Method for treating industrial waste salt by using calcium chloride

Abstract

The invention discloses a method for treating industrial waste salt with calcium chloride, and belongs to the field of chemical engineering. The method comprises the following steps: dissolving industrial waste salt to obtain a near-saturated or saturated salt solution, firstly adjusting the concentration of sulfate ions to promote precipitation of K < + > in the form of potassium sulfate, separating to obtain a potassium sulfate product and post-precipitation liquid # imgabs0 #, cooling and crystallizing the post-precipitation liquid # imgabs1 #, separating to obtain an ammonium chloride product and post-crystallization liquid # imgabs2 #, performing sulfate transformation on the post-crystallization liquid # imgabs3 # by using calcium chloride, and separating to obtain the potassium sulfate product. Separating to obtain a calcium sulfate product and a post-precipitation liquid # imgabs4 #; adjusting the chloride ion concentration of the post-precipitation liquid # imgabs5 by using calcium chloride to promote crystallization and precipitation of Na < + > in the form of sodium chloride, and separating to obtain a sodium chloride product and a crystallization mother liquid # imgabs6 #; the crystallization mother liquor # imgabs7 # is returned to be used for sulfate transformation. According to the method, potassium sulfate, ammonium chloride, calcium sulfate, sodium chloride and other products are sequentially separated from the industrial waste salt, comprehensive resource utilization of the industrial waste salt is achieved, no waste liquid is generated, the technological process is simple, energy consumption is low, and industrial production is facilitated.

Description

Technical Field

[0001] The invention relates to a method for treating industrial waste salt, in particular to a method for treating industrial waste salt with calcium chloride, and belongs to the field of chemical industry. Background Art

[0002] In the industrial production process, after using hydrochloric acid or sulfuric acid, whether it is neutralized with sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide, ammonia or ammonia water, or neutralized with hydrochloric acid or sulfuric acid to neutralize alkaline solutions containing sodium, potassium and ammonia, high-salt wastewater will eventually be formed. Industrial waste salt is the residue obtained by evaporation and concentration of high-salt wastewater. The sources of industrial waste salt are mainly divided into: pesticides, medicine, fine chemicals, printing and dyeing, coal chemical industry and hydrometallurgy according to industry. Industrial waste salt is a solid waste with inorganic salt as the main component. At present, my country's industrial waste salt mainly includes two categories: sodium chloride and sodium sulfate. There are relatively few single salts in industrial waste salt, and most of them are mixed salts. In addition to sodium salts, industrial waste salts may also contain potassium salts, ammonium salts, and organic matter and heavy metals that are harmful to the ecological environment. The sources of industrial waste salt are wide and the composition is complex. It can neither be returned to the chemical industry for direct use nor be stored at will, and it is difficult to treat and dispose of it. Sodium chloride and sodium sulfate in industrial waste salt can only be effectively separated by first adding water to dissolve them, and then evaporating and concentrating them in steps to crystallize them. The processing cost of evaporation and concentration is high, while the selling price of sodium sulfate and sodium chloride is low. It is economically uneconomical to use the dissolution-evaporation crystallization method to separate and recover sodium chloride and sodium sulfate from industrial waste salt. What's worse is that the dissolution-evaporation crystallization method can only separate insoluble impurities in industrial waste salt, while soluble impurities will crystallize out with sodium salt during the evaporation and concentration process of the solution.

