A method for separating vanadium and chromium from high-chromium vanadium slag

Abstract

The application belongs to the technical field of chemical industry, and particularly relates to a method for separating vanadium and chromium from high-chromium vanadium slag, comprising the following steps: obtaining high-chromium vanadium slag, mixing the high-chromium vanadium slag with sodium salt to perform oxidative roasting, and obtaining roasted clinker; performing first chlorination on the roasted clinker under inert gas condition to obtain vanadyl trichloride and first residue; performing second chlorination on the first residue under inert gas condition to obtain vanadyl trichloride and second residue, and the second residue contains chromium elements. The method can realize the separation of vanadium and chromium in the high-chromium vanadium slag by combining oxidative roasting and step-by-step temperature control chlorination; the use of a large amount of organic solvent or the generation of high-concentration acidic wastewater is avoided, the pollution to the environment is reduced, the purpose of green and clean separation of vanadium and chromium is realized, the sustainable development concept is met; the method is suitable for high-chromium vanadium slag with different components, and by adjusting process parameters, efficient separation of vanadium and chromium can be realized, and the method has good industrial application prospect.

Description

Technical Field

[0001] This application belongs to the field of chemical technology, specifically relating to a method for separating vanadium and chromium from high-chromium vanadium slag. Background Technology

[0002] Vanadium and chromium, due to their adjacent positions in the periodic table, exhibit remarkably similar physicochemical properties, often resulting in their co-occurrence and enrichment in minerals such as vanadium-titanium magnetite and chromite. During the smelting of high-chromium vanadium-titanium magnetite, high-chromium vanadium slag, rich in both vanadium and chromium, is typically formed, with vanadium content ranging from 10 wt% to 15 wt% (V₂O₅) and chromium content ranging from 5 wt% to 10 wt% (Cr₂O₃). The complex co-occurrence relationship between vanadium and chromium has made their effective separation a persistent technical challenge in the industry. Currently, common separation methods mainly include acid leaching and alkaline leaching. While acid leaching can dissolve vanadium and chromium, it causes severe corrosion to equipment and generates large amounts of highly concentrated acidic wastewater, resulting in high treatment costs and environmental pollution. Alkaline leaching, although less corrosive to equipment, suffers from poor selective leaching of vanadium and chromium, making the separation efficiency insufficient for industrial production needs. Furthermore, the large amount of waste generated during leaching hinders efficient resource utilization and environmental friendliness. Therefore, developing an efficient, environmentally friendly method for separating vanadium and chromium from high-chromium vanadium slag that is suitable for industrial production has significant practical implications and application value. Summary of the Invention

[0003] This application provides a method for separating vanadium and chromium from high-chromium vanadium slag. By optimizing the process route and parameters, it solves the problems of low efficiency and high pollution of existing separation technologies, and realizes efficient, green and simple separation of vanadium and chromium from high-chromium vanadium slag, thus promoting the large-scale development and utilization of high-chromium vanadium-titanium magnetite resources.

[0004] The method for separating vanadium and chromium from high-chromium vanadium slag according to this application includes the following steps:

[0005] S1. Obtain high-chromium vanadium slag, mix the high-chromium vanadium slag with sodium salt and oxidize and roast to obtain roasted clinker;

[0006] S2. The roasted clinker is subjected to a first chlorination under an inert gas condition to obtain vanadium oxychloride and the first residue.

[0007] S3. The first residue is subjected to a second chlorination under inert gas conditions to obtain vanadium oxychloride and a second residue, the second residue containing chromium.

[0008] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, in step S2: the roasted clinker is mixed with anhydrous aluminum chloride and sodium chloride, and the first chlorination is carried out at a first temperature under inert gas conditions;

[0009] In step S3: the first residue is subjected to a second chlorination at a second temperature under inert gas conditions;

[0010] The second temperature is greater than the first temperature.

