Method for preparing high-purity magnesium oxide by recovering magnesium from ferronickel slag

Abstract

The invention relates to the field of chemical engineering and material engineering, and provides a method for preparing high-purity magnesium oxide by taking ferronickel slag as a raw material, which comprises the following steps: (1) leaching: mixing ferronickel slag and sulfuric acid, leaching under normal-pressure heating and stirring conditions, and taking leachate after leaching; (2) primary crystallization: adding a seed crystal into the leachate, separating out coarse magnesium sulfate through primary crystallization, and carrying out solid-liquid separation to obtain coarse magnesium sulfate; (3) impurity removal: dissolving crude magnesium sulfate in water to obtain a magnesium sulfate crude solution, adding a neutralizing agent into the magnesium sulfate crude solution for neutralizing, hydrolyzing and removing impurities, and filtering to obtain a magnesium sulfate fine solution; (4) secondary crystallization: adding a seed crystal into the magnesium sulfate fine liquid for secondary crystallization to separate out high-purity magnesium sulfate; and (5) calcining: calcining the high-purity magnesium sulfate to obtain the high-purity magnesium oxide. The technology has the advantages of low equipment requirement, low production cost, high magnesium recovery rate, high magnesium oxide purity and high economic added value, and is convenient for industrial application.

Description

Technical Field

[0001] The invention relates to the field of chemical engineering and material engineering, and in particular to a method for recovering magnesium from nickel-ferronickel slag to prepare high-purity magnesium oxide. Background Art

[0002] Ferronickel slag is a type of solid waste generated during the production of ferronickel. It is the fourth largest smelting slag after blast furnace slag, steel slag, and red mud. At present, the utilization rate of ferronickel slag is relatively low. Nowadays, it is mainly disposed of by landfill. This direct landfill method not only has a certain impact on the ecological environment, but also occupies a large amount of land resources. According to the differences in the production methods of ferronickel, ferronickel slag can be divided into blast furnace smelting ferronickel slag and electric furnace smelting ferronickel slag. The content of magnesium oxide in electric furnace smelting ferronickel slag is relatively high, with a mass fraction of about 30%, which has important recycling value. The resource utilization of ferronickel slag is a systematic problem. Turning ferronickel slag into treasure has always been an important research topic for many scientific researchers.

[0003] As a commonly used chemical raw material, the purity of magnesium oxide determines its application field. High-purity magnesium oxide refers to a substance with a MgO content of more than 99%. It has good electrical insulation, thermal conductivity and a large thermal expansion coefficient. It is mainly used in the fields of electronics, national defense and aerospace. At present, the production of high-purity magnesium oxide at home and abroad mainly uses liquid or solid ore as raw materials. First, high-purity magnesium hydroxide is prepared, and then calcined at a certain temperature to obtain high-purity magnesium oxide. Other methods include gas phase method, inorganic acid dissolution method, soda ash method and carbonization method. However, these traditional methods for producing high-purity magnesium oxide have more or less problems of low product grade, generally small production scale and high energy consumption. It is urgent to develop a low-cost, energy-saving and efficient high-purity magnesium oxide production technology.

[0004] At present, although there are reports on the recovery of magnesium from nickel-iron slag, the product has problems of low purity and narrow application range, which makes it difficult to meet the needs of high-end technology and product fields. In addition, the active silicon content in nickel-iron slag is relatively high, and a large amount of silicic acid is easily produced when magnesium is leached, making subsequent solid-liquid separation difficult or even impossible. Therefore, in terms of recovering magnesium from nickel-iron slag, it is still necessary to develop an effective magnesium oxide production technology. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing high-purity magnesium oxide by using nickel-iron slag as a raw material.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing high-purity magnesium oxide using nickel-ferronickel slag as raw material comprises the following steps:

[0008] (1) Leaching: mixing nickel iron slag and sulfuric acid, leaching under normal pressure, heating and stirring, and taking leachate after leaching;

[0009] (2) primary crystallization: adding seed crystals to the leachate to precipitate crude magnesium sulfate through primary crystallization, and obtaining crude magnesium sulfate after solid-liquid separation;

[0010] (3) impurity removal: dissolving crude magnesium sulfate in water to obtain a crude magnesium sulfate solution, adding a neutralizing agent to the crude magnesium sulfate solution to neutralize and hydrolyze the impurities, and filtering to obtain a magnesium sulfate concentrate;

[0011] (4) Secondary crystallization: adding seed crystals to the magnesium sulfate solution for secondary crystallization to precipitate high-purity magnesium sulfate;

[0012] (5) Calcination: Calcine high-purity magnesium sulfate to obtain high-purity magnesium oxide.

