Essential Guide to Mineral Processing & Equipment

Aug. 12, 2024

Essential Guide to Mineral Processing & Equipment

What Is Mineral Processsing in Mining?

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Mineral processing is a form of extractive metallurgy that separates valuable minerals from the ore into a concentrated, marketable product. Mineral processing is also known as mineral dressing.

Mineral processing is conducted at the site of the mine and is a highly mechanical process, with oversight from a central control room.

Gold mineral processing plant

Why Is Mineral Processing Important?

The profitability of a mine is based on how much concentrate of the desirable mineral can be extracted from the ore. As a result, mineral processing is designed to yield the maximum amount of mineral concentrate possible before products hit the market.

If the case cannot be made for profitable yields of valuable minerals, then a mine will not hit the development stage in the lifecycle of a mine.

Mineral processing is used to extract the following materials:

Metals, including aluminum, bauxite, chalcopyrite, chromite, copper, galena, gold, hematite, iron, lead, magnetite, molybdenum, nickel, platinum, silver, sphalerite, tin, and zinc
Rocks, including including building stone, coal, clay, granite, limestone, potash, marble, and sand
Industrial mineral ore, including apatite, barite, diamond, fluorite, garnet, gemstones, quartz, vermiculite, wollastonite, and zircon

Mineral processing is an important step in converting ore into a product that can be sold and used for everyday applications.

What Are the 4 Stages of Mineral Processing?

Aside from profitability, the main objective of mineral processing is to break down ore from its heterogeneous properties and turn it into a homogeneous product to sell. To do this, materials will undergo the following four stages of processing to extract the desired crude material:

1. Crushing and grinding. Crushing and grinding, also called comminution, is the process of reducing the particle size of large rocks to be further processed down the line.

Wet grinding mill

2. Sizing and classification. Sizing and classification is the process of separating different sizes of ore by screens. Finer materials are routed to different stages of the mine than coarser materials.

3. Concentration. Concentration is the process of breaking down the materials until the desired concentration of crude material is reached. There are several different techniques for accomplishing the target concentration including:

Automated ore sorting. Automated ore sorting uses optical sensors to sort the rock into categories. This technology is expanding to include more sensing parameters.
Electrostatic separation. Electrostatic separation consists of electrostatic separators and electrodynamic sensors, also known as high tension rollers. Since these separators rely on electric currents, ore material needs to be dry. Charges are run through the materials and separate from the gangue&#;the undesirable ore that is removed from the profitable minerals. These separators are used to separate mineral sands.
Froth flotation. Froth flotation uses a chemical collector and frother that forms bubbles on the surface of the slurry that hydrophobic materials bind to. The bubbles are collected off the surface of the frother. Activators are used to enable the flotation of one mineral ore while depressants are used to inhibit the flotation of the gangue.

Froth flotation tank

Gravity separation. Gravity separation is the process of separating two or more ore minerals in their respective responses to gravity paired with buoyant forces, centrifugal forces, and/or magnetic forces in a viscous substance.
Magnetic separation. Magnetic separation is the process of using electromagnets to extract the desired mineral ore from a conveyor belt. This process can be used with or without water.

4. Dewatering. Dewatering is the final process of removing the water content of the mineral in order to dispose of the gangue and reach the desired concentrate levels for marketability.

In the next section, we&#;ll take you through the ore&#;s journey from crushing to concentration.

How Does Mineral Processing Work?

Once the ore is transported to the surface of the mine, haulers feed the crushers with tonnes of large rocks, the first step in mineral processing.

After they are crushed to about 15 cm (6 in) in diameter, conveyor belts route the materials into stockpiles near the concentrator building for grinding.

A conveyor belt transports the crushed rock into the concentrator building to be further diminished by SAG grinding mills. There, the ore is either mixed in with water or kept dry and then undergoes the grinding process. Materials are ground to about 5 cm (2 in) in diameter.

SAG grinding mill with a stockpile in the background

The now smaller materials are fed to screens that size ore, resulting in minerals less than 1.3 cm (½ in) to fall through the screens.

The screening process

The smaller ore will go on to the ball grinding mills where they will be further ground down. The larger ore will be routed to a pebble crusher to reduce the size to 1.3 cm (½ in) and will return to the SAG mill stage.

The ball mill product is pumped to cyclones which separate out the coarse material with the fine ore. The coarse mineral ore is routed back to the ball mill stage while the fine minerals are routed to the concentration stage of mining.

Minerals adhere to bubbles in the froth flotation concentration process

During the concentration stage, a cleaner and higher concentration of the desired mineral is produced and ground down to the consistency of talcum powder. This is sent to a thickener where the concentrate settles and dewatering begins.

At this point, the ore is still at about 50% water, so this material is pumped to a filter press to further dewater the mineral ore.

Finally, the minerals are dried to remove the remaining water. The final concentrated mineral percentage differs depending on the mineral and the concentration process used.

The crude material is transferred to another off-site processing plant that smelts or refines the mineral ore into the final raw material.

