A huge amount of brine purification sludge (BS) is discharged from soda plants every year, which results in serious environmental pollution and resource waste. In this work, a modified brine purification route is proposed. First, the brine is purified by adding lime, sodium sulfate, and soda ash sequentially to remove magnesium and calcium ions; meanwhile, the BS is produced. Then, CO2 is mineralized by the sludge through the carbonation reaction. Finally, magnesium sulfate, the product of the carbonation reaction, is used to produce hydromagnesite. The optimal reaction conditions were investigated, under which the magnesium ion leaching efficiency can reach up to 95.54% in the carbonation reaction step and the magnesium ion utilization efficiency can reach up to 99.05% in the hydromagnesite production step. The characterization results indicated that high-purity calcite and hydromagnesite were obtained. Based on the optimal operational condition, the economic analysis for the process was completed and the results showed that the modified route was economically feasible.

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Natural brucite is unstable in aqueous media, was modified with sodium hexametaphosphate(SHMP) as a surface treatment. In order to explore the effect of sodium hexametaphosphate on the surface of brucite were studied by using relative sedimentation measurement, scanning electron microscopy (SEM), Zeta potential, infrared spectroscopy (FT-IR) and extend DLVO theoretical calculation. The sedimentation experiments show that the sodium hexametaphosphate modification have a positive effect on the dispersion of brucite in aqueous media. The sodium hexametaphosphate changes the potential of the burburite particles, which leads to the increase of electrostatic double layer energy between particles. Infrared spectrum analysis shows that sodium hexametaphosphate can form a hydrophilic complex with magnesium ions on the surface of brucite. DLVO extend theoretical calculation shows that the total energy between brucite particles turned from unfavorable to favorable with the increasing particles distance, and the steric hindrance interaction energy plays a dominant role. The results show that sodium hexametaphosphate have a positive effect on the stability of natural brucite suspension.

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