AU641871B2 - Saline wastewater processing - Google Patents

Description

r.

641a871m COMPLETE SPECIFICATION

(ORIGINAL)

For Official Use FORM Short Title: Int. Cl: Application Number: Lodged: Complete specification Lodged: Accepted: Lapsed: Published: Priority: Related Art: Name of Applicant: Katauskas Address of Applican Actual Inventor: Address for Service TO BE COMPLETED BY APPLICANT Aharon Vartan Arakel and Donatus A J '4 t:P0 BOX 481 WEST RYDE NSW 2114f Aharon Vartan Arakel I le e -Sknhip A scats r%.o e- 4 ~?AT~E)GD NSW 2E)67 WAeskkA I\sw 2-t%9 ation for the invention entitled: SALINE Complete S~ec if ic WASTEWATER~ PROCESSING The following statement is a full description of this invention, including the best method of performing it known to me: -2- SALINE WASTEWATER PROCESSING The present invention relates to removal of disolved solids from inorganic saline wastewaters to recover a number of valuable waste products and to minimise disposal costs and potential environmental impacts. One aspect of the invention relates to reduction of the bulk of dissolved solids in particular types of wastewater and another aspect of the invention is to produce a range of valuable salt mineral and slurry products from such wastewaters.

Agricultural, mining, industrial and municipal activities in arid and semi-arid regions of Australia other countries produce large quantities of saline oooo• wastewaters which contain significant amounts of oeooe dissolved salts and are considered potentially dangerous to the environment. Currently most of these 20 liquid wastes are disposed of through the use of retainment, filtration and evaporation ponds as well as discharged into natural waterways. Pollution of waterways occurs due to the latter method of disposal e and the retainment, filtration and evaporation ponds currently in use result in large volumes of waste and S"minimal revenue from any commercially saleable salt chemicals recovered.

-3- It is consequently an object of the present invention to disclose a method of treatment for wastewaters rich in Sulphates, Potassium and Magnesium which process overcomes one or more of the disadvantages with existing processing methods or at least it provides an alternative.

According to the present invention there is disclosed a process for reduction of the dissolved salt content and volume of saline inorganic wastewaters having at least five (molar) percent Sulphate (SO 4 content; being one or more of the following water types; Na-(Mg)-Cl-(S0 4 Na-(Mg.K)-Cl-(SO 4 Na-(Mg)-Cl-(S0 4 Na-Cl, Na-(Mg)- 15 Cl, and having an Mg/2K (molar) ratio greater than 1.4 comprising the steps of;

S•

placing the feed solution in a preconditioning pond to precipitate impurities and raise the specific gravity to at least 1.15; shifting the feed solution to an evaporation pond and continuing evaporation to precipitate NaC1 until the solution reaches a specific gravity of between 1.23 and 1.25; cooling the brine resulting from the aforementioned steps to between Zero and minus t r 4 -4- Five Degrees Celsius and then dewatering the solution to seperate Mirabilite crystals.

In its most basic form above described the present invention gives Halite, Mirabilite and a filtrate suitable for further processing in accordance with the present invention to produce Potassium Chloride, Epsomite a 40% slurry of Magnesium Hydroxide and other products. The Mirabilite produced in accordance with the process of the present invention may also be further processed so as to produce Thenardite and Potassium Sulphate. Production as lastmentioned in accordance with the processes disclosed in the present 15 invention not only gives saleable products but drastically reduces the volume of feed solution.

SWhilst contemporary thinking has resulted in attempts to evaporate wastewater in order to reduce its volume 20 and produce useful products the present invention discloses a comprehensive scheme for multiple evaporation and cooling in order to achieve a range of Suseful products.

