CN1021963C - Method for removing magnesium from sodium chloride solution - Google Patents

Abstract

The present invention relates to a method for removing magnesium from a sodium chloride solution, which is suitable for refining processes of coarse sodium chloride salt water and brine and production processes for preparing MgOH2 from sea water or magnesium chloride brine by an alkali precipitation method. The present invention is characterized in that in the separate process of magnesium precipitation, the concentration of salt water mud is from 20 to 40 g/L, the temperature of the salt water mud is from 15 to 65 DEG C, the stirring intensity is medium, and the pH value is from 9.2 to 11.2; the operation pH value is determined and stably controlled; the reaction speed among ions is slowed; the generation of new nucleus is inhibited; the growing rate is promoted; the settling speed of the mud can reach 3 to 8.1 m/h; the filter factor is increased to 500 to 2980*10+[-7]cm/s; the problem of difficult separation of mud is solved, and the magnesium content of clear liquid is less than 1 ppm.

Description

Method for removing magnesium from sodium chloride solution

The present invention relates to a kind of method of from the sodium chloride solution that contains magnesium ion, removing magnesium ion, be applicable to the treating process of sodium chloride brine and bittern with alkaline precipitation, and the production process of from seawater or magnesium chloride bittern, producing magnesium hydroxide.

The magnesium ion that is contained in the sodium chloride solution is generally all used and is added a kind of alkali precipitation agent (for example Ca(OH) ₂Or NaOH solution etc.), make it to generate the very little Mg(OH of solubility product) ₂The precipitation and remove.But the main drawback of this method is because the magnesium ion in the liquid phase and the cross reaction speed of hydroxide ion are exceedingly fast, to cause the Mg(OH that generates) ₂Crystallization trickle, salty mud is colloidal state, the liquid-solid separation of the salty mud after the demagging is difficulty very, suspension content height, fluctuation are greatly in the refined brine, cause thus making the technico-economical comparison decline that alkali (soda ash or caustic soda) is produced, consuming increases, and cost raises, saltiness height in the slag, contaminate environment; Cause treating process equipment big simultaneously, investment is high.

In existing improvement project, usually adopt and return subsider mud, add means such as flocculation agent, with the strainability that improves mud (as " chlorine industry " 1987 the 9th phases, 4-7 page or leaf: improve brine quality with the salt slurry of handling " and " chlorine industry " 1989 the 8th phases; 9-10 page or leaf " preparation of settling agent and interpolation " is introduced), but effect is undesirable.And the method that U.S. Pat 4336232 is introduced is strict with adding Na earlier ₂CO ₃, add the sequential control addition of NaOH, Na again ₂CO ₃The excessive 0.6g/l that is no less than, the excessive 1g/l that is no less than of NaOH, heavy magnesium process has mechanical stirring and generates easy filtering floss with sedimentary calcium slag in advance is common, adopts and is interrupted mode of operation, and need special strainer to filter.

Deficiency at aforesaid method the objective of the invention is, and proposes a kind ofly can suppress Mg(OH) ₂Nucleus formation speed, promotion Mg(OH) ₂The method of crystal growth speed uses increasing substantially the salty mud settling velocity, makes it to be easy to filtration washing, makes suspension content reduction in the refined brine simultaneously, and the NaCl loss reduces and can prevent the pollution of the environment.

The objective of the invention is to realize by following measure: being provided with an independent heavy magnesium process, in heavy magnesium process, stirring salty mud with medium tenacity, is 15-65 ℃ in the salty mud temperature, Mg(OH in the salty mud) ₂Concentration is under the condition of 20-40g/l, and the working pH value by selecting the working pH value with the oppositely corresponding mode of salty mud temperature, salty mud concentration, and is controlled its fluctuation and is ± the 0.2pH value in the scope of 9.2-11.2.

