A method of recovering chromite

Abstract

The application provides a method for recovering chromite, and relates to the field of mineral processing. The method for recovering chromite comprises the following steps: first crushing chromite raw ore to obtain a first crushing product; first screening the first crushing product to obtain a first screen oversize and a first screen undersize; photoelectric preselection of the first screen oversize to obtain a photoelectric preselection concentrate and a photoelectric preselection tailing; roller pressing treatment of the first screen undersize to obtain a roller pressing product; second screening of the roller pressing product to obtain a second screen undersize, third screening of the second screen undersize to obtain a third screen undersize; desliming treatment of the third screen undersize to obtain fine sludge and coarse-grained gravity separation feed; coarse-grained gravity separation of the coarse-grained gravity separation feed to obtain a first chromite concentrate, a second chromite concentrate and gravity separation fine-grained feed; and grading treatment and fine-grained gravity separation of the gravity separation fine-grained feed to obtain a third chromite concentrate and a tailing. The application can obtain a high-quality chromite concentrate with a high recovery rate.

Description

Technical Field

[0001] This application relates to the field of mineral processing, and more particularly to a method for recovering chromite. Background Technology

[0002] Chromite is an important strategic mineral resource. However, constrained by factors such as insufficient development technology, the resource utilization rate of chromite has remained at a low level. In particular, in some mining areas, the ore bodies are distributed in thin veins, which easily lead to the incorporation of large amounts of surrounding rock during large-scale mining. This results in a decrease in the grade of the raw ore, a significant increase in beneficiation costs, and hinders the recovery and utilization of chromite. Therefore, it is urgent to innovate beneficiation processes and develop efficient and clean comprehensive utilization technologies for chromite to improve the overall level of resource development and utilization.

[0003] In terms of mineral processing technology, chromite beneficiation has evolved from simple physical separation to complex combined processes. Early chromite beneficiation mainly relied on single gravity separation or magnetic separation processes, which had limited processing capacity and low separation efficiency. Taking the Luobusha chromite mine in my country as an example, the traditional "hand-separation + jigging" process could achieve a recovery rate of 95-97%, but this process was highly dependent on ore quality and manual operation, making it difficult to apply to the processing of low-grade or complex ores. For medium- and low-grade ores with a Cr2O3 content of less than 35%, the concentrate grade obtained by conventional gravity separation processes is usually difficult to exceed 40%, with a recovery rate of only about 60%.

[0004] Currently, the mainstream chromite beneficiation process is gravity separation, but its separation effect on fine-grained and low-grade ores is unsatisfactory. While wet high-intensity magnetic separation can handle fine-grained materials, it faces problems of high equipment investment and energy consumption. Furthermore, for ores containing iron in gangue minerals, even with the addition of a magnetic separation stage, it is difficult to obtain high-quality chromite concentrate. Flotation, although suitable for fine-grained disseminated ores, suffers from high reagent consumption and difficult wastewater treatment. For example, when using ammonium salts as collectors, complex depressants such as quinoline nitrodicarboxylate ammonium are required to separate serpentine, further increasing process complexity and cost.

[0005] Furthermore, due to the thin ore body and high stripping ratio of chromite, a large amount of surrounding rock and waste rock are often mixed into the feed. If the ore is directly crushed and ground to the feed size, it is easy to over-grind the chromite, producing too many fine particles that are difficult to recover. For chromite with fine-grained disseminated particles and complex symbiotic relationships with gangue, existing methods are also difficult to effectively recover.

[0006] Therefore, improving the quality and recovery rate of chromite concentrate has become an urgent technical problem to be solved. Summary of the Invention

[0007] The purpose of this application is to provide a method for recovering chromite to solve the above-mentioned problems.

[0008] To achieve the above objectives, this application adopts the following technical solution:

[0009] This application provides a method for recovering chromite, comprising:

[0010] The chromite ore is subjected to a first crushing process to obtain the first crushing product;

[0011] The first crushed product is subjected to a first screening to obtain a first oversize and a first undersize.

[0012] The material over the first sieve is subjected to photoelectric pre-selection to obtain photoelectric pre-selected concentrate and photoelectric pre-selected tailings;

[0013] The first undersize material is subjected to roller pressing to obtain a roller-pressed product;

[0014] The photoelectric pre-selected concentrate is subjected to a second crushing, and the resulting second crushing product is returned to the roller pressing process as feed.

