Method for recovering metal resources from heavy metal dangerous solid waste

Abstract

The invention relates to the technical field of environmental protection, in particular to a method for recovering metal resources from heavy metal dangerous solid waste, which comprises the following steps: in the presence of inert gas, reducing metal oxides in pickling sludge by using ferrophosphorus; in the presence of inert gas, a mixture of the pickling sludge and ferrophosphorus is subjected to high-temperature reduction, so that the metal recovery rate of a reduction product can be effectively improved; meanwhile, ferrophosphorus is used as a reducing agent, so that the recovery rate of chromium in the pickling sludge can be improved.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technology, and more specifically to a method for recovering metal resources from heavy metal hazardous solid waste. Background Art

[0002] In the production process of stainless steel, H 2 SO 4 Pickling and passivation treatments such as HF will produce pickling wastewater. Neutralization and precipitation are the most common industrial treatment methods for this type of wastewater. After treatment, a large amount of chemical sludge containing heavy metals such as Fe, Cr, and Ni is produced, namely stainless steel pickling sludge. According to statistics, the output of pickling sludge accounts for about 3% to 5% of the output of stainless steel. Since the hydroxide precipitation of Cr and Ni in the sludge has strong heavy metal leaching toxicity, it has been included in the "National List of Hazardous Wastes" and belongs to HW17 surface treatment waste. The proper treatment and disposal of pickling sludge has become a bottleneck restricting the sustainable development of the stainless steel industry.

[0003] Due to the high concentration of heavy metals and fluoride ions in stainless steel pickling sludge, from the perspective of solidification stability, solidification and landfilling with dense materials such as cement and lime can achieve the purpose of short-term solidification, but the valuable heavy metals in it have not been reasonably recycled. Sludge solidification and landfilling not only require high treatment costs and occupy a large area of ​​land, but also over time, Cr 6+ The potential threat to the environment is also gradually deepening. Once the environmental effects are complex and non-uniform, the solidification effect will lose its long-term stability. Wet leaching technology can simultaneously leach multiple metal ions by selecting different leaching agents, but the process is relatively complicated, the consumption of leaching agents is large, and multiple leaching products are difficult to separate. A large amount of leaching wastewater and waste residue are generated, and secondary pollution is relatively serious. In recent years, the demand for metal resources such as Cr and Ni has increased day by day, and the waste of resources and environmental governance problems of stockpiling pickling sludge have become increasingly serious. The pyrometallurgical reduction treatment technology that recycles heavy metals in pickling sludge has gradually become an important way to dispose of sludge in the stainless steel industry.

[0004] Fire reduction is the process of reducing solid waste at high temperature to reduce the Cr in sludge. 6+ Cr 3+ Reduced to Cr alloy, including CaO, CaF 2 It can be used as a smelting auxiliary agent and become a raw material for stainless steel smelting. The metal recovery rate of its treatment products is high, and the sludge is completely recycled, so it is widely used in the treatment of hazardous waste in the stainless steel industry. Due to the different pickling treatment processes and materials of different companies, the physical components of stainless steel pickling sludge are complex, and the problem of low Cr deep reduction efficiency still exists in the industrial treatment process.

[0005] Ferrophosphorus is a by-product of the production of yellow phosphorus in phosphorus chemical industry. It is mainly composed of 18%~30% P and 50%~75% Fe. At present, most of the methods for recycling resources in ferrophosphorus are mainly based on the use of less P to prepare chemical materials such as phosphoric acid and phosphates and energy and electrode materials such as lithium iron phosphate; or as an additive and deoxidizer for steel metallurgy to adjust the P content of steel to improve mechanical properties. Among them, the utilization of Fe is also insufficient. Studies have shown that the chemical composition of ferrophosphorus can react with oxidizing substances, and Fe plays a vital role in the reduction of Cr and Ni in pickling sludge. This type of homogeneous reduction reaction improves metal recovery. Summary of the invention

[0006] The purpose of the present invention is to provide a method for recovering metal resources from heavy metal hazardous solid waste to solve the above-mentioned problems. The method for recovering metal resources from heavy metal hazardous solid waste provided by the present invention reduces the mixture of pickling sludge and ferrophosphorus at high temperature, which can effectively improve the metal recovery rate of the reduction product.

[0007] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions: The invention provides a method for recovering metal resources from heavy metal hazardous solid wastes, comprising reducing metal oxides in pickling sludge by using ferrophosphorus in the presence of an inert gas.

[0008] Furthermore, the molar ratio of the ferrophosphorus to the oxygen content of the metal oxides in the pickling sludge is (0.6-1.6):1.

