A pre-grinding washing, pre-selection and comprehensive recovery process for high-mud magnetite

Abstract

The application discloses a kind of high clay magnetite's pre-milling washing ore preselection and comprehensive recovery process, and raw ore is entered screening washing operation after coarse crushing.The ore on screen is dry selected by dry magnetic separator, and dry selection waste rock is finely crushed and then dry sweeping is carried out, and sweeping waste rock is screened into different particle size aggregate products by inertial vibrating screen.The dry selection and sweeping concentrate on screen returns to pre-milling ore bin.Washing screen under material is wet preselected by external magnetic magnetic separator, and preselected concentrate is dehydrated by linear screen, and screen above material is sent to pre-milling ore bin, and screen under material is returned to pre-milling ore bin after thickening magnetic separation and filtration dehydration;Preselected tailings are dehydrated by linear screen, and screen above material is used as rice stone product, and screen under material is combined with thickening magnetic separation tailings, and pumped into cyclone to select sandstone product.The application reduces ore jamming by washing and preselection before entering the mill, pre-throw a large amount of tailings, improves the grade of the mill, reduces the amount of mill, and significantly improves the comprehensive utilization rate of resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetite ore preselection technology, and particularly relates to a pre-grinding ore washing, preselection, and comprehensive recovery method for muddy magnetite. The method is suitable for pre-grinding ore washing, preselection, and comprehensive recovery of high-viscosity magnetite with an iron grade of 20.0-35.0% and a -74μm content of 10% or more. The method is particularly suitable for pre-grinding ore preselection and recovery of magnetite with high mud content, resulting in feed blockage and poor flow, and poor direct dry separation and discarding efficiency. Background Art

[0002] my country boasts abundant iron ore resources of various types, with magnetite being the primary type, accounting for over half of the country's total reserves. While magnetite is easier to separate than siderite and hematite, it often contains large amounts of slime during the mining process, making it difficult to separate the ore.

[0003] The mineral mud contained in magnetite ore is divided into primary mineral mud and secondary mineral mud. Primary mineral mud mainly comes from the weathering or oxidative metamorphism of the ore body, the weathering and mud-forming alteration of the surrounding rock, and the easily muddied mica and chlorite in the iron ore. This type of primary mineral mud has a close relationship with the ore and is therefore more difficult to wash. Secondary mineral mud mostly comes from external factors, such as the fine rock powder generated during ore blasting, loading and unloading, and transportation, the crushing and cracking of the ore body during underground mining, the mineral mud caused by surface muddy water seeping into the ore body through the cracks, and the mixing of surface yellow mud and topsoil in open-pit mining. This type of mineral mud has little to do with the genesis of the ore deposit and is generally easier to clean.

[0004] Mined, muddy magnetite is supplied to the concentrator. The presence of ore mud can cause blockages in crushing, transportation, and silo unloading, hindering grinding, grading, and sorting operations, leading to unstable production in the concentrator system. Due to the high mud content and viscosity, post-crushing dry magnetic separation tailings disposal is ineffective. The discarded tailings contain a high content of magnetic iron, which reduces the recovery rate of magnetic iron in the concentrate. While dry magnetic separation can improve the mill grade, pre-grinding the ore to geological grade using dry separation alone is difficult. If the ore mud content is not addressed in the pre-grinding process, it often leads to severe turbidity in the tailings concentration well after grinding, significantly affecting return water quality. Furthermore, given that most iron ore concentrators currently have insufficient or no tailings ponds, the amount of tailings entering the pond must be minimized during concentrating operations. This means minimizing the amount of tailings entering the mill, thereby increasing the ore grade and reducing the amount entering the mill to reduce the total tailings volume.

[0005] Ore washing is an effective means of pre-treating muddy iron ore. Meishan Iron Mine and Baixiangshan Iron Mine have both adopted a linear screen ore washing process to address the impact of sticky muds such as kaolin and chlorite in the raw ore on the production process, and the process has performed well. In the pre-treatment of muddy magnetite, washing and desludging require combining dry and wet separation processes to quickly discard waste rock, improve the mill grade, and achieve early disposal. Linear vibrating screens are generally only suitable for desludging processes that are relatively easy to clean. Furthermore, the resource utilization of discarded tailings must be considered. These issues require the development of new methods and solutions.

