Method for cooperatively treating chromium-containing sludge and waste sulfuric acid and recycling chromium-containing sludge and waste sulfuric acid

Abstract

The invention discloses a method for co-processing chromium-containing sludge and waste sulfuric acid and recycling the chromium-containing sludge and the waste sulfuric acid, which comprises the following steps: S1, sieving the chromium-containing sludge to remove impurities, mixing a strong acid solution formed by mixing the waste sulfuric acid and concentrated sulfuric acid with the chromium-containing sludge for acid dissolution, and filtering to obtain a trivalent chromium-containing solution; s2, NaOH is added into the solution containing trivalent chromium to adjust the pH value to be alkaline, then an oxidizing agent is added for an oxidation reaction, and a solution containing hexavalent chromium is obtained; s3, adding Na2CO3 into the hexavalent chromium-containing solution for neutralization, and filtering to obtain a sodium chromate-containing solution; and S4, carrying out vacuum evaporative crystallization on the solution containing sodium chromate to obtain sodium chromate crystals. According to the method, the chromium-containing sludge and the waste sulfuric acid are subjected to cooperative treatment, and the purposes of harmlessness and recycling of the multi-source hazardous waste are achieved.

Description

Technical Field

[0001] The invention relates to the field of harmless treatment and resource utilization of industrial hazardous wastes, and in particular to a method for collaboratively treating chromium-containing sludge and waste sulfuric acid and for resource utilization. Background Art

[0002] Chromium-containing sludge is a type of highly toxic and carcinogenic hazardous waste produced by the treatment of chromium-containing wastewater in industrial production processes. It mainly comes from the treatment of chromium-containing wastewater in industries such as metallurgy, electroplating, chemical industry, chromium salts, and leather. The composition of chromium-containing sludge fluctuates greatly with the raw materials and production processes. For example, the chromium-containing sludge in steel enterprises mainly comes from the production and processing of stainless steel. The chromate passivation of cold rolling units such as electrogalvanizing, hot-dip galvanizing, and electrotinning produces a large amount of chromium-containing sludge during the treatment of chromium-containing wastewater. After being pressed and filtered into cakes, the moisture content of chromium-containing sludge is generally 50% to 65%, and the Cr mass content is 0.5% to 25% (such as chromium hydroxide, etc.). Other main components are calcium sulfate, calcium sulfite, Zn, Pt, Fe and other elements.

[0003] Chromium salt is one of the important inorganic chemical products, and its series of products are a type of chemical raw materials that my country focuses on developing. Chromium salt series products are needed in many industries such as advanced alloy materials, electroplating, leather, pigments, spices, printing and dyeing, ceramics, anti-corrosion, catalysis, and medicine. Chromium salt is listed as one of the most competitive resource raw materials in the world. my country's chromium salt production capacity accounts for about 40% of the global output, making it the world's largest producer of chromium salt. Chromium salts mainly include chromic anhydride, sodium chromate, basic chromium sulfate, chromium oxide green, metallic chromium, etc., which are widely used in the fields of chemical industry, refractory materials, and metal materials. Therefore, there are still deficiencies in the existing harmless disposal and resource utilization of chromium-containing sludge. It is of great significance to develop the recovery and effective utilization of chromium salts in chromium-containing sludge.

[0004] At present, the harmless disposal processes of chromium-containing sludge mainly include reagent stabilization, cement kiln co-disposal, remetallurgical sintering and high-temperature melting disposal, etc. Stabilized safe landfill has the disadvantage of occupying a large amount of land, cement kiln co-disposal has strict restrictions on the chromium-containing sludge entering the kiln, remetallurgical sintering disposal does not make full use of chromium salt resources, and high-temperature melting disposal consumes a lot of energy and has difficulty in using by-products.

