Typical Studies of Life-Cycle Assessments

Researchers have presented LCA studies for a wide range of processes. These include bio-diesels (Harding et al., 2008), chemicals (Fantke and Ernstoff,

2018), food (Cucurachi et al., 2019), plastics (Harding et al., 2007), and many more. It is also common to find studies that look only at certain aspects of the LCA, e.g., global warming or carbon footprinting, as well as water footprinting (Pfister et al., 2017). Consultants have also undertaken many more studies for their corporate clients which they keep for internal use only.

In the mining and mineral processing industries, there is a similar interest in LCA studies. These include various minerals and processes, from full LCA studies to impacts of the use of water (Haggard et al., 2015; Northey et al., 2013; Northey et al., 2016; Osman et al., 2017; Ranchod et al., 2015).

There have been few published studies that have used LCA methods to determine the environmental impacts of different acid mine drainage (AMD) treatment technologies. Such studies include both active and passive remediation techniques in different countries which are valuable examples of what is possible with AMD (Table 8.1).

The first case study presented in this chapter is for the active versus passive AMD treatment technologies in New Zealand (Hengen et al., 2014). As discussed in some sections of this chapter, using LCA, it is possible to look at different scenarios and what-if options. In a study by Hengen et al. (2014), eight scenarios were investigated to determine the impacts of various processing options. This is common in LCA where different transport options or suppliers may be of interest. Where comparative studies are involved, and the aim is to compare different options, it is common to draw the system boundary to a 'gate'. This is useful when the excluded portions of the scenarios are identical, and there is more interest in the differences (the actual comparative LCAs investigated) than the absolute final impact of the entire process. In the Hengen et al. (2014) study, it was shown that passive treatment systems had lower environmental impacts than active treatment technologies. Furthermore, the study found that reducing transport distances and using recycled materials could improve environmental burdens.

The LCA is also an effective way to look at different processes, whose final products have the same use (FU). For example, Tuazon and Corder (2008) determined the life-cycle impacts of lime and reused red mud as neutralizing agents for AMD. While these are two distinct products, which would have originated through completely different processing routes, their use (remediating AMD) would be the same and are thus comparable.

However, LCA does not only compare processes. A useful aspect may be to know the hotspots (areas of concern) in a full process. While LCA software gives life-cycle impact values for the entire process, it is also possible to break them down so as to determine which aspect of the process contributed what proportion. This is something that Masindi et al. (2018) studied when looking at distinct aspects of a single process for AMD treatment. Even though there is no other process to compare results to, it can be useful to know that one part of the process might be contributing proportionally higher to LCA impacts than another part. In their study, Masindi et al. (2018) found that electricity was a large contributor to LCA impacts. Reduction of energy needs or replacement of electricity use with renewable energy sources would thus reduce the entire LCA score substantially.

As mentioned previously, setting the goal and scope can be particularly important. This is because not understanding the actual problem in the first place can make deciphering results confusing. Another aspect could be the time under consideration. Depending on the year the data was obtained, or the length of time under consideration, results can vary. Reid et al. (2009) is one such example, where it was found that results could vary depending on what temporal boundaries were set. In this study, if a mine closure period

Title

Location

Aim

Description

LCA Details

1 LCA of active and passive AMD treatment technologies at a coal mine

Stockton Coal Mine, New Zealand

To compare the environmental impacts of different

implemented and optional active and passive AMD treatment methods

Eight scenarios investigated, including limestone and the use of mussel shells

Cradle to gate analysis, including transport and construction.

2 LCA of seawater neutralised red mud for AMD treatment

Mount

Morgan,

Queensland,

Australia

To compare the environmental impacts of different neutralants, lime and seawater neutralised red mud, in controlling acidic water discharges

An

investigation into scenarios of using lime (one scenario) versus reused red mud (three scenarios)

Equivalent neutralisation ability used as a basis. Transport included

Significant

Findings

Recommendations

References

Lime slaking had the greatest LCA impacts, and passive treatment had fewer impacts. Reduced transport significantly reduced scores

Design considerations should include utilizing materials with reduced processing, sourcing local materials and minimizing pumping energy