By way of illustration a number of schemes for treatment of wastewater in accordance with the present invention will be hereafter described with reference to the abovementioned diagrams in which; Figure 1 is a flow chart indicating the basic steps through which an appropriate feed solution may be taken so as to give a number of products. The flow chart additionally indicates inter-relationships between the production of the various products; Figures 2 to 3,4,5 and 6 are further flow charts showing seperately the paths in accordance with the present invention necessary to produce Thenardite, Potassium Sulphate, Potassium Chloride, Epsomite and a Magnesium Hydroxide slurry respectively and; Figure 7 is a table indicating the appropriate thermodynamic conditions and other parameters which the applicant has determined by experimentation are necessary for production of various products in accordance with the present invention.

Feed solutions considered generally suitable for the process disclosed herein are those inorganic saline /o wastewaters with more than 5 mol.% S04 and with the following chemical characteristics: oe -6- Ratio Water Types Mg/2K mol.< 3 Na-(Mg)-Cl-(SO 4 Na-(Mg.K)-C1-(SO 4 3<Mg/2K mol.< 6 Na-(Mg)-Cl-(SO 4 Na-C1 Mg/2K mol. 6 Na-(Mg)-C1 For production of Mirabilite (Na 2

SO

4 .10H 2 0) and Thenardite (Na 2

SO

4 as shown in FIG. 2, the feed solution is first pre-concentrated by solar evaporation to about SG(Specific Gravity)=l.20 and then transferred to an evaporation pond and concentrated by evaporation to SG=1.25; maximum SG at this stage should not exceed 1.29. In summer the concentrated brine is naturally 15 evaporated to 1.30<SG<1.32 and dewatered to produce a 4* salt slurry which is then dissolved in fresh water, S"cooled down to between zero and minus five Degrees ft Celsius and dewatered to produce Mirabilite product.

20 The route for summer Mirabilite production, as shown in FIGS 1 2, can be shortened by applying artificial cooling to filtrate bittern, after initial evaporation, followed by dewatering to produce Mirabilite product.

As a cost-effective alternative, in winter, the resultant concentrated brine can be naturally cooled to temperatures down to between zero and minus five Degrees Celsius then dewatered to produce Mirabilite product.

-7- The Mirabilite thus produced is then dehydrated to Thenardite in several ways. The first and simplest way is t wash the Mirabilite crystals with an appropriate washing liquor, then dewater and dry to produce Thernardite product; the second way utilises a chemical replacement method for obtaining higher productivity involving first the dissolution of Mirabilite by hot steam followed by reaction with Halite and normalisation of the mixture to forty Degrees Celsius then dewatering and drying to obtain Thernardite product. The third way utilises addition of Ethanol to Mirabilate crystals to decrease the solubility of the Na 2

SO

4

-H

2 0 system and hence increase Na 2

SO

4 productivity. The Ethanol in the filtrate is then recovered by distillation.

For production of Potassium Sulphate (K 2 S0 4 as shown in FIG. 3, the Mirabalite product is first dissolved by hot steam, and then subjected to two-step conversion with KC1 according to the following reactions: 2Na2SO4+KC LNa2SO4.3K2S04+6NaCl(First Step Conversion) Na 2

SO

4 3K 2 S0 4 +KC-1K 2 SO4+NaC1 (Second Step Conversion) The first conversion is accomplished by reacting KC1 with solution rich in Mirabilite through continuous mixing for thirty minutes at thirty five Degrees -8- Celsius and then dewatering it to produce Glasserite crystals in NaCI base solution. For the second conversion, the Glasserite crystals are reacted with KC1 through continuous mixing for thirty minutes at fifty Degrees Celsius and the mixture is then cooled down to ambient temperature (twenty-twenty five Degrees Celsius) to obtain K 2

SO

4 crystals in the NaCl base solution, which is then dewatered and dried to produce the final K 2

SO

4 product. As shown in FIGS 1 3, the filtrate bitterns from the conversion reactions are are recycled to maximise Potassium recovery.

For production of Potassium Chloride (KC1), as shown in FIG. 4, the bitterns from dewatering of Mirabilite and Epsomite slurries are first artificially evapoarated to SG=1.36, and left to reach ambient temperature (twenty twenty five Degrees Celsius) then dawatered. The resultant carnallite mixture is subjected to sequential flotation and the solids subsequently separated by centrifuge and dried to produce the final Potassium Chloride product.

