Study on cementing filling technology of full tailings in Dazhai Mine, Yunnan

Dazhai help germanium mine in Linxiang District Lincang 8km north west linear distance selling in the basin, located in the northern section of the western margin of the basin, administrative division Linxiang District Lincang City, Yunnan Province, Zhang Tuo village to help sell the village. Dazhai Mine has independent development, mining, transportation, ventilation, drainage and other systems. The design and production scale is 90,000 t/a, and the actual production is 50,000 t/a. Now adopting the “downward approach level stratified paste filling method” mining, designing high-concentration full tailings cement filling process, on the basis of ensuring the ore recovery rate reaches 93%, the goaf is efficiently and environmentally friendly. Effectively ensure the continuous green mining of the mine [1].

1 filling plan selection

In view of safety, environmental protection and cost requirements, filling materials are preferred for beneficiation tailings, mining waste, industrial waste and local materials [2-3]. At present, the domestic filling process includes mainly graded tailings filling, high-concentration full tailings cementing filling, paste pumping and waste rock cementation filling. Graded tailings filling is currently the most widely used filling process in China. There are two kinds of cementing and non-gelling. The characteristic parameters are: mass concentration of 65%~70%, dehydration amount of 30%~15%[4]; high concentration tailings Cementation filling refers to the whole tailings with the highest sedimentation concentration in static water. The characteristic parameters are: mass concentration 70%~75%, dehydration amount 3%~6% [5]; paste pumping cement filling aggregate mainly is formulated from powder coal ash, slag and the like into the ground, wherein parameters: slurry concentration of 75% to 80%, the amount of dehydration is almost zero, the delivery process is difficult, so the choice of pumping, the paste delivery pump may be employed German-made KOS or KSP two-cylinder hydraulic piston pump and HBT concrete pump produced by Shenyang Construction Machinery Corporation; the aggregate used for waste rock cementation filling is naturally prepared from crushed materials and waste stones produced by excavation, and the cementing material is pure Cement slurry or composed of cement mortar is characterized by higher strength required for filling, but the efficiency is relatively low, so some special measures should be taken to avoid this disadvantage [6-7].

Analyze the existing conditions of Dazhai Mine, and adopt the tailings filling scheme according to the characteristics of the filling process.

2 filling process design

High-concentration full tailings cement filling is mainly composed of filling stations and various pipe networks. The filling station is mainly composed of sand bins, cement bins, feeding materials and mixing pulping.

2.1 Preparation of full tail mortar

2.1.1 Dewatering of the whole tail mortar

The flotation tailings of the plant flotation have a large water content (very low concentration). The whole tailings have high mud content and low permeability. In the dehydration process, excessive fine mud materials should be avoided.

The source of the tailings in the Dazhai Mine filling station is mainly the semi-dry tailings of the tailings reservoir, so the dewatering problem is not prominent. In order to ensure the pulp concentration, the sand surface needs to be 0.2 to 0.5 m above the sand surface.

2.1.2 Pulping of the whole tail mortar

The tailings stored in the silo are generally self-flowing by gravity, but the saturated tailings precipitated in the silo are difficult to be discharged through the DN150 pipeline, and the grit of the upper mouth of the pipeline must be loosened and pulped. The graded tail sand loosening and pulping can be used with water or gas; the whole tail sand can only be compressed, so that the slurry is not diluted, the concentration becomes low, and the concentration requirement is not reached.

In order to maintain the stability of mortar concentration and flow rate discharged from the silo, it is necessary to set a certain number of loose and slurry nozzles at the bottom of the silo (in the silo). The mesh (or spacing) is 0.6-0.8 m2, and the nozzle mounting axis It is perpendicular to the horizontal plane. Before the sand is discharged, the saturated tailings in the silo should be compressed for 20 to 30 minutes. When the sand is discharged, 4 nozzles are always opened above the sanding tube, and the remaining nozzles are rotated to activate the pulping. The pulping device comprises an air compressor, a branch pipe control valve and a gas pressure pulping nozzle. When the 15m high sand bin is full, the pressure of the pulping pressure is 0.4-0.6MPa, and the gas consumption of the compressed gas is 20m3/m3 according to the release amount of the unit mortar.

2.2 cement storage

The steel storage uses steel silos, which require good sealing and moisture resistance. The strength coefficient can meet the requirements of cement full warehouse. The degree of mechanization of cement into and out of the warehouse is high, the dust pollution is less, the quality of cement storage is stable, and the volume utilization of warehouse is high. , the warehouse has less bonding, and the liquidity of the warehouse is good.

The bottom of the cement silo is usually round and frustoconical, the taper angle is not easy to be greater than 60°, and the fluid gasification tube is installed at the height of 1/4 to 1/3 above the lower mouth of the silo to prevent blockage of cement in the silo. The bottom of the bucket is equipped with a plug-in plate and a screw feeder that can adjust the flow rate, and feeds the material into the stirring tank. The feed rate is controlled by the frequency converter to meet the design requirements of the ratio.

2.3 Preparation of filling slurry

After the relevant materials such as the whole tailings, cement and water are prepared according to the requirements, they are stored in a steel silo. The sand silo has the advantages of simple structure, small occupied area, high degree of automation, less mechanical equipment, good sand release continuity, and is suitable for underground pipeline transportation of filling slurry, and its concentration fluctuation is stable at 65%-75%.