[0013] The raw material nickel-iron slag is dried at 90-110°C before leaching for 6-12 hours, and then ball-milled at a speed of 250-300rpm for 4-8 hours. The powder after ball milling is sieved through a 300-mesh sieve, and the powder that does not pass the sieve is continued to be ball-milled for the next batch, and finally the nickel-iron slag powder with a particle size of ≤38μm is obtained for subsequent steps.

[0014] The sulfuric acid is a sulfuric acid solution with a concentration of 5 to 18 mol / L; the sulfuric acid and the nickel-iron slag are mixed at a liquid-to-solid ratio of 5 to 20:1 L / kg.

[0015] The normal pressure heating and stirring conditions are as follows: during leaching under standard pressure, the heating temperature is 140-180° C., the stirring speed is 600-1500 rpm, and the leaching time is 30-150 min.

[0016] The seed crystal is magnesium sulfate of any crystal water, including but not limited to anhydrous magnesium sulfate, magnesium sulfate monohydrate, magnesium sulfate trihydrate, magnesium sulfate hexahydrate, and magnesium sulfate heptahydrate.

[0017] In the primary crystallization step, the seed coefficient is 0.2 to 0.6, the final crystallization temperature ranges from -5 to 35°C, the crystallization time ranges from 2 to 10 hours, and the crystallization stirring speed ranges from 60 to 200 rpm.

[0018] In the impurity removal step, the impurity removal temperature ranges from 50 to 85° C., the stirring speed ranges from 200 to 600 rpm, the reaction time ranges from 60 to 240 min, and the pH value of the solution at the reaction endpoint ranges from 5 to 8.

[0019] The neutralizing agent is any one or more of magnesium oxide, magnesium hydroxide and magnesium carbonate.

[0020] In the secondary crystallization step, the crystallization starting temperature ranges from 60 to 85° C., the crystallization ending temperature ranges from 0 to 35° C., the crystallization time ranges from 1 to 6 hours, and the crystallization time setting can be adjusted according to the crystallization ending temperature.

[0021] In the calcination step, the calcination temperature ranges from 1200 to 1400° C., the calcination time ranges from 30 to 240 minutes, the atmosphere is air, and no flux, mineralizer, heat agent, reducing agent or other substances are added to ensure that no foreign impurities are introduced into the reaction system.

[0022] The raw material ferronickel slag used in the present invention has a particle size of 1 to 10 mm. In order to obtain a higher magnesium ion leaching rate, the ferronickel slag is pre-treated by ball milling so that the particle size of the treated ferronickel slag powder is controlled below 38 μm.

[0023] It needs to be further explained that: in addition to producing high-purity magnesium oxide, the thermal decomposition process of high-purity magnesium sulfate also produces SO2 and O2 gases. Due to the high SO2 concentration and extremely low impurity content in the gas, lime water can be used for adsorption to produce gypsum in small-scale production in the future, while in large-scale industrial production, an industrial method similar to the current lead and zinc smelting industry can be used to produce concentrated sulfuric acid, and it is expected to produce high-purity concentrated sulfuric acid.

[0024] The technical solution of the present invention has the following advantages:

[0025] 1. The present invention adopts the process route of ferronickel slag → crude magnesium sulfate → high-purity magnesium sulfate → high-purity magnesium oxide, separates magnesium oxide in ferronickel slag and converts it into high-purity magnesium oxide, the process flow is short, easy to operate, has low equipment requirements, high magnesium recovery rate, high economic added value, and can be applied to many high-tech fields such as high-purity target materials, substrates, high-performance ceramics, and electronic insulation devices. At the same time, the ferronickel slag resource utilization rate of the present invention is high, which is conducive to the large-scale reduction of the ferronickel slag stock in the future.