[0015] The roller-pressed product is subjected to a second screening to obtain a second oversize and a second undersize. The second oversize is returned to the roller pressing process as feed.

[0016] The second undersize material is subjected to a third sieve separation to obtain the third oversize material and the third undersize material.

[0017] The material over the third screen is subjected to a first grinding process, and the resulting first grinding product is returned to the third screen.

[0018] The material under the third screen is deslimed to obtain fine mud and coarse gravity separation feed.

[0019] The coarse gravity feed is subjected to coarse gravity separation to obtain a first chromite concentrate, a second chromite concentrate, and a fine gravity feed.

[0020] The gravity-separated fine-grained feed is classified to obtain a classified overflow;

[0021] The graded overflow is subjected to fine-grained gravity separation to obtain third chromite concentrate and tailings.

[0022] According to an embodiment of this application, the Cr2O3 grade in the chromite ore is 20-35%.

[0023] According to an embodiment of this application, the P of the first crushed product 95 Between 80 and 130 mm.

[0024] According to an embodiment of this application, the sieve aperture size of the first sieve is 10~30mm.

[0025] According to an embodiment of this application, the sieve aperture size of the second sieve is 2~6mm.

[0026] According to an embodiment of this application, the sieve aperture size of the third sieve is 0.5~1.5mm.

[0027] According to embodiments of this application, the coarse-grain re-selection includes coarse selection, multiple sweeping selections, and multiple fine selections;

[0028] The coarse gravity separation of the feed includes:

[0029] The coarse gravity feed is roughed using a spiral chute to obtain roughing concentrate and roughing tailings.

[0030] The roughing concentrate is subjected to multiple fine-tuning processes using a spiral chute to obtain the first chromite concentrate.

[0031] The roughing tailings are scavenged multiple times using a spiral chute.

[0032] The ratio of the diameter to the radius of the spiral chute used for coarse and sweeping selection is between 0.43 and 0.55.

[0033] The selected spiral chute has a radius-to-diameter ratio between 0.55 and 0.62.

[0034] The middlings produced by the fine selection and the middlings produced by the scavenging are combined and then finely scavenged. The concentrate obtained by fine scavenging is then finely selected again to obtain a second chromite concentrate and a gravity separation fine feed.

[0035] The gravity separation fine feed includes the tailings produced by the scavenging, the tailings produced by the fine scavenging, and the tailings produced by the re-selection.

[0036] According to an embodiment of this application, in the step of coarse re-selection, the number of coarse selections is 1 to 2 times, the number of sweeping selections is 1 to 2 times, the number of fine selections is 2 to 3 times, the number of fine sweeping selections is 1 to 2 times, and the number of re-selection is 2 to 4 times.

[0037] According to an embodiment of this application, the content of -0.074mm in the graded overflow is 65~92%;

[0038] The classification process also yields classified sand; the method further includes: subjecting the classified sand to a second grinding process, and returning the resulting second grinding product to the classification process.

[0039] The equipment for fine particle reseparation of the graded overflow includes a spiral chute and a shaking table;

[0040] The fine particle re-selection of the graded overflow includes: multiple coarse selection and multiple sweeping selection using a spiral chute, and multiple fine selection using a shaking table.

[0041] According to the embodiments of this application, the number of times the spiral chute is used for coarse selection is 1 to 2 times, the number of times the spiral chute is used for sweeping selection is 1 to 2 times, and the number of times the shaking table is used for fine selection is 2 to 3 times.

[0042] Compared with the prior art, the beneficial effects of this application include:

[0043] This application utilizes a pre-selection process to discard waste rock or surrounding rock before it enters the beneficiation process, effectively improving system processing capacity and reducing energy consumption. Roller pressing allows for selective crushing of chromite, preventing the generation of excessive fine particles that are difficult to concentrate during crushing. Coarse-grained gravity separation maximizes the recovery of qualified chromite concentrate and allows for quality-based sorting of the concentrate, increasing product value. For fine-grained chromite, fine grinding followed by fine-grained gravity separation yields qualified chromite concentrate, significantly improving the overall recovery rate of chromite. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0045] Figure 1 This is a flowchart of the chromite recovery method of this application. Detailed Implementation

[0046] As used in this article:

[0047] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0048] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0049] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0050] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0051] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0052] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0053] This application provides a method for recovering chromite, comprising:

[0054] The chromite ore is subjected to a first crushing process to obtain the first crushing product;

[0055] The first crushed product is subjected to a first screening to obtain a first oversize and a first undersize.