The Dazhai Mine filling station is designed as a ground self-flow mixing station. The bottom of the vertical silo made of steel plate is supported by 8 406mm×12mm steel pipes. The pulping step is mainly as follows: firstly, about 70% of the mortar is discharged from the bottom through the vertical sand silo, and then the screw feeder feeds the cement to the cement silo, and the cement silo carries it according to a certain ratio.

After stirring, a high-concentration full-tail mortar of 73.6% to 75.9% is finally produced and transported to the arranged pipe network.

2.4 Filling slurry transport

The high tail cement high concentration cemented filler slurry belongs to a homogeneous homogeneous structure fluid. Since the self-flow is generated by the height difference during the conveying process, the design filling line is controlled at about 3.0. The Dazhai Mine has a drilling height of 1652 to 1330 m and a height difference of 322 m. It is necessary to design a horizontal pipe with a length of 624 m, and the excess part needs to increase the auxiliary assistance of the air pressure boosting aid.

The pressure boosting method is to add a pressure boosting nozzle at a certain distance in the horizontal pipeline. The direction of the nozzle and the flow direction of the mortar are 30°, and the nozzle spacing distance is 50-60 m. The pressure air pipe is laid above the sand pipe, and the gas for the nozzle is supplied by the pressure air pipe. The gas consumption of each nozzle is 0.12 m3/min [9].

2.5 filling holes and pipe network

Filling boreholes should be set up and constructed according to the following requirements: 1 Drilling should be selected at the shortest distance from the filling goaf to reduce the filling line; 2 The lower hole should be as close as possible to the main transport lane to reduce the underground filling roadway Volume and infrastructure investment; 3 borehole verticality control within 1% for accurate alignment in the well; 4 drilling and surface filling station should be located 20m outside the surface collapse line to ensure the safety of filling station and filling drilling; 5 Drilling and ground stations should make use of barren land and barren slopes as much as possible, or reduce land in less land and villages; 6 hole size is determined according to geological conditions and filling pipe diameter, Quaternary soil layer It is 250mm, the bedrock is 170~200mm, the casing has casing and filling pipe, the steel casing is generally 219mm×6mm or 168mm×6mm, the filling pipe is 146mm×12mm, the material is 16Mn or composite ceramic pipe; 7 The casing and the borehole wall are fixed with 42.5 grade Portland cement. The Quaternary (Q4) borehole can be consolidated by mud retaining wall or cement slurry. The sweeping hole cleaning is carried out according to the geological drilling requirements, and the inner pipe is inserted into the back casing. High quality mud between pipe and filling pipe The lower end of the vertical drilling is located in the filling roadway, and the main transportation roadway is generally connected with the borehole filling inner pipe by the ordinary steel pipe, the specification is 133mm×10mm or 127mm×10mm; the stop filling pipe and the main roadway are connected by three-way. The entrance filling pipe adopts a translucent resin pipe 120mm×10mm, and the resin pipe is connected with a three-way, so that the cleaning water is discharged into the transportation lane drainage ditch. The horizontal sand pipe connection can be a GJJ type flexible ring clamp [10].

2.6 filling system automatic control

The automatic control system includes: automatic meter monitoring, display and automatic processing of the microcomputer. In order to strengthen quality control and maintain normal continuous production and management, the filling station should measure and control the tailings, cement and water flow and mortar concentration. The test contents include: sand bin sand level, cement bin material level, mixing tank liquid level, sand concentration, sand discharge flow rate, cement feed amount, prepared filling slurry concentration, lime sand ratio, flow rate and the like.

(1) Measurement control of full tailings slurry. The vertical sand silo water sand interface instrument measures the sand position and stock of the sand silo. The concentration and flow rate of the full tail mortar in the sand discharging pipe at the bottom of the silo are respectively detected by the nuclear density meter and electromagnetic flowmeter installed on the pipeline.

(2) The material level of the cement silo is detected by the radar level gauge set at the top of the warehouse. The cement is transported by the screw feeder at the bottom of the silo, and the cement feedstock is adjusted by controlling the speed of the inverter.

(3) Control of lime sand ratio. According to the designed ratio of lime sand to gray water, the feed amount and water volume of the full tail sand (dry) feeder are calculated, and then the concentration of the whole tail mortar is calculated according to the filling slurry concentration. The above parameters are controlled by a nuclear density meter, a flow meter, a control valve, and a weighing screw feeder, respectively.

(4) The liquid level of the high-concentration mixing tank is detected by the ultrasonic level gauge, and the flow rate of the mixing drum into and out of the mortar is determined according to the upper and lower limits of the rated liquid level of the mixing drum.

In order to ensure the stability of the slurry concentration, a slurry concentration control device is provided. When the concentration is too high, an appropriate amount of fresh water is added to the mixing tank by the electric pinch valve to control the slurry concentration in real time.

The filling slurry flow rate and concentration detection are respectively performed by a nuclear density meter and an electromagnetic flow meter installed on the filling tube at the lower part of the mixing drum.

(5) The main electrical equipment in the filling station, such as feeder, mixing drum, Sand Pump, Water Pump, etc., have their own current and voltage meters, and the filling station should set the total electric power meter.

In order to implement the above automatic detection, control and timely collection of record printing, analysis of filling system operating parameters, the design uses a computer control and display system.

3 Conclusion

After the completion of the Dazhai Mine's full tailings cementation filling station project, the mining efficiency of the mine has been improved, and the beneficiation tailings have all been utilized. It is not necessary to build a new tailings pond, which basically realizes no-waste mining and effectively protects the mining area and its surrounding areas. The natural ecological environment has good economic benefits and social environmental benefits.

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