*3.1. Dissolution of Lead from Pretreated CRT Glass*

In order to determine the optimal operating conditions for the dissolution process, the evolution of the dissolution degree at different acetic acid concentrations was quantified. It can be seen from Figure 1 that the dissolution degree increases over time at all CH3COOH concentrations, the final value being almost three times higher than the initial one. The results also show that the concentration of the leaching agent has a decisive influence on the dissolution rate, since at the concentration of 1 M CH3COOH the dissolution degree is three times higher than at 0.2 M CH3COOH. However, the dissolution degree values increase only with 30% between 0.6 and 1 M CH3COOH while between 0.2 and 0.6 M CH3COOH they increase 110%, which means that above 0.6 M CH3COOH there is no significant gain in efficiency.

**Figure 1.** Dissolution degree vs. time at different CH3COOH concentrations.

In addition to increasing the dissolution degree with increasing CH3COOH concentration, it is important to increase the conversion of the leaching agent in order to exploit the full potential of the leaching solution. To highlight this aspect, the efficiency of CH3COOH utilization was determined, which indicates how much of the leaching agent was converted under different experimental conditions compared to what could theoretically be used for lead dissolution, taking into account the initial amount of CH3COOH in the solution. The results from Figure 2 show that the efficiency of CH3COOH utilization is diminished by increasing the concentration of CH3COOH, the maximum value being reached at a concentration of 0.2 M acetic acid.

**Figure 2.** Efficiency of CH3COOH utilization vs. time at different CH3COOH concentrations.

This tendency can be attributed to a partial order of reaction regarding CH3COOH concentration which means that the amount of acetic acid transformed in the leaching reaction does not increases proportional with the increase in initial CH3COOH concentration. The concentration profiles of Pb2+ shown in Figure 3 sustain the above explanation, considering that the total amount of lead dissolved increases only 171% by increasing the initial concentration of CH3COOH by 400%.

**Figure 3.** Pb2+ concentration profile at different CH3COOH concentrations.

Considering that the above evaluated performance indicators give contradictory conclusions regarding the optimal CH3COOH concentrations, the specific acetic acid consumption for the leaching process was determined which gives a comprehensive overview on the efficiency of the process. The specific acetic acid consumption values, Figure 4, show that the lowest concentration (0.2 M) of CH3COOH allows the most efficient use of the amount of leaching agent present in the system. In contrast, according to Figure 3, the final Pb2+ concentration is the lowest at 0.2 M of CH3COOH which would not ensure the most favorable conditions for the electrodeposition process of lead. Therefore, the intermediate concentration of 0.6 M CH3COOH would be a better option in comparison to 0.2 M CH3COOH, considering that the obtained final Pb2+ concentration (9.25 g/L) represents 80% of the maximum achievable concentration under these dissolution conditions.

**Figure 4.** Specific acetic acid consumption vs. time at different CH3COOH concentrations.

Additionally, taking into account the ecological aspects, to ensure a relatively advanced removal of lead from CRT waste, but with a reasonable yield, the 0.6 M CH3COOH value can be considered as the optimal concentration for the dissolution process.