[0005] In view of the above situation, it is urgent to develop a method for treating chromium-containing sludge, which can solve the problem of chromium-containing sludge disposal in a harmless and resource-based manner and realize the high-value utilization of chromium-containing sludge. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for the coordinated treatment and resource utilization of chromium-containing sludge and waste sulfuric acid, which can achieve the purpose of harmless treatment and resource utilization of multi-source hazardous wastes.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] The first aspect of the present invention provides a method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them, comprising the following steps:

[0009] S1, after the chromium-containing sludge is sieved to remove impurities, a strong acid solution of waste sulfuric acid and concentrated sulfuric acid is mixed with the chromium-containing sludge for acid dissolution, and a solution containing trivalent chromium is obtained after filtering;

[0010] S2, adding NaOH to the solution containing trivalent chromium to adjust the pH value to alkaline, and then adding an oxidant to carry out an oxidation reaction to obtain a solution containing hexavalent chromium;

[0011] S3, adding Na2CO3 to the solution containing hexavalent chromium for neutralization to obtain a solution containing sodium chromate;

[0012] S4, subjecting the solution containing sodium chromate to vacuum evaporation crystallization to obtain sodium chromate crystals.

[0013] Preferably, in step S1:

[0014] The mass fraction of sulfuric acid in the waste sulfuric acid is 5 to 10%;

[0015] The mass fraction of sulfuric acid in the concentrated sulfuric acid is 5 to 30%;

[0016] In the strong acid solution, the mass fraction of sulfuric acid is ≥10%;

[0017] The solid-to-liquid ratio of the chromium-containing sludge to the strong acid solution is 1:5-20.

[0018] Preferably, in step S1, the acid dissolution temperature is 20-80° C., and the acid dissolution time is 20-100 min.

[0019] Preferably, in step S2:

[0020] The NaOH adjusts the solution containing trivalent chromium to a pH of 8 to 10;

[0021] The oxidant is hydrogen peroxide or ozone;

[0022] The amount of the oxidant added is 1 to 5 times the theoretical calculated value of oxidizing trivalent chromium to hexavalent chromium;

[0023] In the oxidation reaction, the reaction temperature is 30 to 90° C. and the reaction time is 30 to 100 minutes.

[0024] Preferably, in step S3, the amount of Na2CO3 used is 0.5% to 10% of the mass of the solution containing hexavalent chromium.

[0025] Preferably, in step S4, during the vacuum evaporation crystallization process, the evaporation rate is controlled to be 140±10 mL / h and the crystallization temperature is controlled to be 90±5°C.

[0026] Preferably, during the vacuum evaporation crystallization, seed crystals are added to the solution containing sodium chromate.

[0027] Preferably, in step S4, the mass fraction of sodium chromate in the sodium chromate crystals is ≥98%, and the average particle size is 150-300 μm.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention extracts chromium-containing sludge with waste sulfuric acid and sulfuric acid mixed solution, adds alkali to adjust the pH of the extract, and then adds an oxidant for oxidation, and then separates Na2CrO4 crystals from Na2CrO4-NaOH-H2O by vacuum evaporation and crystallization. The method of the present invention is low-cost and highly reliable, and achieves the purpose of harmlessness and resource utilization of multi-source hazardous wastes.

[0030] 2. The present invention can solve the problem of chromium-containing sludge disposal in a harmless and resource-based manner. The method of the present invention has low cost and high reliability. It can also coordinate the disposal of waste sulfuric acid and realize the high-value utilization of chromium-containing sludge. It is an effective method for "turning waste into treasure" for solid hazardous waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a schematic flow chart of the method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0033] Combination Figure 1 As shown, the present invention provides a method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them, comprising the following steps:

[0034] S1, after the chromium-containing sludge is sieved to remove impurities, a strong acid solution of waste sulfuric acid and concentrated sulfuric acid is mixed with the chromium-containing sludge for acid dissolution, and a solution containing trivalent chromium is obtained after filtering;

[0035] The chromium-containing sludge is sieved (5 mm) to remove impurities, and a strong acid solution (mass fraction of sulfuric acid ≥ 10%) of waste sulfuric acid (mass fraction of sulfuric acid 5-10%) and concentrated sulfuric acid (mass fraction of sulfuric acid 5-30%) are mixed with the chromium-containing sludge for acid dissolution to dissolve the chromium-containing sludge, and a solution containing trivalent chromium is obtained after filtering;

[0036] In the above process, the chromium-containing sludge is mixed with a strong acid solution at a solid-liquid ratio of 1:5 to 20, the acid dissolution temperature is 20 to 80°C, and the acid dissolution time is 20 to 100 minutes.

