Kaolin Mining Process Explained

Kaolin that occurs in nature is based on the kaolinite group minerals (kaolinite, halloysite, dickite, nacre, illite) as the main mineral, which also can form a kind of clay minerals with quartz sand, feldspar, mica, diaspore and hydromica and motmorillonite. This post mainly introduces the mining methods of kaolin open-pit mines and underground mines, development transportation and mining process.

(1) Open-pit Mining

Kaolin is a loose soil material which is mostly mined by open-pit and underground combined technology. Generally, kaolin open pit mining is changed to tunnel mining after reaching a certain depth. Weathered residual kaolin mines are mostly open-pit mining, other hydrothermal alteration and sedimentary deposits are used for open-pit mining in the shallow part and underground mining in the deep part.

The scale of kaolin mining is generally divided into two methods: Calculated by the amount of ore and calculated by the amount of concentrate. The specific division is as follows:

Kaolin Mining Scale Division Table (thousand t/a)

(2) Development and Transport Mode

The development and transport mode is an important part of kaolin open pit mining design. It aims to build the transport roads between the ground and benches and between all benches, links up the open pit with the ore site, waste dump and industrial sites, and makes new working levels ready.

There are 3 common methods of kaolin open-pit mine’s development and transportation:

• One is the development of narrow-gauge railway, the mine uses 7t, or 10t, or 14t electric locomotives to pull 1m3 mine cars;

• The second is hydraulic transportation. The mine cooperates with water guns and uses sand pumps to transport the slurry from the slurry pool set in the ore block to the ore dressing plant;

• The third is road development and automobile transportation. The mine’s transports ore from the mining face to the concentrator by 17t dump truck. The general weathered residual open-pit kaolin mine is exploited by road.

(3) Open-pit Mining Process

The surface of kaolin deposits is generally covered with a layer of loess of varying thickness. The shallow loess on the surface is about 1 meter, and some ore bodies are even exposed to the surface; the thick loess on the surface can reach more than 10 meters. Open-pit mining of kaolin must strip the loess on the surface of the ore body. After stripping, there are still loess and other debris on the surface of the ore body, you must further clean up the ore deposit. If the kaolin ore body is loosely combined, it can be directly used for slurry mining; if the ore body is tightly combined, it must be manually excavated and broken or blasted.

Small-scale kaolin open-pit mines are mostly excavated with hand picks or pneumatic picks. The topsoil is drilled by blasting methods and transported by narrow-gauge railways. Due to the short sides of mine carts, most of them are loaded manually; large-scale kaolin mines are directly excavated by excavator, after digging, loading into dump truck, kaolin was directly sent to the concentrator.

The hard kaolin rock is stripped by rock drilling and blasting. Usually mines use crawler-type down-the-hole rock drills to drill rock, blast with ammonium nitrate explosives, and then transport ores to the dump site by excavators and dump trucks. The excavator can directly strip the topsoil layer which is transported by a shovel car and loaded by the truck. In some mines, they would like to use bulldozers to collect the topsoil firstly, and then use excavators to load the ore into trucks.

Sandy kaolin ore is mostly mined by water mining and transportation. Because sandy kaolin is soft with a high sand content which is easy to disintegrate in water. After washing by a water gun, the ore slurry flows from the mine trench to the slurry pool. Generally, there is a slurry pool for each block, because the slurry pool is arranged in the block. The slurry is transported to the roughing plant by a slurry pump. This mining method is widely used in the UK because of its simple mining technology, simple equipment, and high labor productivity. Besides, it can enter the pulping process of the concentrator in advance to realize the integration of mining and processing.

(1) Underground Mining

The kaolin underground mining mainly involves digging a series of tunnels underground, which lead directly to the ore body. The main transportation roadway is usually set in the floor 20-40m away from the orebody, and set up a ventilation inclined shaft with a stage height of 25-40m at the edge of the orebody, which can form a diagonal ventilation system.

Kaolin mines that mined by underground mining generally have a solidity coefficient of about 1 to 2. Its soil is soft and fragile, with strong plasticity, strong water absorption and easy expansion. But it also has good water resistance, which is a typical plastic medium.

(2) Development and Transport Mode

 Because the various and complex topography and occurrence conditions of the deposits, there are many ways to open up underground mining.

There are three main types of kaolin undergroun mining development and transportation:

• The first is shaft development. Shafts varied from the positions of ore bodies. Some mine use hanging shafts and some use bottom shafts;

• The second is the development of inclined shafts. When creating main inclined shafts in kaolin mines, the mine mostly use chassis inclined shafts. But in some mines, they would like to apply chassis inclined shafts for shallow mining;

• The third is joint development. Most kaolin mines use flat tunnel-blind inclined shaft development, skip shaft-inclined shaft joint development and other combined transportation methods.

(3) Underground Mining Process

Kaolin underground mining adopts different methods according to the soft thickness of the ore body. Layer caving method is a commonly mining method. During mining, each layer is routed from the roof to the floor, from the boundary of the mining area or the boundary of the mining block to the mine shaft. The mining area is controlled at 800~ 1 000m2, the mining time for each layer is 3 to 4 months, which can reduce the amount of roadway maintenance. Taking into account the time required for the formation of the regenerated roof, the mine will generally suspend the project for 1 to 2 months before mining the next slab. When stopping, mine often use pneumatic picks and hand picks. Some countries will start stope by scraper mining and assembling machines that automatically advance along the road.

When mining kaolin underground mine, you need to take a good underground ventilation measures. Besides, you still need to consider the problem of diluting nitrogen when calculating the air volume. Because the marble of the kaolin mine floor contains pure nitrogen, nitrogen will be ejected from the fissures during the tunneling of the patio, which is prone to accidents.

The kaolin deposits that is mine by the layered caving method, can easily form sinkholes on the surface, which is easy to accumulate rainwater, causing water to drench on the working face. But the residual minerals after stopping, producing the regenerated topping, can swell with water and act as a water barrier. So, there is very little water in the mining face. However, kaolin mines still have to take comprehensive waterproofing measures for surface collapse pits, and pay attention to the problem of caving and roofing. Because ore drawing sometimes loosens the reclaimed roof, makes ore sink unevenly, and let the upper water washed out in a muddy state, which leads to accidents.

 The above is brief introduction of kaolin open-pit mine and underground mine mining methods, development transportation and mining technology. In order to increase the mining recovery rate and ensure the safe production of the mine, in actual mining, you need to fully explore the mine and select the appropriate mining method and technology for mining based on the mine resource analysis report.

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