Toll Milling and Mineral Processing -
A Guide to Equipment, Services, and Applications
As a leading miner, supplier and processor of minerals to precise specifications, African Pegmatite stands ready to mill almost any mineral using a variety of robust, reliable and cutting edge technologies. African Pegmatite’s wide catalogue of milling services are all available on a toll basis, and are backed up by a highly experienced, specialised and knowledgeable team of millers and processing experts, ensuring the right milled product every time, for the most demanding of applications.
Introduction To Toll Milling
Milling is one of the major toll services for minerals offered by African Pegmatite, alongside drying and granulation. Processing minerals requires specialised machinery that’s suited for the type of mineral being milled. There are quite a few machines for mineral milling and each has a unique specialisation. In order to achieve the highest quality according to specifications, it’s essential to have access to and use of the proper machinery.
Toll milling is the exchange of custom milling services and other processing services for a fee or toll. This guide is a review of some of the machines used in African Pegmatite’s cutting-edge milling facilities which are available on a toll basis to businesses. By familiarising themselves with this equipment, businesses can get a better understanding of what services and machines they may need for a superior product.
Every mineral has its own set of characteristics that determine what type of processing is needed to break them down to the chosen specifications. Specifications will generally identify a size range that the particles must be for a certain application. The proper machine(s) must be used depending on the mineral or ore, its hardness on the Mohs scale, its abrasiveness and the desired result, among other considerations.
Using the wrong machine for milling and processing can result in improper processing and wasting of the mineral ore or worse, costly damage to the equipment. It is imperative that businesses contract the use of the machinery that is right for their purposes, although such in-depth knowledge is less vital when experts are hired to mill the materials, but some companies might consider purchasing the machinery themselves to cut the cost of hiring millers. Specialist, highly trained millers are key assets in the efficient and safe processing of minerals. Their in-depth knowledge and wide experience ensures that processing is done in an optimal way, with a much lower likelihood of failure, providing for a superior milled final product.
So How Much Does it Cost to Buy the Equipment for your Business?
The cost of mineral processing equipment is simply far too high and so businesses should not invest in such equipment if processing is not part of their daily operations. Quite simply, the return on investment will not be high enough to justify the capital expenditure if the equipment is not in near constant use. It might seem like a clean solution for those who regularly require custom milling services, but the equipment is just too expensive to be a practical solution for the vast majority of even the most well capitalised businesses. Furthermore, such large and complex machinery requires regular maintenance, near-constant monitoring and spare parts on hand to keep production going in the event of failure. Additionally, because of the size of the machinery, a great deal of space is required for them.
Another aspect for businesses to consider when deciding whether or not to purchase their own milling equipment is the increased safety hazards these machines can create within their facilities. The unforgiving power of crushing and grinding machines require intensive training for inexperienced personnel. That translates into substantially increased labour hours and most likely higher insurance costs. Before buying their own milling equipment, it is crucial that a business reviews all of the effects, both positive and negative, that it will have on the business as a whole.
Purchasing and implementing the necessary machinery outright is highly cost-intensive and probably not as convenient as it might seem, considering the facilities, labour and maintenance. For most industries, the most cost-effective solution is to build a relationship with a reliable, experienced, and reputable mineral milling company for toll milling. The experts at industry partners such as African Pegmatite will know exactly what machine and process are needed to achieve the results required with the mineral or ore to hand.
African Pegmatite is a mineral mining, milling and processing company with decades of experience servicing five continents with completely customisable shipments. African Pegmatite’s cutting-edge facilities contain all of the standard machines listed in this guide, as well as some not mentioned here including some of the most specialised, custom built milling equipment available. The team at African Pegmatite stands ready to advise on idealised specifications, machinery and processing; as well as offering a complete assessment of shipping, packaging and frequency to suit the budgets and production schedules of businesses worldwide.
Mineral Processing Equipment
African Pegmatite uses all of these machines regularly for the processing of a full range of minerals for a variety of customers, providing for a breadth of specifications and requirements across multiple mineral classes. Each type of mill specialises in a particular type of material or a particular type of milling. There are crushers and grinder that produce slightly different results. There are mills that wear materials down through attrition and those that are gravity fed. One thing that’s true of virtually every machine employed by African Pegmatite is that they can be set to produce ground or crushed rocks, aggregates, minerals and ores to the exact specifications of any customer, which is crucial when using these materials for the most demanding industrial purposes like water filtration, pigmentation and more, where quality is essential.
