Industrial brine (brine; bittern; brine water), commonly known as brine, bitter brine, halo-alkali, is an aqueous solution of chloride, sulfate, soluble carbonate and other salts, made from seawater or salt lake water After making table salt (NaCl) through chemical reactions and physical methods, the mother liquor remaining in the salt pond mainly consists of magnesium chloride (MgCl2), calcium sulfate (CaSO4), calcium chloride (CaCl2), sodium chloride (NaCl), etc. Salt substances are bitter and poisonous. After evaporation and cooling, the solute crystals precipitate, which are called halogen blocks.
1. The significance of industrial brine treatment
In order to remove harmful impurities in brine, improve production intensity, extend production time, and carry out comprehensive utilization, purifying brine is extremely important in salt production. One ring. Its main advantage is improved product quality. Since almost all brine contains impurities, some impurities can seriously contaminate the product and even poison the human body. For example, barium yellow brine produced in Sichuan and Hubei contains barium chloride as high as 2 to 4 grams per liter. When the salt is precipitated during the evaporation process, the barium chloride is attached to the salt particles along with the mother liquor. After drying, the barium chloride is precipitated and mixed with the salt to become barium salt. Barium chloride is a toxic substance that can cause poisoning and even death after being eaten by humans.
II. Overview of industrial brine treatment methods
1. Gas blowing method
In natural brine, especially black brine, often contain hydrogen sulfide (H.s). ), it is a colorless and foul-smelling gas with a specific gravity of 1.1906. Hydrogen sulfide is soluble in water, ethanol and glycerin, and generates hydrogen sulfate when dissolved in water. During the salt production process, hydrogen sulfide will react with iron to form iron sulfide, which will pollute the product and corrode equipment. Therefore, hydrogen sulfide must be removed from the brine.
The gas blowing method is used abroad. In the Hengelo Salt Field in the Netherlands, the brine flows through a trough that is 20 feet wide (1 foot = 0.3084 meters), 150 feet long, and 4 feet deep. The brine is blown from bottom to top into the brine between the baffles in the tank, forming small dispersed bubbles to bring out the hydrogen sulfide in the brine. This method can remove most of the hydrogen sulfide, and the remaining small amount of hydrogen sulfide can be added with chlorine after the brine flows out of the aeration tank to oxidize the hydrogen sulfide into free sulfur and settle in the settling tank.
Tower furnace degassing method can also remove hydrogen sulfide. The brine is sprayed down from the top of the tower and comes into counter-current contact with the rising flue gas. The temperature of the brine gradually rises. The solubility of hydrogen sulfide in the brine decreases with the increase of temperature. The escaping hydrogen sulfide is discharged with the smoke, so After several cycles, the hydrogen sulfide can be removed.
In addition to the blowing method, the method of removing hydrogen sulfide can also add green vitriol (FeS04"7H:0) to the black brine containing hydrogen sulfide to generate ferrous sulfide precipitation.
H2S+FeS04?7H20—+FeSI+H2S04+7H20 to remove hydrogen sulfide in brine
2. Scaffold method
Set the stent to concentrate. Brine has a long history in my country. Zigong, Wutongqiao and Penglai in Sichuan all use racks to concentrate brine and remove hydrogen sulfide and calcium sulfate dihydrate. Therefore, in addition to concentrating brine, the rack method is also a method of purifying brine. The support frame method is particularly economical in places with plenty of sunlight and frequent winds. The orientation of the support frame is generally facing east and west to facilitate sunlight. The support frame is made of wood and bamboo, with a height of 7 to 9 meters and a length of 1 to 15 meters. meters, both sides of the frame are paved with thin bamboo branches (or thin willow branches), and a salt water pipe with a diameter of 125 to 150 mm is installed on the top of the frame. There are several 5 mm holes on both sides, and the light salt water is dispersed along the bamboo branches from both sides. Flows to the cement bottom and then flows back to the brine storage tank. From there, the brine is pumped to the top brine pipe for circulation, thereby evaporating water, removing part of the hydrogen sulfide, and oxidizing low-priced iron to high-priced iron, so that after adding lime water, It is easy to generate iron hydroxide and precipitate. When the brine is concentrated to 14-15. B6, CaS0. 2H. 0 will crystallize and form scale on the branches.
3. ) ~ Glauber's Salt Method
This method is widely used in the treatment of barium yellow brine. Lime (or caustic soda) is added to remove iron and magnesium, and Glauber's Salt is added to remove barium. After the reaction, it is extremely difficult to dissolve in water. Precipitated Mg(OH) (solubility product is 1.2×1011), Fe(oH) (solubility product is 1.1×10.36), BaS04 (solubility product is 1.08×1010). , thereby being separated and removed from the brine.
