This research developed a three-step demineralization process for removing scale-forming compounds from brine solutions produced during nanofiltration (NF) of potable water. The process is designed to remove compounds that would produce scale and membrane fouling during further treatment via NF or reverse osmosis (RO). Jar tests were performed to determine the most suitable dosages and mixing times for each reagent. The first step in the demineralization process employs ferric chloride for removing phosphonate scale inhibitors via co-precipitation with ferric hydroxide. The second step of the process increases the solution pH value to promote carbonate mineral precipitation. The third step involves barium sulfate precipitation promoted by barite seed crystals. Saturation indices for precipitation of mineral solids were simulated using the PHREEQC thermodynamic modeling program. Water recovery from the treated brines was modeled using the ROSA package for simulating permeate and concentrate compositions for NF processes. The three-step demineralization process allowed the recovery rate for the brine solution to be as high as the initial feed water, and achieved a total water recovery of > 97%.
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