With such a broad range of milling equipment, and the ability to easily mill down to particle sizes of 45 μm, African Pegmatite offers the widest tolerance of minerals. Optimal milling may be achieved by one or a combination of more than one method, alongside other services such as drying and granulating - all of which are available through expert consultation with specialists at African Pegmatite.
Ball Mill Services
The ball machine crushes materials using centuries-old principles of grinding that have been refined and applied to modern-day equipment. The machine contains various types of balls, depending on the mineral being processed, that grind and crush through repeated impact. The balls are usually chrome steel, but stainless steel, ceramic, and rubber can also be used for less common processing, like explosives. Flint pebbles are another common grinding media.
A large, cylindrical chamber lined with a particular material – either an abrasive-resistant surface or rubber – is partially filled with the balls and the minerals are placed inside the chamber, as well. The rotation of the cylinder causes the balls and minerals to remain in constant impact that slowly wears the mineral to a specific size or powder ratio.
Ball Milling is used in the processing of ceramics, paints, coal, pigments, feldspar, and more. In addition to grinding minerals down, a ball miller is often used to mix or blend materials. It can be used for wet or dry milling. Standard ball milling is performed by rotating the chamber around a horizontal axis. High energy ball milling involves a second, larger chamber in which the smaller agitates, sloshing the contents via centrifugal force. Both types of ball milling can be performed in batches or continuous operation.
A hammer mill is comprised of a steel drum that houses a horizontal shaft that rotates at high speed. Attached to the shaft are numerous hammers that crush the mineral as the shaft rotates. Some hammer mills have several large hammers while others have dozens of smaller hammers.
Generally speaking, all hammer types will be hinged so that they move with a swinging motion and have a very small gap between the extended hammer and the interior of the drum. Hammer mills have existed since 488 A.D. and were once water powered. This type of milling can be used as the primary milling process or can be used as a follow-up to achieve more precise results.
As the mineral is fed through the hopper, the hammers make repetitive impact at high speed and shatter the material. Crushed pieces are sifted through the bottom of the mill and can be process further or used depending on the requirements. In African Pegmatite’s facilities, this process is done on a large scale, but hammer milling can be done on a small scale.
Roller mills are one of the most effective milling machines when it comes to crushing calcite, feldspar, gypsum, clay, marble, glass, or other materials into a fine powder. The roller mill can easily meet the specification of 80 to 600 mesh and is widely used throughout the mining industry.
A roller mill works by grinding materials at high speed with a varying number of heavy, cylindrical rollers being spun around a central vertical shaft. The mineral is fed into the machine through a port in the side and is immediately crushed into powder by the large roller wheels.
A cone crusher is an efficient crushing machine that works by introducing the material into the top where it falls down towards a crushing cone that is pointed up. The cone rotates and agitates inside the cylindrical housing, crushing the mineral between the cone and the interior wall.
The cone can be set to a specific crushing size by raising it towards or lowering it away from the bottom of the cylinder. The crushed material falls through the gap between the cone and cylinder. Materials can be passed through multiple crushers to achieve specifications. Rocks are the most common material crushed in a cone crusher. The crushed rocks are typically used for landscaping, road work, mining, and erosion control.
A roller crusher is a very common type of crusher that’s used across many industries outside of mineral milling with various design alterations. For the purposes of mineral processing, a roller crusher consists of two grinding rollers that rotate in opposite directions towards each other with little space between them. Rocks, ore, or other aggregates are fed into the top of the roller crusher where they fall into the valley where the two wheels meet. The rotation forces the materials between the rollers where they are crushed and the fragments fall through the narrow gap. The size of the gap determines the results of the crushing.
There is another type of roller crusher called a high-pressure grinding roll or HPGR. This type of roller crusher reduces the mineral size through compressive and interparticle pressure. Measurements are determined mathematically beforehand.