For production of Epsomite (MgSO 4 .7H 2 as shown in FIG. 5, the filtrate bittern from the Mirabilite production stream is evaporated to separate the Halite impurity and to increase the bittern density to 1.28< artificially cooled to between zero and minus i 9 five Degrees Celsius then dewatered to produce Epsomite crystals. To increase recovery the Epsomite crystals thus produced are redissolved in hot water, evaporated to SG=1.30, and left to gradually normalise with ambient temperature (twenty twenty five Degrees Celsius) then dewatered and dried to produce the final Epsomite product.

For production of Mg(OH) 2 slurry, as shown in FIG. 6, the bittern filtrate from the KC1 production stream is first diluted with fresh water to 1.05<SG<l.10, then reacted with Lime (CaO) by rapid stirring in a tank.

Thickening by using a slow mixer and subsequent 15 dewatering gives the final Mg(OH) 2 slurry product.

f Depending upon the chemcal composition of the feed solution the scheme of the present invention contemplates that removal of additional salts will be possible by further processing of the filtrate from the 4 4 dewatering steps of the Mirabilite production.

The following specific examples will more precisely illustrate the invention and teach the procedure 25 presently preferred for removal of dissolved solids as waste products based on the integrated processing schedule described herein.

EXAMPLE 1 One thousand litres (about Icu.m) of a single waste stream from a saline groundwater source, which analyzed as 882 mg/1 Calcium, 3159 mg/l Magnesium, 10350 mg/1 Sodium, 4692 mg/1 Potassium, 25 mg/l carbonate and bicarbonate, 6720 mg/1 Sulphate, 18939 mg/l Chloride, and measured 50g/l total dissolved solids (TDS), was first evaporated in a pre-concentration pond to SG=1.20, which produced some impurities (mainly Gypsum) then further concentrated by evaporation to SG=1.25 which produced 25kg of Halite salt. The summer process route shown in FIG. 2 was followed in this case to 15 produce a Mirabilite slurry, which was subsequently dissolved by hot steam. Halite was then added to reach an NaCI to Slurry weight ratio of 3.8 1 and then the solution was brought to forty Degrees Celsius by continuous mixing. Following dewatering and drying of the solids about 8kg Na 2

SO

4 with 96% purity was produced. The Na 2

SO

4 recovery was 93%.

The filtrate bittern from Thenardite production was then subjected to the processing steps shown in FIG. to produce about 6kg of MgSO 4 .7H 2 0 with 74% purity. The MgS 4 .7H 2 0 recovery was 65.5%.

MgSO4.7H20 recovery was 65.5%.

-11- The filtrate bitterns from Thenardite and Epsomite production were then mixed and subjected to processing steps indicated in FIG. 4 to produce about 5kg of KC1.

The KC1 purity was 90.3% and recovery was 58%.

The bulk of KC1 thus produced was then used for production of K 2

SO

4 salt by reacting it with dissolved Mirabilite through the two-step conversion process outlined earlier and shown in IIG. 3. Accordingly, for the first conversion a mixture with an Na 2

SO

4 .10H 2 0 to KC1 to H20 weight ratio of 1 1.82 3.0 was continuously mixed for 1/2 an hour at thirty five Degrees Celsius and then dewatered to produce 15 Glasserite crystals in NaC1 base solution.

For the second conversion a mixture with a Glasserite 4 to KC1 to H20 weight ratio of 1 0.25 0.8 was continuously mixed for half an hour at fifty Degrees 20 Celsius and then cooled down to twenty five Degrees Celsius. Following dewatering and drying about 6kg of

K

2

SO

4 with 96% purity was obtained. The K 2

SO

4 Dvery was 60% and the total Potassium recovery Lor this example was more than By following the processing steps indicated in FIG.6, the filtrate bittern from production of KC1 was first diluted with fresh water to SG=1.10 and after adding a -12near equal amount (by weight) of industrial grade lime powder (85wt% CaO) the mixture was drastically stirred for about 15 minuites. The solution was then thickened by slow mixing and after separating the waste solution dominated by CaCI 2 a 5kg slurry with 40(wt)% Mg(OH) 2 was obtained. The analysis of this slurry indicated less than 5% NaC1 in solution.