4. Mixing method of yellow and black (rock) brine
In areas where black brine or rock brine and barium and yellow brine are produced at the same time, yellow and black (rock) brine are generally used Mixed method. Because there is impurity CaSO in black brine and gypsum brine. There is a large amount of Na in Glauber's salt brine. SO. , both of these substances can react with BaCl in yellow brine to generate BaS0. Precipitation allows both halogens to be refined without consuming treatment chemicals. Where such conditions exist, this method is extremely economical. The basic reaction is:
BaCl2+CaS04--*BaS04l+CaCl2
BaCl2+NazS04--?'BaS044+2NaCl
5. Lime-soda ash Method
When using gypsum brine to make salt, in order to remove calcium and magnesium impurities, the lime-soda ash method is now widely used abroad. The advantages of this method are mature technology, simple equipment and high removal rate. Generally, the magnesium removal rate can reach 97-99%, and the calcium removal rate can reach 98-99%. For brines with low magnesium content, the soda ash method can be used instead of lime.
Ca (HCO.) is contained in certain brine. ,CaSO. ,MgSO. , MgCI. impurities, they react with lime and soda ash to form insoluble precipitates and are separated from the brine.
MgS04+Ca(OH)2---Mg(OH)2l+CaSO.
MgCl-Ca(OH)2-Mg(OH)2I+CaCI.
Ca(HCO.). +Ca(OH):--?2CaC0. I+2H. 0
CaS04+Na2C03--CaC03{+Na2S04
CaCl2+Na2C03-+CaC03l+2NaCl
If two chemicals are added at the same time, the reaction is as follows Proceed in various forms:
CaO+H20—Ca(OH)2
Ca(0H)2+Na2C03--CaC03I+2NaOH
Ca(HC03) 2+2Na0H—-CaC03l+Na2C03+H20
MgSO. +2Na0H--Na2S0. Ten Mg(OH). I
CaS04+Na2C03-CaC03I+Na2S04
The results calculated according to the above reactions are the same, regardless of the JJn* order of lime and soda ash.
6. Lime-Glauber's Salt-Carbonization Method
For products containing MgCI. ,MgSO. ,CaSO. , CaCl: brine, it is very reasonable to use this method, and the least amount of soda ash can be used to ensure good purification. This method is also used in industrial production abroad.
The basis of this method is that lime and Glauber's salt react to generate NaoH, and NaOH reacts with flue gas to generate Na:C0. ,Na. C0. Then it reacts with Ca2+ to generate the insoluble substance CaCO. . The reaction proceeds in two steps.
Step 1
MgCl. +Ca(OH). --Mg(OH). ;+CaCl:
CaCl2+Na2SO. --'CaS04+2NaCl
MgS0. +Ca(OH):--*Mg(OH). I+CaSO.
Ca(OH)2+Na2SOd--*CaS0{+2Na0H
Second step
2NaOH+C02—. ． Na2C03+H20
CaS04+Na2C03-CaC03l+Na2S04
The precipitate obtained in the reaction is Mg(oH). ,CaC0. and CaS0. , and the products obtained in the solution are NaCl and Na:SO. , Therefore, the salt-making mother liquor can be reused and the Glauber's salt in it can be utilized.
CaS0. In NaCl and Na. S0. The solubility in the solution is greatly reduced, and the CaSO generated in the first step of the reaction is reduced. Basically precipitate out. For details, please refer to more relevant technical documents.
7. Caustic soda-soda ash-barium chloride method
This method is suitable for Ca", M92+ and S0.
'The refined brine has very few impurities and can be used for highly demanding edible salt and industrial salt. The reaction is as follows:
MgCl2+2NaOH—+Mg(0H)2l+2NaCl
p>
FeCl. +3NaOH—?Fe(OH). l+3NaCl
CaSO. +Na:C03-CaC03l+Na2SO.
CaCl2+Na2C03-CaC03l+2NaCl
Na: SO{+BaCl2--*BaSOI4+2NaCl
Reaction results: The impurities in the brine are basically removed, and Increase the NaCl content in brine. This kind of brine is ideal for evaporation and plays an important role in preventing scaling, reducing the boiling point of the feed liquid, lowering the viscosity of the feed liquid, and ensuring product quality. However, the chemicals used in this refining method are expensive. If the comprehensive utilization of the product is fully realized, this method can also be used. This method is also used in some salt plants and chemical plants around the world.