Sustainability reporting & water

This paper presents a preliminary compilation and analysis of the water reported to have been consumed by a range of various mineral commodities and compares it to mine production data. This has been undertaken to assess and quantify the ‘embodied water’ of mineral products - a key aspect of sustainability (embodied water is the total water required to produce a good or service).
At present, although the use of formal reporting protocols such as the global reporting initiative (GRI) is increasing, there are still critical weaknesses. Some key aspects to facilitate proper water accounting are not listed in sustainability reports, including the extent of recycled water used, mine site water inventories, the quality of various waters, and impacts on water resources.
Based on the data compiled, there is wide variation in the water used for different mineral commodities as well as for the same commodity. There is little evidence for ‘economies of scale’ in base metals and bulk minerals, though for precious metals (gold, platinum), greater throughput does tend to lead to greater efficiency.
For many mines, there is little evidence of improving efficiency over time, although some mines have made substantive improvements in reducing water consumed. The grade of ore being processed is clearly critical in understanding the embodied water of minerals, with declining ore grades leading to an increased chance of higher embodied water in the future.
Given that many metals are declining in average ore grade, the sensitivity of embodied water to ore grade provides a major sustainability challenge for mining generally. In summary, the embodied water of minerals is clearly significant, and will likely gradually increase in the future, and so must be more completely accounted for to understand a fundamental aspect of sustainability and mining - that of water resources.

The debate about water is often very sensitive due to its fundamental importance to life, society, and the environment - a debate often informed, rightly or wrongly, from historic legacy sites or accidents at mines.
There has been a steadily increasing focus on mining and water issues, leading to more stringent regulations governing water rights and responsibilities, and more attention to water management and potential environmental impacts associated with mining. In particular, over the past decade, the global mining industry has embraced a paradigm shift to include sustainability as part of their mandate for continuing operations. This has been primarily through the industry-led project called ‘Minerals Mining and Sustainable Development’ (MMSD).
The application of sustainability principles to water resources is challenging, due to the large spatial and temporal scale of affected catchments, the potential for significant time lags before problems are evident, and widely differing cultural issues and values associated with water. It is therefore imperative that water issues in mining be addressed and not downplayed as minor; water is, without doubt, a critical sustainability issue facing the mining industry globally.
A fundamental tool for sustainability analyses is that of life-cycle assessment (LCA), which seeks to estimate the total costs of a particular product over its full life.
LCA has introduced the concepts of ‘embodied energy’ (to estimate the potential for energy efficiency and/or greenhouse contributions) and an equivalent term, the ‘embodied water’ of various products. Embodied water is the total water required to produce a good or service.
At present, there is very little information on the underlying factors that contribute to the embodied water of various minerals and metals, but, in concert with evolving global sustainability practice, there are many mining companies that are now actively reporting their performance with respect to a range of sustainability indicators, with water always being a fundamental aspect of such reports. Thus, it is now possible to compile and analyse the embodied water of mining to more accurately inform LCA and other sustainability studies.
This paper provides a preliminary review of the use of water in various mining sectors, and presents an extensive range of compiled data on water consumption in mining.

