阅读说明：本技术 一种天然碱生产工艺 (Natural alkali production process ) 是由 王吉刚 卢立祥 冯青天 于 2021-02-03 设计创作，主要内容包括：本发明提供了一种天然碱生产工艺,通过溶采、预处理、汽提浓缩、十水碳酸钠结晶及分离、十水碳酸钠溶解、一水碳酸钠结晶及分离、一水碳酸钠干燥等步骤得到重质纯碱；利用十水碳酸钠溶解液或浓缩卤水3,通过碳酸氢钠结晶及分离,碳酸氢钠干燥得到碳酸氢钠产品；将十水碳酸钠结晶及分离过程产生的排放液1经苛化,蒸发后回用于碳酸钠的生产；通过煅烧将苛化工段产生的苛化泥回用于苛化工段。通过该工艺可以实现资源的最大化利用。(The invention provides a natural soda production process, which comprises the steps of solution mining, pretreatment, steam stripping concentration, sodium carbonate decahydrate crystallization and separation, sodium carbonate decahydrate dissolution, sodium carbonate monohydrate crystallization and separation, sodium carbonate monohydrate drying and the like to obtain heavy soda; sodium carbonate decahydrate solution or concentrated brine 3 is utilized, sodium bicarbonate is crystallized and separated, and sodium bicarbonate is dried to obtain a sodium bicarbonate product; causticizing and evaporating the discharge liquid 1 generated in the crystallization and separation process of sodium carbonate decahydrate for reuse in the production of sodium carbonate; the causticized mud generated in the causticizing section is recycled for the causticizing section through calcination. The process can realize the maximum utilization of resources.)

1. A natural alkali production process is characterized in that: the method comprises the following steps:

1) dissolving and mining: injecting well injection water into a mine to dissolve sodium carbonate and/or sodium bicarbonate in the well injection water to obtain brine 1 containing sodium carbonate and/or sodium bicarbonate and other soluble salts;

2) pretreatment: removing solid particles and/or TOC contained in the brine 1 to obtain brine 2;

3) stripping and concentrating: most of sodium bicarbonate in the brine 2 is converted into sodium carbonate through steam stripping, and the brine is concentrated to a certain concentration to obtain concentrated brine 3;

4) crystallizing and separating sodium carbonate decahydrate: neutralizing the concentrated brine 3 with concentrated NaOH, then crystallizing in a sodium carbonate decahydrate crystallizer at low temperature, and separating crystal slurry to obtain sodium carbonate decahydrate crystals with low mother liquor residue and a discharge solution 1;

5) dissolving sodium carbonate decahydrate: mixing the obtained sodium carbonate decahydrate crystals with solutions from other steps to dissolve the crystals, and dividing the obtained solution into two parts, one part being brine 4 and the other part being brine 5;

6) crystallizing, separating and drying sodium carbonate monohydrate: evaporating and concentrating brine 4, crystallizing in a sodium carbonate monohydrate crystallizer, and separating crystal slurry to obtain sodium carbonate monohydrate crystals with low mother liquor residue and discharge liquid 2; then drying the sodium carbonate monohydrate crystals to obtain high-quality heavy sodium carbonate; mixing the effluent 2 with the concentrated brine 3, neutralizing, and then feeding into a sodium carbonate decahydrate crystallizer for sodium carbonate decahydrate crystallization and separation;

7) crystallizing, separating and drying sodium bicarbonate: brine 5 is reacted with CO in a sodium bicarbonate crystallizer₂Carrying out carbonization reaction, cooling and crystallizing, and separating crystals to obtain sodium bicarbonate crystals with low mother liquor residue and a discharge liquid 3; then drying the sodium bicarbonate crystals to obtain a sodium bicarbonate product; dischargingThe liquid 3 can be returned to the gas stripping concentration step for recycling and/or used in the solution extraction step;

8) causticizing: causticizing the discharge liquid 1 and the lime milk, clarifying and separating to obtain a dilute NaOH solution and causticized mud; washing and calcining the causticized mud to obtain quick lime for causticization;

9) and (3) evaporation: and (3) evaporating and concentrating the dilute NaOH solution, removing impurities in the dilute NaOH solution to obtain a concentrated NaOH solution, wherein the concentrated NaOH solution can be used for neutralizing residual sodium bicarbonate in the concentrated brine 3.

