阅读说明：本技术 一种分离回收氯碱副产盐泥中的钙镁的方法 (Method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud ) 是由 陈云海 邱永劼 周秀 张燕 张梅 于 2021-07-28 设计创作，主要内容包括：一种分离回收氯碱副产盐泥中的钙镁的方法,包括步骤：1)取氯碱副产盐泥,加水得盐泥浆；2)取部分盐泥浆,分为n份；3)取其中一份盐泥浆,加盐酸调节pH至1-2,加入盐泥浆调节pH至6-7,过滤,取滤液,加入硫酸,过滤,得滤液A1和硫酸钙B1；4)取滤液A1,按照步骤3)重复操作,依次得到滤液A2至An-1、硫酸钙B2至Bn-1；5)取滤液An-1,加入最后一份盐泥浆,加盐酸调节pH至1-2,加盐泥浆调节pH至6-7,过滤,取滤液,加入硫酸钠和/或硫酸镁,过滤,得滤液An和硫酸钙Bn；6)滤液An中加入碳酸钠,过滤,得到碳酸镁C1和滤液D1。本发明可满足分别分离回收钙和镁的需求。(A method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud comprises the following steps: 1) taking the byproduct salt slurry of the chlor-alkali, and adding water to obtain salt slurry; 2) taking part of salt slurry, and dividing into n parts; 3) taking one part of the salt slurry, adding hydrochloric acid to adjust the pH to 1-2, adding the salt slurry to adjust the pH to 6-7, filtering, taking the filtrate, adding sulfuric acid, and filtering to obtain filtrate A1 and calcium sulfate B1; 4) taking the filtrate A1, and repeating the operation according to the step 3) to sequentially obtain filtrate A2-An-1 and calcium sulfate B2-Bn-1; 5) taking the filtrate An-1, adding the last part of salt slurry, adding hydrochloric acid to adjust the pH to 1-2, adding the salt slurry to adjust the pH to 6-7, filtering, taking the filtrate, adding sodium sulfate and/or magnesium sulfate, and filtering to obtain filtrate An and calcium sulfate Bn; 6) adding sodium carbonate into the filtrate An, and filtering to obtain magnesium carbonate C1 and filtrate D1. The invention can meet the requirements of separating and recovering calcium and magnesium respectively.)

1. A method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud is characterized by comprising the following steps:

1) taking the byproduct salt slurry of the chlor-alkali, and adding water to dissolve the byproduct salt slurry into slurry to obtain salt slurry;

2) taking part of the salt slurry, dividing the salt slurry into n parts, and taking the rest part of the salt slurry as the salt slurry to be prepared;

3) taking one part of the salt slurry, adding hydrochloric acid to adjust the pH to 1-2, adding part of the standby salt slurry to adjust the pH to 6-7, filtering, taking the filtrate, adding sulfuric acid, and filtering to obtain filtrate A1 and calcium sulfate B1, wherein the molar weight of the added sulfuric acid is less than that of calcium ions in the filtrate;

4) taking the filtrate A1, and repeating the operation according to the step 3) to sequentially obtain filtrate A2 to filtrate An-1 and calcium sulfate B2 to calcium sulfate Bn-1;

5) taking the filtrate An-1, adding the last part of salt slurry, adding hydrochloric acid to adjust the pH to 1-2, adding part of the standby salt slurry to adjust the pH to 6-7, filtering, taking the filtrate, adding sodium sulfate and/or magnesium sulfate until no precipitate is generated, and filtering to obtain filtrate An and calcium sulfate Bn;

6) adding sodium carbonate into the filtrate An until no precipitate is generated, and filtering to obtain magnesium carbonate C1 and filtrate D1;

7) taking the calcium sulfate obtained in each step, washing with water, and drying to obtain a calcium sulfate product;

8) taking the magnesium carbonate C1 obtained in the step 6), washing with water, and drying to obtain a magnesium carbonate product.

