Production of the Pritti chrome ore mine in South Africa

Puli Di chromium Holdings Limited (Purity Chrome (pty) Ltd. ) Is a joint metallurgical industry (Consolidated Met-allurgical Industrles, referred CMI) subsidiary, located in the outskirts of Naples Württemberg 1km of the Transvaal, South Africa It is a new enterprise built on the Bushveld Com-plex, where several underground mines are already in production. The company includes an underground mine and a chrome beneficiation plant.

In June 1989, FF Alexa-Alex Mining Services signed a contract to complete the 2000m mine development project. At the same time, Davy South Africa (a company of the David International Consortium) signed a contract for the design, construction and trial production of the concentrator. The design of the concentrator was completed by the office of David South Africa in Johannesburg, and the design also included all supporting engineering and power supply engineering.

May 1990, the mine began mining; August, Puli Di company received all mining production operations in October, Johannesburg Branch -CMI joint investment company purchased the Puli Di chrome and ferrochrome business. So far, the company has produced more than 10 million tons of ore.

In September 1992, the Pritti chrome mine was first listed in the ISO9002 quality assurance unit in all chrome ore. This quality system guarantees maintenance and compliance with the overall quality management system. In order to ensure the quality of the final product and satisfy the users, all employees of the company must participate in the planning, monitoring, production and management of the system.

I. Geology and mineralogy

Chromite (FeO·Cr ₂ O ₃ ) is the only chromium mineral with economic value. Chromium is mainly used to produce ferrochrome alloys, which are important raw materials for the production of stainless steel and special steel. In addition, chromium is also used in the production of refractory, tanning, dyeing, chrome and pigment industries.

Occurrence Bushveld chromite manner as in rock heteroaryl formula: ancient copper mineral byproduct pyroxenite and dunite, the inclusion of plagioclase, but is most economically valuable formula Bushveld A pseudo-layered ferrochrome layer in the critical section of a complex. The angle ledges of rocks are on average ⁸⁰ ~ ^250.

Although more than 20 deposits have been discovered in the area, only 13 major deposits have been numbered, namely:

Upper mine layer group: No. 1 and No. 2;

Central mining group: No.1~4;

Lower mine layer group: No.1~7;

Among them, the main ore of the lower ore deposit group (LG6 or Magazine deposit) is regarded as the most economically valuable minable layer.

The Plitti chrome ore is located on the LG6 deposit in the West Belt of the Bush Verde complex, with a thickness of about 1.8 m, of which 40 cm of intermediate waste rock is sandwiched.

Theoretically, chromite is FeO·Cr ₂ O ₃ , but the minerals of the Bushveld complex are mainly complex spinels composed of three isomorphous spinels, namely (FeMg)O·Cr. ₂ O ₃ , (FeMg)O·Al ₂ 0 ₃ and FeO·Fe ₂ O ₃ composition, part of which is replaced by Al ₂ 0 ₃ and Fe ₂ O ₃ instead of Cr ₂ O ₃ , and the other part is replaced by MgO. The Critu chrome ore has a Cr ₂ O ₃ spinel content of about 47.2%.

Figure 1 Typical drilling section

Second, mining

The LG6 deposit of the Pritti chrome ore is 1.8m thick, inclined from north to south, with an inclination of 12.5 ⁰ . The ore layer consists of three parts: a 30cm chromite ore, a 40cm intermediate pyrite interlayer and a 110cm chromite ore. The mining thickness and inclination of the ore layer facilitates mechanized mining. The mining is carried out by the room-column method. The dimensions of the pillars are 13m and 5m, respectively, and the width of the mine is generally 15m. The recovery rate is designed to be 75% to 80%. Every mining lOOm. Leave a row of local pillars as an auxiliary support.

Dig into two dark inclined wells. One is the transport lane of the scraper, and the other is a belt conveyor that transports the ore and serves as a sidewalk. Install an east-west conveyor every 100m along the slope. In order to shorten the transportation time of the scraper, set the unloading point 30m away from the working surface. The mining operation is carried out in two shifts. The white shift is used for rock drilling and charging. The rock drilling uses an ordinary hand-held pneumatic rock drill, and the explosive is a granular explosive of ammonium nitrate-diesel mixture. Night shifts only carry out mining and clearing of the quarry, and seven Toro 150D scrapers clean the ore.

At present, the mine operates a five-day working week, with a sunrise mine volume of 2,000 tons and an annual mining capacity of 460,000 tons. The life expectancy of the mine is 16 years (excluding the mining rights belonging to the northern mining area of ​​JCI). If the northern mining area is included, the mine life can be extended by 18 years.

Figure 2 Schematic diagram of the Prilti chrome ore mining method

Pillar: along the trend of l3m, along the strike 5m; mine width: 15m,

For safety, the actual size is less than 15m

Third, the concentrator

(1) Preparation for mining

The ore is transported from the inclined shaft by the original ore conveyor to the first section of 1.5m×3.6m except for the large screen, and the sieve hole is 100mm. The material on the screen enters the jaw crusher, and the crushed product is returned to the original ore conveyor by the circulating conveyor. The -1OOmm undersize product is transported by a conveyor that can be lifted up and down to the open-pit mine with a capacity of 4000t. The machine is equipped with a winch that can be raised or lowered to reduce the loss.

