Mining Processes

Increasing output with improved mining methods

India, with a large resource base, is a major participant in the global mining industry. The country is endowed with abundant mineral resources that play an important role in the development of industries. However, in recent years, the mining industry has faced various problems such as volatility in commodity prices, reducing surface minerals and increase in the time taken to develop mines. Despite the underperformance of the domestic mining industry, the long-term potential of the sector is huge. At present, the country’s deep-seated mineral deposits remain unexplored.

Better mining techniques that deploy advanced technologies and equipment can play a significant role in driving the country’s mineral production. Primarily, there are two types of mining methods – surface mining and underground mining. Over the years, these techniques have witnessed major technological advancements in a bid to achieve higher efficiency and productivity.

Surface mining

Surface mining is used when deposits of the mineral or ore are found near the surface. It includes various different types of methods such as strip mining, opencast mining and mountaintop removal mining. Opencast mining has been the predominant method for excavation of minerals in the country.

Opencast mining

Opencast mining involves removal of overlying rock and soil material also known as overburden to extract the underlying mineral strata. This technique has widely been adopted due to low cost of operations as compared to underground mining. In 2018-19, Coal India Limited (CIL) produced around 95 per cent of its total output from opencast mining.

One of the major reasons that opencast mining has been widely adopted in the country is that it allows the use of large, efficient and modern equipment that has low labour needs and helps in saving time. Mining companies have increasingly deployed equipment such as draglines, power shovels, bucket wheel excavators and conveyors, and this has led to an increase in productivity.

Large capacity bucket wheel excavators are increasingly being used by mining companies at sites where overburden is loose and has less resistance. Surface miners that help in selective mining and improved separation of mineral ores from waste materials are also preferred. Dragline excavators are used for digging softer material in areas with loose soil and in marshy areas. The technology is far cheaper than the shovel-dumper combination.

Transportation of ore and waste rock forms a crucial element of opencast mining and involves significant costs. The use of telematics and global positioning system allows haul trucks to be tracked and scheduled for maintenance. Further, the use of in-pit crushing and conveying technology has picked up pace. The technology allows the ore to be crushed in the pit and transported out using a conveyor system. A fully mobile pit crushing and conveying system loads the material directly on the hopper of a mobile crushing plant, thereby eliminating the need for dump trucks.

CIL, which has set a production target of 1 billion tonnes, has fast-tracked the process of acquiring high capacity equipment such as rear dumpers, electric rope shovels, hydraulic face shovels and wheel crawler dozers to bolster production. Other trends that are picking up pace in the industry include the use of various digital solutions including unmanned aerial vehicles or drones, trackless equipment (to help in collision avoidance) and use of advanced software for mine planning.

Underground mining methods

Underground mining is used to extract ores from below the earth’s surface. There are two main underground mining methods – bord and pillar mining and longwall mining. Even though the technique has higher mineral extraction ability, it has a witnessed a declining trend in production due to high costs and advanced technology requirements.

Bord and pillar method

In this method, a series of pillars are set up to support the roof while minerals are extracted from between these pillars. In India, most of the underground production comes from this method. Modern bord and pillar methods that involve the use of continuous miners are being increasingly deployed today. The continuous miners cut and load the mineral deposit on to a shuttle car. The shuttle car then hauls the mineral to the feeder breaker which feeds the sized mineral to the conveyor at a consistent rate. A continuous conveying system helps in reducing the time lag between loading and crushing, thus resulting in higher productivity. Moreover, no drilling and blasting is required in this method, which makes it an eco-friendly option.

Longwall mining

Longwall mining involves full extraction of minerals from a section of seam or face using mechanical shearers. For coal, the seam can vary in length from 100 metres to 350 metres. Self-advancing, hydraulically powered roof supporters, coal shearing machines and conveyors parallel to the face are used for coal extraction. Longwall mining has an advantage over the bord and pillar method as it allows greater extraction of coal leading to an increase in productivity.

Though the longwall mining method has been present in the country for several years, it has not achieved the desired success due to low levels of mechanisation. The technique has, however, garnered interest again due to technological advancements. Mecahnised longwall technology has helped countries such as China and Australia reach new heights in production.

Singareni Collieries Company Limited has successfully implemented longwall mining at the Adriyala mines. Various new technologies such as punch entry which allow direct access to coal from the opencast highwall, pretensioned cable bolting for effective roof support, automation systems for reducing manual intervention and a variable frequency drive-controlled unmanned belt conveyor system were introduced in the project. CIL has started longwall mining at Bharat Coking Coal Limited’s Moonidih underground mine and Eastern Coalfields’ Jhanjra mine has also deployed various innovative solutions.

Hindustan Zinc Limited (HZL), the country’s largest integrated zinc producer, is planning to introduce high speed Wi-Fi networks in its underground mines to help in tracking underground equipment, executing remote operation of loaders, automating auxiliaries such as pumping stations and ventilation shafts, and undertaking VoIP-based communication with workers, thereby ensuring their safety.

Other technologies and equipment that are gaining traction in the country include innovative dust suppression systems, process ventilation systems and improved shearers and ploughs. There will also be wider applications of other underground mining equipment such as advanced strata control equipment, mechanised drifting, gas chromatographs, lightweight cap lamps, etc.

Need to increase production from underground mining

There has been a significant decline in output from underground mining as it is an expensive technique. As a result, opencast mining has been preferred due to short-term benefits such as lower costs, low levels of mechanisation and shorter gestation periods. Several underground mines have been closed to lower the cost of mining operations. In 2018-19, CIL, the largest coal producer in the country, produced only 5 per cent of its raw coal from underground mining. The share of underground mining in the company’s total coal production has witnessed a continuous decline from 11.5 per cent in 2008-09 to 7.8 per cent in 2014-15.

Currently, underground mining accounts for less than 10 per cent of the country’s total coal production. This is in stark contrast with other coal producing countries such as China and the US where around 90 per cent and 36 per cent of coal, respectively, is extracted through the underground method.

However, as surface resources are depleting faster, it has become imperative to shift to underground mining. Not only does the technique help in extracting the deep-seated reserves but is also a relatively environment-friendly option. The use of the opencast method has severe environmental implications including land degradation, loss of vegetation, and noise and air pollution.

To reverse the trend of declining output and increase the productivity of underground mines, there is a need to adopt high levels of mechanisation by introducing the use of advanced technologies and state-of-the-art equipment. Various initiatives are being taken, especially by private players, to switch to underground mining techniques. HZL is working towards becoming a fully underground mining company and is planning to convert its Rampur Agucha block, which contributes 75 per cent of its output, to an underground mine by shutting all opencast operations.

The way forward

The adoption of better mining techniques will be a key success factor for the industry as resources become geotechnically complex and companies pursue opportunities in new mining territories. While it is important to introduce innovative and energy efficient equipment for opencast mining, the issue of declining underground mining output needs to be urgently addressed. Though advanced and sustainable mining methods are being adopted by major mining companies, their mass-scale adoption still has a long way to go. The government can play an important role in the industry-wide adoption of these methods by formulating policies that encourage their deployment.

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