[0003] The National List of Hazardous Wastes clearly defines distillation and reaction residues, waste mother liquor and reaction-based wastes generated in the production of chemical synthetic APIs as hazardous wastes. The leakage of industrial waste salt will not only damage the ecological environment and harm people and livestock, but once it dissolves, it will cause soil salinization, endangering the survival and development of surrounding agriculture, forestry and animal husbandry, and even cause serious pollution to surrounding water sources and groundwater, which is extremely harmful. Domestic industrial waste salt disposal technologies include: landfill, high-temperature oxidation, salt washing, etc. At present, the main means of disposal of industrial waste salt in my country is landfill, which is divided into flexible landfill and rigid landfill, but industrial waste salt can only be sent to rigid landfill. The cost of rigid landfill is high and enterprises cannot afford it. In addition, most of the landfills in China are flexible landfills, and the landfill of waste salt is limited. Summary of the invention

[0004] In view of the defects of the treatment methods for industrial waste salt in the prior art, the purpose of the present invention is to provide a method for treating industrial waste salt with calcium chloride. The method adopts sulfate and calcium chloride as non-evaporating crystallizing agents, and sequentially separates potassium sulfate, ammonium chloride, calcium sulfate, sodium chloride and other products from the industrial waste salt, thereby realizing the comprehensive resource utilization of industrial waste salt, and no waste liquid is generated. The process flow is simple, the energy consumption is low, and it is conducive to industrial production.

[0005] In order to achieve the above technical purpose, the present invention provides a method for treating industrial waste salt with calcium chloride, which comprises the following steps:

[0006] 1) Dissolve industrial waste salt to obtain a nearly saturated salt solution or a saturated salt solution;

[0007] The industrial waste salt comprises sodium salt, or comprises sodium salt and potassium salt and / or ammonium salt, and the anions in the sodium salt, potassium salt and ammonium salt comprise Cl - , or contains SO4 2- and Cl - ;

[0008] 2) The nearly saturated salt solution or saturated salt solution uses sulfate to adjust the sulfate ion concentration to meet the SO4 2- / Cl - The molar ratio of ≥0.5 (the sulfate ion concentration in the nearly saturated salt solution or saturated salt solution itself satisfies SO4 2- / Cl - When the molar ratio of ≥0.5, no adjustment is required), and SO4 2- The common ion effect promotes K + Potassium sulfate is precipitated and filtered to obtain potassium sulfate product and precipitated liquid. ;

[0009] When the nearly saturated salt solution or the saturated salt solution does not contain K + When the sulfate ion concentration is adjusted, there is no need to filter and separate the potassium sulfate product, and the process directly proceeds to step 3);

[0010] 3) The liquid after precipitation Through cooling crystallization and filtration separation, the ammonium chloride product and the crystallized liquid are obtained. ;

[0011] After precipitation, the liquid Does not contain NH4 + When , do not proceed to step 3);

[0012] 4) The crystallized liquid Calcium chloride is used to achieve sulfate transformation, and filtered to separate to obtain calcium sulfate product and liquid after precipitation. ;

[0013] 5) The liquid after precipitation Calcium chloride is used to adjust the chloride ion concentration, and Cl - The common ion effect promotes Na + Sodium chloride is crystallized and separated by filtration to obtain sodium chloride product and crystallization mother liquor. ; The crystallization mother liquor Returns for sulfate transformation.

[0014] The method for treating industrial waste salt provided by the present invention first heats the industrial waste salt and stirs it to make it dissolve close to or reach saturation, and then uses sulfate to adjust the SO4 in the solution system by taking advantage of the relatively low solubility of potassium sulfate. 2- Concentration, using SO4 2- The common ion effect promotes K + The potassium sulfate product is recovered by non-evaporative crystallization in the form of potassium sulfate, and the ammonium chloride product can be recovered by directly cooling the precipitated liquid. The ammonium chloride product can be recovered by using calcium chloride as a sulfate conversion agent in the crystallized liquid to convert sulfate into calcium sulfate precipitate with lower solubility, thereby separating and obtaining the calcium sulfate product. Calcium chloride is continuously added to the precipitated liquid as a non-evaporative crystallization agent to significantly increase the chloride ion concentration in the solution system. - The common ion effect of ions forces the sodium chloride to be crystallized out without evaporation, and the sodium chloride crystals are separated, while the crystallization mother liquor is mainly calcium chloride solution, which can be recycled. This method realizes the comprehensive resource utilization of industrial waste salt.