2. The trona production process according to claim 1, characterized in that: the condensate obtained by steam extraction concentration and/or sodium carbonate monohydrate crystallization and separation can be used for the solution mining step.

3. The trona production process according to claim 1, characterized in that: also included is the removal of TOC contained in the system in the effluent 1 and/or in the resulting dilute NaOH solution or concentrated NaOH solution.

4. A process for the production of trona according to claim 3, characterized in that: and removing TOC by adopting an activated carbon adsorption method, an ozone oxidation method or a resin adsorption method.

5. The trona production process according to claim 1, characterized in that: the total alkalinity of the concentrated brine 3 is 22-28 wt% calculated by sodium carbonate.

6. The trona production process according to claim 1, characterized in that: the solution required by the sodium carbonate decahydrate dissolving step is one or more than two of brine 2, condensate generated in the sodium carbonate monohydrate crystallization and separation step and primary steam extract generated in the steam stripping concentration step.

7. The trona production process according to claim 1, characterized in that: CO produced by the stripping concentration step₂Can be used in the crystallization and separation steps of sodium bicarbonateCarrying out carbonization reaction; the raw material required for sodium bicarbonate crystallization can also be used for concentrating brine 3 or from a mixed solution of concentrated brine 3 and brine 5.

8. The trona production process according to claim 1, characterized in that: the mass concentration of the concentrated NaOH solution generated in the evaporation step is 20-35 wt%; preferably, the concentration of concentrated NaOH is between 25 wt% and 30 wt%.

9. The trona production process according to claim 1, characterized in that: the equipment in the step of crystallizing and separating the sodium carbonate decahydrate comprises a two-stage flash evaporator and a one-stage crystallizer, and the sodium carbonate decahydrate is crystallized in the crystallizer after a mixture of the concentrated brine 3 and the discharge liquid 2 sequentially passes through the two-stage flash evaporator; and the bottom of the secondary flash evaporator and the bottom of the crystallizer are both provided with stirring mechanisms.

10. The trona production process according to claim 1, characterized in that: in the step of crystallizing and separating the sodium carbonate decahydrate, an ice machine system is utilized to provide cold energy, and meanwhile, the ice machine system is utilized to heat the sodium carbonate decahydrate dissolved solution; the condenser at the outlet of the compressor in the ice machine system is a two-stage condenser connected in series, wherein the first-stage condenser uses sodium carbonate decahydrate dissolved solution containing sodium carbonate decahydrate crystals as a cold source.

Technical Field

The invention relates to the field of natural alkali production, in particular to a natural alkali production process.

Background

The trona production mainly utilizes trona ore (Na)₂CO₃·NaHCO₃·2H₂O) or nahcolite (NaH)CO₃) After being dissolved, the sodium carbonate monohydrate is prepared by a production process.

US6589497B2 discloses a trona production process, which comprises the steps of brine stripping, evaporation, neutralization, monohydrate caustic soda crystallization, centrifugation and drying to obtain a sodium carbonate product, wherein mother liquor obtained by centrifugation is recycled by a decahydrate process, and mother liquor generated by decahydrate separation is discharged without further recycling.

US5283054 discloses a process for producing trona, in which brine is subjected to evaporation stripping to decompose most of sodium bicarbonate, then sodium bicarbonate is neutralized with caustic soda, decahydrate crystallization is carried out, and the obtained decahydrate crystal is dissolved and used for producing soda monohydrate to obtain heavy soda. The decahydrate capacity required by the process is large, and a large amount of mother liquor generated by decahydrate separation is at least partially discharged to prevent impurities from accumulating in the system and is not completely recycled.

