ABSTRACT

Sustainability is discussed in the context of the electrical energy that is consumed by the mining industry for the production of everyday metal commodities. The results presented are from a study which attempts to quantify global energy consumption attributed specifically to the comminution processes, namely the crushing and grinding of metaliferous ores. It also reflects on the current understanding of eco-efficient comminution practices, a required mineral processing stage that has received a lot of attention in recent years because of the view that mining is directly and indirectly responsible for up to 45% of the global economy and that a large proportion of the consumed energy originates from the beneficiation processes in the production of mineral commodity.

The mining industry has been under pressure to review its approach to energy usage. This is further complicated as a major trend compounding energy use in the mineral extraction industry today is the necessity of having to process more massive, hard and low-grade ore bodies. As a result, a much greater amount of gangue material (waste) is being reduced in size, and to much finer sizes, due to finer mineralisation, to produce the same amount of recoverable metal. This research therefore aims to seek alternative mechanisms/processes in which the minerals can be liberated from the ore resulting in more energy efficient and economical benefits. For this, the high pressure grinding rolls (HPGR) have been considered in recent years as an alternative energy efficient comminution technology to that of the existing inefficient tumbling mills.

The goal of being able to realise a step change improvement in energy efficiency and lessened environmental impacts through reduced equivalent CO2 greenhouse gas (GHG) emissions is being vigorously pursued. From a sustainable viewpoint, the balance between global energy consumption and economic value (currently 2%–4% of gross domestic product (GDP) in industrialised nations) is expected to change in the future. This means that as the economic cost of energy increases, the amount of energy required to do the same amount of work increases at a greater rate, and energy intensive industries such as the mining and mineral processing industry are likely to be the most affected. In particular, major processes such as comminution (crushing and grinding) that consume relatively large quantities of electrical energy generated from coal or oil are targeted.

Direct energy use in the comminution processes is reviewed. It is shown that 0.43% (87 TWh) of the global net electrical energy consumption of 20,000 TWh per annum is used to crush and grind non-ferrous ores. Of this, 33% and 53% of the energy is required to process gold and copper ores, respectively. This suggests that alternative energy efficient comminution technologies should be targeted at gold and copper mining operations in the future to be effective in reducing carbon emissions. As such, new eco-efficient flow sheets that use new devices, process less ore by pre-concentrating the feed to the plant should be considered. In addition, eco-efficient power generation technologies could tackle the problem from an energy supply perspective.

Greater eco-efficiency can also be realised by reducing the consumption of mill liners and grinding media. Though the ‘dollar cost’ of comminution is normally accounted for as a direct electricity expense in the process and is rarely considered for its overall energy cost or ‘embodied energy’ of manufacturing the steel which amounts to up to 4–6 kWh/t. Eco-efficient and sustainable development initiatives are linked to ‘energy cost’ and not always ‘dollar cost’ savings. The direct and indirect energy cost savings and the impact on the environment should be targeted.