CN105018736A - Method for comprehensive recovery of magnesium, aluminum, chromium and iron in carbon ferrochrome smelting slag - Google Patents

Abstract

The invention relates to a comprehensive recovery method for magnesium, aluminum, chromium and iron in carbon ferrochrome smelting slag, which breaks through the traditional jigging method of single recovery of ferrochrome alloy, and greatly improves the recovery rate of valuable metals magnesium and aluminum . This method uses ammonium sulfate activation roasting technology to efficiently convert magnesium, aluminum, chromium, iron and other metals in carbon ferrochromium smelting slag into corresponding water-soluble metal ammonium sulfate salts, and then leaching the roasted products. And further combine the solubility difference of metal ammonium sulfate to realize the separation of each main metal component one by one, and finally realize the efficient and comprehensive recovery of valuable components in carbon ferrochrome smelting slag. The technological process of the present invention is simple, and the recovery rates of magnesium, aluminum, chromium, and iron can respectively reach over 88%, over 82%, over 90%, and over 88%, and its application will be high-value utilization of carbon ferrochromium smelting slag Provide an efficient method.

Description

A method for comprehensive recovery of magnesium, aluminum, chromium and iron in carbon ferrochrome smelting slag

technical field

The invention relates to a comprehensive recovery method for magnesium, aluminum, chromium and iron in carbon ferrochrome smelting slag, in particular to a method for using ammonium sulfate to roast carbon ferrochrome smelting slag and then wet leaching and separately extracting magnesium , aluminum, chromium, iron method.

Background technique

Chromium is an important alloying element in the field of metal materials, mainly used in metallurgy, chemical industry and refractory production. In recent years, my country's stainless steel industry has grown rapidly, and the demand for ferrochrome is increasing. Carbon chromium ferrochrome alloys contain a small amount of silicon, phosphorus, sulfur and other elements in addition to chromium, iron, and carbon. Chromium can significantly improve the mechanical properties of steel and make steel reach special physical and chemical indicators. Therefore, ferrochrome is An important alloying agent for smelting alloy steel; chromium can also significantly improve the wear resistance of cast iron, increase the hardness of cast iron, and make cast iron have good heat resistance, so ferrochrome can be used as an additive in the production of cast iron; in addition, ferrochrome carbon It is also a chromium-containing raw material for the production of silicon-chromium alloys by the slag-free method. Carbon ferrochromium has a wide range of applications and a large demand. It is an important raw material for the national metallurgical industry. In 2013, my country's consumption reached 5.8 million tons.

The smelting process of carbon ferrochrome is as follows: under high temperature, coke is used as reducing agent, silica or bauxite is used as flux, and chromite ore is smelted in reduction electric furnace, and a large amount of slag is produced at the same time. Generally speaking, about 1.1-1.2 tons of carbon ferrochrome smelting slag will be produced for every ton of carbon ferrochrome, and its composition is generally _MgO30-34 % (wt), _Al2O3 26-30% (wt), SiO ₂ 27-33% (wt), Cr ₂ O ₃ <9.0% (wt). It can be seen that the main valuable components in carbon ferrochromium smelting slag are magnesium and aluminum. At the same time, in the smelting process of carbon ferrochrome, due to the high melting point and high viscosity of the slag, it is difficult to completely separate the slag and iron, so a certain amount of carbon ferrochrome will inevitably be entrained in the carbon ferrochrome smelting slag.

Although the value of carbon ferrochromium smelting slag is relatively high, because the magnesium and aluminum in it exist in phases such as spinel and olivine, the structure is stable, and the extraction is difficult. Stockpiled more than 20 million tons. At present, for the treatment process of carbon ferrochromium smelting slag, the current research and application work mainly include the ferrochrome alloy and chromium concentrate entrained in the recovered slag, and the direct use of carbon ferrochrome smelting slag in the production of refractory materials.