US 7507388B 2 and CN 1772615a disclose a trona production process, which produces heavy sodium carbonate product by brine purification and preheating, evaporation & stripping, monohydrate soda crystallization, centrifugation and drying processes, wherein part of monohydrate soda centrifugal mother liquor is recycled by decahydrate process, and the other part is causticized and filtered to obtain caustic soda solution for decahydrate production. Mother liquor generated by the separation of the decahydrate is discharged outside and is not utilized further. In addition, the caustic soda solution obtained by causticization and filtration has a low concentration, generally about 10%.

US9593023B2 discloses a process for the production of sodium carbonate/sodium bicarbonate by pre-treatment of brine, wet decomposition, evaporation, neutralization to obtain concentrated brine, crystallization in a monohydrate soda crystallizer/sodium bicarbonate crystallizer, separation to obtain sodium carbonate/sodium bicarbonate crystals, causticization and concentration of the separated effluent to obtain a NaOH solution with a concentration of more than 25 wt%, which is recycled to the crystallization or upstream of the crystallization. Wherein the causticizing and concentrating process for preparing NaOH solution with concentration of more than 25 wt% can be used for treating effluent generated in the crystallization process of anhydrous alkali/monohydrate alkali/decahydrate/sesquisoda/sodalite, and if the process is used for treating the effluent of the decahydrate crystallizer, the process limits the effluent of the raw material of the decahydrate crystallizer from the monohydrate alkali crystallizer.

US7255841B2 describes a sodium bicarbonate production process, which utilizes the effluent produced in the caustic soda monohydrate step to crystallize decahydrate, and utilizes the obtained decahydrate to produce sodium bicarbonate, wherein the total amount of the effluent produced in the caustic soda decahydrate and sodium bicarbonate steps is less than the amount of the caustic soda monohydrate effluent, thereby effectively reducing the amount of effluent discharged from the system.

US9051627 discloses a process for the production of sodium bicarbonate by means of an ammonium carbonate solution containing at least 2% by weight of sodium chloride or sodium sulphate impurities, the solution being derived in part from an anhydrous soda/monohydrate/heptahydrate/decahydrate/sesquisoda/sodalite crystallizer and also from the effluent of the monohydrate crystallizer. This process limits the amount of sodium chloride or sodium sulfate impurities in the feedstock.

Disclosure of Invention

In view of the above, the present invention aims to provide a process for producing trona, which comprises the steps of solution mining, pretreatment, steam stripping concentration, crystallization and separation of sodium carbonate decahydrate, dissolution of sodium carbonate decahydrate, crystallization and separation of sodium carbonate monohydrate, drying of sodium carbonate monohydrate, etc. to obtain heavy sodium carbonate; sodium carbonate decahydrate solution (brine 5) or concentrated brine 3 is used, sodium bicarbonate is crystallized and separated, and sodium bicarbonate is dried to obtain a sodium bicarbonate product; causticizing and evaporating the discharge liquid 1 generated in the crystallization and separation process of sodium carbonate decahydrate for reuse in the production of sodium carbonate; the causticized mud generated in the causticizing section is recycled for the causticizing section through calcination. The process can realize the maximum utilization of resources.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a process for producing trona comprises the following steps:

1) dissolving and mining: injecting well water into mine (trona ore (Na)₂CO₃·NaHCO₃·2H₂O) or nahcolite ore (NaHCO)₃) Or a bicarbonate ore) to obtain a brine 1 containing sodium carbonate and/or sodium bicarbonate and other soluble salts; (alternatively, brine 1 may be from a salt lake or other subterranean brine, etc., which brine may contain sodium sulfate and/or chlorideSoluble impurities such as sodium, insoluble suspended matter and TOC)

2) Pretreatment: removing solid particles and/or TOC contained in the brine 1 to obtain brine 2;

3) stripping and concentrating: most of sodium bicarbonate in the brine 2 is converted into sodium carbonate through steam stripping, and the brine is concentrated to a certain concentration to obtain concentrated brine 3; (sodium bicarbonate remaining in concentrated brine 3 was neutralized by caustic soda.)

