Modelling of ionic conductivity in nitrate brines to estimate solute concentrations

This work contributes to the thermochemical modelling of nitrate brines to estimate solute concentrations from ionic conductivity and temperature measurements. This indirect determination would allow significant savings in time and monetary costs related to the use of analytical laboratories for saline waters, so it could help to monitor and improve the controls of industrial operations and processes associated with the production of natural saltpeter, dissolution of nitrate fertilizers, leaching operations for ores and concentrates using nitrates, or in water treatments for nitrate residue solutions. The calibration and validation of the mathematical models required in this study were carried out, including the electrolyte parameters for Pitzer's aqueous model and Appelo's ionic conductivity model with the use of the hydrogeochemical code PHREEQC. The methodology used considered different electrolytic systems, such as: seawater, pure nitrate electrolytes, seawater plus nitrate and nitrate brines from the industry, in which the mathematical models were optimized by determining the Pitzer interaction parameters under the assumption of partial dissociation for nitrate electrolytes. In this work, the inverse application of an ionic conductivity model allowed obtaining good estimates of concentrations for solutes present in the studied brines, such as: nitrate, sodium, and chloride in their respective ranges of 0-75 g/L, 0-100 g/L, and 0-140 g/L, with a 95% confidence level.

Automated summary

This study contributes to the thermochemical modeling of nitrate brines by estimating solute concentrations indirectly from ionic conductivity and temperature measurements. The calibration and validation of mathematical models using different electrolytic systems like seawater, pure nitrate electrolytes, seawater plus nitrate, and nitrate brines from the industry were successfully carried out. The inverse application of an ionic conductivity model provided good estimates of concentrations for solutes present in the studied brines with a 95% confidence level.