Process for the treatment of high sulphate waters

Abstract

The present invention relates to an improved process for treating high sulphate waters. In particular, the present invention relates to an improved process by which ettringite is used to treat high sulphate waste waters by controlled precipitation of sulphate and metal ions.

Claims

1. A process for the treatment of sulphate-containing water, the process including: a first reaction stage within which ettringite is used to precipitate precipitated solids from the sulphate-containing water, the precipitated solids being selected from the group consisting of metal compounds, phosphate compounds, sulphate compounds and combinations thereof; a suspended solids removal stage for removal of the precipitated solids produced by the first reaction stage; a further reaction stage including ettringite production from partially-treated sulphate-containing water from the first reaction stage and the addition of an aluminum containing reagent; a suspended solids removal stage for removal of precipitated solids produced by the further reaction stage; a particle separation stage within which some or all of the precipitated solids that are removed within the suspended solids removal stage are separated into an aluminum hydroxide-rich product and a product containing a remainder of the precipitated solids removed by the suspend solids removal stage; and recovery to the further reaction stage of a portion or all of the aluminum hydroxide-rich product as at least a portion of the aluminum containing reagent; and recovery of the ettringite produced by the further reaction stage for use in the first reaction stage.

2. The process of claim 1, wherein the particle separation stage is based on hydrocyclone technology.

3. The process of claim 1, wherein a portion of the product containing the remainder of the precipitated solids is returned to the first reaction stage.

4. The process of claim 3, wherein the portion of the product containing the remainder of the precipitated solids is subjected to a washing or leaching process using a portion of the sulphate-containing water.

5. The process of claim 1, wherein the first reaction stage further comprises a secondary removal stage for removal of the precipitated solids precipitated in the first reaction stage.

6. The process of claim 1, wherein an additional reaction stage is provided before the further reaction stage and where additional ettringite, lime, or hydroxide containing material is added to raise the pH.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail, by way of example only, with reference to the accompanying figures in which:

(2) FIG. 1 depicts a diagram illustrating the process of the present invention; and

(3) FIG. 2 depicts a diagram showing an alternative embodiment of the present invention including an additional reaction stage.

(4) The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of certain embodiments of the present invention by way of the following non-limiting examples.

DESCRIPTION OF THE INVENTION

(5) FIGS. 1 and 2 represent embodiments of the process of the present invention.

Example 1

New Process for Treatment of Sulphate-Rich Waters Utilizing Two Main Reaction Stages

(6) Looking at FIG. 1, high sulphate water enters as stream 1 into the first reaction stage 2. Also entering the first reaction stage is the input of lime or a suitable hydroxide containing material 3 and the ettringite recycle stream 4 from the further reaction stage 19. Optionally, a recycle stream 5 from the gypsum separation stage 9 can also be added. Stream 5 is able to provide a source of seed crystals into the first reaction stage 2. Also, it is able to recycle some of the ettringite that may not have been fully utilised within the first reaction stage 2. Further, when it is sourced from stream 10, as shown here, it is able to recover aluminium hydroxide to the first reaction stage and thence to stream 22.

(7) The product 6 from the first reaction stage 2 is routed to the solids separation stage 7. Some of the separated solids 50 are routed as stream 8 to the gypsum separation stage 9. In this embodiment of the process it is assumed that a hydrocyclone based technology is utilised within the separation stage 9. The remainder of the separated solids 51 are routed to the solids discard 12.

(8) The solids discard arrangement can utilise whatever facilities and technology that may be appropriate to the location and nature of the water treatment facility. For convenience, but only for convenience, the solids discard is shown here as a single facility that receives a combined stream that is made up from all the different residue streams 11, 26, 33, 42, 45 and 51. However, one or more of these residue streams could be routed separately or in combination(s) to one or more alternative facilities, as may be appropriate to the contents of the particular residue stream and to the location and nature of the water treatment facility.

(9) A portion 5 of the gypsum concentrate 10 from the gypsum separation stage 9 can, if desired, be recycled to the first reaction stage 2, as noted above. Stream 5 could also be sourced from stream 50 or stream 51. The remainder of the gypsum concentrate 11 is routed to the solids discard 12.

(10) The clarified water 18 from the solids separation stage 7 is then forwarded to the further reaction stage 19. The further reaction stage 19 also receives an additional input of lime and/or a calcium and/or hydroxide containing material 20; a portion 21, all or none of the Al(OH).sub.3 rich product 22 that is created within the separation stage 9 and, if appropriate, a portion 23 of the solids output 30 from the suspended solids separation stage 29 that follows the further reaction stage 19. Stream 23 can be sourced from either before or after the optional buffer storage facility 32.

