阅读说明：本技术 一种含硫酸钠废盐的提纯方法 (Purification method of waste salt containing sodium sulfate ) 是由 张研 刘红雨 王宇斌 马久强 周清云 刘朝晖 于 2021-06-23 设计创作，主要内容包括：本发明提供了一种含硫酸钠废盐的提纯方法,以废水车间蒸发脱盐工序产出的废盐及脱盐浓缩前的原水为主要原料,将溶液温度升至40-45℃至盐分基本全部溶解,过滤除去体系中的大部分有机杂质,再将滤液温度降至5-10℃时,析出硫酸钠盐,离心分离得到的母液排至溴车间提溴分离得到成品溴,结晶盐通过加入纯水重新溶解、降温结晶后得到的重结晶盐。该方法操作简便、节约成本、安全环保,通过重结晶方式最终得到的硫酸钠盐纯度高,色泽好,溶解后的COD值低,均达到合格标准。(The invention provides a purification method of sodium sulfate-containing waste salt, which takes waste salt produced in an evaporation and desalination process of a wastewater workshop and raw water before desalination and concentration as main raw materials, the temperature of the solution is raised to 40-45 ℃ until salt is basically dissolved, most organic impurities in the system are removed by filtration, sodium sulfate is separated out when the temperature of filtrate is reduced to 5-10 ℃, mother liquor obtained by centrifugal separation is discharged to a bromine workshop for bromine extraction and separation to obtain finished bromine, and crystallized salt is obtained by adding pure water for redissolution, cooling and crystallizing. The method is simple and convenient to operate, cost-saving, safe and environment-friendly, the sodium sulfate salt finally obtained by the recrystallization method is high in purity and good in color, and the dissolved COD value is low and reaches the qualified standard.)

1. A purification method of waste salt containing sodium sulfate takes materials discharged from an evaporation and concentration process of a bromine-containing product wastewater treatment workshop as raw materials, and is characterized in that: the method comprises the following steps:

1) adding the raw materials into a washing kettle, adding a certain amount of raw water before evaporation and concentration, starting stirring, opening a steam valve to raise the temperature in the kettle to 40-45 ℃, and stirring and dissolving for 1-2 hours;

2) after most of salt in the kettle is dissolved, filtering to remove organic insoluble substances included in the materials;

3) pumping the filtrate into a washing kettle, starting stirring, introducing a cooling medium to start cooling crystallization, stopping cooling crystallization operation when the temperature of materials in the kettle is reduced to 5-10 ℃, and pumping the materials in the kettle into a centrifugal machine for solid-liquid separation to obtain recrystallized salt;

4) adding the obtained recrystallized salt into a washing kettle again, adding a certain proportion of pure water or tap water, heating to dissolve, cooling to crystallize, collecting the recrystallized salt obtained after centrifugal separation, and discharging the centrifugal mother liquor obtained after each separation into a raw water tank;

5) and (4) carrying out outdoor tedding, weighing and packaging on the collected recrystallized salt to obtain a sodium sulfate salt product.

2. The method for purifying waste salt containing sodium sulfate according to claim 1, characterized in that: in the step 2), the materials in the kettle are pumped into a plate frame machine to be subjected to medium pressure filtration to remove organic insoluble substances in the materials.

3. The method for purifying the waste salt containing sodium sulfate according to claim 2, characterized in that: and 3) pumping the mother liquor containing bromine to a bromine blowing workshop to extract bromine after the step 3).

4. The method for purifying waste salt containing sodium sulfate according to claim 1, characterized in that: in the step 4), the recrystallized salt is added into the washing kettle again, heated and dissolved, and can be directly cooled and crystallized without filtering.

5. The method for purifying waste salt containing sodium sulfate according to claim 1, characterized in that: discharging the centrifugal mother liquor separated in the step 4) into a raw water pool for recrystallization until the chroma and purity of the recrystallized salt reach qualified standards.

