CN114652995B - Method for reducing detoxication and roasting chromium slag without calcium by natural pyrite-aided mechanochemical dry method - Google Patents
Method for reducing detoxication and roasting chromium slag without calcium by natural pyrite-aided mechanochemical dry method Download PDFInfo
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- 239000011651 chromium Substances 0.000 title claims abstract description 97
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 title claims abstract description 95
- 229910052804 chromium Inorganic materials 0.000 title claims abstract description 95
- 239000002893 slag Substances 0.000 title claims abstract description 87
- 238000000034 method Methods 0.000 title claims abstract description 47
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 title claims description 5
- 239000011575 calcium Substances 0.000 title claims description 5
- 229910052791 calcium Inorganic materials 0.000 title claims description 5
- JOPOVCBBYLSVDA-UHFFFAOYSA-N chromium(6+) Chemical compound [Cr+6] JOPOVCBBYLSVDA-UHFFFAOYSA-N 0.000 claims abstract description 47
- 238000002386 leaching Methods 0.000 claims abstract description 31
- NIFIFKQPDTWWGU-UHFFFAOYSA-N pyrite Chemical compound [Fe+2].[S-][S-] NIFIFKQPDTWWGU-UHFFFAOYSA-N 0.000 claims abstract description 24
- 229910052683 pyrite Inorganic materials 0.000 claims abstract description 24
- 239000011028 pyrite Substances 0.000 claims abstract description 24
- 239000000463 material Substances 0.000 claims abstract description 12
- 238000000498 ball milling Methods 0.000 claims description 41
- 239000000843 powder Substances 0.000 claims description 14
- 239000000203 mixture Substances 0.000 claims description 9
- 238000002156 mixing Methods 0.000 claims description 6
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- 238000001035 drying Methods 0.000 claims description 4
- 238000011068 loading method Methods 0.000 claims description 2
- 231100000419 toxicity Toxicity 0.000 abstract description 21
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- 230000008569 process Effects 0.000 abstract description 9
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 abstract description 6
- 239000002994 raw material Substances 0.000 abstract description 5
- 230000009467 reduction Effects 0.000 abstract description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 abstract description 3
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- 238000009837 dry grinding Methods 0.000 abstract 1
- 231100000252 nontoxic Toxicity 0.000 abstract 1
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- 239000003638 chemical reducing agent Substances 0.000 description 9
- 238000006722 reduction reaction Methods 0.000 description 8
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- 238000005516 engineering process Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
- 238000001514 detection method Methods 0.000 description 3
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- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 description 2
- 229910000359 iron(II) sulfate Inorganic materials 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
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- 229910052979 sodium sulfide Inorganic materials 0.000 description 2
- GRVFOGOEDUUMBP-UHFFFAOYSA-N sodium sulfide (anhydrous) Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 2
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- MBMLMWLHJBBADN-UHFFFAOYSA-N Ferrous sulfide Chemical compound [Fe]=S MBMLMWLHJBBADN-UHFFFAOYSA-N 0.000 description 1
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
- A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
- A62D3/37—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents by reduction, e.g. hydrogenation
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- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
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- B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
- B09B5/00—Operations not covered by a single other subclass or by a single other group in this subclass
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- A—HUMAN NECESSITIES
- A62—LIFE-SAVING; FIRE-FIGHTING
- A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
- A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
- A62D2101/40—Inorganic substances
- A62D2101/43—Inorganic substances containing heavy metals, in the bonded or free state
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
The invention belongs to the technical field of clean treatment and resource recycling of calcium-free roasting chromium slag, and particularly discloses a method for one-step reduction and fixation of hexavalent chromium in the calcium-free roasting chromium slag by using a natural pyrite-aided mechanochemical method, wherein the detoxified calcium-free roasting chromium slag can be reused. The method has simple operation steps, a certain amount of natural pyrite and the calcium-free roasting chromium slag are uniformly mixed, and the nontoxic chromium slag can be obtained by dry grinding for a certain time on a ball mill. The calcium-free roasting chromium slag obtained by the treatment method disclosed by the invention meets the requirement of chromium slag pollution treatment environmental protection technical Specification (HJ/T301-2007) that hexavalent chromium leaching toxicity is less than 0.05mg/L, and can be comprehensively utilized as a material for producing buildings, blast furnace ironmaking and the like. The raw material used in the invention is cheap and easily available natural pyrite, no secondary pollutants such as wastewater, carbon dioxide and the like are generated in the treatment process, the method is efficient, low in cost and environment-friendly, is suitable for industrial production, and has good industrial application prospect.
