IM 2021 June 21 | Page 6

Anglo American says it trialling microwave pre-conditioning at Amandelbult
WORLD PROSPECTS

LKAB & Montanuniversität Leoben to test new raise caving mining

When mining depths in underground mines increase , so do the challenges .

Therefore , an entirely new method has been developed – raise caving . This is a major groundbreaking step towards a safer , more efficient mine . “ Raise caving has been developed for efficient mining at great depth ,” says Matthias Wimmer , Section Manager in the Department of Mining Engineering at iron ore miner LKAB in Kiruna . Rock stresses increase as mining moves to ever greater depth . A more complex geometry , in combination with rockmechanical challenges , places demands on new , sustainable and innovative solutions for the mine of the future . And , underground , safety is paramount . “ Our exploration results are extremely promising and open the way for mining under our current main levels far into the future , beyond 2060 . But this also places demands on new technology , on solutions and methods that are adapted for new conditions ,” says Wimmer .
The greater mining depth has necessitated the development of the new method , raise caving . Both the method and the machine concept , which is an essential part of the mining method , have been developed by LKAB in close collaboration with Montanuniversität Leoben , in Austria . Large-scale testing will begin next year in the Kiruna mine . “ We still have a huge amount of work ahead of us . Two test areas will be developed : one for the machine concept and one for the mining method . Initially , individual components will be tested step-wise . Thereafter ,
the complete system will be tested ,” explains
Wimmer .
The method currently applied in LKAB ’ s underground mines , large-scale sublevel caving , has been very successful . This is an effective method that enables mining of large volumes at a relatively low cost . However , there is some question as to how appropriate this method is for mining at ever greater depth . “ There are some mines with production at extreme depths , down to as much as 4,000 m . However , mines in which some form of large-scale caving is applied have not yet reached such depths . And there is a lot of uncertainty as to whether they can maintain viable production volumes in the longer term ,” says Wimmer . In other words , the application of caving methods at depth is largely unproven .
Raise caving , as opposed to sublevel caving , is a method that enables mining of the orebody from bottom to top , instead of from top to bottom . In other words , the sequence is reversed , and the technology shift has several advantages , not least in terms of safety . “ Rock stresses can never be eliminated in a mine but , with this method , we are able to determine where seismic events occur , far from the active infrastructure . This means that we allow events , but in specially predetermined places ,” explains Wimmer .
In addition , this “ upside-down ” method , in combination with good draw control , allows good conditions for mining more ore and significantly less waste rock , since dilution is avoided . But raise caving presents even more
possibilities . “ Since the infrastructure and drifting , ie , developing roads in the mine , can be reduced , we have the prerequisites for improving efficiency by as much as 50 %.”
Raises are bored and that is the starting point for mining in slices and caving the ore from the bottom to top . This means that mining starts in the raises and is not done horizontally and conventionally by means of so-called drifts . This implies that no people work directly with drilling and blasting , in a conventional sense , within the raises . “ Concurrently with development of the raise caving method , we have worked with machine development . This is a highly automated machine that can both drill and charge via the raises . We are also developing a module for , among other tasks , rock reinforcement and hydraulic fracturing ,” says Wimmer . www . lkab . com ; www . unileoben . ac . at
Anglo American says it trialling microwave pre-conditioning at Amandelbult

Anglo American says it is in the process of achieving a world first in the industry by taking microwave technology underground to pre-condition rock . The technology works by creating fractures along natural grain boundaries – the interface between minerals – within the rock face . The process significantly reduces the energy needed to weaken or break down the natural rock face at the earliest stage , before it is mechanically crushed and milled . Using microwave technology in this way , also allows more of the ore to be recovered because of the smaller particles generated , making it easier to process and adding value as a result .

A newly announced project at Amandelbult platinum mine in South Africa it says will deliver immediate and valuable data regarding the actual impact of microwave pre-conditioning insitu and represents another important step forward in Anglo American ’ s FutureSmart Mining™ programme . Its greatest value is expected to be realised when it is combined with technologies like hard rock cutting , coarse particle recovery ( CPR ) and hydraulic dry stacking . Microwave treatment of ores containing metal has long been investigated as a means to enhance recovery and reduce energy required for liberation and comminution , by ‘ softening ’ minerals . When the ore is exposed to microwaves , the different minerals in the rock have different heat signatures , expanding and cooling at different rates and causing microfractures . These cracks , which happen along mineral boundaries , mean it is much less energy intensive to liberate and then crush and mill the rock .
It also has potential downstream in comminution . During the recent Technical and Innovation Update presented by Anglo
American on May 11 , Donovan Waller , Group Head of Technical Development , also stated : “ Microwave is a really interesting new technology that I do not think you would have heard too much of before . Some minerals respond well to microwaves which pass seamlessly through the waste . This differential heating causes stresses and microfractures in the rock , causing the rocks to soften and hence they melt quicker , resulting in an increased throughput . In addition , they tend to break along the ore grain boundaries meaning that liberation becomes easier . We are currently looking at rolling out a unit on the Los Bronces pebble circuit . The technology is applicable across PGMs as well as copper .”
In addition to rockface deployment at Amandelbult and pebble circuit potential at Los Bronces , the company is also looking at potential rollouts at Mogalakwena , Collahuasi and Quellaveco . It referred to a further implementation CAPEX spend of $ 400-700 million . www . angloamerican . com
4 International Mining | JUNE 2021