The working pH value is relevant with mud content (crystal seed amount) with temperature.In general, the salty mud temperature is low, mud content is low, and then salty mud working pH value is tending towards raising; Vice versa.When the salty mud temperature be 15 ℃, when concentration is 20g/l, the pH value is 11.2; The salty mud temperature is that 65 ℃, concentration are 40g/l, and the pH value is 9.2.Determine the working pH value like this, the interionic cross reaction speed that slowed down can be controlled the generation of new nucleus simultaneously effectively under the effect of high concentration slurry, impel nuclei growth, thereby improves salty mud settling velocity and strainability.The angle of the metallization processes that conforms to the principle of simplicity and minimizing energy consumption considers that temperature can be selected in low scope, preferably at 20-30 ℃.

Mg(OH in the crystal seed mud) ₂Particle diameter preferably is controlled at below 5 μ, to improve crystal seed activity.

For the sodium chloride solution, crystal seed mud and the alkali precipitation agent that contain magnesium ion are mixed rapidly, their should be added simultaneously continuously, and the in addition stirring of medium tenacity.

Enter the sodium chloride solution that contains magnesium ion of heavy magnesium process, its pH value should be greater than 9.2, in order to avoid the magnesium ion in the solution is precipitated out outside the characteristic condition of the present invention's regulation in advance in a large number.NaCl concentration is not limit in the described solution, and magnesium ion concentration is preferably less than 17g/l, and magnesium calcium when other impurity is not limit; Certainly, for well, can reduce the consumption of alkali when the calcium in the described solution, Mg content are low.

Accompanying drawing 1 is for precipitating the process flow sheet of magnesium ion from sodium chloride solution with the alkali precipitation agent;

Accompanying drawing 2 is the process flow sheet that precipitates magnesium ion when using caustic soda soda ash method from sodium chloride solution.

Further specify below in conjunction with accompanying drawing.

As shown in Figure 1, near saturated crude brine (or bittern) with return mud and alkali precipitation agent and add to continuously in the heavy magnesium groove with medium stirring intensity, the salt-water mud temperature can be selected in 15-65 ℃ of scope in the heavy magnesium groove, salt-water mud concentration is 20-40g/l, and the interpolation speed of crude brine is given according to the production capacity balance by flowmeter. When NaOH was used in the alkali precipitation agent, the scope of working pH value was 9.2-10.6; When using Ca(OH)₂The time, the scope of working pH value is 10-11.2. When the working pH value less than 9.8 the time, should in adjustment tank, add Ca(OH)₂Or NaOH is transferred to OH in the liquid phase^-Concentration is about 0.1g/l. Carrying out in time, the salt-water mud that overflows from adjustment tank flows to earlier a hydraulic mixer, add simultaneously the concentration prepare in advance and be one thousandth to ten thousand/five polyacrylamide (PAM), Sodium Polyacrylate (TXY) or carboxymethyl cellulose (CMC) in hydraulic mixer, addition be 100,000 of salt-water mud gross weight/to 1,000,000/. Salt-water mud after mixing enters subsider sedimentation separation body refuse, and the concentration of hydraulic mixture of subsider underflow is 95-150g/l, and classified machine classification, Mg(OH in the overflow of grader)₂Particle diameter less than 5 μ accounts for 95%, turns back to heavy magnesium groove as crystal seed, and the grader underflow enters filter and filters and wash. Subsider overflow and filter filtrate are merged into the demagging refined brine, and wherein magnesium ion content is less than 1ppm. The purification of calcium ion is added Na by usual method in the salt solution₂CO ₃Or (NH₄） ₂CO ₃Remove.