The separation of ferrochrome alloy and chrome concentrate in carbon ferrochrome smelting slag mainly adopts methods such as magnetic separation and gravity separation. The magnetic separation process is based on the fact that the unreacted chromite in the carbon ferrochrome smelting slag has weak magnetism and the ferrochrome alloy has strong magnetism, and the magnetic separation intensity is controlled to recover the ferrochrome and chromite in the slag; this process only needs The waste slag is crushed and sieved into different particle sizes and then magnetically separated. China's Jilin Ferroalloy Factory has used magnetic separation technology to recover magnetic components from carbon ferrochrome smelting slag. After carbon ferrochrome smelting slag is crushed and ball milled to a particle size of less than 0.9mm, it can be recovered from carbon ferrochrome smelting slag. More than 90% Cr ₂ O ₃ component. Aiming at the high-value ferrochromium alloy in carbon ferrochrome smelting slag, the continuous practice of many ferroalloy factories at home and abroad proves that it can be recovered by jigging gravity separation technology; at the beginning of this century, Mintek, a South African research institution, successfully developed a carbon The AFS process for recovering metal alloys from plain ferrochrome smelting slag has been commercialized in six ferrochrome companies around the world. The recovered alloys contain less than 2% slag and can be sold directly.

The utilization of carbon ferrochrome smelting slag also includes the production of refractory materials (non-burned magnesia chrome bricks and non-burned magnesia bricks), glass-ceramics, substitutes for plugging magnesia, cement admixtures and road paving, etc. Based on the phase diagram, Li Zhijian, Dou Shuju and others added sintered magnesia to carbon ferrochrome smelting slag to develop an alkaline refractory material, which is used for masonry ferromanganese lining. The service life is two times that of the original magnesia brick lining. times. Wang Zhiqiang, Ma Chun and others used 30% to 40% carbon ferrochromium smelting slag, 30% to 40% silicomanganese slag, and 20% to 30% sodium calcium cullet to melt at 1420 ° C for 1 hour, and Heat treatment under an appropriate temperature system can obtain glass-ceramics whose main crystal phase is diopside.

Although the various carbon ferrochrome slag utilization processes mentioned above have their obvious characteristics and advantages, the main valuable components of magnesium and aluminum in the carbon ferrochrome slag have not been utilized at high value, resulting in waste of resources .

Contents of the invention

The purpose of the present invention is to provide a technically feasible, economical and reasonable ammonium sulfate roasting method for the comprehensive recovery of carbon ferrochrome in order to overcome the ineffective use of valuable metals such as magnesium and aluminum in the existing carbon ferrochrome smelting slag treatment method A new method for valuable metals such as magnesium, aluminum, chromium and iron in smelting slag.

The purpose of the present invention is achieved through the following technical solutions.

A method for the comprehensive recovery of magnesium, aluminum, chromium and iron in carbon ferrochrome smelting slag, which uses ammonium sulfate roasting activation and roasting product leaching-multi-metal separation to achieve high efficiency of valuable metals such as magnesium, aluminum, chromium and iron. The method of extraction and recovery, the ammonium sulfate roasting process converts the magnesium, aluminum, chromium, iron and other metals in the carbon ferrochromium smelting slag into corresponding roasted products of metal ammonium sulfate salts that are easily soluble in water, and the roasted products are leached by aqueous solution According to the solubility difference of metal ammonium sulfate, the main metal components in the leachate can be separated one by one. It is characterized in that the operation process of the method comprises:

(a) After grinding the carbon ferrochrome slag until more than 80% of the particles are less than 74 μm, mix the ammonium sulfate and carbon ferrochrome slag evenly according to a certain mass ratio;

(b) After step (a), the mixture of ammonium sulfate and carbon ferrochrome smelting slag is placed in a rotary kiln for roasting at a certain temperature for a certain period of time, and the roasting tail gas is absorbed with water;

(c) After step (b), leaching the calcined material with an aqueous solution at a certain volume-to-mass ratio and a certain temperature for a certain period of time, after the leaching ends, the liquid and solid are separated, the solid phase is residual silicon slag, and the liquid phase is magnesium, aluminum, chromium , The leaching solution of metal ammonium sulfate salt of iron;

(d) After the step (c) is finished, the leaching solution of the metal ammonium sulfate salt is cooled to a certain temperature and stirred for a certain period of time, and then separated from the liquid and solid to obtain the ammonium aluminum sulfate dodecahydrate product, and the liquid phase is the liquid after aluminum removal;

(e) After step (d), use the tail gas absorption liquid or ammonia water obtained in step (b) to neutralize the liquid after aluminum removal to near neutrality at a certain temperature, control the pH value at 6-8, and then separate the liquid and solid, and the solid The phase is a mixture of chromium hydroxide and iron hydroxide, which will become chrome black when calcined, and the liquid phase is magnesium-rich liquid;