(11) Normally, a portion 23 of the solids output would only need to be returned to the reaction stage 19 if the reactor design for this reaction stage is unable to maintain a sufficient quantity of seed crystals within the reactor for optimum reaction conditions.

(12) Depending upon the aluminium and the sulphate content of the process feed water stream 1, the aluminum content of the various reagents that are added to the process and/or the efficiency of the separation stage 9, it may be necessary to include a source of soluble aluminium within or alongside the overall reagent input stream 20.

(13) If only a portion 21 of the aluminium hydroxide concentrate 22 is used within the further reaction stage 19, then the remainder 26 is routed to the residue discard 12. Preferably, but not shown here, the remainder 26 will be routed through a buffer storage facility so that a stock of recovered aluminum concentrate can be maintained for use within a process re-start or when there is a shortage of aluminium within the inputs to the process.

(14) The reacted product 28 from the further reaction stage 19 is routed to a suspended solids separation stage 29. As noted above, some of the separated suspended solids 30 from separation stage 29 can be returned (stream 23) to the further reaction stage 19 as a source of seed crystals. The remainder 52 or all of the separated solids 30 can be routed to the buffer storage facility 32.

(15) In many situations there will be more ettringite produced within the process than can be dissolved within the reaction stage 2. The excess can either be discharged as indicated by stream 33 or via another route (not shown here) to the discard facility 12, or to an alternative discharge facility.

(16) The clarified water 35 from the suspended solids separation stage 29 are then passed to a further polishing reaction stage 36 where an appropriate ferric iron based or other appropriate treatment/final adjustment reagent 37 is added. Whenever necessary, in order to achieve the desired final pH, a controlled amount of a pH adjusting acidic reagent 38 would also be added. The reagent 37 may consist of a number of different reagents which are added as a blended mixture, individually or in partial combination. Similarly, the acidic reagent 38 may consist of a number of different reagents which are added as a blended mixture, individually or in partial combination.

(17) The product 39 from the polishing reaction and pH reduction stage 36 is then routed to a further suspended solids removal stage 41 where the residues from the polishing reactions, including aluminium hydroxide from any unreacted aluminium, would be removed. The separated solids 42 from this suspended solids removal stage 41 would normally be routed to the residues discard 12. However, as this residue stream can often contain a significant proportion of aluminium hydroxide, it is sometimes appropriate to route these residues back to one of the previous reaction stages so as to reclaim the aluminium for further use. The selection as to which reactor to return them to will be situation specific and will be dependent on the nature and quantity of the other components that are removed within this polishing stage.

(18) Normally, after this polishing reaction stage, it is necessary to carry out a further minor pH adjustment to the clarified output 43. In addition, it is sometimes necessary to add further components in order to satisfy any particular requirements that may be imposed by the discharge or re-use criteria. Any such further additions are shown as one or more inputs 40.

(19) Within many of the discharges from industry and/or from mining activities, the dissolved nitrogen content may be too high for the proposed re-use or discharge criteria. This nitrogen can be present as both inorganic nitrogen containing compounds, organic nitrogen containing compounds or as a mixture of both. Other organic compounds could also be present, including phosphorous containing compounds. There are a number of well-established technologies for removing these contaminants and the selection of the appropriate technology or technologies will be dictated by the specific nature and quantities of the contaminants, the local circumstances, costs and operator preferences. Location 44 is the typical position within the above described overall treatment process where these nitrogen and other contaminating compounds would normally be removed. Any solid, sludge or other residues 45 from this location would normally join the overall residue discard 12, as shown. However, depending upon what has to be removed, it may be appropriate to route them, or some of them, to another process outlet.

(20) The finally treated water 46 would then be available for re-use or discharge.

Example 2

New Process for Treatment of Sulphate-Rich Waters Utilizing Three Main Reaction Stages

(21) Turning to FIG. 2, high sulphate water enters at 1 into the first reaction stage 2. Also entering the first reaction stage is the input of lime or a hydroxide containing material 3, the ettringite concentrate 4 and, if desired, an aluminium containing recycle stream 5 from the gypsum separation stage 9. The product 6 from the reaction stage 2 is routed to the solids separation stage 7. The separated solids 8 are routed to the gypsum separation stage 9, which in this embodiment of the process it is assumed that a hydrocyclone based technology is utilised. A portion 5 of the gypsum concentrate 10 can be recycled to the first reaction stage 2 as noted above as a source of seed crystals. The remainder of the gypsum concentrate 11 is routed to the solids discard 12. As noted above, this discard arrangement can utilise whatever facilities and technology that may be appropriate to the location and nature of the water treatment facility.