As shown in Figure 2, when adopting recovered brine, when washing lotion and new water-soluble solution crude salt are produced refined brine, should in a carbonating groove, pass into CO₂Gas (or flue gas) carries out the carbonating processing to recovered brine and washing lotion, and the pH value of control carbonating solution is to be advisable below 9.2, makes NaOH be converted into Na₂CO ₃, the Na of generation₂CO ₃Amount should be enough to guarantee that the calcium ion in the crude brine all generates CaCO₃, and at least excessive 0.4-0.6g/l, otherwise, should replenish Na₂CO ₃ Carbonating is finished liquid and is added to new water and produces crude brine in the salt-dissolving bucket, simultaneously deliming. Rough salt solution is added in the heavy magnesium groove with medium stirring intensity continuously, and returning concentration from the classifier overflow mouth of subsider underflow simultaneously is that the mud of 95-150g/l advances to sink the magnesium groove, and keeps Mg(OH in the heavy magnesium groove)₂Concentration is 20-40g/l. Contain NaOH15-25%(weight) the interpolation speed of solution determined by working pH value in the given heavy magnesium groove, by the interpolation speed of auto-adjustment control NaOH solution. Processing temperature can be selected in the 15-65 ℃ of scope and carry out in the heavy magnesium groove, but preferably carries out under 20-30 ℃, and so not only can reduce the steam consumption can also process simplification. Heavy magnesium groove volume stops in groove by the salt-water mud total amount and was designed to suitable in 20-40 minute. Carrying out mud with process can flow into adjustment tank from heavy magnesium groove overfall continuously, adjusts the pH value, makes OH^-Concentration is about 0.1 grams per liter, enters the hydraulic mixer of subsider top, toward wherein adding the flocculant solution for preparing, enters subsider again. The subsider underflow is through hydroclone classification, and the overflow of hydrocyclone turns back to heavy magnesium groove, and underflow then advances filter and filters and wash. The filter residue moisture content is about about 50%, can fully utilize or store up. Washing lotion then turns back to the carbonating groove. Subsider overflow and filter filtrate are merged into refined brine, magnesium＜1ppm in the liquid phase, calcium＜4ppm.

The present invention and prior art relatively have following advantages:

1. salt-water mud has good sedimentation strainability, and its sinking speed is 3-8.1m/h, and filtration coefficient is 500-2980 * 10^-7Cm/s, thus the production capacity of sedimentation filter plant improved significantly.

2. salt refining process operation is continuous, stable, and it is few to cross alkali number, Suspension content is low, and calcium is less than 4ppm in the refined brine, and magnesium is less than 1ppm.

3. technical process and equipment are simple, can combine closely with existing brine rectification process, heavy magnesium process automatically-controlled continuous.

4. two alkali consumptions are few, and chlor-alkali plant can outsourcing soda, does not consume or consume less hydrochloric acid; NaCl loss is little, and body refuse can fully utilize or store up, and eliminates or has alleviated environmental pollution, and social benefit and overall economic efficiency are good.

Embodiment:

1. with 10 liters of crude brines, its chemical constitution (g/l) is NaCl312, Ca ²⁺0.69, Mg ²⁺0.79, SO ^2- ₄2.20 the pH value is 7.2 in the time of 20 ℃.The chemical constitution of the milk of lime that agent is used as alkali precipitation (g/l) is: CaO136.80, Mg0.76, Fe ₂O ₃0.02, Al ₂O ₃0.22, SiO ₂0.54 the pH value is 12.45 in the time of 20 ℃.The mud of using as crystal seed is to contain Mg(OH) ₂Be that master, concentration of hydraulic mixture are 98g/l.Crude brine, milk of lime and the mud of using as crystal seed, be added to continuously in the heavy magnesium groove of Φ a 200 * 120mm, keeping the salty mud temperature is 20 ℃ ± 0.5 ℃, salty mud concentration 30 ± 2g/l, and the interpolation speed of milk of lime is 11.2 ± 0.2 given by the working pH value.The heavy magnesium activity duration amounts to 144 minutes.After heavy magnesium operation is finished, salty mud being moved on in the settlement barrel of Φ a 200 * 600mm, is millesimal PAM solution 15ml toward the previously prepared concentration of the interior interpolation of settlement barrel, leaves standstill 30 minutes after stirring up and down, and recording settling velocity is 4.2m/h.Take out 9.8 liters of supernatant liquors with siphonage, remaining 5.78 liters of compression zone mud are 0.06MPa in vacuum tightness, and filtration area is 630cm ²Process device of the false end in filter, obtain 4.53 liters of filtrates in 151 seconds of filtration time, filter factor is 1429 * 10 ^-7Cm/s.Supernatant liquor and filtrate are merged into demagging salt solution.Its chemical constitution (g/l) is: NaCl311.80, Ca ²⁺1.52, Mg ²⁺0.0008, SO ^2- ₄2.19.With 3 liters of 50 ℃ of hot water filter cake is carried out not the dump washing, NaCl concentration 1.81g/l in the last washing lotion.The filter cake oven dry is weighed 565 grams altogether, and its chemical constitution (% weight) is: MgO66.74, CaO0.8, Fe ₂O ₃0.29, Al ₂O ₃0.21, SiO ₂0.47, Cl ^-0.23, igloss 31.08.