[0015] In the method for treating industrial waste salt provided by the present invention, calcium chloride is used as both a sulfate conversion agent and a non-evaporation crystallization agent for sodium chloride, and the calcium chloride remaining in the non-evaporation crystallization mother liquor can be recycled for sulfate conversion, so that the effect of calcium chloride is maximized while avoiding the generation of waste liquid.

[0016] As a preferred solution, the industrial waste salt is dissolved at a temperature of 25-65° C. to obtain a nearly saturated solution or a saturated solution at the temperature. Making the industrial salt into a saturated or nearly saturated solution is beneficial to the subsequent non-evaporative crystallization process of various salts.

[0017] As a preferred solution, the nearly saturated salt solution or saturated salt solution is adjusted by sulfate to meet the concentration of sulfate ions SO4 2- / Cl - The molar ratio is 0.5~0.6. When the nearly saturated salt solution or saturated salt solution contains K + When adjusting SO4 2- / Cl - The molar ratio is ≥0.5, SO4 can be used 2- The common ion effect promotes K +Of course, the addition of sulfate is mainly used to consume the calcium ions in the calcium chloride required for the non-evaporative crystallization of sodium chloride. Therefore, SO4 2- / Cl - The molar ratio is preferably controlled at 0.5~0.6.

[0018] As a more preferred solution, the sulfate includes sodium sulfate and / or ammonium sulfate. The use of sodium sulfate or ammonium sulfate can avoid the introduction of new impurity metal ions. The sulfate is added in solid form, or dissolved in water to form a solution containing sodium sulfate and / or ammonium sulfate.

[0019] As a preferred solution, when the industrial waste salt contains organic impurities and / or other inorganic impurities, it is necessary to perform impurity removal pretreatment, and the impurity removal pretreatment includes at least one of the following methods:

[0020] When the industrial waste salt contains organic impurities, the industrial waste salt is subjected to pyrolysis or oxidation treatment;

[0021] When the industrial waste salt contains insoluble inorganic impurities, filtering the nearly saturated solution or saturated solution formed by dissolving the industrial waste salt;

[0022] When the industrial waste salt contains water-soluble inorganic impurities, the near-saturated solution or saturated solution formed by dissolving the industrial waste salt is subjected to anion impurity removal treatment and cationic impurity removal treatment: the anion impurity removal treatment process is: adding iron salt and / or aluminum salt, and adjusting the pH of the solution system to 3.5-6.5, stirring for 0.5-1.5h, and removing anion impurities including phosphate and silicate; the cationic impurity removal treatment process is: using lime-soda method to remove Mg 2+ , Fe 3+ , Mn 2+ 、Zn 2+ and Cu 2+ After adding iron salt and / or aluminum salt, phosphate in the solution is precipitated as iron phosphate or aluminum phosphate, while silicate is precipitated as iron silicate or aluminum silicate. The amount of iron salt and / or aluminum salt added is 1 to 1.5 times the stoichiometric amount. The iron salt and aluminum salt are preferably at least one of iron sulfate, aluminum sulfate, iron nitrate, and aluminum nitrate. Use lime-soda method to remove Mg 2+ , Fe 3+ , Mn 2+ 、Zn 2+ and Cu 2+ After removing the cationic impurities, the pH of the solution system was adjusted to 6~8 with hydrochloric acid.

[0023] As a preferred solution, the cooling crystallization temperature is below 15°C. The crystallization temperature should not be too low. Generally, 5 to 15°C is more suitable, and 10 to 15°C is more preferred.

[0024] As a preferred solution, the conditions for the sulfate transformation are: calcium chloride is added in an amount to adjust Ca 2+ / SO4 2- The molar ratio is ≥ 1, the temperature is 25-95°C, and the time is 0.25-2.5h. The sulfate conversion process is to convert calcium chloride and soluble sulfate into calcium sulfate precipitate and soluble chloride salt. The calcium sulfate precipitate can be one or more of calcium sulfate dihydrate, calcium sulfate hemihydrate, and anhydrous calcium sulfate. The further preferred temperature is 40-80°C.