[0011] In the above technical solution, when high-chromium vanadium slag is mixed with sodium salt for oxidative roasting, various chlorinated vanadates and water-soluble chromates are generated, including Na4V2O7, Na3VO4, NaVO3, and Na2CrO4. The ratio of different types of chlorinated vanadates and water-soluble chromates generated during roasting can be adjusted by changing the amount of sodium salt added. For example, reducing the amount of sodium salt added will reduce the amount of water-soluble chromates generated, thus decreasing the chromium leaching rate, but it will promote the formation of more NaVO3, which is easily converted during the first chlorination process, thereby improving the efficiency of the first chlorination. Vanadium extraction rate; vanadates, AlCl3 and NaCl are mixed, with AlCl3 as the chlorinating agent. NaCl can form a liquid phase with AlCl3 at about 110℃, effectively reducing the volatilization of AlCl3. At the first temperature, NaVO3 preferentially undergoes chlorination to generate VOCl3 in gaseous form, which can be recovered by condensation. Na4V2O7 and Na3VO4 are chlorinated only at a second temperature higher than the first temperature. Therefore, using a stepwise temperature-controlled chlorination method to chlorinate various vanadates into VOCl3 not only achieves efficient vanadium recovery but also saves energy.

[0012] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, the method further includes the following step after step S3:

[0013] S4. Dissolve the second residue in water, filter and collect the filtrate, precipitate the filtrate and recover the chromium from the precipitate.

[0014] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, the method further includes the following steps before step S1:

[0015] The high-chromium vanadium slag raw material is sieved and dried to obtain high-chromium vanadium slag.

[0016] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, the vanadium content in the high-chromium vanadium slag is 10wt%~15wt% based on V2O5, and the chromium content is 5wt%~10wt% based on Cr2O3.

[0017] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, the sodium salt includes sodium carbonate, and the mass ratio of sodium carbonate to high-chromium vanadium slag is 0.2:1 to 0.6:1.

[0018] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, in step S1, the oxidative roasting temperature is 700~1000℃ and the time is 1.5~2.5h.

[0019] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, the mass ratio of roasted clinker to anhydrous aluminum chloride is 1:2, and the mass ratio of anhydrous aluminum chloride to sodium chloride is 3:2.

[0020] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, in step S2, the first temperature is 150~170℃ and the time is 1.5~2.5h; in step S3, the second temperature is 230~250℃ and the time is 1.5~2.5h.

[0021] As a preferred embodiment of the method for separating vanadium and chromium from high-chromium vanadium slag according to this application, in step S4, the temperature at which the second residue dissolves in water is 80°C and the time is 1.5~2.5h.

[0022] The method for separating vanadium and chromium from high-chromium vanadium slag proposed in this application has the following advantages: it can achieve the separation of vanadium and chromium from high-chromium vanadium slag by combining oxidative roasting and stepwise temperature-controlled chlorination; it avoids the use of large amounts of organic solvents or the generation of high-concentration acidic wastewater, reducing environmental pollution and achieving the goal of green and clean separation of vanadium and chromium, which is in line with the concept of sustainable development; it is applicable to high-chromium vanadium slag with different compositions, and by adjusting the process parameters, it can achieve efficient separation of vanadium and chromium, and has good prospects for industrial application. Detailed Implementation

[0023] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0024] The technical solution proposed in this application includes the following steps:

[0025] S1. Obtain high-chromium vanadium slag, mix the high-chromium vanadium slag with sodium salt and oxidize and roast to obtain roasted clinker;

[0026] Specifically, high-chromium vanadium slag raw material is passed through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag; Na2CO3 and high-chromium vanadium slag are mixed evenly at a mass ratio of 0.2:1 to 0.6:1 and oxidized and roasted at 700 to 1000℃ for 1.5 to 2.5 hours to obtain roasted clinker; specifically, the mass ratio of Na2CO3 to high-chromium vanadium slag can be any one of 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1 or any two of them, and the oxidized roasting temperature can be any one of 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ or any two of them.

[0027] S2. The roasted clinker is subjected to a first chlorination under an inert gas condition to obtain vanadium oxychloride and the first residue.

