Evaluation of mortar produced with boiler blowdown brine

Abstract

During boiler operation the concentration of water impurities can cause harmful effects such as scale deposits, corrosion, and embrittlement. Periodic water removal (blowdown) is necessary to maintain boiler operation, but introduces the problem of how to manage the waste brine material. This study explores the utilization of a simulated boiler blowdown brine for incorporation into cement-based materials, particularly for non-structural applications like cemented backfill. General use limestone (GUL) cement, and an ordinary Portland cement (OPC) were employed as binders in mortar mixtures, along with additional mortar mixtures where a portion of the binder was replaced with sodium silicate and waste brine. Compressive strength and electrical resistivity were monitored over time, along with thin section microscopy of the hardened mortar mixtures. Moreover, a monolithic leaching test was performed to assess nitrate leaching. The results indicate that blowdown brine that has been pre-treated with sodium silicate can be feasibly used to develop cemented backfill mixtures. A good linear correlation between the measured electrical resistivity and compressive strength test results is established for all mortar mixes. Cumulative nitrate leached from brine mortar mixtures were lower than 40 mg/L. Microscopic observations illustrate that the porosity was lower for mortars made with OPC. Optical and scanning electron microscope analyses show mm scale pockets of the sodium silicate waste brine mixture distributed within the paste fraction.