[0026] 2. The present invention uses magnesium oxide as an impurity remover, which reacts with sulfuric acid in the solution to generate magnesium sulfate. The purification process not only does not introduce foreign impurities, but also further increases the magnesium ion concentration in the purified solution while achieving the purification goal, thereby improving the yield of the product high-purity magnesium oxide.

[0027] 3. The solvent sulfuric acid concentration used in the present invention is relatively high. In the subsequent primary crystallization process, the high concentration sulfuric acid in the crystallization stock solution can produce a "common ion" effect, which is conducive to improving the crystallization rate of magnesium sulfate. After the primary crystallization, the acid content of the intermediate product crude magnesium sulfate is significantly reduced, which can significantly reduce the amount of neutralizer used in the impurity removal process.

[0028] 4. The purification method adopted by the present invention has a good removal effect on various impurities contained in the solution, with a high impurity removal rate and a low magnesium loss rate, thereby ensuring the purity of the final magnesium oxide product.

[0029] 5. The present invention uses a one-step pyrolysis process to calcine high-purity magnesium sulfate prepared from nickel-iron slag within a temperature range that can be easily reached by an industrial rotary kiln. The pyrolysis process does not add any flux, mineralizer, thermal agent, reducing agent or other substances, thereby ensuring that no foreign impurities are introduced into the reaction system, thereby achieving the goal of preparing high-purity magnesium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the XRD of the nickel iron slag raw material used in the present invention. All diffraction peaks correspond to the (Mg, Fe)2SiO4 phase, which has the same diffraction pattern as the Mg2SiO4 in the standard card. 2+ (0.072nm) and Fe 2+ The ionic radius of Fe is similar to that of Fe (0.078nm). 2+ It enters the Mg2SiO4 lattice to form (Mg,Fe)2SiO4 phase, which is a new solid solution composed of Mg2SiO4 and Fe2SiO4. The raised background near 23 degrees is due to the presence of a large amount of amorphous SiO2 in the nickel-iron slag.

[0031] Figure 2 This is a process flow chart of the present invention for preparing high-purity magnesium oxide using nickel-iron slag as raw material. Using nickel-iron slag as raw material, high-purity magnesium oxide is prepared mainly through six processes including pretreatment, leaching, primary crystallization, impurity removal, secondary crystallization, and calcination, and the tail gas is adsorbed with lime milk for harmless treatment.

[0032] Figure 3 The XRD diagram of the solid phase product obtained by calcining high-purity magnesium sulfate at different temperatures of the present invention. When the calcination temperature is 1150°C, the pyrolysis temperature is insufficient, and a large amount of magnesium sulfate phase remains in the product. When the temperature reaches 1200°C, the magnesium sulfate is completely decomposed and the magnesium oxide phase is almost completely generated, but it exists in the form of a mixed phase composed of a cubic phase and a tetragonal phase, and there is a weak impurity phase in the low-angle area. When the temperature reaches 1250°C, the magnesium sulfate is completely transformed into a single magnesium oxide cubic phase.

[0033] Figure 4 This is a SEM of the high-purity magnesium oxide produced in Example 1 of the present invention. The magnesium oxide particles are agglomerated by many grains of irregular geometric shapes, and the grain sizes vary from submicron to tens of microns. DETAILED DESCRIPTION

[0034] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0035] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0036] The nickel-iron slag phase structure used in the embodiment is as follows Figure 2 The main chemical composition is shown in Table 1. It can be seen that the SiO2 content in the slag is 52wt%, and the MgO content is 36.3wt%. It has the characteristics of high Si and Mg content and low Fe, Al and Ca content.

[0037] Table 1 shows the main chemical composition (wt%) of the raw material ferronickel slag.