(22) The clarified water 13 from the solids separation stage 7 is then forwarded to the additional reaction stage 14 where additional ettringite 34 (see below), lime or a hydroxide containing material 15 is added. The precipitated solids that are created within this reaction stage are then separated within the second solids separation stage 16. The separated solids 17 are directed to the residue discard 12 and the clarified water 18 is passed on to the further reaction stage 19.

(23) The further reaction stage 19 also receives an additional input of lime or a hydroxide containing material 20; a portion 21, all or none of the separated aluminium hydroxide concentrate 22 that is created within the separation stage 9, if appropriate, an additional source of aluminium and, if appropriate, a portion 23 of the fine solids output 24 from the optional ettringite separation unit 25. In this embodiment of the process it is also assumed that a hydrocyclone based technology is utilised. If only a portion 21 of the aluminium hydroxide concentrate 22 is used within the further reaction stage 19, then the remainder 26 is routed to the residue discard 12. Preferably, but not shown here, the remainder 26 will be routed through a buffer storage facility so that a stock of recovered aluminium concentrate can be maintained for use within a process re-start or when there is a shortage of aluminium within the inputs to the process.

(24) Similarly, the portion 27 of the fine solids output 24 from the ettringite separation stage 25 that is not recycled to the further reaction stage 19 is also routed to the residue discharge 12. In this instance, less benefit can be achieved from a buffer storage facility for portion 27 relative to the benefit that can be obtained from a buffer storage facility for the portion 26. However, a suitable buffer facility could be provided for this portion 27.

(25) The reacted product 28 from the further reaction stage 19 is routed to the third suspended solids separation stage 29. The separated suspended solids 30 from this third separation stage are routed to an optional ettringite separation unit 25 from where the separated concentrate of ettringite 31 is routed to an optional buffer storage facility 32. From this buffer storage facility 32, or directly, the concentrate 4 is directed back to the first reaction stage 2.

(26) If, as noted above, there is an excess of aluminium available and if it is beneficial to the control of the ionic balance between sulphate and calcium, then an input of ettringite concentrate 34 to the additional reaction stage 14 can also be made. If there is an excess of ettringite concentrate, then the excess 33 can be routed to the residue discharge 12.

(27) The clarified water 35 from the suspended solids separation stage 29 are then passed to a further polishing reaction stage 36 where an appropriate ferric iron based or other appropriate treatment/final adjustment reagent 37 is added together with a controlled addition of a pH adjusting acidic reagent 38. The reagent 37 may consist of a number of different reagents which are added as a blended mixture, individually or in partial combination. Similarly, the acidic reagent 38 may consist of a number of different reagents which are added as a blended mixture, individually or in partial combination.

(28) The product 39 from the polishing reaction stage is then routed to a further suspended solids removal stage 41 where the residues from the polishing reactions would be removed together with any unreacted aluminium. The separated solids 42 from this suspended solids removal stage 41 would normally be routed to the residues discard. However, as this residue stream can often contain a significant proportion of aluminium hydroxide, it is sometimes appropriate to route these residues back to one of the previous reaction stages so as to reclaim the aluminium for further use. The selection as to which reactor to return them to will be situation specific and will be dependent on the nature and quantity of the other components that are removed within this polishing stage.

(29) Normally, after this polishing reaction stage, it is necessary to carry out a further minor pH adjustment to the clarified output 43. In addition, it is sometimes necessary to add further components in order to satisfy particular requirements that may be imposed by the discharge or re-use criteria. Any such further additions are shown as one or more inputs 40.

(30) Within many of the discharges from industry and/or from mining activities, the dissolved nitrogen content may be too high for the proposed re-use or discharge criteria. This nitrogen can be present as both inorganic nitrogen containing compounds, organic nitrogen containing compounds or as a mixture of both. Other organic compounds could also be present, including phosphorous containing compounds. There are a number of well-established technologies for removing these contaminants and the selection of the appropriate technology or technologies will be dictated by the specific nature and quantities of the contaminants, the local circumstances, costs and operator preferences. Location 44 is the typical position within the above described overall treatment process where these nitrogen and other contaminating compounds would be removed. Any solid, sludge or other residues 45 from this location would normally join the overall residue discard 12, as shown. However, depending upon what has to be removed, it may be appropriate to route them, or some of them, to another process outlet.

(31) The finally treated water 46 would then be available for re-use or discharge.