*3.4. Economic Evaluation*

Table 9 presents the direct and indirect costs, as well as profit for a basic plant that recycles 8 tons of batteries per day. In this simulation, the cost of shredding was not considered. However, the non-magnetic fraction (plastic, carton, etc.) and the final residue were considered waste products that would need to be transported over 50 km with a disposal cost of \$CAD 75 per ton of residue. This cost included loading, transport, and landfill calculated at \$CAD 28.2 per ton of batteries. In addition to chemical products, labor costs and utilities costs were the two other important parameters, from an economic point of view, which accounted for 18.5 and 10.0% of the total direct costs, respectively.

A total cost of \$CAD 1260 per ton was calculated, of which the direct and indirect costs were calculated as \$CAD 725.7 and \$CAD 534.5 per ton, respectively. Regarding the cost simulation, cost distribution was dominated by indirect costs including amortization (9.6%), financing (15.8%), and marginal social benefits (1.5%). The revenue was calculated as \$CAD 1359.6 per ton, whereas Zn, MnO2, and MnCO3 values were estimated as \$CAD 527.4, \$CAD 451.6, and \$CAD 357.8 per ton, respectively.

Figure 5 illustrates the variation in cost as a function of the recovery capacity of the plant. Indirect costs showed an influence on total cost, and costs decreased with the increase in recovery capacity. Total costs were evaluated to be \$CAD 1015 and \$CAD 913 per ton for treatment capacities of 16 and 24 t/day, respectively, equivalent to 40 and 60% of batteries sold in the Canadian market.

**Figure 5.** Exploitation costs and revenues depending on the processing capacity of the recovery plant.


**Table 9.** Parameters related to hydrometallurgical recovery in spent alkaline battery.

#### **4. Conclusions**

In this study, we established a pilot process for the recycling of metals in spent alkaline batteries, including physical separation techniques and hydrometallurgical steps. Spent batteries were crushed and attrited to separate out and collect the metallic powder. Metallic powder was then treated using sulfuric acid leaching. The first leaching for zinc and a part of manganese included the use of 2 M H2SO4 for 45 min at ambient temperature and a solid content of 40% (*w*/*v*). Under these conditions, up to 87% of zinc was solubilized. In the second leaching step, 0.45 g Na2S2O5 was added per 1 g metallic powder in 1.34 M H2SO4, resulting in up to 97% of manganese being dissolved. The dissolved manganese was recovered by precipitation in the form of MnO2 and MnCO3, whereas zinc was recovered in metallic form by electrowinning. Notably, the leaching efficacy remained high, even after three cycles of processing with recirculated water. Furthermore, results from our technical and economic simulation indicate that the suggested process for recycling spent alkaline batteries is economically competitive and feasible. It is necessary to highlight that the profits from the process greatly depend on the market

price of zinc, manganese (IV) oxide, and manganese carbonate. However, despite economic challenges, the process of recycling alkaline batteries reduces negative environmental impacts.

**Author Contributions:** Conceptualization, J.-F.B., G.M., L.-H.T. and K.T.; methodology, K.T., A.D.J.; software, J.-F.B.; validation, J.-F.B., G.M., L.-H.T. and K.T.; formal analysis, K.T. and A.D.J.; investigation, K.T. and A.D.J.; data curation, A.D.J. and K.T.; writing—original draft preparation, L.-H.T.; writing—review and editing, L.-H.T, K.T., J.-F.B. and G.M.; supervision, J.-F.B. and G.M.; project administration, J.-F.B.; funding acquisition, J.-F.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Natural Sciences and Engineering Research Council of Canada, grant number RGPIN-2019-05767.X.

**Acknowledgments:** The authors thank Call2recycle for samples supporting.

**Conflicts of Interest:** The authors declare no conflict of interest.

## **References**


© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