[0025] As a preferred solution, the precipitation solution is adjusted to a CaCl2 concentration of 1 to 10 mol / L using calcium chloride. When the CaCl2 concentration reaches above 1 mol / L, the precipitation solution is treated with Cl - The common ion effect of ions promotes the efficient precipitation of sodium ions in the form of sodium chloride. The temperature for non-evaporative crystallization of sodium chloride is preferably 25-125°C, and more preferably room temperature, such as 25°C.

[0026] As a preferred solution, the sodium chloride crystals precipitated from the crystallization are washed with a saturated sodium chloride solution at 25-65° C. During the washing process, the solid-liquid ratio is 1:0.5-5 g / mL and the washing time is 0.25-2.5 h. The washing solution can be used repeatedly until the impurities therein are enriched to a level close to affecting the quality of the sodium chloride product, and then the solution is opened and returned to be used as a dissolving solution for industrial waste salt.

[0027] Compared with the prior art, the technical solution of the present invention has the following advantages and effects:

[0028] The present invention ingeniously uses cheap calcium chloride as a scavenger in the process of treating industrial waste salt. The calcium chloride is used as a sulfate conversion agent and a non-evaporative crystallization agent for sodium chloride. At the same time, the calcium chloride in the non-evaporative crystallization mother liquor is returned for sulfate conversion, thereby realizing recycling and maximizing the effect of calcium chloride.

[0029] The present invention can sequentially separate products such as potassium sulfate, ammonium chloride, calcium sulfate and sodium chloride from the process of industrial waste salt treatment, thus realizing the comprehensive resource utilization of industrial waste salt.

[0030] The present invention can completely adsorb trace organic matter remaining after pyrolysis of industrial waste salt during the calcium sulfate precipitation process, and the obtained precipitated calcium sulfate can completely decompose the adsorbed trace organic matter after calcination, thereby eliminating the worries about the comprehensive utilization of industrial waste salt resources.

[0031] The grade of the refined sodium chloride obtained from the industrial waste salt of the present invention is ≥99.5%, reaching the quality standard of the superior refined industrial salt, and the grade of the by-product calcium sulfate product is above 98%. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with examples. The following examples are intended to illustrate the present invention rather than to further limit the present invention.

[0033] Example 1

[0034] First, add water to the industrial waste salt containing 25.46% NaCl and 74.28% Na2SO4 produced by the metallurgical enterprise, stir and heat to dissolve, and prepare a nearly saturated solution at 65°C. Then add 0.1 mol / L ferric sulfate solution, adjust the solution pH to 4.3, stir at constant temperature for 1 hour, filter to remove anionic impurities such as phosphorus and silicon, and then add Ca to the filtrate. 2+ / CO3 2- A mixture of lime milk and sodium carbonate in a molar ratio of 1:1 was adjusted to pH 10.5, stirred for 0.5 h, filtered to remove cationic impurities such as calcium, magnesium, iron, copper, and zinc, and then the purified liquid was heated to 75 ° C and the Ca 2+ / SO4 2- The molar ratio is 1.3. 20% calcium chloride solution is added to the purified liquid with stirring for 1 hour to transform the sodium sulfate therein. The calcium sulfate dihydrate product with a purity of 99.4% and its precipitated liquid are obtained by filtration, washing and drying. Calcium chloride is then added to the precipitated liquid to raise the CaCl2 concentration to 1.5 mol / L. - The common ion effect produced by the ions forces the sodium chloride in the solution to selectively crystallize and precipitate without evaporation and concentration, and then is filtered, washed (using a saturated sodium chloride solution at 65°C for washing, with a solid-liquid ratio of 1:2 g / mL and a washing time of 1 h), and dried to obtain a refined sodium chloride product with a purity of 99.7%. The obtained non-evaporable crystallization mother liquor of sodium chloride is returned and used as a transformation liquid for sodium sulfate, so that calcium chloride can be used as both a transformation agent for sodium sulfate and a non-evaporable crystallization agent for sodium chloride in the process of treating industrial waste salt.