(f) After step (e), add a certain amount of ammonium sulfate solid to the magnesium-enriched liquid and stir for a period of time, then separate the liquid and solid, the solid phase is magnesium ammonium sulfate hexahydrate crystals, and the liquid phase is ammonium sulfate solution;

(g) After step (f) is finished, the ammonium sulfate solution is evaporated and crystallized, the solid obtained by crystallization is returned to step (a) and step (f), and the crystallization mother liquor is returned to the leaching process in step (c);

(h) After step (f) ends, process ammonium magnesium sulfate hexahydrate crystals for a certain period of time at a certain temperature and a liquid-solid ratio (volume to mass ratio) with a certain concentration of ammonia solution, after liquid-solid separation, the liquid phase is an ammonium sulfate solution And return to step (g), merge with the ammonium sulfate solution that step (f) obtains and enter the evaporative crystallization process, the solid phase is the magnesium hydroxide product.

The method of the present invention is characterized in that the mass ratio of ammonium sulfate to carbon ferrochrome smelting slag in step (a) is 2:1-10:1.

The method of the present invention is characterized in that: in step (b), the calcination temperature is 300-550° C., and the calcination time is 2-8 hours.

The method of the present invention is characterized in that: in step (c), the volume-to-mass ratio during leaching of the calcined material is 2:1-10:1, the leaching temperature is 25°C-130°C, and the leaching time is 0.5-5h.

The method of the present invention is characterized in that: in the step (d), the cooling crystallization temperature of the leaching solution is 20° C. to 40° C., and the cooling crystallization time is 0.5 to 5 hours.

The method of the present invention is characterized in that the temperature for neutralizing and removing iron in step (e) is 25°C to 90°C.

The method of the present invention is characterized in that: the addition amount of ammonium sulfate solid in the step (f) is to control the mass concentration of ammonium sulfate in the magnesium-rich liquid to be 10% to 40%, and the time for stirring and crystallizing out ammonium magnesium sulfate hexahydrate is 0.5 ~3h.

The method of the present invention is characterized in that: the concentration of the ammonia solution in step (h) is 5% to 25%, the temperature for processing magnesium ammonium sulfate hexahydrate crystals is 25°C to 100°C, and the liquid-solid ratio is 2:1 to 10 :1, the processing time is 0.5~5h.

A method for comprehensive recovery of magnesium, aluminum, chromium and iron in carbon ferrochrome smelting slag breaks through the traditional jigging method of single recovery of ferrochrome alloy, and greatly improves the recovery rate of valuable metals magnesium and aluminum. This method uses ammonium sulfate activation roasting technology to efficiently convert magnesium, aluminum, chromium, iron and other metals in carbon ferrochromium smelting slag into corresponding water-soluble metal ammonium sulfate salts, and then leaching the roasted products. And further combine the solubility difference of metal ammonium sulfate to realize the separation of each main metal component one by one, and finally realize the efficient and comprehensive recovery of valuable components in carbon ferrochrome smelting slag. The invention has simple technological process and high recovery rate of magnesium, aluminum, chromium and iron, and its application will provide an effective method for high-value utilization of carbon ferrochrome smelting slag.

Description of drawings

Fig. 1 is the applicable process flow chart of the present invention.

specific implementation plan

The implementation process and steps of the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that these examples are only used to further illustrate the experimental scheme of the present invention, and are not used to limit the present invention. The composition of the carbon ferrochrome smelting slag used in the embodiment of the present invention is: MgO38.42%, _Al2O324.74 %, _SiO224.90 %, _Cr4.88 %, Fe3.28%, carbon ferrochrome smelting slag The composition of can also be other specific content, which cannot be used to limit the protection scope of the present invention.