4) Crystallizing and separating sodium carbonate decahydrate: neutralizing the concentrated brine 3 with concentrated NaOH, then crystallizing in a sodium carbonate decahydrate crystallizer at low temperature, and separating crystal slurry to obtain sodium carbonate decahydrate crystals with low mother liquor residue and a discharge solution 1;

5) dissolving sodium carbonate decahydrate: mixing the obtained sodium carbonate decahydrate crystals with solutions from other steps to dissolve the crystals, and dividing the obtained solution into two parts, one part being brine 4 and the other part being brine 5;

6) crystallizing, separating and drying sodium carbonate monohydrate: evaporating and concentrating brine 4, crystallizing in a sodium carbonate monohydrate crystallizer, and separating crystal slurry to obtain sodium carbonate monohydrate crystals with low mother liquor residue and discharge liquid 2; then drying the sodium carbonate monohydrate crystals to obtain high-quality heavy sodium carbonate; mixing the effluent 2 with the concentrated brine 3, neutralizing, and then putting into a sodium carbonate decahydrate crystallizer for sodium carbonate decahydrate crystallization and separation;

7) crystallizing, separating and drying sodium bicarbonate: brine 5 is reacted with CO in a sodium bicarbonate crystallizer₂Carrying out carbonization reaction, cooling and crystallizing, and separating crystals to obtain sodium bicarbonate crystals with low mother liquor residue and a discharge liquid 3; then drying the sodium bicarbonate crystals to obtain a sodium bicarbonate product; the discharged liquid 3 can be returned to the gas stripping concentration step for recycling and/or used in the solution extraction step;

8) causticizing: causticizing the discharge liquid 1 and the lime milk, clarifying and separating to obtain a dilute NaOH solution and causticized mud; washing and calcining the causticized mud to obtain quick lime for causticization;

9) and (3) evaporation: and (3) evaporating and concentrating the obtained dilute NaOH solution, crystallizing part of sodium chloride and/or sodium sulfate impurities in the dilute NaOH solution due to the increase of the concentration, and removing the impurities to obtain a concentrated NaOH solution, wherein the concentrated NaOH solution can be used for neutralizing residual sodium bicarbonate in the concentrated brine 3.

Further, the condensate obtained by steam concentration and/or sodium carbonate monohydrate crystallization and separation can be used for the solution extraction step.

Further, the method also comprises the step of removing TOC contained in the system in the effluent 1 and/or removing TOC contained in the system in the obtained dilute NaOH solution or concentrated NaOH solution.

Further, TOC is removed by an activated carbon adsorption method, an ozone oxidation method or a resin adsorption method.

Preferably, activated carbon adsorption is used.

Further, the total alkalinity of the concentrated brine 3 is 22 wt% -28 wt% calculated by sodium carbonate.

Further, the solution required by the sodium carbonate decahydrate dissolving step can be one or more than two of brine 2, condensate generated in the steam-water sodium carbonate crystallization and separation step and primary steam extract in the steam stripping and concentration step.

Further, the stripping concentration step produces CO₂Can be used for the carbonation reaction in the steps of sodium bicarbonate crystallization and separation; the raw material required for sodium bicarbonate crystallization can also come from concentrated brine 3 or from a mixed solution of concentrated brine 3 and brine 5.

Further, the mass concentration of the concentrated NaOH solution generated in the evaporation step is 20-35 wt%; preferably, the concentration of concentrated NaOH is between 25 wt% and 30 wt%.

Further, the equipment in the step of crystallizing and separating the sodium carbonate decahydrate comprises a two-stage flash evaporator and a one-stage crystallizer, and the mixture of the concentrated brine 3 and the discharge liquid 2 is crystallized in the crystallizer after sequentially passing through the two-stage flash evaporator to obtain the sodium carbonate decahydrate; and the bottom of the secondary flash evaporator and the bottom of the crystallizer are both provided with stirring mechanisms.

Further, an ice machine system is used for providing cold energy in the crystallization and separation steps of the sodium carbonate decahydrate, and the ice machine system is used for heating the dissolved solution of the sodium carbonate decahydrate; the condenser at the outlet of the compressor in the ice machine system is a two-stage condenser connected in series, wherein the first-stage condenser uses sodium carbonate decahydrate dissolved solution containing sodium carbonate decahydrate crystals as a cold source.

