A method for removing Cr(VI) from wastewater by preparing manganese-iron oxalate composite oxide using iron-rich manganese slag

Abstract

The present invention discloses a method for removing Cr(VI) from wastewater by preparing oxalate manganese-iron composite oxide using iron-rich manganese slag. The steps are as follows: first, the iron-rich manganese slag just discharged from the filter press workshop is transported to a slurry mixing tank, and then water and sulfuric acid in a set ratio are added to the slurry mixing tank. After the mixture is evenly mixed, solid-liquid separation is performed to obtain a leachate and a leach residue; second, iron powder and oxalic acid in a set ratio are added to the leachate, and after sufficient reaction, solid-liquid separation is performed to obtain a solid precipitate, which is the oxalate manganese-iron composite oxide; finally, the oxalate manganese-iron composite oxide in a set ratio is added to a certain concentration of chromium-containing wastewater, and Cr(VI) is removed from the chromium-containing wastewater under set reaction temperature, current density, reaction pH and other conditions, so that the wastewater can meet the discharge standards. The overall process of the present invention has the advantages of simple operation and low cost. It can not only effectively improve the recycling of iron and manganese resources in the iron-rich manganese slag, but also achieve efficient removal of Cr(VI) from wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental pollution control, and in particular to a method for removing Cr(VI) from wastewater by preparing manganese-iron oxalate composite oxide using iron-rich manganese slag. Background Art

[0002] Manganese is a strategic resource, with over 90% of it used in the steel industry. As the saying goes, "No manganese, no steel." Currently, the primary method for producing manganese metal is electrolysis. Iron-rich manganese slag is a solid waste generated during the secondary filtration process of electrolytic manganese production. In recent years, due to the depletion of high-grade manganese ore in my country, high-iron manganese ore has become the primary source of electrolytic manganese metal production. Every ton of manganese metal produced generates 2-5 tons of iron-rich manganese slag, and the current method of disposing of this slag is primarily through stockpiling. The fine particles and high moisture content of this slag carry heavy metals such as iron and manganese, which enter the surrounding soil and groundwater through weathering and surface runoff, polluting the surrounding environment. Therefore, resourceful utilization of this slag has become a pressing challenge for the electrolytic manganese industry.

[0003] Chromium exists in nature in the form of metallic chromium, trivalent chromium, and hexavalent chromium. Hexavalent chromium compounds have been identified as a significant carcinogen by the World Cancer Council. Currently, the main treatment technologies for chromium-containing wastewater include chemical reduction precipitation, ion exchange, electrochemical treatment, and adsorption. Chemical reduction precipitation is a relatively mature method for treating chromium-containing wastewater, but the chemicals added during the wastewater treatment process can react chemically, leading to secondary pollution. The ion exchange method is characterized by simple operation, high separation efficiency, and good effluent quality, but high-concentration acidic oxidizing wastewater reduces the life of the membrane and is costly. The adsorption method has the advantages of large adsorption capacity, simple operation, and high efficiency. The electrochemical treatment method has the advantages of high chromium removal rate and heavy metal recovery, and is simple to operate.

[0004] Currently, domestic and international scholars have conducted the following research on the treatment of chromium-containing wastewater pollution. For example, patent CN202011393986.5 proposes a method for advanced treatment of chromium-containing wastewater. This invention first uses modified coal ash to adsorb chromium in the wastewater, then uses ferrous salts to reduce high-valent chromium to low-valent chromium, which is then precipitated. Next, barium salts are added to remove residual chromium through a precipitation reaction between barium ions and chromium ions. This invention is characterized by its ability to gradually reduce the chromium content in the chromium-containing wastewater until the chromium is substantially removed. Another example is patent CN201110320761.1, which proposes a method for treating chromium-containing wastewater with a biological agent. This method adds a biological agent to the resulting solution at a mass volume concentration of 0.1 to 0.6 g / L, depending on the chromium content in the wastewater. Calcium hydroxide is then added to the resulting solution to adjust the pH and perform a hydrolysis reaction. After the reaction is complete, flotation is performed and the scum is scraped off. Currently, these patents for chromium-containing wastewater removal effectively remove hexavalent chromium from wastewater, but there is room for improvement in terms of treatment process and economic benefits.