In assessing the embodied water of mineral products in a strategic sense, one must be able to make fair and accurate comparisons for the same output. That is, the data should be effectively equivalent and for the same components. For mining projects, there are a number of factors that can affect the embodied water of a metal or mineral output, including:
• Climate conditions (e.g. temperate, arid, tropical)
• Primary water source: surface water, ground water, or saline water (marine or otherwise)
• Ore mineralogy and geochemistry (especially as this affects processing)
• Tailings and waste rock/overburden management (especially as this affects water management)
• Type of commodity (e.g. uranium requires extensive dust suppression)
• The extent of re-use and recycling
• Minesite water management regime (e.g. allowable discharges or not; treatment)
• Surrounding communities, land uses, and/or industries (e.g. towns, national parks, farms)
• Project design and configuration (e.g. open cut and/or underground mining, concentrator and/or smelter, hydrometallurgical plant, heap leaching, solvent extraction, electrowinning)
• The initial moisture content of the ore and waste rock
• If the mine is above or below the water table; and
• Surrounding hydrogeological conditions (e.g. high permeability aquifers; artesian ground water depressurisation issues).
For example, two open cut porphyry copper mines with flotation mills both produce a concentrate output but one is located in the tropics while another is in an arid region; although the project configuration may be nearly identical, the water resource needs and impacts will be very different.
Thus, although it is critical to understand the embodied water per unit copper, there is no absolute figure which could be argued as ‘acceptable.’ Rather, it is critical to think of the embodied water relative to similar projects or industry averages, as these can point to opportunities to target and realise water savings, improve project efficiency, and thereby reduce embodied water and improve sustainability performance.
The recent emergence of sustainability reporting frameworks now facilitate a more comprehensive picture of water consumption and use in the mining industry. The most common protocol used by the mining industry is the ‘Global Reporting Initiative’ (GRI) (now in its third edition, GRI 2006), which requires them to report a range of sustainability indicators covering environmental, economic, social, and human rights aspects of mining. There is a range of key environmental indicators and data that are considered ‘core’ to report against, as well as a range of additional or voluntary indicators. Thus, it is possible to link production data with water data from sustainability reporting and analyse embodied water more comprehensively than in the past.
With regards to the long-term sustainability of mining and water resources, there are a number of fundamental issues that need to be considered. First, the ever-expanding scale of modern mining will require more water to meet growing demands for minerals and metals. Second, long-term declines in ore grades for most metals, e.g. copper or gold, will require ever-increasing amounts of ore to be mined and processed to sustain mineral supply, again suggesting increasing water requirements.
To achieve a large ore throughput, projects are typically open cut, giving rise to substantive quantities of waste rock, overburden, and tailings, which needs to be managed with respect to potential impacts on surface and ground water resources.
Third, more refractory ores are now commonly being exploited; these often require more intensive processing and thereby have relatively higher embodied water than less refractory ores.
Fourth, the role of mineral processing technology is critical in understanding embodied water - e.g. will heap leaching and solvent extraction-electrowinning realise a lower or higher embodied water than conventional flotation and smelting? Given declining ore grades and more refractory ores, the long-term direction for mineral processing technology is critical to ensure that the embodied water does not increase significantly in the future.
Related to this dilemma is the potential compromise between water and energy; that is, reducing embodied water at the cost of increasing embodied energy (e.g. desalination).
However, at present, there is minimal data publicly available to enable substantive analysis of all of these issues. The embodied water of mineral products is clearly a fundamental aspect of sustainable development, and is directly linked to a region’s economic, social, and environmental health. To understand the existing embodied water of mineral products and the potential trends for embodied water in the future, the remainder of this paper compiles and analyses publicly reported data on water and mineral production. As research in the field of sustainability reporting and mining is in its infancy, the work presented in this paper is considered preliminary, though hopefully still useful.

Methodology
Individual mine production data from annual corporate reports were compiled and compared with water consumption data published in sustainability reports (on an annual basis).
To the extent practicable for consistency and comparability, water consumption data was defined as what had been reported as total consumption, including recycled water. Mines have been excluded from the master data set where it was clear that data reported was only raw or recycled water and not both (this is a very small number relative to the master data set). The accumulated data for individual mines range from a single year to nearly 15 years.
Data were analysed with respect to two key metrics: water consumed per tonne of ore processed and water consumed per unit metal/mineral produced (e.g. kL/t ore vs. t ore/year, kL/t metal vs. ore grade). The data have been grouped into principal ore type, since such mines commonly have similar processing and infrastructure. Site specific aspects, such as underground or open cut mining, heap leaching, solvent extraction or flotation milling, and climatic regime have not yet been analysed in detail, though it appears that some limited interpretation is possible.

Results
In general, the higher the ore throughput, the more likely that unit water consumption per tonne of ore will be lower (i.e. economies of scale), but as ore throughput declines, there is an increasing likelihood that unit water consumption per tonne of ore will be relatively higher (particularly for gold). It is perhaps not surprising that for many significantly different ore types, the unit water consumption is within the same magnitude (e.g. copper, nickel, uranium); this is most likely related to the similar nature of the processing configurations utilised (e.g. grinding, flotation, hydrometallurgy). At common ore throughputs (between 0.1 and 20 Mt/year), there is a degree of scatter in the data, which is likely related to mine site differences, reporting issues, or other factors (discussed further below).
The ore grades for the metallic ores analysed vary significantly, from about 0.3 per cent Cu to 22.5 per cent Pb + Zn, with the results suggesting that as metallic ore grades decline, there is a strong probability of an increase in embodied water for that metal(s). For gold, platinum group minerals, and diamonds, similar results are apparent, with large ore throughputs showing relative water efficiencies (due to economies of scale); at lower throughputs, while there is significant scatter, it is also clear that lower grades have an increasing chance of very high embodied water per unit metal/mineral.