Furthermore, the pretreatment adopts a sand filter to remove insoluble substances contained in the brine 1.

Further, the stripping concentration may comprise multiple stages, preferably, two-stage stripping and two-stage concentration.

Specifically, the stripping concentration has 2 stripping towers, and the liquid from the first stripping tower is a first-level stripping liquid.

Further, the crystallization temperature of the sodium carbonate decahydrate is 15-30 ℃; the temperature of the sodium carbonate monohydrate crystallization is 35-109 ℃.

Further, the evaporation step adopts a process of triple effect evaporation or MVR, at least part of soluble salt impurities contained in the system is discharged from the evaporation step crystallization, and the soluble salt impurities contained in the system are sodium chloride and/or sodium sulfate.

Further, a centrifuge is adopted for separating sodium carbonate decahydrate crystals.

Further, a centrifuge is adopted for separating the sodium carbonate monohydrate crystals.

Further, the ash milk required by causticization is generated by the reaction of CaO and ash dissolving water in an ash dissolving machine, wherein the ash dissolving water is one or a mixture of brine 1, brine 2 and condensate in any proportion.

Further, the causticized mud needs to be washed before being calcined so as to control the content of Na ions in the feed of the calciner; furthermore, the washing equipment adopts a vacuum belt filter; further, the Na ion content in the feed to the calciner is controlled to be less than or equal to 0.5 wt%.

Further, the causticized mud is calcined by a rotary kiln.

Compared with the prior art, the natural alkali production process has the following advantages: (1) the natural alkali production process organically combines a sodium carbonate decahydrate production process, a sodium carbonate monohydrate production process and a causticization method caustic soda process, is used for treating trona ore or nahcolite ore with high impurity content such as sodium chloride/sodium sulfate, and can effectively reduce the content of sodium chloride/sodium sulfate impurities in a sodium carbonate product by firstly producing sodium carbonate decahydrate and then producing sodium carbonate monohydrate by using a sodium carbonate decahydrate product. Meanwhile, the discharged liquid generated in the production process of the sodium carbonate decahydrate is subjected to causticization treatment to obtain caustic soda which is reused in the production process of the sodium carbonate decahydrate, so that the emission reduction is realized, and simultaneously, the resources in the discharged liquid are recycled. And the problem of outsourcing of caustic soda required in the production of trona in remote areas can be solved.

(2) The natural alkali production process adopts a two-stage series flash evaporation and crystallization process in the sodium carbonate decahydrate crystallization and separation steps, the flash evaporation and crystallization operation pressure is reduced in a gradient manner, the flash evaporation amount of each stage is controlled, crystallization is facilitated, and crystal formation in the crystallization process can be better controlled through the gradient flash evaporation. In addition, the secondary flash evaporator and the crystallizer creatively adopt a bottom stirring mode, so that the liquid levels in the secondary flash evaporator and the crystallizer are updated faster, the removal of water is accelerated, and the enlargement of the crystal particle size is facilitated.

(3) According to the trona production process, the two-stage series condensation process is adopted in the ice machine system used in the sodium carbonate decahydrate crystallization and separation steps, wherein the first-stage condenser utilizes the sodium carbonate decahydrate dissolved solution with sodium carbonate decahydrate crystals as a cold source, so that the consumption of circulating water is reduced, meanwhile, the condenser provides heat for dissolving the sodium carbonate decahydrate crystals, and the energy consumption of the system is effectively reduced through thermal coupling.

(4) Compared with the prior art which adopts concentrated brine to produce the sodium bicarbonate, the sodium carbonate decahydrate solution, in particular the sodium carbonate decahydrate solution dissolved by the condensate, has lower impurity content such as sodium chloride/sodium sulfate and the like, so that the final product sodium bicarbonate has lower impurity content and better quality.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

fig. 1 is a flow chart of a trona production process according to an embodiment of the invention.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

The following examples 1-2 are all mining for the same region of alkali mine.