[0006] Therefore, it is necessary to study a pre-grinding ore washing and pre-selection process for mud-containing magnetite, which includes the comprehensive application of ore washing and desludging, dry separation and waste disposal, wet separation, and waste rock resource utilization. Summary of the Invention

[0007] The purpose of the present invention is to address the problems of the existing technology such as poor adaptability to the pre-selection of high-mud iron ore, serious clogging, poor sorting effect, low resource utilization, and large tailings discharge, and to provide a pre-grinding ore washing and comprehensive recovery process for high-mud magnetite with good mud washing effect, high screening efficiency, low tailings discharge, and high resource utilization.

[0008] To achieve the above-mentioned object of the present invention, a pre-grinding ore washing, preselection and comprehensive recovery process of high-mud content magnetite of the present invention is implemented by the following steps:

[0009] 1) The coarsely crushed ore is fed into the screening and washing process to wash away the surface mud and obtain the ore above the screen and the ore pulp below the screen respectively;

[0010] In step 1, the particle size of the coarsely crushed ore is generally 0-300mm. The screening and washing process uses a double-layer banana screen with an upper mesh size of 20-50mm and a lower mesh size of 8-12mm. Both layers require flushing water pipes. Desludging high-mud ore through the double-layer banana screen not only improves desludging efficiency, but also loosens the fine mud, leaving virtually no mud clumps.

[0011] 2) feeding the oversize ore obtained in step 1) into a dry magnetic separator for bulk dry separation, discharging bulk dry separation waste rock, and obtaining bulk dry separation concentrate, which is returned to the pre-grinding ore bin;

[0012] In this step, the dry magnetic separator preferably uses a magnetic drum, which is used as a belt head pulley and has a magnetic field strength of 0.35 to 0.45T.

[0013] 3) The large dry-selected waste rock discharged in step 2) is finely crushed, and the finely crushed waste rock is subjected to dry magnetic scavenging. The scavenged concentrate is returned to the pre-grinding ore bin. The waste rock ejected from the scavenging is fed into a double- or triple-deck vibrating screen and sieved into three or four different size aggregate products. The screen hole size can be flexibly adjusted according to market demand.

[0014] In this step, the fine crushing operation adopts the displacement of the fine crushing jaw crusher, and the discharge opening range is adjustable in the range of 30 to 50 mm.

[0015] In this step, the dry magnetic separation and sweeping is preferably performed using a magnetic drum, which is used as a belt head pulley, and the magnetic field strength is 0.40 to 0.50 T; the vibrating screen is preferably a double-layer reciprocating linear vibrating inertia screen, which screens the incoming waste rock into 0 to 5 mm, 5 to 20 mm, and 20 to 30 mm particle size aggregate products - aggregate 1, aggregate 2, and aggregate 3. The installation angle of the double-layer reciprocating linear vibrating inertia screen is 5 to 10 degrees.

[0016] 4) feeding the undersize slurry material obtained in step 1) into a wet magnetic separation pre-selection operation to obtain a wet magnetic separation pre-selection concentrate and a wet magnetic separation pre-selection tailings, respectively;

[0017] The wet magnetic separation pre-selection process described in this step utilizes an external magnetic drum separator with a magnetic field strength of 0.30-0.60T, an inclination adjustment range of 0-10°, and a drum speed range of 0-17rpm. In contrast to conventional drum separators, where the magnetic system is located inside the drum, the external magnetic separator is located outside the drum, with the drum providing the separation space. The drum's axial direction is oriented toward the slurry flow direction. In this type of separator, material is separated within the drum, resulting in a longer separation zone and higher separation efficiency.

[0018] 5) The wet magnetic separation pre-selected concentrate obtained in step 4) is dehydrated through a linear dewatering screen, and the material on the screen is sent to the pre-grinding ore bin. The material under the screen is concentrated and magnetically separated, filtered and dehydrated, and then returned to the pre-grinding ore bin, and the concentrated magnetic separation tailings are discharged;

[0019] The mesh size of the linear dewatering screen in this step is displaced by 1 mm; the concentrated magnetic separation preferably adopts a wet permanent magnetic drum magnetic separator, the magnetic field strength is in the range of 0.30 to 0.40 T, and the concentration of the concentrated magnetic separation concentrate is controlled at 40% to 55%; the filtration equipment preferably adopts a permanent magnetic outer filter cartridge vacuum filter, the cylinder speed is 0.5 to 2 r / min, and the filter cake moisture content is controlled at 8 to 10%.

