*2.4. Analytical Methods*

Liquid samples were filtered using G6 glass fiber paper (Fisher brand, Fisher Scientific, Ottawa, ON, Canada, pore size = 1.5 μm) to remove solid particles, and stored in 5% HNO3 before analysis. Solid samples were dissolved with nitric and hydrochloric acid (HNO3 and HCl, respectively) before analysis. Metal mobility in the final residual (after the second leaching step) was evaluated using the toxicity characteristic leaching procedure (TCLP)—Method 1311. The metal concentrations in all samples were determined using an inductively coupled plasma-optical emission spectrometer (ICP–OES) (model 725–ES, Agilent Technologies, Santa Clara, CA, USA).

#### *2.5. Techno-Economic Evaluation of the Hydrometallurgical Process*

The economic simulation for a battery recycling plant required a large number of parameters (variables) in order to estimate the economic performance of the process. For this study, a computer model was developed to evaluate both direct and indirect costs of the proposed recycling process. This model included more than 260 input variables to define, among others, the various processing steps, capitalization, and operating parameters. The techno-economic analysis was based on parameters and efficiency values obtained from pilot-scale experiments, but increased to a basis of 2800 tons of batteries processed per year (t·y<sup>−</sup>1). This capacity represents the actual amount of batteries collected in Canada. Therefore, the capacity plant was developed for 8 tons per day (t·d−1), with a running time of 8 h per day, and annual operation of 350 d·y<sup>−</sup>1. Once the capacity of the plant was established, it was possible to adjust the dimensions of the required equipment, according to the specific process. The total cost was established based on variable equations including dimensions and capacity of equipment, purchase costs and transport of equipment, electric and thermal requirements, as well as energy consumption, as recorded in previous studies [23]. Depreciation and annual interest charges were estimated using a 20-year equipment lifetime, as well as a working capital of 15% of fixed capital costs. In addition, used market parameters were defined as follows: An inflation rate of 2%, an annual interest rate of 5%, and an annual discount rate of 6%. Table 2 presents the basic operating parameters taken from the Canadian market and relevant literature [23–25].


**Table 2.** Basic operating parameters, market parameters, and capitalization parameters of the techno-economic model for recycling spent alkaline batteries.


**Table 2.** *Cont*.