[0038]

[0039] Example 1

[0040] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0041] S1. Pretreatment: First, the nickel-iron slag is dried at 105° C. for 12 h, and then ball-milled. The ball-to-material ratio during ball milling is 3:1, the rotation speed of the planetary ball mill is set to 300 rpm, the revolution speed is 600 rpm, and the ball milling time is 6 h. The powder after ball milling is sieved with a 300-mesh sieve to obtain nickel-iron slag fine powder with a particle size not exceeding 38 μm. The powder that does not pass the sieve is returned to the next batch for further ball milling. Finally, all batches of sieved materials are mixed together, and the obtained nickel-iron slag fine powder is used as the solute for the subsequent leaching step.

[0042] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 15Mol / L under the condition of a liquid-solid ratio of 20:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 180°C, the stirring rate is 600rpm, the stirring time is 120min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and after the filtration is completed, wash the filter cake twice with a 3Mol / L hot sulfuric acid solution, mix the washing liquid with the previous filtrate to obtain about 400ml of magnesium sulfate solution, which is used as the subsequent crystallization stock solution of magnesium sulfate.

[0043] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.5 as a seed crystal, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 85°C, the crystallization final temperature to 25°C, the crystallization time to 6h, stir during the cooling process, and the stirring rate is 60rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0044] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it with water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 85°C, the reaction time is 2h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0045] S5. Secondary crystallization: magnesium sulfate semen was used as the stock solution for secondary crystallization, magnesium sulfate heptahydrate with a seed coefficient of 0.3 was added thereto as a seed crystal, and the beaker was placed in a water bath to control the cooling rate of the crystallization stock solution. The initial crystallization temperature was set to 60°C, the final crystallization temperature was set to 25°C, and the crystallization time was set to 6h. When the solution temperature dropped to 25°C, the slurry was taken out and vacuum filtered to obtain a magnesium sulfate secondary crystallization product.

[0046] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1250℃, and the calcination time is 120min, generating solid phase magnesium oxide and tail gas. The tail gas is a mixture of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0047] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.58%. The specific chemical composition is shown in Appendix 2.

[0048] Example 2

[0049] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0050] S1. Pretreatment: same as in Example 1.

[0051] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 11Mol / L under the condition of a liquid-to-solid ratio of 10:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 170°C, the stirring rate is 600rpm, the stirring time is 60min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and wash the filter cake twice with a 5Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution. The solution obtained under this condition is used as the crystallization stock solution of magnesium sulfate in the subsequent sequence.

[0052] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.2 as a seed crystal, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 85°C, the crystallization final temperature to 25°C, the crystallization time to 10h, stir during the cooling process, and the stirring rate is 60rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0053] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it in water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 75°C, the reaction time is 2h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0054] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.3 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 70°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 5h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0055] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1200℃, the calcination time is 240min, and solid-phase magnesium oxide and tail gas are generated. The tail gas is a mixed gas of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0056] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.50%. The specific chemical composition is shown in Appendix 2.

[0057] Example 3

[0058] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0059] S1. Pretreatment: same as in Example 1.

[0060] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 15Mol / L under the condition of a liquid-to-solid ratio of 20:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 160°C, the stirring rate is 900rpm, the stirring time is 60min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and wash the filter cake twice with a 5Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution. The solution obtained under this condition is used as the crystallization stock solution of subsequent magnesium sulfate.

[0061] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.6 as a seed crystal, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 85°C, the crystallization final temperature to 25°C, the crystallization time to 2h, stir during the cooling process, and the stirring rate is 70rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0062] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it in water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 75°C, the reaction time is 1.5h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0063] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.3 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 80°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 4h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0064] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1300℃, the calcination time is 120min, and solid phase magnesium oxide and tail gas are generated. The tail gas is a mixed gas of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0065] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.64%. The specific chemical composition is shown in Appendix 2.

[0066] Example 4

[0067] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0068] S1. Pretreatment: same as in Example 1.

[0069] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 13Mol / L under the condition of a liquid-to-solid ratio of 15:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 180°C, the stirring rate is 1500rpm, the stirring time is 60min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and wash the filter cake twice with a 3Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution. The solution obtained under this condition is used as the crystallization stock solution of magnesium sulfate in the subsequent sequence.