[0005] Studies have found that iron-manganese oxides containing variable valence elements and surface charges have good surface activity and have good purification functions for toxic and harmful inorganic pollutants. At the same time, the use of electrochemical redox reactions on the electrode plates can achieve the purpose of strengthening the removal of substances to be removed in wastewater. To this end, the present invention is based on the process of preparing oxalic acid manganese iron composite oxides from iron-rich manganese slag based on the large amount of iron, manganese and other resources entrained in the iron-rich manganese slag, and combined with electric field enhancement means to establish an electric field-coordinated oxalic acid manganese iron composite oxide for the efficient removal of Cr (VI) in wastewater. The present invention provides a method for the high-resource utilization of iron-rich manganese slag and the removal of Cr (VI) in wastewater. Summary of the Invention

[0006] The technical solution adopted by the present invention is a method for removing Cr(VI) from wastewater by preparing manganese-iron oxalate composite oxide using iron-rich manganese slag, and the specific steps are as follows:

[0007] (1) First, the iron-manganese-rich slag just discharged from the filter press workshop is transported to the slurry mixing tank, and water with a solid-liquid ratio of 1:3~8 and sulfuric acid with a volume ratio of 1:3~12 to water are added. After sufficient stirring and mixing, solid-liquid separation is performed to obtain leaching residue and leachate.

[0008] (2) Then, iron powder with a solid-liquid ratio of 1:50 to 120 and oxalic acid with a mass ratio of 1:2 to 8 to the leachate are added to the leachate obtained in step (1), and the reaction is carried out under conditions such as a reaction temperature of 273 to 353 K and a reaction time of 1 to 30 h, followed by solid-liquid separation to obtain a solid precipitate, which is manganese iron oxalate composite oxide.

[0009] (3) Finally, the manganese iron oxalate composite oxide with a solid-liquid ratio of 1g:1L to the chromium-containing wastewater was added to the chromium-containing wastewater of 200~900mg / L. The reaction was carried out at a pH of 1~10 and a current density of 0~60 mA / cm 2 , temperature of 283~343K, electric field time of 30~240 min, anode and cathode plates being nickel foam plates, DSA plates or a combination of the two, etc., Cr(VI) in chromium-containing wastewater can be removed, and the wastewater can be discharged in compliance with the standards.

[0010] Compared with the prior art, the present invention has the following benefits:

[0011] (1) The present invention successfully prepared manganese iron oxalate composite oxide using iron-rich manganese slag, which can be used to remove Cr(VI) in wastewater, realizing the resource utilization of iron-rich manganese slag.

[0012] (2) The present invention utilizes electric field to cooperate with manganese iron oxalate composite oxide to achieve efficient removal of Cr(VI) in wastewater. The entire process is simple and low-cost. While resource-recycling the iron-rich manganese slag, it can enhance the removal of Cr(VI) in wastewater.

[0013] (3) The present invention can enhance the removal of Cr(VI) in wastewater while efficiently utilizing the iron and manganese resources in the iron-rich manganese slag, providing a new idea for the added value utilization of the iron and manganese resources in the iron-rich manganese slag. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be described in detail below to better illustrate the purpose, technical solution, and advantages of the present invention. Obviously, the embodiments described are only part of the present invention and not all of it. All other implementations derived by those skilled in the art without inventive work are within the scope of protection of the present invention.

[0015] Example 1

[0016] First, 9 kg of iron-rich manganese slag just discharged from the filter press workshop was transported to the slurry mixing tank, and then 27 L of water and 3 L of sulfuric acid were added to the slurry mixing tank. After mixing evenly, solid-liquid separation was performed to obtain leachate and leach residue. Secondly, 234 g of iron powder and 5.5 kg of oxalic acid were added to the leachate. After sufficient reaction under the conditions of reaction temperature of 283 K and reaction time of 24 h, solid-liquid separation was performed to obtain the solid precipitate, which was manganese oxalate iron composite oxide. Finally, 0.5 kg of manganese oxalate iron composite oxide was added to 500 L of chromium-containing wastewater (400 mg / L) and the reaction was carried out at an initial pH of 7 and a current density of 20 mA / cm 2, temperature of 298K, electric field time of 40 min, and nickel foam plates as the anode and cathode plates to remove Cr(VI) from the chromium-containing wastewater. After treatment, the removal amount of Cr(VI) in the chromium-containing wastewater reached 143.48 mg / g, and the removal amount of total chromium reached 165 mg / g.

