Partial desalination of seawater for mining processes through a fluidized bed bioreactor filled with immobilized cells of Bacillus subtilis LN8B

Abstract

The use of non-desalinated seawater for mining purposes is not recommendable because of the high salinity and the presence of some ions, that is, Ca2+ and Mg2+, that can hamper the mineral tailings separation process besides being responsible for scaling formation in pipelines and equipment. To remove these ions from seawater, a novel treatment involving a biomineralization process was tested using a fluidized bed bioreactor (FBB) filled with immobilized beads of the halotolerant ureolytic strain Bacillus subtilis LN8B. The FBB was operated in batch mode according to a sequence of six cycles of eight days. The highest efficiency in removing Ca2+ and Mg2+ occurred in the first cycle for both ions, achieving the removal rate of ~100% by day four for Ca2+ and ~80% by day six for Mg2+, respectively. Precipitates from FBB were mainly composed of ~70.2% of hydromagnesite, and ~17.8% of aragonite. Furthermore, the efficiency of biologically pretreated seawater (BSw) was evaluated as mineral tailings sedimentation medium and compared with three types of water: (i) tap water (Tw); (ii) seawater (Sw); and (iii) distilled water, (Dw). The results showed that the settling velocity in BSw was the highest (i.e., 6.23 ± 0.48 m h−1).