[0020] 6) The wet magnetic pre-selected tailings obtained in step 4) are dewatered through a linear dewatering screen, and the material above the screen is sold as a raw material. The material below the screen is combined with the concentrated magnetic tailings obtained in step 5) and then pumped into a hydrocyclone-linear dewatering screen to separate the construction sand and gravel products. The discharged fine tailings are fed into a tailings treatment system for treatment.

[0021] The linear dewatering screen in step 6) preferably has a mesh size of 3 mm. The particle size of the above-screened sand and gravel product is 3 to 12 mm, and the particle size of the construction sand and gravel product separated by the hydrocyclone and the linear dewatering screen is 0 to 3 mm. Products of this size are in high demand and command a high price.

[0022] The present invention flushes away the ore mud on the surface of high-mud ore through screening and washing operations, thereby reducing ore blockage; the dry selection and wet selection processes are combined to pre-discharge a large amount of tailings, thereby reducing the amount fed into the mill and improving the grade fed into the mill; at the same time, a variety of rice stone and sand and gravel products are produced, thereby improving the comprehensive utilization rate of resources. The present invention is particularly suitable for pre-grinding washing and pre-selection comprehensive recovery of high-mud and high-viscosity magnetite with an iron grade of 20.0-35.0% and a -74μm ratio of ≥10% in the raw ore.

[0023] Compared with the existing technology, the pre-grinding ore washing, preselection and comprehensive recovery process of high-mud magnetite of the present invention has the following beneficial effects:

[0024] (1) The screening and washing operation of the present invention adopts a double-layer banana screen for washing and desludging. The double-layer banana screen adopts a continuous multi-angle screen surface design, generally with an angle design of 5-25°, which can make the material move quickly and be quickly layered, increase the probability of near-gap particles passing through the screen, and improve the ore washing and screening efficiency. It has advanced technology, reliable operation, and good ore washing and desludging effect.

[0025] (2) In view of the mud-containing characteristics of the magnetite entering the mill, the present invention adopts a comprehensive application of dry selection and waste disposal and wet pre-selection before entering the mill, which can discard more than 30% of the tailings, greatly reducing the amount of ore entering the mill, improving the grade entering the mill, and reducing the operating cost of the subsequent grinding process.

[0026] (3) The wet magnetic separation pre-selection equipment adopts an external magnetic drum magnetic separator, which is different from the structural principle of the conventional drum magnetic separator. The magnetic system of the external magnetic drum magnetic separator is located outside the separation drum, and the material is sorted inside the separation drum. The separation belt is long, and the slurry flows along the axial direction of the separation drum. The sorted minerals are swept and selected multiple times as the drum rotates, realizing the pre-selection of coarse particles of weakly magnetic minerals, which can ensure higher sorting efficiency and mineral processing recovery rate.

[0027] (4) After the waste rock is finely crushed and swept, it is screened into aggregate products of different particle sizes through an inertial vibrating screen. The main components of the inertial vibrating screen are the screen frame and the inertial vibrator. The exciting force generated by the rotation of the vibrator's eccentric wheel is transmitted to the screen box, causing the screen to vibrate. The inertial vibrating screen has a small amplitude but a high frequency. It is a screening equipment with high productivity and screening efficiency. It is simple to operate, easy to install, and has low energy consumption. It is particularly suitable for aggregate screening operations where waste rock has been pre-discarded.

[0028] (5) The waste rock discarded by dry selection is screened into aggregate products of different particle sizes. The tailings discarded by wet pre-selection are classified by cyclone and dewatered by screening to obtain rice stone and sand and gravel of different specifications for construction. The waste rock discarded by dry and wet pre-selection of mud-containing magnetite is recycled and reused. While reducing the amount of solid waste, it not only greatly improves the resource recovery rate, but also significantly improves the economic benefits of mineral processing.

