Loesche technology

Gold mining practices have stagnated in the face of continuously changing technology. Mining companies today face a completely new battery of challenges to recover minerals.

Historically the reefs were rich and large profits were made with ordinary recovery circuits but today mines are dealing with complicated ores that require fine grinding to allow a 92% – 98% recovery rate just to stay in the game.

Read more about gold mining

From humble beginnings 113 years ago, family owned business Loesche a has taken the vertical roller mill (VRM) to the forefront of modern day milling.

This article first appeared in Mining Review Africa Issue 9, 2019
Read the full digimag here or subscribe to receive a print copy here

Being well established in the cement industry with a 55% market share worldwide, the company has taken the proven design concepts and adapted it to the ore industry, specifically gold, copper, phosphates and iron. To support the equipment, Loesche has a team of highly qualified staff dedicated to ensuring customer service and satisfaction is achieved.

New opportunities in ore comminution

Ore deposits today are characterised by significant variations in their mineralogy.

The particle size is critical for a sufficient degree of mineral liberation to expose the mineral and the grindability of the ores fluctuate, hence the beneficiation process and especially the comminution process must be flexible.

To identify the best process route, conventional and new technologies have been investigated by Loesche.

Dry and wet grinding technologies were compared in terms of grinding performance and product quality. Through significant laboratory work done, improved flotation performances of dry ground products have led to the design of a completely new beneficiation process.

The Loesche VRM has adaptable grinding modules which are already proven to be the way forward in other mining industries, allowing for variant mineral ores to be milled efficiently to the required particle size.

The VRM, depending on the roller size, has a high reduction ratio; feed from 80 mm to 140 mm to a product of P80 at 75 µm in one pass, the mill is a closed circuit on its own having the comminution and classification of product in a single machine.

Sulphide copper-gold ores are usually sorted by flotation. The standard comminution process to grind the ore to flotation fineness, mostly consists of coarse crushing followed by SAG milling or wet ball mill circuits, or alternatively multiple stage crushing followed by rod and ball milling.

The two most common compressive comminution technologies are the high pressure grinding roller (HPGR) and the vertical-roller-mill (VRM). For now, the HPGR has already presented in a noteworthy number of mining projects whereas VRM technology, a new entrant, is still not fully accepted.

This is considered a resistance to change considering that VRM technology has a clearly dominant position in classical dry, compressive comminution applications like grinding of cement or granulated blast-furnace slag.

The VRM produces a steeper particle size distribution, reducing wastage in the form of ultra-fines and oversize, by this the VRM allows for a good flotation size range having more particles exposed to the floatation process.

Loesche comminution principles

Loesche VRM comminution technology is a particle on particle in bed grinding principle, cracking the ore on the mineral lines to expose more minerals to the floatation process with very low specific wear on the liners to produce cleaner concentrates.

Consequently, efficiency in energy used can be as much as 40% – 45% less than a wet ball mill circuit – noticed with all power going into the comminution of the ore.

Smarter process control ensures consistent grinding to the correct size whilst the mill is in operation. All this is done in a dry process, reducing the oxidation of the float product.

Dry comminution downstream effects

Dry product allows for a surge silo to operate between the comminution and recovery circuits which ensures accurate, constant feed. This consistent flow with cleaner concentrates reduces reagent consumption.

By this a smaller footprint can be envisaged, reducing water absorption and evaporation. Increased water reclamation and less pollutants will be experienced affecting the nett operating expenditure to process a ton of ore.

Mining houses adapting to new environments

Challenges from the strict environmental regulations have allowed Loesche VRM technology to become the future in comminution, enabling mining houses to operate in previously difficult conditions not suited to wet processes.

This will allow mines to embrace electrical and water scarcities whilst improving the economics of low grade and complicated ore bodies.

Proof of concept

For companies wanting to establish that the VRM technology is the way forward, Loesche offers the mobile ore grinding plant (OGP) to run live tests on site.

The OGP is a modular containerised comminution circuit laboratory where a Loesche milling specialist will be on hand performing various grinding tests until the optimum solution is reached for downstream processes.

Guarantees for throughput, power consumption and wear element consumption rates can be determined during the same proof of concept phase.