Overall, in this example, 92(wt)% of the total dissolved solids where extracted as impurities, Halite, Mirabilite, Thenardite, Epsomite, Potassium Chloride and Potassium Sulphate salts and as Magnesium Hydroxide slurry. Apart from a minor quantity of CaC1 2 -rich waste 15 solution which resulted from Mg(OH) 2 slurry production the bulk of filtrates from solid-liquid separation stages are recycled within the process system either as a feed or as an additive for comprehensive utilisation of the saline wastewater.

S. EXAMPLE 2 a* a In another run similar to that of EXAMPLE 1 the same 25 feed solution was subjected to the process route for Thenardite production as shown in FIGS 1 2. However following Halite replacement and dewatering the Na 2

SO

4 crystals were redissolved in fresh water and -13recrystallised by cooling to zero Degrees Celsius. The Na 2

SO

4 recovery rate was 98% although the Na 2

SO

4 productivity remained the same as in EXAMPLE 1 (8kg/cu.m.). For production of Epsomite and KC1 salts, the procedures in EXAMPLE 1 were followed. However, for the production of K 2

SO

4 the weight ratio for Na 2

SO

4 .10H 2 0 to KC1 to H 2 0 in the first conversion was changed to 1 0.35: 0.5. The procedure for mixing, dewatering and the second conversion was the same as in EXAMPLE 1. In this case the K 2

SO

4 recovery was 78%, while the K 2

SO

4 purity remained at 96%.

It will be apparent to those familiar with saline 15 processing that the present invention offers a comprehensive and highly flexible processing scheme for recovery of the salt products from inorganic saline wastewaters. The flexibilty of the system relates to its ability to recycle both the solids and the filtrates to produce different useful and saleable combinations of available waste products according to feedstock characteristics and product market demand.

*o*2

S

Claims (12)

1. A process for reduction of the dissolved salt content and volume of saline inorganic wastewaters having at least five (molar) percent Sulphate (SO 4 content; being one or more of the following water types; Na-(Mg)-Cl-(S0 4 Na-(Mg.K)-Cl-(S0 4 Na- (Mg)-Cl-(S0 4 Na-Cl, Na-(Mg)-Cl, and having an Mg/2K (molar) ratio greater than 1.4 comprising the steps of; 15 placing the feed solution in a .e preconditioning pond to precipitate impurities and raise the specific gravity to at least 1.15; shifting the feed solution to an evaporation pond and continuing evaporation to precipitate NaCl until the solution reaches a specific gravity of between 1.23 and 1.25; **SSS* cooling the brine resulting from the 25 aforementioned steps to between Zero and minus S Five Degrees Celsius and then dewatering the solution to seperate Mirabilite crystals.

2. A process in accordance with claim 1 wherein artificial cooling is employed and the brine prior to cooling step is preconditioned according to the following steps: the brine is further evaporated until its specific gravity reaches between 1.30 and 1.32; the brine is dewatered to leave a salt slurry; the salt slurry is dissolved in water; the brine is cooled to between Zero and minus Five Degrees Celsius; the brine is dewatered to recover Mirabilite o crystals.

3. A method of producing Thenardite including the

4. processes of either claims 1 or claim 2 and the following further steps: 25 washing the Mirabilite crystals with an S" appropriate washing liquor; -16- a 9 o0.60. 20 o« dewatering the resulting solution for solid/liquor separation and; drying the solid recovered in the preceding step to produce Thenardite. 4. A method of producing Thenardite including the processes of either claims 1 or claim 2 and the following further steps: dissolving the Mirabilite by using hot steam; introducing a stoichiometric amount of Halite to the dissolved Mirabilite at a reaction temperature of between thirty eight and forty two Degrees Celsius; dewatering the reaction product for solid/ liquor separation; drying the solid obtained in the previous step to produce stable Thenardite.

