Separation method of soluble chlorine salt in household garbage incineration fly ash lixivium

Abstract

The invention relates to a method for recovering mixed salts (mainly containing calcium chloride, sodium chloride and potassium chloride) from a household garbage incineration fly ash leaching solution, and particularly provides two separation technical schemes. The traditional separation method generally needs to use a large amount of decalcifying agent, so that the cost is high, calcium chloride cannot be effectively recycled, and the problem of resource waste exists. In order to solve the problems, the invention selectively dissolves calcium chloride in the mixed salt by adopting a specific organic solvent (such as ethanol or methanol) and utilizing the characteristics that the solubility of calcium chloride in the solvent is high, the solubility of sodium chloride and potassium chloride is low, and the boiling point is relatively low. And a calcium chloride product can be recovered after solvent evaporation. Furthermore, the residual mixed salt is further washed using the specific organic solvent to remove entrained calcium chloride, thereby obtaining a mixed salt containing predominantly sodium chloride and potassium chloride. According to the technical scheme 1, the mixed salt subjected to separation and calcium removal is subjected to dissolution treatment under the high-temperature condition, potassium chloride is dissolved, the particle size of sodium chloride crystals is promoted to be increased, the sodium chloride crystals are obtained through solid-liquid separation, and then mother liquor is cooled and crystallized to recover potassium chloride. According to the technical scheme 2, the mixed salt subjected to separation and calcium removal is subjected to aging treatment so as to promote particle size increase of sodium chloride and potassium chloride crystals, then the aged mixed salt is separated by adopting a flotation method, and sodium chloride and potassium chloride products are recycled respectively.

Description

Technical Field

[0001] The present invention relates to a method for recovering calcium chloride (calcium chloride dihydrate or anhydrous calcium chloride), sodium chloride, and potassium chloride from the leachate of municipal solid waste incineration fly ash. Background Art

[0002] Incineration is a method widely used in municipal solid waste treatment, which has the advantages of energy recovery and waste reduction. However, the fly ash generated during incineration contains heavy metals and toxic organic pollutants, so it is classified as hazardous waste. Traditional treatment methods include landfill after solidification stabilization and heat treatment methods, but these methods have obvious disadvantages: the solidification method cannot realize the resource utilization of fly ash and occupies land; the heat treatment method has a high treatment cost.

[0003] In recent years, a variety of fly ash resource utilization methods have been developed and applied at home and abroad. Among them, the more common one is to wash or acid-leach the fly ash and then perform heat treatment to realize the resource utilization and harmlessness of fly ash. In this process, the fly ash leachate generated contains high concentrations of soluble chlorides, mainly including calcium chloride, sodium chloride, and potassium chloride. However, there are still problems of high reagent cost and difficulty in recovering calcium chloride in the current separation technology for soluble chlorides in fly ash leachate.

[0004] The existing mainstream chloride separation technologies mainly include using sodium carbonate or sodium bicarbonate to precipitate calcium chloride in the leachate, and then obtaining sodium chloride and potassium chloride through evaporation crystallization. Due to the high content of calcium chloride in the leachate, the cost of the decalcification reagent accounts for a relatively large proportion in the overall treatment cost.

[0005] Therefore, if the recovery of calcium chloride in the leachate can be realized, not only the treatment cost can be reduced, but also the product value can be significantly improved, thus making the related fly ash resource utilization technologies more economically feasible. Summary of the Invention

[0006] The present invention aims to develop a method that can effectively recover calcium chloride (calcium chloride dihydrate or anhydrous calcium chloride), sodium chloride, and potassium chloride from fly ash leachate. The present invention proposes two technical solutions.

[0007] The technical solution 1 is as follows.

[0008] A. After removing heavy metals and other pollutants, the fly ash leachate mainly containing calcium chloride, sodium chloride, and potassium chloride is subjected to evaporation and drying treatment to obtain mixed salt 1. Spray drying treatment can also be directly carried out to obtain mixed salt 1. According to the different calcium chloride products to be recovered, appropriate drying methods and temperatures are selected. If anhydrous calcium chloride is desired to be recovered, the moisture in the mixed salt 1 should be completely evaporated; if calcium chloride dihydrate is desired to be recovered, two bound waters of calcium chloride should be retained, which can be achieved by controlling the drying temperature.