[0070] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.4 as a seed crystal to the stock solution, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 80°C, the crystallization final temperature to 25°C, the crystallization time to 4h, stir during the cooling process, and the stirring rate is 80rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0071] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it with water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 75°C, the reaction time is 2h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 7, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0072] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.3 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 60°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 3h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0073] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1250℃, and the calcination time is 150min, to generate solid phase magnesium oxide and tail gas. The tail gas is a mixture of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0074] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.58%. The specific chemical composition is shown in Appendix 2.

[0075] Example 5

[0076] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0077] S1. Pretreatment: same as in Example 1.

[0078] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 8Mol / L under the condition of a liquid-to-solid ratio of 8:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 180°C, the stirring rate is 600rpm, the stirring time is 60min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and wash the filter cake twice with a 5Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution. The solution obtained under this condition is used as the crystallization stock solution of magnesium sulfate in the subsequent sequence.

[0079] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.5 as a seed crystal, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 80°C, the crystallization final temperature to 25°C, the crystallization time to 9h, stir during the cooling process, and the stirring rate is 60rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0080] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it in water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 75°C, the reaction time is 2h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 8, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0081] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.3 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 75°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 4h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0082] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1300℃, the calcination time is 120min, and solid phase magnesium oxide and tail gas are generated. The tail gas is a mixed gas of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0083] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.65%. The specific chemical composition is shown in Appendix 2.

[0084] Example 6

[0085] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0086] S1. Pretreatment: same as in Example 1.

[0087] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 15Mol / L under the condition of a liquid-to-solid ratio of 20:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 140°C, the stirring rate is 600rpm, the stirring time is 150min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and wash the filter cake twice with a 5Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution. The solution obtained under this condition is used as the crystallization stock solution of subsequent magnesium sulfate.

[0088] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.5 as a seed crystal, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 85°C, the crystallization final temperature to 25°C, the crystallization time to 6h, stir during the cooling process, and the stirring rate is 60rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0089] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it with water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 65°C, the reaction time is 3h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0090] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.4 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 60°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 5h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0091] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1300℃, the calcination time is 60min, and solid phase magnesium oxide and tail gas are generated. The tail gas is a mixed gas of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0092] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.70%. The specific chemical composition is shown in Appendix 2.

[0093] Example 7

[0094] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0095] S1. Pretreatment: same as in Example 1.

[0096] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 10Mol / L under the condition of a liquid-to-solid ratio of 5:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 180°C, with a stirring rate of 600rpm, stirring time of 30min, standing for 30min, taking out the flask, filtering the leached slurry with a Buchner funnel, and washing the filter cake twice with a 3Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution, and the solution obtained under this condition is used as the crystallization stock solution of magnesium sulfate in the subsequent sequence.

[0097] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.5 as a seed crystal to the stock solution, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 75°C, the crystallization final temperature to 25°C, the crystallization time to 8h, stir during the cooling process, and the stirring rate is 60rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0098] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it with water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 75°C, the reaction time is 2h, and stirring is performed at the same time, the stirring speed is 600rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0099] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.3 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 60°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 2h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0100] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1350℃, the calcination time is 90min, and solid phase magnesium oxide and tail gas are generated. The tail gas is a mixed gas of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0101] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.62%. The specific chemical composition is shown in Appendix 2.

[0102] Example 8

[0103] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material, comprising the following steps:

[0104] S1. Pretreatment: same as in Example 1.

[0105] S2, leaching: weigh 20g of nickel-iron slag fine powder and place it in a three-necked flask, add a sulfuric acid solution with a concentration of 5Mol / L under the condition of a liquid-solid ratio of 20:1 (ml / g), then move the flask into a constant temperature heating jacket, stir while heating, and start constant temperature stirring when the solution is heated to 180°C, the stirring rate is 600rpm, the stirring time is 100min, and after standing for 30min, take out the flask, filter the leached slurry with a Buchner funnel, and wash the filter cake twice with a 5Mol / L hot sulfuric acid solution after the filtration. The washing solution obtained is mixed with the previous filtrate to obtain about 400ml of magnesium sulfate solution. The solution obtained under this condition is used as the crystallization stock solution of magnesium sulfate in the subsequent sequence.