Description
Technical Field
The invention belongs to the technical field of clean treatment and resource recycling of calcium-free roasting chromium slag, and particularly relates to a chromium-containing waste slag dry detoxification method based on a mechanochemical method.
Background
As an important industrial raw material, the chromium salt is commonly used in the industries of chemical industry, metallurgy, electronics, light industry and the like, and plays a vital role in the construction and development of national economy. However, a large amount of solid waste, namely, calcium-free calcined chromium slag, is discharged during the chromium salt production process.
The calcium-free roasting chromium slag is strong alkaline, has a pH value of about 11-12.5 and contains 1130-8500mg/kg hexavalent chromium. Hexavalent chromium has the characteristics of strong oxidizing property, high solubility, high migration speed and the like, and the toxicity of the hexavalent chromium is about 100 times of that of trivalent chromium, so the hexavalent chromium is one of three internationally recognized carcinogenic metals. The improper disposal of the calcium-free calcined chromium slag can pose serious threats to human health and ecological environment. Therefore, the effective treatment of the calcium-free roasting chromium slag has important significance.
The detoxification method of the calcium-free roasting chromium slag is a method for reducing the toxicity of the calcium-free roasting chromium slag to a safety standard, and the key of detoxification is to reduce hexavalent chromium with strong toxicity to trivalent chromium. According to different processes, the detoxification technology of the calcium-free roasting chromium slag is divided into a chemical reduction method, a microbial reduction method, an immobilization/stabilization method and the like. Wherein, the chemical reduction method has the widest application range and the highest economic benefit, and can realize large-scale industrialized application. The chemical reduction method can be classified into wet detoxification and dry detoxification according to the reduction state of the calcium-free roasting chromium slag.
The wet detoxication of the calcium-free roasted chromium slag is generally divided into two steps, namely leaching hexavalent chromium in the calcium-free roasted chromium slag by water or acid, and reducing the hexavalent chromium into trivalent chromium by a proper reducing agent, wherein the common reducing agents include ferrous sulfate, nano zero-valent iron, ferrous sulfide, calcium polysulfide, sodium sulfide and the like. The key point of the wet detoxification is that a large amount of acid is consumed to leach hexavalent chromium wrapped in a solid matrix of the calcium-free roasting chromium slag, and the hexavalent chromium is contacted with a reducing agent to perform a reduction reaction, so that the treatment cost of the calcium-free roasting chromium slag is increased, and the detoxified calcium-free roasting chromium slag is not as stable as the dry detoxification.
The existing dry detoxication method of the calcium-free roasting chromium slag is a method for reducing hexavalent chromium in the calcium-free roasting chromium slag into trivalent chromium by utilizing reducing substances under the high temperature condition and fixing the trivalent chromium, and common reducing agents include carbon powder, coal dust, coal gangue, biomass and the like. Although the existing high-temperature dry detoxification technology can effectively realize detoxification of the calcium-free roasting chromium slag, the process needs a stable strong reducing atmosphere, and in addition, the process also needs an extremely high reducing temperature of 800-1300 ℃, the equipment requirement is high, and meanwhile, the dust and smoke amount is amplified, so that greenhouse gases and secondary pollution are generated. Therefore, searching for low-cost reducing agents and developing an economical and efficient calcium-free roasting chromium slag detoxification process are problems to be solved in the current research.
Disclosure of Invention
Aiming at the defects existing in the existing calcium-free roasting chromium slag detoxification technology, the invention aims to provide a method for assisting mechanochemical process by using cheap and easily available natural pyriteThe new method for reducing and fixing hexavalent chromium in the calcium-free roasting chromium slag not only can detoxify the chromium slag and reduce CO at normal temperature 2 The emission of the greenhouse gases is reduced, the treatment cost is reduced, and the use of corrosive agents such as strong acid and strong alkali and the high-temperature treatment environment of 800-1300 ℃ are avoided.
In order to achieve the above purpose, the present invention provides the following technical scheme:
a method for reducing detoxication of calcium-free roasting chromium slag by a natural pyrite-assisted mechanochemical dry method comprises the following specific steps:
(1) Naturally drying the calcium-free roasting chromium slag or drying the chromium slag by artificial equipment to ensure that the moisture content of the chromium slag is less than 3 percent;
(2) Roasting the dried calcium-free chromium slag in the step (1) and a certain amount of FeS 2 Uniformly mixing natural pyrite with the content of more than or equal to 90 percent, and then loading the mixture and ball-milling beads into a ball-milling tank according to a certain ball-material ratio;
(3) Subjecting the mixture obtained in step (2) to mechanochemical treatment (i.e., ball milling treatment) on a ball mill;
(4) And after the treatment is finished, qualified calcium-free roasting chromium slag with the leaching concentration of hexavalent chromium reaching the standard is obtained.