Hengen et al. (20141

Red mud has the potential for reuse, but due to the requirement of approximately 12 times more mud by mass, insufficient conclusions were drawn

Further studies involving more detailed analysis are needed, including management issues associated with the physical and chemical stability of red mud

Tuazon

and

Corder

(2008)

3 Assessing the sustainability of AMD treatment

Mpumalanga Province, South Africa

To assess the environmental sustainability of a typical AMD treatment process, identify environmental hotspots and avenues to improve its environmental sustainability

Investigating AMD from an integrated coal mine treatment system using magnesite, lime, soda ash and CO,

LCA of a single integrated system, including process contribution analysis.

Economic and social aspects also investigated

4 LCA of mine tailings management

Quebec,

Canada

To quantify and compare the environmental burdens of different mine tailings management methods, specifically relating to the contribution of the land-use category

To develop the inventory of six tailings management scenarios to limit the formation of AMD

Life-cycle stages included development, operation, and closure

The system had a high environmental impact, due to electricity requirements, particularly due to South African coal-fired electricity generation

Use of renewable energy and sourcing gaseous C02 from other production processes, e.g., flue gas, can reduce the environmental impact by up to 81%. Mineral recovery from AMD can also mitigate the environmental footprint. More research is needed

Masindi et al. (2018)

The best scenario was shown, but it was seen that different temporal boundaries could affect results

Future results should be applied with caution since mineral ore grade, topography of the site, and soil characteristics could significantly influence the environmental impacts

Reid et al. (2009)

Title

Location

Aim

Description

LCA Details

Significant

Findings

Recommendations

References

5 LCAofa passive remediation system

Mina

concepcion

sulphide

mine,

Southwest

Spain

(Iberian

Pyrite Belt)

To perform an LCA for dispersed alkaline substrate (DAS) technology, effective for metal-rich and acid waters

LCA to quantify the environmental impacts associated with an AMD passive treatment plant

LCA included construction, operation, waste handling, and water treatment

Construction creates initial environmental impacts, but upstream manufacturing impacts are most significant

The results could be used to support decision making of a restoration plan for the Odiel River basin. Results may also contribute to more environmentally friendly mining by supplying insights into the environmental impacts related to AMD treatment

Martinez et al. (2019)

6 LCAof flotation process to prevent acid rock drainage

Not location specific

To evaluate the environmental consequences of a desulfurisation flotation unit for the prevention of acid rock drainage

LCA for the treatment of a tailings slurry generated from a base-metal sulfide ore

One scenario using conventional dewatering and further processing, with a second scenario using desulfurisation flotation and further processing

Desulfurisation flotation resulted in a decrease in some LCAI scores, but increases in others

While holistic and systemic, LCA tools can be deficient in reliably and comprehensively accessing all environmental impacts for solid mineral waste systems. Future studies will need to be more detailed

Broadhurst et al. (2015)

of under ten years was used, versus greater than ten years, the best to worst ecosystem quality scenario results were inverted. It was also shown that the longer the period under consideration, the greater the differences in these environmental impacts.

A further consideration to the time aspect is how to include the construction phase of the process, which should be included if the LCA is truly 'cradle-to-grave'. In the first year of operation, a substantial part of the environmental impact would be due to the construction phase, while as time passes, the relative average yearly impact of the construction phase becomes smaller due to less (or no) construction in those years. At some point, it may become insignificant enough not to be of concern, as is the case in a study by Martinez et al. (2019), where it was determined that after 4.5 years, the impacts of construction were insignificant. Actually, it is a common assumption that the construction phase is considered negligible and ignored. This is particularly true for projects that have processing facilities with projected lifespans of a few decades or more, or because this information is no longer available, or difficult to find.

The final case study presented looked at a desulfurisation flotation process versus a conventional system to prevent acid rock drainage formation at a base metals facility (Broadhurst et al. 2015). The study showed that while the LCA method was able to determine improvements in some LCIA category results, there could be conflicting results in other categories. It also showed that although the LCA method is holistic and systemic, there could be cases where the impact of categories are not appropriate for the system being investigated.

 
Source
< Prev   CONTENTS   Source   Next >