[0009] B. Use a specific organic solvent in which calcium chloride and water are highly soluble, while sodium chloride and potassium chloride have relatively low solubility and low boiling point to dissolve calcium chloride and its bound water in the mixed salt 1. The specific organic solvent can be ethanol, methanol, or their mixtures, but is not limited thereto. If the particle size of the mixed salt 1 is large, the mixed salt 1 should be ground into powder before dissolution to accelerate dissolution. The ratio of the mixed salt 1 to the specific organic solvent can be controlled by measuring the density, refractive index, or viscosity of the liquid phase at the corresponding temperature.

[0010] C. Obtain the mixed salt 2 and the liquid phase 1 through solid-liquid separation.

[0011] D. Evaporate the liquid phase 1 obtained in step C to obtain anhydrous calcium chloride or calcium chloride dihydrate products, and at the same time condense and recover the specific organic solvent.

[0012] E. Wash the mixed salt 2 obtained in step D with the specific organic solvent and perform solid-liquid separation to obtain the mixed salt 3. The number of washing times can be determined according to the actual operation conditions, either once or multiple times.

[0013] F. Evaporate the washed mixed salt 3 to obtain the mixed salt 4 mainly containing sodium chloride and potassium chloride, and condense and recover the specific organic solvent.

[0014] G. Grind the mixed salt 4 into powder and add it to an aqueous solution of sodium chloride and potassium chloride. Dissolve potassium chloride at high temperature and at the same time promote the growth of sodium chloride crystals.

[0015] H. Perform solid-liquid separation while it is hot to obtain sodium chloride crystals and the liquid phase 2.

[0016] I. Cool the liquid phase 2 to precipitate potassium chloride crystals. During this process, potassium chloride seeds can be added and the cooling rate can be controlled to promote the formation of potassium chloride crystals with larger particle size.

[0017] J. Perform solid-liquid separation to obtain potassium chloride and the liquid phase 3, and return the liquid phase 3 to step G. Decalcification treatment should be performed on the liquid phase 3 continuously or intermittently.

[0018] The technical solution 2 is as follows.

[0019] A. After removing heavy metal and other pollutants, perform evaporation and drying treatment on the fly ash leachate mainly containing calcium chloride, sodium chloride, and potassium chloride to obtain the mixed salt 1. Spray drying treatment can also be directly performed to obtain the mixed salt 1. According to the different calcium chloride products to be recovered, select the appropriate drying method and temperature. If anhydrous calcium chloride is desired to be recovered, the moisture in the mixed salt 1 should be completely evaporated; if calcium chloride dihydrate is desired to be recovered, two bound waters of calcium chloride should be retained, which can be achieved by controlling the drying temperature.

[0020] B. Use a specific organic solvent in which calcium chloride and water are easily soluble, while sodium chloride and potassium chloride have relatively low solubility and low boiling point to dissolve calcium chloride and its bound water in the mixed salt 1. The specific organic solvent can be ethanol, methanol and their mixtures, but is not limited thereto. If the particle size of the mixed salt 1 is large, the mixed salt 1 should be ground into powder before dissolution to accelerate dissolution. The ratio of the mixed salt 1 to the specific organic solvent can be controlled by measuring the density, refractive index or viscosity of the liquid phase at the corresponding temperature.

[0021] C. Obtain the mixed salt 2 and the liquid phase 1 through solid-liquid separation.

[0022] D. Evaporate the liquid phase 1 obtained in step C to obtain anhydrous calcium chloride or calcium chloride dihydrate products, and condense and recover the specific organic solvent at the same time.

[0023] E. Wash the mixed salt 2 obtained in step D with the specific organic solvent, and perform solid-liquid separation to obtain the mixed salt 3. The number of washing times can be determined according to the actual operation conditions, which can be either once or multiple times.

[0024] F. Evaporate the washed mixed salt 3 to obtain the mixed salt 4 mainly containing sodium chloride and potassium chloride, and condense and recover the specific organic solvent.

[0025] G. Grind the mixed salt 4 into powder and add it to the aqueous solution of sodium chloride and potassium chloride for aging treatment to promote the growth of sodium chloride and potassium chloride crystals to a particle size range suitable for flotation.