[0106] S3, primary crystallization: Place the crystallization stock solution in a large beaker, add magnesium sulfate heptahydrate with a seed coefficient (ratio of magnesium mass in the seed to magnesium mass in the stock solution) of 0.5 as a seed crystal to the stock solution, then place the beaker in a water bath, control the cooling rate of the crystallization stock solution, set the crystallization starting temperature to 70°C, the crystallization final temperature to 25°C, the crystallization time to 8h, stir during the cooling process, and the stirring rate is 60rpm. When the solution temperature drops to 25°C, take out the slurry and perform vacuum filtration to obtain a primary crystallization product, crude magnesium sulfate.

[0107] S4, impurity removal: put the crude magnesium sulfate obtained by cooling and crystallization into a beaker, dissolve it with water, and obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 65°C, the reaction time is 1h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium oxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium oxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0108] S5. Secondary crystallization: The magnesium sulfate semen after impurity removal is used as the stock solution for secondary crystallization, and magnesium sulfate heptahydrate with a seed coefficient of 0.4 is added to the stock solution as a seed crystal, and then the beaker is placed in a water bath to control the cooling rate of the crystallization stock solution. The crystallization starting temperature is set to 70°C, the crystallization final temperature is set to 25°C, and the crystallization time is set to 3h. When the solution temperature drops to 25°C, the slurry is taken out and vacuum filtered to obtain a magnesium sulfate secondary crystal product.

[0109] S6, calcination: the secondary crystallization product of magnesium sulfate is kept at 200℃ for a period of time for dehydration, and then the dehydrated product is placed in a tube furnace for calcination. The calcination temperature is 1400℃, the calcination time is 30min, and solid phase magnesium oxide and tail gas are generated. The tail gas is a mixed gas of sulfur dioxide and oxygen, which is absorbed and neutralized by lime milk solution.

[0110] The solid phase product obtained in the above steps was tested and found to have a magnesium oxide purity of 99.62%. The specific chemical composition is shown in Appendix 2.

[0111] Example 9

[0112] The present embodiment relates to a method for preparing high-purity magnesium oxide using nickel-iron slag as a raw material. Except that the impurity remover in the S4 impurity removal step is different from that in Example 1, the remaining steps are exactly the same as those in Example 1. The S4 impurity removal step in this embodiment is as follows: the crude magnesium sulfate obtained by cooling and crystallization is placed in a beaker and dissolved with water to obtain a crude magnesium sulfate solution. The beaker is placed in a water bath, the reaction temperature is set to 85°C, the reaction time is 2h, and stirring is performed at the same time, the stirring speed is 500rpm, and magnesium hydroxide is added while stirring to neutralize and hydrolyze the impurities, and the impurities undergo a hydrolysis reaction to form a precipitate. When the end point pH value of the solution is 6, stop adding magnesium hydroxide, continue heating and stirring for 2h, and then perform vacuum filtration to obtain magnesium sulfate semen.

[0113] The solid phase product obtained in the above steps was tested and the purity of magnesium oxide reached 99.56%. The specific chemical composition is shown in Appendix 2.

[0114] The main chemical components of the high-purity oxidized magnesium prepared in Examples 1 to 9 are summarized in Table 2.

[0115] Table 2 Main chemical composition (wt%) of high purity magnesium oxide prepared in Examples 1 to 9

[0116]

[0117]

[0118] As can be seen from Table 2, the main chemical component of the products of the technical solutions of each embodiment is MgO, and its purity is above 99wt%. When calcined at 1250°C or above, the purity of the product is above 99.5wt%. The impurity content of the product is very low, mainly Fe, Si, Al, Ca and other elements, which come from the raw material nickel-iron slag.

[0119] Example 10

[0120] A method for preparing high-purity magnesium oxide using nickel-ferronickel slag as raw material, characterized in that it comprises the following steps:

[0121] The raw nickel-iron slag was dried at 90°C for 6 hours before leaching, and then ball-milled at a speed of 250 rpm for 4 hours. The powder after ball milling was sieved through a 300-mesh sieve, and the powder that did not pass the sieve was continued to be ball-milled for the next batch, and finally the nickel-iron slag powder with a particle size of ≤38 μm was obtained for subsequent steps.