6. The method for purifying waste salt containing sodium sulfate according to claim 5, characterized in that: the process of discharging the centrifugal mother liquor into the raw water pool for recrystallization is repeated for 1-2 times.

Technical Field

The invention relates to the technical field of industrial waste salt purification processes, in particular to a purification method of sodium sulfate-containing waste salt.

Background

Sodium sulfate is generated as an intermediate product in the process of preparing the brominated flame retardant, most of the sodium sulfate, a small amount of sodium bromide and a small amount of organic matters in the system are mixed together to be separated as workshop plate frame materials in the process of evaporating, concentrating and desalting waste water, the components of the materials are mixed, and the materials with high chroma are regarded as industrial waste salts.

According to research, three main methods for treating byproduct waste salt in chemical production are known: salt washing method, high-temperature treatment method and soda preparation method. The salt washing method is to wash the byproduct waste salt with saturated alkaline salt solution or organic solvent, and to wash and filter the toxic and harmful organic substances in the waste salt by using the principle of similarity and intermiscibility. The method is only suitable for the byproduct salt slag with single component and low content of toxic and harmful organic substances, but secondary pollution such as organic solvent, washing water and the like also occurs in the treatment process. Meanwhile, the content of toxic and harmful chemical substances in the secondary salt is generally not fixed, so that the addition amount and the cyclic application batch of the organic solvent or the alkali washing water are difficult to control. The high-temperature treatment method is to roast waste salt at a high temperature of not less than 500 ℃, and the used incineration equipment is generally a fluidized bed furnace, a rotary kiln and the like. At high temperature, a small amount of organic matters contained in the waste salt can be decomposed into gas, so that the removal effect is achieved. The most difficult problems of this method are: the salt is easy to melt, ring and block at high temperature (higher than the melting point of the salt), so that the equipment cannot normally rotate, and the additional treatment cost is too high, so that the industrialization is difficult to realize. The soda process is to prepare saturated waste salt solution and then to add nitrogen, solid ammonium carbide or carbon dioxide under certain conditions. After reacting for a period of time, sodium bicarbonate solid is separated out, and the sodium carbonate is prepared at high temperature after separation and washing. The main component of the separated mother liquor is ammonium chloride, and after freezing and precipitation, the ammonium chloride is put into the alkali preparation process for recycling.

The three methods introduced above are not suitable for treating industrial by-product sodium sulfate, namely, the treatment cost is too high, the occupied area is large, or the actual operation problem is complicated, so that the process for purifying sodium sulfate, which is simple and convenient to operate, saves cost, is safe and environment-friendly, is especially important.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for purifying sodium sulfate-containing waste salt, which is simple and convenient to operate, cost-saving, safe and environment-friendly.

Based on the problems, the technical scheme provided by the invention is to provide a purification method of waste salt containing sodium sulfate, which takes materials discharged from an evaporation and concentration process in a bromine-based product wastewater treatment workshop as raw materials and comprises the following steps:

1) adding the raw materials into a washing kettle, adding a certain amount of raw water before evaporation and concentration, starting stirring, opening a steam valve to raise the temperature in the kettle to 40-45 ℃, and stirring and dissolving for 1-2 hours;

2) after most of salt in the kettle is dissolved, filtering to remove organic insoluble substances included in the materials;

3) pumping the filtrate into a washing kettle, starting stirring, introducing a cooling medium to start cooling crystallization, stopping cooling crystallization operation when the temperature of materials in the kettle is reduced to 5-10 ℃, and pumping the materials in the kettle into a centrifugal machine for solid-liquid separation to obtain recrystallized salt;

4) adding the obtained recrystallized salt into a washing kettle again, adding a certain proportion of pure water or tap water, heating to dissolve, cooling to crystallize, collecting the recrystallized salt obtained after centrifugal separation, and discharging the centrifugal mother liquor obtained after each separation into a raw water tank;

5) and (4) carrying out outdoor tedding, weighing and packaging on the collected recrystallized salt to obtain a sodium sulfate salt product.