2. with chemical constitution (g/l) be: NaCl305, Ca ²⁺0.23, Mg ²⁺0.46, SO ^2- ₄1.42 the pH value is 10 liters of 7.1 crude brines in the time of 20 ℃.Contain Mg(OH in the mud as crystal seed) ₂95g/l, NaCl304g/l wherein is that 22% NaOH is a precipitation agent with concentration, and is 40% Na with concentration ₂CO ₃Solution is the precipitation agent of deliming.In crude brine, add Na by stoichiometry slowly ₂CO ₃12.5 gram stirred 30 minutes down at 40 ℃, be added to continuously in the heavy magnesium groove of Φ a 200 * 120mm who has a medium stirring intensity with crystal seed mud and NaOH solution then, the predetermined interpolation speed of crude brine be 4 liters/time.Temperature is 60 ± 0.5 ℃ in the groove, and keeping salty mud concentration is 27-28g/l.NaOH solution then adds by given working pH value, and the working pH value is 9.2 ± 0.2.Total operation time is 146 minutes, makes 16.15 liters of salty muds altogether.Salty mud is moved on in the settlement barrel of Φ a 200 * 600mm, adjusting the pH value with NaOH solution is 10.6, adding previously prepared concentration then is millesimal PAM solution 18ml, leaves standstill 20 minutes after stirring up and down, and recording settling velocity is 7.2m/h.Take out 10.12 liters of supernatant liquors with siphonage, remaining 6 liters of compression zone mud are that 0.06MPa, filtration area are 630cm in vacuum tightness ²Strainer of the false end in filter, obtain 4.8 liters of filtrates in 122 seconds of filtration time, filter factor is 1874 * 10 ^-7Cm/s.The merging of supernatant liquor and filtrate amount to 14.92.Its chemical constitution (g/l) is: NaCl302.50, Ca ²⁺0.0005, Mg ²⁺0.00088, SO ^2- ₄1.40, Na ₂CO ₃0.42.Filter cake is carried out not the dump washing with 3 liters of 50 ℃ of hot water, NaCl concentration 2.10g/l in the last washing lotion.The filter cake oven dry is weighed 574.2 altogether, and its chemical constitution (% weight) is: MgO68.10, CaO0.56, Cl ^-0.23, igloss 30.89.Contain NaCl48.80g/l in the washing lotion.