Example 1

Take a certain quality of carbon ferrochrome smelting slag, and grind it until more than 80% of the particles are less than 74 μm, mix ammonium sulfate and carbon ferrochrome smelting slag evenly at a mass ratio of 4:1; place the mixture on a rotary Roast in the kiln at 350°C for 6 hours, and absorb the tail gas generated during the roasting process with water to form an alkaline absorption liquid for later use; after the roasting reaction is completed, the roasted material is leached with water at 120°C for 0.5h, and the volume-to-mass ratio during leaching is 3:1 After the leaching is finished, liquid-solid separation is carried out, the solid phase is residual silicon slag, and the liquid phase is a metal ammonium sulfate solution containing magnesium, aluminum, chromium and iron; the metal ammonium sulfate solution is cooled to 25°C and stirred for 0.5h, After liquid-solid separation, the ammonium aluminum sulfate dodecahydrate product and the liquid after aluminum removal are obtained; the liquid after aluminum removal is neutralized at 60°C with an alkaline absorption liquid to a pH value of 7.0, and then the liquid-solid separation is performed, and the solid phase is hydroxide The mixture of chromium and ferric hydroxide is reserved for roasting to prepare chrome black, and the liquid phase is magnesium-rich liquid; ammonium sulfate crystals are added to the magnesium-rich liquid so that the mass concentration of ammonium sulfate in the magnesium-rich liquid is 20%, and stirred for 0.5h , and then liquid-solid separation to obtain magnesium ammonium sulfate hexahydrate crystals and ammonium sulfate solution; the magnesium ammonium sulfate hexahydrate crystals were treated with 25% ammonia solution at a liquid-solid ratio of 3:1 and a temperature of 60°C for 2 hours, after liquid-solid separation Obtain magnesium hydroxide product and ammonium sulfate solution; mix magnesium ammonium sulfate hexahydrate crystals with ammonium sulfate solution produced during the preparation of magnesium hydroxide products, and evaporate and crystallize to obtain ammonium sulfate crystals, which are recycled for a new batch of chromium carbon The roasting process of iron smelting slag and the preparation process of magnesium ammonium sulfate hexahydrate crystals, and the leaching process of ammonium sulfate evaporated mother liquor used for roasting materials. After carbon ferrochrome smelting slag is processed by this process, the recoveries of Mg, Al, Cr and Fe in the slag are 88.15%, 82.68%, 90.75% and 88.73% respectively.

Example 2

Take a certain quality of carbon ferrochrome smelting slag, and grind it until more than 80% of the particles are less than 74 μm, mix ammonium sulfate and carbon ferrochrome smelting slag evenly at a mass ratio of 5:1; place the mixture on a rotary Roast in the kiln at 400°C for 4 hours, and absorb the tail gas generated during the roasting process with water to form an alkaline absorption liquid for later use; after the roasting reaction is completed, the roasted material is leached with water at 90°C for 2 hours, and the volume-to-mass ratio during leaching is 4:1. After leaching, carry out liquid-solid separation, the solid phase is the residual silicon slag, and the liquid phase is the metal ammonium sulfate solution containing magnesium, aluminum, chromium and iron; the metal ammonium sulfate solution is cooled to 35°C and stirred for 2 hours, and the liquid phase is Solid separation to obtain ammonium aluminum sulfate dodecahydrate product and aluminum-removed liquid; neutralize the aluminum-removed liquid at 80°C with alkaline absorption liquid to pH 6.5, then separate liquid-solid, and the solid phase is chromium hydroxide and The mixture of ferric hydroxide is reserved for roasting to prepare chrome black, and the liquid phase is magnesium-rich liquid; ammonium sulfate crystals are added to the magnesium-rich liquid so that the mass concentration of ammonium sulfate in the magnesium-rich liquid is 30%, and stirred for 1h, and then liquid Solid separation to obtain ammonium magnesium sulfate hexahydrate crystals and ammonium sulfate solution; treat ammonium magnesium sulfate hexahydrate crystals with 15% ammonia solution at a liquid-solid ratio of 5:1 and a temperature of 80°C for 1 hour, and obtain hydroxide after liquid-solid separation Magnesium products and ammonium sulfate solution; mix magnesium ammonium sulfate hexahydrate crystals with ammonium sulfate solution produced during the preparation of magnesium hydroxide products, and evaporate and crystallize to obtain ammonium sulfate crystals, which are recycled for a new batch of carbon ferrochrome smelting slag The roasting process and the preparation process of magnesium ammonium sulfate hexahydrate crystals, the ammonium sulfate evaporated mother liquor is used in the leaching process of the roasted material. After carbon ferrochrome smelting slag is processed by this process, the recoveries of Mg, Al, Cr and Fe in the slag are 90.23%, 86.77%, 93.38% and 94.81%, respectively.