Figure 3 Pritti concentrator process diagram and main equipment table

The ore of the open-pit mine is fed to the inclined conveyor by two 45t/h vibration feeders and transported to a 1.5m×3.6m double-layer sieving screen with two buffer tanks under the screen.

The ore is wet-screened and divided into three parts; -100 ~ +20mm (block ore) and -20 ~ +0.8mm (grain), these two parts are respectively fed into two heavy medium beneficiation systems, -0.8mm (powder mine) , sent to the spiral beneficiation workshop.

(2) Spiral heavy medium mineral processing system

The +20mm product screened by the grading sieve is first de-sanded on a 1.2m×3m ore preparation sieve and then enters the volute sorter. This sorting machine is a highly efficient equipment, and its product recycling and discharging methods are novel. The product and the waste stone are discharged to a double-layer split dewatering spray washing sieve of l.2m×4.8m, and the ferrosilicon medium is recovered. The medium used is cyclone 60 (swirl 60), and the sieved chrome concentrate is sent from the product conveyor to the 200t capacity product bin, and the waste rock is discharged to the intermediate waste rock pile.

The medium recovered in the dewatering section of the sieve is directly returned to the normal heavy medium pump tank, and then pumped back to the medium distribution box in front of the snail heavy medium sorting machine, and the lean medium is pumped to the cylindrical magnetic separator of 0.9m×O.9m for recycling. medium. The recovered medium is fed into the ultra-concentrated medium pump pool, passes through the demagnetization coil, enters the centrifugal concentrator, and returns to the normal medium pump pool.

The concentration is controlled by a nuclear concentration meter, and the concentration meter drives the airflow diverter to work. The water removed from the magnetic separator is de-sanded in a cyclone, and the overflow is used as flushing water for the dewatering spray screen.

(3) Dynamic vortex heavy medium mineral processing system

The -20～+0.8mm product sieved by the grading sieve is first deslimed on the sieve prepared by 0.9m×2.4m, and then fed into the dynamic vortex sorter (DWP).

The characteristic of DWP is that the mine is fed into the sorting machine by gravity, and the cyclone is different, and it is required to feed the ore and the medium under pressure. In DWP, heavy sinking material (generally abrasive material) settles almost immediately and exits through the tangential discharge opening on the upper side. At the exit, the speed and centrifugal force are quite low and the wear is minimal. The suspended material moves downward by means of a vortex and is no longer in contact with the metal until it reaches the vortex outlet tube. Due to the low wear rate in the equipment, high separation efficiency is always maintained.

Figure 4 General layout of the concentrator

Right side: heavy medium dressing workshop, middle: crushing and screening workshop, left side: product pile

Figure 5 snail heavy medium sorting machine

The product and waste rock were discharged to a 1.2 m × 4.8 m layered dewatering spray screen to recover the ferrosilicon medium. The medium used in the DWP system is ground 100D ferrosilicon. The recovery of normal and dilute media is similar to that of the snail system, and only the concentration is completed.

The crumb-like chrome concentrate obtained from the dewatering spray screen is transported from the product conveyor to the 100 t product bin, and the waste rock is discharged to the intermediate waste rock pile.

Figure 6 David Dynamic vortex heavy medium beneficiation system

Figure 7 spiral concentrator

(4) Spiral beneficiation workshop

The sieved slurry from the grading sieve enters the feed pump tank of the spiral beneficiation workshop, is pumped into the distribution tank, and is distributed to 23 MET double-head rough-selection spiral concentrators. The coarsely selected concentrate enters the distribution box of the selected spiral (22 double heads). The selected concentrate enters the 24-stream distribution box and is distributed to the secondary selection section. The secondary selected concentrate is dehydrated and becomes a chemical grade concentrate; the second selected medium ore is dehydrated and is a metallurgical grade concentrate; the second selected tailings is returned to the selected section. The drainage of the concentrate pile flows into the collection basin and is recovered by the sealed water pump. The dried concentrate is shipped from the front loader.

Figure 8 Concentrate dewatering and powder concentrate heap in spiral beneficiation workshop

The tailings of the rough-selected spiral concentrator are first concentrated by a concentration cyclone to the concentration required by the sweeping spiral concentrator, and then enter the sweeping slurry distribution box. The sweep is selected from 5 MET double-head spiral concentrators. The tailings are transported to the tailings pond. The medium-mineral products, including sweeping concentrates and selected tailings, are pumped together to the concentrate cyclone and then into the selected slurry distribution tank.

All concentrates from the three beneficiation systems are shipped to the ferrochrome smelter of the United Metallurgical Industries, located in Rustenburg. The recovery rates of the three systems were: volute beneficiation -78%, DWP-92%, and spiral beneficiation -90%. The various product specifications are listed in the table below.

Product specifications

The average losses of ferrosilicon per ton of ore fed by the volute system and the DWP system are 160g and 240g, respectively.

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