Attritor mills are a type of ball mill that are sometimes referred to as stirred ball mills. They come in a variety of sizes for many different industries from labs to factory floors. Attritor mills are best suited for ceramics, food, pigment mixing, paper coating, iron production, glazes, pharmaceuticals, coal, and chemicals. The balls inside the attritor mill can be made of various materials, but must be stronger than the material to be milled.
A vertical centre shaft inside a cylindrical tank is fixed with arms that spin around the shaft at high speed. The arms can vary slightly in design. The tank is partially filled with balls and then the mineral is introduced. When the arms spin, they make impact with the material and the balls, both of which fly around the tank making impact with each other at high speeds. If the material is softer than the balls, it will be pulverised into a fine powder.
The jaw crusher is the primary crusher type used in the mining and ore crushing industry. It is made up of two panels that are arranged in a V shape with a small gap at the bottom. The size of the panels and gap depends on the specifications for the rocks, ore, or other aggregates to be crushed. One of the panels in the V configuration oscillates towards and away from the other panel. This allows bits of rock or other material to fall further into the V when the panel moves away, and then be crushed when the panel moves back in. The crushed fragments fall through the gap at the bottom of the panels. This sort of chewing motion gives the jaw crusher its name.
Drying and Granulating
As part of offering a complete processing solution to customers, African Pegmatite also offers drying and granulating services alongside toll milling. The addition of drying and granulating to an already wide and varied catalogue of toll milling services underlines the commitment of African Pegmatite to be the go-to partner for toll processing solutions.
For granulating, it is true that most of the milling techniques as described above can easily achieve a granulated product if the machinery is suitably configured. In addition to this, African Pegmatite boasts a range of powder decks and screens to guarantee particle sizes in the specified range. The principles of size exclusion, bulk density and specific gravity are used by the granulating equipment to ensure consistent particle size.
Moisture in a milled product in may cases is not a problem, however there are some applications which demand the driest of mineral powders. African Pegmatite has the facilities to reduce moisture in almost any mineral powder to less than 1%. Comprehensive drying is provided by a rotary dryer, which tumbled the mineral through drums heated to as high as 250 °C - providing an even yet thorough removal of liquids, moisture and residues.
Additional benefits may also be gleaned from the drying process, such as the driving off of contaminants and oily residues from other processing pathways. For the most sensitive cases, such as those destined for medical device uses, an effective heat treatment may remove and/or disable bacteria and pathogens.
Custom Milling Services and Toll Processing
Mineral processing is an area as broad as it is essential. Although deep operational information is not required, customers may find it beneficial to familiarise themselves with some of the machinery used in mineral processing and toll milling as a first step towards establishing a solution that works best for their business, alongside African Pegmatite’s expert consultation.
These are but a few of the machines we have at the disposal of African Pegmatite, ready to process any ore and minerals to precise requirements that will ensure optimal performance in the most demanding of applications. With the equipment listed here and many others as part of the widest bouquet of mineral processing equipment, any milling request, regardless of mineral hardness or abrasiveness can be easily fulfilled to any businesses’ exacting specifications. In subsequent articles, the functions of each machine in more detail will be discussed, including some highly specialised services that can be offered.
Toll processing allows businesses to get professional class results and optimal performance from their materials to be processed without adding the complication and high capital expanse of a purchasing dedicated milling for their business.
The use of African Pegmatite’s highly specialised services when needed will save businesses time, money and resources. African Pegmatite’s team and equipment can be relied upon to provide the service and high quality end product that businesses expect and deserve.
African Pegmatite is located in South Africa and is proud and able to provide mining and milling services for industries across five continents, working closely with valued clients for both short projects and ongoing services.
- The processing and milling of rocks, ores and other compounds is a complex, energy intensive and financially demanding undertaking
- Toll milling is the process by which a customer contracts a service provider to utilise their facilities, expertise and experience to process the mineral
- African Pegmatite proudly boasts a comprehensive range of equipment to satisfy virtually any milling requirement down to the micron scale
- Additional added value services such as granulation and drying are available
African Pegmatite offers the widest selection of mineral processing equipment available on a toll milling basis for short or long term projects, for an expansive range of minerals and ores. Utilising proven and reliable methods alongside cutting edge technology, all backed up by the most knowledgeable and experienced team, African Pegmatite is the ideal mineral processing partner.