[0026] H. Perform flotation separation on the aged mixed salt 4 to obtain sodium chloride and potassium chloride.

[0027] The basis of the present invention.

[0028] 1. In step B of both Technical Solution 1 and Technical Solution 2, a specific organic solvent is used to dissolve and separate calcium chloride. This is mainly based on the fact that calcium chloride has a high solubility in specific organic solvents such as ethanol and methanol, while sodium chloride and potassium chloride have relatively low solubility in such solvents. Through the solvent extraction method, calcium chloride can be effectively separated from the mixed salt, and high-purity calcium chloride can be obtained, with a purity exceeding 98%. In addition, since the boiling points of these specific organic solvents are relatively low, the separation of calcium chloride and its crystal water from the solvent can be achieved during evaporation. At the same time, considering that calcium chloride has strong hygroscopicity, the moisture in the mixed salt will not accumulate in the solvent.

[0029] 2. In step B of Technical Solution 1 and Technical Solution 2, by measuring the density, refractive index or viscosity of the liquid phase, the addition ratio of Mixed Salt 1 and the specific organic solvent is regulated. Since the calcium chloride concentration in the liquid phase has a significant impact on the physical properties (density, refractive index and viscosity) of the liquid phase, this principle can be utilized for control. For example, when ethanol is used as the solvent, the density of anhydrous ethanol at room temperature is approximately 0.79 g / mL, and the viscosity is approximately 1.3 cps. While the density of the saturated calcium chloride solution in ethanol at room temperature can reach approximately 1.0 g / mL, and the viscosity can be as high as several thousand cps.

[0030] 3. In step E of Technical Solution 1 and Technical Solution 2, the Mixed Salt 2 is washed with the specific organic solvent. This is because the Mixed Salt 2 has a small particle size and is in powder form. After solid-liquid separation, it still contains a relatively large amount of the residual specific organic solvent. If it is directly evaporated without washing, the calcium chloride content in the obtained mixed salt can be as high as approximately 10%, which will affect the subsequent separation effect of sodium chloride and potassium chloride. After two washes with the specific organic solvent and then evaporation treatment, the calcium chloride content in the mixed salt can be reduced to less than 1%.

[0031] 4. In step G of Technical Solution 1, by dissolving potassium chloride under high-temperature conditions, the growth of sodium chloride crystals is promoted simultaneously. This is based on the characteristics that the solubility of potassium chloride in water increases significantly with the increase of temperature, while the solubility of sodium chloride changes little with temperature. Therefore, under high-temperature conditions such as 100 °C, potassium chloride can be fully dissolved in the solution. Since the sodium chloride crystals are in powder form, direct solid-liquid separation is likely to cause problems such as a decrease in the purity of sodium chloride and incomplete separation. There is always a dynamic equilibrium reaction of dissolution and precipitation on the crystal surface. Crystals with a smaller particle size tend to dissolve, while crystals with a larger particle size tend to grow. After a period of reaction, the small-particle-size crystals gradually disappear, and the average particle size of the crystals increases significantly. This phenomenon is called crystal aging. Under high-temperature conditions, the crystal aging process is accelerated. Therefore, in this step, while dissolving potassium chloride, the particle size of sodium chloride crystals can be promoted to grow until it reaches a particle size suitable for solid-liquid separation.

[0032] 5. In step I of Technical Solution 1, taking advantage of the characteristics that the solubility of potassium chloride in water changes greatly with temperature while the solubility of sodium chloride changes little, potassium chloride is precipitated by cooling the liquid phase 2. Due to the precipitation of potassium chloride, sodium chloride in the liquid phase is in an unsaturated state and thus will not precipitate. To avoid the formation of a large number of potassium chloride crystals with a small particle size, potassium chloride crystal seeds can be added in this step and the cooling rate can be controlled. Excessive fine crystals will cause difficulties in solid-liquid separation, thereby reducing the purity of the obtained potassium chloride.

[0033] 6. In step J of Technical Solution 1, the liquid phase 3 is decalcified because the mixed salt 2 still contains a small amount of calcium chloride. If it operates for a long time, the concentration of calcium chloride will gradually increase, affecting the process stability.