[0056] The material over the first sieve is subjected to photoelectric pre-selection to obtain photoelectric pre-selected concentrate and photoelectric pre-selected tailings;

[0057] The first undersize material is subjected to roller pressing to obtain a roller-pressed product;

[0058] The photoelectric pre-selected concentrate is subjected to a second crushing, and the resulting second crushing product is returned to the roller pressing process as feed.

[0059] The roller-pressed product is subjected to a second screening to obtain a second oversize and a second undersize. The second oversize is returned to the roller pressing process as feed.

[0060] The second undersize material is subjected to a third sieve separation to obtain the third oversize material and the third undersize material.

[0061] The material over the third screen is subjected to a first grinding process, and the resulting first grinding product is returned to the third screen.

[0062] The material under the third screen is deslimed to obtain fine mud and coarse gravity separation feed.

[0063] The coarse gravity feed is subjected to coarse gravity separation to obtain a first chromite concentrate, a second chromite concentrate, and a fine gravity feed.

[0064] The gravity-separated fine-grained feed is classified to obtain a classified overflow;

[0065] The graded overflow is subjected to fine-grained gravity separation to obtain third chromite concentrate and tailings.

[0066] In some embodiments, the rolling process is performed in a high-pressure roller mill.

[0067] In some embodiments, the desliming process is carried out in a hydrocyclone. The desliming process yields an overflow and underflow, with the overflow being fine mud and the underflow being coarse gravity separation feed.

[0068] Coarse-grained gravity separation is carried out in a spiral chute.

[0069] According to an embodiment of this application, the Cr2O3 grade in the chromite ore is 20-35%.

[0070] For example, the Cr2O3 grade in chromite ore can be 20%, 25%, 30%, 35%, or any value between 20% and 35%.

[0071] In some embodiments, the chromite ore has a Cr2O3 grade of 25.80% and gangue minerals including talc 17.49%, pyroxene 8.12%, quartz 1.53% and amphibole 1.06%.

[0072] According to an embodiment of this application, the P of the first crushed product 95 Between 80 and 130 mm.

[0073] According to an embodiment of this application, the screen aperture size of the first screening is 10~30mm. The selection of the screen aperture size of the first screening mainly depends on the lower limit of the feed particle size for photoelectric pre-selection and the upper limit of the feed particle size for the high-pressure roller mill. The lower limit of the photoelectric pre-selection process is 8~10mm, and the upper limit of the feed particle size for the high-pressure roller mill is 30mm.

[0074] For example, the sieve aperture size of the first sieve is 10mm, 15mm, 20mm, 25mm, 30mm or any value between 10 and 30mm.

[0075] According to an embodiment of this application, the screen aperture size of the second screening is 2-6 mm. The selection of the screen aperture size of the second screening mainly depends on the upper limit of the particle size of the crushed product of the high-pressure roller mill. The typical upper limit of the particle size of a high-pressure roller mill is 2-6 mm. If it exceeds this range, it is difficult to give full play to the advantages of the high-pressure roller mill itself, and the best results cannot be achieved in terms of processing capacity, energy consumption and particle size distribution of the crushed product.

[0076] For example, the sieve aperture size of the second sieve is 2mm, 3mm, 4mm, 5mm, 6mm or any value between 2 and 6mm.

[0077] According to an embodiment of this application, the sieve aperture size of the third screening is 0.5~1.5mm. The selection of the sieve aperture size of the third screening mainly depends on the particle size of the chromite. The chromite applicable to this application has a monomer liberation degree of about 80% at a particle size of 1mm. If the particle size is too large, some chromite will not be liberated, and the Cr2O3 grade in the concentrate will be difficult to reach the product sales grade. If the particle size is too small, it will aggravate energy consumption and generate too many excessively fine particles that are not easy to recover.

[0078] For example, the sieve aperture size of the third sieve is 0.5mm, 0.7mm, 1mm, 1.2mm, 1.5mm or any value between 0.5 and 1.5mm.

