US 4,569,676 A · Separation and purification of salts in a non-convective solar pond

Abstract

Brine containing at least two salts, one or more of the salts having a higher hydrated form and a lower hydrated or anhydrous form, is fed to a non-convective solar pond and one of the salts having a higher hydrated form and a lower hydrated or anhydrous form is crystallized in a higher hydrated form, dehydrated to a lower hydrated form, and recovered from the bottom of the pond in solid, pure form essentially free from the other salts in the brine. To effect separation, the salt having a higher hydrated form and a lower hydrated or anhydrous form, which is to be recovered in pure form must be present in the pond in an essentially saturated concentration. The concentrations of any of the other salts must generally not exceed saturation concentration at the temperature in the top layer of the pond, and must not exceed saturation concentration at the conditions in the bottom layer of the pond. Concentrations of other salts in the pond must be controlled such that the required density gradient is maintained.

Claims21

Dependent claims

A method for the treatment in a non-convective solar pond having an upper portion and a lower portion and including an upper convective zone and a lower convective zone of a mixed brine containing a desired salt having a higher hydrated form and a lower hydrated or anhydrous form and containing at least one other salt, said method comprising the steps of:

(a) adding said mixed brine to the upper portion of said non-convective solar pond;
(b) establishing a concentration gradient in said pond for the desired salt which increases with the depth in said pond;
(c) establishing a concentration gradient in said pond for said at least one other salt which decreases with depth in said pond;
(d) maintaining a temperature in said lower convective zone which is at least equal to the transition temperature between a higher hydrated form and a lower hydrated form or the anhydrous form of the desired salt;
(e) crystallizing the desired salt in a higher hydrated form in said upper portion by evaporation and/or cooling so that the concentration exceeds the saturation concentration;
(f) dehydrating the desired salt crystallized in the higher hydrated form to a lower hydrated or the anhydrous form in said lower convective zone;
(g) separating and purifying the desired salt in the lower hydrated or the anhydrous form in said lower convective zone;
(h) and recovering the desired salt in the lower hydrated or the anhydrous form substantially free from said at least one other salt from said lower convective zone.

5 more elements

(a) adding said mixed brine to the upper portion of said non-convective solar pond;
(b) establishing a concentration gradient in said pond for the desired salt which increases with the depth in said pond;
(c) establishing a concentration gradient in said pond for said at least one other salt which decreases with depth in said pond;
(d) maintaining the concentration of said at least one other salt in the lower convective zone below the saturation concentration of said at least one other salt in the solution in the lower convective zone;
(e) maintaining a temperature in said lower convective zone which is at least equal to the transition temperature between a higher hydrated form and a lower hydrated form or the anhydrous form of the desired salt;
(f) maintaining the temperatures in said pond at values in the range of about 0.degree. to 100.degree. C.;
(g) crystallizing at least a portion of the desired salt in a higher hydrated form in the upper portion by evaporation and/or cooling so that the concentration exceeds the saturation concentration;
(h) dehydrating at least a portion of the desired salt crystallized in the higher hydrated form to a lower hydrated or the anhydrous form in the lower convective zone;
(i) maintaining the pond non-convective by controlling the density gradient;
(j) separating and purifying the desired salt in the lower hydrated or the anhydrous form in the lower convective zone;
(k) withdrawing solution from said upper convective zone;
and
(l) recovering the desired salt in the lower hydrated or the anhydrous form substantially free from said at least one other salt from said lower convective zone.

10 more elements

A method for the continuous treatment of a mixed brine in a non-convective solar pond having an upper portion and a lower portion and including an upper convective zone and a lower convective zone, said mixed brine comprising a desired salt having a higher hydrated form and a lower hydrated form or anhydrous form and transition temperatures therebetween, and a plurality of other salts, said other salts comprising one or more salts not having a higher and a lower hydrated or anhydrous form and one or more salts having a higher and a lower hydrated or anhydrous form, which method comprises the steps of:

(a) adding said mixed brine to the upper portion of said pond;
(b) maintaining the concentration of the desired salt in the upper convective zone below saturation concentration;
(c) increasing the concentration of the desired salt in the upper portion by evaporation and/or cooling so that the concentration exceeds the saturation concentration, whereby desired salt crystallizes in a higher hydrated form;
(d) maintaining the concentration of said other salts at a value not exceeding saturation concentration in the lower convective zone;
(e) dehydrating desired salt crystallized in its higher hydrated form in the lower convective zone and forming solution including water liberated by said dehydrating in the lower convective zone;
(f) dissolving in said solution formed in the lower convective zone any of said other salts not having a higher and a lower hydrated or anhydrous form that may have crystallized;
(g) recovering desired salt in the lower hydrated or anhydrous form from the bottom portion of the pond, the recovered desired salt being purified and substantially free of said other salts;
(h) withdrawing solution from the upper convective zone;
and
(i) maintaining the pond non-convective by controlling the density gradient.

7 more elements

Dependencies are inferred from the claim text.

Separation and purification of salts in a non-convective solar pond

Life of this patent

Separation and purification of salts in a non-convective solar pond

Life of this patent

Abstract

Claims21