Example 3

Take a certain quality of carbon ferrochrome smelting slag, and grind it until more than 80% of the particles are less than 74 μm, mix ammonium sulfate and carbon ferrochrome smelting slag evenly at a mass ratio of 3:1; place the mixture on a rotary Roast in the kiln at 450°C for 4 hours, and absorb the tail gas generated during the roasting process with water; after the roasting reaction is completed, the roasted material is leached with water at 70°C for 1.5 hours, the volume to mass ratio during leaching is 4:1, and liquid is carried out after leaching. Solid separation, the solid phase is residual silicon slag, and the liquid phase is metal ammonium sulfate solution containing magnesium, aluminum, chromium, and iron; the metal ammonium sulfate solution is cooled to 30°C and stirred for 1 hour, and then the liquid and solid are separated to obtain ten Aluminum ammonium sulfate dihydrate product and liquid after aluminum removal; use ammonia water to neutralize the liquid after aluminum removal at 60°C to a pH value of 8.0, and then separate the liquid and solid, and the solid phase is a mixture of chromium hydroxide and iron hydroxide, which is reserved as Roasting to prepare chrome black, the liquid phase is magnesium-enriched liquid; add ammonium sulfate crystals to the magnesium-enriched liquid, so that the mass concentration of ammonium sulfate in the magnesium-enriched liquid is 40%, and stir for 0.5h, then liquid-solid separation, to obtain hexahydrate sulfuric acid Magnesium ammonium crystals and ammonium sulfate solution; Magnesium ammonium sulfate hexahydrate crystals are treated with 10% ammonia solution at a liquid-solid ratio of 8:1 and a temperature of 50°C for 3 hours, and the liquid-solid separation is performed to obtain magnesium hydroxide product and ammonium sulfate solution; Mix ammonium sulfate hexahydrate crystals with ammonium sulfate solution produced during the preparation of magnesium hydroxide products, and evaporate and crystallize to obtain ammonium sulfate crystals, which are recycled for the roasting process of a new batch of carbon ferrochrome smelting slag and sulfuric acid hexahydrate In the preparation process of magnesium ammonium crystals, the ammonium sulfate evaporates the mother liquor and returns it to the leaching process of the roasted material. After carbon ferrochrome smelting slag is processed by this process, the recoveries of Mg, Al, Cr, and Fe in the slag are 92.66%, 84.57%, 92.23%, and 91.36%, respectively.

Example 4

Take a certain quality of carbon ferrochrome smelting slag, and grind it until more than 80% of the particles are less than 74 μm, mix ammonium sulfate and carbon ferrochrome smelting slag evenly at a mass ratio of 6:1; place the mixture on a rotary Roast at 400°C for 3 hours in the kiln, and absorb the tail gas generated during the roasting process with water; after the roasting reaction, leaching the roasted material with water at 50°C for 3 hours, the volume-to-mass ratio during leaching is 6:1, and liquid-solid Separation, the solid phase is residual silicon slag, and the liquid phase is a metal ammonium sulfate solution containing magnesium, aluminum, chromium, and iron; the metal ammonium sulfate solution is cooled to 25°C and stirred for 2 hours, and the liquid and solid are separated to obtain twelve Ammonium aluminum sulfate water product and liquid after aluminum removal; neutralize the liquid after aluminum removal with ammonia water at 40°C to a pH value of 7.0, then separate the liquid and solid, and the solid phase is a mixture of chromium hydroxide and iron hydroxide, which is reserved for roasting Prepare chrome black, the liquid phase is magnesium-enriched liquid; add ammonium sulfate crystals to the magnesium-enriched liquid, so that the mass concentration of ammonium sulfate in the magnesium-enriched liquid is 15%, and stir for 3 hours, then liquid-solid separation, to obtain ammonium magnesium sulfate hexahydrate Crystals and ammonium sulfate solution; Magnesium ammonium sulfate hexahydrate crystals were treated with 25% ammonia solution at a liquid-solid ratio of 4:1 and a temperature of 70°C for 1.5 hours, and the magnesium hydroxide product and ammonium sulfate solution were obtained after liquid-solid separation; Ammonium magnesium sulfate hexahydrate crystals are mixed with ammonium sulfate solution produced during the preparation of magnesium hydroxide products, and evaporated and crystallized to obtain ammonium sulfate crystals, which are recycled for the roasting process of a new batch of carbon ferrochrome smelting slag and magnesium sulfate hexahydrate In the preparation process of ammonium crystals, the ammonium sulfate evaporates the mother liquor and returns it to the leaching process of the roasted material. After the carbon ferrochrome smelting slag is processed by this process, the recoveries of Mg, Al, Cr and Fe in the slag are 91.25%, 86.97%, 91.09% and 92.92%, respectively.