[0029] (6) The present invention performs pre-grinding pretreatment and recovery of mud-containing magnetite through processes such as ore washing and desludging, comprehensive application of dry selection and wet selection, and resource utilization of discarded waste rock, thereby reducing the amount fed into the mill, improving the grade fed into the mill, and reducing the grinding and selection operating costs. The mud-containing magnetite is subjected to ore washing and pre-selection treatment to obtain high-grade iron ore and construction sand and gravel products fed into the mill, thereby realizing the comprehensive development and utilization of mud-containing magnetite resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a principle process flow chart of a pre-grinding ore washing, preselection and comprehensive recovery process for high-mud content magnetite. DETAILED DESCRIPTION

[0031] To further illustrate the present invention, a pre-grinding ore washing, preselection and comprehensive recovery process for high-mud content magnetite according to the present invention is further described in detail below with reference to the accompanying drawings and examples. However, the present invention is not limited to the examples.

[0032] The magnetite selected in the embodiment is a magnetite ore from a mining company in Anhui Province, with low TFe grade, high mud content, and a moisture content of 7.28%. The chemical multi-element analysis results of the raw ore are shown in Table 1.

[0033] Table 1 Chemical multi-element analysis results of raw ore (%)

[0034] Ingredients TFe MnO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO MgO S P <![CDATA[TiO2]]> Content 27.33 0.110 28.70 0.40 7.82 3.1 6.14 0.026 0.168

[0035] The test ore samples were mixed and then divided for particle size composition analysis. The results of the original ore particle size composition analysis are shown in Table 2.

[0036] Table 2 Analysis results of particle size composition of raw ore samples

[0037]

[0038] The results in Table 2 show that the raw ore has a TFe grade of 27.33%. The -0.074mm fraction accounts for 13.66% of the coarsely crushed ore (particle size 0-300mm), with a grade of 11.46% and a cumulative fraction of -1mm particles accounting for 23.77%. The ore contains a large amount of secondary mud and fine-grained rock, resulting in severe dilution and a very low grade. The current concentrator process directly performs two-stage dry magnetic separation and discarding after coarse crushing. Due to the lack of ore washing and the influence of ore mud, the dry separation and discarding efficiency is not ideal, with a discarding yield of only 24.50%. The mill grade has only increased from 27.33% to 36.52%. Ore blockages frequently occur in the ore feed bin and conveyor belts, making the concentrator's production system less efficient.

[0039] Depend on Figure 1 As shown in the process flow chart of the present invention, a pre-grinding ore washing, pre-selection and comprehensive recovery process for high-mud magnetite can be used to remove surrounding rock and secondary mud mixed in during the mining process and restore the geological grade of the ore. The pre-grinding ore washing and pre-selection process of the present invention first requires washing the raw ore to remove a large amount of secondary mud. After washing, the raw ore is then subjected to dry tailings discarding and wet pre-selection tailings discarding. Specifically, the following processes and steps are included:

[0040] 1) The coarsely crushed 0-300mm ore is fed into a double-layer banana screen for screening and washing to remove the surface mud, and the ore on the screen and the slurry material under the screen (i.e., the surface mud material) are obtained respectively; the upper sieve hole size of the double-layer banana screen is 30mm, and the lower sieve hole size is 12mm. Both the upper and lower screens need to be equipped with flushing water pipes.

[0041] 2) The oversize ore obtained in step 1) is fed into a dry magnetic separator for bulk dry separation, the bulk dry separation waste rock is discharged, and the bulk dry separation concentrate is obtained, and the bulk dry separation concentrate is returned to the pre-grinding ore bin; the dry magnetic separator uses a magnetic drum, and the magnetic field strength of the magnetic drum is 0.4T.

[0042] 3) The large dry-selected waste rock discharged in step 2) is finely crushed using a fine-crushing jaw crusher with a discharge opening size of 30 mm. The finely crushed waste rock is subjected to dry magnetic scavenging. The dry magnetic separation equipment uses a magnetic drum with a magnetic field strength of 0.45 T. The scavenged concentrate is returned to the pre-grinding ore bin. The waste rock ejected from the scavenging is fed into a reciprocating linear vibrating inertia screen (double-layer vibrating screen) to screen three different particle size aggregate products: Aggregate 1, Aggregate 2, and Aggregate 3.

