Kinetic study of magnesium dissolution using a magnesium oxide industrialby-product

Abstract

Phosphorus recovery via struvite precipitation in wastewater treatment plants (WWTPs) is a key technology fornutrient recovery. This work investigates the dissolution kinetics of an industrial low-grade magnesium oxide(LG-MgO) by-product as an alternative to common magnesium sources for struvite precipitation. The main aimswere to develop a parsimonious dissolution kinetic model capable of predicting the release of magnesium intothe solution with accuracy and studying the influence of temperature on dissolution kinetics. The simultaneousfitting of all the experiments by non-linear regression rendered overall process values of the dissolution model’sfrequency factor (498,606 L3.22 min 1 mmol 1.74), activation energy (37.51 kJ⋅mol 1), and reaction order(2.74). The goodness-of-fit for all experiments was evaluated by the total sum of squared residuals and R2 coefficients,being excellent under all conditions. The estimated kinetic coefficient values showed a temperaturedependentvariation of the kinetic coefficient, increasing from 0.079 to 0.219 L3.22 min 1 mmol 1.74 when thetemperature increased from 15 to 35 ◦C. The magnesium dissolution was fast in the first 5 min, where 40–78 % ofmagnesium dissolved with respect to the initial magnesium in the solid. Despite the assumptions made in themodel derivation, the developed kinetic model provides a practical, reliable, and easy-to-use tool for WWTPs toestimate the LG-MgO dosage required to achieve targeted magnesium concentrations, thereby improving reagentuse efficiency and phosphorus recovery.