[0009] Furthermore, the inert gas is selected from at least one of nitrogen and argon; preferably, the inert gas has an intake flow rate of 50 mL / min.

[0010] Further, the water content of the pickling sludge is 3.53%, and the loss on ignition is 19.24%; And / or, the iron content of the ferrophosphorus is 50% to 75%.

[0011] Furthermore, the reduction is carried out in a tube furnace; preferably, the heating rate of the tube furnace is 5° C. / min.

[0012] Furthermore, the reduction conditions include: the reduction temperature is 900° C. to 1350° C.; and the reduction time is 0.5 hour to 3.0 hours.

[0013] Furthermore, after the reduction, the temperature is further reduced; preferably, the temperature reduction is specifically: reducing the temperature to 500° C. at a rate of 5° C. / min, and then naturally cooling to room temperature.

[0014] Beneficial effects: The present invention provides a method for recovering metal resources from heavy metal hazardous solid wastes. In the presence of an inert gas, a mixture of pickling sludge and ferrophosphorus is subjected to high-temperature reduction, which can effectively improve the metal recovery rate of the reduction product; at the same time, ferrophosphorus is used as a reducing agent to improve the recovery rate of chromium in the pickling sludge; The method described in the present invention proves that after the coordinated high-temperature reduction of ferrophosphorus and pickling sludge, the leaching toxicity of the reduction product is effectively improved; at the same time, the alloy in the reduction product can be directly reused in steel production, the magnetic powder can be used as a raw material for the catalyst, and the non-magnetic tailings can be disposed of as general solid waste; in addition, ferrophosphorus itself is a by-product, thus expanding the resource utilization industry chain of ferrophosphorus. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 The effect of the amount of ferrophosphorus on the metal recovery rate of the reduction product in the present invention is shown; Figure 2 The effect of reduction temperature on the metal recovery rate of the reduction product in the present invention is shown; Figure 3 The effect of reduction time on the metal recovery rate of the reduction product in the present invention is shown; Figure 4 The effect of reduction temperature on Cr (a) and Ni (b) leaching toxicity in the present invention is shown. DETAILED DESCRIPTION

[0017] The present invention will be further explained below in conjunction with the embodiments.

[0018] The pickling sludge described in the present invention is taken from the Lantian electroplating base in Wenzhou, Zhejiang Province, and is in the form of yellow mud cakes. It is crushed into powder, dried at 105° C. for 24 hours, and passed through a 100-mesh sieve. The moisture content of the pickling sludge is 3.53%, and the loss on ignition is 19.24%.

[0019] The ferrophosphorus described in the present invention is purchased from Henan Huijin Technology Co., Ltd., and has an iron content of 70% to 75%.

[0020] Unless otherwise specified in the present invention, the room temperature is 25°C.

[0021] Example The pickling sludge was mixed with ferrophosphorus, pressed into a crucible until the pickling sludge powder and ferrophosphorus were compacted and formed, and then covered and reduced at high temperature in a tubular furnace; before the tubular furnace was heated, an inert gas (high-purity nitrogen, gas purity ≥ 99.999%) was introduced into the furnace to exclude the air in the furnace, and the inert gas was always input during the experiment. The heating rate of the tubular furnace was 5℃ / min, and the inert gas inlet flow rate was 50mL / min. After rising to the set temperature (900℃~1350℃), the temperature was kept for the set time (0.5 hours~3.0 hours). After the time was over, the temperature was lowered to 500℃ at a rate of 5℃ / min, and then naturally cooled to room temperature. The reduction product was taken out, crushed and ground, the iron, chromium and nickel metal contents were determined, and the recovery rates of iron, chromium and nickel were calculated.

[0022] Specifically: Examples 1-7 respectively experimentally studied the recovery rates of iron, chromium and nickel metals in the reduction products at different ferrophosphorus dosages (the molar ratios of ferrophosphorus to the oxygen content of metal oxides in pickling sludge were 0.6:1, 0.8:1, 1.0:1, 1.1:1, 1.2:1, 1.4:1 and 1.6:1, respectively), wherein the reduction temperature was 1300°C and the reduction time was 1.5h. The experimental data are shown in Tables 1 and Figure 1 ; Examples 8-13 respectively experimentally studied the recovery rates of iron, chromium and nickel metals in the reduction products at different reduction temperatures (900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1350°C), wherein the phosphorus and iron dosage was 1.1:1 and the reduction time was 1.5h; the experimental data are shown in Tables 2 and Figure 2 ; Examples 14-19 respectively experimentally studied the recovery rates of iron, chromium and nickel metals in the reduction products at different reduction times (0.5h, 1.0h, 1.5h, 2.0h, 2.5h and 3.0h), wherein the phosphorus iron dosage was 1.1:1 and the reduction temperature was 1300°C; the experimental data are shown in Tables 3 and Figure 3 .

