Page 108 - Materials Chemistry, Second Edition

Life Cycle Evaluation for Alkaline Battery Waste Treatment 89

toxic substances (heavy metals, carcinogenic substances, or pesticides). The relative
incidence of the various environmental effects is established through a weighting
operation by which the results obtained are converted, through the use of appropri-
ate numerical factors, to determine the levels of damage equivalent to the different
environmental impacts.
The damage avoided due to the recovery of materials is remarkable. It is
interesting to note that the impact caused by the electricity consumption of the
hydrometallurgical process and the use of chemicals such as sulfuric acid and
potassium hydroxide is largely offset by the recovery of materials (zinc, potas-
sium, and final BP).
The diagram in Figure 5.7 shows on the ordinate, the years of life lived with
disability and on the abscissa, the input and output data for the recycling of 1 kg of
alkaline batteries. The highest value, which means great damage, is attributed to the
use of potassium carbonate, followed by the consumption of electricity, zinc oxide,
and sulfuric acid. The avoided damage (negative values) results from the recovery of
metallic zinc and potassium.
Quantitative amounts of the impacts (produced and avoided) are reported in
Table 5.4.
Characterization factors are calculated and expressed using reference units (e.g.,
kg 1,4-dichlorobenzene (1,4-DB) equivalent, kg CFC-11 (trichlorofluoromethane)
equivalent, etc.).
If we take into account, for example, the impact on the category Marine aquatic
ecotoxicity, the value attributed to the use of potassium carbonate (3062.47 kg 1,4-
DB eq) is totally balanced by the avoided impact generated by the recovery of potas-
sium sulfate (−4565.79 kg 1,4-DB eq). The recovery of zinc oxalate generates an
avoided impact of (−6031.03 kg 1,4-DB eq).
In total, the impact reported in this category is negative (−6297.41 kg 1,4-DB eq).
This means that all the generated impacts, including that caused by power consump-
tion (786.15 kg 1,4-DB eq), are cancelled, and environmental benefits are generated.
Similar trends can be seen for the other impact categories. According to a litera-
ture review, recycling scenarios demonstrate environmental benefit compared with
landfilling. It is important to develop a voluntary primary battery collection and
recycling program as a net positive for the environment compared with disposal to
landfill with other domestic garbage (Olivetti et al., 2011).

5.6 CONCLUSIONS
The cradle-to-gate analysis carried out in this case study confirms what was
already expected: the recovery of materials (potassium, zinc oxalate, zinc, and BP
final) from the hydrometallurgical process and their reuse generate environmental
benefits due to avoidance of the production of these compounds from raw mate-
rials. All the impacts generated to run the recycling process (especially the use
of chemicals and energy consumption) are balanced by the avoided impacts due
to materials recovery. The LCA method provides instruments to understand the
potentialities of clean industrial technologies and processes moving toward more
sustainable development.