2. The method for separating and recovering calcium and magnesium in the chlor-alkali byproduct salt mud of claim 1, wherein the step 2) is to divide part of the salt mud into 4 parts.

3. The method for separating and recovering calcium and magnesium from chlor-alkali by-product salt sludge as claimed in claim 1, wherein the water after washing in step 7) and the water after washing in step 8) are used as the water for dissolving chlor-alkali by-product salt sludge in step 1).

4. The method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt sludge as claimed in claim 1, wherein the concentration of hydrochloric acid added in step 3), step 4) and step 5) is 32%.

5. The method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud as claimed in claim 1, wherein the filtrate D1 obtained in step 6) is used in a chlor-alkali production system.

6. The method for separating and recovering calcium and magnesium in chlor-alkali by-product salt sludge as recited in claim 1, wherein the concentration of sulfuric acid added in step 3) is 78%.

7. The method for separating and recovering calcium and magnesium in chlor-alkali by-product salt sludge as recited in claim 1 or 5, wherein the molar amount of sulfuric acid added in step 3) is 90% of the molar amount of calcium ions in the filtrate.

8. The method for separating and recovering calcium and magnesium in the chlor-alkali byproduct salt mud as claimed in claim 1, wherein the system temperature is 40-80 ℃ after the pH is adjusted to 6-7 in step 3) and step 5).

9. The method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud as claimed in claim 8, wherein the system temperature is 40-60 ℃.

Technical Field

The invention relates to the field of chemical industry, in particular to a method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud.

Background

After the chlor-alkali production enterprises adopt the brine alkali-making process, the byproduct salt mud is obviously increased.

The by-product salt mud mainly comprises calcium carbonate, magnesium hydroxide, sodium chloride and water, and also comprises impurities of iron salt and aluminum salt, wherein the content of calcium (calculated as Ca) is about 19 percent, and the content of magnesium (calculated as Mg) is about 8 percent. At present, most chlor-alkali production enterprises directly carry out landfill treatment according to common solid wastes, thereby causing the waste of resources.

Therefore, how to effectively recycle calcium and magnesium in the chlor-alkali byproduct salt mud is an urgent problem to be solved by those skilled in the art.

Disclosure of Invention

The invention aims to provide a method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud, which has the advantages of simple steps and convenient operation, can gradually increase the contents of magnesium and sodium chloride without heating, evaporating and concentrating, meets the requirements of separating and recovering calcium and magnesium respectively, recovers the obtained sodium chloride filtrate to chlor-alkali production, and effectively reduces chlor-alkali salt consumption.

The technical scheme of the invention is as follows: a method for separating and recovering calcium and magnesium in chlor-alkali byproduct salt mud comprises the following steps:

1) taking the byproduct salt slurry of the chlor-alkali, and adding water to dissolve the byproduct salt slurry into slurry to obtain salt slurry;

2) taking part of the salt slurry, dividing the salt slurry into n parts, and taking the rest part of the salt slurry as the salt slurry to be prepared;

3) taking one part of the salt slurry, adding hydrochloric acid to adjust the pH to 1-2, adding part of the standby salt slurry to adjust the pH to 6-7, filtering, taking the filtrate, adding sulfuric acid, and filtering to obtain filtrate A1 and calcium sulfate B1, wherein the molar weight of the added sulfuric acid is less than that of calcium ions in the filtrate;

4) taking the filtrate A1, and repeating the operation according to the step 3) to sequentially obtain filtrate A2 to filtrate An-1 and calcium sulfate B2 to calcium sulfate Bn-1;

5) taking the filtrate An-1, adding the last part of salt slurry, adding hydrochloric acid to adjust the pH to 1-2, adding part of the standby salt slurry to adjust the pH to 6-7, filtering, taking the filtrate, adding sodium sulfate and/or magnesium sulfate until no precipitate is generated, and filtering to obtain filtrate An and calcium sulfate Bn;

6) adding sodium carbonate into the filtrate An until no precipitate is generated, and filtering to obtain magnesium carbonate C1 and filtrate D1;

7) taking the calcium sulfate obtained in each step, washing with water, and drying to obtain a calcium sulfate product;

8) taking the magnesium carbonate C1 obtained in the step 6), washing with water, and drying to obtain a magnesium carbonate product.