[0079] According to embodiments of this application, the coarse-grain re-selection includes coarse selection, multiple sweeping selections, and multiple fine selections;

[0080] The coarse gravity separation of the feed includes:

[0081] The coarse gravity feed is roughed using a spiral chute to obtain roughing concentrate and roughing tailings.

[0082] The roughing concentrate is subjected to multiple fine-tuning processes using a spiral chute to obtain the first chromite concentrate.

[0083] The roughing tailings are scavenged multiple times using a spiral chute.

[0084] The diameter-to-rectangle ratio of the spiral chute for roughing and scavenging is between 0.43 and 0.55. This range of diameter-to-rectangle ratio can ensure a large lateral inclination angle, prioritize the processing of large quantities of ore, quickly discard tailings, and improve processing capacity.

[0085] The selected spiral chute has a diameter-to-reflection ratio between 0.55 and 0.62. This range of diameter-to-reflection ratio can ensure a smaller lateral inclination angle, a gentler ore flow, and more thorough separation, which is beneficial to improving the grade of the concentrate.

[0086] The middlings produced by the fine selection and the middlings produced by the scavenging are combined and then finely scavenged. The concentrate obtained by fine scavenging is then finely selected again to obtain a second chromite concentrate and a gravity separation fine feed.

[0087] The gravity separation fine feed includes the tailings produced by the scavenging, the tailings produced by the fine scavenging, and the tailings produced by the re-selection.

[0088] For example, the diameter ratio of the spiral chute for coarse and sweeping selection is 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52, 0.53, 0.54, 0.55 or any value between 0.43 and 0.55, while the diameter ratio of the spiral chute for fine selection is 0.55, 0.56, 0.57, 0.58, 0.59, 0.60, 0.61, 0.62 or any value between 0.55 and 0.62.

[0089] In some embodiments, coarse grain reselection is performed in a spiral chute.

[0090] In some embodiments, the equipment for combining the middlings produced by the fine selection with the middlings produced by the scavenging and then performing fine scavenging, and the equipment for further fine selection of the concentrate obtained from fine scavenging, are spiral chutes.

[0091] According to an embodiment of this application, in the step of coarse re-selection, the number of coarse selections is 1 to 2 times, the number of sweeping selections is 1 to 2 times, the number of fine selections is 2 to 3 times, the number of fine sweeping selections is 1 to 2 times, and the number of re-selection is 2 to 4 times.

[0092] For example, in the coarse-grain re-selection step, the number of coarse selections is 1 or 2, the number of sweeping selections is 1 or 2, the number of fine selections is 2 or 3, the number of fine sweeping selections is 1 or 2, and the number of re-selection is 2, 3, 4, or any value between 2 and 4.

[0093] According to an embodiment of this application, the content of -0.074mm in the graded overflow is 65~92%;

[0094] For example, the -0.074mm content of the graded overflow is 65%, 67%, 70%, 72%, 75%, 77%, 78%, 80%, 82%, 85%, 87%, 90%, 92%, or any value between 65% and 92%.

[0095] The classification process also yields classified sand; the method further includes: subjecting the classified sand to a second grinding process, and returning the resulting second grinding product to the classification process.

[0096] The equipment for fine particle reseparation of the graded overflow includes a spiral chute and a shaking table;

[0097] The fine particle re-selection of the graded overflow includes: multiple coarse selection and multiple sweeping selection using a spiral chute, and multiple fine selection using a shaking table.

[0098] According to the embodiments of this application, the number of times the spiral chute is used for coarse selection is 1 to 2 times, the number of times the spiral chute is used for sweeping selection is 1 to 2 times, and the number of times the shaking table is used for fine selection is 2 to 3 times.

[0099] For example, the number of times the spiral chute is used for coarse selection is 1 or 2 times, the number of times the spiral chute is used for sweeping selection is 1 or 2 times, and the number of times the shaking table is used for fine selection is 2 or 3 times.

[0100] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0101] Example 1

[0102] Example 1 provides a method for recovering chromite, such as... Figure 1 As shown, the specific steps include the following:

[0103] 1) The raw material was a chromite ore from South Africa. The Cr2O3 grade in the sample was 25.80%. The gangue minerals were mainly silicate minerals such as talc (17.49%), pyroxene (8.12%), quartz (1.53%), and amphibole (1.06%). Some of the pyroxene contained iron and had weak magnetism.