Example (1):

as shown in fig. 1, a process for producing trona comprises the following steps:

(1) pumping 65-75 deg.C well injection liquid (sodium carbonate concentration about 2 wt%) into trona ore (Na)₂CO₃·NaHCO₃·2H₂O) to obtain brine 1, the main component of which is Na₂CO₃:12.78wt％,NaHCO₃:7.5wt％,NaCl：1.5wt％，Na₂SO₄：0.11wt％,TSS:50ppm。2284t/h。

(2) Pretreatment: the TSS (total suspended solids) was reduced to 10 ppm.

(3) Stripping and concentrating: concentrating the brine 2 by two-stage steam stripping to obtain concentrated brine 3 containing Na as main component₂CO₃:21～24wt％,NaHCO₃:1.5～3wt％,NaCl：2.02wt％，Na₂SO₄：0.15wt％。

(4) Crystallizing and separating sodium carbonate decahydrate: neutralizing concentrated brine 3 with concentrated NaOH solution, crystallizing with sodium carbonate decahydrate, and separating to obtain 1078t/h sodium carbonate decahydrate crystal, and simultaneously generating 330t/h effluent 1, wherein the effluent 1 mainly comprises Na₂CO₃:11～15wt％,NaHCO₃:0～1wt％,NaCl：8.5～13wt％，Na₂SO₄：0.8～1.4wt％。

The equipment in the sodium carbonate decahydrate crystallization and separation step comprises a two-stage flash evaporator and a one-stage crystallizer, and the sodium carbonate decahydrate is crystallized in the crystallizer after a mixture of concentrated brine 3 and discharge liquid 2 sequentially passes through the two-stage flash evaporator; and the bottom of the secondary flash evaporator and the bottom of the crystallizer are both provided with stirring mechanisms.

The flash evaporation and crystallization operation pressure is reduced in a cascade manner, the flash evaporation amount of each stage is controlled, crystallization is facilitated, and crystal formation in the crystallization process can be better controlled through the flash evaporation of the feeding cascade. In addition, the secondary flash evaporator and the crystallizer creatively adopt a bottom stirring mode, so that the liquid levels in the secondary flash evaporator and the crystallizer are updated faster, the removal of water is accelerated, and the enlargement of the crystal particle size is facilitated.

In the step of crystallizing and separating the sodium carbonate decahydrate, an ice machine system is utilized to provide cold energy, and meanwhile, the ice machine system is utilized to heat the sodium carbonate decahydrate dissolved solution; the condenser at the outlet of the compressor in the ice machine system is a two-stage condenser connected in series, wherein the first-stage condenser uses sodium carbonate decahydrate dissolved solution containing sodium carbonate decahydrate crystals as a cold source.

The process of two-stage series condensation is adopted, wherein the first-stage condenser utilizes sodium carbonate decahydrate dissolving liquid with sodium carbonate decahydrate crystals as a cold source, the consumption of circulating water is reduced, meanwhile, the condenser provides heat for dissolving the sodium carbonate decahydrate crystals, and the energy consumption of the system is effectively reduced through thermal coupling.

(5) Dissolving sodium carbonate decahydrate: and (3) dissolving sodium carbonate decahydrate by using the primary steam extract from the steam stripping concentration step to obtain sodium carbonate decahydrate solution with total alkalinity (calculated by sodium carbonate) of 27-30 wt% at 1660t/h, wherein about 1570t/h is used as brine 4 for producing sodium carbonate monohydrate, and the rest is used as brine 5 for producing sodium bicarbonate.

(6) Crystallizing, separating and drying sodium carbonate monohydrate: the brine 4 is crystallized and separated in the step of sodium carbonate monohydrate to obtain 375t/h sodium carbonate monohydrate crystals, and meanwhile 476t/h effluent 2 is generated, wherein the effluent 2 mainly comprises Na₂CO₃:26～30wt％,NaHCO₃1 to 2 wt%, NaCl: 2-3 wt%, and the crystallization temperature is 104 ℃. Drying the sodium carbonate monohydrate crystals to obtain a 316t/h sodium carbonate product, wherein the content of sodium carbonate is 99.79 percent, and the content of sodium chloride is lower than 1000 ppm.

