A novel brine precipitation process for higher water recovery

• Scale-forming compounds are removed from NF concentrate to enable higher water recovery in second stage NF or RO.
• Co-precipitation of phosphonate-based antiscalant by ferric chloride increases precipitation of scale-forming compounds.
• Precipitation process on NF concentrate enabled the secondary membrane to be run with 85% recovery.
• Studied all of the supersaturated compounds in the brine namely: calcite, magnesite, barite, dolomite, and huntite.
• Based on the optimized method, 82% of calcium, 61% of alkalinity, 98% of barium and 31% of the conductivity are removed.

A three-step demineralization process for removing scale-forming substances from brine solutions produced from nanofiltration (NF) of water was developed. The process is designed to remove substances that would lead to scale and membrane fouling during additional stages of NF or reverse osmosis (RO). 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%.