringite process, which is, however, complicated and expensive and, therefore, unsuitable for purifying the large amounts of aqueous solutions produced in the mining or pulp industries or in effluent purification and for removing sulphate. In the Ettringite process, calcium hydroxide is used to increase the pH value to about 12, whereupon the aluminium trioxide added into the suspension to be processed forms a precipitate together with the sulphate. This well- known sulphate precipitation method is complicated and expensive and is, therefore, for the present rarely used in industrial applications.
Soluble sulphate ending up from effluent treatment plants in natural waters is due especially to the fact that acidic iron sulphate originating in the mining industry is intentionally added into the effluent because it precipitates phosphorus as iron phosphate. The soluble sulphate remains in the treated effluent. The only partly purified effluent contains organic matter, the bacteria responsible for oxidising which first consume the soluble oxygen from the water, and if this is lacking, take the oxygen from the sulphate. The sulphate converts into extremely toxic hydrogen
sulphide. Hydrogen sulphide destroys organisms living in natural waters efficiently. It is, therefore, important not to discharge sulphate-containing effluents into nature.
The aim of the invention is to provide an easy-to-use and economical process suita- ble for treating large amounts of aqueous solutions in such a way that the end result is water purified of sulphates, which can be discharged into nature without it being harmful.
This aim is achieved by the method according to the invention, on the basis of the characteristics disclosed in the accompanying claim 1. The dependent claims disclose preferred embodiments of the invention.
The invention is illustrated in greater detail in the following, with reference to the accompanying drawing, in which:
Figure 1 shows a general diagram of the device used for implementing the method of the invention according to one embodiment.
An aqueous solution and/or suspension in a container 1 is heated to a temperature within the range +40°C-+50°C, while mixing calcium carbonate CaC03 into it. Increasing the temperature speeds up the process. The calcium carbonate is in powder form and it is added and mixed into the aqueous solution and/or suspension in an amount which increases the pH of the aqueous solution and/or suspension to a value of approximately 8.4, the amount being sufficient in relation to the amount of sulphate to be precipitated. Irrespective of the calcium carbonate content, the pH reaches a constant value and the pH value does not have to be separately adjusted.
The aqueous solution and/or suspension is pumped from the container 1 through an electrolytic cell 2 provided with an aluminium electrode. Aluminium hydroxide and hydrogen gas are produced in the cell 2 by means of an electric current. Structurally, the cell may be, for example, of the type described in patent publication
EP1583719 or WO2011/018556. The cells may be aluminium cells with one or more electrodes.
The aqueous solution and the sulphate-containing suspension contained by it are conveyed from the cell 2 into a precipitation basin 3, which is connected to a collection basin 5 through a flow channel 4 close to the bottom. At the bottom of the basin 3 and the flow channel 4 may be, for example, a belt conveyor or several screw conveyors, by means of which the precipitate is conveyed into the collection basin or directly to the filter. If so desired, some polymer may be added after the cell 2, which stabilises the precipitate and flock produced. In a preferred embodiment of the invention, the aqueous solution and the suspension are cooled or allowed to cool in the collection basin 5 to a temperature of typically below 30°C, in which it crystallises and forms a solid substance which rises to the surface of the water, resembles ice, floats, and contains uniform blocks, "a flock". It has been found that during cooling, the flock crystallises into a coarsely structured or spongy "sulphate ice" which is lighter than water and rises to the surface and can thus be easily removed, for example, by scraping with a scraper conveyor 8 and conveying through a pipe or chute 6 to further treatment. The "sulphate ice" formed is a metal complex compound which contains aluminium and calcium in addition to sulphate and, depending on the solution purified, may also con- tain sodium, potassium and magnesium and small amounts of other metals, chloride and other anions. A complex compound typically also contains crystal water.
Sulphate can be removed from an aqueous solution or suspension also by filtering at the basin 3 precipitate stage. The precipitate is formed by means of a molecular sieve provided by aluminium hydroxide to which the sulphate, calcium and other ions formed in the electrolysis adhere.
From the aqueous solution or suspension removed from the cell 2 is, therefore, separated either the precipitate formed or the flock, that is, "sulphate ice" formed after cooling. The latter alternative is easier to implement on a large scale because the natural process takes care of the separation in such a way that recovery of only solid matter is required.
In a preferred embodiment of the invention, the aqueous solution and/or suspen- sion purifying or purified in connection with the formation of the precipitate or flock
can, if necessary, be conveyed back to the aqueous solution and/or suspension to be purified in order to reduce its conductance typically to a value of less than 4 mS/cm (e.g. 3.5 mS/cm) for the electrolysis treatment. In Figure 1, this is implemented with a pipe 7 which extends from the bottom of the rear part of the con- tainer 5.
The aqueous solution and/or suspension purifying or purified in connection with the formation of the precipitate or flock can be conveyed to another electrolytic cell 12 for further purification. There may be the desired number of such cascade connec- tion stages depending on the desired degree of purification. In each cascade stage may be a desired number of cells 2 in parallel to provide sufficient treatment capacity.
The aluminium cells may also be arranged in such a way that they form a horizontal channel system through which the sulphate-containing water is passed.