The detoxified calcium-free roasting chromium slag can be used as a material for producing building and blast furnace ironmaking.
The invention adopts cheap and easily available natural pyrite as a detoxication raw material, realizes the reduction detoxication of the calcium-free roasting chromium slag under the condition of normal temperature solid phase by mechanochemical treatment, can save a large amount of chemical reagents, reduces the treatment cost of the calcium-free roasting chromium slag, does not generate secondary pollutants such as wastewater, carbon dioxide and the like in the treatment process, and is suitable for industrial production.
Based on the technical scheme provided by the invention, the addition amount of the natural pyrite in the step (2) is 1-20% of the mass of the dried calcium-free roasting chromium slag, for example, 1.25-19%, 1.5-18%, 2.0-17% and the like, preferably 3-8%, and more preferably 4-6%.
On the basis of the technical scheme provided by the invention, the ball-to-material ratio in the step (2) is 5:1-15:1, for example, 6:1-14.5:1, 6.5:1-14:1, 7:1-13.5:1 and the like can be selected, preferably 8:1-12:1, and further preferably 9:1-11:1.
Based on the technical scheme provided by the invention, the ball milling rotation speed of the mechanochemical treatment in the step (3) is 100-650 rpm, for example, 150-640 rpm, 180-620 rpm, 200-610 rpm and the like can be selected, preferably 400-650 rpm, and more preferably 500-600 rpm.
On the basis of the technical scheme provided by the invention, the ball milling time for the mechanochemical treatment in the step (3) is 0.5-5.0 h, for example, 0.6-4.9 h, 0.7-4.7 h, 0.8-4.5 h and the like can be selected, preferably 1.0-3.0 h, and more preferably 1.5-2.5 h.
The invention relates to a method for reducing detoxication and roasting chromium slag without calcium by using natural pyrite-assisted mechanochemical dry method, which comprises the following steps after optimizing the process conditions:
(1) Naturally drying the calcium-free roasting chromium slag to make the moisture content of the chromium slag less than 2%;
(2) Adding natural pyrite accounting for 1-20% of the mass of the dried calcium-free roasting chromium slag in the step (1), uniformly mixing, and then filling the mixture and ball-milling beads into a ball-milling tank, wherein the ball-material ratio is controlled to be 5:1-15:1;
(3) Mechanically and chemically treating the mixture obtained in the step (2) for 0.5 to 5 hours under the ball milling condition of 100 to 650 rpm;
(4) And after the treatment is finished, qualified calcium-free roasting chromium slag with the leaching concentration of hexavalent chromium reaching the standard is obtained.
Regarding the mechanism of the natural pyrite to reduce hexavalent chromium, in the strongly alkaline environment of chromium slag, the reaction route is likely to be:
FeS 2 +CrO 4 2- +4H 2 O→Fe(OH) 3 ↓+Cr(OH) 3 ↓+2S 0 ↓+2OH -
hexavalent chromium in the calcium-free calcined chromium slag is reduced to trivalent chromium, and forms a chromium phase with low toxicity, low solubility and low mobility in the environment, thereby realizing thorough detoxification of the chromium slag.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) The invention provides a method for treating calcium-free roasting chromium slag, which is simple to operate, does not need to consume a large amount of acid and alkali reagents like the traditional wet detoxification, and does not need to need high temperature of 800-1300 ℃ like the traditional dry detoxification;
(2) Compared with reducing agents such as ferrous sulfate, sodium sulfide, reducing coal and the like which are commonly used in the traditional detoxification technology, the natural pyrite is used as a detoxification raw material, is low in cost and easy to obtain, and is a natural green pollution-free environment-friendly raw material;
(3) According to the invention, the reduction detoxification of the calcium-free roasting chromium slag is realized under the condition of normal temperature solid phase by mechanochemical treatment, and secondary pollutants such as waste water and carbon dioxide are not generated in the treatment process, so that the method is high in detoxification efficiency, green and environment-friendly, and suitable for industrial production;
(4) The calcium-free roasting chromium slag obtained by the treatment method accords with hexavalent chromium leaching toxicity less than 0.05mg/L specified in chromium slag pollution control environmental protection technical Specification (HJ/T301-2007), and can be used as a material for producing buildings, blast furnace ironmaking and other aspects for comprehensive utilization;
(5) The method is particularly suitable for clean treatment and resource recycling of the calcium-free roasting chromium slag, and has important industrial application value.