[0028] Specifically, the roasted clinker is mixed with AlCl3 and NaCl, wherein the mass ratio of roasted clinker to AlCl3 is 1:2 and the mass ratio of AlCl3 to NaCl is 3:2. Under inert gas conditions, the reaction temperature is controlled at 150~170℃ for the first chlorination, and the reaction time is 1.5~2.5h, to obtain VOCl3 and the first residue. VOCl3 is in gaseous state, and partial extraction of vanadium is achieved by condensation and collection. Specifically, the reaction temperature of the first chlorination can be any one of 150℃, 155℃, 160℃, 165℃, and 170℃ or any range between two of them.

[0029] S3. The first residue is subjected to a second chlorination under inert gas conditions to obtain vanadium trichloride and a second residue, the second residue containing chromium.

[0030] Specifically, the first residue is subjected to a second chlorination under inert gas conditions, with the reaction temperature controlled at 230~250℃, for a reaction time of 1.5~2.5h, to obtain VOCl3 and a second residue. VOCl3 is in gaseous state and is collected by condensation for further extraction of vanadium; while chromium remains in the second residue. Specifically, the reaction temperature for the second chlorination can be any one of 230℃, 235℃, 240℃, 245℃, and 250℃, or any range between two of them. The second residue is dissolved in water and leached at 80℃ for 1.5~2.5h. After filtration, the filtrate is subjected to precipitation treatment to recover the chromium from the precipitate.

[0031] Using the above technical solution, vanadium and chromium are separated from high-chromium vanadium slag, with a vanadium leaching rate ≥75% and a chromium recovery rate ≥40%. Preferably, the vanadium leaching rate is ≥80% and the chromium recovery rate is ≥85%.

[0032] The technical solution of this application will be further described below with reference to specific embodiments.

[0033] The embodiments and comparative examples of this application use high-chromium vanadium slag raw materials produced by a domestic company. The vanadium content in the high-chromium vanadium slag raw materials is 11.5 wt% (V2O5) and the chromium content is 7.34 wt% (Cr2O3).

[0034] Example 1

[0035] High-chromium vanadium slag raw material was passed through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and high-chromium vanadium slag were mixed evenly at a mass ratio of 0.6:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 800℃ for 2 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was then mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask under an inert gas atmosphere. Under controlled conditions, the reaction temperature was maintained at 160℃ for the first chlorination, and the reaction time was 2 hours, yielding VOCl3 and a first residue. The generated gaseous VOCl3 was collected by condensation. The first residue was then subjected to a second chlorination under inert gas conditions, with the reaction temperature controlled at 240℃, for a second time of 2 hours, yielding VOCl3 and a second residue. The generated gaseous VOCl3 was collected by condensation. The second residue was dissolved in water and leached at 80℃ for 2 hours. After filtration, the filtrate was subjected to precipitation treatment to achieve chromium recovery. Testing showed that the vanadium extraction rate was 85%, and the chromium recovery rate was 90%.

[0036] Example 2

[0037] High-chromium vanadium slag raw material was sieved through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.45:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 1000℃ for 1.5 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was then mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask under an inert gas atmosphere. Under controlled conditions, the reaction temperature was set at 170℃ for the first chlorination, and the reaction time was 1.5 h, yielding VOCl3 and a first residue. The generated gaseous VOCl3 was collected by condensation. The first residue was then subjected to a second chlorination under inert gas conditions at a controlled temperature of 250℃ for 1.5 h, yielding VOCl3 and a second residue. The generated gaseous VOCl3 was collected by condensation. The second residue was dissolved in water and leached at 80℃ for 1.5 h. After filtration, the filtrate was subjected to precipitation treatment to recover chromium. Testing showed that the vanadium extraction rate was 83% and the chromium recovery rate was 86%.