The above method is one of the embodiments of the present invention. Improvements can also be made without departing from the process principle of the present invention. These should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect and patent of the present invention. practicality.

Claims (8)

1. the method for magnesium, aluminium, chromium, iron synthetical recovery in carbon ferrochrome metallurgical slag, is characterized in that the operating process of the method comprises:

A ammonium sulfate mixes according to certain mass ratio with carbon ferrochrome metallurgical slag after levigate for the carbon ferrochrome metallurgical slag particle to more than 80% is less than 74 μm by ();

B () step (a) terminates after, the compound of ammonium sulfate and carbon ferrochrome metallurgical slag is placed in rotary kiln roasting certain hour under certain temperature, and baking tail gases water is absorbed;

C () step (b) terminates after, the roasting material aqueous solution is leached certain hour under certain volume quality when certain temperature, leaching terminates rear solid-liquor separation, and solid phase is remaining white residue, and liquid phase is the leach liquor of sulfuric acid metal ammonium salt of magnesium, aluminium, chromium, iron;

D () step (c) terminates after, the leach liquor of sulfuric acid metal ammonium salt be cooled to certain temperature and stir certain hour, by solid-liquor separation, obtaining Monoaluminum monoammonium disulfate Dodecahydrate product, liquid phase is liquid after aluminium;

E () step (d) terminates after, the tail gas absorption liquid obtained by step (b) or ammoniacal liquor neutralize except liquid after aluminium is to weakly acidic pH at a certain temperature, control ph is 6 ~ 8, rear solid-liquor separation, solid phase is the mixture of chromium hydroxide and ironic hydroxide, namely calcining becomes chrome black, and liquid phase is rich magnesium liquid;

F () step (e) terminates after, add a certain amount of ammonium sulfate solids and stir for some time, rear solid-liquor separation in rich magnesium liquid, solid phase is six Magnesium sulfate heptahydrate ammonium crystal, and liquid phase is ammoniumsulphate soln;

G () step (f) terminates after, ammoniumsulphate soln is carried out evaporative crystallization, the solid that crystallization obtains is back to step (a) and step (f), and crystalline mother solution is back to the leaching process in step (c);

H () step (f) terminates after, under certain temperature and liquid-solid ratio (volume mass ratio), six Magnesium sulfate heptahydrate ammonium crystal certain hours are processed with certain density ammonia soln, rear solid-liquor separation, liquid phase is ammoniumsulphate soln and is back to step (g), the ammoniumsulphate soln obtained with step (f) merges and enters evaporative crystallization operation, and solid phase is magnesium hydroxide products.

2. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, is characterized in that: the mass ratio that in step (a), ammonium sulfate mixes with carbon ferrochrome metallurgical slag is 2:1 ~ 10:1.

3. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, is characterized in that: in step (b), maturing temperature is 300 ~ 550 DEG C, and roasting time is 2 ~ 8h.

4. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, it is characterized in that: volume mass when roasting material leaches in step (c) is than being 2:1 ~ 10:1, extraction temperature is 25 DEG C ~ 130 DEG C, and extraction time is 0.5 ~ 5h.

5. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, is characterized in that: in step (d), the temperature of leach liquor crystallisation by cooling is 20 DEG C ~ 40 DEG C, and the crystallisation by cooling time is 0.5 ~ 5h.

6. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, is characterized in that: in step (e) neutralization except the temperature of aluminium is 25 DEG C ~ 90 DEG C.

7. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, it is characterized in that: in step (f), the addition of ammonium sulfate solids is the mass concentration of ammonium sulfate in the rich magnesium liquid of control is 10% ~ 40%, and the time that stirred crystallization goes out six Magnesium sulfate heptahydrate ammoniums is 0.5 ~ 3h.

8. the method for magnesium, aluminium, chromium, iron synthetical recovery in a kind of carbon ferrochrome metallurgical slag according to claim 1, it is characterized in that: in step (h), the concentration of ammonia soln is 5% ~ 25%, the temperature processing six Magnesium sulfate heptahydrate ammonium crystal is 25 DEG C ~ 100 DEG C, liquid-solid ratio is 2:1 ~ 10:1, and the treatment time is 0.5 ~ 5h.