Water Efficiency
With respect to water efficiency, the compiled data demonstrate two principal aspects. First, the consumption of water per tonne of ore milled with respect to ore throughput shows a degree of variability between and within metals and minerals, as demonstrated by the standard deviation being close or equal to the average water consumption.
Some mining projects consume significantly more water than other similar projects. For example, one lead–zinc–silver mine consumes 8–11 kL of water per tonne of ore compared to all others at 0.6–2.5 kL/t ore, or a gold mine that consumes 28–48 kL/t compared to all others at 0.5–3 kL/t ore; given site-specific issues and consistency over time, it is believed these examples represent valid data.
The trend over time for many mines, though not presented, is variable - with some mines showing efficiency improvements while others have increased water consumption. In general, particularly for precious metals (e.g. gold), data suggests that as ore throughput declines, there is an increased likelihood of higher water consumption. Second, with respect to throughput scale, there is surprisingly no clear evidence that larger scale leads to greater efficiency in base metals and bulk minerals. For example, some porphyry copper projects milling 10–30 Mt/year consume less water per tonne of ore than a porphyry copper project milling 120-130 Mt/year. For gold, platinum, and diamonds, however, there is reasonable evidence that a larger project scale does lead to greater efficiency. It cannot be automatically assumed, therefore, that larger-scale projects will help drive economies of scale and lower water consumption per tonne of ore processed. Additionally, larger-scale projects inevitably require larger total volumes of water.

Embodied Water
The embodied water of the mineral commodities presented varies significantly, both between and within ore types. Gold clearly has the highest embodied water per tonne of mineral/metal, with platinum very close behind; this is presumably due to the very low grade of gold and platinum ores (i.e. parts per million compared to percent for base metals). Conversely, the embodied water of base metals varies significantly, clearly related to the ore grades of copper versus lead–zinc or uranium ores. For example, lead–zinc has an embodied water of about 29.2 kL/t Zn ± Pb ( ± Cu) while copper has 172 kL/t Cu, and uranium 505 kL/t U3O8, where ore grade is typically 10-15 per cent Zn ± Pb, 1-2 per cent Cu and 0.04-0.3 per cent U3O8, respectively.
Lead–zinc and copper ores are often processed first through flotation, meaning the embodied water is largely a function of ore grade, while uranium is processed using hydrometallurgical techniques and the ore grade is fractions of a percent (e.g. 0.04-0.3 per cent U3O8).
The underlying variability in water consumption, both for a given mineral type and between mineral types, suggests that there are a number of factors likely to influence water consumption and hence embodied water. This could include mine type (open cut or underground), ore mineralogy, mill configuration and design (e.g. flotation, hydrometallurgy), water quality, project age, climate (arid, temperate, tropical), long distance slurry pipelines (e.g.>25 km), and finally whether a smelter and refinery is also included. This makes the issue of equivalence between sites somewhat problematic. Further research is required to undertake the complex process and statistical analysis that might be able to illuminate the principal contributions of the numerous factors identified in the potential embodied water of metals and minerals.