[0038] Example 3

[0039] High-chromium vanadium slag raw material was passed through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.2:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 800℃ for 2 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was then mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask under an inert gas atmosphere. Under controlled conditions, the reaction temperature was maintained at 160℃ for the first chlorination, and the reaction time was 2 hours, yielding VOCl3 and a first residue. The generated gaseous VOCl3 was collected by condensation. The first residue was then subjected to a second chlorination under inert gas conditions, with the reaction temperature controlled at 240℃, for a second time of 2 hours, yielding VOCl3 and a second residue. The generated gaseous VOCl3 was collected by condensation. The second residue was dissolved in water and leached at 80℃ for 2 hours. After filtration, the filtrate was subjected to precipitation treatment to achieve chromium recovery. Testing showed that the vanadium extraction rate was 76%, and the chromium recovery rate was 41%. Reducing the amount of Na2CO3 added would decrease the amount of chlorinated vanadates and water-soluble chromates produced during roasting, thus leading to a decrease in both the vanadium extraction rate and the chromium leaching rate.

[0040] Example 4

[0041] High-chromium vanadium slag raw material was sieved through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.6:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 700℃ for 2.5 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was then mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask under inert gas conditions. Under controlled reaction temperature of 150℃, a first chlorination was carried out for 2.5 hours, yielding VOCl3 and a first residue. The gaseous VOCl3 generated was collected by condensation. The first residue was then subjected to a second chlorination under inert gas conditions at 230℃ for 2.5 hours, yielding VOCl3 and a second residue. The gaseous VOCl3 generated by condensation was collected. The second residue was dissolved in water and leached at 80℃ for 2.5 hours. After filtration, the filtrate was subjected to precipitation treatment to recover chromium. Testing showed that the vanadium extraction rate was 80%, and the chromium recovery rate was 89%.

[0042] Comparative Example 1

[0043] High-chromium vanadium slag raw material was sieved through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.6:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 800℃ for 2 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4. The mixture was placed in a three-necked flask and subjected to a chlorination reaction under inert gas conditions at a controlled temperature of 160℃ for 2 hours to obtain VOCl₃ and residue. The generated gaseous VOCl₃ was collected by condensation. The residue was dissolved in water and leached at 80℃ for 2 hours. After filtration, the filtrate was subjected to precipitation treatment to recover chromium. The vanadium extraction rate was 43%, and the chromium recovery rate was 94%.

[0044] Except for the absence of a second chlorination at the second temperature, the comparative example was identical to Example 1. Its vanadium extraction rate was significantly lower than that of Example 1, indicating that the vanadium extraction was not thorough enough with only one chlorination reaction at a lower first temperature. Its chromium leaching rate was slightly higher than that of Example 1. This is because in Example 1, the second chlorination made the first residue react more thoroughly, and the pH of the solution changed after the second residue dissolved in water, thus affecting the chromium leaching rate. By adjusting the pH of the solution during leaching, the chromium recovery rate in Example 1 could be made consistent with that of Comparative Example 1.

[0045] Comparative Example 2

[0046] High-chromium vanadium slag raw material was sieved through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.45:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 1000℃ for 1.5 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask. Under inert gas conditions, the reaction temperature was controlled at 170℃ for a chlorination reaction for 1.5 hours, yielding VOCl₃ and residue. The generated gaseous VOCl₃ was collected by condensation. The residue was dissolved in water and leached at 80℃ for 1.5 hours. After filtration, the filtrate was subjected to precipitation treatment to recover chromium. Testing showed that the vanadium extraction rate was 50%, and the chromium recovery rate was 86%.

[0047] Comparative Example 3

[0048] High-chromium vanadium slag raw material was sieved through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.2:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 800℃ for 2 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask. Under inert gas conditions, the reaction temperature was controlled at 160℃ for a chlorination reaction for 2 hours to obtain VOCl₃ and residue. The generated gaseous VOCl₃ was collected by condensation. The residue was dissolved in water and leached at 80℃ for 2 hours. After filtration, the filtrate was subjected to precipitation treatment to recover chromium. The vanadium extraction rate was 66%, and the chromium recovery rate was 41%.