[0035] Example 2

[0036] Take the industrial waste salt produced by the pharmaceutical company, which contains 65.32% NaCl, 34.57% Na2SO4 and a small amount of organic matter, first pyrolyze it to remove the organic matter, then add water, stir and heat it to make it dissolve nearly saturated at 50℃, filter out insoluble impurities, and add saturated sodium sulfate solution to the filtrate to remove SO4 2- / Cl - The molar ratio of Ca 2+ / SO4 2-The molar ratio is 1.1, and 30% calcium chloride solution is added to the solution with stirring for 1.5 hours to transform the sodium sulfate therein, and the precipitated calcium sulfate and its precipitated liquid are filtered. The precipitated calcium sulfate is then washed, dried, and calcined to completely decompose the trace organic matter adsorbed during the precipitation process to obtain an anhydrous calcium sulfate product with a purity of 98.7%, and then calcium chloride is continued to be added to the obtained precipitated liquid to increase the CaCl2 concentration to 2.8 mol / L. No evaporation and concentration are required. Cl - The common ion effect produced by the ions forces the sodium chloride in the solution to selectively crystallize and precipitate, which is then filtered, washed (using a saturated sodium chloride solution at 50°C, with a solid-liquid ratio of 1:2.5 g / mL and a washing time of 1.5 h), and dried to obtain a refined sodium chloride product with a purity of 99.5%. The obtained sodium chloride non-evaporated crystallization mother liquor is returned and used as a transformation liquid for sodium sulfate.

[0037] Example 3

[0038] First, add water to the industrial waste salt produced by the chemical industry, which contains 66.65% NaCl, 23.46% KCl, and 9.63% NH4Cl, stir and dissolve it at high temperature to make a nearly saturated solution at 60°C, and then add ammonium sulfate to the filtrate to remove SO4 2- / Cl - The molar ratio was adjusted to 0.56, using SO4 2- The common ion effect produced forces the K + Selectively precipitate in the form of K2SO4, filter to obtain potassium sulfate crystals and its precipitated liquid, cool the precipitated liquid to 15℃ to crystallize ammonium chloride, filter to obtain ammonium chloride crystals and its crystallized liquid, and then press Ca 2+ / SO4 2- The molar ratio is 1.01. A 25% calcium chloride solution is added to the obtained crystallized liquid with stirring and heating to 60°C. The stirring time is 1.0h to transform the sodium sulfate therein. The precipitated calcium sulfate and its precipitated liquid are filtered. The precipitated calcium sulfate is then washed and dried to obtain a dihydrate calcium sulfate product with a purity of 99.3%. Calcium chloride is then added to the obtained precipitated liquid to raise the CaCl2 concentration to 3.2mol / L. No evaporation and concentration are required. Cl - The common ion effect produced by the ions forces the sodium chloride in the solution to selectively crystallize and precipitate, which is then filtered, washed (using a saturated sodium chloride solution at 60°C, with a solid-liquid ratio of 1:2.5 g / mL and a washing time of 1.0 h), and dried to obtain a refined sodium chloride product with a purity of 99.3%. The obtained sodium chloride non-evaporated crystallization mother liquor is returned and used as a transformation liquid for sodium sulfate.

