Evaluation of parameters controlling calcium recovery and CO2 uptake from desalination reject brine: An optimization approach

Mahmud, Nafis; Ibrahim, Mohamed H.; Fraga Alvarez, Daniela V.; Esposito, Daniel V.; El-Naas, Muftah H.

Evaluation of parameters controlling calcium recovery and CO2 uptake from desalination reject brine: An optimization approach

2022

Mahmud, Nafis | Ibrahim, Mohamed H. | Fraga Alvarez, Daniela V. | Esposito, Daniel V. | El-Naas, Muftah H.

A multistage process scheme for extracting valuable minerals from desalination reject brine while simultaneously sequestering CO₂ has been proposed. As a part of the proposed scheme, simultaneous removal of calcium ions and CO₂ uptake of a magnesium free reject brine was investigated in an inert particle spouted bed reactor (IPSBR) by reacting CO₂ with reject brine in presence of NaOH. Response surface methodology was applied to optimize the effect of NaOH dosage, gas flowrate and salinity on the reaction with the target of maximizing calcium removal and CO₂ uptake. A second order regression model was generated for both target responses. The predicted responses for both targets were in good agreement with the obtained experimental response. Based on a multivariate optimization, the optimum conditions for NaOH, flowrate and salinity for simultaneous calcium removal and CO₂ uptake were found to be 5 g/L, 2 L/min and 75 g/L, respectively. Under these conditions, 100% removal of Ca²⁺ ions from the brine could be achieved with a CO₂ uptake of 5.4 g/L. Moreover, the solid products obtained under the optimum conditions were characterized confirming the formation of high purity calcium carbonates. Based on optimized conditions, the proposed multistage process scheme promises to produce highly pure Mg(OH)₂ and CaCO₃, while sequestering 5400 tons of CO₂ for every million tons of brine treated. The scheme can be further improved by incorporating an electrolysis unit to produce HCl along with NaOH that can be recirculated to eliminate the need for any external addition of NaOH, thus, creating a sustainable process for reject brine management and CO₂ sequestration.

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