[0037] S2, adding NaOH to the solution containing trivalent chromium to adjust the pH value to alkaline, and then adding an oxidant to carry out an oxidation reaction to obtain a solution containing hexavalent chromium;

[0038] In this step, NaOH is added to the solution containing trivalent chromium to adjust the pH value to alkaline, at which time the pH value of the solution is 8 to 10, and then an oxidant is added to carry out an oxidation reaction. The oxidant used is hydrogen peroxide or ozone, and the amount of the oxidant added is 1 to 5 times the theoretical calculated value of oxidizing trivalent chromium to hexavalent chromium; in the oxidation reaction, the reaction temperature is 30 to 90° C., and the reaction time is 30 to 100 minutes.

[0039] S3, adding Na2CO3 to the solution containing hexavalent chromium for neutralization, and filtering to obtain a solution containing sodium chromate;

[0040] In this step, Na2CO3 is added to the solution containing hexavalent chromium for neutralization, CO3 2+ After combining with the residual Fe, Ca, Mg and other metal ions in the solution, Cr is precipitated in the form of sodium chromate, and a solution containing sodium chromate is obtained after filtration, and the solution also contains sodium hydroxide and sodium sulfate. In the above process, the amount of Na2CO3 used is 0.5% to 10% of the mass of the solution containing hexavalent chromium.

[0041] S4, subjecting the solution containing sodium chromate to vacuum evaporation crystallization to obtain sodium chromate crystals.

[0042] In this step, the solution containing sodium chromate is subjected to vacuum evaporation crystallization, the evaporation rate is controlled to be 140±10mL / h, the crystallization temperature is controlled to be 90±5°C, and sodium chromate crystals are obtained with or without adding seed crystals;

[0043] In the sodium chromate crystals obtained above, the mass fraction of sodium chromate is ≥98%, and the average particle size is 150-300 μm.

[0044] Example 1

[0045] The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them is as follows:

[0046] (1) 1 part of waste sulfuric acid (sulfuric acid mass fraction 10%) was mixed with 1 part of sulfuric acid solution with a mass fraction of 14% to obtain a mixed sulfuric acid solution with a concentration of 12%. The chromium-containing sludge and the sulfuric acid solution were oscillated and mixed at a solid-liquid ratio of 1:15 for 40 minutes, the temperature was controlled at 40° C., and a chromium (III)-containing solution was obtained after filtration.

[0047] (2) NaOH solution (mass fraction 2%) was added to the chromium (III)-containing filtrate to adjust the pH to 8-9, and H2O2 was slowly added in an amount three times the theoretical calculated amount. The reaction temperature was controlled at 40°C and the reaction time was 40 min to obtain a solution containing Cr(VI). The measured Cr(VI) conversion rate was 97.5%.

[0048] (3) adding 2% by weight of Na2CO3 to a solution containing Cr(VI) to neutralize the solution, separating the residual metal ions Fe, Ca, and Mg in the solution in the form of precipitation, and filtering to obtain a solution containing sodium chromate, which also contains sodium hydroxide and sodium sulfate;

[0049] (4) The solution containing sodium chromate was crystallized by vacuum evaporation, with the evaporation rate controlled at 140 mL / h and the crystallization temperature at 90° C. without adding seed crystals, to obtain sodium chromate crystals with a mass fraction of 98.2% and an average crystal size of 150 μm.

[0050] Example 2

[0051] The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them is as follows:

[0052] (1) 1 part of waste sulfuric acid (sulfuric acid mass fraction 6%) was mixed with 2 parts of sulfuric acid solution with a mass fraction of 15% to obtain a mixed sulfuric acid solution with a concentration of 12%. The chromium-containing sludge and the sulfuric acid solution were oscillated and mixed at a solid-liquid ratio of 1:18 for 60 minutes, the temperature was controlled at 60° C., and a chromium (III)-containing solution was obtained after filtration.

[0053] (2) NaOH solution (mass fraction 2%) was added to the chromium (III)-containing filtrate to adjust the pH to 8-9, and H2O2 was slowly added in an amount 2.5 times the theoretical calculated amount. The reaction temperature was controlled at 60°C and the reaction time was 60 min to obtain a solution containing Cr(VI). The measured Cr(VI) conversion rate was 98.5%.