And 2) taking part of the salt slurry, and equally dividing into 4 parts.

And (3) using the water obtained after the washing in the step 7) and the water obtained after the washing in the step 8) as the water for dissolving the chlor-alkali byproduct salt mud in the step 1).

The concentration of the hydrochloric acid added in the steps 3), 4) and 5) is 32 percent.

The filtrate D1 obtained in the step 6) is used for a chlor-alkali production system.

The concentration of the sulfuric acid added in step 3) was 78%.

The molar amount of the sulfuric acid added in the step 3) is 90 percent of the molar amount of the calcium ions in the filtrate.

After the pH value is adjusted to 6-7 in the step 3) and the step 5), the system temperature is 40-80 ℃.

Preferably, the temperature of the system is 40-60 ℃.

Adopt above-mentioned technical scheme to have following beneficial effect:

1. the separation and recovery method of the invention firstly prepares the byproduct salt mud of the chlor-alkali into slurry with water, divides part of the salt mud into n parts, and separates iron ions and aluminum ions in the salt mud by adjusting the pH to 6-7, so that the subsequent filtrate does not contain impurities such as iron ions or aluminum ions and the like, the aim of separating calcium ions and magnesium ions in the filtrate independently is realized, and pure calcium sulfate products and magnesium carbonate products are obtained.

2. According to the separation and recovery method, the salt slurry is added into the filtrate for separating the calcium ions in batches, so that the concentration of the magnesium ions in the salt slurry is gradually increased, and thus when sulfuric acid is subsequently added for separating the calcium ions, the separation efficiency and the separation purity of the calcium ions can be effectively improved, and the defect of high energy consumption in the traditional method for improving the concentration of the magnesium ions by evaporation concentration is overcome.

3. According to the separation and recovery method, the molar weight of sulfuric acid added into the filtrate (separated from iron ions and aluminum ions) obtained in the steps 3) and 4) is less than that of calcium ions in the filtrate, so that the filtrate obtained by filtering contains hydrogen ions, magnesium ions in the filtrate keep an ionic state, the purity of calcium sulfate obtained by separation can be effectively improved, and the loss amount of the magnesium ions is reduced. According to the separation and recovery method, sodium sulfate and/or magnesium sulfate are/is added into the filtrate obtained in the step 5) to replace sulfuric acid, so that the concentration of magnesium ions in the system can be prevented from being reduced, even the concentration of the magnesium ions is effectively improved, the concentration of the magnesium ions is kept at a higher level (3.8-4%), calcium ions in the system are completely separated in a calcium sulfate form, the yield of the calcium ions can be effectively improved, and the purity of subsequently obtained magnesium carbonate is ensured.

4. According to the separation and recovery method, after the pH is adjusted to 6-7 in the steps 3) to 5), the temperature of the system is controlled to be 40-80 ℃, so that the filtering effect and efficiency can be effectively improved, further, the temperature of the system is controlled to be 40-60 ℃, on the basis of meeting the requirement of high-efficiency filtering, the purpose of directly utilizing neutralization heat can be achieved, the temperature rise through an external heating mode is avoided, the energy consumption of separation and recovery is effectively reduced, and the recovery cost of calcium and magnesium in the chlor-alkali byproduct salt mud is further reduced.

5. The concentration of the hydrochloric acid used in the invention is 32%, and the concentration of the sulfuric acid used in the invention is 78%, on the basis of ensuring that the salt in a dissolving system is in an ionic state and separating calcium ions, the concentration of the calcium ions and magnesium ions in the system can be effectively prevented from being reduced, and the purification concentration and yield of the calcium ions and magnesium ions are ensured.