[0023] Table 1

[0024] Figure 1 The above data reflect the recovery rate variation trend of the three metals Fe, Cr and Ni in the reduction products obtained in Examples 1-7 of the present invention. Figure 1 It can be seen that with the increase of ferrophosphorus dosage, the recovery rates of the three metals show a trend of first increasing and then decreasing. When the ferrophosphorus dosage is 1.6, the Fe recovery rate reaches the highest 93.3%, and the Cr and Ni recovery rates are 90.2% and 88.2% respectively; the Cr and Ni recovery rates reach the highest 93.4% and 92.1% when the ferrophosphorus dosage is 1.1, and the Fe recovery rate is 92.5%.

[0025] Table 2

[0026] Under the conditions of 1.1 ferrophosphorus addition and 1.5h reduction time, the reduction temperature was taken as the experimental factor. The experimental results are as follows: Figure 2 As shown, Figure 2 This shows the influence of temperature on the recovery rate of the three metals obtained in Examples 8-13 of the present invention. Figure 2 It can be seen that when the reduction temperature increases from 900℃ to 1350℃, the Fe recovery rate increases from 84.5% to 92.6%; the Ni recovery rate increases from 82.8% to 93.3%; and the Cr recovery rate increases from 88.1% to 94.0%. It can be seen that increasing the reduction temperature has a positive promoting effect on the total recovery rate of the three metals. Under the same temperature conditions, the Cr recovery rate is higher than that of Fe and Ni. This is because Cr is the most difficult metal to reduce among the three metals and can only be reduced after reaching a certain temperature condition. The Fe and Ni reduced in the first step will participate in the reduction process of Cr, positively promoting the reduction of Cr from Cr oxide to Cr and Fe magnetic minerals, and finally Cr and Ni are reduced from NiFe in the form of metal. 2 O 4 and FeCr 2 O 4 Therefore, increasing the reduction temperature can achieve the reduction of NiFe 2 O 4 and FeCr 2 O 4 Further reduction and effective regulation of the reduction products.

[0027] In addition, when the reduction temperature is 1350℃, the reduction product has serious fault collapse phenomenon and forms different degrees of adhesion with the inner wall of the crucible. This is because there is a high content of co-solvent CaF in the sludge. 2 (Original sludge CaF 2 Mass is 18.50%), Fe 2 O 3 The FeO produced in the reaction reduces the melting point of refractory substances. The increase in temperature promotes the reduction reaction of ferrophosphorus and metal oxides in pickling sludge, and improves the recovery rate of metals in the reduction product. However, if the temperature is too high, the reduction product will melt and be difficult to separate.

[0028] Table 3

[0029] Under the conditions of 1.1 ferrophosphorus addition and 1300℃ reduction temperature, the reduction time was used as the experimental factor. The results are as follows: Figure 3 As shown, Figure 3This shows the influence of time on the recovery of the three metals obtained in Examples 14-19 of the present invention. Figure 3 It can be seen that the recovery rates of the three metals in the reduction product increase with time and tend to balance. When the reduction time is 3.0 hours, the recovery rates of Fe, Cr, and Ni reach the highest values, which are 96.2%, 97.5%, and 97.0%, respectively. As the reduction time increases, the reduced metal particles gradually enrich and converge to form metal particles with regular shapes, which are easier to be screened out in the subsequent separation process.

[0030] In order to further illustrate the superiority of the present invention, the present invention continues to study the leaching toxicity of the pickling sludge and the reduction products obtained by using different reduction times, and the statistics are as follows; Leaching toxicity determination A nitric acid / sulfuric acid mixed solution (extractant A) was used to simulate the leaching toxicity of harmful components in solid waste when it was disposed of in an irregular landfill or land used after being rendered harmless (HJ / T299-2007); or an acetic acid buffer solution (extractant B) was used to simulate the leaching toxicity of harmful components in solid waste after it entered a sanitary landfill under the influence of landfill leachate (HJ / T300-2007).

[0031] Wherein, the leaching agent A is: a mixture of concentrated sulfuric acid and concentrated nitric acid in a mass ratio of 2:1 is added into water, so that the pH of the nitric acid / sulfuric acid mixed solution is 3.20±0.05.

[0032] Extraction agent B: Dilute 17.25 ml of glacial acetic acid to 1 L with water. The pH value of the prepared acetate buffer solution is 2.64 ± 0.05.