Claims
1. A method for the removal of sulphate from an aqueous solution and/or suspension, characterised in that
- an aqueous solution and/or suspension is heated to a temperature within the range +40°C-+50°C,
- calcium carbonate is added and mixed into the aqueous solution and/or suspension in an amount which increases the pH of the aqueous solution and/or suspension to a value of approximately 8.4,
- the aqueous solution and/or suspension is pumped through an electrolytic cell or set of cells provided with an aluminium electrode and aluminium hydroxide is produced in the cell or set of cells by means of an electric current, and
- the precipitate or flock formed is separated from the aqueous solution and/or suspension removed from the cell or set of cells.
2. A method as claimed in claim 1, characterised in that the aqueous solution and/or suspension removed from the cell or set of cells and the precipitate formed are cooled or allowed to cool to a temperature below 30°C, thus forming a flock which rises to the surface, which is removed from the aqueous solution and/or sus- pension.
3. A method as claimed in claim 1 or 2, characterised in that the aqueous solution and/or suspension purifying or purified in connection with the formation of the precipitate or flock is conveyed back to the aqueous solution and/or suspension to be purified in order to reduce its conductance for the electrolysis treatment.
4. A method as claimed in any of the claims 1 to 3, characterised in that the aqueous solution and/or suspension purifying or purified in connection with the formation of the precipitate or flock is conveyed to another electrolytic cell or set of cells for further purification.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI20145319 | 2014-04-02 | ||
| FI20145319A FI126851B (en) | 2014-04-02 | 2014-04-02 | A method for removing sulfate from an aqueous solution |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2015150636A1 true WO2015150636A1 (en) | 2015-10-08 |
Family
ID=54239439
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/FI2015/050228 WO2015150636A1 (en) | 2014-04-02 | 2015-03-31 | Method for removal of sulphate from aqueous solution |
Country Status (2)
| Country | Link |
|---|---|
| FI (1) | FI126851B (en) |
| WO (1) | WO2015150636A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20160194208A1 (en) * | 2012-11-02 | 2016-07-07 | Strategic Metals Ltd. | Methods and systems using electrochemical cells for processing metal sulfate compounds from mine waste and sequestering co2 |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011018556A1 (en) * | 2009-08-14 | 2011-02-17 | Hannu Suominen | Method and apparatus for the purification of hydrogen sulfide -containing aqueous solutions |
| WO2014033361A1 (en) * | 2012-08-27 | 2014-03-06 | Outotec Oyj | Method for removing sulphate, calcium and/or other soluble metals from waste water |
| WO2014096549A1 (en) * | 2012-12-20 | 2014-06-26 | Outotec Oyj | Method of treating industrial water |
| US20140246371A1 (en) * | 2013-03-01 | 2014-09-04 | Baker Hughes Incorporated | Process for removing sulfate and system for same |
-
2014
- 2014-04-02 FI FI20145319A patent/FI126851B/en not_active IP Right Cessation
-
2015
- 2015-03-31 WO PCT/FI2015/050228 patent/WO2015150636A1/en active Application Filing
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2011018556A1 (en) * | 2009-08-14 | 2011-02-17 | Hannu Suominen | Method and apparatus for the purification of hydrogen sulfide -containing aqueous solutions |
| WO2014033361A1 (en) * | 2012-08-27 | 2014-03-06 | Outotec Oyj | Method for removing sulphate, calcium and/or other soluble metals from waste water |
| WO2014096549A1 (en) * | 2012-12-20 | 2014-06-26 | Outotec Oyj | Method of treating industrial water |
| US20140246371A1 (en) * | 2013-03-01 | 2014-09-04 | Baker Hughes Incorporated | Process for removing sulfate and system for same |
Non-Patent Citations (2)
| Title |
|---|
| EL-NAAS M. H. ET AL.: "Assessment of electrocoagulation for the treatment of petroleum refinery wastewater.", JOURNAL OF ENVIRONMENTAL MANAGEMENT, vol. 91, no. 1, 2009, pages 180 - 185, XP026709048, ISSN: 0301-4797 * |
| ORESCANIN V. ET AL.: "A combined CaO/electrochemical treatment of the acid mine drainage from the ''Robule'' Lake.", JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH, PART A (TOXIC/HAZARDOUS SUBSTANCES AND ENVIRONMENTAL ENGINEERING, vol. 47, no. 8, 1 July 2012 (2012-07-01), pages 1186 - 1191, XP055229194, ISSN: 1093-4529 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20160194208A1 (en) * | 2012-11-02 | 2016-07-07 | Strategic Metals Ltd. | Methods and systems using electrochemical cells for processing metal sulfate compounds from mine waste and sequestering co2 |
| US9695050B2 (en) * | 2012-11-02 | 2017-07-04 | Terra Co2 Technologies Ltd. | Methods and systems using electrochemical cells for processing metal sulfate compounds from mine waste and sequestering CO2 |
Also Published As
| Publication number | Publication date |
|---|---|
| FI20145319A (en) | 2015-10-03 |
| FI126851B (en) | 2017-06-30 |
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