Drawings
FIG. 1 is an XPS chart obtained in example 1, wherein (a) and (b) are XPS charts of surface chromium elements of raw calcium-free calcined chromium slag and detoxified calcium-free calcined chromium slag (in the case of 600 rpm), respectively;
FIG. 2 is a graph showing the effect of ball milling speed on hexavalent chromium leaching toxicity and fixation rate in calcium-free calcined chromium slag in example 1;
FIG. 3 is a graph showing the effect of ball milling time on hexavalent chromium leaching toxicity and fixation rate in calcium-free calcined chromium slag in example 2.
Detailed Description
The applicant will now describe the invention in further detail with reference to specific examples which are only intended to aid in the understanding of the invention, but the scope of the invention is not limited thereto.
The calcium-free calcined chromium slags used in examples 1 to 4 were all provided by Hubei corporation, and the hexavalent chromium content of the calcium-free calcined chromium slags (naturally dried to a moisture content of less than 3%) was 4256mg/kg (measured according to Method 3060A of the United states environmental protection agency), and the main chemical compositions and contents are shown in Table 1:
TABLE 1 main chemical composition and content (wt.%) of calcium-free roasting chromium slag
| Composition of the components | Cr 2 O 3 | Fe 2 O 3 | Al 2 O 3 | CaO | MgO | SiO 2 | Moisture content |
| Content of | 7.62 | 47.03 | 11.14 | 6.57 | 5.40 | 7.37 | 2.80 |
The residual components are mainly as follows: na (Na) 2 O and TiO 2 。
Example 1
8g of calcium-free roasting chromium slag and FeS 2 The natural pyrite powder with the content of 93.1 percent (pyrite purchased from the upper fort of Hunan is ground into powder, the same is adopted in examples 2-4 and is not repeated), the powder is evenly mixed and added into a ball milling tank, the adding amount of the natural pyrite powder is 5 percent of the mass of the calcium-free roasting chromium slag, the ball-material ratio is controlled to be 10:1, the ball milling rotating speed is set to be 600rpm, the ball milling time is 3 hours, and then the mechanical force chemical treatment is carried out on a ball mill. After the reaction is finished, toxicity leaching tests (Method 1311, US EPA, and examples 2-4 for leaching toxicity) are carried out on calcium-free roasting chromium slag (refer to a solid mixture extracted from a ball milling tank and separated from ball milling beads, and the same is true for examples 2-4), wherein the leaching concentration of hexavalent chromium in the original calcium-free roasting chromium slag before the reaction is measured by adopting the Method is smaller than 0.05mg/L, and the leaching concentration of hexavalent chromium in the original calcium-free roasting chromium slag before the reaction is measured by adopting the Method is 171.01mg/L.
In addition, under the same conditions, the ball milling rotation speed was changed to 100, 200, 300, 400, 500 and 600rpm, and the obtained hexavalent chromium leaching toxicity and fixation ratio data are shown in Table 2.
TABLE 2 influence of ball milling speed on hexavalent chromium leaching toxicity and fixation ratio
| Ball milling rotation speed/rpm | Hexavalent chromium leaching toxicity/(mg/L) | Hexavalent chromium fixation/% |
| 100 | 180.32 | 0.00 |
| 200 | 182.22 | 0.00 |
| 300 | 140.64 | 17.76 |
| 400 | 88.92 | 48.00 |
| 500 | 30.48 | 82.17 |
| 600 | Not detected 1 | 100.00 |
Note 1: "undetected" means that the leaching concentration of hexavalent chromium is below the detection limit of spectrophotometry (0.004 mg/L).
The data of table 2 is plotted as shown in fig. 2. The result shows that the fixing rate of hexavalent chromium is increased from 17.76% to 100% as the ball milling speed is increased from 300rpm to 600rpm, and the leaching concentration of hexavalent chromium is reduced below the detection limit. The ball milling rotation speed has a direct relation with the energy transmission process of the mechanochemical reaction, and the higher the mechanical ball milling rotation speed is, the more energy is generated and transmitted due to ball milling collision, and the higher the efficiency of the mechanochemical reaction is.
The leaching toxicity/(mg/L) of hexavalent chromium expressed by concentration in the first two data is higher than that of the original calcium-free roasting chromium slag, namely 171.01mg/L, because:
the leaching toxicity of the chromium slag refers to how much hexavalent chromium can be extracted from the original chromium slag, with only about 90% of the hexavalent chromium in the original chromium slag being leached, leaving about 10% fixed in the mineral matrix of the chromium slag. Under the conditions of 100rpm and 200rpm, the damage of chromium slag by mechanical force causes that part of hexavalent chromium immobilized in mineral matrix can be leached again, but the leaching toxicity of hexavalent chromium is not reduced but increased because pyrite cannot be activated under the condition of low-energy ball milling (the ball milling rotating speed is not more than 200 rpm) and cannot generate oxidation-reduction reaction with hexavalent chromium.