[0054] (3) adding 5.0% by weight of Na2CO3 to a solution containing Cr(VI) to neutralize the solution, separating the residual metal ions Fe, Ca, and Mg in the solution in the form of precipitation, and filtering to obtain a solution containing sodium chromate, which also contains sodium hydroxide and sodium sulfate;

[0055] (4) The sodium chromate solution was subjected to vacuum evaporation crystallization with an evaporation rate of 140 mL / h and a crystallization temperature of 90° C., and sodium chromate seed crystals were added to obtain sodium chromate crystals with a mass fraction of 98.4% and an average crystal size of 300 μm.

[0056] Example 3

[0057] The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them is as follows:

[0058] (1) 1 part of waste sulfuric acid (sulfuric acid mass fraction 8%) was mixed with 1 part of sulfuric acid solution with a mass fraction of 17% to obtain a mixed sulfuric acid solution with a concentration of 14%. The chromium-containing sludge and the sulfuric acid solution were oscillated and mixed at a solid-liquid ratio of 1:20 for 80 minutes, the temperature was controlled at 80° C., and a chromium (III)-containing solution was obtained after filtration.

[0059] (2) NaOH solution (mass fraction 2%) was added to the chromium (III)-containing filtrate to adjust the pH to 8-9, and ozone was slowly added in an amount of 4 times the theoretical calculated amount. The reaction temperature was controlled at 80° C. and the reaction time was 80 min to obtain a solution containing Cr(VI). The measured Cr(VI) conversion rate was 98.6%.

[0060] (3) adding 7.5% by weight of Na2CO3 to a solution containing Cr(VI) to neutralize the solution, separating the residual metal ions Fe, Ca, and Mg in the solution in the form of precipitation, and filtering to obtain a solution containing sodium chromate, which also contains sodium hydroxide and sodium sulfate;

[0061] (4) The sodium chromate solution was subjected to vacuum evaporation crystallization with an evaporation rate of 140 mL / h and a crystallization temperature of 90° C. without adding seed crystals to obtain sodium chromate crystals with a mass fraction of 98.5% and an average crystal size of 160 μm.

[0062] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them, characterized in that: The following steps are involved: S1, after the chromium-containing sludge is sieved to remove impurities, a strong acid solution of waste sulfuric acid and concentrated sulfuric acid is mixed with the chromium-containing sludge for acid dissolution, and a solution containing trivalent chromium is obtained after filtering; S2, adding NaOH to the solution containing trivalent chromium to adjust the pH value to alkaline, and then adding an oxidant to carry out an oxidation reaction to obtain a solution containing hexavalent chromium; S3, adding Na2CO3 to the solution containing hexavalent chromium for neutralization, and filtering to obtain a solution containing sodium chromate; S4, subjecting the solution containing sodium chromate to vacuum evaporation crystallization to obtain sodium chromate crystals.

2. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 1, characterized in that: In step S1: The mass fraction of sulfuric acid in the waste sulfuric acid is 5 to 10%; The mass fraction of sulfuric acid in the concentrated sulfuric acid is 5 to 30%; In the strong acid solution, the mass fraction of sulfuric acid is ≥10%; The solid-to-liquid ratio of the chromium-containing sludge to the strong acid solution is 1:5-20.

3. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 1, characterized in that: In the step S1, the acid dissolution temperature is 20-80° C., and the acid dissolution time is 20-100 min.

4. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 1, characterized in that: In step S2: The NaOH adjusts the solution containing trivalent chromium to a pH of 8 to 10; The oxidant is hydrogen peroxide or ozone; The amount of the oxidant added is 1 to 5 times the theoretical calculated value of oxidizing trivalent chromium to hexavalent chromium; In the oxidation reaction, the reaction temperature is 30 to 90° C. and the reaction time is 30 to 100 minutes.

5. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 1, characterized in that: In the step S3, the amount of Na2CO3 used is 0.5% to 10% of the mass of the solution containing hexavalent chromium.

6. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 1, characterized in that: In the step S4, during the vacuum evaporation crystallization process, the evaporation rate is controlled to be 140±10 mL / h and the crystallization temperature is controlled to be 90±5°C.

7. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 6, characterized in that: During the vacuum evaporation crystallization, seed crystals are added to the solution containing sodium chromate.

8. The method for collaboratively treating chromium-containing sludge and waste sulfuric acid and recycling them as resources according to claim 1, characterized in that: In the step S4, in the sodium chromate crystals, the mass fraction of sodium chromate is ≥98%, and the average particle size is 150-300 μm.

Images