The applicant verifies that the purity of the calcium sulfate hemihydrate separated by the separation and recovery method is higher than 99.0 percent, the yield is higher than 90 percent, and the purity of the magnesium carbonate separated is higher than 98.5 percent, and the yield is higher than 60 percent.

The following is a further description with reference to specific examples.

Detailed Description

In the invention, the used salt mud is a brine refining byproduct, wherein the content of calcium ions is 19 percent, and the content of magnesium ions is 8 percent. The sulfuric acid used was the by-product content (H) of Chongqing Tian Productal chemical Co., Ltd₂SO₄)75 percent of hydrochloric acid is 31 percent of hydrochloric acid (HCl) produced by Chongqing Productal chemical Co. The purity of sodium carbonate is 98 percent in industrial grade and 98 percent in sodium sulfate, and the method is used for denitration of Chongqing Nature chemical Co LtdAnd (4) by-production.

Example 1

1000g of salt slurry is taken, 1000g of washing water is added for pulping, and a first portion of salt slurry is obtained. Adding hydrochloric acid, controlling the pH value at the end point to be 1-2, stirring and reacting for 15min, then adding partial salt slurry, adjusting the pH to be 6-7, performing suction filtration, and separating filter residue and reaction liquid, wherein the leaching rate of calcium and magnesium is 93%. And adding 520g of 75% sulfuric acid into the filtrate, and performing suction filtration to obtain 1400g of calcium sulfate filter cake, 3237g of filtrate and 50g of acid-leached filter residue. And adding 1000g of salt slurry into the filtrate for the second time, supplementing hydrochloric acid until the pH value is 2, reacting for 15min, and adjusting the pH value to be 7 by using the salt slurry. And (4) carrying out suction filtration to obtain 190g of filter residue, adding 530g of sulfuric acid into the filtrate, carrying out suction filtration after reaction to obtain 1500g of calcium sulfate filter cake and 4024g of filtrate. And adding 1000g of salt slurry into the filtrate for three times, supplementing hydrochloric acid until the pH is 2, reacting for 15min, and adjusting the pH to 7 by using the salt slurry. And performing suction filtration to obtain 150g of filter residue, adding 510g of sulfuric acid into the filtrate, performing suction filtration after reaction to obtain 1670g of calcium sulfate filter cake and 4843g of filtrate. Adding 1000g of salt slurry into the filtrate four times, supplementing hydrochloric acid until the pH value is 2, reacting for 15min, and adjusting the pH value to be 7 by using the salt slurry. And (4) carrying out suction filtration to obtain 180g of filter residue, adding 714g of sodium sulfate into the filtrate, carrying out suction filtration after reaction to obtain 1890g of calcium sulfate filter cake and 5118g of filtrate. The magnesium content in the filtrate was 3.93%. 4271g of calcium sulfate filter cake is washed and dried to obtain 2563g of calcium sulfate hemihydrate with 98.67% content and 92% yield. 906g of sodium carbonate is added into the filtrate, filter cake is obtained after the reaction is finished, and 680g of magnesium carbonate sample with 44.01 percent (calculated by MgO) and 56 percent yield is obtained after washing and drying. The filtrate was adjusted to pH 11 with 50% sodium hydroxide and filtered under suction to give 5300g of brine.