In addition, the obtained mixture of the effluent 2 and the concentrated brine 3 enters a sodium carbonate decahydrate crystallization and separation process after neutralization.

(7) Crystallizing sodium bicarbonate, separating and drying: brine 5 is put in a sodium bicarbonate crystallizerWith CO from stripping concentration₂And after the gas is subjected to carbonization reaction, cooling and crystallizing at the crystallization temperature of 70-80 ℃. After the obtained sodium bicarbonate crystals are separated and dried, a sodium bicarbonate product with the purity of 99.75 wt% and the sodium chloride content of about 400ppm is obtained at 25.3 t/h. The obtained discharge liquid 3 is mixed with brine 2 at about 66t/h and then enters a steam stripping concentration step.

Compared with the prior art in which concentrated brine is adopted to carry out the production process of sodium bicarbonate, the sodium carbonate decahydrate solution has lower impurity content such as sodium chloride/sodium sulfate and the like, so that the final product sodium bicarbonate has lower impurity content and better quality.

(8) Causticizing: and causticizing the discharged liquor 1 to obtain a dilute NaOH solution with the concentration of 7-9 wt%, wherein the concentration is about 296 t/h. The causticized mud generated in the causticizing procedure is about 54t/h, wherein the calcium carbonate is contained in the causticized mud, and 13t/h of active calcium oxide is obtained after calcination. The amount of the externally-supplemented calcium oxide is 6.6 t/h.

The causticized mud needs to be washed before being calcined so as to control the content of Na ions in the feed of the calciner; the washing equipment adopts a vacuum belt filter, and the Na ion content in the feeding material of the calcining furnace is controlled to be less than or equal to 0.5 wt%. The causticized mud is calcined by a rotary kiln.

(9) And (3) evaporation: after triple effect evaporation is carried out on the dilute NaOH solution, a concentrated NaOH solution with the concentration of 30 wt% is obtained, wherein the concentration is about 76t/h, the TOC content is 0.6-0.9 wt%, and meanwhile, about 43t/h of impurities are discharged, and the main components are sodium chloride and limestone. The concentrated NaOH solution passed through the TOC removal unit to reduce the TOC content to less than 0.35 wt% for neutralization of concentrated brine 3.

The total sodium of the production process from the trona ore is about 174t/h, the produced sodium carbonate is 316.8t/h, the sodium bicarbonate is 25.3t/h, about 45t/h sodium carbonate returns to the trona ore along with the water injected into the well for solution mining, and the rest sodium is lost in the production process. The sodium utilization efficiency was about 94.2%.

Example (2):

as shown in fig. 1, a process for producing trona comprises the following steps:

(1) pumping 65-75 deg.C well injection liquid (sodium carbonate concentration about 2 wt%) into trona ore (Na)₂CO₃·NaHCO₃·2H₂O) to obtain brine 1, the main component of which is Na₂CO₃:12.78wt％,NaHCO₃:7.5wt％,NaCl：1.2wt％，Na₂SO₄：0.11wt％,TSS:50ppm。2206t/h。

(3) Pretreatment: the TSS (total suspended solids) was reduced to 10 ppm.

(3) Stripping and concentrating: concentrating the brine 2 by two-stage steam stripping to obtain concentrated brine 3 containing Na as main component₂CO₃:21～24wt％,NaHCO₃:1.5～3wt％,NaCl：1.7wt％，Na₂SO₄：0.16wt％。

(4) Crystallizing and separating sodium carbonate decahydrate: neutralizing concentrated brine 3 with concentrated NaOH solution, crystallizing and separating sodium carbonate decahydrate to obtain 1000t/h sodium carbonate decahydrate crystal, and simultaneously generating 258t/h effluent 1, wherein the effluent 1 mainly comprises Na₂CO₃:11～15wt％,NaHCO₃:0～1wt％,NaCl：8.5～13wt％，Na₂SO₄：0.8～1.4wt％。

(5) Dissolving sodium carbonate decahydrate: and (3) dissolving sodium carbonate decahydrate by using the primary steam extract from the steam stripping concentration step to obtain a sodium carbonate decahydrate solution with the total alkalinity (calculated by sodium carbonate) of 27-30 wt% of about 1500t/h, wherein about 1410t/h is used as brine 4 for producing sodium carbonate monohydrate, and the rest is used as brine 5 for producing sodium bicarbonate.