[0122] (1) Leaching: Mix the nickel-iron slag and sulfuric acid, and leach under normal pressure heating and stirring conditions, and take the leachate after leaching; the sulfuric acid is a sulfuric acid solution with a concentration of 5 Mol / L; sulfuric acid and nickel-iron slag are mixed at a liquid-solid ratio of 5:1 L / kg. The normal pressure heating and stirring conditions are that the heating temperature is 140°C, the stirring speed is 600 rpm, and the leaching time is 30 min when leaching under standard pressure.

[0123] (2) Primary crystallization: adding seed crystals to the leachate, precipitating crude magnesium sulfate through primary crystallization, and obtaining crude magnesium sulfate after solid-liquid separation; the seed crystal coefficient is 0.2, the crystallization end temperature range is -5°C, the crystallization time range is 2h, and the crystallization stirring speed range is 60rpm.

[0124] (3) Impurity removal: dissolving crude magnesium sulfate in water to obtain a crude magnesium sulfate solution, adding a neutralizing agent to the crude magnesium sulfate solution for neutralization and hydrolysis to remove impurities, and filtering to obtain a magnesium sulfate concentrate; the impurity removal temperature range is 50° C., the stirring speed range is 200 rpm, the reaction time range is 60 min, and the pH value range of the solution reaction endpoint is 5.

[0125] (4) Secondary crystallization: adding seed crystals to the magnesium sulfate concentrate to perform secondary crystallization to precipitate high-purity magnesium sulfate; the crystallization starting temperature range is 60-85°C, the crystallization ending temperature range is 0°C, the crystallization time range is 1h, and the crystallization time setting can be adjusted according to the crystallization ending temperature.

[0126] (5) Calcination: Calcination of high-purity magnesium sulfate to obtain high-purity magnesium oxide. The calcination temperature range is 1200°C, the calcination time range is 30 minutes, the atmosphere is air, and no flux, mineralizer, heat agent, reducing agent or other substances are added to ensure that no foreign impurities are introduced into the reaction system.

[0127] Embodiment 11

[0128] A method for preparing high-purity magnesium oxide using nickel-ferronickel slag as raw material, characterized in that it comprises the following steps:

[0129] The raw nickel-iron slag was dried at 110°C for 12 h before leaching, and then ball-milled at a speed of 300 rpm for 8 h. The powder after ball milling was sieved through a 300-mesh sieve, and the powder that did not pass the sieve was continued to be ball-milled for the next batch, and finally the nickel-iron slag powder with a particle size of ≤38 μm was obtained for subsequent steps.

[0130] (1) Leaching: Mix the nickel-iron slag and sulfuric acid, and leach under normal pressure heating and stirring conditions, and take the leachate after leaching; the sulfuric acid is a sulfuric acid solution with a concentration of 18 Mol / L; the sulfuric acid and the nickel-iron slag are mixed at a liquid-solid ratio of 20:1 L / kg. The normal pressure heating and stirring conditions are that the heating temperature is 180°C, the stirring speed is 1500 rpm, and the leaching time is 150 min when leaching under standard pressure.

[0131] (2) Primary crystallization: adding seed crystals to the leachate, precipitating crude magnesium sulfate through primary crystallization, and obtaining crude magnesium sulfate after solid-liquid separation; the seed crystal coefficient is 0.6, the crystallization end temperature range is 35°C, the crystallization time range is 10 hours, and the crystallization stirring speed range is 200 rpm.

[0132] (3) Impurity removal: dissolving crude magnesium sulfate in water to obtain a crude magnesium sulfate solution, adding a neutralizing agent to the crude magnesium sulfate solution for neutralization and hydrolysis to remove impurities, and filtering to obtain a magnesium sulfate concentrate; the impurity removal temperature range is 85° C., the stirring speed range is 600 rpm, the reaction time range is 240 min, and the pH value range of the solution reaction endpoint is 8.