Copper and gold concentrate

Mineral Processing Equipment

Below is a list of equipment used at each stage of mineral processing:

Crushing and grinding equipment
- Cone crushers
- Gyratory crushers
- Jaw crushers
- SAG mill grinders
- Rod mill grinders
- Ball mill grinders
- Pebble crushers
Sizing and classification equipment
- Bar screens
- Banana screens
- Fine screens
- Flip flop screens
- Grizzlies
- Multi-deck screens
  
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- Radial sieves
- Vibratory screens
- Wedge wire screens
- Wire mesh screens
- Fluidized classifiers
- Spiral classifiers
- Gas cyclones
- Hydrocyclones
- Ore sorters
- Rake classifiers
- Rotating trommels
Concentration equipment
- Cleaners
- Recleaners
- Roughers
- Scavengers
Dewatering equipment
- Dewatering screens
- Thickeners/clarifiers
- Belt press/membrane filter press
- Fluidised beds
- Hearth dryers
- Rotary dryers
- Rotary tray dryers
- Spray dryers

Some Questions about Grinding Stage Before Mineral ...

In this paragraph, we answers some common questions about grinding and classifying stage before mineral processing.

I. What is commonly used one-stage grinding classification process?

There are three kinds of milling classification process in commonly used.

1.One closed-stage grinding only contain process of check classification, which is widely used in nonferrous metal and ferrous metal processing plant at present.

2.One closed-stage grinding process combines pre-classification and check classification.

3.One closed-stage grinding process with control classification, which is very uneven feed size, difficult to properly load balls, and low grinding efficiency, is rarely used in mineral processing plant.

II. What are the commonly processes for two-stage grinding classification?

There are mainly three commonly processes for two-stage grinding classification:

1. The two-stage and one-stage closed-circuit grinding and classification process is applicable to beneficiation plant with large feed size and production scale.

2. The two-stage and two-stage closed-circuit grinding process, often used for the final product which is required by the size less than 0.15mm in large and medium-sized beneficiation plant.

3. Stage separation two-stage closed-circuit grinding and classification process, which is applicable to the case where a considerable number of useful minerals in the first stage of grinding products have reached monomer dissociation, can reduce grinding costs and improve metal recovery.

Compared with the second stage grinding and classification process, the number of classifiers in the first stage grinding grading process is less and the investment is low. Easy to operate in production, and also easy to adjust. There is no intermediate product transportation between sections, and multiple series of grinders can be placed on the same level. The equipment configuration is simple, and the shut down of one sectionof mill or classifier will not affect the work of another section of mill, and the shut down loss is small. And each series can be installed larger equipment. However, at the same time, in the first stage of grinding and classification process, the grain size range of the mill is wide, it is difficult to properly load the ball, the mill efficiency is low, and it is not easy to get the coarse final product.

III. What is grinding fineness?

We usually use the fineness standard, which can go through 200 mesh sieve screen, as the fineness of the product with the percentage of the product to achieve the fineness of the total expressed, such as grinding fineness -200 mesh 50% or -0.074mm 50%. The greater the percentage, the finer the product.

Commonly for most ores, the finer grinding fineness is, the better mineral desorption effect. So that the recovery rate can be improved. Therefore, under certain treatment capacity, grinding fineness will be improved as much as possible. But some mineral grinding fine too fine easy to produce slime, so grinding fineness is not the finer the better, generally reach the most useful mineral monomer separation fineness. In addition, on the premise of ensuring the mineral processing index, appropriately relaxing the grinding fineness can reduce the energy consumption of grinding grading operation and improve productivity.

There are many factors affecting grinding fineness, including the property of raw ore, crushing particle size, ore feed size, the number and size ratio of steel balls, the size of classifier openings and so on.

IV. What is the production capacity of grinding mill?

The production capacity of the mill can be divided into two parameters, namely, the production capacity of the mill and the utilization coefficient of the mill.

1. Production capacity of the mill

This parameter refers to the amount of ore processed by the mill per hour in unit t/(stage · h) with a certain amount of ore feed and product size.

2. Utilization coefficient of mill

This parameter is usually expressed by the English letter q, which refers to the average value of the amount of ore processed by the mill in the effective volume per unit of time. The unit ist/(m3·h), which is one of the important indexes to measure the working quality of the mill. When the grain size of the ore and the grain size of the productare similar, the properties and operating conditions of the ore in the mill can be judged by using the parameter of the mill. By increasing the utilization coefficient of the mill, the production capacity of the mill can be effectively improved.

The influencing factors of these two parameters mainly include feeding property, particle size requirements of the product, type and model of the grinding mill,mill speed, grinding medium, filling rate and so on. In order to improve the output of the grinding mill, it can be achieved by reducing the feed size and removing the surrounding rock and stone in advance, that means, improving the quality of the raw ore to prompt the grindability of the ore and increase the processing capacity of grinding, so as to reduce the energy consumption while increasing the output of the grinding mill.

V. What is the operability of grinding and classifying processing?

The operability of the grinding and classifying processing can also be called the operation rate, which refers to the percentage of the calendar hours that grinding mill-classifier group actually works. In the concentrator, the operability is usually calculated once a month, and the monthly average operation rate is calculated for the whole year.

The purpose of calculating the operability is to determine the energy consumption of the grinding mill. Generally, the energy consumption of grinding and classifying processing accounts for most of the energy consumption of the total concentrator. Moreover, the operability can be used to determine the management level of concentrator, and analyze the reasons affecting grinding mill - classifier can not operatenormally. Under the normal operation condition of concentrator, increasing the operability can reduce the concentrate cost and improve the economic benefit.

&#; Grinding

For more information, please visit Mineral Separation Equipment.