[0104] 2) The coarsely crushed chromite ore is further crushed using the first crushing method to obtain the crushed product P. 95 It is 110mm;

[0105] 3) The crushed product 1 is screened to obtain the product above the screen of screen 1 and the product below the screen of screen 1. The screen aperture size of screen 1 is 20mm.

[0106] 4) Perform photoelectric pre-selection on the product oversize of screening 1 to obtain photoelectric pre-selected concentrate and photoelectric pre-selected tailings;

[0107] 5) The product undersize from screening 1 is crushed by a high-pressure roller mill to obtain the crushed product from the high-pressure roller mill.

[0108] 6) The photoelectric pre-selected concentrate is crushed 2 to obtain the crushed 2 product, which is returned to the high-pressure roller mill feed.

[0109] 7) The crushed product of the high pressure roller mill is screened 2 to obtain the oversize product and undersize product of screen 2. The oversize product of screen 2 is returned to the feed of the high pressure roller mill. The screen size of screen 2 is 3mm.

[0110] 8) The product undersize from screening 2 is screened 3 to obtain the product oversize from screening 3 and the product undersize from screening 3. The screen aperture size of screening 3 is 0.8mm.

[0111] 9) Grind the product over the 3rd sieve into 1st ore, and return the ground product to the 3rd sieve.

[0112] 10) The product under the third screening screen is deslimed by hydrocyclone, the overflow is fine mud, and the sand is coarse gravity separation feed.

[0113] 11) The coarse-grained gravity feed was subjected to spiral sluice gravity separation to obtain chromite concentrate 1, chromite concentrate 2, and fine-grained gravity feed, respectively. The coarse-grained gravity separation process involved one roughing pass, two scavenging passes, and two cleaning passes. The middlings were combined for fine scavenging, followed by a second cleaning pass, which consisted of one fine scavenging pass and two second cleaning passes. The diameter ratio of the spiral sluices for roughing and scavenging was 0.46; the diameter ratio of the spiral sluices for cleaning was 0.58.

[0114] 12) The fine-grained feed from gravity separation is classified to obtain classification overflow and classification sand. The -0.074mm content of the classification overflow is 78%.

[0115] 13) A combined spiral sluice and shaking table process was used to process the fine-grained feed for gravity separation to obtain chromite concentrate 3 and tailings. The spiral sluice roughing was performed twice, the spiral scavenging was performed once, and the shaking table cleaning was performed twice.

[0116] Comparative Example 1

[0117] To fully compare the advantages and disadvantages of chromium recovery processes from chromite ore, a comparative experiment was conducted using an on-site chromite ore recovery process to study the differences in product indicators between the two different processes. The on-site chromite ore recovery process was gravity separation. The gravity separation process consisted of one roughing stage, one scavenging stage, and two cleaning stages using a spiral sluice box, with middlings returned sequentially.

[0118] Example 1 and Comparative Example 1 were carried out under the same ore feed properties.

[0119] The product indicators of the mineral processing processes of Example 1 and Comparative Example 1 are listed in Table 1.

[0120] Table 1. Comparison of product indicators of mineral processing processes in Example 1 and Comparative Example 1

[0121]