5. A process in accordance with claim 3 wherein Ethanol is added to the Mirabilate crystals in order to decrease the soluability of the Na2SO4-H20 system and hence to increase Thenardite yeild. 25 -17-

6. A method of producing Potassium Sulphate including the processes of either claims 1 or claim 2 and the following further steps: dissolution of the Mirabilite by introduction of hot steam; reacting a stoichiometric amount of KC1 with the Mirabilite solution through continuous mixing for in excess of fifteen minutes at between thirty three and thirty seven Degrees Celsius; 15 dewatering the product from the previous e« step to produce Glasserite crystals in NaC1 base solution; S. reacting the Glasserite crystals with a 20 stoichiometric amount of KC1 in hot water 0. *0 through continuous mixing for in excess of twenty minutes between forty eight and fifty two Degrees Celsius; **S0 25 cooling the mixture from the previous step to between twenty and twenty five Degrees Celsius; 1 j -18- dewatering the resulting NaC1 base solution to recover K 2 SO 4 crystals; drying the K 2 SO 4 crystals to give stable Potassium Sulphate.

7. A method of producing Epsomite (MgSO 4 .7H20) using the processes of either of claims 1 or claim 2 and the following further steps: recovering the filtrate from the dewatering of the Mirabilite crystals and evaporating such bittern until a specific gravity of between 1.28 and 1.30 is reached so as to separate the Halite impurity; S. o cooling the bittern to between zero and minus five Degrees Celsius; g dewatering the bittern and recovering Epsomite crystals. 25

8. A method of producing Epsomite in accordance with claim 7 but including the following further steps: -19- redissolving the Epsomite crystals obtained in step of the preceeding claim in hot water; evaporating the resulting solution until it reaches a specific gravity of between 1.29 and 1.31; leaving the solution to gradually normalise at an ambient temperature of between twenty and twenty five Degrees Celsius; dewatering the solution to recover Epsomite crystals; e e drying the Epsomite crystals to form a stable product.

9. A method of producing Potassium Chloride comprising the following steps: performing the process steps defined in any one of claims 1, 2, 7 or 8 hereof up to at least 0.5 the first dewatering step listed in said claims and then recovering the filtrate from one or more of the steps mentioned in said claims; subjecting said filtrate or filtrates from the dewatering of the Mirabilate or Epsomite slurries to evaporation until a specific gravity of between 1.35 and 1.37 is reached; slowly cooling the resulting bittern to a temperature of between twenty and twenty five Degrees Celsius; dewatering the bittern to recover a carnallite mixture; subjecting the carnallite solution to one or 15 more flotations wherein air or Carbon Dioxide is bubbled through the solution; dewatering the flotation product to recover the Potassium Chloride crystals as a foam; drying the Potassium Chloride to produce a stable product. :25

10. A method of producing a Magnesium Hydroxide slurry (Mg(OH) 2 comprising the steps of: -21- performing the steps listed in claim 9. hereof up to and including step (f) recovering the filtrate and diluting same with fresh water until a specific gravity of between 1.05 and 1.10 is achieved; reacting the diluted solution with Lime (CaO) by rapid stirring thickening the solution by slow mixing; dewatering the product to recover the .:15 Magnesium Hydroxide slurry product.

11. A method of producing Potassium Sulphate in accordance with claim 6 wherein the Potassium Chloride introduced at steps and is manufactured in accordance with the method described in claim 9 hereof. -22-

12. A processing scheme for saline wastewater substantially as hereinbefore described with reference to the accompanying flow charts. DATED this 8th day of January, 1993. Aharon Vartan Arakel and Donatus Katauskas by their patent attorneys Barker, Blenkinship Associates