[0017] Example 2

[0018] First, 9 kg of iron-rich manganese slag just discharged from the filter press workshop was transported to the slurry mixing tank, and then 27 L of water and 3 L of sulfuric acid were added to the slurry mixing tank. After mixing evenly, solid-liquid separation was performed to obtain leachate and leach residue. Secondly, 234 g of iron powder and 5.5 kg of oxalic acid were added to the leachate. After sufficient reaction under the conditions of reaction temperature of 283 K and reaction time of 24 h, solid-liquid separation was performed to obtain the solid precipitate, which was manganese oxalate iron composite oxide. Finally, 0.5 kg of manganese oxalate iron composite oxide was added to 500 L of chromium-containing wastewater (400 mg / L) and the reaction was carried out at an initial pH of 2 and a current density of 20 mA / cm 2 , temperature of 298K, electric field time of 40 min, and nickel foam plates as the anode and cathode plates to remove Cr(VI) from the chromium-containing wastewater. After treatment, the removal amount of Cr(VI) in the chromium-containing wastewater reached 359.78 mg / g, and the removal amount of total chromium reached 378 mg / g.

[0019] Example 3

[0020] First, 9 kg of iron-rich manganese slag just discharged from the filter press workshop was transported to the slurry mixing tank, and then 27 L of water and 3 L of sulfuric acid were added to the slurry mixing tank. After mixing evenly, solid-liquid separation was performed to obtain leachate and leach residue. Secondly, 234 g of iron powder and 5.5 kg of oxalic acid were added to the leachate. After sufficient reaction under the conditions of reaction temperature of 283 K and reaction time of 24 h, solid-liquid separation was performed to obtain the solid precipitate, which was manganese oxalate iron composite oxide. Finally, 0.5 kg of manganese oxalate iron composite oxide was added to 500 L of chromium-containing wastewater (400 mg / L) and the reaction was carried out at an initial pH of 2 and a current density of 20 mA / cm 2 , temperature of 298K, electric field time of 60 min, and nickel foam plates as the anode and cathode plates to remove Cr(VI) from chromium-containing wastewater. After treatment, the removal amount of Cr(VI) in the chromium-containing wastewater reaches 399 mg / g, and the removal amount of total chromium reaches 399 mg / g, so the wastewater can meet the discharge standards.

[0021] Through the specific examples, it can be concluded that the removal amount of Cr(VI) and total chromium reaches 399 mg / g, and the removal rate reaches 99.75%. 1 ton of iron-rich manganese slag can actually treat 55.6 x 10 3 L chromium-containing wastewater, the current efficiency exceeds 72%.

[0022] The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Within the technical scope disclosed by the present invention, any form that can be easily modified or replaced should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be within the scope of the above claims.

Claims

1. A method for removing Cr(VI) from wastewater by preparing manganese-iron oxalate composite oxide using iron-rich manganese slag, characterized in that: The steps include: First, the iron-rich manganese slag just discharged from the filter press workshop is transported to a slurry mixing tank, and then a set proportion of water and sulfuric acid are added to the slurry mixing tank, and after being evenly mixed, solid-liquid separation is performed to obtain a leachate and a leaching residue; secondly, a set proportion of iron powder and oxalic acid are added to the leachate, and after sufficient reaction under certain conditions, solid-liquid separation is performed to obtain a solid precipitate, which is an oxalate manganese iron composite oxide; finally, the set proportion of the oxalate manganese iron composite oxide is added to a certain concentration of chromium-containing wastewater, and Cr(VI) in the chromium-containing wastewater is removed under the set reaction temperature, current density, and reaction pH conditions, so that the wastewater can achieve its discharge standard; the concentration of the chromium-containing wastewater is 200-900 mg / L, the solid-liquid ratio of the oxalate manganese iron composite oxide to the chromium-containing wastewater is 1g:1L; the set reaction pH value is 1-10; the current density is 0-60 mA / cm 2 , the temperature is 283~343K, the electric field time is 30~240min, and the anode and cathode plates are one or more of nickel foam plates and DSA plates.

2. The method for removing Cr(VI) from wastewater by preparing ferromanganese oxalate composite oxide using iron-rich manganese slag as claimed in claim 1, characterized in that: The solid-liquid ratio of the iron-manganese-rich slag to water in the slurry mixing tank is 1:3-8; the volume ratio of 98% concentrated sulfuric acid to water is 1:3-12.

3. The method for removing Cr(VI) from wastewater by preparing ferromanganese oxalate composite oxide using iron-rich manganese slag as claimed in claim 1, characterized in that: The solid-liquid ratio of the iron powder to the leachate is 1:50-120; the mass ratio of oxalic acid to the leachate is 1:2-8.

4. The method for removing Cr(VI) from wastewater by preparing ferromanganese oxalate composite oxide using iron-rich manganese slag as claimed in claim 1, characterized in that: The step of adding iron powder and oxalic acid in a set ratio to the leachate is carried out under the following reaction conditions: reaction temperature of 273-353 K and reaction time of 1-30 h.