[0133] (4) Secondary crystallization: adding seed crystals to the magnesium sulfate concentrate to perform secondary crystallization to precipitate high-purity magnesium sulfate; the crystallization starting temperature range is 85°C, the crystallization ending temperature range is 35°C, the crystallization time range is 6 hours, and the crystallization time setting can be adjusted according to the crystallization ending temperature.

[0134] (5) Calcination: Calcination of high-purity magnesium sulfate to obtain high-purity magnesium oxide. The calcination temperature range is 1400°C, the calcination time range is 240 minutes, the atmosphere is air, and no flux, mineralizer, heat agent, reducing agent or other substances are added to ensure that no foreign impurities are introduced into the reaction system.

[0135] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing high-purity magnesium oxide using ferronickel slag as raw material, characterized in that: The steps include: (1) Leaching: mixing nickel iron slag and sulfuric acid, leaching under normal pressure, heating and stirring, and taking leachate after leaching; (2) primary crystallization: adding seed crystals to the leachate to precipitate crude magnesium sulfate through primary crystallization, and obtaining crude magnesium sulfate after solid-liquid separation; (3) impurity removal: dissolving crude magnesium sulfate in water to obtain a crude magnesium sulfate solution, adding a neutralizing agent to the crude magnesium sulfate solution to neutralize and hydrolyze the impurities, and filtering to obtain a magnesium sulfate concentrate; (4) Secondary crystallization: adding seed crystals to the magnesium sulfate solution for secondary crystallization to precipitate high-purity magnesium sulfate; (5) Calcination: Calcine high-purity magnesium sulfate to obtain high-purity magnesium oxide.

2. The method according to claim 1, characterized in that The raw material nickel-iron slag is dried at 90-110°C before leaching for 6-12 hours, and then ball-milled at a speed of 250-300rpm for 4-8 hours. The powder after ball milling is sieved through a 300-mesh sieve, and the powder that does not pass the sieve is continued to be ball-milled for the next batch, and finally the nickel-iron slag powder with a particle size of ≤38μm is obtained for subsequent steps.

3. The method according to claim 1, characterized in that The sulfuric acid is a sulfuric acid solution with a concentration of 5 to 18 mol / L; the sulfuric acid and the nickel-iron slag are mixed at a liquid-to-solid ratio of 5 to 20:1 L / kg.

4. The method according to claim 1, characterized in that: The normal pressure heating and stirring conditions are as follows: during leaching under standard pressure, the heating temperature is 140-180° C., the stirring speed is 600-1500 rpm, and the leaching time is 30-150 min.

5. The method according to claim 1, characterized in that The seed crystal is magnesium sulfate of any crystal water, including but not limited to anhydrous magnesium sulfate, magnesium sulfate monohydrate, magnesium sulfate trihydrate, magnesium sulfate hexahydrate, and magnesium sulfate heptahydrate.

6. The method according to claim 1, characterized in that In the primary crystallization step, the seed coefficient is 0.2 to 0.6, the final crystallization temperature ranges from -5 to 35°C, the crystallization time ranges from 2 to 10 hours, and the crystallization stirring speed ranges from 60 to 200 rpm.

7. The method according to claim 1, characterized in that In the impurity removal step, the impurity removal temperature ranges from 50 to 85° C., the stirring speed ranges from 200 to 600 rpm, the reaction time ranges from 60 to 240 min, and the pH value of the solution at the reaction endpoint ranges from 5 to 8.

8. The method according to claim 1, characterized in that: The neutralizing agent is any one or more of magnesium oxide, magnesium hydroxide and magnesium carbonate.

9. The method according to claim 1, characterized in that: In the secondary crystallization step, the crystallization starting temperature ranges from 60 to 85° C., the crystallization ending temperature ranges from 0 to 35° C., the crystallization time ranges from 1 to 6 hours, and the crystallization time setting can be adjusted according to the crystallization ending temperature.

10. The method according to claim 1, characterized in that In the calcination step, the calcination temperature ranges from 1200 to 1400° C., the calcination time ranges from 30 to 240 minutes, the atmosphere is air, and no flux, mineralizer, heat agent, reducing agent or other substances are added to ensure that no foreign impurities are introduced into the reaction system.

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