Method for improving chromium leaching efficiency of electroplating sludge

Abstract

The invention provides a method for improving the chromium leaching efficiency of electroplating sludge, which comprises the following steps: adding a roasting agent into chromium-containing electroplating sludge, and roasting at 500-1000 DEG C; leaching the roasted material with water, and then filtering and drying; adding a roasting agent into the dried filter residues, and carrying out secondary roasting at 500-1000 DEG C; and washing the material subjected to secondary roasting with water. According to the method, through two-step roasting, water leaching with the specific solid-to-liquid ratio, gradient heating and roasting atmosphere optimization, the leaching rate can be increased to 99% or above and is remarkably higher than that of a traditional method, and the recovery rate and the utilization efficiency of chromium resources are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of electroplating sludge treatment technology, and specifically to a method for improving the chromium leaching efficiency of electroplating sludge. Background Technology

[0002] As a crucial component of the manufacturing industry, the electroplating process generates electroplating sludge, which poses a significant environmental challenge. Electroplating sludge contains high levels of heavy metals, particularly chromium, which, due to its high toxicity and carcinogenicity, poses a serious threat to the environment and human health. Therefore, the effective leaching and recovery of chromium from electroplating sludge is not only necessary for resource recycling but also an essential requirement for environmental protection.

[0003] Traditional chromium leaching methods, such as chemical leaching, typically use strong acids or alkalis as leaching agents. While these methods can leach chromium, they suffer from low efficiency, high costs, and secondary pollution. Especially when treating electroplating sludge, due to its complex composition containing various heavy metals and organic matter, traditional leaching methods often fail to achieve ideal chromium leaching efficiency and may generate large amounts of toxic byproducts, causing secondary environmental pollution.

[0004] In recent years, some improved leaching technologies have been proposed, such as bioleaching and electrochemical leaching. These methods have improved the leaching efficiency of chromium to some extent and reduced costs, but they still have problems such as complex operation, long processing cycles, and high equipment requirements. In addition, these methods often require pretreatment of electroplating sludge in practical applications, which increases the complexity and cost of the treatment process.

[0005] To address the shortcomings of existing technologies, this invention aims to provide a new method for improving the chromium leaching efficiency of electroplating sludge. Summary of the Invention

[0006] A method for improving the chromium leaching efficiency of electroplating sludge includes the following steps: S1: Add calcining agent A to chromium-containing electroplating sludge and calcine it at 500-1000℃; S2: Leach the material after S1 roasting with water, and then filter it; S3: Dry the filter residue obtained in S2; S4: Add calcining agent B to the filter residue dried in S3 and calcinate it again at 500-1000℃; S5: Wash the material obtained from the second roasting in S4 with water.

[0007] Further, the calcining agent A mentioned in S1 is at least one of sodium carbonate, sodium nitrate, or sodium hydroxide, preferably sodium carbonate.

[0008] Furthermore, the chromium content in the chromium-containing electroplating sludge described in S1 is 5~10wt%, and the mass ratio of calcining agent A to the chromium-containing electroplating sludge is (0.1-0.5):1.

[0009] Furthermore, the roasting atmosphere described in S1 is air, and the air intake flow rate is 2-5 L / min.

[0010] Furthermore, the mass ratio of water to chromium-containing electroplating sludge in S2 is (1.5-2.5):1, preferably 2:1; the leaching time in S2 is 1-3 hours, and the leaching temperature is 20-50°C.

[0011] Further, the calcining agent B mentioned in S4 is at least one of sodium nitrate, sodium carbonate, or sodium hydroxide, preferably sodium nitrate; the mass ratio of the calcining agent B to the dried filter residue in S4 is (0.05-0.3):1.

[0012] Furthermore, the roasting atmosphere described in S4 is air, the air inlet flow rate is 2-5 L / min, and the roasting time is 2-5 h.

[0013] Furthermore, the calcination atmosphere described in S4 is a mixture of air and O3, with a volume ratio of air to O3 of (0.4-20):1, an inlet flow rate of 2-5 L / min, and a calcination time of 2-5 h.

[0014] Furthermore, the calcination described in S4 is a gradient heating calcination, specifically: adding calcining agent B to the dried filter residue in S3, calcining at 500-550℃ for 0.5-1.5h, and then heating to 600-1000℃ for 1-3h; the calcination atmosphere is a mixture of air, O3 and NO2, with a volume ratio of (16-18):(1-3):1; the inlet flow rate is 2-5L / min.

[0015] Furthermore, the water washing process described in S5 uses an acidic aqueous solution with a pH of 2-4; the acid is at least one of sulfuric acid, hydrochloric acid, or nitric acid; the water washing time in S5 is 1-3 hours, and the water washing temperature is 20-50℃.