[0034] 7. In step G of Technical Solution 2, the mixed salt 4 is aged so that the sodium chloride and potassium chloride crystals can grow to a particle size range suitable for flotation because there is always a dynamic equilibrium reaction of dissolution and precipitation on the crystal surface. Crystals with smaller particle sizes tend to dissolve, while crystals with larger particle sizes tend to grow. After a period of reaction, the small particle size crystals gradually disappear, and the average particle size of the crystals increases significantly. And the crystal particle size has a significant impact on the flotation effect. Too large or too small particle sizes will both cause the flotation effect to deteriorate.

[0035] The present invention has the following beneficial effects.

[0036] 1. The two technical solutions proposed by the present invention can realize the recovery of calcium chloride, sodium chloride, and potassium chloride in the fly ash leachate, while traditional methods can usually only recover sodium chloride and potassium chloride. Therefore, adopting the technical solutions of the present invention can not only obtain more types of products but also significantly improve the resource utilization efficiency.

[0037] 2. Adopting the technical solutions of the present invention can effectively reduce the usage amount of decalcifying agents, thereby reducing the treatment cost and enhancing the economy and sustainability of the process.

[0038] 3. The three products obtained by Technical Solution 1 of the present invention have high purity and higher market value, further improving the economic benefits of resource recovery.

[0039] 4. In Technical Solution 2 of the present invention, the separation of sodium chloride and potassium chloride can be carried out at room temperature, thereby effectively reducing energy consumption and further improving the economy of the process.

[0040] Description of the drawings.

[0041] Figure 1 It is the process flow chart of Technical Solution 1, which is a further illustration of Technical Solution 1 rather than a restrictive description.

[0042] Figure 2 It is the process flow chart of Technical Solution 2, which is a further illustration of Technical Solution 1 rather than a restrictive description.

[0043] The best implementation mode of the present invention.

[0044] In a municipal solid waste incineration plant, the fly ash is treated by an acid leaching process or a water washing process for fly ash to obtain a fly ash leachate, and heavy metals and other pollutants in the leachate are removed. Subsequently, the purified leachate is evaporated and dried to obtain a mixed salt 1, with calcium chloride existing in the form of calcium chloride dihydrate. Since the municipal solid waste incineration plant can provide a large amount of waste heat, the waste heat resources can be fully utilized to reduce the treatment cost. At the same time, making calcium chloride exist in the form of calcium chloride dihydrate can significantly reduce the temperature required for drying and further reduce energy consumption.

[0045] The mixed salt 1 generated by different incineration plants is uniformly sent to a salt separation enterprise for separation treatment, which can simplify the internal treatment process of the incineration plant. At the same time, centralized salt separation treatment can also improve the salt separation efficiency, further optimize resource utilization and reduce the overall treatment cost.

[0046] After grinding the mixed salt 1 into a powder, anhydrous ethanol is used to dissolve the calcium chloride dihydrate in it, and after solid-liquid separation, a mixed salt 2 and a liquid phase 1 are obtained. Evaporation treatment of the liquid phase 1 can obtain a calcium chloride dihydrate product, and anhydrous ethanol is recovered by condensation. Among them, the grinding treatment of the mixed salt 1 is to accelerate the dissolution of calcium chloride dihydrate; the selection of anhydrous ethanol as the solvent is based on its advantages such as low toxicity, low boiling point, and low price.

[0047] The mixed salt 2 is washed twice with anhydrous ethanol, and then solid-liquid separation is carried out to obtain a mixed salt 3.

[0048] Evaporation treatment is carried out on the mixed salt 3 to recover anhydrous ethanol and obtain a mixed salt 4.

[0049] After grinding the mixed salt 4 into a powder, it is added to an aqueous solution of sodium chloride and potassium chloride. At high temperature, potassium chloride is dissolved, and at the same time, the growth of sodium chloride crystals is promoted. Since the mixed salt 4 obtained by evaporation is prone to caking, it is necessary to carry out grinding treatment again to accelerate dissolution and ensure the reaction effect. Subsequently, solid-liquid separation is carried out while it is hot to obtain sodium chloride crystals and a liquid phase 2. The sodium chloride crystals are dried to obtain a sodium chloride product.