3. bittern chemical constitution (g/l) is: NaCl243.82, Ca ²⁺0.46, Mg ²⁺16.52, SO ²⁺ ₄1.34 the pH value is 10 liters of 7.1 crude brines in the time of 30 ℃.With milk of lime is precipitation agent, and the chemical constitution of milk of lime is with example 1.With containing Mg(OH) ₂The mud of 95g/l is crystal seed, the linear velocity that former bittern, crystal seed mud and milk of lime are added to a stirring rake end of blade continuously is in the heavy magnesium groove of Φ 200 * 120mm of 2.8-3m/s, the predetermined interpolation speed of crude brine be 4 liters/time, keeping the interior temperature of groove is 30 ± 0.5 ℃, and salty mud concentration is 38 ± 2g/l.The pH value is 10.8 ± 0.2.Total operation time is 128 minutes.Make 13.56 liters of salty muds altogether.Salty mud is moved on in the settlement barrel of Φ a 200 * 600mm, adding previously prepared concentration is millesimal PAM solution 14ml, leaves standstill 20 minutes after stirring up and down, and recording settling velocity is 5.6m/h.Take out 8.1 liters of supernatant liquors with siphonage, remaining 5.5 liters of compression zone mud are 0.05MPa in vacuum tightness, and filtration area is 630cm ²Strainer of the false end in filter, filtration time 188 seconds, 1.8 centimetres of filter cake thickness average out to obtain 4.2 liters of filtrates, filter factor is 1277 * 10 ^-7Cm/s.The merging of supernatant liquor and filtrate amount to 12.3 liters.Its chemical constitution (g/l) is: NaCl206.72, Mg ²⁺0.00092, SO ^2- ₄1.35.Filter cake inclined with 3 liters of 50 ℃ of hot water wash, NaCl concentration is 2.20g/l in the last wash water.Filter cake oven dry back weighs 516 grams altogether, and its chemical constitution (% weight) is: MgO67.20, CaO1.62, Cl ^-0.38, igloss 31.02.Contain NaCl42.86g/l in the washing lotion.

Claims (10)

1, a kind of method of removing magnesium from sodium chloride solution is with NaOH or Ca (OH) ₂Be precipitation agent, make magnesium ion be Mg (OH) ₂Separate out, adding addition then is that 100,000 of salty mud gross weight/extremely millionth polyacrylamide, sodium polyacrylate or carboxymethyl cellulose are flocculation agent, isolate Mg (OH) ₂Throw out the invention is characterized in:

In independent heavy magnesium process, add crystal seed mud and precipitation agent, precipitation agent during with NaOH the working pH value be 9.2-10.6, usefulness Ca (OH) ₂The time working pH value be 10-11.2, be Mg (OH) in 15-65 ℃, salt slurries mud in the salty mud temperature ₂Concentration is under the condition of 20-40g/1, by determining the working pH value with the oppositely corresponding mode of temperature, concentration, and it is stabilized in ± 0.2pH, when the working pH value less than 9.8 the time, in the adjustment process of sinking behind the magnesium, again with NaOH or Ca (OH) ₂Adjust salty mud pH value to OH ^-Concentration is 0.1g/1.

2, method according to claim 1 is characterized in that: described sodium chloride solution is crude brine, bittern, seawater and magnesium chloride bittern.

3, method according to claim 1 and 2 is characterized in that: the magnesium ion concentration＜17g/l in the described sodium chloride solution.

4, method according to claim 1 and 2 is characterized in that: when sinking magnesium, described sodium chloride solution, alkali precipitation agent and crystal seed mud are added continuously in the heavy magnesium groove simultaneously.

5, method according to claim 1 and 2 is characterized in that: to recovered brine, carbonating is to its pH value＜9.2 in advance.

6, method according to claim 1 and 2 is characterized in that: described precipitation agent is prefabricated into and contains NaOH15-25%(weight) the aqueous solution or contain the Ca(OH of CaO136.80g/) ₂Suspension liquid.

7, method according to claim 1 and 2 is characterized in that: described flocculation agent is prefabricated into the aqueous solution that weight concentration is 0.1-0.05%.

8, method according to claim 1 and 2 is characterized in that: the Mg(OH in the described crystal seed mud) ₂Particle diameter less than 5 μ.

9, method according to claim 8 is characterized in that: the overflow with the subsider underflow after classified is as crystal seed mud.

10, method according to claim 1 and 2 is characterized in that: the stirring intensity of heavy magnesium process is that the linear velocity of stirring arm end of blade is 2.8-3m/s.

Images