[0016] The beneficial effects of this invention are as follows: This invention, through two-step roasting, specific solid-liquid ratio water leaching, gradient heating, and optimized roasting atmosphere, can increase the leaching rate to over 99%, significantly higher than traditional methods, greatly improving the recovery rate and utilization efficiency of chromium resources. This method is simple to operate, and the roasting agent used is readily available and relatively low in cost, making the entire chromium leaching process more economical and efficient. Detailed Implementation

[0017] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0018] Example 1 (1) Roasting: Add 3g of sodium carbonate to 10g of chromium-containing electroplating sludge (chromium content 5wt%), mix well, and calcine at 900℃ for 2 hours; wherein the calcination atmosphere is air, and the air inlet flow rate is 3.5 L / min.

[0019] (2) Leaching: Mix the calcined material from step (1) with 20g of water, stir for 2 hours at room temperature, then filter and collect the filtrate.

[0020] (3) Filter residue treatment: The filter residue obtained in step (2) is dried until the moisture content is less than 5%.

[0021] (4) Secondary roasting: The dried filter residue from step (3) was mixed evenly with sodium nitrate and then calcined at 800°C for 3 hours. The amount of sodium nitrate added was 20% of the mass of the dried filter residue. The calcination atmosphere was air with an air flow rate of 3.5 L / min.

[0022] (5) Secondary washing: Add sulfuric acid to water to adjust the pH to 4, mix the calcined material from step (4) with 30g of water with pH=4, stir for 1.5 hours at room temperature, then filter and collect the filtrate.

[0023] (6) Results: The leaching rate of chromium reached 99.0% as determined by atomic absorption spectrometry.

[0024] Example 2 (1) Roasting: Add 4g of sodium carbonate to 10g of chromium-containing electroplating sludge (chromium content 5 wt%), mix well, and calcine at 1000℃ for 3 hours; wherein the calcination atmosphere is air, and the air inlet flow rate is 3.5 L / min.

[0025] (2) Leaching: Mix the calcined material from step (1) with 20g of water, stir for 3 hours at room temperature, then filter and collect the filtrate.

[0026] (3) Filter residue treatment: The filter residue obtained in step (2) is dried until the moisture content is less than 3%.

[0027] (4) Secondary roasting: The dried filter residue from step (3) was mixed evenly with sodium nitrate and then calcined at 800°C for 3 hours. The amount of sodium nitrate added was 25% of the mass of the dried filter residue. The calcination atmosphere was air with an air flow rate of 3.5 L / min.

[0028] (5) Secondary washing: Add sulfuric acid to water to adjust the pH to 4, mix the calcined material from step (4) with 30g of water with pH=4, stir for 1.5 hours at room temperature, then filter and collect the filtrate.

[0029] (6) Results: The leaching rate of chromium was determined to be 99.1% by atomic absorption spectrometry.

[0030] Example 3 Unlike Example 2, the roasting atmosphere in step (4) of the second roasting is 70% air + 30% O3, and the air inlet flow rate is 3.5 L / min. The remaining steps are the same as in Example 2.

[0031] The leaching rate of chromium reached 99.7% as determined by atomic absorption spectrometry.

[0032] Example 4 Unlike Example 2, the roasting atmosphere in step (4) of the second roasting is 85% air + 15% O3, with an air inlet flow rate of 3.5 L / min, and the rest is the same as in Example 2.

[0033] The leaching rate of chromium reached 99.4% as determined by atomic absorption spectrometry.

[0034] Example 5 Unlike Example 2, the roasting atmosphere in step (4) of the second roasting is 45% air + 55% O3, and the air inlet flow rate is 3.5 L / min. The rest is the same as in Example 2.

[0035] The leaching rate of chromium reached 99.6% as determined by atomic absorption spectrometry.

[0036] Example 6 Unlike Example 2, step (4) is as follows: the filter residue dried in step (3) is mixed evenly with sodium nitrate, and then calcined at 500°C for 1 hour, and then heated to 800°C for 2 hours; wherein, the mass of sodium nitrate added is 25% of the mass of the dried filter residue, the calcination atmosphere is 85% air + 10% O3 + 5% NO2, the air inlet flow rate is 3.5 L / min, and the rest is the same as in Example 2.

[0037] The leaching rate of chromium reached 99.7% as determined by atomic absorption spectrometry.

[0038] Example 7 Unlike Example 1, sodium nitrate in step (4) is replaced with sodium carbonate, otherwise it is the same as in Example 1.