[0050] The liquid phase 2 is cooled to precipitate potassium chloride crystals. To prevent the formation of a large number of fine crystals, potassium chloride crystal seeds need to be added during this process, and the temperature is reduced at a relatively slow speed, so as to promote the orderly growth of crystals and obtain potassium chloride crystals with a larger particle size, which is convenient for subsequent solid-liquid separation.

[0051] Solid-liquid separation gives potassium chloride crystals and a liquid phase 3. The potassium chloride crystals are dried to obtain a potassium chloride product.

[0052] The liquid phase 3 is returned to the step of dissolving the mixed salt 4 at high temperature for recycling. It is necessary to carry out decalcification treatment on the liquid phase 3 regularly to prevent the accumulation of calcium chloride in the system, which affects the process stability and product purity.

[0053] Industrial applicability of the present invention.

[0054] The technical solution of the present invention can effectively recover calcium chloride, sodium chloride and potassium chloride in the fly ash leachate, improving the efficiency of waste resource utilization. Through the separation and treatment of the mixed salts, not only important salt resources are recovered, but also the resource utilization rate can be greatly increased, meeting the current social requirements for waste recycling and resource circular utilization.

[0055] By utilizing the waste heat in the domestic waste incineration plant, the energy consumption required in the treatment process can be effectively reduced.

[0056] The present invention can obtain high-purity sodium chloride, potassium chloride and calcium chloride products, which have high economic value in the market, can meet the needs of industrial production for these chemicals, and improve the market competitiveness of the products.

Claims

1. A method for separating a mixed salt of calcium chloride, sodium chloride and potassium chloride, comprising the following steps: a. Mix the mixed salt 1 mainly containing calcium chloride, sodium chloride and potassium chloride with a specific organic solvent to dissolve calcium chloride, perform solid-liquid separation to obtain a mixed salt 2 and a liquid phase 1; b. Evaporate the liquid phase 1 to recover calcium chloride and condense and recover the specific organic solvent; c. Wash the mixed salt 2 with a specific organic solvent, perform solid-liquid separation to obtain a mixed salt 3; d. Evaporate the mixed salt 3 to obtain a mixed salt 4 mainly containing sodium chloride and potassium chloride, and condense and recover the specific organic solvent; e. Mix the mixed salt 4 with an aqueous solution of sodium chloride and potassium chloride, dissolve potassium chloride under high temperature conditions, and at the same time promote the increase in the particle size of sodium chloride crystals; f. Perform hot solid-liquid separation to obtain sodium chloride and a liquid phase 2; g. Cool the liquid phase 2 to crystallize potassium chloride, and perform solid-liquid separation to obtain solid potassium chloride.

2. A method for separating a mixed salt of calcium chloride, sodium chloride and potassium chloride, comprising the following steps: a. Mix the mixed salt 1 mainly containing calcium chloride, sodium chloride and potassium chloride with a specific organic solvent to dissolve calcium chloride, perform solid-liquid separation to obtain a mixed salt 2 and a liquid phase 1; b. Evaporate the liquid phase 1 to recover calcium chloride and condense and recover the specific organic solvent; c. Wash the mixed salt 2 with a specific organic solvent, perform solid-liquid separation to obtain a mixed salt 3; d. Evaporate the mixed salt 3 to obtain a mixed salt 4 mainly containing sodium chloride and potassium chloride, and condense and recover the specific organic solvent; e. Mix the said mixed salt 4 with an aqueous solution of sodium chloride and potassium chloride, and perform an aging treatment to increase the particle sizes of sodium chloride crystals and potassium chloride crystals; f. Perform flotation separation on the aged mixed salt 4 to obtain sodium chloride and potassium chloride.

3. The method according to claim 1 or 2, wherein The said specific organic solvent is selected from ethanol or methanol.

4. The method according to claim 1 or 2, wherein In step a, the ratio of the mixed salt to the specific organic solvent is determined by measuring the density, refractive index or viscosity of the liquid phase at the corresponding temperature.

5. The method according to claim 1 or 2, wherein In step c, the mixed salt 2 is washed twice with a specific organic solvent.

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