(6) Crystallizing, separating and drying sodium carbonate monohydrate: the brine 4 is crystallized and separated in the step of sodium carbonate monohydrate to obtain 375t/h of sodium carbonate monohydrate crystals, and simultaneously, 336t/h of effluent 2 is generated, wherein the effluent 2 mainly comprises Na₂CO₃:26～30wt％,NaHCO₃1 to 2 wt%, NaCl: 2-3.5 wt%, and the crystallization temperature is 104 ℃. Drying the sodium carbonate monohydrate crystals to obtain a 316t/h sodium carbonate product, wherein the content of sodium carbonate is 99.79 percent, and the content of sodium chloride is lower than 1000 ppm.

In addition, the obtained mixture of the effluent 2 and the concentrated brine 3 enters a sodium carbonate decahydrate crystallization and separation process after neutralization.

(7) Crystallizing sodium bicarbonate, separating and drying: brine 5 is combined with CO from stripping concentration in sodium bicarbonate crystallizer₂And after the gas is subjected to carbonization reaction, cooling and crystallizing at the crystallization temperature of 70-80 ℃. After the obtained sodium bicarbonate crystals are separated and dried, a sodium bicarbonate product with the purity of 99.75 wt% and the sodium chloride content of about 400ppm is obtained at 25.3 t/h. The obtained discharge liquid 3 is mixed with brine 2 at about 66t/h and then enters a steam stripping concentration step.

(8) Causticizing: the effluent 1 can be mixed with 32t/h brine 1, and then causticized to obtain a dilute NaOH solution with the concentration of 8-11 wt%, wherein the concentration is about 245 t/h. The causticized mud generated in the causticizing procedure is about 58t/h, wherein 33.68t/h calcium carbonate is contained, and 18.9t/h active calcium oxide is obtained after the calcium carbonate is mixed with the externally supplemented 12.6t/h calcium carbonate and then calcined.

The causticized mud needs to be washed before being calcined so as to control the content of Na ions in the feed of the calciner; the washing equipment adopts a vacuum belt filter, and the Na ion content in the feeding material of the calcining furnace is controlled to be less than or equal to 0.5 wt%. The causticized mud is calcined by a rotary kiln.

(9) And (3) evaporation: after triple effect evaporation is carried out on the dilute NaOH solution, a concentrated NaOH solution with the concentration of 30 wt% is obtained, wherein the concentration is about 78t/h, the TOC content is 0.6-0.9 wt%, and meanwhile, about 43t/h of impurities are discharged, and the main components are sodium chloride and limestone. The concentrated NaOH solution passed through the TOC removal unit to reduce the TOC content to less than 0.35 wt% for neutralization of concentrated brine 3.

The total sodium of the production process from the trona ore is about 170t/h, the produced sodium carbonate is 316.8t/h, the sodium bicarbonate is 25.3t/h, about 45t/h sodium carbonate returns to the trona ore along with the water injected into the well for solution mining, and the rest sodium is lost in the production process. The sodium utilization efficiency was about 96.5%.

Comparative example:

by contrast with the production process disclosed in US5283054, the waste liquid produced by the separation of decahydrate crystals is discharged or partially discharged.

The same sodium carbonate and sodium bicarbonate products were produced based on the brine composition of step (1) of example (1) above, resulting in about 330t/h of waste liquor containing about 43t/h of sodium carbonate and 2.3t/h of sodium bicarbonate. Meanwhile, about 23t/h of caustic soda (one hundred percent of NaOH content) needs to be consumed in the production process, and about 31t/h of sodium carbonate needs to be additionally consumed for preparing the caustic soda. The sodium utilization efficiency was about 87.8%.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.