Example 2
8g of calcium-free roasting chromium slag and FeS 2 Mixing natural pyrite powder with 93.1% content, adding into ball milling tank, adding pyrite powder with 4% of calcium-free roasting chromium slag, controlling ball-material ratio to 9:1, setting ball milling rotation speed to 600rpm, ball milling for 3h, and performing mechanochemical treatment on ball mill. After the reaction is finished, toxicity leaching tests are carried out on the calcium-free roasting chromium slag, and the leaching concentration of hexavalent chromium is less than 0.05mg/L.
In addition, under the same conditions, the ball milling time is changed to be 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 hours respectively, and the obtained hexavalent chromium leaching toxicity and fixation ratio data are shown in Table 3.
TABLE 3 influence of ball milling time on hexavalent chromium leaching toxicity and fixation ratio
| Ball milling time/h | Hexavalent chromium leaching toxicity/(mg/L) | Hexavalent chromium fixation/% |
| 0.5 | 97.82 | 42.80 |
| 1.0 | 48.73 | 71.50 |
| 1.5 | 16.08 | 90.60 |
| 2.0 | 4.96 | 97.26 |
| 2.5 | 1.27 | 99.26 |
| 3.0 | Not detected 1 | 100.00 |
Note 1: "undetected" means that the leaching concentration of hexavalent chromium is below the detection limit of spectrophotometry (0.004 mg/L).
The data of table 3 is plotted as shown in fig. 3. The results show that the fixation rate of hexavalent chromium is significantly improved with the prolongation of the mechanochemical treatment time. After 3.0 hours of treatment, hexavalent chromium is not detected in the leaching solution, and the fixing rate reaches 100%, which indicates that the mechanochemical reaction is completed.
Example 3
8g of calcium-free roasting chromium slag and FeS 2 Mixing natural pyrite powder with 93.1% content, adding into a ball milling tank, adding pyrite powder with 8% of the calcium-free roasting chromium slag mass, controlling the ball-material ratio to 8.5:1, setting the ball milling rotating speed to 550rpm, ball milling for 2.0h, and performing mechanical force chemical treatment on the ball mill. After the reaction is finished, toxicity leaching tests are carried out on the calcium-free roasting chromium slag, and the leaching concentration of hexavalent chromium is less than 0.05mg/L.
Example 4
8g of calcium-free roasting chromium slag and FeS 2 Mixing natural pyrite powder with 93.1% content, adding into ball milling tank, adding pyrite powder with 6% of calcium-free roasting chromium slag, controlling ball-material ratio to 10:1, setting ball milling rotation speed to 650rpm, ball milling for 2.0h, and performing mechanochemical treatment on ball mill. After the reaction is finished, toxicity leaching tests are carried out on the calcium-free roasting chromium slag, and the leaching concentration of hexavalent chromium is less than 0.05mg/L.
The foregoing is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It will be clear to a person skilled in the art that several embodiments are possible, all falling within the scope of protection of the invention, depending on the scope of protection defined by the claims and the technical solutions presented in the present description.
Claims (3)
1. A method for reducing detoxication and roasting chromium slag without calcium by pyrite-aided mechanochemical dry method is characterized by comprising the following steps:
(1) Drying the calcium-free roasting chromium slag until the moisture content is less than 3%;
(2) Roasting the dried calcium-free chromium slag in the step (1) and a certain amount of FeS 2 Uniformly mixing natural pyrite powder with the content of more than or equal to 90%, and then loading the mixture into a ball milling tank together with ball milling beads according to a certain ball-material ratio, wherein the adding amount of the natural pyrite powder is 4-8% of the mass of the dried calcium-free roasting chromium slag, and the ball-material ratio is 8.5-10:1;
(3) Performing mechanochemical treatment on the mixture obtained in the step (2) by adopting a ball mill, namely performing ball milling treatment, wherein the ball milling rotating speed is controlled to be 600-650 rpm, and the ball milling time is controlled to be 3-5 h;
(4) And after the treatment is finished, qualified calcium-free roasting chromium slag with hexavalent chromium leaching concentration less than 0.05mg/L is obtained.
2. The method according to claim 1, wherein FeS in the natural pyrite powder in step (2) 2 The content is more than or equal to 93 percent.
3. The method of claim 1, wherein the natural pyrite powder in the step (2) is added in an amount of 4-6% of the mass of the dried calcium-free roasted chromium slag.
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