Claims

1. A method for treating industrial waste salt with calcium chloride, characterized in that: The following steps are involved: 1) Dissolve industrial waste salt to obtain a nearly saturated salt solution or a saturated salt solution; The industrial waste salt comprises sodium salt, or comprises sodium salt and potassium salt and / or ammonium salt, and the anions in the sodium salt, potassium salt and ammonium salt comprise Cl - , or contains SO4 2- and Cl - ; 2) The nearly saturated salt solution or saturated salt solution uses sulfate to adjust the sulfate ion concentration to meet the SO4 2- / Cl - The molar ratio is ≥0.5, and SO4 2- The common ion effect promotes K + Potassium sulfate is precipitated and filtered to obtain potassium sulfate product and precipitated liquid. ; When the nearly saturated salt solution or the saturated salt solution does not contain K + When the sulfate ion concentration is adjusted, there is no need to filter and separate the potassium sulfate product, and the process directly proceeds to step 3); 3) The liquid after precipitation Through cooling crystallization and filtration separation, the ammonium chloride product and the crystallized liquid are obtained. ; After precipitation, the liquid Does not contain NH4 + When , do not proceed to step 3); 4) The crystallized liquid Calcium chloride is used to achieve sulfate transformation, and filtered to separate to obtain calcium sulfate product and liquid after precipitation. ; 5) The liquid after precipitation Calcium chloride is used to adjust the chloride ion concentration, and Cl - The common ion effect promotes Na + Sodium chloride is crystallized and separated by filtration to obtain sodium chloride product and crystallization mother liquor. ; The crystallization mother liquor Returns for sulfate transformation.

2. A method for treating industrial waste salt with calcium chloride according to claim 1, characterized in that: The industrial waste salt is dissolved at a temperature of 25-65° C. to obtain a nearly saturated solution or a saturated solution at the temperature.

3. A method for treating industrial waste salt with calcium chloride according to claim 1 or 2, characterized in that: The nearly saturated salt solution or saturated salt solution is adjusted by sulfate to meet the concentration of sulfate ions SO4 2- / Cl - The molar ratio = 0.5~0.

6.

4. A method for treating industrial waste salt with calcium chloride according to claim 3, characterized in that: The sulfate includes sodium sulfate and / or ammonium sulfate.

5. A method for treating industrial waste salt with calcium chloride according to claim 1, characterized in that: When the industrial waste salt contains organic impurities and / or other inorganic impurities, it is necessary to perform impurity removal pretreatment, and the impurity removal pretreatment includes at least one of the following methods: When the industrial waste salt contains organic impurities, the industrial waste salt is subjected to pyrolysis or oxidation treatment; When the industrial waste salt contains insoluble inorganic impurities, filtering the nearly saturated solution or saturated solution formed by dissolving the industrial waste salt; When the industrial waste salt contains water-soluble inorganic impurities, the near-saturated solution or saturated solution formed by dissolving the industrial waste salt is subjected to anion impurity removal treatment and cationic impurity removal treatment: the anion impurity removal treatment process is: adding iron salt and / or aluminum salt, and adjusting the pH of the solution system to 3.5-6.5, stirring for 0.5-1.5h, and removing anion impurities including phosphate and silicate; the cationic impurity removal treatment process is: using lime-soda method to remove Mg 2+ , Fe 3+ , Mn 2+ 、Zn 2+ and Cu 2+ Cationic impurities included.

6. A method for treating industrial waste salt with calcium chloride according to claim 1, characterized in that: The temperature of the cooling crystallization is below 15°C.

7. A method for treating industrial waste salt with calcium chloride according to claim 1, characterized in that: The conditions for the sulfate transformation are: calcium chloride is added in an amount to adjust the Ca 2+ / SO4 2- The molar ratio is ≥1, the temperature is 25~95℃, and the time is 0.25~2.5h.

8. A method for treating industrial waste salt with calcium chloride according to claim 1, characterized in that: The post-precipitation liquid Calcium chloride was used to adjust the CaCl2 concentration to 1-10 mol / L.

9. A method for treating industrial waste salt with calcium chloride according to claim 1, characterized in that: The sodium chloride crystals precipitated by the crystallization are washed with a saturated sodium chloride solution at 25-65° C. During the washing process, the solid-liquid ratio is 1:0.5-5 g / mL and the washing time is 0.25-2.5 h.

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