Sustainability Reporting
A critical issue in ensuring that the embodied water is equivalent between operations is the clarity of data reported.
Some companies and/or mines appear to report data under EN8 (total water withdrawal by source) differently than other similar mines. When projects with a similar configuration (mill, climate, mine type, etc.) report significantly different water consumption, is this due to greater conservation/efficiency or a different way of compiling the data?
In addition, the proportion of water reportedly re-used or recycled (indicator EN10, voluntary) for the same mine can vary significantly over time.
Sometimes this is due to the implementation of water efficiency projects, or changing mine ownership, corporate sustainability assessment, or reporting procedures, but more commonly there is no explanation given for major fluctuations over time. For example, one copper-gold mine used to report total water consumption of about 2.2-2.6 GL/year (5 years data), but this suddenly changed to 0.6 GL/year (3 years data), without any report of water recycling or any discussion of changing corporate reporting practice. As this mine has undergone no change in configuration during this time, the sudden decline in reported total water consumption has been cautiously interpreted to be due to a high degree (~75 per cent) of water recycling and a change in corporate ownership and associated policies and procedures, though the relevant sustainability reports do not discuss or elaborate on such aspects.
Given that many companies do not report re-use or recycling under EN10, it is difficult to trust data under EN8 since almost all mines practice water re-use and recycling (some even claim 100 per cent recycling), e.g. reclaim water from a tailings dam.
A substantive volume of water at mining projects is often contained in either water retention ponds or tailings storage facilities. In theory, indicator EN9 (water resources significantly affected by withdrawal of water) could be adopted to report year end totals for such water storage. In practice, it would be easier to report against by assigning separate indicators to such water resource aspects.
Additionally, many mining projects treat large volumes of contaminated waters to a standard that minimises potential environmental issues (e.g. to allow discharge during a wet season). This water is not ‘consumed’ directly in milling and so is variably included or not as total water consumed (i.e. indicator EN8) in reports.
A further area of weakness in the current GRI guidelines is that of water quality. At present, there is no indicator for the quality of the water consumed, the water source, or the potentially impacted water resources. Typically, water is generally judged suitable for particular uses based on salinity, although trace elements can be very important (primarily nutrients, heavy metals, or radionuclides), especially in acid and metalliferous drainage situations where mine drainage is causing severe pollution. Thus, in assessing the equivalent ‘embodied water’ of minerals, should water of any water quality be considered equal?
When there are multiple sources of water of varying quality for a given mining project, how should this be assessed and reported? Furthermore, how should impacts on water resources of varying water quality, such as seawater versus fresh water, be treated in terms of sustainability reporting?
These questions are clearly critical in any realistic assessment of embodied water with respect to mining and sustainability but current practice cannot address them.
The number of mining companies using the GRI guidelines for sustainability reporting is increasing, and this is helping to facilitate greater consistency in reports. However, the fact that indicator EN10 remains voluntary severely hampers trust in other reported data, such as water consumed (EN8—like the Cu–Au example).
Given the significant degree of water re-use and recycling in most mining projects, it makes sense that indicator EN10 should be core. There is also a strong case to consider reporting other water streams for mining projects such as stored waters in tailings facilities and retention ponds as well as treated waters. Most of this data, if not all, is already collected to facilitate sound operational performance and manage associated water-related risks.
All that needs to occur is for existing data to be used more systematically for sustainability reporting. In order to address this in the future, reporting procedures need to be tightened and public sustainability reporting needs to be more transparent, explicit, and consistent over time. For example, GRI indicators EN9 and EN10 could be made compulsory, with new indicators for water quality and minesite water inventories.
The choice of smelting technology significantly affects the embodied water for numerous metals (e.g. Norgate and Lovel 2006). For complete life cycle assessments of the embodied water of metals and minerals, it is critical to ensure that all relevant stages are assessed, although this is often beyond the scope of mining companies alone (unless they also operate smelters and refineries in conjunction with projects, e.g. Mt Isa, Olympic Dam).
It is clear that sustainability reporting of water issues is still evolving and that the scale and complexity of these issues is only beginning to be realised with respect to mining.

Conclusion
This paper has presented a preliminary compilation and analysis of the water reported to have been consumed by a range of various mineral commodities with respect to mine production data. This has been undertaken to assess and quantify the embodied water of mineral products, a key aspect of sustainability.
At present, although the use of formal reporting protocols such as the GRI is increasing, there are still critical weaknesses. Some key aspects to facilitate proper water accounting are not reported in sustainability reports, including the extent of recycled water used, minesite water inventories, the quality of various waters, and the impacts on water resources.
Based on the compiled data, there is wide variation in the amount of water used for different mineral commodities as well as for the same commodity. There is little evidence for ‘economies of scale’ in base metals and bulk minerals, though for precious metals (gold, platinum), greater throughput does tend to lead to greater efficiency.
For many mines, there is little evidence of improving efficiency over time, although some mines have apparently made substantive improvements in reducing water consumed.
The potential factors underlying the variability in embodied water, such as mine type, mill configuration, ore characteristics, climate, requires further research.
The grade of ore being processed is clearly critical in understanding the embodied water of minerals, with declining ore grades leading to an increased chance of higher embodied water into the future. Given that many metals are declining in average ore grade, the sensitivity of embodied water to ore grade provides a major sustainability challenge for mining generally.
In summary, the embodied water of minerals is clearly significant, looks likely to gradually increase in the future, and must be more completely accounted for to understand a fundamental aspect of sustainability, that of water resources.

* Dr Gavin Mudd - Department of Civil Engineering, Institute for Sustainable Water Resources, Monash University, Victoria. Email: Gavin.Mudd@eng.monash.edu.au