[0049] Comparative Example 4

[0050] High-chromium vanadium slag raw material was passed through a 200-mesh sieve and dried at 100℃ for 4 hours to obtain high-chromium vanadium slag. Na₂CO₃ and the high-chromium vanadium slag were mixed evenly at a mass ratio of 0.6:1, placed in a corundum crucible, and oxidized and roasted in a muffle furnace at 800℃ for 2 hours, ensuring sufficient oxygen in the furnace during the roasting process to obtain roasted clinker. The roasted clinker was mixed evenly with AlCl₃ and NaCl, with a mass ratio of roasted clinker:AlCl₃:NaCl of 3:6:4, and placed in a three-necked flask. Under inert gas conditions, the reaction temperature was controlled at 240℃ for a chlorination reaction for 2 hours to obtain VOCl₃ and residue. The generated gaseous VOCl₃ was collected by condensation. The residue was dissolved in water and leached at 80℃ for 2 hours. After filtration, the filtrate was subjected to precipitation treatment to recover chromium. The vanadium extraction rate was 74%, and the chromium recovery rate was 89%.

[0051] The comparative example is identical to Example 1 except that the chlorination reaction was not carried out at the first temperature. However, its vanadium extraction rate is lower than that of Example 1, indicating that the vanadium extraction is not thorough enough when only the chlorination reaction is carried out once at a higher second temperature.

[0052] Based on the above examples and comparative examples, it can be seen that when separating vanadium and chromium from high-chromium vanadium slag, the stepwise temperature-controlled chlorination method can greatly improve the vanadium extraction rate, while having virtually no impact on the chromium recovery rate.

[0053] The method for separating vanadium and chromium from high-chromium vanadium slag proposed in this application has the following advantages: it can achieve the separation of vanadium and chromium from high-chromium vanadium slag by combining oxidative roasting and stepwise temperature-controlled chlorination; it avoids the use of large amounts of organic solvents or the generation of high-concentration acidic wastewater, reducing environmental pollution and achieving the goal of green and clean separation of vanadium and chromium, which is in line with the concept of sustainable development; it is applicable to high-chromium vanadium slag with different compositions, and by adjusting the process parameters, it can achieve efficient separation of vanadium and chromium, and has good prospects for industrial application.

[0054] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for separating vanadium and chromium from high-chromium vanadium slag, characterized in that, Includes the following steps: S1. Obtain high-chromium vanadium slag, mix the high-chromium vanadium slag with sodium salt and oxidize and roast to obtain roasted clinker, wherein the vanadium content in the high-chromium vanadium slag is 10wt%~15wt% based on V2O5, and the chromium content is 5wt%~10wt% based on Cr2O3, wherein the sodium salt includes sodium carbonate, and the mass ratio of sodium carbonate to the high-chromium vanadium slag is 0.2:1~0.6:1; S2. The roasted clinker is subjected to a first chlorination under inert gas conditions to obtain vanadium oxychloride and a first residue. S3. The first residue is subjected to a second chlorination under inert gas conditions to obtain vanadium trichloride and a second residue, wherein the second residue contains chromium. In step S2: the roasted clinker is mixed with anhydrous aluminum chloride and sodium chloride, and chlorinated for the first time at a first temperature under inert gas conditions; In step S3: the first residue is subjected to a second chlorination at a second temperature under inert gas conditions; The second temperature is greater than the first temperature; In step S2, the first temperature is 150~170℃ and the time is 1.5~2.5h; in step S3, the second temperature is 230~250℃ and the time is 1.5~2.5h.

2. The method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that, The process after step S3 also includes: S4. Dissolve the second residue in water, filter and collect the filtrate, and perform precipitation treatment on the filtrate to recover the chromium in the precipitate.

3. The method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that, The steps preceding step S1 also include: The high-chromium vanadium slag raw material is sieved and dried to obtain high-chromium vanadium slag.

4. The method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that, In step S1, the oxidative calcination temperature is 700~1000℃ and the time is 1.5~2.5h.

5. A method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that, The mass ratio of the roasted clinker to the anhydrous aluminum chloride is 1:2, and the mass ratio of the anhydrous aluminum chloride to the sodium chloride is 3:

2.

6. A method for separating vanadium and chromium from high-chromium vanadium slag according to claim 2, characterized in that, In step S4, the temperature at which the second residue dissolves in water is 80°C and the time is 1.5~2.5h.