[0033] (1) In the pickling sludge of the present invention, the metals such as Fe, Cr, and Ni are mostly present in the form of hydroxide precipitation, which has strong dissolution and migration ability in an acidic environment. In order to explore the leaching toxicity range of the pickling sludge used in the experiment, the pickling sludge was analyzed and determined according to the method in the above standard, and the results are shown in Table 4.

[0034] Among them, the concentrations of Cr and Ni in the sulfuric acid / nitric acid mixed solution leaching mode (leaching agent A) reached 74.9 mg / L and 10.3 mg / L respectively; in the acetic acid leaching mode (leaching agent B), the concentrations of Cr and Ni were 88.5 mg / L and 14.4 mg / L respectively.

[0035] Table 4 Leaching toxicity standard limit and sludge leaching value

[0036] It can be seen from the records in Table 4 that the concentrations of Cr and Ni in the two leaching modes are far higher than the standard limits, which proves that the pickling sludge described in the present invention is directly landfilled or directly disposed of as solid waste, and the leaching of Cr and Ni in the sludge causes serious harm to the environment.

[0037] (2) Effect of different reduction temperatures on the leaching of metal ions from the reduction products; In Examples 8-13 of the present invention, under the conditions of 1.1 ferrophosphorus addition and 1.5 h of reduction time, the reduction temperature was used as the experimental factor, and the leaching toxicity of the obtained reduction products was determined by the above method. The results are shown in Tables 5 and Figure 4 .

[0038] Table 5 Leaching toxicity standard limit and reduction product leaching value

[0039] from Figure 4 It can be seen that when leaching with a nitric acid / sulfuric acid mixed solution (leaching agent A), the leaching of the reduced product Cr ion does not change significantly with the reduction temperature; the leaching concentration of Ni ion is the highest at 900°C, and it decreases significantly at 1000°C; when leaching with an acetic acid buffer solution (leaching agent B), the leaching concentration of the reduced product Cr ion is the highest at 900°C, and it decreases significantly after 1000°C; Ni ion decreases significantly at 1300°C. This shows that the higher the reduction temperature, the deeper the reduction reaction, and the lower the leaching concentration of the reduced product metal ion. At the same time, the leaching toxicity of the reduced product at all temperatures is lower than that of the pickling sludge described in the present invention, proving that after the high-temperature reduction of ferrophosphorus and pickling sludge, the leaching toxicity of the reduced product is effectively improved.

[0040] Finally, the present invention studies the leaching toxicity of tailings. With reference to the leaching concentration limit in (GB5085.3-2007), the obtained reduction product is crushed, sieved, and the alloy is screened out. The undersize is further separated by magnetic separation (magnetic field strength is 350mT) to obtain magnetic powder and non-magnetic tailings. The tailings are analyzed and measured according to the above method, and the leaching toxicity is shown in Table 6 below.

[0041] Table 6 Leaching toxicity standard limit and tailings leaching value

[0042] From the records in Table 6 above, it can be seen that the detection concentrations of Fe, Ni and Cr in the tailings leaching toxicity were all undetectable, indicating that the concentrations of Cr and Ni metals in the tailings after screening were both lower than 0.001 mg / L, and had no leaching toxicity characteristics, which met the national general waste disposal standards, reduced the potential risk of harmless treatment of heavy metal leaching, and achieved the purpose of metal recycling and waste treatment.

[0043] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited by the description of the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

[0044] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for recovering metal resources from heavy metal hazardous solid waste, characterized in that: The method comprises reducing metal oxides in pickling sludge by using ferrophosphorus in the presence of an inert gas.

2. The method according to claim 1, characterized in that The molar ratio of the ferrophosphorus to the oxygen content of the metal oxides in the pickling sludge is (0.6-1.6):

1.

3. The method according to claim 1, characterized in that The inert gas is selected from at least one of nitrogen and argon; preferably, the inlet flow rate of the inert gas is 50 mL / min.

4. The method according to claim 1, characterized in that: The water content of the pickling sludge is 3.53%, and the loss on ignition is 19.24%; And / or, the iron content of the ferrophosphorus is 50% to 75%.

5. The method according to claim 1, characterized in that The reduction was carried out in a tube furnace.

6. The method according to claim 5, characterized in that The heating rate of the tube furnace is 5°C / min.

7. The method according to claim 1, characterized in that The reduction conditions include: the reduction temperature is 900° C. to 1350° C.; and the reduction time is 0.5 hour to 3.0 hours.

8. The method according to claim 1, characterized in that After the reduction, the method further comprises a cooling step.

9. The method according to claim 8, characterized in that The cooling is specifically as follows: the tube furnace is cooled to 500° C. at a rate of 5° C. / min, and then naturally cooled to room temperature.

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