Page 104 - Materials Chemistry, Second Edition

Life Cycle Evaluation for Alkaline Battery Waste Treatment 85

4 (
4 (
3 (
Mn O solid) + 2H SO solution) → 2MnSO sol) + 2H O + ½ O 2 (5.6)
2
2
2
Regarding emissions, the chemical treatment plant has only one emission point
in the air, the chimney of the scrubber, from which only hydrogen should be emitted
at less than 50% of the explosive limit. Drainage of distilled water is expected as an
output from the vacuum concentrator; this may be partially used within the process
or discharged into the sewerage system.
5.5 LIFE CYCLE IMPACT EVALUATION

5.5.1 reSuLtS and diScuSSion
For the evaluation of the impacts, the methods CML 2000 and ReCiPe end-
point (H) present in the software SimaPro 8.2 were used. The characterization
method CML 2000, developed by Leiden University of Amsterdam, is a mid-
points method that focuses attention on the following categories of environmen-
tal impact: consumption of abiotic resources, greenhouse effect, depletion of
the stratospheric ozone layer, human toxicity, ecotoxicity, photochemical forma-
tion of ozone, acidification, and eutrophication. The impacts of each of these
categories are reported in appropriate units of measurement. For example, the
greenhouse effect or global warming potential (GWP) is calculated in kilograms
of CO .
2
The ReCiPe method also includes a method of assessment of the damages
expressed as

• Harm to human health (unit: Disability Adjusted Life Years [DALY], which
means that life years are weighted according to the disability caused by
various diseases)
• Damage to ecosystems (unit: species/year, i.e., number of species in danger
of extinction per year)
• Damage to resources, expressed in dollars

Figure 5.3 shows the diagram of the flows involved in the hydrometallurgical pro-
cess derived from the inventory table. The impact result is indicated as a percentage
of equivalent CO produced and therefore, refers to the impact category GWP.
2
The diagram is obtained on the basis of the inventory data and refers to the recy-
cling of 1 kg of alkaline batteries. The flows in input (indicated in red) are the con-
stituents of BP (mainly zinc oxide, manganese oxide, and carbon black), treatment
with sulfuric acid and subsequent neutralization with potash, and the power con-
sumption. The flows in output (in green) refer to the materials recovered for possible
reuse. The percentage impact of the output flows is negative, because they indicate
avoided impacts.
Figure 5.4 is another useful way to present the amount of CO produced or
2
avoided. The main impacts are associated with the use of potassium carbonate and
electricity consumption, while the main contribution to avoiding the impact is asso-
ciated with material recovery (potassium sulfate, zinc, etc.).