Production of low sodium salt with balanced mineral content
A process is provided for preparing a salt product with reduced sodium content including the step of providing a concentrated brine, which is typically seawater, to which has been added potassium chloride. The mixture is transferred to a crystallizer unit where at least a portion of the mix is transferred to the crystallizer through a washing column. Liquid is evaporated from the crystallizer such that crystals form, crystals are passed from the crystallizer through said washing column to a separating unit such that in the passing through the washing column the crystals are rinsed with the brine portion being transferred as a counter current through the column. The inventive process is characterized by recycling of the brine from which the salt crystallizes, thus all main ingredients of the mixed input brine reach a steady equilibrium concentration in the mother liquor in the crystallizer. These will then precipitate as crystals, as more of the respective substances gets added to the mother liquor through inflow of mixed input brine. None of the liquor is purged out of the system as in conventional salt crystallizers. All the components in the feed are substantially contained in the product from the crystallizer either as crystalline material or soluble ingredients.
1. A process for preparing a salt product derived from sea water, comprising trace minerals from sea water, comprising the steps of
(a) providing a concentrated brine from sea water,
(b) transferring the concentrated brine to a crystalliser unit,
(c) building up and maintaining a mother liquor substantially saturated in main salt constituents, including sodium chloride, magnesium chloride, magnesium sulphate, potassium chloride and potassium sulphate,
(d) evaporating liquid from said crystalliser such that crystals of different salts form into particles with substantially homogeneous composition including double salts,
(e) transferring crystals from said crystalliser through a wash unit such that said crystals are rinsed off mother liquor on the crystal surfaces that leaves the crystalliser with the crystals, said rinsing performed with a rinsing liquid which is transferred after the rinsing to the crystalliser,
(f) collecting said rinsed crystals and transferring them to separating unit where excess liquid is removed from the crystals, and optionally drying the crystals, and
(g) feeding back separated excess liquid to the crystalliser, thereby obtaining a salt product comprising trace minerals.
2. The process of claim 1 , wherein said concentrated brine from seawater is prepared by a process including a evaporation step to precipitate calcium sulphate, which is separated from the brine.
3. The process of claim 1 further comprising mixing potassium chloride with said concentrated brine from sea water prior to the transferring to said crystalliser.
4. The process of claim 1 , wherein at least a portion of said concentrated brine is used as said rinsing liquid by transferring at least a portion of said concentrated brine to the crystalliser through said wash unit.
5. The process of claim 1 , wherein said rinsing liquid is water or a salt solution, such as a sodium chloride solution.
6. The process of claim 4 , wherein said wash unit is a washing column.
7. The process of claim 1 , wherein the content of trace minerals in the salt product substantially reflects the concentration of said trace minerals in sea water.
8. The process of claim 1 , wherein in the range of about 1 to 100% vol/vol of said concentrated brine is transferred through said wash unit to the crystalliser.
9. The process of claim 1 , wherein said separating unit is a centrifuge.
10. The process of claim 1 , wherein said concentrated brine comprises in the range of about 5-30 wt % salt concentration and preferably in the range of 15-30 wt % and more preferably in the range of 25-30 wt %.
11. The process of claim 1 , wherein potassium chloride is mixed with said brine to obtain a mixed brine with a wt:wt ratio of K to Na in the range of about 1:27 to about 5:1.
12. The process of claim 11 , wherein said salt product comprises in the range of 2-70 wt % KCl, and in the range of 20-68 wt % NaCl.
13. The process of claim 1 , wherein after an initial phase where saturation steady state is reached in the crystalliser mother liquor, the mother liquor level is kept substantially constant by regulating inflow to the crystalliser and temperature in the crystalliser is kept substantially constant.
14. The process of claim 1 , wherein brine is not purged during operation, but rather material only leaves the system as the salt product or soluble trace minerals obtained from the separation unit, and as vapors from the crystalliser.
15. The process of claim 3 where potassium chloride is extracted from geothermal brine.
16. The process of claim 1 , wherein said crystalliser comprises two units, an evaporating unit and a crystallising unit, and wherein in step d), liquid evaporates from said evaporating unit and crystals form in said crystallising unit.
17. The process of claim 16 , wherein said crystallising unit is kept at a lower temperature than said evaporating unit.