1225 To simulate the monthly evolution of reactive mineralogy over multidecadal time horizons, the sequential month-by-month run was automated using Python + phreeqpy/IPhreeqc. In each iteration, the script executed the file for the month, read the SELECTED_OUTPUT, identified the remaining moles of each kinetic reagent (columns with the prefix k_ in the PHREEQC code output), updated the next file by replacing the -m values, and adjusted the -time_step according to an external table (Excel) of monthly contact times. This cycle was repeated for each scenario, allowing the progressive depletion of reactants and monthly climate forcing to control the system response in a coupled manner without coupling external flow models. Each monthly infiltration pulse mixes a fraction of meteoric water with the resident water in the package using a sequential mixing scheme, followed by oxygen-controlled reactions and subsequent drainage of the system. This sequence was modeled as a one-dimensional column, where changes in water quality and mineral transformation are evaluated month by month. Figure 1 schematically shows this conceptual dynamic applied to the simulated system. Figure 1 - Conceptual model of monthly infiltration, reaction, and drainage under climatic pulses in a filled pit The validation of depletion rates was performed by comparing the simulated response with experimental results from moisture cells (accelerated test) under a standard protocol for weathering and leachate generation. Based on time series of pH, sulfate, and metals in effluents, empirical Langmuir and Weibull models on cumulative release/depletion were adjusted, and their characteristic constants were compared with the effective rates implicit in the kinetics implemented in PHREEQC (depletion of remaining moles and production of dissolved species). 3. RESULTS The results were analyzed based on monthly outputs aggregated on an annual scale, reporting for each year the minimum, maximum, and average values, as well as the “band” (Max-Min) as a measure of intra-annual variability associated with hydrological pulses. Two configurations were evaluated: a scenario with transient hydroclimatic forcing (scenario 1; period 2026-2100) and a scenario with stationary average With O₂ penetration No O₂ penetration Precipitation Drainage per month Simulated final effluent quality in the tailings pond per month Precipitation of secondary mineral phases under the new chemical conditions Infiltration according to recharge rate (%)
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