[0043] 4) feeding the undersize slurry material obtained in step 1) into a wet magnetic pre-selection operation to obtain a wet magnetic pre-selection concentrate and a wet magnetic pre-selection tailings, respectively; the wet magnetic pre-selection operation uses an external magnetic drum magnetic separator with a magnetic field strength of 0.45T.

[0044] 5) The wet magnetic separation pre-selected concentrate obtained in step 4) is dehydrated by a linear dewatering screen with a sieve size of 1 mm, and the material on the screen is sent to the pre-grinding ore bin. The material under the screen is concentrated and magnetically separated by a wet permanent magnetic drum magnetic separator with a magnetic field strength of 0.4 T, and then filtered by an external filter cartridge vacuum filter and returned to the pre-grinding ore bin, and the concentrated magnetic separation tailings are discharged.

[0045] 6) The wet magnetic separation pre-selected tailings obtained in step 4) are dewatered through a linear dewatering screen, and the 3-12 mm material on the screen is sold as a gravel product. The -3 mm material under the screen is combined with the concentrated magnetic separation tailings obtained in step 5) and then pumped into a hydrocyclone-linear dewatering screen to separate the construction sand and gravel product, the sand and gravel product having a particle size of 0-3 mm; the discharged fine tailings are fed into a tailings treatment system for treatment.

[0046] After washing and pre-selecting the mud-containing magnetite according to the above process and steps, the main product - iron coarse concentrate with a TFe grade of 46.20% was obtained. At the same time, the discarded tailings were processed to obtain by-product 1 - rice stone (3-12 mm), by-product 2 - sand and gravel (0-3 mm), and by-product 3 - aggregate products of different particle sizes (0-5 mm, 5-20 mm, 20-30 mm).

[0047] Based on a plant capacity of processing 1 million tons of raw ore per year, the plant can produce over 150,000 tons of milled stone and sand and gravel, as well as 230,000 tons of aggregate products annually, which can be sold as construction materials. This generates over 10 million yuan in annual profits for the company, effectively utilizing the tailings as a resource. Through the ore washing and pre-selection process, the pre-disposal rate has increased from 24.5% to 45.14%, significantly reducing the amount of ore entering the mill, improving the ore grade, and reducing milling and selection operating costs by over 5 yuan per ton. This solution offers significant economic benefits, achieving energy savings and consumption reductions while also improving the overall utilization of resources.

[0048] The above are merely preferred embodiments of the method of the present invention, but the scope of protection of the method of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the method of the present invention should be based on the scope of protection defined in the claims.

Claims

1. A pre-grinding washing, pre-selection and comprehensive recovery process for high-mud magnetite, characterized in that This is accomplished using the following steps: 1) The coarsely crushed ore is fed into the screening and washing process to obtain the oversize ore and undersize slurry materials respectively; 2) feeding the oversize ore obtained in step 1) into a dry magnetic separator for bulk dry separation, discharging bulk dry separation waste rock, and obtaining bulk dry separation concentrate, which is returned to the pre-grinding ore bin; 3) The large dry-selected waste rock discharged in step 2) is finely crushed, and the obtained finely crushed waste rock is subjected to dry magnetic scavenging. The obtained scavenged concentrate is returned to the pre-grinding ore bin, and the waste rock discharged from the scavenging is fed into a double-layer or triple-layer vibrating screen and screened into three or four aggregate products of different particle sizes; 4) feeding the undersize slurry material obtained in step 1) into a wet magnetic pre-selection operation to obtain a wet magnetic pre-selection concentrate and a wet magnetic pre-selection tailings, respectively; 5) The wet magnetic separation pre-selected concentrate obtained in step 4) is dehydrated through a linear dewatering screen, and the material on the screen is sent to the pre-grinding ore bin. The material under the screen is concentrated and magnetically separated, filtered and dehydrated, and then returned to the pre-grinding ore bin, and the concentrated magnetic separation tailings are discharged; 6) The wet magnetic pre-selected tailings obtained in step 4) are dewatered through a linear dewatering screen, and the material above the screen is sold as a raw material. The material below the screen is combined with the concentrated magnetic tailings obtained in step 5) and then pumped into a hydrocyclone-linear dewatering screen to separate the construction sand and gravel products. The discharged fine tailings are fed into a tailings treatment system for treatment.

2. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud content magnetite according to claim 1, characterized in that: The particle size of the raw ore after coarse crushing in step 1) is required to be 0-300 mm. The equipment used in the screening and washing operation is a double-layer banana screen, the upper sieve hole size is 20-50 mm, the lower sieve hole size is 8-12 mm, and the upper and lower layers of screens are equipped with flushing water pipes.

3. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud content magnetite according to claim 1, characterized in that: The dry magnetic separator described in step 2) uses a magnetic drum, which is used as a belt head pulley, and the magnetic field strength is 0.35 to 0.45T.

4. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud magnetite according to claim 1, characterized in that: The fine crushing operation described in step 3) uses a fine crushing jaw crusher with a discharge opening range of 30 to 50 mm.

5. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud content magnetite according to claim 1, characterized in that: The dry magnetic separation and sweeping described in step 3) uses a magnetic drum, which is used as a belt head pulley, and the magnetic field strength is 0.40-0.50T; the vibrating screen uses a double-layer reciprocating linear vibrating inertia screen to screen the incoming waste rock into 0-5mm, 5-20mm, and 20-30mm particle size aggregate products - aggregate 1, aggregate 2, and aggregate 3. The installation angle of the double-layer reciprocating linear vibrating inertia screen is 5-10°.

6. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud content magnetite according to claim 1, characterized in that: The wet magnetic separation pre-selection operation described in step 4) adopts an external magnetic drum magnetic separator with a magnetic field strength of 0.30 to 0.60 T, an inclination adjustment range of 0 to 10 degrees, and a separation drum speed range of 0 to 17 rpm.

7. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud magnetite according to claim 1, characterized in that: The mesh size of the linear dewatering screen in step 5) is 1 mm; the concentrated magnetic separation adopts a wet permanent magnetic drum magnetic separator with a magnetic field strength of 0.30 to 0.40 T, and the concentration of the concentrated magnetic separation concentrate is controlled at 40% to 55%; the filtration equipment adopts a permanent magnetic outer filter cartridge vacuum filter with a drum speed of 0.5 to 2 r / min, and the moisture content of the filter cake is controlled at 8 to 10%.

8. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud magnetite according to claim 1, characterized in that: The mesh size of the linear dewatering screen in step 6) is 3 mm; the particle size of the above-screen rice stone product is 3 to 12 mm, and the particle size of the construction sand and gravel product separated by the hydrocyclone and the linear dewatering screen under the screen is 0 to 3 mm.

9. The process for pre-grinding ore washing, preselection and comprehensive recovery of high-mud magnetite according to claim 2, characterized in that: The dry magnetic separator described in step 2) uses a magnetic drum, which is used as a belt head pulley, and the magnetic field strength is 0.35 to 0.45 T; The fine crushing operation described in step 3) adopts a fine crushing jaw crusher with a discharge opening range of 30-50 mm. The dry magnetic separation and sweeping adopts a magnetic drum, which is used as a belt head pulley and has a magnetic field strength of 0.40-0.50 T. The vibrating screen adopts a double-layer reciprocating linear vibrating inertia screen to screen the incoming waste rock into 0-5 mm, 5-20 mm, and 20-30 mm particle size aggregate products - aggregate 1, aggregate 2, and aggregate 3. The installation angle of the double-layer reciprocating linear vibrating inertia screen is 5-10°. The wet magnetic separation pre-selection operation described in step 4) uses an external magnetic drum magnetic separator with a magnetic field strength of 0.30 to 0.60 T, an inclination adjustment range of 0 to 10 degrees, and a separation drum speed range of 0 to 17 rpm; The mesh size of the linear dewatering screen in step 5) is 1 mm; the concentrated magnetic separation adopts a wet permanent magnetic drum magnetic separator with a magnetic field strength of 0.30 to 0.40 T, and the concentration of the concentrated magnetic separation concentrate is controlled at 40% to 55%; the filtration equipment adopts a permanent magnetic outer filter cartridge vacuum filter with a drum speed of 0.5 to 2 r / min, and the moisture content of the filter cake is controlled at 8 to 10%; The mesh size of the linear dewatering screen in step 6) is 3 mm; the particle size of the above-screen rice stone product is 3 to 12 mm, and the particle size of the construction sand and gravel product separated by the hydrocyclone and the linear dewatering screen under the screen is 0 to 3 mm.

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