Sodium carbonate recovery from waste streams and impounded sodium carbonate decahydrate deposits
View Patent ↗A process is described for recovering sodium carbonate or other sodium-based chemicals from sodium-bearing streams, including in particular mine water, evaporative pond water and sodium carbonate decahydrate deposits, recycle and purge streams, and other waste streams. In the process sodium bicarbonate-bearing streams are decarbonized to reduce the sodium bicarbonate concentration in a combination with other sodium-bearing streams, resulting in a liquor suitable as feed to a sodium carbonate decahydrate or sodium carbonate monohydrate process. The sodium bicarbonate stream is combined in a mix tank with other sodium carbonate bearing streams where the concentration is adjusted to form a liquor suitable to feed a sodium decahydrate or sodium carbonate monohydrate evaporation/crystallization step. In the process the combination of the various sodium-bearing streams is decarbonized to below 3.5% sodium bicarbonate when fed to a sodium decahydrate process and to below 1% sodium bicarbonate when fed to a sodium carbonate monohydrate process. The feed streams are adjusted in sodium carbonate concentration by higher concentrated sodium carbonate-bearing streams or by addition of sodium carbonate decahydrate produced from said streams or recovered form evaporation pond deposits, are then processed to produce sodium carbonate decahydrate or sodium carbonate monohydrate or further processed to form other sodium carbonate salts.
1. A sodium carbonate monohydrate process for recovering refined soda ash from waste deposits that contain sodium carbonate and sodium bicarbonate, by combining at least two aqueous streams derived from streams of waste sodium carbonate deposits that contain sodium carbonate and sodium bicarbonate and that contain sodium carbonate in amounts too dilute to be effectively separately recovered by a monohydrate process, comprising:
a. proportioning and pretreating the said waste streams in a mix tank to produce a combined feed stream enriched in and containing at least 29% sodium carbonate, and reducing the sodium bicarbonate and sodium sulfate contained in said waste streams to below a concentration of 3.5% sodium bicarbonate and less than about 1.4% of sodium sulfate; and
b. introducing said proportioned and pretreated waste streams directly to a monohydrate process to produce the refined soda ash product.
2. The method of claim 1 wherein in the pretreatment the bicarbonate level of the waste streams is reduced by stream stripping.
3. The method of claim 1 wherein in the pretreatment the bicarbonate level of the waste streams is reduced by causticization.
4. The method of claim 1 wherein in the pretreatment the bicarbonate level is reduced to below about 1.0 percent.
5. The process of claim 1 wherein the source of the pretreated waste stream is selected from mine water, pond water, containment basins and impounded sodium decahydrate deposits.
6. The method of claim 1 wherein the source of the pretreated waste stream comprises impounded sodium decahydrate deposits enriched by introducing warm water.
7. A process according the claim 1 wherein at least one of the waste streams is enriched in sodium carbonate concentration by a step selected from:
a. combining streams of lesser sodium carbonate concentration with streams of higher sodium carbonate concentrations;
b. enriching streams of lesser sodium carbonate concentration with decahydrate crystals; and
c. evaporating water from the waste stream by a means selected from the third effect of a triple effect crystallizer train, cooling towers, evaporator coolers and air cooled spray evaporator/crystallizer, and a combination of the above steps.
8. The method of claim 1 wherein sodium carbonate decahydrate crystals are combined with mother liquor from the monohydrate process is introduced with the waste streams to the monohydrate process.
9. The process of claim 1 wherein a purge stream from the monohydrate process is combined with the waste stream to the monohydrate process.