In the step 2), the materials in the kettle are pumped into a plate frame machine to be filtered under the medium pressure so as to remove organic insoluble substances in the materials.

And 3) after the step 3), pumping the bromine-containing mother liquor to a bromine blowing workshop to extract bromine.

In the step 4), the recrystallized salt is added into the washing kettle again, heated and dissolved, and can be directly cooled and crystallized without filtering.

Further, discharging the centrifugal mother liquor after each separation in the step 4) into a raw water pool for recrystallization until the chroma and purity of the recrystallized salt reach qualified standards.

Furthermore, the process of discharging the centrifugal mother liquor into the raw water pool for recrystallization is repeated for 1-2 times. The invention has the advantages and beneficial effects that:

according to the invention, a sodium sulfate product with qualified chromaticity and purity is finally obtained according to the principle that the solubility of sodium sulfate is firstly increased and then decreased along with the temperature, the temperature of the solution is only required to be increased to 40-45 ℃, the salt in the solution is basically completely dissolved, most organic impurities in the system can be removed through filtration, most sodium sulfate in the filtrate can be separated out when the temperature of the filtrate is decreased to 5-10 ℃ according to the solubility difference of sodium sulfate, and the bromine content of centrifugal mother liquor obtained through solid-liquid separation is more than or equal to 50 g/l; after pretreatment, discharging the centrifugal mother liquor to a bromine blowing workshop, and extracting bromine to separate to obtain a finished product of bromine; the obtained crystallized salt is re-dissolved by adding pure water, and the recrystallized salt obtained after cooling crystallization has obviously improved chroma and purity, the purity of the sodium sulfate salt finally obtained by recrystallization is not lower than 98 percent, the chroma is white, and the COD value after dissolution is not more than 500 mg/l.

Drawings

FIG. 1 is a schematic diagram of a process for purifying industrial waste salt containing sodium sulfate.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings and examples.

Example 1 a purification process of waste salt containing sodium sulfate, evaporating to desalt and getting solid material, putting into washing kettle and adding a certain amount of raw water, the following steps are carried out in sequence:

(1) heating for dissolution: starting stirring, opening a steam valve to raise the temperature of the materials in the kettle to 45 ℃, and stirring and dissolving for 1 hour;

(2) and (3) filtering and removing impurities: after most of salt of the materials in the kettle is dissolved, a pump is started to convey the materials in the kettle to a plate frame machine for medium pressure filtration to remove organic insoluble substances in the materials, the amount of insoluble floc in filtrate is ensured to be too low, and if the floc is not completely removed, the plate frame filter pressing operation needs to be repeated.

(3) Cooling and crystallizing: the method comprises the steps of pumping plate frame filtrate into a washing kettle again by using a pump, starting stirring, introducing a cooling medium to start cooling crystallization, cooling the material in the kettle to 10 ℃, observing through a sight cup or a sampling cup in the kettle, stopping cooling crystallization after most salt of the material is separated out, conveying the material in the kettle to a centrifugal machine by using the pump to perform solid-liquid separation, packaging and collecting the obtained recrystallized salt, and discharging bromine-containing mother liquor to a bromine blowing workshop by using the pump to extract bromine.

(4) Repeated dissolution, cooling and crystallization: and adding the obtained recrystallized salt into the washing kettle again, adding a certain proportion of pure water or tap water, heating to dissolve, cooling to crystallize, collecting the recrystallized salt obtained after centrifugal separation, and discharging the centrifugal mother liquor obtained after each separation into a raw water tank until the chromaticity and purity of the recrystallized salt reach the qualified standards.

(5) Tedding and packaging: and (3) tedding the collected recrystallized salt outdoors, removing free moisture in the recrystallized salt, weighing and packaging to obtain a sodium sulfate salt product with the purity of 98.5 percent and the chroma of white, wherein the dissolved COD value is 420 mg/l.

While one embodiment of the present invention has been described in detail, the description is only a preferred embodiment of the present invention and should not be taken as limiting the scope of the invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.