[0122] Compared with Comparative Example 1, the chromite concentrate index in Example 1 was significantly improved, and a chromite product with differentiated quality was obtained. According to the method provided in this application: (1) 15.89% of waste rock is pre-removed by photoelectric pre-selection process before the chromite ore is fed into the beneficiation process, which relatively improves the processing capacity of the subsequent grinding and beneficiation system and reduces the power consumption and steel consumption per unit of raw ore; (2) 6.33% of fine mud is removed by hydrocyclone before the chromite ore is fed into the beneficiation process, which provides favorable conditions for the efficient enrichment of fine chromite ore in the subsequent gravity separation process; (3) The Cr2O3 recovery rate in the total chromite concentrate obtained in Example 1 is 23.28 percentage points higher than that in Comparative Example 1. At the same time, Example 1 obtained three different qualities of chromite concentrate, of which the yield of chromite concentrate 1 is 29.15% and the Cr2O3 grade is 46.27%, the yield of chromite concentrate 2 is 13.33% and the Cr2O3 grade is 42.36%, and the yield of chromite concentrate 3 is 6.68% and the Cr2O3 grade is 38.64%. The grade of chromite concentrate directly determines its uses and market value. Different grades correspond to different industrial application scenarios and price ranges. High-grade chromite concentrate (Cr2O3≥44%) is mainly used in high-value-added fields, such as stainless steel and special alloys. The acquisition of high-value-added products realizes the high-value utilization of chromite resources.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0124] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method of recovering chromite, characterized by, The method comprises the following steps: first crushing of a chromite ore to obtain a first crushing product; first screening of the first crushing product to obtain a first oversize and a first undersize; photoelectric pre-concentration of the first oversize to obtain a photoelectric pre-concentration concentrate and a photoelectric pre-concentration tailing; roller pressing of the first undersize to obtain a roller pressing product; second crushing of the photoelectric pre-concentration concentrate to obtain a second crushing product as a feed returning to the roller pressing; second screening of the roller pressing product to obtain a second oversize and a second undersize, the second oversize as a feed returning to the roller pressing; third screening of the second undersize to obtain a third oversize and a third undersize; first grinding of the third oversize to obtain a first grinding product returning to the third screening; desliming of the third undersize to obtain fine sludge and coarse-grained gravity separation feed; coarse-grained gravity separation of the coarse-grained gravity separation feed to obtain a first chromite concentrate, a second chromite concentrate and gravity separation fine-grained feed; classification of the gravity separation fine-grained feed to obtain a classification overflow; fine-grained gravity separation of the classification overflow to obtain a third chromite concentrate and a tailing; the coarse-grained gravity separation comprises roughing, multiple scavenging and multiple cleaning; the coarse-grained gravity separation of the coarse-grained gravity separation feed comprises: roughing of the coarse-grained gravity separation feed by a spiral chute to obtain a roughing concentrate and a roughing tailing; multiple cleaning of the roughing concentrate by a spiral chute to obtain the first chromite concentrate; multiple scavenging of the roughing tailing by a spiral chute; the spiral chute for roughing and scavenging has a ratio of pitch diameter of 0.43-0.55; the spiral chute for cleaning has a ratio of pitch diameter of 0.55-0.62; the middlings from the cleaning and the middlings from the scavenging are combined for fine scavenging, and the concentrate from the fine scavenging is re-cleaned to obtain the second chromite concentrate and the gravity separation fine-grained feed; the gravity separation fine-grained feed comprises the tailing from the scavenging, the tailing from the fine scavenging and the tailing from the re-cleaning.

2. The method of recovery of chromite according to claim 1, characterized in that, The chromite ore has a Cr2O3 grade of 20-35%.

3. The method of recovering chromite according to claim 1, characterized by, P of the first broken product is 0.5~1.5mm 95 between 80~130mm.

4. The method of recovering chromite according to claim 1, characterized by, The first screening has a screen size of 10-30 mm.

5. The method of recovering chromite according to claim 1, characterized by, The second screening has a screen size of 2-6 mm.

6. The method of recovering chromite according to claim 1, characterized by, The third screening has a screen size of 0.5-1.5 mm.

7. The method of recovering chromite according to claim 1, characterized by, In the step of coarse-grained gravity separation, the roughing is performed 1-2 times, the scavenging is performed 1-2 times, the cleaning is performed 2-3 times, the fine scavenging is performed 1-2 times and the re-cleaning is performed 2-4 times.

8. The method of recovering chromite according to any one of claims 1 to 7, characterized in that, The classification overflow has a -0.074 mm content of 65-92%. The classification also obtains classification sand, and the method further comprises second grinding of the classification sand to obtain a second grinding product returning to the classification. The equipment for fine-grained gravity separation of the classification overflow comprises a spiral chute and a shaking table. The fine-grained gravity separation of the classification overflow comprises multiple roughing and multiple scavenging by the spiral chute and multiple cleaning by the shaking table.

9. The method of recovering chromite according to claim 8, characterized by, The roughing is performed 1-2 times by the spiral chute, the scavenging is performed 1-2 times by the spiral chute, and the cleaning is performed 2-3 times by the shaking table. The roughing is performed 1-2 times by the spiral chute, the scavenging is performed 1-2 times by the spiral chute, and the cleaning is performed 2-3 times by the shaking table.

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