Example 2

1000g of salt slurry is taken, 1000g of washing water is added for pulping, and a first portion of salt slurry is obtained. Adding hydrochloric acid, controlling pH value at 1-2 at the end point, stirring for reacting for 18min, adding partial salt slurry, adjusting pH to 6-7, filtering, and separating filter residue and reaction solution, wherein the leaching rate of calcium and magnesium is 94%. 530g of 75% sulfuric acid is added into the filtrate, 1450g of calcium sulfate filter cake is obtained by suction filtration, 3437g of filtrate and 40g of filter residue are obtained by acid leaching. And adding 1000g of salt slurry into the filtrate for the second time, supplementing hydrochloric acid until the pH value is 2, reacting for 15min, and adjusting the pH value to be 7 by using the salt slurry. And performing suction filtration to obtain 200g of filter residue, adding 510g of sulfuric acid into the filtrate, performing suction filtration after reaction to obtain 1440g of calcium sulfate filter cake, and obtaining 4150g of filtrate. And adding 1000g of salt slurry into the filtrate for three times, supplementing hydrochloric acid until the pH is 2, reacting for 15min, and adjusting the pH to 7 by using the salt slurry. And performing suction filtration to obtain 160g of filter residue, adding 540g of sulfuric acid into the filtrate, performing suction filtration after reaction to obtain 1670g of calcium sulfate filter cake and 4843g of filtrate. Adding 1000g of salt slurry into the filtrate four times, supplementing hydrochloric acid until the pH value is 2, reacting for 15min, and adjusting the pH value to be 7 by using the salt slurry. And performing suction filtration to obtain 200g of filter residue, adding 720g of sodium sulfate into the filtrate, performing suction filtration after reaction to obtain 1900g of calcium sulfate filter cake and 5208g of filtrate. The magnesium content in the filtrate was 3.94%. 4371g of washed calcium sulfate filter cake, and 2623g of calcium sulfate hemihydrate, 98.67% content and 93% yield are obtained after drying. 926g of sodium carbonate is added into the filtrate, after the reaction is finished, a filter cake is obtained by suction filtration, and 702g of magnesium carbonate sample with the content of 44.12 percent (calculated by MgO) and the yield of 58 percent is obtained by washing and drying. The filtrate was adjusted to pH 11 by adding 50% sodium hydroxide and filtered under suction to give 5100g of brine.

Example 3

1000g of salt slurry is taken, 1100g of washing water is added for pulping, and a first portion of salt slurry is obtained. Adding hydrochloric acid, controlling pH value at 1-2 at the end point, stirring for reacting for 18min, adding partial salt slurry, adjusting pH to 6-7, filtering, and separating filter residue and reaction solution, wherein the leaching rate of calcium and magnesium is 94%. Adding 515g of 75% sulfuric acid into the filtrate, and performing suction filtration to obtain 1450g of calcium sulfate filter cake, 339g of filtrate and 60g of acid-leached filter residue. And adding 1000g of salt slurry into the filtrate for the second time, supplementing hydrochloric acid until the pH value is 2, reacting for 15min, and adjusting the pH value to be 7 by using the salt slurry. And (3) performing suction filtration to obtain 120g of filter residue, adding 509g of sulfuric acid into the filtrate, performing suction filtration after reaction to obtain 1523g of calcium sulfate filter cake and 3603g of filtrate. And adding 1000g of salt slurry into the filtrate for three times, supplementing hydrochloric acid until the pH is 2, reacting for 15min, and adjusting the pH to 7 by using the salt slurry. And carrying out suction filtration to obtain 180g of filter residue, adding 539g of sulfuric acid into the filtrate, carrying out suction filtration after reaction to obtain 1465g of calcium sulfate filter cake, and obtaining 4299g of filtrate. Adding 1000g of salt slurry into the filtrate four times, supplementing hydrochloric acid until the pH value is 2, reacting for 15min, and adjusting the pH value to be 7 by using the salt slurry. And filtering to obtain 210g of filter residue, adding 785g of sodium sulfate into the filtrate, and filtering to obtain 1833g of calcium sulfate filter cake and 5557g of filtrate after reaction. The magnesium content in the filtrate was 4.08%. 4571g of the calcium sulfate filter cake is washed, 2523g of calcium sulfate hemihydrate is obtained after drying, the content is 98.77%, and the yield is 90%. And adding 952g of sodium carbonate into the filtrate, performing suction filtration after the reaction to obtain a filter cake, washing and drying to obtain 757g of a magnesium carbonate sample with the content of 44.16 percent (calculated by MgO) and the yield of 63 percent. The filtrate was adjusted to pH 11 by the addition of 50% sodium hydroxide and filtered under suction to give 5400g of brine.