A novel brine precipitation process for higher water recovery

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 N97%. © 2016 Elsevier B.V. All rights reserved.

This research developed a new brine treatment process that is applicable to brines that are supersaturated with respect to barite, and to multiple calcium carbonate and magnesium carbonate mineral solids. Effective precipitation of carbonate mineral solids first required removal of a phosphonate scale inhibitor via co-precipitation with ferric hydroxide. When Na2CO3 was used for promoting carbonate mineral precipitation, substantial amounts of calcite were precipitated even when the pH was kept below the Mg(OH)2 saturation value. Although Ba2 + is removed in the first two steps of the process via nucleation on other solids, high levels of Ba2+ removal can only be achieved via homoepitaxial templating using barite itself as a seed crystal. The overall process allowed the same 85% recovery in the second stage NF as was used in the first stage. The kinetics of the proposed process may be improved via implementation in fluidized bed crystallization reactor [21] or using membrane assisted crystallization [22]. Acknowledgments Fig. 9. Effect of mixing time on SI values after addition of 5 g/L of barite seed crystals.