[0039] The leaching rate of chromium reached 98.5% as determined by atomic absorption spectrometry.

[0040] Example 8 Unlike Example 2, step (4) is as follows: the filter residue dried in step (3) is mixed evenly with sodium nitrate, and then calcined at 500°C for 1 hour, and then heated to 800°C for 2 hours; wherein, the mass of sodium nitrate added is 25% of the mass of the dried filter residue, the calcination atmosphere is 85% air + 15% O3, the air inlet flow rate is 3.5 L / min, and the rest is the same as in Example 2. The leaching rate of chromium reached 98.8% as determined by atomic absorption spectrometry.

[0041] Example 9 Referring to steps (1) and (2) of Example 1, the roasting time and temperature in step (1) were adjusted. The data on the chromium leaching rate (%) after the first roasting as a function of time and temperature are shown in Table 1.

[0042] Table 1

[0043] Example 10 Referring to steps (1) and (2) of Example 1, the roasting temperature in step (1) was set to 800℃ and the roasting time was 2 hours. The amount of sodium carbonate added in step (1) was adjusted. The data on the change of chromium leaching rate (%) with the amount of sodium carbonate added after the first roasting are shown in Table 2.

[0044] Table 2

[0045] In the above embodiments, the proportions of the calcination atmosphere are all volume ratios.

[0046] The data above shows that by controlling the leaching solid-liquid ratio, two-step roasting, and roasting atmosphere, the chromium leaching rate can be increased to >98%. A comparison of Examples 6 and 8 shows that introducing a small amount of NO2 into the roasting atmosphere creates a synergistic effect with air and O3, promoting the conversion of trivalent chromium to hexavalent chromium at a medium temperature (500℃), reducing roasting energy consumption. This also avoids the problem of trivalent chromium being encapsulated in calcium and iron oxides (calcium and iron impurities in electroplating sludge formed under high-temperature conditions) during direct high-temperature (800℃) roasting, thus preventing efficient oxidation to hexavalent chromium. This method is simple to operate, uses readily available raw materials, and has relatively low cost, making the entire chromium leaching process more economical and efficient.

Claims

1. A method for improving the chromium leaching efficiency of electroplating sludge, characterized in that, Includes the following steps: S1: Add calcining agent A to chromium-containing electroplating sludge and calcine it at 500-1000℃; S2: Leach the material after S1 roasting with water, and then filter it; S3: Dry the filter residue obtained in S2; S4: Add calcining agent B to the filter residue dried in S3 and calcinate it again at 500-1000℃; S5: Wash the material obtained from the second roasting in S4 with water.

2. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The calcining agent A mentioned in S1 is at least one of sodium carbonate, sodium nitrate, or sodium hydroxide, preferably sodium carbonate.

3. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The chromium content in the chromium-containing electroplating sludge described in S1 is 5~10wt%, and the mass ratio of calcining agent A to the chromium-containing electroplating sludge is (0.1-0.5):

1.

4. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The roasting atmosphere described in S1 is air, with an air intake flow rate of 2-5 L / min.

5. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The mass ratio of water to chromium-containing electroplating sludge in S2 is (1.5-2.5):1, preferably 2:1; the leaching time in S2 is 1-3 hours, and the leaching temperature is 20-50℃.

6. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The calcining agent B mentioned in S4 is at least one of sodium nitrate, sodium carbonate, or sodium hydroxide, preferably sodium nitrate; the mass ratio of the calcining agent B to the dried filter residue in S4 is (0.05-0.3):

1.

7. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The roasting atmosphere described in S4 is air, with an air inlet flow rate of 2-5 L / min and a roasting time of 2-5 h.

8. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The roasting atmosphere described in S4 is a mixture of air and O3, with a volume ratio of air to O3 of (0.4-20):1, an inlet flow rate of 2-5 L / min, and a roasting time of 2-5 h.

9. A method for improving the chromium leaching efficiency of electroplating sludge according to claim 6, characterized in that, The calcination described in S4 is a gradient heating calcination, specifically: adding calcining agent B to the dried filter residue in S3, calcining at 500-550℃ for 0.5-1.5h, and then raising the temperature to 600-1000℃ for 1-3h; the calcination atmosphere is a mixture of air, O3 and NO2, with a volume ratio of (16-18):(1-3):1; the inlet flow rate is 2-5L / min.

10. The method for improving the chromium leaching efficiency of electroplating sludge according to claim 1, characterized in that, The washing process described in S5 uses an acidic aqueous solution with a pH of 2-4; the acid is at least one of sulfuric acid, hydrochloric acid, or nitric acid; the washing time in S5 is 1-3 hours, and the washing temperature is 20-50℃.

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